Connexins in Nerve Regeneration and Inherited Neuropathy

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DESCRIPTION (provided by applicant): A fundamental principle underlying this grant is that connexin 32 (Cx32) is required for normal function of Schwann cells. Though mutations in Cx32 cause alterations in channel function and are clearly associated with the X-Linked Charcot-Marie-Tooth Disease (CMTX), the pathogenesis of this disorder remains to be elucidated. The localization of Cx32 to the paranodes and Schmidt-Lantermann incisures of the myelinating Schwann cell has lead to the hypothesis that Cx32 forms reflexive gap junctions within noncompact myelin and provides a "short circuit" pathway between the ab- and adaxonal cytoplasm of the myelinating Schwann cell. However, data suggest that: 1) mice lacking Cx32 show reduced capacity for regeneration associated myelination; 2) Cx32 is expressed and regulated in cultures of primary Schwann cells; 3) Schwann cells expressing two different mutant forms of Cx32 have strikingly different effects on regeneration in a xenograft model and 4) Schwann cells cultured from Cx32 knockout mice show increased death. These findings lead to the hypothesis that Cx32 is required for normal function of non-myelin-associated Schwann cells, especially those that are proliferating in response to nerve injury and participating in nerve regeneration. Aim 1 will use morphometry, whole animal electrophysiology and behavioral and biochemical assessments to examine the hypothesis that loss of Cx32 is detrimental to normal regenerative Capacity. Aim 2 will use Schwann cell culture and the dual patch clamp technique to examine the hypothesis that: 1) Cx32 is functionally expressed in proliferating adult Schwann cells in primary culture; 2) its expression levels are regulated by GGF (which is thought to induce Schwann cell proliferation during Wallerian degeneration); and 3) loss of Cx32 mediated cell-cell channels leads to increased Schwann cell death. Aim 3 will use primary Schwann cells in culture and the nerve transection model to examine the hypotheses that expression of Cx32 is required to prevent apoptotic cell death and/or limit proliferation of Schwann cells. The experiments outlined in this proposal should play a key role in understanding the role of Cx32 in the Schwann cell and how mutations in Cx32 lead to inherited peripheral neuropathy.