Lipid droplets promote aberrant liquid-liquid phase separation of alpha-synuclein impairing energy homeostasis.

Alpha-synuclein (αSyn) inclusions are a defining neuropathological feature of Parkinson's disease, but the cellular events that initiate their formation and promote neurotoxicity remain incompletely understood. Aberrant liquid-liquid phase separation has emerged as a potential early step in αSyn dysregulation, yet the physiological triggers and functional consequences of this process are unclear. Here, we show that lipid droplets promote the spontaneous phase separation of wild-type and E46K mutant αSyn into condensates. These condensates sequester lipid droplets and impair their turnover, indicating disruption of cellular lipid homeostasis. Mitochondria in close proximity to αSyn condensates exhibit reduced membrane potential and increased mitophagy. Correlative light and electron microscopy further reveals αSyn oligomers associated with mitochondrial membranes displaying structural abnormalities. Together, these findings identify lipid droplets as drivers of aberrant αSyn phase separation and suggest that lipid droplet-rich condensates contribute to mitochondrial dysfunction and impaired energy homeostasis. Given the enrichment of lipid droplets within neuromelanin-containing dopaminergic neurons of the substantia nigra, this mechanism may be relevant to the selective neuronal vulnerability observed in Parkinson's disease.