Cell Metabolism Review

Hyperinsulinism and Diabetes: Genetic Dissection of b Cell Metabolism-Excitation Coupling in Mice

Maria Sara Remedi1,* and Colin G. Nichols1 1Department of Cell Biology and Physiology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA *Correspondence: [email protected] DOI 10.1016/j.cmet.2009.10.011

The role of metabolism-excitation coupling in insulin secretion has long been apparent, but in recent years, in parallel with studies of human hyperinsulinism and diabetes, genetic manipulation of proteins involved in glucose transport, metabolism, and excitability in mice has brought the central importance of this pathway into sharp relief. We focus on these animal studies and how they provide important insights into not only metabolic and electrical regulation of insulin secretion, but also downstream consequences of alterations in this pathway and the etiology and treatment of insulin-secretion diseases in humans.

Introduction: Human Diseases Highlight the Importance directly or indirectly via Ca-dependent processes. These include of b Cell Metabolism-Excitation Coupling CAPN10 (calpain10, an intracellular calcium-dependent cysteine The pathway from glucose entry into the b cell, through metabo- protease), SLC30A8 (a zinc transporter), KCNJ11 (the pore- 2+ lism to electrical signaling and intracellular [Ca ](Figure 1), is forming subunit of the KATP channel), and KCNQ1 (pore-forming critical in control of insulin secretion, and it is becoming subunit of a voltage-gated K channel). Others, including increasingly apparent that many of the relevant genes underlying CDKAL1, HHEX, HNF4A, IGF2BP2, PPARG, and TCF7L2, are human diabetes and hyperinsulinism are found in this pathway. potentially involved in b cell growth or proliferation and may indi- Established steps in response to elevated blood glucose are rectly affect insulin secretion (Pascoe et al., 2008; Stancakova uptake through glucose transporters, conversion to glucose-6- et al., 2009). phosphate by glucokinase, and metabolism to generate ATP. A During the last 10 years or so, while these genetic bases of rise in cytoplasmic [ATP]:[ADP] leads to ATP-sensitive potas- human disease have been identified, detailed knowledge of sium (KATP) channel closure at the plasma membrane, which, in vivo b cell function has come from genetically modified in turn, results in membrane depolarization, opening of mice. We focus on how these studies, in dissecting M-E coupling voltage-dependent Ca2+, and voltage-gated K+ channels (Dukes in vivo, inform islet function in the intact animal and the dysfunc- and Philipson, 1996; Philipson, 1999; Rorsman and Trube, 1986; tions that result in hyperinsulinism and diabetes. In many cases, Su et al., 2001). Calcium entry through Ca2+ channels results in different gene products fulfill similar roles in human and mouse 2+ increased intracellular calcium concentration ([Ca ]i), which, in b cells, and extrapolation from mouse to man is not automatic. turn, triggers insulin exocytosis (Ashcroft and Rorsman, 1990; Nevertheless, emerging themes from mouse studies not only MacDonald et al., 2005). provide mechanistic insights to the metabolic regulation of Congenital hyperinsulinism of infancy (HI), characterized by insulin secretion and the downstream consequences of altered constitutive insulin secretion despite low blood glucose (Ayns- genes, but in many cases may directly predict and inform the ley-Green, 1981), can result from abnormalities in several genes etiology of the human diseases. involved in metabolism-excitation (M-E) coupling, including loss- of-function (LOF) mutations in the KATP channel and gain-of- Mouse Models of Altered Glucose Uptake and Glucose function (GOF) mutations in glucokinase (GCK), glutamate dehy- Metabolism drogenase, or short-chain acyl-CoA dehydrogenase (Palladino Loss of Membrane Glucose Transporters Causes et al., 2008). Conversely, permanent and transient neonatal dia- Diabetes betes mellitus (PNDM, TNDM) can result from LOF mutations in Although both GLUT1 and GLUT2 isoforms may be present in glucokinase and GOF mutations in the b cell KATP channel human islets (Richardson et al., 2007), GLUT2 is the main isoform subunits (Smith et al., 2007). Maturity onset diabetes of the expressed in rodent pancreatic b cells (Efrat et al., 1994; Tho- young 2 (MODY-2) results from weaker LOF mutations in GCK rens, 2001). Inactivation of GLUT2 (GLUT2À/À) in mice leads to (Cuesta-Munoz et al., 2004; Gloyn, 2003a), and monogenic severe hyperglycemia accompanied by high circulating fatty diabetes caused by mitochondrial DNA mutation results from acids, and GLUT2À/À mice die within the first 3 weeks after birth defective b cell secretion (Maassen, 2002). Recent genome- (Guillam et al., 1997). Isolated islets show loss of first-phase and wide association studies (GWAS) identified multiple polymor- reduced second-phase glucose-stimulated insulin secretion phisms associated with type 2 diabetes (Cauchi et al., 2008; (GSIS) (Guillam et al., 1997), reflecting a lack of glucose uptake Sladek et al., 2007; Unoki et al., 2008; Yasuda et al., 2008; into the b cell. Re-expression of glucose transporters in GLUT2 Zeggini et al., 2007), and again, many are in or near several knockout islets (using recombinant lentiviral expression or by genes that encode for proteins involved in b cell M-E coupling crossing with mice overexpressing GLUT2 or GLUT1 under Rip

442 Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. Cell Metabolism Review

control) restores normal GSIS (Guillam et al., 2000; Thorens et al., 2000). Alterations in Glucokinase Activity Cause Diabetes and Hyperinsulinism Following entry into the b cell, glucose is phosphorylated by GCK and then metabolized through glycolytic and oxidative pathways (Matschinsky, 1996)(Figure 1B). In humans, GOF mutations in either GCK or mitochondrial glutamate dehydrogenase (GDH) cause HI, elevating [ATP]:[ADP] at any ambient glucose concen-

tration and suppressing KATP channel activity (Page et al., 1992; Sakura et al., 1998). Reiterating key features, mice overexpress- ing yeast hexokinase (Epstein et al., 1992a) or the GCK gene itself (Shiota et al., 2001) are relatively hyperinsulinemic. Conversely, homozygous inactivating GCK mutations cause PNDM (Gloyn et al., 2002 ; Gloyn, 2003a; Njolstad et al., 2001). Mice with deletion of the GCK gene in pancreatic b cells and neurons, but not in the liver (by targeted disruption of the appro- priate exon 1 variant), showed severe perinatal diabetes and died shortly after birth (Grupe et al., 1995; Terauchi et al., 1995). Confirming the critical role of b cell GCK, transgenic re-expression only in b cells reversed diabetes in 50% of the mice (Grupe et al., 1995). Whereas homozygous LOF GCK mutations cause PNDM (Gloyn, 2003a), heterozygous LOF mutations, resulting in only partial reduction of GCK activity, underlie MODY-2 (Cuesta- Munoz et al., 2004; Gloyn, 2003a), characterized by impaired insulin secretion and diabetes onset in early adulthood, typically not worsening over time (Fajans et al., 2001). Heterozygous b cell GCK+/À mutant mice show glucose intolerance and impaired GSIS (Bali et al., 1995; Grupe et al., 1995; Sakura et al., 1998), but again, the diabetes does not progress, reiterating the MODY-2 phenotype. Why the phenotype is nonprogressive in humans and mice is interesting, given that the level of hyper- glycemia that is reached (typically fasted blood glucose of 125–135 mg/dl; Codner et al., 2006; Fajans et al., 2001; Sheha- deh et al., 2005) is one that progresses to uncontrollable levels in other forms of diabetes, including human type 2 (Guillausseau et al., 2008; Matveyenko and Butler, 2008). Insulin levels are typically normal, such that decreased insulin/glucose ratio suggests increased insulin sensitivity in humans and mice (Grupe et al., 1995; Katagiri et al., 1992; Terauchi et al., 1995). Chronic (48–96 hr) exposure of GCK+/À islets to high glucose concentration enhances glucose responsivity, whereas similar exposure of wild-type islets induces dysfunction (Sreenan et al., 1998). As we discuss below, an emerging idea from

Figure 1. Schematic Illustration of the Glucose-Stimulated Insulin cessation of insulin secretion. Factors that impair ATP production or down- Secretory Pathway in b Cells stream signaling are expected to suppress GSIS. Several genes that directly (A) Hematoxylin and eosin-stained paraffin section of mouse pancreas. The or indirectly alter ATP production and therefore underlie a diabetic or hyperin- pancreas is composed of exocrine tissue and endocrine tissue (islet of Lang- sulinemic phenotype when mutated (humans and/or mouse models) are erhans). Islets contain different cell types, including the insulin-secreting shown in color: glucose transporter 2 (GLUT2), glucokinase (GK), nicotinamide b cells. Arrows point to exocrine and endocrine tissue. nucleotide transhydrogenase (Nnt), uncoupling protein 2 (UCP2), mitochon- (B) Schematic illustration of the b cell glucose-stimulated insulin secretion drial DNA mutations (mtDNA), and glutamate dehydrogenase (GDH). Muta- pathway. Glucose entering the b cell through glucose transporters (GLUT2) tions that may indirectly affect channel activity are also shown. is phosphorylated by glucokinase (GK) and metabolized by glycolysis (cyto- (C) Schematic illustration of the electrical activity of b cells and the temporal plasm) and tricarboxylic acid (TCA) cycle (mitochondria). A rise in the [ATP]: response to elevated glucose. In low (3 mM) glucose, the membrane is hyper- + [ADP] ratio resulting from oxidative metabolism inhibits the ATP-sensitive K polarized due to KATP activity, intracellular Ca ([Ca]) is low, and insulin is not channels (KATP) at the cell surface, causing membrane depolarization and secreted. When glucose is elevated to stimulatory levels (11 mM), KATP chan- opening of voltage-dependent Ca2+ channels (VDCC). This results in a rise nels close, and the membrane depolarizes due to L-type VDCC activity. Bursts of intracellular [Ca2+], which stimulates insulin secretion. Voltage-dependent of APs, involving both VDCC and Kv channels, result in elevated [Ca], which, in outward K+ channels (Kv) are involved in membrane repolarization and turn, triggers insulin secretion.

Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. 443 Cell Metabolism Review

multiple transgenic animals is that secondary progression of show upregulation of UCP2 mRNA in b cells (Kassis et al., 2000; diseases may depend critically on the underlying cellular mech- Zhang et al., 2001). Knockout of the UCP2 gene in the ob/ob anisms. ‘‘Underexcited’’ islets, such as those with reduced mouse background improved GSIS and reduced blood glucose metabolic flux, may respond well to chronic restoration of excit- (Zhang et al., 2001). ability, whereas ‘‘hyperstimulation’’ of otherwise normal islets In C57Bl6 mice, reported by some groups to exhibit impaired may be detrimental. insulin secretion relative to other strains (Toye et al., 2005), A first polygenic mouse model of noninsulin-dependent dia- mutations in the nicotinamide nucleotide transhydrogenase betes mellitus (Terauchi et al., 1997) was obtained by crossing (Nnt) have been identified. Nnt is a nuclear-encoded mitochon- heterozygous GCK+/À mice (Terauchi et al., 1995) with homozy- drial protein catalyzing reversible reduction of NADP+ by NADH gous insulin receptor substrate 1 knockout (IRS-1À/À) mice. and promoting proton translocation across the membrane and Parental IRS-1À/À mice were insulin resistant but did not develop detoxification of ROS (Arkblad et al., 2005; Hoek and Rydstrom, diabetes due to compensatory b cell hyperplasia (Araki et al., 1988). Accumulation of ROS in the mitochondrial matrix can 1994; Tamemoto et al., 1994). Importantly, GCK+/À/IRS-1À/À increase UCP2 activity, enhancing proton leakage and impairing mice showed hyperglycemia despite b cell hyperplasia and ATP production (Echtay et al., 2002; Krauss et al., 2003). Nnt- became overtly diabetic with age (Terauchi et al., 1997), experi- transgenic mice showed impaired glucose tolerance and loss mentally confirming that genetic combination of insulin resis- of both b cell ATP synthesis and GSIS, consistent with a direct tance and reduced insulin secretion can lead to diabetes. effect of impaired ATP production on KATP channel activity Any consequences of GCK deficiency on electrical activity (Freeman et al., 2006). No mutations in mitochondrial enzymes should be absent in animals that lack glucose-regulated KATP have been reported in human diabetes, but a few mutations in channels. Perinatal lethality was avoided in GCKÀ/À/Kir6.2À/À mitochondrial DNA (mtDNA) have. Mitochondria are a major double knockout mice, although they were still insulin deficient source of free radicals, as a result of electrons leaking into the and still died prematurely (Remedi et al., 2005). However, hetero- mitochondrial matrix reacting with molecular oxygen. An zygous GCK+/À animals, which were markedly diabetic on the A3243G mutation in the tRNA(Leu(UUR)) gene was identified Kir6.2 wild-type background, became only mildly glucose intol- as a common diabetes-causing mitochondrial DNA mutation. erant on the Kir6.2À/À background, essentially behaving like Mutation carriers exhibit reduced first- and second-phase insulin Kir6.2À/À mice (see below) (Remedi et al., 2005), confirming secretion (Maassen et al., 2004), although the underlying molec- that a major feature of GCK deficiency is indeed reduced excit- ular mechanisms are unclear. A mouse model of mitochondrial ability via enhanced KATP channel activity. diabetes was generated by disruption of the nuclear gene Alteration of Mitochondrial Proteins Involved Tfam, a transcriptional activator essential for mtDNA expression in Regulation of ATP Production and Expenditure: in b cells (Silva et al., 2000). These mice showed depletion of Indirect Action via Electrical Signaling mtDNA and developed diabetes at 5 weeks. Again, consistent Mitochondria provide the major ATP-generating capacity of with impaired M-E coupling, dispersed b cells demonstrated b cells (Erecinska et al., 1992; Maechler and Wollheim, 2001). hyperpolarized mitochondria, impaired Ca2+ signaling, and Overactive mitochondrial metabolism will increase cytosolic decreased GSIS. As in other models in which the primary defect

[ATP]:[ADP], leading to closure of b cell KATP channels and is in M-E coupling, older Tfam mutant mice showed reduced enhancing secretion (see below) (Figure 1). Conversely, impaired b cell mass, indicating secondary progression (Silva et al., mitochondrial metabolism will decrease [ATP]:[ADP], preventing 2000). Recently, a transgenic mouse expressing mutant mtDNA

KATP channel closure and suppressing secretion (Wallace, 2001). polymerase g (D181A polyg) under insulin promoter control Uncoupling proteins (UCPs) dissociate mitochondrial substrate was generated (Bensch et al., 2009) to cause accumulation oxidation from ATP synthesis (Figure 1). UCP2 activation of mtDNA mutations in b cells. Despite males being overtly contributes to decreased reactive oxygen species (ROS) forma- diabetic and females being glucose intolerant by 6 weeks of tion and free fatty acid transport/metabolism but mostly reduces age, GSIS was normal in isolated islets, suggesting a non-islet the efficiency of ATP generation (Arsenijevic et al., 2000; Himms- mechanism. Hagen and Harper, 2001; Nishikawa et al., 2000; Samec et al., Oxygen-sensing pathways have also been implicated in 1998). UCP2 is present in b cells, and consistent with above modulation of insulin secretion: both b cell-specific (bVhlKO) predictions, UCP2À/À mice demonstrate increased circulating and whole-pancreas (VhlKO) knockout of von Hippel-Lindau insulin, without changes in peripheral insulin sensitivity (Joseph (VHL) protein, which controls the degradation of hypoxia-induc- et al., 2002; Zhang et al., 2001). UCP2À/À islets show increased ible factor (HIF), are glucose intolerant. Isolated islets show [ATP] and hypersecretion of insulin at any glucose concentration altered expression of b cell glucose transporter and glycolytic (Joseph et al., 2002; Zhang et al., 2001). When fed a high-fat diet, genes, impaired glucose uptake and metabolism, and reduced these mice show improved b cell glucose sensitivity, enhanced GSIS (Cantley et al., 2009; Zehetner et al., 2008). Hif1a is GSIS, and increased insulin content (Joseph et al., 2002). expressed in these b cells, and deletion of Hif1a restores Several animal models support the idea that UCP2 upregulation GSIS in these mice (Cantley et al., 2009; Zehetner et al., and consequent inefficient ATP production is a feature of gluco- 2008). b-cell-specific Vhl-deficient mice hypersecrete insulin lipotoxic conditions (Chan et al., 1999). Mice and rats fed a at low glucose concentration but have impaired GSIS and 2+ high-fat diet show upregulation of UCP2 gene expression and increased [Ca ]i (Cantley et al., 2009; Zehetner et al., 2008). elevated plasma lipids (Briaud et al., 2002; Chan et al., 2001). Thus, impaired mitochondrial oxidation and/or oxygen-sensing Fa/fa rats (leptin-receptor deficient) and ob/ob mice (leptin defi- mechanisms may all contribute to altered secretion via altered cient) are popular models of obesity-induced diabetes, and both M-E coupling.

444 Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. Cell Metabolism Review

Genetic Manipulation of KATP Channels: Mouse Models GSIS. Mice expressing mutant KATP channels with reduced of Hyperinsulinism and Diabetes ATP sensitivity only in pancreatic b cells (Kir6.2[DN2-30]) devel-

KATP Knockout and Dominant-Negative Mice as Models oped severe NDM and died within days of birth (Koster et al., of Hyperinsulinemia 2000), predicting the subsequent demonstration that GOF muta- b cell KATP channels are complexes of the sulfonylurea receptor 1 tions in Kir6.2 (KCNJ11) and SUR1 (ABCC8) are common causes (SUR1, ABCC8) and the potassium channel Kir6.2 (KCNJ11) of human TNDM and PNDM (Gloyn et al., 2004; Hattersley and (Clement et al., 1997; Inagaki et al., 1995; Sakura et al., 1995; Ashcroft, 2005). These mutations reduce sensitivity to ATP Shyng and Nichols, 1997). In humans, LOF mutations in these inhibition by decreasing the affinity of the ATP-binding pocket genes are major causes of HI (Aguilar-Bryan et al., 2001; Dunne for the nucleotide or by allosterically decreasing ATP affinity et al., 2004; Huopio et al., 2002a; Stanley, 2002). Reduction of (Ashcroft, 2006; Nichols, 2006). Recently, inducible KATP GOF channel expression at the cell surface, loss of MgADP stimula- transgenic mice under Cre-recombinase control have been tion, or abolished channel activity are primary defects (Dunne generated (Girard et al., 2009; Remedi et al., 2009). Both rat et al., 1997; Nestorowicz et al., 1998; Nichols et al., 1996; Shyng insulin promoter (Rip-Cre)- (Herrera, 2002) and tamoxifen-induc- et al., 1998). Kir6.2À/À and SUR1À/À mice (Miki et al., 1998; ible Pdx1PBCreERTM (Zhang et al., 2005) (Pdx-Cre)-driven Seghers et al., 2000; Shiota et al., 2002), as well as mice express- transgenes lead to severe glucose intolerance around weaning ing a dominant-negative Kir6.2 mutant transgene in b cells (Rip-Cre) or within 2 weeks after tamoxifen injection (Pdx-Cre) (Kir6.2[AAA] [Koster et al., 2002] or Kir6.2[G132S] [Miki et al., and progress to severe diabetes (Girard et al., 2009; Remedi 1997], both of which disrupt the selectivity filter) have been gener- et al., 2009). They also show growth retardation and dramatic ated. Kir6.2À/À and SUR1À/À mice (Miki et al., 1998; Seghers reduction of insulin content accompanied by profound loss of et al., 2000; Shiota et al., 2002) lacking KATP in multiple tissues b cell mass over time (Remedi et al., 2009). Importantly, synge- and Kir6.2[G132S] mice that specifically lack b cell KATP (Miki neic islet transplantation or chronic treatment with glibencla- et al., 1997) show a complex and surprising phenotype that mide, initiated prior to tamoxifen induction, not only prevented does not trivially replicate human HI. These mice reportedly the development of diabetes, but also maintained both pancre- demonstrate transient hyperinsulinemia and hypoglycemia as atic islet architecture and b cell mass (Remedi et al., 2009). neonates, but islets from adult SUR1À/À or Kir6.2À/À mice show Control-based genetic studies (Gloyn, 2003b), metanalysis a dramatic loss of insulin secretion at all glucose concentrations, (Nielsen et al., 2003; Schwanstecher et al., 2002), and GWAS and the animals are relatively hypoinsulinemic (Miki et al., 1998; (Saxena et al., 2007; Zeggini et al., 2007) have established the Seghers et al., 2000; Shiota et al., 2002). In Kir6.2[G132S] mice, E23K polymorphism in Kir6.2 as a risk factor in type 2 diabetes. loss of b cell mass was reported (Miki et al., 1997), although Although early studies failed to demonstrate a significant effect hyperglycemia was apparently spontaneously improved and of E23K on recombinant KATP channel properties (Riedel et al., insulin content even increased in older mice (Oyama et al., 2006). 2003; Sakura et al., 1996), subsequent studies reveal a small However, b-cell-specific Kir6.2[AAA] dominant-negative mice, rightward shift in ATP sensitivity (Schwanstecher et al., 2002; which lose KATP channel activity in only 70% of b cells, exhibit Villareal et al., 2009). Such GOF behavior is predicted to elevated circulating insulin levels that persist through adulthood, suppress GSIS, consistent with the findings in nondiabetic indi- with essentially normal insulin content and islet morphology (Kos- viduals who carry this polymorphism (Chistiakov et al., 2009; ter et al., 2002). Heterozygous Kir6.2+/À and SUR1+/À mice, with Florez et al., 2004; Nielsen et al., 2003; Villareal et al., 2009). In

60% reduction in KATP density in every cell, show a similar addition to severely diabetic transgenic mice (Koster et al., phenotype (Remedi et al., 2006). Thus, whereas heterozygous 2000), additional KATP GOF (Kir6.2[DN2-30]) transgenic mouse Kir6.2+/À and SUR1+/À mice, as well as Kir6.2[AAA] mice, all lines with lower levels of transgene expression exhibit normal show enhanced glucose tolerance and increased GSIS (Remedi islet morphology and insulin content but are glucose intolerant et al., 2006), Kir6.2À/À and SURÀ/À mice (100% reduction in (and more so on high-fat diet) (Koster et al., 2006), reiterating

KATP density) are glucose intolerant. Complete lack of KATP activity the general phenotype of humans carrying the E23K polymor- has been reported in b cells from some HI patients (Kane et al., phism (Villareal et al., 2009). 1996), but the phenotype of many HI mutations would suggest that KATP is unlikely to be completely absent (de Lonlay et al., Mouse Models of Altered Ca Channels 2002; Huopio et al., 2002a, 2002b; Shyng et al., 1998), and active The Role of L-Type High-Voltage-Activated Ca Channels

