Date of Award

1-1-2018

Document Type

Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Keith A. Choate

Abstract

Connexins are gap junction proteins that assemble between adjacent cells, directly linking their cytoplasm and permitting the passage of ions and other small molecules between them. Previously, mutations in GJB3, GJB4, and GJA1, encoding connexins 31, 30.3, and 43 respectively, have been reported to cause erythrokeratodermia variabilis et progressiva (EKVP). EKVP is a rare, inherited skin disease whose symptoms include transient figurate erythema, localized or generalized scaling, and palmoplantar keratoderma. EKVP presents at birth or in early infancy and is induced by stress, friction, or warm conditions. Our lab has previously identified two de novo mutations in GJA1, p.E227D and p.A44V in three patients with EKVP, who did not exhibit mutations in either GJB3 or GJB4. Tissue sections and transiently transfected HeLa cells were shown to mislocalize mutant connexin protein to the cytoplasm instead of the cell membrane, with partial retention of mutant protein in the cis-Golgi. Mutations in GJB2, encoding for connexin 26, have been shown to cause keratitis-ichthyosis-deafness syndrome via increased hemichannel activity, suggesting that altered electrophysiology plays a role in connexin mutations causing skin disease. To evaluate hemichannel activity in our GJA1 mutations causing EKVP, we performed two-electrode voltage-clamp of Xenopus oocytes injected with wild-type and mutant GJA1 cRNA. We found the mutants to dramatically increase oocyte membrane currents relative to wild-type and uninjected controls. The p.A44V mutants increased hemichannel activity ninefold whereas the p.E227D mutants increased hemichannel activity sixfold when compared to wild-type injected controls. These findings further support the hypothesis that altered electrophysiology plays a role in the development of cutaneous disease in patients expressing connexin mutations.

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