Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

Mario Delmar,1 Dale W. Laird,2 Christian C. Naus,3 Morten S. Nielsen,4 Vytautas K. Verselis,5 and Thomas W. White6

1The Leon H. Charney Division of , New York University School of Medicine, New York, New York 10016 2Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario N6A5C1, Canada 3Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada 4Department of Biological Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen 2200, Denmark 5Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, New York 10461 6Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York 11790 Correspondence: [email protected]

Inherited or acquired alterations in the structure and function of have long been associated with disease. In the present work, we review current knowledge on the role of in diseases associated with the heart, nervous system, cochlea, and skin, as well as and pleiotropic syndromes such as oculodentodigital dysplasia (ODDD). Although incomplete by virtue of space and the extent of the topic, this review emphasizes the fact that connexin function is not only associated with channel formation. As such, both canonical and noncanonical functions of connexins are fundamental components in the pathophysiology of multiple connexin related disorders, many of them highly debilitating and life threatening. Improved understanding of connexin biology has the potential to advance our understanding of mechanisms, diagnosis, and treatment of disease.

he demand for intercellular communication nexon or hemichannel that after trafficking to Tarose with the evolution of multicellular or- the plasmamembrane docks with a connexon ganisms and in vertebrates, direct communica- from a neighboring cell and form an intercellu- tion occurs at aggregates of intercellular chan- lar channel (see Fig. 1). Humans express 21 dif- nels called gap junctions. The gap junctional ferent connexion isoforms, each with its own channels are comprised of connexins, in which distinct biophysical properties and expression each connexin has four membrane spanning do- pattern. Although all connexins form cell–cell mains, two extracellular loops, one intracellular channels, it has become clear that connexins loop, and intracellular amino and carboxyl ter- also have functions that are unrelated to inter- mini (for a general review on connexins, see cellular coupling. Undocked hemichannels can Nielsen et al. 2012). Six connexins form a con- open and exchange substances or ions between

Editors: Carien M. Niessen and Alpha S. Yap Additional Perspectives on Cell–Cell Junctions available at www.cshperspectives.org Copyright © 2017 Cold Spring Harbor Laboratory Press; all rights reserved Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348

1 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

M. Delmar et al.

E1 E2

TM 1-4 Connexon NT CL CT Connexin

Gap junction channel

Figure 1. Connexin structure and organization. Connexins have four transmembrane domains (TM1–4), two extracellular loops (E1–2), a cytoplasmic loop (CL), and cytoplasmic amino and carboxyl termini (NT and CT). Six connexins oligomerize to form a connexon, also known as a hemichannel, which dock with a connexon from a neighboring cell to form an intercellular gap junctional channel. Gap junctional channels form densely packed plaques that appear as a pentalaminar structure in electron microscopy (EM) (between arrows in left panel). Scalebar, 100 nm. (From Axelsen et al. 2013, reprinted, with permission, from the authors.)

the cytoplasm and the extracellular environ- gin of disease. There is also emerging literature ment, which may exert signaling as well as path- on the role of connexins as components of mul- ophysiological functions (Nielsen et al. 2012). timolecular complexes, whereby loss of con- Furthermore, some connexins have channel-in- nexin integrity can disrupt functions seemingly dependent functions often associated with their foreign to those classically ascribed to either ability to bind and organize cytoskeletal and gap junctions, or connexin hemichannels. Con- signaling components (e.g., Cx43) (Leo-Macias nexins do not live in silos, isolated from other et al. 2016a). Because connexins are expressed in components of the cellular landscape. In the most cells of the human body and exert multiple end, many years of studies on multiple “mono- roles, their dysfunction is often associated with genic” syndromes have taught us that most dis- disease as summarized in Table 1. At this point, eases, including the inheritable ones, result it seems pertinent to begin with a disclaimer. At from the balance of function within multimo- this writing, the words “connexin” and “disease” lecular constellations. The same becomes ap- bring close to two thousand articles in PubMed. parent when one reviews the topic of connexins We have attempted to reduce a large body of and disease. literature into a few pages and in doing so, we are for sure guilty of excluding many outstand- Cx43 IN OCULODENTODIGITAL ing contributions that have moved the field for- DYSPLASIA ward. The present review touches on a limited number of diseases that may be representative of The library of connexin-linked diseases has the gamet of morbidities that result from alter- grown over the past two decades to include ations in the structure and/or function of con- many rare syndromes and conditions. One of nexin proteins. We purposely chose to speak the best studied connexin-linked diseases is the about “connexins and disease,” rather than multisystem development disorder known as “gap junctions and disease.” The former seeks oculodentodigital dysplasia (ODDD), which is to emphasize the fact that connexins are not now known to be caused by nearly 80 distinct only gap junction-forming proteins. There is a mutations in the GJA1 encoding Cx43 solid body of literature showing that membrane (Paznekas et al. 2003, 2009; Laird 2014). Almost hemichannels can play a critical role in the ori- all ODDD patients have one normal GJA1 allele

2 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

Table 1. Disease causing connexin mutations in humans Connexin Gene Disease name Phenotype Functional alterations Cx26 GJB2 Deafness Deafness Loss of connexin expression PPK Skin disease and Gain of hemichannel function KID deafness Gain of hemichannel function Skin disease and deafness Cx30 GJB6 Deafness Deafness Unknown HED Skin disease Gain of hemichannel function Cx30.3 GJB4 EKVP Skin Disease Cx31 GJB3 EKVP Skin disease Gain of hemichannel function Deafness Deafness Cx32 GJB1 CMTX1 Peripheral neuropathy Loss of GJ channel function and occasional CNS involvement Cx40 GJA5 AF Atrial fibrillation Loss of GJ channel function Loss of proper GJ channel trafficking Cx43 GJA1 ODDD Multiple defects Loss of GJ channel function EKVP depending on Loss of proper GJ channel trafficking PPK mutation Gain of hemichannel function Trans-dominant effects on other connexins Cx46 GJA3 Cataract Cataract Gain of hemichannel function Loss of hemichannel function Loss of GJ channel function Cx47 GJC2 PMLD Multiple CNS defects Loss of GJ channel function LMPH1C lymphedema Loss of proper GJ channel trafficking Loss of hemichannel function Nonchannel effects also likely Cx50 GJA8 Cataract Cataract Gain of hemichannel function Loss of hemichannel function Loss of GJ channel function For review on cataract causing mutations, see Berthoud and Ngezahayo (2017), otherwise see text for references. PPK, with deafness; KID, keratitis-ichtyosis-deafness syndrome; HED, hidrotic ectodermal dysplasia; EKVP, erythrokeratodermia variabilis et progressiva; CMTX1, Charcot-Marie-Tooth neuropathy X type 1; AF, atrial fibrillation; ODDD, oculodentodigital dysplasia; PMLD, Pelizaeus–Merzbacher-like disease; LMPH1C: hereditary lymphedema type IC

consistent with autosomal dominant inheri- reasons that remain unclear, the health status of tance of disease. Patients with ODDD typically ODDD patients tends to worsen with age pre- have ocular defects including small eyes, dental sumably because of changes in the CNS (De abnormalities related to the loss of tooth enam- Bock et al. 2013a). The plethora of affected or- el, soft tissue fusion of the fingers and toes, and gans in ODDD is somewhat predictable given skeletal defects particularly in craniofacial bones that Cx43 is highly expressed in most human (Paznekas et al. 2003, 2009; Laird 2014). In ad- tissues. What was less predicted is the finding dition to these common traits that are found in that a Cx43-rich organ, like the heart, is most most ODDD patients, patients variably present often disease-free in ODDD patients, raising with any number of comorbidities that include questions as to the mechanisms involved (Laird central nervous system (CNS) defects, bladder 2014; Kelly et al. 2015). The most prevalent ex- incontinence, skin disorders or more than a planation for how the heart is exempt from dis- half-dozen other rare conditions (Paznekas ease in ODDD is rooted in compensatory mech- et al. 2003, 2009; Laird 2014). Interestingly, for anisms in which other members of the 21

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 3 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

M. Delmar et al.

connexin family are expressed in the same car- CONNEXINS IN CANCER diac cells that co-express Cx43. Alternatively, and as discussed in a later section of this review, The year 2016 marks the 50th anniversary of some evidence supports the premise that the Loewenstein and Kanno’s discovery that inter- heart can tolerate massive reductions in Cx43 cellular communication was absent in liver tu- before disease becomes evident (Flenniken mor cells (Loewenstein and Kanno 1966). Ensu- et al. 2005; Kalcheva et al. 2007; Dobrowolski ing studies interrogating connexin and gap et al. 2008). junction levels in a variety of tumor cell types Over the past decade, more than two dozen and in vivo tumors were relatively consistent Cx43 mutants have been expressed and interro- with connexins having tumor suppressive prop- gated in either reference-cells or tissue-relevant erties (Yamasaki et al. 1995; Mesnil 2002; Naus cells to assess their trafficking, assembly, and and Laird 2010). This position was supported by functional status (Shibayama et al. 2005; Pazne- a diverse set of studies that reported restored kas et al. 2009; De Bock et al. 2013a; Laird 2014). growth control in tumor cells engineered to ec- These studies were combined with discoveries topically express connexins (Zhu et al. 1991; from three genetically modified mouse models Naus et al. 1992). Other studies showed that that mirrored ODDD, to elucidate the genotype tumor-promoting agents and cancer-causing vi- relationship of ODDD mutants to phenotype ruses typically shutdown gap junctional inter- outcomes as they translate to clinical symptoms cellular communication (GJIC) in cells destined in humans (Flenniken et al. 2005; Kalcheva et al. to be transformed (Crow et al. 1992). Probably 2007; Dobrowolski et al. 2008). Collectively, the most compelling evidence linking connexins these studies revealed that GJA1 gene mutations to tumorigenesis was from findings in genetical- can cause ODDD by at least ten different mech- ly modified mice that either lacked a connexin or anisms that can be subclassified as either loss-of- expressed a loss-of-function connexin mutant. function or gain-of-function mutations (Kelly For instance, mice lacking Cx32 were much et al. 2015). Loss-of-function mutants include more susceptible to chemical- or radiation-in- those that fail to properly traffic to the cell sur- duced liver and/or lung tumors whereas mice face and are retained within compartments as- expressing a Cx43 loss-of-function mutant in sociated with secretion. Other mutants an ErbB2 overexpressing background had in- are still able to assemble structural gap junctions creased mammary gland tumor metastasis to but the resulting channels are functionally dead. the lungs (Temme et al. 1997; King and Lampe Gain-of-function mutants may traffic properly 2004a,b; Plante et al. 2011). to the cell surface but assemble into hyperactive Over the past two decades, strategic studies connexin “hemichannels.” Still other mutants in have revealed that the role of connexins and gap this class interact inappropriately with co-ex- junctions in cancer is much more complex than pressed connexins and show aberrant transdo- originally proposed. First, more exhaustive anal- minant effects on a broader range of connexin yses of tumor types in situ and of stages of dis- channels (De Bock et al. 2013a; Laird 2014). ease have revealed that some tumors are con- Studies from harvested patient dermal fibro- nexin-rich, and that high connexin-expression blasts have further resolved the impact of in metastatic disease may even be a negative ODDD-linked mutants in a more native envi- prognostic indicator (Ito et al. 2000; Naus and ronment, in which the mutant and endogenous Laird 2010; Zhang et al. 2015). Second, the Cx43 levels are appropriately balanced in this mechanism by which connexins act in tumor predominantly autosomal dominant disease cells is not limited to GJIC; in fact, several stud- (Churko et al. 2011; Esseltine et al. 2015). Even ies support a GJIC-independent action of con- with increased knowledge of the genetic and nexins mediated through connexin “hemichan- mechanistic basis of ODDD, no treatments are nels” or the connexin interactome (Krutovskikh available for ODDD other than surgical inter- et al. 2000; McLachlan et al. 2006; Zhang et al. ventions such as digit separation surgeries. 2014). Third, the large 21 member connexin

