| Parkinson's disease is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. alpha-synuclein, a small protein localizing to the nucleus and the synapse, plays a central role in the pathogenesis of both rare autosomal dominant and prevalent sporadic forms of the disease. The mechanism by which alpha-synuclein induces loss of dopaminergic neurons is unknown.; In the first part of my dissertation, I examined the role of nuclear alpha-synuclein in promoting neurotoxicity. Targeting alpha-synuclein to the nucleus promoted toxicity, while cytoplasmic sequestration was protective in both neuroblastoma cells and transgenic Drosophila. Since alpha-synuclein has been shown to physically bind histones (Goers et al., 2003), we examined whether over-expression of alpha-synuclein affected histone acetylation levels. We created stable cell lines of synNLS and syn NES, and found that histone H3 was significantly hypoacetylated in stable synNLS cells, relative to untransfected cells and stably transfected synNES cells. Toxicity of alpha-synuclein was rescued by administration of histone deacetylase inhibitors in both cell culture and transgenic flies. alpha-synuclein associated with histones, reduced the level of acetylated histone H3 in cultured cells, and inhibited acetylation in histone acetyltransferase assays. These results suggest that alpha-synuclein may mediate toxicity in the nucleus by influencing histone acetylation states.; In the second part of my dissertation, I identified calmodulin as a genetic mediator of alpha-synuclein dependent toxicity. In the Drosophila brain, reducing calmodulin expression suppressed alpha-synuclein-dependent toxicity, whereas overexpressing wild-type calmodulin enhanced toxicity. Administration of calmodulin antagonists also rescued alpha-synuclein toxicity. These exciting findings potentially implicate the calmodulin signaling network in Parkinson's disease pathogenesis, and raise a number of interesting questions regarding the specific mechanisms by which calmodulin may influence alpha-synuclein neurotoxicity.; In conclusion, I have described two novel mechanisms influencing alpha-synuclein toxicity. First, I showed that alpha-synuclein acts in the nucleus to inhibit histone acetylation and promote neurotoxicity. Second, I identified calmodulin as a genetic modifier of alpha-synuclein toxicity. Taken together, this dissertation provides a major contribution to our understanding of mechanisms underlying neurotoxicity in Parkinson's disease, and carries implications for future studies investigating these mechanisms at the cellular and organismal levels. |
