Picomolar concentrations of oligomeric alpha-synuclein sensitizes TLR4 to play an initiating role in Parkinson's disease pathogenesis.

Abstract

Despite the wealth of genomic and transcriptomic data in Parkinson’s disease (PD), the initial molecular events are unknown. Using LD score regression analysis we show significant enrichment in PD heritability within regulatory sites for LPS-activated mono-cytes and that TLR4 expression is highest within human substantia nigra, the most af-fected brain region, suggesting a role for TLR4 inflammatory responses. We then per-formed extended incubation of cells with physiological concentrations of small alpha synuclein oligomers observing the development of a TLR4-dependent sensitized in-flammatory response with time, including TNF-α production. ROS and cell death in primary neuronal cultures were significantly reduced by TLR4 antagonists revealing that an indirect inflammatory mechanism involving cytokines produced by glial cells makes a major contribution to neuronal death. Prolonged exposure to low levels of al-pha synuclein oligomers sensitizes TLR4 responsiveness in astrocytes and microglial, explaining how they become pro-inflammatory, and may be an early causative event in PD.