4 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

family has potentially diverse roles in as neurological functions. It is thus not surprising some connexins may show tumor suppressive that the nervous system expresses up to 12 of the properties in some tumor types whereas a sec- 21 connexin family members. ond connexin subtype may provide no benefit Within the mammalian PNS, gap junctions (Yu et al. 2014; Yang et al. 2015). This outcome are primarily associated with the myelinating may be rooted in a naïve understanding of what Schwann cells. Here, Cx32 forms reflexive gap passes through each connexin channel type in junctions between the lamellae connect- vivo. Lastly, epidemiological studies linking the ing the Schwann cell cytoplasm with the adaxo- functional status of connexins to cancer onset nal cell compartment inside the myelin sheath. and disease progression is still lacking. For in- This arrangement allows for diffusion of ions stance, there are hundreds-of-thousands of pa- and small molecules across the apposed cell tients worldwide that have severely impaired membranes comprising the myelin sheath. Cx26 function, which typically manifests as Cx32 forming these gap junctions thus plays a hearing loss (Chan and Chang 2014), but there critical role in the homeostasis of myelinated ax- are no known reports that these patients are at ons. Indeed, this essential function of Cx32 ac- increased risk for cancer in organs that are rich counts for the pathologyseen in the first reported in Cx26, such as the liver. human connexin disease, namely Charcot-Ma- Going forward, the question remains as to rie-Tooth neuropathy X type 1 (CMTX1), a pro- whether connexins are a viable target in cancer gressive peripheral neuropathy characterized by prevention or treatment. At present, although a mixed pathology of demyelination and axonal connexins are currently being targeted in clini- degeneration (Bergoffen et al. 1993). With more cal trials to stimulate and accelerate chronic than 400 different mutations in the GJB1 gene wound repair (Becker et al. 2016), no trials tar- encoding Cx32, CMTX1 is the second most geting connexins in cancer have been initiated. common form of CMT (Kleopa and Sargianni- In fact, although evidence suggests connexin up- dou 2015). Both in vitro and invivomodels of the regulation or functional activity may be benefi- disease indicate that most Cx32 mutations give cial to reduce cancer onset and primary tumor rise to an inability of the mutant Cx32 to form growth, complexing evidence suggest that some functional gap junctions (Kleopa et al. 2012). connexins may provide the tumor with an ad- Within the mammalian CNS, various cell vantage in metastatic disease. Therefore, caution types express more than 10 different connexins, must be exercised when considering targeting reflecting the complexity and diverse network of connexins in cancer. Nevertheless, as genotyp- intercellular communication. These channels ing patient tumors becomes more routine, it is have distinct functions within the different cell possible to imagine where it is beneficial to tar- types and their expression can change dramati- get connexins in a subset of tumors as part of a cally during neurodevelopment (Cina et al. combinatorial treatment program. 2007) and injury (Freitas-Andrade and Naus 2016). To date, three of these , GJB1 (Cx32), GJC2 (Cx47), and GJA1 (Cx43), when CONNEXINS AND NEUROLOGICAL mutated are associated with CNS disorders DISORDERS (Abrams and Scherer 2012). The nervous system is comprised of multiple cell The main connexins expressed in the CNS types arrayed in complex interconnections. One are Cx43 and Cx30 (Nagy et al. 1999); both are way these various cell types interact and com- highly expressed in astrocytes. To a lesser extent, municate is through gap junctions related to astrocytic Cx26 has also been reported (Nagy their functional roles (Decrock et al. 2015). Dis- et al. 2001). Within these cells, gap junctions tinct connexins are expressed in unique cell form a functional syncytium of coupled astro- types in the peripheral nervous system (PNS) cytes, contributing to extracellular homeostasis and CNS; the specificity of this expression un- through spatial buffering (Scemes and Spray derlies the critical roles of each of these cells in 2012). Astrocytic Cx43 has been shown to un-

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 5 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

M. Delmar et al.

derlie gap junctions functioning to spatially Cx36 (Dobrenis et al. 2005), and Cx29 (Moon buffer K+ and glutamate (Wallraff et al. 2006; et al. 2010). Microglia thus appear to be very Giaume et al. 2010), whereas Cx30 modulates dynamic in their connexin expression profile. astrocyte glutamate transport and morphology The vascular cells in the CNS express several of astrocytic processes at the synaptic cleft, connexins (Cx37, Cx40, Cx43), which contrib- thereby controlling hippocampal excitatory ute to interendothelial coupling, as well as het- synaptic transmission (Pannasch et al. 2014). erocellular coupling with astrocytes (De Bock Substantial evidence has implicated Cx43 in et al. 2011, 2013b; Ransom and Giaume 2012). neuroprotection in models of ischemic and neu- These play an important role in determining rodegenerative conditions (Decrock et al. 2015; astrocyte and endothelial contributions to the Freitas-Andrade and Naus 2016). In the context blood brain barrier (BBB) (De Bock et al. of human mutations of the GJA1, these are as- 2014). This has been shown using Cx43/Cx30 sociated with the previously mentioned ODDD double knockout mice (Ezan et al. 2012). These (Paznekas et al. 2003; Huang et al. 2013), a dis- mice show a compromised BBB function under order that can also display CNS issues (Lod- stress caused by increased hydrostatic vascular denkemper et al. 2002; Abrams and Scherer pressure and shear stress, swelling of astrocytic 2012) as discussed in the paragraphs above. endfeet caused by edema, as well as reduced Oligodendrocytes express several connexins expression of -4 and β-dystroglycan, (Cx32, Cx29/31.1, Cx47), which have been involved in anchoring astrocyte endfeet to the shown to be necessary for proper myelination perivascular basal lamina. Endothelial functions (Menichella et al. 2003), as well as potassium are closely regulated by junctional interactions buffering (Menichella et al. 2006). Loss of with astrocytes; specifically important are the both Cx32 and Cx47 in the CNS causes severe connexins expressed in astrocytic endfeet (Fro- demyelination in mice (Menichella et al. 2003; ger et al. 2010; Pannasch et al. 2011). Odermatt et al. 2003). Therefore, it was not Depending on the maturity of the CNS, neu- surprising that loss-of-function mutations in rons can express several different connexins, in- GJC2 encoding Cx47 in humans causes Peli- cluding Cx36 (Belluardo et al. 2000; Venance zeaus–Merzbacher-like disease, a severe hypo- et al. 2000; Rash et al. 2012), Cx30.2 (i.e., human myelinating leukodystrophy (Uhlenberg et al. Cx31.9) (Kreuzberg et al. 2008), Cx31.1 (Dere 2004). Mutations in GJB1, encoding Cx32, can et al. 2008), Cx40 (Personius et al. 2007), and also result in CNS symptoms (Abrams and Cx45 (Li et al. 2008). This presumably reflects Scherer 2012). not only the diversity of neuronal cell types, but Microglia constitutes the innate immune also varying functions in the developing CNS. system of the CNS. The literature reports con- Knockout (Fushiki et al. 2003; Cina et al. 2009) flicting findings as to which connexins are and knockdown (Elias et al. 2007) of Cx43 dis- present in microglia, but these discrepancies rupts neuronal migration in the developing most likely arise as a result of different states of mouse brain, implying a possible role for gap microglial activation (Gajardo-Gomez et al. junctions in neurodevelopmental disorders. 2016). The microglia have been reported to ex- Knockout of Cx36 in mice results in near com- press Cx43 and form gap junctions (Eugenin plete loss of neuronal gap junctions in the ma- et al. 2001), whereas other studies have not ob- ture CNS (Deans et al. 2001; Hormuzdi et al. served Cx43immunoreactivity inmicroglia (Mei 2001; Long et al. 2002; De Zeeuw et al. 2003). et al. 2010; Theodoric et al. 2012). Furthermore, Surprisingly, the phenotype of these mice is Cx43 has been shown to not form gap junctions rather mild, and includes loss of synchronous in microglia (Wasseff and Scherer 2014), but inhibitory activity in the hippocampus (Deans rather form hemichannels (Takeuchi et al. et al. 2001) and visual defects in the rod path- 2006). Expression of other connexins in micro- way (Guldenagel et al. 2001). No human muta- glia has also been described, including Cx32 tions of the GJD2 gene encoding Cx36 have been (Dobrenis et al. 2005; Maezawa and Jin 2010), reported.

6 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

SKIN DISEASES AND CONNEXINS ical studies using cysteine scanning revealed that many of the residues mutated in KID syndrome Eleven clinically defined skin diseases with over- lined the hemichannel pore, and that calcium lapping phenotypes are caused by mutations regulation of the hemichannels differed. Some in five distinct connexin genes (Lilly et al. of the KID mutations become insensitive to 2016). Six of these disorders are caused by inhibition of hemichannel activity by extracellu- mutations in GJB2, causing a majority of the lar Ca2+, whereas others showed only modest functional research to focus on Cx26. The pre- impairment in Ca2+ gating. However, mutant ponderance of evidence suggests that the skin hemichannels with modestly impaired gating diseases caused by connexin mutations are a showed a substantially increased permeability result of dominant gains-of-function. In palmo- to Ca2+ (Sanchez et al. 2010, 2013, 2016). plantar keratoderma with deafness (PPK), Thus, KID syndrome mutations all show hemi- the Cx26 mutations modify the function of channel gain-of-function that produce epider- wild-type Cx43, resulting in leaky heteromeric mal pathology, but through different mecha- hemichannels (Shuja et al. 2016). In KID kera- nisms, potentially explaining the phenotypic titis-ichtyosis-deafness (KID) syndrome, Cx26 heterogeneity among patients carrying different mutations form active hemichannels with in- mutations. The epidermis maintains an extracel- creased calcium permeability, or altered regula- lular calcium gradient, with the highest levels in tion by calcium, voltage, and pH (Lee and White the granular layer and an abrupt reduction in the 2009; Sanchez and Verselis 2014; Sanchez et al. cornified layer, and calcium is a key regulator of 2014, 2016). A detailed understanding of these keratinocyte differentiation (Elsholz et al. 2014). subtle functional differences will be necessary to The altered Ca2+ permeation properties of KID develop mechanistic-based therapies for con- hemichannels would almost certainly disrupt nexin-related skin diseases. this gradient and affect keratinocyte differentia- The five connexins linked to skin disease tion. Additional studies using mouse models of have overlapping patterns of expression. In nor- KID syndrome have provided further support mal adult human skin, Cx26 is restricted to basal for mutant hemichannels disrupting calcium keratinocytes in palmoplantar skin, whereas homeostasis in vivo. Transgenic mice expressing Cx43 is expressed in all epidermal layers. Cx26 KID develop epidermal pathology, and in- and Cx43 are also present in sweat glands and creased hemichannel activity was detected in hair follicles. In contrast, Cx30, Cx30.3, and primary keratinocytes isolated from KID lesions Cx31 are only expressed in the upper differenti- (Mese et al. 2011; Schutz et al. 2011). When the ated epidermal layers (Salomon et al. 1994; Di epidermal calcium gradient was examined in the et al. 2001). A large induction of Cx26 expres- skin of these mice, it was found to be elevated in sion is observed across the epidermis in human both the intra- and extracellular compartments skin after wounding, or other pathological and of the cornified layer. This change in Ca2+ ho- experimental changes in skin thickness (Rivas meostasis was associated with defects in the epi- et al. 1997; Labarthe et al. 1998; Lucke et al. dermal water barrier and altered lipid secretion 1999; Rouan et al. 2001), which could have pro- in the affected skin (Bosen et al. 2015). found consequences on pathology caused by Increased hemichannel activity has been dominant gain-of-function mechanisms follow- compellingly linked to specific Cx26 mutations ing Cx26 mutation. causing KID syndrome, raising the question as Recent studies have begun to elucidate how to whether there may be a generalized role for increased hemichannel activity could contribute dysregulated hemichannels in some of the other to changes in epidermal homeostasis associated connexin skin disorders. Evidence that altered with the connexin genodermatoses. Hemichan- hemichannel function may also play a role in nels form aqueous pores, allowing inorganic other connexin genodermatoses comes from ions and metabolites to pass between the cyto- studies of Cx30 mutations associated with hi- plasm and extracellular space. Electrophysiolog- drotic ectodermal dysplasia (HED). Expression

