EPIDERMAL ADHESION and CLINICAL CORRELATIONS DESMOSOMES HEMIDESMOSOMES/BMZ CONNEXINS/GAP JCTS Rich Nichols OVERVIEW 4 Main types of cellular junctions between keratinocytes Mechanical, biochemical and signalling interactions Desmosomes—coupled with IFs Adherens junctions—coupled with actin— movement Gap junctions—clusters of connexons; connections between cytoplasm Tight junctions—barrier integrity and permeability OVERVIEW Desmosomes Present throughout epidermis Increase in size and number as keratinocytes migrate upward Link IFs to cell membrane Function in signal transduction Assembly occurs in Ca++-dependent and phosphorylation-dependent fashion OVERVIEW Adherens Bind actin instead of keratin Ifs PLAKOGLOBIN is the only protein found in both desmosomes and adherens jcts Establishment of adherens jcts is essential for desmosome assembly OVERVIEW Tight Jcts Mediate cell adhesion, paracellular communication Play role in epidermal differentiation, barrier function, and proliferation Barrier and fenceÆrestricts solutes, proteins and lipids to certain tissues Major proteins Claudins Occludin and Zo-1 interact with connexins OVERVIEW Gap Jcts Connect cytoplasm of opposing cells More later OVERVIEW Cell-cell interactionsÆimportant in develop and maintenance of tissue structure and function Desmosomes most prominent in tissues subject to mechanical stress Desmosomes also found in myocytes, lymph system, meninges DESMOSOMES Intercellular adhesive junctions Anchor IF cytoskeleton network to plasma membrane Maintain tissue integrity Function in cell adhesion and transduction of intracellular signals DESMOSOMES Abnormal desmosomal structure or disruption causes: Cells to round Separate (acantholysis) Form blisters and vesicles in the epidermis Exfoliation of several epidermal layers DESMOSOMES Inner Plaque Attachment site of cytokeratin filaments to Desmosomal proteins (Desmoplakin). IFs loop thru plaque Outer Plaque (close to plasma membrane) Site of interaction between plakoglobin, desmoplakin I and II, keratocalmin, desmoyokin, (desmogleins, and desmocollins). Also Plectin and IFAP (Int. Fil. Ass. Prot.) Extracellular or Core Transmembrane proteins (cadherins): Desmogleins 1 & 3 and Desmocollin. Core includes plasma membranes DESMOPLAKINS I & II I—250kd protein (plakin); completely intracellular; dumbbell shaped. The head is within the outer plaque while the tail is within the inner plaque Associated diseases Paraneoplastic pemphigus Ag: 250, 230, 210, 190, 170, 160, 130 • All members of plakin family as well as desmogleins are targeted in paraneoplastic pemphigus EM Major (Desmoplakins I and II) Carvajal Desmoplakin II—210 kDa PLAKOGLOBIN 83kd protein associated with the cytoplasmic portion of cadherins (desmoglein and desmocollin) Plakoglobin and plakophilin are members of armadillo family of nuclear and jct proteins (also β-catenin) DESMOSOMAL CADHERINS Six transmembrane glycoprotiens needed for cell adhesion. Six Proteins Desmogleins 1-3 Dsg 1 & 3 in stratified squamous epithelia Dsg2 in all desmosome-containing tissue Desmocollins 1-3 DESMOSOMES Cadherins are calcium-dependent cell-cell adhesion molecules—adhesive glycoproteins (Dsg1 Dsg3 Dsc1) Classic cadherins (E-,P-,N-cadherins) are present in adherens junctions Again, the big difference: Adherens jcts—coupled with actin cytoskeleton Desmosomes—coupled with intermediate filament network DESMOSOMES All cadherins have extracellular conserved AA sequences (calcium-binding) Intracellular parts are different Desmosomes always have pairs of Dsg and Dsc “Cell Adhesion Zipper theory” Adherens—quick but weak cellular adhesion Desmosomes—slow but strong cellular adhesion DESMOGLEIN 1 Desmoglein 1 is a 160kD protein Primarily expressed in the upper dermis But present throughout epidermis Very low level in mucous membranes Disease Associations Pemphigus Foliaceus and erythematosus: Have IgG to extracellular epitope of Desmoglein 1. Pemphigus Herpetiformis Penicillamine induced blisters. DESMOGLEINS Abs in pemphigus possibly: Interfere with desmoglein adherence via steric hindrance Disruption via signal transduction Exfoliative toxin in SSSS specifically cleaves desmoglein 1 DESMOGLEIN 3 Desmoglein 3 (130kD), is expressed primarily in the lower epidermis. Cell-Cell adhesion mediated primarily by Dsg3 in Mucous Membranes Disease Associations P. vulgaris: Polyclonal IgG4 to extracellular component. P. vegetans IgA Pemphigus Intraepidermal Neutrophilic type DESMOGLEIN COMPENSATION Abs to Dsg 1—superficial epidermis, no mucous membranes Abs to Dsg3—mucous membranes, no or limited skin blisters Abs to Dsg1 and Dsg3—skin and mucous membranesÆsplit suprabasal??? DESMOCOLLIN 1 