Mutant Cx43 in Skin Differentiation and Disease

Connexin43 (Cx43) is expressed within keratinocytes, dermal fibroblasts, and the hair follicle epithelium. Since Cx43 is so widely expressed in resident cells of the skin, we speculated that this connexin would play an essential role in skin homeostasis, hair growth and wound healing. Mutations in the gene which encodes Cx43 lead to a disease called oculodentodigital dysplasia (ODDD) and patients expressing the frame-shift mutants (fs230 or fs260) develop a skin disease called palmar plantar hyperkeratosis. In addition, patients with ODDD often develop hair which is dry, sparse, and slow growing. To study skin abnormalities associated with ODDD, hair growth and wound healing assays were performed on a mouse model of ODDD (G60S mice). Cutaneous wounds performed on the G60S mice healed slower than wounds performed on wild-type (WT) littermate mice suggesting that fibroblasts and/or keratinocytes expressing mutant Cx43 may be impaired in their ability to heal wounds. Fibroblasts derived from G60S mice and from two ODDD patients expressing the D3N and V216L Cx43 mutant revealed defects in the ability of fibroblasts to proliferate, migrate, and differentiate into myofibroblasts while keratinocytes derived from the G60S mouse demonstrated an enhancement in cell proliferation but no change in migration. To investigate the ability of keratinocytes expressing mutant Cx43 to differentiate, organotypic epidermal cultures were engineered to express full-length Cx43 or various ODDD mutants (G21R, G138R, G60S, fs230 and fs260). In comparison to full-length Cx43, organotypic epidermal cultures expressing the fs260 mutant significantly lowered the levels of endogenous Cx43, levels of Cx26, and developed nuclei within the stratum corneum. Hair regrowth was also found to be delayed in the G60S mice and this delay was attributed to a reduction in the mitotic activity of hair follicle cells. In addition, hair fibers from G60S mice were thinner, shorter, displayed cuticle degradation in the distal region and nodule formation in the proximal hair fiber region when compared to WT derived hair fibers. Collectively, our results suggest the mutant Cx43 impairs the function of fibroblasts during wound healing and a reduced proliferation of the hair follicle epithelium likely leads to defects in hair growth observed in ODDD patients