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 7 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

M. Delmar et al.

of these mutants in vitro caused cell death that ing the sensory hair cells as well as in the lateral was correlated with large voltage-activated cur- wall containing the stria vascularis (Lautermann rents in cells expressing mutant proteins. In ad- et al. 1998; Ahmad et al. 2003; Forge et al. 2003; dition, cells expressing the mutant connexins Zhao and Yu 2006; Liu and Zhao 2008). The had a much higher rate of ATP leakage than stria vascularis is responsible for producing en- controls, suggesting that hemichannel-mediated dolymph and generating the endocochlear po- ATP release may contribute to HED syndrome tential, EP, which is critical for proper signal pathology (Essenfelder et al. 2004). In a similar transduction in hair cells. Both Cxs show widely fashion, Cx31 mutations linked to erythrokera- overlapping patterns of expression and an abun- todermia variabilis et progressiva (EKVP) and dance of GJs indicative of extensive interconnec- Cx43 mutations causing keratoderma-hypotri- ted cellular networks. There is also surface ex- chosis-leukonychia totalis syndrome (KHLT) pression of Cx26 in basolateral and apical were both shown to result in increased hemi- regions of supporting cells in regions devoid of channel activity, Ca2+, or ATP leakage, and cell cell–cell contacts, indicating the presence of death when expressed in transfected cells (Chi hemichannels that can communicate with peri- et al. 2012; Wang et al. 2015). lymphatic and endolymphatic compartments A growing body of evidence suggests that (Majumder et al. 2010). many, if not a majority, of the connexin muta- The majority of nonsyndromic Cx26 muta- tions associated with distinct skin diseases con- tions are deletions, truncations, and frameshifts sistently acquire unique gain-of-function activ- indicating that loss of GJ and/or hemichannel ities. So far, the most prominent mechanism is function results in hearing loss. However, there the formation of dysregulated hemichannels are a number of dominant, missense mutations that either increase ATP leakage, or disrupt that produce functional channels and result in Ca2+ homeostasis within keratinocytes and in syndromes in which hearing loss is accompa- the extracellular gradient. Further study of dis- nied by severe skin disorders, such as KID syn- ease-causing mutations coupled with additional drome (reviewed above) (Lee and White 2009; analysis of transgenic mice expressing them in Xu and Nicholson 2013). native epidermis will continue to provide new Studies of Cx26 knockout (KO) mice and mechanistic insight into the pathophysiology of transgenics with dominant-negative activity the connexin genodermatoses. are in general agreement that loss of Cx26 chan- nel function, even when restricted to supporting cells in the sensory epithelium, produces deaf- CONNEXINS AND DEAFNESS ness and leads to eventual death of supporting One of the most common causes of autosomal cells and hair cells (Cohen-Salmon et al. 2002; recessive, nonsyndromic, sensorineural deafness Kudo et al. 2003; Maeda et al. 2007; Sun et al. is mutation of the GJB2 gene encoding the Cx26 2009). Reports of hearing loss before evidence of gap junction (GJ) protein. Remarkably, although cell death or rundown of the EP have suggested a mutations in more than 90 genes have been iden- role for Cx26 in the developing cochlea (Wang tified that are associated with deafness, Cx26 et al. 2009; Liang et al. 2012; Chen et al. 2014). mutations account for as much as 50% of hear- Knockout of Cx30 in mice was also reported to ing loss characterized as severe to profound. Mu- cause deafness with rundown of the EP (Teub- tations in the GJB6 gene encoding Cx30 also ner et al. 2003; Schutz et al. 2010). However, cause deafness, but are much less frequent. expression of Cx26 was shown to decrease in In addition to forming GJ channels that sig- the cochleae of Cx30 null mice (Ahmad et al. nal between cells, Cxs can function as undocked 2007; Ortolano et al. 2008) and when Cx26 ex- hemichannels that signal across the plasma pression was preserved or increased in Cx30- membrane, as outlined in the introduction. In null mice, hearing loss was prevented (Ahmad the cochlea, Cx26 and Cx30 are expressed in the et al. 2007; Boulay et al. 2013). Increasing Cx30 supporting cells of the organ of Corti surround- expression in Cx26 null mice did not prevent

8 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

hearing loss (Qu et al. 2012). Thus, the presence lates between patient phenotype and aberrant of Cx26, but not Cx30 channels in the sensory hemichannel function are emerging and their epithelium is crucial for hearing, whereas either identification should shed light on the roles con- Cx26 or Cx30 in the stria vascularis appears nexins play in cochlear function and provide capable of maintaining hearing. avenues for treatment. Mechanistically, although GJs in the stria vascularis are undoubtedly important for K+ CONNEXINS AND HEART DISEASE transport and maintenance of the EP, a role for GJs in K+ transport within the sensory epi- Cardiac cells mainly contain the connexins thelium is not supported (Cohen-Salmon et al. Cx43>Cx40>Cx45>Cx31.9 (please note that 2002; Kudo et al. 2003; Wangemann 2006; Zde- human Cx31.9 is the homolog of mouse bik et al. 2009; Patuzzi 2011). Rather, GJs likely Cx30.2) with Cx43 being the overall dominating communicate nutrients and signaling mole- and the sole in the ventric- cules, as shown for glucose and inositol triphos- ular myocardium. Gap junctions have been sug- phate (IP3), which presumably maintain sen- gested to play a role in a number of cardiac pa- sory epithelial integrity and aid in proper hair thologies, causing both electrical and structural cell function (Beltramello et al. 2005; Zhang disturbances. et al. 2005; Chang et al. 2008, 2009). Early observations showed that acute ische- Hearing loss in syndromic deafness likely mia caused an increase in tissue resistivity, most differs from the nonsyndromic form with mu- likely by uncoupling of gap junctions (Wojtczak tant hemichannels that are overactive and/or 1979; Kleber et al. 1987), and uncoupling corre- show altered Ca2+ permeability leading to cell lated with the appearance of arrhythmia (Smith dysfunction and death (Stong et al. 2006; Gerido et al. 1995). Acute uncoupling occurs with a et al. 2007; Mese et al. 2008; Lee et al. 2009; time course similar to that of intracellular aci- Sanchez et al. 2010, 2013, 2014, 2016; Terrinoni dosis and increased calcium (Carmeliet 1999), et al. 2010; Levit et al. 2011, 2011; Mhaske et al. conditions that are known to close Cx43 gap 2013; Garcia et al. 2015). For a number of syn- junction channels (Burt 1987; Firek and Wein- dromic deafness mutants, overactive hemichan- gart 1995; Morley et al. 1996); but in addition to nels have been shown to be a consequence of direct chemical gating, changes in Cx43 phos- weakened inhibition by extracellular divalent phorylation (Beardslee et al. 2000; Axelsen et al. cations, particularly Ca2+ and by pH (Gerido 2006; Lampe et al. 2006) and lipid metabolites et al. 2007; Lee et al. 2009; Sanchez et al. 2010, (Fluri et al. 1990; Hofgaard et al. 2008; Mollerup 2013, 2014, 2016; Levit et al. 2011; Mhaske et al. et al. 2011) may also contribute. Evidence sug- 2013). These mutant hemichannels can cause gests that uncoupling makes hearts more prone excessive membrane depolarization and initiate to reentrant arrhythmias, based on studies using damaging membrane signaling. Altered perme- pharmacological uncoupling (Ohara et al. ability can also lead to damaging membrane sig- 2002), prevention of uncoupling (Xing et al. naling as suggested for the G45E KID syndrome 2003; Lewandowski et al. 2008), and genetic ab- mutation that is characterized by enhanced Ca2+ lation of Cx43 (Danik et al. 2004). At least in permeability (Sanchez et al. 2010). Patients car- some studies, ablation of Cx40 lowers atrial con- rying this mutation show profound deafness duction velocity and increases atrial fibrillation corroborated by brainstem audiometry (Gilliam (AF) risk (Hagendorff et al. 1999; Verheule et al. and Williams 2002; Janecke et al. 2005; Griffith 1999; Bagwe et al. 2005), aligning well with stud- et al. 2006). An autopsy of a G45E patient ies linking Cx40 mutations and AF in humans showed widespread vestibulo-cochlear dysplasia (Gollob et al. 2006), of which at least one muta- in the organ of Corti with no evidence of a de- tion replicates the phenotype when expressed in veloped sensory epithelium (Griffith et al. 2006), mice (Lubkemeier et al. 2013a). More recently, a plausibly explained by excessive Ca2+ entry and mutation in Cx43 has also been linked to AF cell death during cochlear development. Corre- (Sinner et al. 2014).

