Establishing mechanism-based therapeutics for Parkinson’s disease (PD), Lewy body dementia (LBD) and other synucleinopathies is a biomedical priority. Neuropathological and genetic discoveries implicate α-synuclein (αS) in familial and ‘sporadic’ PD. Recent publications identify significant lipid components with misfolded αS in Lewy bodies and Lewy neurites, transforming how we conceptualize PD pathogenesis, as lipids are central to many fundamental cellular processes and are highly abundant in the brain. αS has physiologic and pathogenic interactions with phospholipid membranes and fatty acids (FAs) and alters lipid homeostasis. Here, we propose in vitro and in vivo approaches to dissect the interplay of αS with lipid membranes. Experiments are focused on advancing PD-dysregulated LIPE (hormone sensitive lipase) as a candidate therapeutic target for PD/LBD in vivo and establishing the mechanism of rescue centered on αS:lipid membrane interactions at the synapse. We posit a dynamic relationship between normal and pathological forms of αS and FAs. Our central hypothesis is that αS dyshomeostasis results in cellular FA metabolism imbalance, altering αS:membrane interactions and disease phenotypes. This hypothesis underpins the PI’s central goal in this R01: to return the abnormal disease- associated cellular lipid/FA content to equilibrium in several compelling cellular and in vivo models of PD and LBD. This proposal has 2 distinct Aims focused on advancing monounsaturated FA therapeutic strategies, addressing mechanistic and therapeutic questions. 1. We propose a mechanistic dissection of αS:membrane interactions at the synapse, investigating disease-associated synaptic vesicle abnormalities, αS aggregation, and the role of membrane FA composition in disease phenotype rescue. 2. We propose to evaluate LIPE as a therapeutic target for reversal of motor deficits and αS neuropathology with detailed genetic, biochemical, and pharmacological analyses in multiple mouse PD/LBD/synucleinopathy models. The PI has already reported a FA target for PD, SCD inhibition, now in human PD clinical trials. Additionally, the PI has published data generated in support of this proposal in patient-derived neurons identifying LIPE (a functionally distinct, innovative target) as a candidate PD/LBD therapeutic target. These 2 distinct but complementary Aims should advance mechanistic understanding of αS:membrane interactions and progress a candidate therapeutic target (LIPE) for lipid dysfunction in PD and LBD.