Desmocollin 1 is associated with IgA pemphigus Subcorneal Pustular Dermatosis type. Left: How do you distinguish from other clinical entity? QUESTION Name a disease with a defect in plakoglobin? ANSWER Naxos Disease AR Diffuse NEPPK Wooly Hair RVCM QUESTION What is disease and defect of: Striate PPK, Wooly Hair and LVCM? ANSWER Carvajal Syndrome Desmoplakin CONNEXINS/GAP JCTS Gap Jcts Gap jcts directly connect cytoplasm of opposing cells 6 Connexins form annular hemichannel named a Connexon Max diameter of central pore in hemichannel is 2 nm Connexons cluster together and dock with connexons on opposing cells to form gap jcts Gap Jct channels can be homotypic, heterotypic, or heteromeric (see pic) CONNEXINS/GAP JCTS Gap Jcts essential for cell-cell communication and skin integrity Half-life of each connexin is short (hours) Thus, constant assembly and degradation Tissue distribution is distinct Particularly important in cardiovascular, GI, reproductive, and immune systems Also nerves, skin, ears, eyes CONNEXINS/GAP JCTS Gap jcts allow passage of small molecules <1 kDa in size Aqueous channels allow passage of metabolites, ions Open/Closed channels depends on pH, voltage, Ca++ concentration, & phosphorylation Defects result in deafness, cataracts, neuropathy, and skin disease Mediates differentiation (keratinocyte) and tissue repair Defect? Defect? Defect? CONNEXINS/GAP JCTS Cx 26 mutationsÆnon-syndromic hearing impairment Ionic environment of inner ear sensory epithelia Cell death in cochlear epithelial network and sensory hair cells Charcot-Marie ToothÆCx 32 results in impaired diffusion of nutrients and signalling molecules into peripheral nerves EKVÆCx31 (GJB 3) and Cx 30.3 (GJB4) Vohwinkel’s with hearing impairmentÆCx26 Hidrotic Ectodermal DysplasiaÆCx30 BASEMENT MEMBRANE ZONE Attachment of Keratinocytes to Basement membrane via Hemidesmosome and basement membrane proteins. BASEMENT MEMBRANE ZONE MAJOR COMPONENTS Cytoskeleton Inner Plaque Outer Plaque Lamina Lucida Lamina Densa Anchoring Fibrils Dermis ORIGIN OF BMZ From Keratinocytes (ectodermal) Proteins in HDs: Plectin, BPAG1, BPAG2, integrins α6β4 IV and VII collagen Laminins 5 and 6 Heparan Sulfate Proteoglycans (HSPG) ORIGIN OF BMZ From Dermal Fibroblasts (mesodermal) Nidogen (entactin) Types IV and VII collagen Plasma membrane of basal keratinocytes, via integrins, provides localization and organizational cues CYTOSKELETON Major components of cytoskeleton include Keratin 5 (basic) and Keratin 14 (acidic). They form heterodimers that combine into 10nm intermediate filaments that insert into the inner plaque. Associated Disease Epidermolysis Bullosa Simplex INNER PLAQUE BP antigen 1 (230kDa; plakin) Main protein of inner plaque Connects plaque to cytoskeleton K5-14 via C- terminus Also connects inner plaque to outer plaque via N- terminus, which binds BP180 and β4 integrin, and ERBIN (Erb-B2 tyrosine kinase receptor) Completely intracellular Associated Disease Bullous pemphigoid Paraneoplastic pemhigus INNER PLAQUE Other Components Plectin: 500 kDa Is an IFAP in the Plakin family Works with BPAG1 (230) to attach cytoskeleton to inner plaque Also attaches to β4 integrin, BPAG2 to connect to outer plaque (also to actin) Associated Disease EBS with muscular dystrophy OUTER PLAQUE Transmembrane proteins link to inner plaque and extend to the lamina lucida. Components BP Ag 2 (180kDa) aka type XVII collagen: Transmembrane prot. with extracellular C- terminus Links lamina densa to anchoring filaments (BP230 and α6β4 integrin) Associated diseases BP, Pemphigoid Gestationis, CP, GABEB BPAG2 (180 kDa) BP, PG, CP, LABD, GABEB Auto-Abs target NC16A in: BP, PG, and LABD In CP, target is most distal carboxy terminus Thought to increase likelihood of scar OUTER PLAQUE α6β4-Integrin All integrins are heterodimeric transmembrane proteins, most bind actin unlike α6β4-Integrin Links cytoskeleton with laminin 5&1 in lamina lucida. β4 subunit interacts with BP230 and plectin in the inner plaque. C-Terminus binds to BP180 Associated Disease JEB-PA Ocular CP (β4) LAMINA LUCIDA Contains the Anchoring Filaments Major Components Laminin 5 (epiligrin) Uncein LAD-1 Laminin 6-7-10 (3 above are more important) LAMINA LUCIDA Laminin 5 Heterodimer α3β3γ2 Links α6β4-Integrin to lamina densa and type VII collagen. Binds NC1 region of type VII collagen Associated diseases Cicatricial Pemphigoid (antiepiligrin CP): IgG to α3 portion Herlitz-JEB: Point mutation causes stop codon in laminin 5, all subunits have been involved. LAMINA LUCIDA Uncein Related to Laminin 5, with a similar function. Associated Diseases Recessive-JEB Cicatricial Pemphigoid (EBA Like) LAMINA LUCIDA LAD-1 (ladinin; LAD97):