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 9 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

M. Delmar et al.

Gap junctions are not only involved in elec- nexins and their impact on cardiac electrophys- trical abnormalities but also in determining in- iology remains unclear. farct size after ischemia. Uncoupling was origi- Recent evidence shows that connexins have nally suggested to have beneficial effects by functions unrelated to intercellular coupling, preventing spread of tissue damage. In support and likely consequent to the fact that connexins of this notion, chemical uncoupling reduces are components of a protein interacting network infarct size in animal models as first described (a “connexome”) that includes molecules classi- by Garcia-Dorado and coworkers (1997). Al- cally defined as belonging to mechanical junc- though based on rather nonspecific inhibitors, tions and to the voltage-gated these observations were initially a strong argu- complex (Agullo-Pascual et al. 2014a,b). As a ment against the development of anti-arrhyth- component of the connexome, Cx43 actually mic therapies aimed at keeping gap junctions helps organize the microtubular network (Fran- open. Using anti-arrhythmic peptides (rotigap- cis et al. 2011; Agullo-Pascual et al. 2013a,b). In tide and danegaptide) to keep gap junctions fact, mislocalization of Cx43 can alter the traf- open, however, decreased rather than increased ficking of other proteins; along those lines, infarct size (Haugan et al. 2006; Hennan et al. knocking Cx43 out in mice reduces the cardiac 2006; Skyschally et al. 2013). The issue of the sodium current and contributes to arrhythmia relation between gap junction availability and susceptibility (Jansen et al. 2012). Knockdown cardiac homeostasis extends not only to whether of Cx43, removal of the carboxyl terminus, or of a gap junction channel is present, but also to the tubulin binding domain also reduced the whether those channels can be regulated by surface expression of NaV1.5 in HL-1 cells the intraceullular milieu. For example, infarct (Agullo-Pascual et al. 2014b). Similarly, removal size was increased in mice expressing carboxy- of the PDZ-binding domain of Cx43 led to de- terminal truncated Cx43, which does not re- creased sodium current and lethal arrhythmias spond to pH and calcium induced gating (Maass (Lubkemeier et al. 2013b). Conversely, treating et al. 2009). Furthermore, reducing Cx43 to 50% hearts injured by cryo-ablation with a peptide by genetic ablation did not alter infarct size in containing the carboxy-terminal PDZ-binding mice (Schwanke et al. 2002). In contrast, pre- domain improved Cx43 localization and re- – conditioning was lost in the Cx43+/ mice duced arrhythmia burden (O’Quinn et al. (Schwanke et al. 2002) independent of an effect 2011). Electrophysiological recordings indicat- on intercellular coupling (Li et al. 2004), an ob- ed that conduction velocity was increased, but to servation that led to the somewhat surprising what extent this finding could be explained by discovery that Cx43 locates to mitochondria preservation of sodium current, was not tested. and protects them from ischemic damage The role of the gap junction plaque on action (Boengler et al. 2005). This observation adds potential propagation may extend beyond the to a growing list of coupling-independent effects formation of the gap junction channel per se. of connexins, as discussed below. In recent years, the concept of ephaptic or elec- Following ischemia, gap junctions distribute trical field-mediated propagation has re- heterogeneously with lateralization in the infarct emerged, placing the ephaptic phase as periph- border zone and these areas of disarray also dis- eral to the gap junction (in the “perinexus” as play reentrant arrhythmias on local stimulation defined by the Gourdie laboratory (Rhett et al. (Peters et al. 1997). Similar disarray is observed 2011). Ephaptic coupling occurs when influx of under several pathological conditions including sodium leads to a local extracellular negative heart failure (Kostin et al. 2003), systemic (Kos- potential, which effectively depolarizes the op- tin et al. 2004), and pulmonary (Chkourko et al. posing membrane. Conditions for this to occur 2012) hypertension; and although it is often as- are predominantly a large and dense sodium sumed that lateralized gap junctions are not current, and closely positioned membranes functional, a study suggests that they are (Cabo (Sperelakis 2002). These conditions are possibly et al. 2006). The issue of lateralization of con- met at the intercalated disc. In addition to the

10 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

perinexus (Rhett et al. 2012), sodium channels Agullo-Pascual E, Lin X, Pfenniger A, Lubkemeier I, Wil- are confronted against each other at the adhe- lecke K, Rothenberg E, Delmar M. 2013a. A novel non- canonical role of cx43 in the heart: Ensuring the arrival of “ ” 10: sion/excitability nodes, mini-nodes of Ranvier Nav1.5 to the intercalated disk. Heart Rhythm 1742. where clusters of N-cadherin organize sodium Agullo-Pascual E, Reid DA, Keegan S, Sidhu M, Fenyo D, channels into dense clusters (Leo-Macias et al. Rothenberg E, Delmar M. 2013b. Super-resolution fluo- rescence microscopy of the cardiac connexome reveals 2016b). Evidence for ephaptic coupling includes plakophilin-2 inside the connexin43 plaque. Cardiovasc the finding that extracellular edema, contrary to Res 100: 231–240. expectation from cable theory, decreases rather Agullo-Pascual E, Cerrone M, Delmar M. 2014a. Arrhyth- than increases CV (Veeraraghavan et al. 2012). mogenic cardiomyopathy and : Dis- eases of the connexome. FEBS Lett 588: 1322–1330. Ephaptic theory may also explain the paradox +/– Agullo-Pascual E, Lin X, Leo-Macias A, Zhang M, Liang FX, that in heterozygous Cx43 mice, reduction of Li Z, Pfenniger A, Lubkemeier I, Keegan S, Fenyo D, et al. connexin abundance does not associate with 2014b. Super-resolution imaging reveals that loss of the changes in conduction velocity (Morley et al. C-terminus of connexin43 limits microtubule plus-end capture and NaV1.5 localization at the intercalated disc. 1999; Stein et al. 2009). Cardiovasc Res 104: 371–381. Ahmad S, Chen S, Sun J, Lin X. 2003. Connexins 26 and 30 are co-assembled to form gap junctions in the cochlea of CONCLUDING REMARKS mice. Biochem Biophys Res Commun 307: 362–368. Ahmad S, Tang W, Chang Q, Qu Y, Hibshman J, Li Y, Sohl G, Limitations in pharmacological tools and in Willecke K, Chen P, Lin X. 2007. Restoration of con- methods for studying connexin function in nexin26 protein level in the cochlea completely rescues fi hearing in a mouse model of human connexin30-linked vivo initially made it dif cult to directly link deafness. Proc Natl Acad Sci 104: 1337–1341. connexin function to disease. It is ∼30 years Axelsen LN, Stahlhut M, Mohammed S, Larsen BD, Nielsen since the identification of the genes coding for MS, Holstein-Rathlou NH, Andersen S, Jensen ON, fi gap junction proteins, which enabled us to link Hennan JK, Kjolbye AL. 2006. Identi cation of ische- mia-regulated phosphorylation sites in connexin43: A connexins to specific functions by the discovery possible target for the antiarrhythmic peptide analogue of disease-causing mutations. In some cases, rotigaptide (ZP123). J Mol Cell Cardiol 40: 790–798. mutations confirmed our understanding of con- Axelsen LN, Calloe K, Holstein-Rathlou NH, Nielsen MS. 2013. Managing the complexity of communication: Reg- nexins as gap junctional channels that provide ulation of gap junctions by post-translational modifica- intercellular coupling, but in other cases, new tion. Front Pharmacol 4: 130. noncanonical functions have emerged. The Bagwe S, Berenfeld O, Vaidya D, Morley GE, Jalife J. 2005. combined genetic and functional investigations Altered right atrial excitation and propagation in con- nexin40 knockout mice. Circulation 112: 2245–2253. have led to enormous leaps in understanding not Beardslee MA, Lerner DL, Tadros PN, Laing JG, Beyer EC, only the function of these proteins but also their Yamada KA, Kleber AG, Schuessler RB, Saffitz JE. 2000. role in inherited and in acquired diseases. In Dephosphorylation and intracellular redistribution of both cases, we have learned that rarely is a dis- ventricular connexin43 during electrical uncoupling in- duced by ischemia. Circ Res 87: 656–662. ease caused by a single molecule, without the Becker DL, Phillips AR, Duft BJ, Kim Y, Green CR. 2016. complicity of its neighbors. Phenotypes are the Translating connexin biology into therapeutics. Semin reflection of a constellation of molecules that Cell Dev Biol 50: 49–58. work together, or fail to do so. Among the Belluardo N, Mudo G, Trovato-Salinaro A, Le Gurun S, Charollais A, Serre-Beinier V, Amato G, Haefliger JA, many challenges ahead is to gain a better under- Meda P, Condorelli DF. 2000. Expression of connexin36 standing of how these constellations are formed, in the adult and developing rat brain. Brain Res 865: 121– and how connexins operate within them so that 138. we can better connect the two poles of a spec- Beltramello M, Piazza V, Bukauskas FF, Pozzan T, Mam- mano F. 2005. Impaired permeability to Ins(1,4,5)P3 in trum: connexin and disease. a mutant connexin underlies recessive hereditary deaf- ness. Nat Cell Biol 7: 63–69. Bergoffen J, Scherer SS, Wang S, Scott MO, Bone LJ, Paul DL, REFERENCES Chen K, Lensch MW, Chance PF, Fischbeck KH. 1993. Connexin mutations in X-linked Charcot-Marie-Tooth 262: – Abrams CK, Scherer SS. 2012. Gap junctions in inherited disease. Science 2039 2042. human disorders of the central nervous system. Biochim Berthoud VM, Ngezahayo A. 2017. Focus on lens connexins. Biophys Acta 1818: 2030–2047. BMC Cell Biol 18: 6.

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 11 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

