| Summary: | 碩士 === 國立清華大學 === 分子醫學研究所 === 105 === Abnormal aggregates resulting from mutations in the intermediate filament (IF) proteins are pathological hallmarks of a wide range of neurodegenerative diseases. This is exemplified by Alexander disease (AxD), a primary genetic disorder of astrocytes caused by dominant mutations in the gene encoding the glial filament protein GFAP. This disease is characterized by excessive accumulation of GFAP in an aggregated form known as Rosenthal fibers within astrocyte cell bodies and processes. Abnormal GFAP aggregation also occurs in other pathological conditions, such as giant axon neuropathy (GAN). GAN is caused by recessive mutations in the gene encoding gigaxonin, which is predicted to be an E3 ligase adaptor. Although GAN represents the only disease that causes a generalized disorganization of IFs in a range of cell types, the molecular mechanisms by which mutations in gigaxonin affect the IF cytoskeletal system are unknown. Recent studies have demonstrated that the main function of gigaxonin is to target IF proteins for degradation through the proteasomal pathway. We therefore sought to determine whether gigaxonin is involved in degradation of GFAP. Using a lentiviral transduction system, we demonstrated that gigaxonin levels influence the degradation of GFAP IFs in primary rat astrocytes and in SW13 cell lines stably expressing this IF protein. Gigaxonin was similarly involved in the degradation of some but not all AxD-associated GFAP mutants. Gigaxonin directly binds to GFAP, and proteasomal inhibition by MG-132 reversed the clearance of GFAP in cells achieved by overexpressing gigaxonin. Together, these findings identified gigaxonin as an important factor that targets the glial-specific IF protein GFAP for degradation through the proteasome pathway. Our studies provide a critical foundation for future studies with a goal towards reducing or reversing pathological accumulation of GFAP as a potential therapeutic strategy for AxD and other related diseases characterized by IF aggregation.
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