KATP channels and diazoxide sensitivity have been detected in in Hyperinsulinemia and Diabetes some patients (Henwood et al., 2005; Lin et al., 2006). The prog- The Cav1 subfamily, comprising four members (Cav1.1 to Cav1.4) ress of the disease can be complex, and although surgical removal (Hofmann et al., 1999), generates L-type voltage-dependent Ca of excess pancreatic tissue may result in diabetes, it is also channels (VDCCs) involved in insulin secretion (Ichii et al., 2005; observed that some nonsurgically treated patients spontaneously Mears, 2004; Yang and Berggren, 2005a, 2005b). Cav1.2 and cross over to diabetes (Grimberg et al., 2001; Huopio et al., 2002a; Cav1.3 may be the dominant subunits (Barg et al., 2001; À/À Leibowitz et al., 1995). Apparent recapitulation of this complex Iwashima et al., 1993; Yang et al., 1999)(Figure 1). Cav1.3 phenotype in mice with variable loss of KATP channels suggests mice are viable with no major disturbances in insulin secretion that a similar mechanism may be operating in mice and humans. even though they show deafness, bradycardia, and arrhythmias

Overactive b Cell KATP Channel in Mice Causes Neonatal (Platzer et al., 2000), suggesting that Cav1.3 is not normally À/À Diabetes a major player in mouse b cell insulin secretion. Cav1.2 mice GOF KATP channel mutations resulting in ‘‘overactive’’ b cell die in utero before day 15, presumably because of lack of func- channels are expected to decrease excitability and suppress tional VDCC in the heart (Seisenberger et al., 2000), obviating

Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. 445 Cell Metabolism Review

À/À study of b cell roles, but b-cell-specific knockout (b-Cav1.2 ) and hypoinsulinemia, with normal b cell morphology and insulin mice (deleted exons in one allele of Cav1.2 and ‘‘floxed’’ exons content (Philipson et al., 1994). Conversely, Kv2.1 knockout in the other, using Cre/loxP recombination) exhibit decreased (Kv2.1À/À) mice show reduced fasting blood glucose level and VDCC and a marked reduction in insulin exocytosis in response elevated serum insulin (Jacobson et al., 2007), with enhanced to initial membrane depolarization (first-phase) but unaffected GSIS. Isolated Kv2.1À/À b cells exhibit increased glucose- second-phase secretion (Schulla et al., 2003). The b cell Cav1.2 induced AP duration, but firing frequency is diminished (Jacob- is sensitive to dihydropyridines (DHPs), and these drugs almost son et al., 2007), consistent with loss of Kv currents and À/À 2+ abolish GSIS in b cell lines (Minami et al., 2002). Cav1.2 b cells enhanced Ca entry during the AP, leading to increased insulin 2+ show no DHP-sensitive VDCC, but glucose-induced [Ca ]i oscil- secretion. SNARE proteins also affect insulin exocytosis (Daniel lations and action potential (AP) firing persist, suggesting that et al., 1999). Syntaxin-1A (STX-1A) directly binds and regulates 2+ L-type channels are necessary for insulin secretion, but not for Ca channels (Yang et al., 1999), KATP (Kang et al., 2002), and 2+ electrical activity and [Ca ]i oscillations, perhaps indicating Kv2.1 channels in b cells (Leung et al., 2003, 2005). Transgenic compensatory overexpression of non-L-type channels in b cells mice overexpressing STX-1A in b cells demonstrate fasting lacking Cav1.2 (Schulla et al., 2003). Timothy syndrome, due to hyperglycemia and reduced plasma insulin (Lam et al., 2005),

Cav1.2 overactivity, is characterized by deafness, webbing of with reduced Cav currents but little change in the Kv and KATP fingers and toes, congenital heart disease, and severe arrhyth- currents (Lam et al., 2005). mias and is associated with hypoglycemia (Splawski et al., Multiple other K channels may be involved in insulin secretion

2004), probably due to Cav1.2 overactivity in b cells. It seems and may ultimately be shown to be involved in secretion defects. likely that LOF polymorphisms or mutations of L-type VDCC in Variants in the voltage-gated potassium channel KCNQ1 gene humans should be associated with diabetic syndromes, but have recently been associated with susceptibility to type 2 dia- none have yet been identified, and we speculate that this is again betes, impaired fasting glucose, and b cell function in various because of compensatory upregulation of other subunits. populations (Hu et al., 2009; Tan et al., 2009; Unoki et al., 2008; Non-L-Type High-Voltage-Activated Ca Channels Yasuda et al., 2008). KCNQ1À/À mice demonstrate enhanced in the Regulation of Insulin Secretion insulin sensitivity and glucose tolerance, as well as decreased The role of non-L-type, high-voltage-activated Ca channels (e.g., fed and fasting glucose and insulin levels (Boini et al., 2009),

Cav2.3 R-type Ca channel) in b cells is controversial, and some broadly consistent with a role in secretion, but the evidence for studies indicate their absence in human islets (Braun et al., KCNQ1 expression in islets is weak (Jonsson et al., 2009; Mussig 2008; Yang and Berggren, 2005b). But there is evidence for et al., 2009; Stancakova et al., 2009), and further investigation is association of Cav2.3 polymorphisms with impaired insulin needed. The evidence that the KCNQ1 locus harbors control secretion and development of type 2 diabetes (Holmkvist et al., elements that influence the imprinting of neighboring genes 2007). They appear to play a role in second-phase insulin secre- (Lee et al., 1997; Smilinich et al., 1999), some associated with tion by mobilizing insulin reserve granules to the readily releas- type 2 diabetes, suggests that the mechanism responsible for À/À able pool in mice. Cav2.3 (CACNA1E) knockout (Cav2.3 ) type 2 diabetes susceptibility may extend beyond the direct mice show impaired glucose tolerance and GSIS (Pereverzev effect of KCNQ1 (McCarthy, 2008). The role of Ca-activated et al., 2002). In addition, genetic or pharmacological (using potassium channels in b cell function remains controversial. Early 2+ + R-type channel blocker SNX482) ablation of Cav2.3 channels studies demonstrated the presence of Ca -dependent K strongly suppresses second-phase secretion, but the first phase conductances in b cells (Atwater et al., 1983), and recent studies À/À is unaltered (Jing et al., 2005). Pancreatic cells from Cav2.3 have argued for roles of small conductance SK channels in rodent mice show reduction of Ca2+ signaling and impairment of insulin b cells (Tamarina et al., 2003); large conductance BK channels granule recruitment after the initial exocytotic burst (Jing et al., may also be prominent in human b cells (Braun et al., 2008), but 2005). again, more studies are clearly needed.

Voltage-Dependent Outward K+ Current: Repolarization Genetic Alterations of Calmodulin in Hyperglycemia of b Cells and Insulin Secretion and Neonatal Diabetes Pancreatic b cells have prominent voltage-dependent outward Calmodulin and protein kinase C are two b cell calcium-binding K+ (Kv) currents that mediate AP repolarization (Dukes and proteins with multiple potential roles in secretion (Hubinont Philipson, 1996; Philipson, 1999; Rorsman and Trube, 1986; Su et al., 1984; Prentki and Matschinsky, 1987; Sugden et al., 1979). et al., 2001), and both Kv1 (KCNA) and Kv2 (KCNB) channel fami- Calmodulin may be a major calcium buffer, and transgenic mice lies are involved (MacDonald et al., 2001)(Figure 1C). Kv2.1 that overexpress calmodulin (CaM) specifically in pancreatic expression is high in b cells (MacDonald et al., 2001; Roe b cells develop severe diabetes within hours after birth, demon- et al., 1996), and adenovirus-mediated expression of domi- strating elevated blood glucose and glucagonlevelsand amarked nant-negative Kv2.1 reduced (60%–70%) b cell delayed rectifier reduction in insulin levels (Epstein et al., 1992b), very much like currents and markedly enhanced GSIS (MacDonald et al., 2001). that seen in GOF Kir6.2 transgenic mice (Remedi et al., 2009). A Perfusion of mouse pancreas with Kv2.1 antagonists enhances similar phenotype was found in transgenic mice overexpressing first- and second-phase insulin secretion but, as expected, inactive CaM-8 and containing a deletion of eight amino acids does not affect basal insulin levels (MacDonald et al., 2002). Phi- in the central helix (Ribar et al., 1995), suggesting a mechanism lipson and colleagues (Philipson et al., 1994) generated Kv2.1- involving Ca2+ buffering rather than downstream calmodulin overexpressing transgenic mice under Rip control. Although signaling and consistent with Ca2+-sensitive pools of insulin expression levels were variable, the mice showed hyperglycemia granules: vesicles colocalized with VDCC (Pertusa et al., 1999).

446 Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. Cell Metabolism Review

Integrating the Models: Emerging Themes and Future can result simply from loss of insulin secretion due to failure of Directions M-E coupling. At the earliest stages of the disease (Koster M-E Coupling Leads to Ca2+: So What? et al., 2000; Remedi et al., 2009) and chronically when protected In a 2002 review, we systematically compared the phenotypic against the systemic consequences (Remedi et al., 2009), b cells consequences of transgenic manipulation of multiple genes in do not deteriorate and maintain normal insulin content even pancreatic b cells (Nichols and Koster, 2002). Although genes though secretion in response to glucose remains refractory. obviously involved in pancreatic development lead to loss of However, in the untreated situation, there is rapid deterioration: b cells and inevitably insulin-dependent diabetes, many b cell mass is lost, and insulin content disappears (Girard et al., signaling molecules have relatively mild consequences, except 2009; Koster et al., 2000; Remedi et al., 2009). These models, for those involved directly in coupling glucose uptake, through therefore, provide important tools to understand the basis of metabolism, to electrical signaling (e.g., GLUT2, GCK, Kir6.2, this secondary failure. There are many hypotheses behind the SUR1). In these cases, even minor over- or underactivity leads ‘‘glucotoxic’’ death of b cells in diabetes (Poitout and Robertson, to under- or oversecretion and marked hyperinsulinism or dia- 2008). It is clear that, in some animal models, it can result from betes. This is dramatic in the case of KATP, in which even rela- ‘‘overstimulation’’ by glucose (Grill and Bjorklund, 2001) and, tively small shifts in the ATP sensitivity lead to severe diabetes because this can be protected against by infusion of diazoxide (Girard et al., 2009; Koster et al., 2000; Remedi et al., 2009), (Guldstrand et al., 2002; Sako and Grill, 1990), implicitly involves glucokinase knockout (Grupe et al., 1995; Terauchi et al., hyperactivation of Ca2+ stimulation. Grill and Bjorklund (2001) 1995), or calmodulin overexpression (Epstein et al., 1992b; Ribar examined long-term effects of diazoxide treatment on b cell et al., 1995). The data from human NDM patients are entirely function in islets transplanted from normal rats into syngeneic consistent: monogenic NDM is caused by loss of glucokinase recipients previously made diabetic by streptozotocin (Hira- and by GOF mutations in KATP (Gloyn et al., 2004; Gloyn, matsu et al., 2000). After 8 weeks transplant, function was 2003a). In the latter case, the more severe the ATP insensitivity, improved, implying a protection against overstimulation and the more severe the disease, but even mild shifts in ATP sensi- consequent ‘‘Ca2+ toxicity’’ (which could lead to multiple path- tivity can cause neonatal disease (Hattersley and Ashcroft, ways of cell death, including Ca-dependent proteases and 2005; Sivaprasadarao et al., 2007). apoptosis). Such a mechanism may well occur in otherwise The reiteration of very similar phenotypes for mutations in normal islets facing an abnormal ‘‘glucose load,’’ but in the these genes seems quite telling: at least at early stages of life, case of reduced signaling through M-E coupling, this does not the pathway from glucose metabolism, initiated by glucokinase seem possible, given that, even in late stages of disease, islets 2+ 2+ activity, through excitability to elevated [Ca ]i is critical and remain refractory to stimulation and intracellular [Ca ] remains cannot be compromised. The calmodulin-overactive mouse is low (Girard et al., 2009; Remedi et al., 2009). Potential mecha- interesting in this regard. Early studies indicated that the primary nisms of ‘‘glucotoxicity’’ without Ca2+ toxicity are manifold, defect is probably the consequent increase in Ca2+ buffering, including the generation of advanced glycosylation end products 2+ leading to depressed [Ca ]i, given that the phenotype is the (AGE) and other potentially toxic compounds (Del Prato et al., same when an inactive mutant is overexpressed (Easom, 1999; 2007; Grill and Bjorklund, 2001; Zhao et al., 2009), and the islets Epstein et al., 1992b; Ribar et al., 1995), indicating that failure from these animals will, therefore, provide models for future 2+ of [Ca ]i elevation is causal. studies of the mechanisms of glucotoxic loss of b cells and So what are the broader implications for b cell function and insulin content in the face of low intracellular [Ca2+]. diabetes? Sulfonylureas are effective treatments for NDM due M-E Coupling Leads to Ca2+: Surprises, Too to KATP mutations (Hattersley and Ashcroft, 2005; Pearson A clear picture emerging from animal models is that reduced M-E 2+ et al., 2006; Wambach et al., 2009), providing generally better coupling leads to reduced [Ca ]i and reduced insulin secretion, control of blood glucose than insulin and potentially without with remarkably small tolerance limits, and this is borne out in the long-term failure found in type 2 patients (Rustenbeck, humans by the finding that NDM results from relatively small

