14-3-3s reduce propagation and toxicity of pathologic alpha-synuclein in the in vivo preformed fibril model

Alpha-synuclein (syn) is the key component of proteinaceous aggregates termed Lewy Bodies (LBs) that pathologically define a group of disorders known as synucleinopathies, including Parkinsons Disease (PD) and Dementia with Lewy Bodies (DLB). Syn is hypothesized to misfold and spread throughout the brain in a prion-like fashion. Transmission of syn necessitates the release of misfolded syn from one cell and the uptake of that syn by another, in which it can template the misfolding of endogenous syn upon cell internalization. 14-3-3 proteins are a family of highly expressed brain proteins that are neuroprotective in multiple PD models. We have previously shown that 14-3-3{theta} acts as a chaperone to reduce syn aggregation, cell-to-cell transmission, and neurotoxicity in the in vitro pre-formed fibril (PFF) model. In this study, we expanded our studies to test the impact of 14-3-3s on syn toxicity in the in vivo syn PFF model. We used both transgenic expression models and adenovirus associated virus (AAV)-mediated expression to examine whether 14-3-3 manipulation impacts behavioral deficits, syn aggregation, and neuronal loss in the PFF model. 14-3-3{theta} transgene overexpression in cortical and amygdala regions rescued social dominance deficits induced by PFFs at 6 months post injection, whereas 14-3-3 inhibition by transgene expression of the competitive 14-3-3 peptide inhibitor difopein in the cortex and amygdala accelerated social dominance deficits. The behavioral rescue by 14-3-3{theta} overexpression was associated with delayed syn aggregation induced by PFFs in these brain regions. Conversely, 14-3-3 inhibition by difopein in the cortex and amygdala accelerated syn aggregation and cortical pyramidal neuron loss induced by PFFs. 14-3-3{theta} overexpression by AAV in the substantia nigra (SN) also delayed syn aggregation in the SN and partially rescued PFF-induced dopaminergic cell loss in the SN. 14-3-3 inhibition in the SN accelerated nigral syn aggregation and increased PFF-induced dopaminergic cell loss. These data indicate a neuroprotective role for 14-3-3{theta} against syn toxicity in vivo.