M. Delmar et al.

Boengler K, Dodoni G, Rodriguez-Sinovas A, Cabestrero A, Cohen-Salmon M, Ott T, Michel V, Hardelin JP, Perfettini I, Ruiz-Meana M, Gres P, Konietzka I, Lopez-Iglesias C, Eybalin M, Wu T, Marcus DC, Wangemann P, Willecke Garcia-Dorado D, Di Lisa F, et al. 2005. Connexin 43 in K, et al. 2002. Targeted ablation of connexin26 in the cardiomyocyte mitochondria and its increase by ischemic inner ear epithelial gap junction network causes hearing preconditioning. Cardiovasc Res 67: 234–244. impairment and cell death. Curr Biol 12: 1106–1111. Bosen F, Celli A, Crumrine D, Vom Dorp K, Ebel P, Jastrow Crow DS, Kurata WE, Lau AF. 1992. Phosphorylation of H, Dormann P, Winterhager E, Mauro T, Willecke K. connexin43 in cells containing mutant src oncogenes. 2015. Altered epidermal lipid processing and calcium dis- Oncogene 7: 999–1003. tribution in the KID syndrome mouse model Cx26S17F. Danik SB, Liu F, Zhang J, Suk HJ, Morley GE, Fishman GE, FEBS Lett 589: 1904–1910. Gutstein DE. 2004. Modulation of cardiac gap junction Boulay AC, del Castillo FJ, Giraudet F, Hamard G, Giaume expression and arrhythmic susceptibility. Circ Res 95: C, Petit C, Avan P, Cohen-Salmon M. 2013. Hearing is 1035–1041. normal without connexin30. J Neurosci 33: 430–434. Deans MR, Gibson JR, Sellitto C, Connors BW, Paul DL. Burt JM. 1987. Block of intercellular communication: Inter- 2001. Synchronous activity of inhibitory networks in neo- action of intracellular H+ and Ca2+. Am J Physiol 253: cortex requires electrical synapses containing con- C607–C612. nexin36. Neuron 31: 477–485. Cabo C, Yao J, Boyden PA, Chen S, Hussain W, Duffy HS, De Bock M, Culot M, Wang N, Bol M, Decrock E, De Vuyst Ciaccio EJ, Peters NS, Wit AL. 2006. Heterogeneous gap E, da Costa A, Dauwe I, Vinken M, Simon AM, et al. 2011. junction remodeling in reentrant circuits in the epicardial Connexin channels provide a target to manipulate brain border zone of the healing canine infarct. Cardiovasc Res endothelial calcium dynamics and blood–brain barrier 72: 241–249. permeability. J Cereb Blood Flow Metab 31: 1942–1957. Carmeliet E. 1999. Cardiac ionic currents and acute ische- De Bock M, Kerrebrouck M, Wang N, Leybaert L. 2013a. mia: From channels to arrhythmias. Physiol Rev 79: 917– Neurological manifestations of oculodentodigital dyspla- 1017. sia: A Cx43 of the central nervous system? Front Pharmacol 4: 120. Chan DK, Chang KW. 2014. GJB2-associated hearing loss: Systematic review of worldwide prevalence, genotype, and De Bock M, Wang N, Decrock E, Bol M, Gadicherla AK, auditory phenotype. Laryngoscope 124: E34–E53. Culot M, Cecchelli R, Bultynck G, Leybaert L. 2013b. Endothelial calcium dynamics, connexin channels and Chang Q, Tang W, Ahmad S, Zhou B, Lin X. 2008. Gap blood–brain barrier function. Prog Neurobiol 108: 1–20. junction mediated intercellular metabolite transfer in the cochlea is compromised in connexin30 null mice. De Bock M, Vandenbroucke RE, Decrock E, Culot M, Cec- – PLoS ONE 3: e4088. chelli R, Leybaert L. 2014. A new angle on blood CNS interfaces: A role for connexins? FEBS Lett 588: 1259– Chang Q, Tang W, Ahmad S, Stong B, Leu G, Lin X. 2009. 1270. Functional studies reveal new mechanisms for deafness caused by connexin mutations. Otol Neurotol 30: 237– Decrock E, De Bock M, Wang N, Bultynck G, Giaume C, 240. Naus CC, Green CR, Leybaert L. 2015. Connexin and pannexin signaling pathways, an architectural blueprint Chen S, Sun Y, Lin X, Kong W. 2014. Down regulated con- for CNS physiology and pathology? Cell Mol Life Sci 72: nexin26 at different postnatal stage displayed different 2823–2851. types of cellular degeneration and formation of organ of Corti. Biochem Biophys Res Commun 445: 71–77. Dere E, Zheng-Fischhofer Q, Viggiano D, Gironi Carnevale UA, Ruocco LA, Zlomuzica A, Schnichels M, Willecke K, Chi J, Li L, Liu M, Tan J, Tang C, Pan Q, Wang D, Zhang Z. Huston JP, Sadile AG. 2008. Connexin31.1 deficiency in 2012. Pathogenic connexin-31 forms constitutively active the mouse impairs object memory and modulates open- hemichannels to promote necrotic cell death. PLoS ONE fi 7: eld exploration, acetylcholine esterase levels in the stri- e32531. atum, and cAMP response element-binding protein levels Chkourko HS, Guerrero-Serna G, Lin X, Darwish N, Pohl- in the striatum and piriform cortex. Neuroscience 153: mann JR, Cook KE, Martens JR, Rothenberg E, Musa H, 396–405. Delmar M. 2012. Remodeling of mechanical junctions De Zeeuw CI, Chorev E, Devor A, Manor Y, Van Der Giessen and of microtubule-associated proteins accompany car- 9: – RS, De Jeu MT, Hoogenraad CC, Bijman J, Ruigrok TJ, diac connexin43 lateralization. Heart Rhythm 1133 French P, et al. 2003. Deformation of network connectiv- 1140 e1136. ity in the inferior olive of connexin 36-deficient mice is Churko JM, Shao Q, Gong XQ, Swoboda KJ, Bai D, Sampson compensated by morphological and electrophysiological J, Laird DW. 2011. Human dermal fibroblasts derived changes at the single neuron level. J Neurosci 23: 4700– from oculodentodigital dysplasia patients suggest that pa- 4711. 32: tients may have wound-healing defects. Hum Mutat Di WL, Rugg EL, Leigh IM, Kelsell DP. 2001. Multiple epi- – 456 466. dermal connexins are expressed in different keratinocyte Cina C, Bechberger JF, Ozog MA, Naus CC. 2007. Expres- subpopulations including connexin 31. J Invest Dermatol sion of connexins in embryonic mouse neocortical devel- 117: 958–964. 504: – opment. J Comp Neurol 298 313. Dobrenis K, Chang HY, Pina-Benabou MH, Woodroffe A, Cina C, Maass K, Theis M, Willecke K, Bechberger JF, Naus Lee SC, Rozental R, Spray DC, Scemes E. 2005. Human CC. 2009. Involvement of the cytoplasmic C-terminal and mouse microglia express connexin36, and functional domain of connexin43 in neuronal migration. J Neurosci gap junctions are formed between rodent microglia and 29: 2009–2021. neurons. J Neurosci Res 82: 306–315.

12 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

Dobrowolski R, Sasse P, Schrickel JW, Watkins M, Kim JS, Gajardo-Gomez R, Labra VC, Orellana JA. 2016. Connexins Rackauskas M, Troatz C, Ghanem A, Tiemann K, Degen and pannexins: New insights into microglial functions J, et al. 2008. The conditional connexin43G138R mouse and dysfunctions. Front Mol Neurosci 9: 86. mutant represents a new model of hereditary oculoden- Garcia-Dorado D, Inserte J, Ruiz-Meana M, Gonzalez MA, 17: – todigital dysplasia in humans. Hum Mol Genet 539 Solares J, Julia M, Barrabes JA, Soler-Soler J. 1997. Gap 554. junction uncoupler heptanol prevents cell-to-cell pro- Elias LA, Wang DD, Kriegstein AR. 2007. Gap junction gression of hypercontracture and limits necrosis during adhesion is necessary for radial migration in the neocor- myocardial reperfusion. Circulation 96: 3579–3586. 448: – tex. Nature 901 907. Garcia IE, Maripillan J, Jara O, Ceriani R, Palacios-Munoz A, Elsholz F, Harteneck C, Muller W, Friedland K. 2014. Cal- Ramachandran J, Olivero P, Perez-Acle T, Gonzalez C, cium—A central regulator of keratinocyte differentiation Saez JC, et al. 2015. Keratitis--deafness syn- in health and disease. Eur J Dermatol 24: 650–661. drome-associated Cx26 mutants produce nonfunctional Esseltine JL, Shao Q, Huang T, Kelly JJ, Sampson J, Laird gap junctions but hyperactive hemichannels when co-ex- DW. 2015. Manipulating Cx43 expression triggers gene pressed with wild type Cx43. J Invest Dermatol 135: 1338– reprogramming events in dermal fibroblasts from oculo- 1347. dentodigital dysplasia patients. Biochem J 472: 55–69. Gerido DA, DeRosa AM, Richard G, White TW. 2007. Ab- Essenfelder GM, Bruzzone R, Lamartine J, Charollais A, errant hemichannel properties of Cx26 mutations causing Blanchet-Bardon C, Barbe MT, Meda P, Waksman G. skin disease and deafness. Am J Physiol Cell Physiol 293: 2004. Connexin30 mutations responsible for hidrotic ec- C337–C345. todermal dysplasia cause abnormal hemichannel activity. Giaume C, Koulakoff A, Roux L, Holcman D, Rouach N. Hum Mol Genet 13: 1703–1714. 2010. Astroglial networks: A step further in neuroglial Eugenin EA, Eckardt D, Theis M, Willecke K, Bennett MV, and gliovascular interactions. Nat Rev Neurosci 11: 87–99. Saez JC. 2001. Microglia at brain stab wounds express Gilliam A, Williams ML. 2002. Fatal septicemia in an infant connexin 43 and in vitro form functional gap junctions with keratitis, ichthyosis, and deafness (KID) syndrome. after treatment with interferon-gamma and tumor necro- Pediatr Dermatol 19: 232–236. α 98: – sis factor- . Proc Natl Acad Sci 4190 4195. Gollob MH, Jones DL, Krahn AD, Danis L, Gong XQ, Shao Ezan P, Andre P, Cisternino S, Saubamea B, Boulay AC, Q, Liu X, Veinot JP, Tang AS, Stewart AF, et al. 2006. Doutremer S, Thomas MA, Quenech’du N, Giaume C, Somatic mutations in the connexin 40 gene (GJA5)in Cohen-Salmon M. 2012. Deletion of astroglial connexins atrial fibrillation. N Engl J Med 354: 2677–2688. weakens the blood-brain barrier. J Cereb Blood Flow Griffith AJ, Yang Y, Pryor SP, Park HJ, Jabs EW, Nadol JB Jr, 32: – Metab 1457 1467. Russell LJ, Wasserman DI, Richard G, Adams JC, et al. Firek L, Weingart R. 1995. Modification of gap junction 2006. Cochleosaccular dysplasia associated with a con- conductance by divalent cations and protons in neonatal nexin 26 mutation in keratitis-ichthyosis-deafness syn- rat heart cells. J Mol Cell Cardiol 27: 1633–1643. drome. Laryngoscope 116: 1404–1408. Flenniken AM, Osborne LR, Anderson N, Ciliberti N, Flem- Guldenagel M, Ammermuller J, Feigenspan A, Teubner B, ing C, Gittens JE, Gong XQ, Kelsey LB, Lounsbury C, Degen J, Sohl G, Willecke K, Weiler R. 2001. Visual trans- Moreno L, et al. 2005. A Gja1 missense mutation in a mission deficits in mice with targeted disruption of the mouse model of oculodentodigital dysplasia. Develop- gap junction gene connexin36. J Neurosci 21: 6036–6044. 132: – ment 4375 4386. Hagendorff A, Schumacher B, Kirchhoff S, Luderitz B, Wil- Fluri GS, Rudisuli A, Willi M, Rohr S, Weingart R. 1990. lecke K. 1999. Conduction disturbances and increased Effects of arachidonic acid on the gap junctions of neo- atrial vulnerability in connexin40-deficient mice analyzed natal rat heart cells. Pflugers Arch 417: 149–156. by transesophageal stimulation. Circulation 99: 1508– Forge A, Becker D, Casalotti S, Edwards J, Marziano N, 1515. Nevill G. 2003. Gap junctions in the inner ear: Compar- Haugan K, Marcussen N, Kjolbye AL, Nielsen MS, Hennan ison of distribution patterns in different vertebrates and JK, Petersen JS. 2006. Treatment with the gap junction assessement of connexin composition in mammals. J modifier rotigaptide (ZP123) reduces infarct size in rats Comp Neurol 467: 207–231. with chronic myocardial infarction. J Cardiovasc Phar- Francis R, Xu X, Park H, Wei CJ, Chang S, Chatterjee B, Lo C. macol 47: 236–242. 2011. Connexin43 modulates cell polarity and directional Hennan JK, Swillo RE, Morgan GA, Keith JC Jr, Schaub RG, cell migration by regulating microtubule dynamics. PLoS Smith RP, Feldman HS, Haugan K, Kantrowitz J, Wang ONE 6: e26379. PJ, et al. 2006. Rotigaptide (ZP123) prevents spontaneous Freitas-Andrade M, Naus CC. 2016. Astrocytes in neuro- ventricular arrhythmias and reduces infarct size during protection and neurodegeneration: The role of con- myocardial ischemia/reperfusion injury in open-chest nexin43 and pannexin1. Neuroscience 323: 207–221. dogs. J Pharmacol Exp Ther 317: 236–243. Froger N, Orellana JA, Calvo CF, Amigou E, Kozoriz MG, Hofgaard JP, Banach K, Mollerup S, Jorgensen HK, Olesen Naus CC, Saez JC, Giaume C. 2010. Inhibition of cyto- SP, Holstein-Rathlou NH, Nielsen NS. 2008. Phosphati- kine-induced connexin43 hemichannel activity in astro- dylinositol-bisphosphate regulates intercellular coupling cytes is neuroprotective. Mol Cell Neurosci 45: 37–46. in cardiac myocytes. Pflugers Arch 457: 303–313. Fushiki S, Perez Velazquez JL, Zhang L, Bechberger JF, Car- Hormuzdi SG, Pais I, LeBeau FE, Towers SK, Rozov A, Buhl len PL, Naus CC. 2003. Changes in neuronal migration in EH, Whittington MA, Monyer H. 2001. Impaired electri- neocortex of connexin43 null mutant mice. J Neuropathol cal signaling disrupts gamma frequency oscillations in Exp Neurol 62: 304–314. connexin 36-deficient mice. Neuron 31: 487–495.