2002). Total loss of mouse b cell GCK (i.e., a more severe defect changes in ATP sensitivity of the KATP channel. But there are than likely present in most human LOF mutations; Njolstad et al., surprises on the other side of the ‘‘see-saw.’’ The lack of hyper-

2001, 2003; Porter et al., 2005) results in failure to close KATP insulinism (in fact, relative hypoinsulinism) in mice completely channels (Sakura et al., 1998), and consequent diabetes is lacking KATP channels is not readily explained (Dufer et al., at least partially abrogated by removal of KATP channels in 2004). Our studies have demonstrated that partial loss of KATP GKÀ/À/Kir6.2À/À double knockout mice (Remedi et al., 2005). has the expected effect of shifting secretion to lower glucose This suggests that GCK underactivity and potentially any other levels, leading to enhanced glucose tolerance, but below defects upstream of KATP, i.e., between glucose uptake and a certain level (<15% of normal KATP)(Nichols et al., 2007; KATP closure, might be treatable at the level of the KATP channel, Remedi et al., 2006), there is crossover to marked undersecre- and it is interesting that a recent report (Turkkahraman et al., tion due to downregulation of secretion itself in the face of a 2+ 2008) indeed suggests that such treatment may be effective in maintained elevated [Ca ]i. Although this might be ascribed GCK-dependent human NDM. to some form of Ca2+ toxicity, it appears to be very labile and Secondary Consequences of Altered M-E Coupling readily reversible; the phenotype is closely replicated by chronic As discussed above, it is clear from studies of calmodulin over- pharmacological block of channel activity in mice implanted expressors (Epstein et al., 1992b; Ribar et al., 1995), GCK knock- with slow-release high-dose glibenclamide pellets, yet this outs (Grupe et al., 1995; Terauchi et al., 1995), and KATP GOF phenotype is completely reversed within hours of removal of mice (Koster et al., 2000; Remedi et al., 2009) that diabetes the drug (Remedi and Nichols, 2008). Again, such findings point

Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. 447 Cell Metabolism Review

to previously unconsidered mechanisms and may be of rele- Barg, S., Ma, X., Eliasson, L., Galvanovskis, J., Gopel, S.O., Obermuller, S., vance to humans. First, as discussed, there are reports that HI Platzer, J., Renstrom, E., Trus, M., Atlas, D., et al. (2001). Fast exocytosis with few Ca(2+) channels in insulin-secreting mouse pancreatic B cells. patients with LOF KATP mutations can cross over to a glucose- Biophys. J. 81, 3308–3323. intolerant phenotype later in life, even without pancreatectomy Bensch, K.G., Mott, J.L., Chang, S.W., Hansen, P.A., Moxley, M.A., (de Lonlay et al., 2002; Dunne et al., 2004; Mazor-Aronovitch Chambers, K.T., de Graaf, W., Zassenhaus, H.P., and Corbett, J.A. (2009). et al., 2009). Second, chronic sulfonylurea treatment inevitably Selective mtDNA mutation accumulation results in beta-cell apoptosis and fails in type 2 patients, again potentially involving chronic down- diabetes development. Am. J. Physiol. Endocrinol. Metab. 296, E672–E680. regulation of secretion that can be reversed by b cell ‘‘rest’’ Boini, K.M., Graf, D., Hennige, A.M., Koka, S., Kempe, D.S., Wang, K., (Guldstrand et al., 2002; Pfutzner et al., 2006; Sargsyan et al., Ackermann, T.F., Foller, M., Vallon, V., Pfeifer, K., et al. (2009). Enhanced insulin sensitivity of gene-targeted mice lacking functional KCNQ1. Am. 2008). J. Physiol. Regul. Integr. Comp. Physiol. 296, R1695–R1701.

Braun, M., Ramracheya, R., Bengtsson, M., Zhang, Q., Karanauskaite, J., Concluding Remarks Partridge, C., Johnson, P.R., and Rorsman, P. (2008). Voltage-gated ion chan- Clearly, mice and humans are not genetically the same, and nels in human pancreatic beta-cells: electrophysiological characterization and role in insulin secretion. Diabetes 57, 1618–1628. differential islet morphology is a relevant issue. We do not suggest that animal models can supplant clinical experience or Briaud, I., Kelpe, C.L., Johnson, L.M., Tran, P.O., and Poitout, V. (2002). Differ- ential effects of hyperlipidemia on insulin secretion in islets of langerhans from that the implications from animal models can automatically hyperglycemic versus normoglycemic rats. Diabetes 51, 662–668. translate to clinical relevance. However, many major players in M-E coupling are likely to be the same in humans and mouse, Cantley, J., Selman, C., Shukla, D., Abramov, A.Y., Forstreuter, F., Esteban, M.A., Claret, M., Lingard, S.J., Clements, M., Harten, S.K., et al. (2009). Dele- and recent studies show marked parallels in disease etiology tion of the von Hippel-Lindau gene in pancreatic beta cells impairs glucose and progression resulting from their derangement in mouse and homeostasis in mice. J. Clin. Invest. 119, 125–135. man. Given the undisputed experimental advantages of the Cauchi, S., Meyre, D., Durand, E., Proenc¸a, C., Marre, M., Hadjadj, S., mouse, both genetically and physiologically, mouse models Choquet, H., De Graeve, F., Gaget, S., Allegaert, F., et al. (2008). Post will continue to provide important avenues for explaining basic genome-wide association studies of novel genes associated with type 2 dia- betes show gene-gene interaction and high predictive value. PLoS ONE 3, mechanisms of M-E coupling, but also the molecular basis of e2031. and therapeutic possibilities for treating diseases that result Chan, C.B., MacDonald, P.E., Saleh, M.C., Johns, D.C., Marban, E., and from M-E coupling derangement. Wheeler, M.B. (1999). Overexpression of uncoupling protein 2 inhibits glucose-stimulated insulin secretion from rat islets. Diabetes 48, 1482–1486.

ACKNOWLEDGMENTS Chan, C.B., De Leo, D., Joseph, J.W., McQuaid, T.S., Ha, X.F., Xu, F., Tsushima, R.G., Pennefather, P.S., Salapatek, A.M., and Wheeler, M.B. Our own experimental work has been supported by National Institutes of (2001). Increased uncoupling protein-2 levels in beta-cells are associated Health Grant DK69445 (to C.G.N.). We are additionally grateful to the Washing- with impaired glucose-stimulated insulin secretion: mechanism of action. ton University DRTC (DK20579) for reagent support. Diabetes 50, 1302–1310. Chistiakov, D.A., Potapov, V.A., Khodirev, D.C., Shamkhalova, M.S., Shesta- REFERENCES kova, M.V., and Nosikov, V.V. (2009). Genetic variations in the pancreatic ATP-sensitive potassium channel, beta-cell dysfunction, and susceptibility to type 2 diabetes. Acta Diabetol. 46, 43–49. Aguilar-Bryan, L., Bryan, J., and Nakazaki, M. (2001). Of mice and men: K(ATP) channels and insulin secretion. Recent Prog. Horm. Res. 56, 47–68. Clement, J.P., IV, Kunjilwar, K., Gonzalez, G., Schwanstecher, M., Panten, U., Aguilar-Bryan, L., and Bryan, J. (1997). Association and stoichiometry of Araki, E., Lipes, M.A., Patti, M.E., Bruning, J.C., Haag, B., III, Johnson, R.S., K(ATP) channel subunits. Neuron 18, 827–838. and Kahn, C.R. (1994). Alternative pathway of insulin signalling in mice with targeted disruption of the IRS-1 gene. Nature 372, 186–190. Codner, E., Deng, L., Perez-Bravo, F., Roman, R., Lanzano, P., Cassorla, F., and Chung, W.K. (2006). Glucokinase mutations in young children with hyper- Arkblad, E.L., Tuck, S., Pestov, N.B., Dmitriev, R.I., Kostina, M.B., Stenvall, J., glycemia. Diabetes Metab. Res. Rev. 22, 348–355. Tranberg, M., and Rydstrom, J. (2005). A Caenorhabditis elegans mutant lack- ing functional nicotinamide nucleotide transhydrogenase displays increased Cuesta-Munoz, A.L., Huopio, H., Otonkoski, T., Gomez-Zumaquero, J.M., sensitivity to oxidative stress. Free Radic. Biol. Med. 38, 1518–1525. Nanto-Salonen, K., Rahier, J., Lopez-Enriquez, S., Garcia-Gimeno, M.A., Sanz, P., Soriguer, F.C., and Laakso, M. (2004). Severe persistent hyperinsu- Arsenijevic, D., Onuma, H., Pecqueur, C., Raimbault, S., Manning, B.S., linemic hypoglycemia due to a de novo glucokinase mutation. Diabetes 53, Miroux, B., Couplan, E., Alves-Guerra, M.C., Goubern, M., Surwit, R., et al. 2164–2168. (2000). Disruption of the uncoupling protein-2 gene in mice reveals a role in immunity and reactive oxygen species production. Nat. Genet. 26, 435–439. Daniel, S., Noda, M., Straub, S.G., and Sharp, G.W. (1999). Identification of the docked granule pool responsible for the first phase of glucose-stimulated Ashcroft, F.M. (2006). From molecule to malady. Nature 440, 440–447. insulin secretion. Diabetes 48, 1686–1690.

