Objective: To investigate functional alterations of the p.V15A variant in alpha-Synuclein (α-Syn) in Parkinson’s disease (PD).

Background: PD is marked by the loss of dopaminergic neurons and the presence of Lewy bodies mainly containing aggregated α-Syn. Pathogenic variants in the SNCA gene encoding α-Syn are a rare cause of PD. To date, only a few pathogenic variants have been identified and functionally characterized. We here present a novel PD patient carrying the p.V15A variant (NM_001146055: c.44T>C) and its in-depth functional characterization.

Method: The patient underwent a detailed neurological examination and genetic testing by gene panel analysis. To elucidate the impact of p.V15A on α-Syn function and aggregation properties, we used several approaches, including stably transfected SH-SY5Y cell cultures, induced pluripotent stem cell (iPSC)-derived neuronal cultures, a fly model, and biophysical assays. We conducted Western blot analysis to assess α-Syn expression and the homeostasis of apoptosis; native dot blotting was performed to evaluate α-Syn aggregation using an aggregate-specific antibody [MJFR-14-6-4-2]. We further conducted GRP75 and LAMP-1 immunostaining to evaluate the mitochondrial network (form factor analysis) and lysosomal homeostasis, respectively. α-Syn variants were ubiquitously expressed in flies and behavior was evaluated.

Results: The 50-year-old patient had PD onset of 41 years and rapid progression. At 42 years, he presented with early cognitive decline and hallucinations. His mother also had PD (onset 50 years, passed away 7 years later). While the p.V15A variant affects the conformational properties of the protein triggering a weakening of the binding to liposomes, mutant protofibrils increasingly aggregate in the presence of liposomes. Further, activation of apoptosis was increased, mitochondrial branching decreased, and lysosomal homeostasis impaired in mutant SH-SY5Y cells compared to controls. Native dot blotting revealed increased α-Syn aggregation in mutant iPSC-derived dopaminergic neurons. Moreover, p.V15A decreases the flying ability and survival of mutant flies.

Conclusion: Using a multimodal approach, we demonstrate that the p.V15A mutation has molecular effects comparable to those of well-established pathogenic variants and thus can be considered as pathogenic, too.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/characterization-of-the-pathogenic-%ce%b1-synuclein-variant-p-v15a-in-parkinsons-disease/