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 13 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

M. Delmar et al.

Huang T, Shao Q, MacDonald A, Xin L, Lorentz R, Bai D, Kudo T, Kure S, Ikeda K, Xia AP, Katori Y, Suzuki M, Kojima Laird DW. 2013. Autosomal recessive GJA1 (Cx43) gene K, Ichinohe A, Suzuki Y, Aoki Y, et al. 2003. Transgenic mutations cause oculodentodigital dysplasia by distinct expression of a dominant-negative connexin26 causes de- mechanisms. J Cell Sci 126: 2857–2866. generation of the organ of Corti and non-syndromic deaf- Ito A, Katoh F, Kataoka TR, Okada M, Tsubota N, Asada H, ness. Hum Mol Genet 12: 995–1004. Yoshikawa K, Maeda S, Kitamura Y, Yamasaki H, et al. Labarthe MP, Bosco D, Saurat JH, Meda P, Salomon D. 1998. 2000. A role for heterologous gap junctions between mel- Upregulation of connexin 26 between keratinocytes of anoma and endothelial cells in metastasis. J Clin Invest psoriatic lesions. J Invest Dermatol 111: 72–76. 105: – 1189 1197. Laird DW. 2014. Syndromic and non-syndromic disease- Janecke AR, Hennies HC, Gunther B, Gansl G, Smolle J, linked Cx43 mutations. FEBS Lett 588: 1339–1348. Messmer EM, Utermann G, Rittinger O. 2005. GJB2 mu- Lampe PD, Cooper CD, King TJ, Burt JM. 2006. Analysis of tations in keratitis-ichthyosis-deafness syndrome includ- 133A: – connexin43 phosphorylated at S325, S328 and S330 in ing its fatal form. Am J Med Genet A 128 131. normoxic and ischemic heart. J Cell Sci 119: 3435–3442. Jansen JA, Noorman M, Musa H, Stein M, de Jong S, van der Lautermann J, ten Cate WJ, Altenhoff P, Grummer R, Traub Nagel R, Hund TJ, Mohler PJ, Vos MA, van Veen TA, et O, Frank H, Jahnke K, Winterhager E. 1998. Expression of al. 2012. Reduced heterogeneous expression of Cx43 re- the gap-junction connexins 26 and 30 in the rat cochlea. sults in decreased Nav1.5 expression and reduced sodium Cell Tissue Res 294: 415–420. current that accounts for arrhythmia vulnerability in con- ditional Cx43 knockout mice. Heart Rhythm 9: 600–607. Lee JR, White TW. 2009. Connexin-26 mutations in deafness and skin disease. Expert Rev Mol Med 11: e35. Kalcheva N, Qu J, Sandeep N, Garcia L, Zhang J, Wang Z, Lampe PD, Suadicani SO, Spray DC, Fishman GI. 2007. Lee JR, Derosa AM, White TW. 2009. Connexin mutations Gap junction remodeling and cardiac arrhythmogenesis causing skin disease and deafness increase hemichannel in a murine model of oculodentodigital dysplasia. Proc activity and cell death when expressed in Xenopus oo- 129: – Natl Acad Sci 104: 20512–20516. cytes. J Invest Dermatol 870 878. Kelly JJ, Simek J, Laird DW. 2015. Mechanisms linking con- Leo-Macias A, Agullo-Pascual E, Delmar M. 2016a. The nexin mutations to human diseases. Cell Tissue Res 360: cardiac connexome: Non-canonical functions of con- 701–721. nexin43 and their role in cardiac arrhythmias. Semin 50: – King TJ, Lampe PD. 2004a. The gap junction protein con- Cell Dev Biol 13 21. nexin32 is a mouse lung tumor suppressor. Cancer Res 64: Leo-Macias A, Agullo-Pascual E, Sanchez-Alonso JL, Kee- 7191–7196. gan S, Lin X, Arcos T, Feng Xia L, Korchev YE, Gorelik J, King TJ, Lampe PD. 2004b. Mice deficient for the gap junc- Fenyo D, et al. 2016b. Nanoscale visualization of func- tional adhesion/excitability nodes at the intercalated disc. tion protein connexin32 exhibit increased radiation-in- 7: duced tumorigenesis associated with elevated mitogen- Nat Commun 10342. activated protein kinase (p44/Erk1, p42/Erk2) activation. Levit NA, Mese G, Basaly MG, White TW. 2011. Patholog- Carcinogenesis 25: 669–680. ical hemichannels associated with human Cx26 muta- Kleber AG, Riegger CB, Janse MJ. 1987. Electrical uncou- tions causing Keratitis-Ichthyosis-Deafness syndrome. 1818: – pling and increase of extracellular resistance after induc- Biochim Biophys Acta 2014 2019. tion of ischemia in isolated, arterially perfused rabbit Lewandowski R, Procida K, Vaidyanathan R, Coombs W, papillary muscle. Circ Res 61: 271–279. Jalife J, Nielsen MS, Taffet SM, Delmar M. 2008. RXP- Kleopa KA, Sargiannidou I. 2015. Connexins, gap junctions E: A connexin43-binding peptide that prevents action 103: – and peripheral neuropathy. Neurosci Lett 596: 27–32. potential propagation block. Circ Res 519 526. Kleopa KA, Abrams CK, Scherer SS. 2012. How do muta- Li X, Heinzel FR, Boengler K, Schulz R, Heusch G. 2004. Role tions in GJB1 cause X-linked Charcot-Marie-Tooth dis- of connexin 43 in ischemic preconditioning does not in- ease? Brain Res 1487: 198–205. volve intercellular communication through gap junctions. 36: – Kostin S, Rieger M, Dammer S, Hein S, Richter M, Klove- J Mol Cell Cardiol 161 163. korn WP, Bauer EP, Schaper J. 2003. Gap junction remod- Li X, Kamasawa N, Ciolofan C, Olson CO, Lu S, Davidson eling and altered connexin43 expression in the failing KG, Yasumura T, Shigemoto R, Rash JE, Nagy JI. 2008. human heart. Mol Cell Biochem 242: 135–144. Connexin45-containing neuronal gap junctions in rodent Kostin S, Dammer S, Hein S, Klovekorn WP, Bauer EP, retina also contain connexin36 in both apposing hemi- Schaper J. 2004. Connexin 43 expression and distribution plaques, forming bihomotypic gap junctions, with scaf- folding contributed by zonula occludens-1. J Neurosci 28: in compensated and decompensated cardiac hypertrophy – in patients with aortic stenosis. Cardiovasc Res 62: 426– 9769 9789. 436. Liang C, Zhu Y, Zong L, Lu GJ, Zhao HB. 2012. Cell degen- Kreuzberg MM, Deuchars J, Weiss E, Schober A, Sonntag S, eration is not a primary causer for Connexin26 (GJB2) fi 528: – Wellershaus K, Draguhn A, Willecke K. 2008. Expression de ciency associated hearing loss. Neurosci Lett 36 of connexin30.2 in interneurons of the central nervous 41. system in the mouse. Mol Cell Neurosci 37: 119–134. Lilly E, Sellitto C, Milstone LM, White TW. 2016. Connexin Krutovskikh VA, Troyanovsky SM, Piccoli C, Tsuda H, Asa- channels in congenital skin disorders. Semin Cell Dev Biol 50: – moto M, Yamasaki H. 2000. Differential effect of subcel- 4 12. lular localization of communication impairing gap junc- Liu YP, Zhao HB. 2008. Cellular characterization of con- tion protein connexin43 on tumor cell growth in vivo. nexin26 and connnexin30 expression in the cochlear lat- Oncogene 19: 505–513. eral wall. Cell Tissue Res 333: 395–403.