Ashcroft, F.M., and Rorsman, P. (1990). ATP-sensitive K+ channels: a link de Lonlay, P., Fournet, J.C., Touati, G., Groos, M.S., Martin, D., Sevin, C., between B-cell metabolism and insulin secretion. Biochem. Soc. Trans. 18, Delagne, V., Mayaud, C., Chigot, V., Sempoux, C., et al. (2002). Heterogeneity 109–111. of persistent hyperinsulinaemic hypoglycaemia. A series of 175 cases. Eur. J. Pediatr. 161, 37–48. Atwater, I., Rosario, L., and Rojas, E. (1983). Properties of the Ca-activated K+ channel in pancreatic beta-cells. Cell Calcium 4, 451–461. Del Prato, S., Bianchi, C., and Marchetti, P. (2007). beta-cell function and anti-diabetic pharmacotherapy. Diabetes Metab. Res. Rev. 23, 518–527. Aynsley-Green, A. (1981). Nesidioblastosis of the pancreas in infancy. Dev. Med. Child Neurol. 23, 372–379. Dufer, M., Haspel, D., Krippeit-Drews, P., Aguilar-Bryan, L., Bryan, J., and Drews, G. (2004). Oscillations of membrane potential and cytosolic Ca(2+) Bali, D., Svetlanov, A., Lee, H.W., Fusco-DeMane, D., Leiser, M., Li, B., concentration in SUR1(À/À) beta cells. Diabetologia 47, 488–498. Barzilai, N., Surana, M., Hou, H., and Fleischer, N. (1995). Animal model for maturity-onset diabetes of the young generated by disruption of the mouse Dukes, I.D., and Philipson, L.H. (1996). K+ channels: generating excitement in glucokinase gene. J. Biol. Chem. 270, 21464–21467. pancreatic beta-cells. Diabetes 45, 845–853.

448 Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. Cell Metabolism Review

Dunne, M.J., Kane, C., Shepherd, R.M., Sanchez, J.A., James, R.F., Johnson, Guillam, M.T., Hummler, E., Schaerer, E., Yeh, J.I., Birnbaum, M.J., Beermann, P.R., Aynsley-Green, A., Lu, S., Clement, J.P., IV, Lindley, K.J., Seino, S., and F., Schmidt, A., Deriaz, N., Thorens, B., and Wu, J.Y. (1997). Early diabetes and Aguilar-Bryan, L. (1997). Familial persistent hyperinsulinemic hypoglycemia abnormal postnatal pancreatic islet development in mice lacking Glut-2. Nat. of infancy and mutations in the sulfonylurea receptor. N. Engl. J. Med. 336, Genet. 17, 327–330. 703–706. Guillam, M.T., Dupraz, P., and Thorens, B. (2000). Glucose uptake, utilization, Dunne, M.J., Cosgrove, K.E., Shepherd, R.M., Aynley-Green, A., and Lindley, and signaling in GLUT2-null islets. Diabetes 49, 1485–1491. K.J. (2004). Hyperinsulinism in Infancy: From Basic Science to Clinical Disease. Physiol. Rev. 84, 239–275. Guillausseau, P.J., Meas, T., Virally, M., Laloi-Michelin, M., Medeau, V., and Kevorkian, J.P. (2008). Abnormalities in insulin secretion in type 2 diabetes Easom, R.A. (1999). CaM kinase II: a protein kinase with extraordinary talents mellitus. Diabetes Metab. 34 (Suppl 2), S43–S48. germane to insulin exocytosis. Diabetes 48, 675–684. Guldstrand, M., Grill, V., Bjorklund, A., Lins, P.E., and Adamson, U. (2002). Echtay, K.S., Roussel, D., St-Pierre, J., Jekabsons, M.B., Cadenas, S., Stuart, Improved beta cell function after short-term treatment with diazoxide in obese J.A., Harper, J.A., Roebuck, S.J., Morrison, A., Pickering, S., et al. (2002). subjects with type 2 diabetes. Diabetes Metab. 28, 448–456. Superoxide activates mitochondrial uncoupling proteins. Nature 415, 96–99. Hattersley, A.T., and Ashcroft, F.M. (2005). Activating mutations in Kir6.2 and Efrat, S., Tal, M., and Lodish, H.F. (1994). The pancreatic beta-cell glucose neonatal diabetes: new clinical syndromes, new scientific insights, and new sensor. Trends Biochem. Sci. 19, 535–538. therapy. Diabetes 54, 2503–2513.

Epstein, P.N., Boschero, A.C., Atwater, I., Cai, X., and Overbeek, P.A. (1992a). Henwood, M.J., Kelly, A., MacMullen, C., Bhatia, P., Ganguly, A., Thornton, Expression of yeast hexokinase in pancreatic beta cells of transgenic mice P.S., and Stanley, C.A. (2005). Genotype-Phenotype Correlations in Children reduces blood glucose, enhances insulin secretion, and decreases diabetes. with Congenital Hyperinsulinism Due to Recessive Mutations of the Adenosine Proc. Natl. Acad. Sci. USA 89, 12038–12042. Triphosphate-Sensitive Potassium Channel Genes. J. Clin. Endocrinol. Metab. 90, 789–794. Epstein, P.N., Ribar, T.J., Decker, G.L., Yaney, G., and Means, A.R. (1992b). Elevated beta-cell calmodulin produces a unique insulin secretory defect in Herrera, P.L. (2002). Defining the cell lineages of the islets of Langerhans using transgenic mice. Endocrinology 130, 1387–1393. transgenic mice. Int. J. Dev. Biol. 46, 97–103.

Erecinska, M., Bryla, J., Michalik, M., Meglasson, M.D., and Nelson, D. (1992). Himms-Hagen, J., and Harper, M.E. (2001). Physiological role of UCP3 may be Energy metabolism in islets of Langerhans. Biochim. Biophys. Acta 1101, export of fatty acids from mitochondria when fatty acid oxidation predomi- 273–295. nates: an hypothesis. Exp. Biol. Med. 226, 78–84. Fajans, S.S., Bell, G.I., and Polonsky, K.S. (2001). Molecular mechanisms Hiramatsu, S., Hoog, A., Moller, C., and Grill, V. (2000). Treatment with and clinical pathophysiology of maturity-onset diabetes of the young. diazoxide causes prolonged improvement of beta-cell function in rat islets N. Engl. J. Med. 345, 971–980. transplanted to a diabetic environment. Metabolism 49, 657–661. Florez, J.C., Burtt, N., de Bakker, P.I., Almgren, P., Tuomi, T., Holmkvist, J., Hoek, J.B., and Rydstrom, J. (1988). Physiological roles of nicotinamide Gaudet, D., Hudson, T.J., Schaffner, S.F., Daly, M.J., et al. (2004). Haplotype nucleotide transhydrogenase. Biochem. J. 254, 1–10. structure and genotype-phenotype correlations of the sulfonylurea receptor and the islet ATP-sensitive potassium channel gene region. Diabetes 53, Hofmann, F., Illes, P., Aktories, K., and Meyer, D.K. (1999). Voltage- 1360–1368. dependent calcium channels: from structure to function. Br. J. Pharmacol. 127, 1060–1063. Freeman, H., Shimomura, K., Cox, R.D., and Ashcroft, F.M. (2006). Nicotin- amide nucleotide transhydrogenase: a link between insulin secretion, glucose metabolism and oxidative stress. Biochem. Soc. Trans. 34, 806–810. Holmkvist, J., Tojjar, D., Almgren, P., Lyssenko, V., Lindgren, C.M., Isomaa, B., Tuomi, T., Berglund, G., Renstrom, E., and Groop, L. (2007). Polymorphisms Girard, C.A., Wunderlich, F.T., Shimomura, K., Collins, S., Kaizik, S., Proks, P., in the gene encoding the voltage-dependent Ca(2+) channel Ca (V)2.3 Abdulkader, F., Clark, A., Ball, V., Zubcevic, L., et al. (2009). Expression of an (CACNA1E) are associated with type 2 diabetes and impaired insulin secretion. activating mutation in the gene encoding the KATP channel subunit Kir6.2 in Diabetologia 50, 2467–2475. mouse pancreatic beta cells recapitulates neonatal diabetes. J. Clin. Invest. 119, 80–90. Hu, C., Wang, C., Zhang, R., Ma, X., Wang, J., Lu, J., Qin, W., Bao, Y., Xiang, K., and Jia, W. (2009). Variations in KCNQ1 are associated with type 2 diabetes Gloyn, A.L. (2003a). Glucokinase (GCK) mutations in hyper- and hypogly- and beta cell function in a Chinese population. Diabetologia 52, 1322–1325. cemia: maturity-onset diabetes of the young, permanent neonatal diabetes, and hyperinsulinemia of infancy. Hum. Mutat. 22, 353–362. Hubinont, C.J., Best, L., Sener, A., and Malaisse, W.J. (1984). Activation of protein kinase C by a tumor-promoting phorbol ester in pancreatic islets. Gloyn, A.L. (2003b). The search for type 2 diabetes genes. Ageing Res. Rev. 2, FEBS Lett. 170, 247–253. 111–127. Huopio, H., Shyng, S.L., Otonkoski, T., and Nichols, C.G. (2002a). K(ATP) Gloyn, A.L., Ellard, S., Shield, J.P., Temple, I.K., Mackay, D.J., Polak, M., channels and insulin secretion disorders. Am. J. Physiol. Endocrinol. Metab. Barrett, T., and Hattersley, A.T. (2002). Complete glucokinase deficiency is 283, E207–E216. not a common cause of permanent neonatal diabetes. Diabetologia 45, 290. Huopio, H., Vauhkonen, I., Komulainen, J., Niskanen, L., Otonkoski, T., and Gloyn, A.L., Pearson, E.R., Antcliff, J.F., Proks, P., Bruining, G.J., Slingerland, Laakso, M. (2002b). Carriers of an inactivating beta-cell ATP-sensitive K(+) A.S., Howard, N., Srinivasan, S., Silva, J.M.C.L., Molnes, J., et al. (2004). Acti- channel mutation have normal glucose tolerance and insulin sensitivity and vating mutations in the gene encoding the ATP-sensitive potassium-channel appropriate insulin secretion. Diabetes Care 25, 101–106. subunit Kir6.2 and permanent neonatal diabetes. N. Engl. J. Med. 350, 1838–1849. Ichii, H., Inverardi, L., Pileggi, A., Molano, R.D., Cabrera, O., Caicedo, A., Messinger, S., Kuroda, Y., Berggren, P.O., and Ricordi, C. (2005). A novel Grill, V., and Bjorklund, A. (2001). Overstimulation and beta-cell function. method for the assessment of cellular composition and beta-cell viability in Diabetes 50 (Suppl 1), S122–S124. human islet preparations. Am. J. Transplant. 5, 1635–1645.

Grimberg, A., Ferry, R.J., Jr., Kelly, A., Koo-McCoy, S., Polonsky, K., Glaser, Inagaki, N., Gonoi, T., Clement, J.P., VI, Namba, N., Inazawa, J., Gonzalez, G., B., Permutt, M.A., Aguilar-Bryan, L., Stafford, D., Thornton, P.S., et al. Aguilar-Bryan, L., Seino, S., and Bryan, J. (1995). Reconstitution of IKATP: (2001). Dysregulation of insulin secretion in children with congenital hyperinsu- an inward rectifier subunit plus the sulfonylurea receptor. Science 270, linism due to sulfonylurea receptor mutations. Diabetes 50, 322–328. 1166–1170.

