Enhanced mTORC1 signaling and protein synthesis in pathologic -synuclein cellular and animal models of Parkinson's disease

Pathologic alpha-synuclein plays an important role in the pathogenesis of alpha-synucleinopathies such as Parkinson's disease (PD). Disruption of proteostasis is thought to be central to pathologic alpha-synuclein toxicity; however, the molecular mechanism of this deregulation is poorly understood. Complementary proteomic approaches in cellular and animal models of PD were used to identify and characterize the pathologic alpha-synuclein interactome. We report that the highest biological processes that interacted with pathologic alpha-synuclein in mice included RNA processing and translation initiation. Regulation of catabolic processes that include autophagy were also identified. Pathologic alpha-synuclein was found to bind with the tuberous sclerosis protein 2 (TSC2) and to trigger the activation of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1), which augmented mRNA translation and protein synthesis, leading to neurodegeneration. Genetic and pharmacologic inhibition of mTOR and protein synthesis rescued the dopamine neuron loss, behavioral deficits, and aberrant biochemical signaling in the alpha-synuclein preformed fibril mouse model and Drosophila transgenic models of pathologic alpha-synuclein-induced degeneration. Pathologic alpha-synuclein furthermore led to a destabilization of the TSC1-TSC2 complex, which plays an important role in mTORC1 activity. Constitutive overexpression of TSC2 rescued motor deficits and neuropathology in alpha-synuclein flies. Biochemical examination of PD postmortem brain tissues also suggested deregulated mTORC1 signaling. These findings establish a connection between mRNA translation deregulation and mTORC1 pathway activation that is induced by pathologic alpha-synuclein in cellular and animal models of PD.