Research in the Cellular Neurology Unit focuses on the molecular mechanisms underlying a number of neurodegenerative disorders, including Parkinson's disease, dystonia, and spastic paraplegia. These disorders, which together afflict millions of Americans, worsen insidiously over a number of years, and treatment options are limited for many of them. Our laboratory is investigating hereditary forms of these disorders, using molecular and cell biology approaches to study how mutations in disease genes ultimately result in cellular dysfunction. Over the past year, our laboratory has been concentrating on """"""""disease-related"""""""" members of the dynamin-like family of GTPases -- particularly Drp1 and atlastin. We have found that the Drp1 GTPase, which is critical for mitochondrial division, interacts with the deafness-dystonia protein DDP. In collaboration with Drs. Richard Youle (NINDS) and Morgan Sheng (HHMI, MIT), we are currently probing the role of this interaction in mitochondrial division as well as the deafness-dystonia syndrome. We have also identified an intramolecular interaction within the Drp1 protein; mutation of a single amino acid residue critical for this intramolecular interaction markedly reduces GTPase activity of the Drp1 protein. Another major project involves the characterization and functional analysis of the herediatry spastic paraplegia type 3A (SPG3A) protein, atlastin-1. We have found that atlastin-1 is an oligomeric integral membrane GTPase, most likely tetrameric, localized to the cis-Golgi cisternae and endoplasmic reticulum (ER) within neurons, particularly pyramidal cells of the cerebral cortex. Thus, atlastin-1 may be involved in ER-Golgi membrane dynamics or vesicle trafficking. Ongoing studies of atlastin-1 are focusing on how subtle changes in structure of the atlastin-1 protein resulting from disease-causing point mutations alter atlastin-1 GTPase activity, Golgi structure and dynamics, and atlastin-1 oligomerization. We have also identified several other human atlastin-like proteins (atlastin-2 and -3) and are currently analyzing their localizations and functions. In addition, we have recently begun studying the hereditary spastic paraplegia (SPG20; Troyer's syndrome) gene spartin. We have generated antibodies for localization studies, and yeast 2-hybrid screening has identified four interacting proteins. We anticipate that these studies will allow us to unravel the cellular functions of the SPG20 protein spartin, as well as the effects of patient mutations on these cellular functions. Lastly, in collaboration with Dr. Mark Cookson's laboratory (NIA), we have found that a point mutation (L166P) of the DJ-1 protein, which causes a form of autosomal recessive Parkinson's disease (PARK7), causes the protein to be degraded through the proteosome. Thus, Parkinson's disease due to this mutation may essentially be due to the loss of DJ-1 protein. We are currently investigating the functional roles of protein modification of the DJ-1 protein by sumoylation and ubiquitination, and any role that these may play in disease pathogenesis. Taken together, we expect that our studies will advance our understanding of the molecular pathogenesis of the hereditary neurological disorders discussed above. Such an understanding at the molecular and cellular levels will hopefully lead to novel treatments to prevent progression of these disorders.
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