14 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

Loddenkemper T, Grote K, Evers S, Oelerich M, Stogbauer F. meability to large cationic molecules. Am J Physiol Cell 2002. Neurological manifestations of the oculodentodigi- Physiol 295: C966–C974. 249: – tal dysplasia syndrome. J Neurol 584 595. Mese G, Sellitto C, Li L, Wang HZ, Valiunas V, Richard G, Loewenstein WR, Kanno Y. 1966. Intercellular communica- Brink PR, White TW. 2011. The Cx26-G45E mutation tion and the control of tissue growth: Lack of communi- displays increased hemichannel activity in a mouse model cation between cancer cells. Nature 209: 1248–1249. of the lethal form of keratitis-ichthyosis-deafness syn- Long MA, Deans MR, Paul DL, Connors BW. 2002. Rhyth- drome. Mol Biol Cell 22: 4776–4786. micity without synchrony in the electrically uncoupled Mesnil M. 2002. Connexins and cancer. Biol Cell 94: 493– inferior olive. J Neurosci 22: 10898–10905. 500. Lubkemeier I, Andrie R, Lickfett L, Bosen F, Stockigt F, Mhaske PV, Levit NA, Li L, Wang HZ, Lee JR, Shuja Z, Brink Dobrowolski R, Draffehn AM, Fregeac J, Schultze JL, Bu- PR, White TW. 2013. The human Cx26-D50A and Cx26- kauskas FF, et al. 2013a. The connexin40A96S mutation A88V mutations causing keratitis-ichthyosis-deafness from a patient with atrial fibrillation causes decreased syndrome display increased hemichannel activity. Am J atrial conduction velocities and sustained episodes of in- Physiol Cell Physiol 304: C1150–C1158. duced atrial fibrillation in mice. J Mol Cell Cardiol 65: 19– Mollerup S, Hofgaard JP, Braunstein TH, Kjenseth A, Leithe 32. E, Rivedal E, Holstein-Rathlou NH, Nielsen MS. 2011. Lubkemeier I, Requardt RP, Lin X, Sasse P, Andrie R, Norepinephrine inhibits intercellular coupling in rat car- Schrickel JW, Chkourko H, Bukauskas FF, Kim JS, Frank diomyocytes by ubiquitination of connexin43 gap junc- fi M, et al. 2013b. Deletion of the last ve C-terminal amino tions. Cell Commun Adhes 18: 57–65. acid residues of connexin43 leads to lethal ventricular Moon Y, Choi SY, Kim K, Kim H, Sun W. 2010. Expression arrhythmias in mice without affecting coupling via gap of connexin29 and 32 in the penumbra region after trau- junction channels. Basic Res Cardiol 108: 348. matic brain injury of mice. Neuroreport 21: 1135–1139. Lucke T, Choudhry R, Thom R, Selmer IS, Burden AD, Hodgins MB. 1999. Upregulation of connexin 26 is a Morley GE, Taffet SM, Delmar M. 1996. Intramolecular in- teractions mediate pH regulation of connexin43 channels. feature of keratinocyte differentiation in hyperprolifera- 70: – tive epidermis, vaginal epithelium, and buccal epithelium. Biophys J 1294 1302. J Invest Dermatol 112: 354–361. Morley GE, Vaidya D, Samie FH, Lo C, Delmar M, Jalife J. Maass K, Chase SE, Lin X, Delmar M. 2009. Cx43 CT do- 1999. Characterization of conduction in the ventricles of main influences infarct size and susceptibility to ventric- normal and heterozygous Cx43 knockout mice using op- 10: – ular tachyarrhythmias in acute myocardial infarction. tical mapping. J Cardiovasc Electrophysiol 1361 1375. Cardiovasc Res 84: 361–367. Nagy JI, Patel D, Ochalski PA, Stelmack GL. 1999. Con- Maeda Y, Fukushima K, Kawasaki A, Nishizaki K, Smith RJ. nexin30 in rodent, cat and human brain: Selective expres- 2007. Cochlear expression of a dominant-negative sion in gray matter astrocytes, co-localization with con- GJB2 construct delivered through the round window nexin43 at gap junctions and late developmental R75W 88: – membrane in mice. Neurosci Res 58: 250–254. appearance. Neuroscience 447 468. Maezawa I, Jin W. 2010. Rett syndrome microglia damage Nagy JI, Li X, Rempel J, Stelmack G, Patel D, Staines WA, dendrites and synapses by the elevated release of gluta- Yasumura T, Rash JE. 2001. Connexin26 in adult rodent mate. J Neurosci 30: 5346–5356. central nervous system: Demonstration at astrocytic gap junctions and colocalization with connexin30 and con- Majumder P, Crispino G, Rodriguez L, Ciubotaru CD, An- 441: – selmi F, Piazza V, Bortolozzi M, Mammano F. 2010. ATP- nexin43. J Comp Neurol 302 323. mediated cell-cell signaling in the organ of Corti: The role Naus CC, Laird DW. 2010. Implications and challenges of of connexin channels. Purinergic Signal 6: 167–187. connexin connections to cancer. Nat Rev Cancer 10: 435– McLachlan E, Shao Q, Wang HL, Langlois S, Laird DW. 441. 2006. Connexins act as tumor suppressors in three-di- Naus CC, Elisevich K, Zhu D, Belliveau DJ, Del Maestro RF. mensional mammary cell organoids by regulating differ- 1992. In vivo growth of C6 glioma cells transfected with entiation and angiogenesis. Cancer Res 66: 9886–9894. connexin43 cDNA. Cancer Res 52: 4208–4213. Mei X, Ezan P, Giaume C, Koulakoff A. 2010. Astroglial Nielsen MS, Axelsen LN, Sorgen PL, Verma V, Delmar M, connexin immunoreactivity is specifically altered at β- Holstein-Rathlou NH. 2012. Gap junctions. Compr Phys- amyloid plaques in β-amyloid precursor protein/preseni- iol 2: 1981–2035. 171: – lin1 mice. Neuroscience 92 105. Odermatt B, Wellershaus K, Wallraff A, Seifert G, Degen J, Menichella DM, Goodenough DA, Sirkowski E, Scherer SS, Euwens C, Fuss B, Bussow H, Schilling K, Steinhauser C, Paul DL. 2003. Connexins are critical for normal myeli- et al. 2003. Connexin 47 (Cx47)-deficient mice with en- nation in the CNS. J Neurosci 23: 5963–5973. hanced green fluorescent protein reporter gene reveal pre- Menichella DM, Majdan M, Awatramani R, Goodenough dominant oligodendrocytic expression of Cx47 and dis- DA, Sirkowski E, Scherer SS, Paul DL. 2006. Genetic play vacuolized myelin in the CNS. J Neurosci 23: 4549– and physiological evidence that oligodendrocyte gap 4559. junctions contribute to spatial buffering of potassium re- Ohara T, Qu Z, Lee MH, Ohara K, Omichi C, Mandel WJ, leased during neuronal activity. J Neurosci 26: 10984– Chen PS, Karagueuzian HS. 2002. Increased vulnerability 10991. to inducible atrial fibrillation caused by partial cellular Mese G, Valiunas V, Brink PR, White TW. 2008. Con- uncoupling with heptanol. Am J Physiol Heart Circ Phys- nexin26 deafness associated mutations show altered per- iol 283: H1116–H1122.

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 15 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

M. Delmar et al.

O’Quinn MP, Palatinus JA, Harris BS, Hewett KW, Gourdie Rhett JM, Ongstad EL, Jourdan J, Gourdie RG. 2012. Cx43 RG. 2011. A peptide mimetic of the connexin43 carboxyl associates with Nav1.5 in the cardiomyocyte perinexus. J terminus reduces gap junction remodeling and induced Membr Biol 245: 411–422. 108: arrhythmia following ventricular injury. Circ Res Rivas MV, Jarvis ED, Morisaki S, Carbonaro H, Gottlieb AB, – 704 715. Krueger JG. 1997. Identification of aberrantly regulated Ortolano S, Di Pasquale G, Crispino G, Anselmi F, Mam- genes in diseased skin using the cDNA differential display mano F, Chiorini JA. 2008. Coordinated control of con- technique. J Invest Dermatol 108: 188–194. nexin 26 and connexin 30 at the regulatory and functional Rouan F, White TW, Brown N, Taylor AM, Lucke TW, Paul 105: – level in the inner ear. Proc Natl Acad Sci 18776 DL, Munro CS, Uitto J, Hodgins MB, Richard G. 2001. 18781. trans-dominant inhibition of connexin-43 by mutant Pannasch U, Vargova L, Reingruber J, Ezan P, Holcman D, connexin-26: Implications for dominant connexin disor- Giaume C, Sykova E, Rouach N. 2011. Astroglial networks ders affecting epidermal differentiation. J Cell Sci 114: scale synaptic activity and plasticity. Proc Natl Acad Sci 2105–2113. 108: – 8467 8472. Salomon D, Masgrau E, Vischer S, Ullrich S, Dupont E, Pannasch U, Freche D, Dallerac G, Ghezali G, Escartin C, Sappino P, Saurat JH, Meda P. 1994. Topography of mam- Ezan P, Cohen-Salmon M, Benchenane K, Abudara V, malian connexins in human skin. J Invest Dermatol 103: Dufour A, et al. 2014. Connexin 30 sets synaptic strength 240–247. by controlling astroglial synapse invasion. Nat Neurosci Sanchez HA, Verselis VK. 2014. Aberrant Cx26 hemichan- 17: – 549 558. nels and Keratitis-Ichthyosis-Deafness Syndrome: In- Patuzzi R. 2011. Ion flow in stria vascularis and the produc- sights into syndromic hearing loss. Front Cell Neurosci tion and regulation of cochlear endolymph and the en- 8: 354. 277: – dolymphatic potential. Hearing Res 4 19. Sanchez HA, Mese G, Srinivas M, White TW, Verselis VK. Paznekas WA, Boyadjiev SA, Shapiro RE, Daniels O, Woll- 2010. Differentially altered Ca2+ regulation and Ca2+ per- nik B, Keegan CE, Innis JW, Dinulos MB, Christian C, meability in Cx26 hemichannels formed by the A40V and Hannibal MC, et al. 2003. Connexin 43 (GJA1) mutations G45E mutations that cause keratitis ichthyosis deafness cause the pleiotropic phenotype of oculodentodigital dys- syndrome. J Gen Physiol 136: 47–62. 72: – plasia. Am J Hum Genet 408 418. Sanchez HA, Villone K, Srinivas M, Verselis VK. 2013. The Paznekas WA, Karczeski B, Vermeer S, Lowry RB, Delatycki D50N mutation and syndromic deafness: Altered Cx26 M, Laurence F, Koivisto PA, Van Maldergem L, Boyadjiev hemichannel properties caused by effects on the pore and SA, Bodurtha JN, et al. 2009. GJA1 mutations, variants, intersubunit interactions. J Gen Physiol 142: 3–22. and connexin 43 dysfunction as it relates to the oculoden- Sanchez HA, Bienkowski R, Slavi N, Srinivas M, Verselis VK. 30: – todigital dysplasia phenotype. Hum Mutat 724 733. 2014. Altered inhibition of Cx26 hemichannels by pH Personius KE, Chang Q, Mentis GZ, O’Donovan MJ, Balice- and Zn2+ in the A40V mutation associated with kerati- Gordon RJ. 2007. Reduced gap junctional coupling leads tis-ichthyosis-deafness syndrome. J Biol Chem 289: to uncorrelated motor neuron firing and precocious neu- 21519–21532. 104: romuscular synapse elimination. Proc Natl Acad Sci Sanchez HA, Slavi N, Srinivas M, Verselis VK. 2016. Syn- – 11808 11813. dromic deafness mutations at Asn 14 differentially alter Peters NS, Coromilas J, Severs NJ, Wit AL. 1997. Disturbed the open stability of Cx26 hemichannels. J Gen Physiol connexin43 gap junction distribution correlates with the 148: 25–42. location of reentrant circuits in the epicardial border zone Scemes E, Spray DC. 2012. Extracellular K+ and astrocyte of healing canine infarcts that cause ventricular tachycar- signaling via connexin and pannexin channels. Neuro- 95: – dia. Circulation 988 996. chem Res 37: 2310–2316. Plante I, Stewart MK, Barr K, Allan AL, Laird DW. 2011. Schutz M, Scimemi P, Majumder P, De Siati RD, Crispino G, Cx43 suppresses mammary tumor metastasis to the lung Rodriguez L, Bortolozzi M, Santarelli R, Seydel A, Sonn- in a Cx43 mutant mouse model of human disease. Onco- tag S, et al. 2010. The human deafness-associated con- 30: – gene 1681 1692. nexin 30 T5M mutation causes mild hearing loss and Qu Y, Tang W, Zhou B, Ahmad S, Chang Q, Li X, Lin X. reduces biochemical coupling among cochlear non-sen- 2012. Early developmental expression of connexin26 in sory cells in knock-in mice. Hum Mol Genet 19: 4759– the cochlea contributes to its dominate functional role in 4773. the cochlear gap junctions. Biochem Biophys Res Com- Schutz M, Auth T, Gehrt A, Bosen F, Korber I, Strenzke N, 417: – mun 245 250. Moser T, Willecke K. 2011. The connexin26 S17F mouse Ransom B, Giaume C. 2012. Gap junctions and hemichan- mutant represents a model for the human hereditary ker- nels. In Neuroglia (Kettenmann H, Ransom BR), pp. 292– atitis-ichthyosis-deafness syndrome. Hum Mol Genet 20: 305. Oxford University Press, New York. 28–39. Rash JE, Kamasawa N, Davidson KG, Yasumura T, Pereda Schwanke U, Konietzka I, Duschin A, Li X, Schulz R, Heusch AE, Nagy JI. 2012. Connexin composition in apposed gap G. 2002. No ischemic preconditioning in heterozygous junction hemiplaques revealed by matched double-repli- connexin43-deficient mice. Am J Physiol Heart Circ Phys- ca freeze-fracture replica immunogold labeling. J Membr iol 283: H1740–H1742. 245: – Biol 333 344. Shibayama J, Paznekas W, Seki S, Taffet S, Jabs EW, Delmar Rhett JM, Jourdan J, Gourdie RG. 2011. Connexin 43 con- M, Musa H. 2005. Functional characterization of con- nexon to gap junction transition is regulated by zonula nexin43 mutations found in patients with oculodentodi- occludens-1. Mol Biol Cell 22: 1516–1528. gital dysplasia. Circ Res 96: e83–e91.