Grupe, A., Hultgren, B., Ryan, A., Ma, Y.H., Bauer, M., and Stewart, T.A. (1995). Iwashima, Y., Pugh, W., Depaoli, A.M., Takeda, J., Seino, S., Bell, G.I., and Transgenic knockouts reveal a critical requirement for pancreatic beta cell Polonsky, K.S. (1993). Expression of calcium channel mRNAs in rat pancreatic glucokinase in maintaining glucose homeostasis. Cell 83, 69–78. islets and downregulation after glucose infusion. Diabetes 42, 948–955.

Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. 449 Cell Metabolism Review

Jacobson, D.A., Kuznetsov, A., Lopez, J.P., Kash, S., Ammala, C.E., and Maassen, J.A., ‘T Hart, L.M., Van Essen, E., Heine, R.J., Nijpels, G., Jahangir Philipson, L.H. (2007). Kv2.1 ablation alters glucose-induced islet electrical Tafrechi, R.S., Raap, A.K., Janssen, G.M., and Lemkes, H.H. (2004). Mitochon- activity, enhancing insulin secretion. Cell Metab. 6, 229–235. drial diabetes: molecular mechanisms and clinical presentation. Diabetes 53, S103–S109. Jing, X., Li, D., Olofsson, C.S., Salehi, A., Surve, V.V., Caballero, J., Ivarsson, R., Lundquist, I., Pereverzev, A., Schneider, T., et al. (2005). CaV2.3 calcium MacDonald, P.E., Ha, X.F., Wang, J., Smukler, S.R., Sun, A.M., Gaisano, H.Y., channels control second-phase insulin release. J. Clin. Invest. 115, 146–154. Salapatek, A.M., Backx, P.H., and Wheeler, M.B. (2001). Members of the Kv1 and Kv2 voltage-dependent K(+) channel families regulate insulin secretion. Jonsson, A., Isomaa, B., Tuomi, T., Taneera, J., Salehi, A., Nilsson, P., Groop, Mol. Endocrinol. 15, 1423–1435. L., and Lyssenko, V. (2009). A variant in the KCNQ1 gene predicts future type 2 diabetes and mediates impaired insulin secretion. Diabetes 58, 2409–2413. MacDonald, P.E., Sewing, S., Wang, J., Joseph, J.W., Smukler, S.R., Sakellar- opoulos, G., Saleh, M.C., Chan, C.B., Tsushima, R.G., Salapatek, A.M., and Joseph, J.W., Koshkin, V., Zhang, C.Y., Wang, J., Lowell, B.B., Chan, C.B., Wheeler, M.B. (2002). Inhibition of Kv2.1 voltage-dependent K+ channels in and Wheeler, M.B. (2002). Uncoupling protein 2 knockout mice have enhanced pancreatic beta-cells enhances glucose-dependent insulin secretion. J. Biol. insulin secretory capacity after a high-fat diet. Diabetes 51, 3211–3219. Chem. 277, 44938–44945.

Kane, C., Shepherd, R.M., Squires, P.E., Johnson, P.R., James, R.F., Milla, MacDonald, P.E., Joseph, J.W., and Rorsman, P. (2005). Glucose-sensing P.J., Aynsley-Green, A., Lindley, K.J., and Dunne, M.J. (1996). Loss of func- mechanisms in pancreatic beta-cells. Philos. Trans. R. Soc. Lond. B Biol. tional KATP channels in pancreatic beta-cells causes persistent hyperinsuline- Sci. 360, 2211–2225. mic hypoglycemia of infancy. Nat. Med. 2, 1344–1347. Maechler, P., and Wollheim, C.B. (2001). Mitochondrial function in normal and Kang, Y., Huang, X., Pasyk, E.A., Ji, J., Holz, G.G., Wheeler, M.B., Tsushima, diabetic beta-cells. Nature 414, 807–812. R.G., and Gaisano, H.Y. (2002). Syntaxin-3 and syntaxin-1A inhibit L-type calcium channel activity, insulin biosynthesis and exocytosis in beta-cell lines. Matschinsky, F.M. (1996). Banting Lecture 1995. A lesson in metabolic Diabetologia 45, 231–241. regulation inspired by the glucokinase glucose sensor paradigm. Diabetes 45, 223–241. Kassis, N., Bernard, C., Pusterla, A., Casteilla, L., Penicaud, L., Richard, D., Ricquier, D., and Ktorza, A. (2000). Correlation between pancreatic islet Matveyenko, A.V., and Butler, P.C. (2008). Relationship between beta-cell uncoupling protein-2 (UCP2) mRNA concentration and insulin status in rats. mass and diabetes onset. Diabetes Obes. Metab. 10 (Suppl 4), 23–31. Int. J. Exp. Diabetes Res. 1, 185–193. Mazor-Aronovitch, K., Landau, H., and Gillis, D. (2009). Surgical versus Katagiri, H., Asano, T., Ishihara, H., Inukai, K., Anai, M., Miyazaki, J., Tsukuda, non-surgical treatment of congenital hyperinsulinism. Pediatr. Endocrinol. K., Kikuchi, M., Yazaki, Y., and Oka, Y. (1992). Nonsense mutation of glucoki- Rev. 6, 424–430. nase gene in late-onset non-insulin-dependent diabetes mellitus. Lancet 340, McCarthy, M.I. (2008). Casting a wider net for diabetes susceptibility genes. 1316–1317. Nat. Genet. 40, 1039–1040. Koster, J.C., Marshall, B.A., Ensor, N., Corbett, J.A., and Nichols, C.G. (2000). Mears, D. (2004). Regulation of insulin secretion in islets of Langerhans by Targeted overactivity of beta cell K(ATP) channels induces profound neonatal Ca(2+)channels. J. Membr. Biol. 200, 57–66. diabetes. Cell 100, 645–654. Miki, T., Tashiro, F., Iwanaga, T., Nagashima, K., Yoshitomi, H., Aihara, H., Koster, J.C., Remedi, M.S., Flagg, T.P., Johnson, J.D., Markova, K.P., Nitta, Y., Gonoi, T., Inagaki, N., Miyazaki, J., and Seino, S. (1997). Abnormal- Marshall, B.A., and Nichols, C.G. (2002). Hyperinsulinism induced by ities of pancreatic islets by targeted expression of a dominant-negative targeted suppression of beta cell KATP channels. Proc. Natl. Acad. Sci. USA KATP channel. Proc. Natl. Acad. Sci. USA 94, 11969–11973. 99, 16992–16997. Miki, T., Nagashima, K., Tashiro, F., Kotake, K., Yoshitomi, H., Tamamoto, A., Koster, J.C., Remedi, M.S., Masia, R., Patton, B., Tong, A., and Nichols, C.G. Gonoi, T., Iwanaga, T., Miyazaki, J., and Seino, S. (1998). Defective insulin (2006). Expression of ATP-insensitive KATP channels in pancreatic beta-cells secretion and enhanced insulin action in KATP channel- deficient mice. underlies a spectrum of diabetic phenotypes. Diabetes 55, 2957–2964. Proc. Natl. Acad. Sci. USA 95, 10402–10406.

Krauss, S., Zhang, C.-Y., Scorrano, L., Dalgaard, L.T., St-Pierre, J., Grey, S.T., Minami, K., Yokokura, M., Ishizuka, N., and Seino, S. (2002). Normalization of and Lowell, B.B. (2003). Superoxide-mediated activation of uncoupling protein Intracellular Ca2+ Induces a Glucose-responsive State in Glucose-unrespon- 2 causes pancreatic {beta} cell dysfunction. J. Clin. Invest. 112, 1831–1842. sive beta -Cells. J. Biol. Chem. 277, 25277–25282.

Lam, P.P., Leung, Y.M., Sheu, L., Ellis, J., Tsushima, R.G., Osborne, L.R., and Mussig, K., Staiger, H., Machicao, F., Kirchhoff, K., Guthoff, M., Schafer, S.A., Gaisano, H.Y. (2005). Transgenic mouse overexpressing syntaxin-1A as Kantartzis, K., Silbernagel, G., Stefan, N., Holst, J.J., et al. (2009). Association a diabetes model. Diabetes 54, 2744–2754. of type 2 diabetes candidate polymorphisms in KCNQ1 with incretin and insulin secretion. Diabetes 58, 1715–1720. Lee, M.P., Hu, R.J., Johnson, L.A., and Feinberg, A.P. (1997). Human KVLQT1 gene shows tissue-specific imprinting and encompasses Beckwith-Wiede- Nestorowicz, A., Glaser, B., Wilson, B.A., Shyng, S.L., Nichols, C.G., Stanley, mann syndrome chromosomal rearrangements. Nat. Genet. 15, 181–185. C.A., Thornton, P.S., and Permutt, M.A. (1998). Genetic heterogeneity in familial hyperinsulinism. Hum. Mol. Genet. 7, 1119–1128. Leibowitz, G., Glaser, B., Higazi, A.A., Salameh, M., Cerasi, E., and Landau, H. (1995). Hyperinsulinemic hypoglycemia of infancy (nesidioblastosis) in clinical Nichols, C.G. (2006). KATP channels as molecular sensors of cellular metabo- remission: high incidence of diabetes mellitus and persistent beta-cell lism. Nature 440, 470–476. dysfunction at long-term follow-up. J. Clin. Endocrinol. Metab. 80, 386–392. Nichols, C.G., and Koster, J.C. (2002). Diabetes and insulin secretion: whither Leung, Y.M., Kang, Y., Gao, X., Xia, F., Xie, H., Sheu, L., Tsuk, S., Lotan, I., KATP? Am. J. Physiol. Endocrinol. Metab. 283, E403–E412. Tsushima, R.G., and Gaisano, H.Y. (2003). Syntaxin 1A binds to the cyto- plasmic C terminus of Kv2.1 to regulate channel gating and trafficking. Nichols, C.G., Shyng, S.L., Nestorowicz, A., Glaser, B., Clement, J.P., J. Biol. Chem. 278, 17532–17538. Gonzalez, G., Aguilarbryan, L., Permutt, M.A., and Bryan, J. (1996). Adenosine Diphosphate As an Intracellular Regulator Of Insulin Secretion. Science 272, Leung, Y.M., Kang, Y., Xia, F., Sheu, L., Gao, X., Xie, H., Tsushima, R.G., and 1785–1787. Gaisano, H.Y. (2005). Open form of syntaxin-1A is a more potent inhibitor than wild-type syntaxin-1A of Kv2.1 channels. Biochem. J. 387, 195–202. Nichols, C.G., Koster, J.C., and Remedi, M.S. (2007). beta-cell hyperexcit- ability: from hyperinsulinism to diabetes. Diabetes Obes. Metab. 9 (Suppl 2), Lin, Y.-W., MacMullen, C., Ganguly, A., Stanley, C.A., and Shyng, S.-L. (2006). 81–88. A novel KCNJ11 mutation associated with congenital hyperinsulinism reduces the intrinsic open probability of beta-cell ATP-sensitive potassium channels. Nielsen, E.M., Hansen, L., Carstensen, B., Echwald, S.M., Drivsholm, T., J. Biol. Chem. 281, 3006–3012. Glumer, C., Thorsteinsson, B., Borch-Johnsen, K., Hansen, T., and Pedersen, O. (2003). The E23K variant of Kir6.2 associates with impaired post-OGTT Maassen, J.A. (2002). Mitochondrial diabetes: pathophysiology, clinical serum insulin response and increased risk of type 2 diabetes. Diabetes 52, presentation, and genetic analysis. Am. J. Med. Genet. 115, 66–70. 573–577.

