Cell models of lipid-rich α-synuclein aggregation validate known modifiers of α-synuclein biology and identify stearoyl-CoA desaturase.

Microscopy of Lewy bodies in Parkinson's disease (PD) suggests they are not solely filamentous deposits of α-synuclein (αS) but also contain vesicles and other membranous material. We previously reported the existence of native αS tetramers/multimers and described engineered mutations of the αS KTKEGV repeat motifs that abrogate the multimers. The resultant excess monomers accumulate in lipid membrane-rich inclusions associated with neurotoxicity exceeding that of natural familial PD mutants, such as E46K. Here, we use the αS "3K" (E35K+E46K+E61K) engineered mutation to probe the mechanisms of reported small-molecule modifiers of αS biochemistry and then identify compounds via a medium-throughput automated screen. αS 3K, which forms round, vesicle-rich inclusions in cultured neurons and causes a PD-like, l-DOPA-responsive motor phenotype in transgenic mice, was fused to YFP, and fluorescent inclusions were quantified. Live-cell microscopy revealed the highly dynamic nature of the αS inclusions: for example, their rapid clearance by certain known modulators of αS toxicity, including tacrolimus (FK506), isradipine, nilotinib, nortriptyline, and trifluoperazine. Our automated 3K cellular screen identified inhibitors of stearoyl-CoA desaturase (SCD) that robustly prevent the αS inclusions, reduce αS 3K neurotoxicity, and prevent abnormal phosphorylation and insolubility of αS E46K. SCD inhibition restores the E46K αS multimer:monomer ratio in human neurons, and it actually increases this ratio for overexpressed wild-type αS. In accord, conditioning 3K cells in saturated fatty acids rescued, whereas unsaturated fatty acids worsened, the αS phenotypes. Our cellular screen allows probing the mechanisms of synucleinopathy and refining drug candidates, including SCD inhibitors and other lipid modulators.

Nortriptyline inhibits aggregation and neurotoxicity of alpha-synuclein by enhancing reconfiguration of the monomeric form.

The pathology of Parkinson's disease and other synucleinopathies is characterized by the formation of intracellular inclusions comprised primarily of misfolded, fibrillar α-synuclein (α-syn). One strategy to slow disease progression is to prevent the misfolding and aggregation of its native monomeric form. Here we present findings that support the contention that the tricyclic antidepressant compound nortriptyline (NOR) has disease-modifying potential for synucleinopathies. Findings from in vitro aggregation and kinetics assays support the view that NOR inhibits aggregation of α-syn by directly binding to the soluble, monomeric form, and by enhancing reconfiguration of the monomer, inhibits formation of toxic conformations of the protein. We go on to demonstrate that NOR inhibits the accumulation, aggregation and neurotoxicity of α-syn in multiple cell and animal models. These findings suggest that NOR, a compound with established safety and efficacy for treatment of depression, may slow progression of α-syn pathology by directly binding to soluble, native, α-syn, thereby inhibiting pathological aggregation and preserving its normal functions.