16 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

Shuja Z, Li L, Gupta S, Mese G, White TW. 2016. Con- encoding gap junction protein α 12 (connexin 46.6) cause nexin26 mutations causing palmoplantar keratoderma Pelizaeus-Merzbacher-like disease. Am J Hum Genet 75: and deafness interact with connexin43, modifying gap 251–260. junction and hemichannel properties. J Invest Dermatol 136: – Veeraraghavan R, Salama ME, Poelzing S. 2012. Interstitial 225 235. volume modulates the conduction velocity-gap junction Sinner MF, Tucker NR, Lunetta KL, Ozaki K, Smith JG, relationship. Am J Physiol Heart Circ Physiol 302: H278– Trompet S, Bis JC, Lin H, Chung MK, Nielsen JB, et al. H286. 2014. Integrating genetic, transcriptional, and functional Venance L, Rozov A, Blatow M, Burnashev N, Feldmeyer D, analyses to identify 5 novel genes for atrial fibrillation. Circulation 130: 1225–1235. Monyer H. 2000. Connexin expression in electrically cou- pled postnatal rat brain neurons. Proc Natl Acad Sci 97: Skyschally A, Walter B, Schultz Hansen R, Heusch G. 2013. 10260–10265. The antiarrhythmic dipeptide ZP1609 (danegaptide) when given at reperfusion reduces myocardial infarct Verheule S, van Batenburg CA, Coenjaerts FE, Kirchhoff S, size in pigs. Naunyn Schmiedebergs Arch Pharmacol Willecke K, Jongsma HJ. 1999. Cardiac conduction ab- 386: 383–391. normalities in mice lacking the gap junction protein con- 10: – Smith WTt, Fleet WF, Johnson TA, Engle CL, Cascio WE. nexin40. J Cardiovasc Electrophysiol 1380 1389. 1995. The Ib phase of ventricular arrhythmias in ischemic Wallraff A, Kohling R, Heinemann U, Theis M, Willecke K, in situ porcine heart is related to changes in cell-to-cell Steinhauser C. 2006. The impact of astrocytic gap junc- electrical coupling. Circulation 92: 3051–3060. tional coupling on potassium buffering in the hippocam- Sperelakis N. 2002. An electric field mechanism for trans- pus. J Neurosci 26: 5438–5447. mission of excitation between myocardial cells. Circ Res Wang Y, Chang Q, Tang W, Sun Y, Zhou B, Li H, Lin X. 2009. 91: 985–987. Targeted connexin26 ablation arrests postnatal develop- Stein M, van Veen TA, Remme CA, Boulaksil M, Noorman ment of the organ of Corti. Biochem Biophys Res Commun M, van Stuijvenberg L, van der Nagel R, Bezzina CR, 385: 33–37. Hauer RN, de Bakker JM, et al. 2009. Combined reduction Wang H, Cao X, Lin Z, Lee M, Jia X, Ren Y, Dai L, Guan L, of intercellular coupling and membrane excitability dif- Zhang J, Lin X, et al. 2015. Exome sequencing reveals ferentially affects transverse and longitudinal cardiac con- mutation in GJA1 as a cause of keratoderma-hypotricho- duction. Cardiovasc Res 83: 52–60. sis-leukonychia totalis syndrome. Hum Mol Genet 24: Stong BC, Chang Q, Ahmad S, Lin X. 2006. A novel mech- 243–250. anism for connexin 26 mutation linked deafness: Cell Wangemann P. 2006. Supporting sensory transduction: Co- death caused by leaky gap junction hemichannels. Laryn- fl goscope 116: 2205–2210. chlear uid homeostasis and the endocochlear potential. J Physiol 576: 11–21. Sun Y, Tang W, Chang Q, Wang Y, Kong W, Lin X. 2009. Connexin30 null and conditional connexin26 null mice Wasseff SK, Scherer SS. 2014. Activated microglia do not display distinct pattern and time course of cellular degen- form functional gap junctions in vivo. J Neuroimmunol eration in the cochlea. J Comp Neurol 516: 569–579. 269: 90–93. Takeuchi H, Jin S, Wang J, Zhang G, Kawanokuchi J, Kuno Wojtczak J. 1979. Contractures and increase in internal lon- R, Sonobe Y, Mizuno T, Suzumura A. 2006. Tumor ne- gitudinal resistance of cow ventricular muscle induced by crosis factor-α induces neurotoxicity via glutamate re- hypoxia. Circ Res 44: 88–95. lease from hemichannels of activated microglia in an au- Xing D, Kjolbye AL, Nielsen MS, Petersen JS, Harlow KW, 281: – tocrine manner. J Biol Chem 21362 21368. Holstein-Rathlou NH, Martins JB. 2003. ZP123 in- Temme A, Buchmann A, Gabriel HD, Nelles E, Schwarz M, creases gap junctional conductance and prevents reen- Willecke K. 1997. High incidence of spontaneous and trant during myocardial ische- chemically induced liver tumors in mice deficient for mia in open chest dogs. J Cardiovasc Electrophysiol 14: 7: – connexin32. Curr Biol 713 716. 510–520. Terrinoni A, Codispoti A, Serra V, Didona B, Bruno E, Nis- Xu J, Nicholson BJ. 2013. The role of connexins in ear tico R, Giustizieri M, Alessandrini M, Campione E, Me- and skin physiology—Functional insights from disease- lino G. 2010. Connexin 26 (GJB2) mutations, causing KID associated mutations. Biochim Biophys Acta 1828: 167– Syndrome, are associated with cell death due to calcium 178. gating deregulation. Biochem Biophys Res Commun 394: 909–914. Yamasaki H, Mesnil M, Omori Y, Mironov N, Krutovskikh V. 1995. Intercellular communication and carcinogenesis. Teubner B, Michel V, Pesch J, Lautermann J, Cohen-Salmon 33: – M, Sohl G, Jahnke K, Winterhager E, Herberhold C, Har- Mutat Res 181 188. delin JP, et al. 2003. Connexin30 (Gjb6)-deficiency causes Yang J, Qin G, Luo M, Chen J, Zhang Q, Li L, Pan L, Qin S. severe hearing impairment and lack of endocochlear po- 2015. Reciprocal positive regulation between Cx26 and tential. Hum Mol Genet 12: 13–21. PI3K/Akt pathway confers acquired gefitinib resistance Theodoric N, Bechberger JF, Naus CC, Sin WC. 2012. Role of in NSCLC cells via GJIC-independent induction of gap junction protein connexin43 in astrogliosis induced EMT. Cell Death Dis 6: e1829. by brain injury. PLoS ONE 7: e47311. Yu M, Zhang C, Li L, Dong S, Zhang N, Tong X. 2014. Uhlenberg B, Schuelke M, Ruschendorf F, Ruf N, Kaindl Cx43 reverses the resistance of A549 lung adenocarci- AM, Henneke M, Thiele H, Stoltenburg-Didinger G, noma cells to cisplatin by inhibiting EMT. Oncol Rep Aksu F, Topaloglu H, et al. 2004. Mutations in the gene 31: 2751–2758.

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 17 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

M. Delmar et al.

Zdebik AA, Wangemann P, Jentsch TJ. 2009. Potassium ion Zhang A, Hitomi M, Bar-Shain N, Dalimov Z, Ellis L, Vel- movement in the inner ear: Insights from genetic disease pula KK, Fraizer GC, Gourdie RG, Lathia JD. 2015. Con- and mouse models. Physiology 24: 307–316. nexin 43 expression is associated with increased malig- Zhang Y, Tang W, Ahmad S, Sipp JA, Chen P, Lin X. 2005. nancy in prostate cancer cell lines and functions to 6: – Gap junction-mediated intercellular biochemical cou- promote migration. Oncotarget 11640 11651. pling in cochlear supporting cells is required for nor- Zhao HB, Yu N. 2006. Distinct and gradient distributions mal cochlear functions. Proc Natl Acad Sci 102: 15201– of connexin26 and connexin30 in the cochlear sensory 15206. epithelium of guinea pigs. J Comp Neurol 499: 506– Zhang J, O’Carroll SJ, Henare K, Ching LM, Ormonde S, 518. Nicholson LF, Danesh-Meyer HV, Green CR. 2014. Zhu D, Caveney S, Kidder GM, Naus CC. 1991. Transfection Connexin hemichannel induced vascular leak suggests a of C6 glioma cells with connexin 43 cDNA: Analysis of new paradigm for cancer therapy. FEBS Lett 588: 1365– expression, intercellular coupling, and cell proliferation. 1371. Proc Natl Acad Sci 88: 1883–1887.

18 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a029348 Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Connexins and Disease

Mario Delmar, Dale W. Laird, Christian C. Naus, Morten S. Nielsen, Vytautas K. Verselis and Thomas W. White

Cold Spring Harb Perspect Biol published online August 4, 2017

Subject Collection Cell-Cell Junctions

Vascular Endothelial (VE)-Cadherin, Endothelial Signaling by Small GTPases at Cell−Cell Adherens Junctions, and Vascular Disease Junctions: Protein Interactions Building Control Maria Grazia Lampugnani, Elisabetta Dejana and and Networks Costanza Giampietro Vania Braga Adherens Junctions and Desmosomes Making Connections: Guidance Cues and Coordinate Mechanics and Signaling to Receptors at Nonneural Cell−Cell Junctions Orchestrate Tissue Morphogenesis and Function: Ian V. Beamish, Lindsay Hinck and Timothy E. An Evolutionary Perspective Kennedy Matthias Rübsam, Joshua A. Broussard, Sara A. Wickström, et al. Cell−Cell Contact and Receptor Tyrosine Kinase The Cadherin Superfamily in Neural Circuit Signaling Assembly Christine Chiasson-MacKenzie and Andrea I. James D. Jontes McClatchey Hold Me, but Not Too Tight−−Endothelial Cell−Cell Mechanosensing and Mechanotransduction at Junctions in Angiogenesis Cell−Cell Junctions Anna Szymborska and Holger Gerhardt Alpha S. Yap, Kinga Duszyc and Virgile Viasnoff Connexins and Disease Beyond Cell−Cell Adhesion: Sensational Mario Delmar, Dale W. Laird, Christian C. Naus, et Cadherins for Hearing and Balance al. Avinash Jaiganesh, Yoshie Narui, Raul Araya-Secchi, et al. Cell Junctions in Hippo Signaling Cell−Cell Junctions Organize Structural and Ruchan Karaman and Georg Halder Signaling Networks Miguel A. Garcia, W. James Nelson and Natalie Chavez Loss of E-Cadherin-Dependent Cell−Cell Adhesion Cell Biology of Tight Junction Barrier Regulation and the Development and Progression of Cancer and Mucosal Disease Heather C. Bruner and Patrick W.B. Derksen Aaron Buckley and Jerrold R. Turner

For additional articles in this collection, see http://cshperspectives.cshlp.org/cgi/collection/

Copyright © 2017 Cold Spring Harbor Laboratory Press; all rights reserved Downloaded from http://cshperspectives.cshlp.org/ on October 1, 2021 - Published by Cold Spring Harbor Laboratory Press

Desmosomes and Intermediate Filaments: Their Integration of Cadherin Adhesion and Consequences for Tissue Mechanics at Adherens Junctions Mechthild Hatzfeld, René Keil and Thomas M. René Marc Mège and Noboru Ishiyama Magin

For additional articles in this collection, see http://cshperspectives.cshlp.org/cgi/collection/

Copyright © 2017 Cold Spring Harbor Laboratory Press; all rights reserved