450 Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. Cell Metabolism Review

Nishikawa, T., Edelstein, D., Du, X.L., Yamagishi, S., Matsumura, T., Kaneda, Remedi, M.S., Rocheleau, J.V., Tong, A., Patton, B.L., McDaniel, M.L., Piston, Y., Yorek, M.A., Beebe, D., Oates, P.J., Hammes, H.P., et al. (2000). Normal- D.W., Koster, J.C., and Nichols, C.G. (2006). Hyperinsulinism in mice with izing mitochondrial superoxide production blocks three pathways of hypergly- heterozygous loss of K(ATP) channels. Diabetologia 49, 2368–2378. caemic damage. Nature 404, 787–790. Remedi, M.S., Kurata, H.T., Scott, A., Wunderlich, F.T., Rother, E., Kleinrid- Njolstad, P.R., Sovik, O., Cuesta-Munoz, A., Bjorkhaug, L., Massa, O., ders, A., Tong, A., Bruning, J.C., Koster, J.C., and Nichols, C.G. (2009). Barbetti, F., Undlien, D.E., Shiota, C., Magnuson, M.A., Molven, A., et al. Secondary consequences of beta cell inexcitability: identification and preven- (2001). Neonatal diabetes mellitus due to complete glucokinase deficiency. tion in a murine model of K(ATP)-induced neonatal diabetes mellitus. Cell N. Engl. J. Med. 344, 1588–1592. Metab. 9, 140–151.

Njolstad, P.R., Sagen, J.V., Bjorkhaug, L., Odili, S., Shehadeh, N., Bakry, D., Ribar, T.J., Epstein, P.N., Overbeek, P.A., and Means, A.R. (1995). Targeted Sarici, S.U., Alpay, F., Molnes, J., Molven, A., et al. (2003). Permanent neonatal overexpression of an inactive calmodulin that binds Ca2+ to the mouse diabetes caused by glucokinase deficiency: inborn error of the glucose-insulin pancreatic beta-cell results in impaired secretion and chronic hyperglycemia. signaling pathway. Diabetes 52, 2854–2860. Endocrinology 136, 106–115.

Oyama, K., Minami, K., Ishizaki, K., Fuse, M., Miki, T., and Seino, S. (2006). Richardson, C.C., Hussain, K., Jones, P.M., Persaud, S., Lobner, K., Boehm, Spontaneous recovery from hyperglycemia by regeneration of pancreatic A., Clark, A., and Christie, M.R. (2007). Low levels of glucose transporters beta-cells in Kir6.2G132S transgenic mice. Diabetes 55, 1930–1938. and K+ATP channels in human pancreatic beta cells early in development. Diabetologia 50, 1000–1005. Page, R., Hattersley, A., and Turner, R. (1992). Beta-cell secretory defect caused by mutations in glucokinase gene. Lancet 340, 1162–1163. Riedel, M.J., Boora, P., Steckley, D., de Vries, G., and Light, P.E. (2003). Kir6.2 polymorphisms sensitize beta-cell ATP-sensitive potassium channels to acti- Palladino, A.A., Bennett, M.J., and Stanley, C.A. (2008). Hyperinsulinism in vation by acyl CoAs: a possible cellular mechanism for increased susceptibility infancy and childhood: when an insulin level is not always enough. Clin. to type 2 diabetes? Diabetes 52, 2630–2635. Chem. 54, 256–263. Roe, M.W., Worley, J.F., III, Mittal, A.A., Kuznetsov, A., DasGupta, S., Mertz, Pascoe, L., Frayling, T.M., Weedon, M.N., Mari, A., Tura, A., Ferrannini, E., and R.J., Witherspoon, S.M., III, Blair, N., Lancaster, M.E., McIntyre, M.S., et al. Walker, M. (2008). Beta cell glucose sensitivity is decreased by 39% in non- (1996). Expression and function of pancreatic beta-cell delayed rectifier diabetic individuals carrying multiple diabetes-risk alleles compared with K+ channels. Role in stimulus-secretion coupling. J. Biol. Chem. 271, those with no risk alleles. Diabetologia 51, 1989–1992. 32241–32246.

Pearson, E.R., Flechtner, I., Njolstad, P.R., Malecki, M.T., Flanagan, S.E., Rorsman, P., and Trube, G. (1986). Calcium and delayed potassium currents in Larkin, B., Ashcroft, F.M., Klimes, I., Codner, E., Iotova, V., et al. (2006). mouse pancreatic beta-cells under voltage-clamp conditions. J. Physiol. 374, Switching from insulin to oral sulfonylureas in patients with diabetes due to 531–550. Kir6.2 mutations. N. Engl. J. Med. 355, 467–477. Rustenbeck, I. (2002). Desensitization of insulin secretion. Biochem. Pharma- Pereverzev, A., Mikhna, M., Vajna, R., Gissel, C., Henry, M., Weiergraber, M., col. 63, 1921–1935. Hescheler, J., Smyth, N., and Schneider, T. (2002). Disturbances in glucose- tolerance, insulin-release, and stress-induced hyperglycemia upon disruption Sako, Y., and Grill, V.E. (1990). A 48-hour lipid infusion in the rat time- of the Ca(v)2.3 (alpha 1E) subunit of voltage-gated Ca(2+) channels. Mol. dependently inhibits glucose- induced insulin secretion and B cell oxidation Endocrinol. 16, 884–895. through a process likely coupled to fatty acid oxidation. Endocrinology 127, 1580–1589. Pertusa, J.A., Sanchez-Andres, J.V., Martin, F., and Soria, B. (1999). Effects of calcium buffering on glucose-induced insulin release in mouse pancreatic Sakura, H., Bond, C., Warren-Perry, M., Horsley, S., Kearney, L., Tucker, S., islets: an approximation to the calcium sensor. J. Physiol. 520, 473–483. Adelman, J., Turner, R., and Ashcroft, F.M. (1995). Characterization and variation of a human inwardly-rectifying-K-channel gene (KCNJ6): a putative Pfutzner, A., Lorra, B., Abdollahnia, M.R., Kann, P.H., Mathieu, D., Pehnert, C., Oligschleger, C., Kaiser, M., and Forst, T. (2006). The switch from sulfonylurea ATP-sensitive K-channel subunit. FEBS Lett. 367, 193–197. to preprandial short- acting insulin analog substitution has an immediate and comprehensive beta-cell protective effect in patients with type 2 diabetes mel- Sakura, H., Wat, N., Horton, V., Millns, H., Turner, R.C., and Ashcroft, F.M. litus. Diabetes Technol. Ther. 8, 375–384. (1996). Sequence variations in the human Kir6.2 gene, a subunit of the beta- cell ATP-sensitive K-channel: no association with NIDDM in while Caucasian Philipson, L.H. (1999). Beta-cell ion channels: keys to endodermal excitability. subjects or evidence of abnormal function when expressed in vitro. Diabetolo- Horm. Metab. Res. 31, 455–461. gia 39, 1233–1236.

Philipson, L.H., Rosenberg, M.P., Kuznetsov, A., Lancaster, M.E., Worley, J.F., Sakura, H., Ashcroft, S.J., Terauchi, Y., Kadowaki, T., and Ashcroft, F.M. III, Roe, M.W., and Dukes, I.D. (1994). Delayed rectifier K+ channel overexpres- (1998). Glucose modulation of ATP-sensitive K-currents in wild-type, sion in transgenic islets and beta-cells associated with impaired glucose homozygous and heterozygous glucokinase knock-out mice. Diabetologia responsiveness. J. Biol. Chem. 269, 27787–27790. 41, 654–659.

Platzer, J., Engel, J., Schrott-Fischer, A., Stephan, K., Bova, S., Chen, H., Samec, S., Seydoux, J., and Dulloo, A.G. (1998). Role of UCP homologues in Zheng, H., and Striessnig, J. (2000). Congenital deafness and sinoatrial node skeletal muscles and brown adipose tissue: mediators of thermogenesis or dysfunction in mice lacking class D L-type Ca2+ channels. Cell 102, 89–97. regulators of lipids as fuel substrate? FASEB J. 12, 715–724.

Poitout, V., and Robertson, R.P. (2008). Glucolipotoxicity: fuel excess and Sargsyan, E., Ortsater, H., Thorn, K., and Bergsten, P. (2008). Diazoxide- beta-cell dysfunction. Endocr. Rev. 29, 351–366. induced beta-cell rest reduces endoplasmic reticulum stress in lipotoxic beta-cells. J. Endocrinol. 199, 41–50. Porter, J.R., Shaw, N.J., Barrett, T.G., Hattersley, A.T., Ellard, S., and Gloyn, A.L. (2005). Permanent neonatal diabetes in an Asian infant. J. Pediatr. 146, Saxena, R., Voight, B.F., Lyssenko, V., Burtt, N.P., de Bakker, P.I., Chen, H., 131–133. Roix, J.J., Kathiresan, S., Hirschhorn, J.N., Daly, M.J., et al. (2007). Genome-wide association analysis identifies loci for type 2 diabetes and Prentki, M., and Matschinsky, F.M. (1987). Ca2+, cAMP, and phospholipid- triglyceride levels. Science 316, 1331–1336. derived messengers in coupling mechanisms of insulin secretion. Physiol. Rev. 67, 1185–1248. Schulla, V., Renstrom, E., Feil, R., Feil, S., Franklin, I., Gjinovci, A., Jing, X.J., Laux, D., Lundquist, I., Magnuson, M.A., et al. (2003). Impaired insulin secre- Remedi, M.S., and Nichols, C.G. (2008). Chronic antidiabetic sulfonylureas tion and glucose tolerance in beta cell-selective Ca(v)1.2 Ca2+ channel null in vivo: reversible effects on mouse pancreatic beta-cells. PLoS Med. 5, e206. mice. EMBO J. 22, 3844–3854.

Remedi, M.S., Koster, J.C., Patton, B.L., and Nichols, C.G. (2005). ATP-Sensi- Schwanstecher, C., Meyer, U., and Schwanstecher, M. (2002). K(IR)6.2 tive K+ Channel Signaling in Glucokinase-Deficient Diabetes. Diabetes 54, polymorphism predisposes to type 2 diabetes by inducing overactivity of 2925–2931. pancreatic beta-cell ATP-sensitive K(+) channels. Diabetes 51, 875–879.

Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. 451 Cell Metabolism Review

Seghers, V., Nakazaki, M., DeMayo, F., Aguilar-Bryan, L., and Bryan, J. (2000). Tamarina, N.A., Wang, Y., Mariotto, L., Kuznetsov, A., Bond, C., Adelman, J., Sur1 knockout mice. A model for K(ATP) channel-independent regulation of and Philipson, L.H. (2003). Small-conductance calcium-activated K+ channels insulin secretion. J. Biol. Chem. 275, 9270–9277. are expressed in pancreatic islets and regulate glucose responses. Diabetes 52, 2000–2006. Seisenberger, C., Specht, V., Welling, A., Platzer, J., Pfeifer, A., Kuhbandner, S., Striessnig, J., Klugbauer, N., Feil, R., and Hofmann, F. (2000). Functional Tamemoto, H., Kadowaki, T., Tobe, K., Yagi, T., Sakura, H., Hayakawa, T., embryonic cardiomyocytes after disruption of the L-type alpha1C (Cav1.2) Terauchi, Y., Ueki, K., Kaburagi, Y., Satoh, S., et al. (1994). Insulin resistance calcium channel gene in the mouse. J. Biol. Chem. 275, 39193–39199. and growth retardation in mice lacking insulin receptor substrate-1. Nature 372, 182–186. Shehadeh, N., Bakri, D., Njolstad, P.R., and Gershoni-Baruch, R. (2005). Clinical characteristics of mutation carriers in a large family with glucokinase Tan, J.T., Nurbaya, S., Gardner, D., Ye, S., Tai, E.S., and Ng, D.P. (2009). diabetes (MODY2). Diabet. Med. 22, 994–998. Genetic variation in KCNQ1 associates with fasting glucose and beta-cell function: a study of 3,734 subjects comprising three ethnicities living in Shiota, M., Postic, C., Fujimoto, Y., Jetton, T.L., Dixon, K., Pan, D., Grimsby, J., Singapore. Diabetes 58, 1445–1449. Grippo, J.F., Magnuson, M.A., and Cherrington, A.D. (2001). Glucokinase gene locus transgenic mice are resistant to the development of obesity-induced Terauchi, Y., Sakura, H., Yasuda, K., Iwamoto, K., Takahashi, N., Ito, K., Kasai, type 2 diabetes. Diabetes 50, 622–629. H., Suzuki, H., Ueda, O., Kamada, N., et al. (1995). Pancreatic beta-cell- specific targeted disruption of glucokinase gene. Diabetes mellitus due to Shiota, C., Larsson, O., Shelton, K.D., Shiota, M., Efanov, A.M., Hoy, M., defective insulin secretion to glucose. J. Biol. Chem. 270, 30253–30256. Lindner, J., Kooptiwut, S., Juntti-Berggren, L., Gromada, J., et al. (2002). Sulfonylurea receptor type 1 knock-out mice have intact feeding-stimulated Terauchi, Y., Iwamoto, K., Tamemoto, H., Komeda, K., Ishii, C., Kanazawa, Y., insulin secretion despite marked impairment in their response to glucose. Asanuma, N., Aizawa, T., Akanuma, Y., Yasuda, K., et al. (1997). Development J. Biol. Chem. 277, 37176–37183. of non-insulin-dependent diabetes mellitus in the double knockout mice with disruption of insulin receptor substrate-1 and beta cell glucokinase genes. Shyng, S., and Nichols, C.G. (1997). Octameric stoichiometry of the KATP Genetic reconstitution of diabetes as a polygenic disease. J. Clin. Invest. 99, channel complex. J. Gen. Physiol. 110, 655–664. 861–866.

Shyng, S.L., Ferrigni, T., Shepard, J.B., Nestorowicz, A., Glaser, B., Permutt, Thorens, B. (2001). GLUT2 in pancreatic and extra-pancreatic gluco- M.A., and Nichols, C.G. (1998). Functional analyses of novel mutations in detection. Mol. Membr. Biol. 18, 265–273. the sulfonylurea receptor 1 associated with persistent hyperinsulinemic hypoglycemia of infancy. Diabetes 47, 1145–1151. Thorens, B., Guillam, M.T., Beermann, F., Burcelin, R., and Jaquet, M. (2000). Transgenic reexpression of GLUT1 or GLUT2 in pancreatic beta cells rescues Silva, J.P., Kohler, M., Graff, C., Oldfors, A., Magnuson, M.A., Berggren, P.O., GLUT2-null mice from early death and restores normal glucose- stimulated and Larsson, N.G. (2000). Impaired insulin secretion and beta-cell loss in insulin secretion. J. Biol. Chem. 275, 23751–23758. tissue-specific knockout mice with mitochondrial diabetes. Nat. Genet. 26, 336–340. Toye, A.A., Lippiat, J.D., Proks, P., Shimomura, K., Bentley, L., Hugill, A., Mijat, V., Goldsworthy, M., Moir, L., Haynes, A., et al. (2005). A genetic and physio- Sivaprasadarao, A., Taneja, T.K., Mankouri, J., and Smith, A.J. (2007). Traf- logical study of impaired glucose homeostasis control in C57BL/6J mice. ficking of ATP-sensitive potassium channels in health and disease. Biochem. Diabetologia 48, 675–686. Soc. Trans. 35, 1055–1059. Turkkahraman, D., Bircan, I., Tribble, N.D., Akcurin, S., Ellard, S., and Gloyn, A.L. (2008). Permanent neonatal diabetes mellitus caused by a novel homozy- Sladek, R., Rocheleau, G., Rung, J., Dina, C., Shen, L., Serre, D., Boutin, P., gous (T168A) glucokinase (GCK) mutation: initial response to oral sulphony- Vincent, D., Belisle, A., Hadjadj, S., et al. (2007). A genome-wide association lurea therapy. J. Pediatr. 153, 122–126. study identifies novel risk loci for type 2 diabetes. Nature 445, 881–885. Unoki, H., Takahashi, A., Kawaguchi, T., Hara, K., Horikoshi, M., Andersen, G., Smilinich, N.J., Day, C.D., Fitzpatrick, G.V., Caldwell, G.M., Lossie, A.C., Ng, D.P., Holmkvist, J., Borch-Johnsen, K., Jorgensen, T., et al. (2008). SNPs Cooper, P.R., Smallwood, A.C., Joyce, J.A., Schofield, P.N., Reik, W., et al. in KCNQ1 are associated with susceptibility to type 2 diabetes in East Asian (1999). A maternally methylated CpG island in KvLQT1 is associated with an and European populations. Nat. Genet. 40, 1098–1102. antisense paternal transcript and loss of imprinting in Beckwith-Wiedemann syndrome. Proc. Natl. Acad. Sci. USA 96, 8064–8069. Villareal, D.T., Koster, J.C., Robertson, H., Akrouh, A., Miyake, K., Bell, G.I., Patterson, B.W., Nichols, C.G., and Polonsky, K.S. (2009). Kir6.2 variant Smith, A.J., Taneja, T.K., Mankouri, J., and Sivaprasadarao, A. (2007). Molec- E23K increases ATP-sensitive K+ channel activity and is associated with ular cell biology of KATP channels: implications for neonatal diabetes. Expert impaired insulin release and enhanced insulin sensitivity in adults with normal Rev. Mol. Med. 9, 1–17. glucose tolerance. Diabetes 58, 1869–1878.

Splawski, I., Timothy, K.W., Sharpe, L.M., Decher, N., Kumar, P., Bloise, R., Wallace, D.C. (2001). Mouse models for mitochondrial disease. Am. J. Med. Napolitano, C., Schwartz, P.J., Joseph, R.M., Condouris, K., et al. (2004). Genet. 106, 71–93. Ca(V)1.2 calcium channel dysfunction causes a multisystem disorder including arrhythmia and autism. Cell 119, 19–31. Wambach, J.A., Marshall, B.A., Koster, J.C., White, N.H., and Nichols, C.G. (2009). Successful sulfonylurea treatment of an insulin-naive neonate with Sreenan, S., Cockburn, B., Baldwin, A., Ostrega, D., Levisetti, M., Grupe, A., diabetes mellitus due to a KCNJ11 mutation. Pediatr. Diabetes, in press. Bell, G., Stewart, T., Roe, M., and Polonsky, K. (1998). Adaptation to hypergly- Published online July 29 2009.. 10.1111/j.1399-5448.2009.00557.x cemia enhances insulin secretion in glucokinase mutant mice. Diabetes 47, 1881–1888. Yang, S.N., Larsson, O., Branstrom, R., Bertorello, A.M., Leibiger, B., Leibiger, I.B., Moede, T., Kohler, M., Meister, B., and Berggren, P.O. (1999). Syntaxin 1 Stancakova, A., Kuulasmaa, T., Paananen, J., Jackson, A.U., Bonnycastle, interacts with the L(D) subtype of voltage-gated Ca(2+) channels in pancreatic L.L., Collins, F.S., Boehnke, M., Kuusisto, J., and Laakso, M. (2009). Associa- beta cells. Proc. Natl. Acad. Sci. USA 96, 10164–10169. tion of 18 confirmed susceptibility loci for type 2 diabetes with indices of insulin release, proinsulin conversion, and insulin sensitivity in 5,327 nondiabetic Yang, S.N., and Berggren, P.O. (2005a). Beta-cell CaV channel regulation in Finnish men. Diabetes 58, 2129–2136. physiology and pathophysiology. Am. J. Physiol. Endocrinol. Metab. 288, E16–E28. Stanley, C.A. (2002). Advances in Diagnosis and Treatment of Hyperinsulinism in Infants and Children. J. Clin. Endocrinol. Metab. 87, 4857–4859. Yang, S.N., and Berggren, P.O. (2005b). CaV2.3 channel and PKClambda: new players in insulin secretion. J. Clin. Invest. 115, 16–20. Su, J., Yu, H., Lenka, N., Hescheler, J., and Ullrich, S. (2001). The expression and regulation of depolarization-activated K+ channels in the insulin-secreting Yasuda, K., Miyake, K., Horikawa, Y., Hara, K., Osawa, H., Furuta, H., Hirota, cell line INS-1. Pflugers Archiv - European. J. Physiol. 442, 49–56. Y., Mori, H., Jonsson, A., Sato, Y., et al. (2008). Variants in KCNQ1 are associ- ated with susceptibility to type 2 diabetes mellitus. Nat. Genet. 40, 1092–1097. Sugden, M.C., Christie, M.R., and Ashcroft, S.J. (1979). Presence and possible role of calcium-dependent regulator (calmodulin) in rat islets of Langerhans. Zeggini, E., Weedon, M.N., Lindgren, C.M., Frayling, T.M., Elliott, K.S., Lango, FEBS Lett. 105, 95–100. H., Timpson, N.J., Perry, J.R., Rayner, N.W., Freathy, R.M., et al. (2007).

452 Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. Cell Metabolism Review

Replication of genome-wide association signals in UK samples reveals risk loci negatively regulates insulin secretion and is a major link between obesity, for type 2 diabetes. Science 316, 1336–1341. beta cell dysfunction, and type 2 diabetes. Cell 105, 745–755.

Zhang, H., Fujitani, Y., Wright, C.V., and Gannon, M. (2005). Efficient recombi- Zehetner, J., Danzer, C., Collins, S., Eckhardt, K., Gerber, P.A., Ballschmieter, nation in pancreatic islets by a tamoxifen-inducible Cre-recombinase. Genesis P., Galvanovskis, J., Shimomura, K., Ashcroft, F.M., Thorens, B., et al. (2008). 42, 210–217. PVHL is a regulator of glucose metabolism and insulin secretion in pancreatic beta cells. Genes Dev. 22, 3135–3146. Zhao, Z., Zhao, C., Zhang, X.H., Zheng, F., Cai, W., Vlassara, H., and Ma, Z.A. (2009). Advanced glycation end products inhibit glucose-stimulated insulin Zhang, C.Y., Baffy, G., Perret, P., Krauss, S., Peroni, O., Grujic, D., Hagen, T., secretion through nitric oxide-dependent inhibition of cytochrome c oxidase Vidal-Puig, A.J., Boss, O., Kim, Y.B., et al. (2001). Uncoupling protein-2 and adenosine triphosphate synthesis. Endocrinology 150, 2569–2576.

Cell Metabolism 10, December 2, 2009 ª2009 Elsevier Inc. 453