Cellular events in heritable peripheral neuropathies

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DESCRIPTION (provided by applicant): Heritable-demyelinating neuropathies with an estimated incidence of 1:2,500 in the general population, including Charcot-Marie-Tooth disease type 1A (CMT1A), account for a significant portion of peripheral nerve disorders leading to muscle atrophy and functional impairment. Advances in human genetics have led to the identification of specific gene defects associated with a large fraction of inherited neuropathies, however the cellular athogenesis elicited by the genetic alterations is not well understood. In the majority of CMT1A patients the peripheral myelin protein 22 (PMP22) gene on chromosome 17 is duplicated, while in a smaller but significant fraction, single point mutations in PMP22 have been identified. Morphological studies of CMT1A nerve biopsies revealed abnormal intracellular accumulation of PMP22 in the Schwann cell cytoplasm and in the endoneurial tissue. Cell culture studies show changes in the intracellular trafficking of mutant PMP22s, and intracellular retention of the overproduced wild-type protein in newly defined cytoplasmic inclusions, termed aggresomes. How altered intracellular trafficking of the mutant or overproduced PMP22 triggers the cascade of events leading to nerve pathology is not known. The hypothesis of this research application is that the changes in intracellular glial protein trafficking alter the biochemical integrity of the Schwann cell membrane, thus have a direct role in initiating the pathogenesis of the neuropathies. The aim of the project is to understand the mechanisms underlying the changes in PMP22 localization in CMT1A Schwann cells and to identify potential targets for therapeutic interventions. Experiments will be performed at the subcellular level in myelinating cocultures of neuropathy Schwann cells and peripheral neurons, as well as in ex vivo neuropathy nerve preparations. The turnover rate and the subcellular trafficking of PMP22 and other myelin proteins, including protein zero, will be determined biochemically and morphologically, with and without the use of pharmacological agents known to affect specific steps in protein processing. Particular emphasis will be placed on evaluating the involvement of the ubiquitin-proteasome, protein degradative, pathway in the regulation of PMP22 protein turnover. In depth understanding of the cellular mechanisms of pathogenesis in peripheral neuropathies is essential for the future design of effective pharrnacological therapies.