Differential microglial responses to structurally distinct alpha-synuclein polymorphs

Synucleinopathies are age-related neurological disorders which include dementia with Lewy bodies (DLB), Parkinson’s disease (PD), and multiple system atrophy (MSA). The diseases are characterized by the abnormal deposition and aggregation of a-synuclein and neuroinflammation. Recent studies have demonstrated the existence of structurally distinct a-synuclein aggregates in this group of the diseases. While the correlation between specific forms of a-synuclein and distinct pathological characteristics has been extensively studied, their relationship to neuroinflammation remains elusive. Here, we examined the effects of structurally distinct a-synuclein polymorphs on microglial neuroinflammation. Human induced pluripotent stem cells (iPSCs)-derived microglia (iMicroglia) were treated with a-synuclein polymorphs including EGCG stabilized a-synuclein oligomers (EO), kinetically stable a-synuclein oligomers (KSO), dopamine stabilized a-synuclein oligomers (DO), a-synuclein preformed fibrils (PFF), sonicated a-synuclein preformed fibrils (sPFF), and matured a-synuclein fibrils (Fib). Microglial gene expressions were accessed by transcriptome analysis and Toll-like receptor agonist activities were determined by HEK-Blue TLR reporter assay. Exposures to kinetically stable a-synuclein oligomers and matured a-synuclein fibrils induced the expression of microglial cytokines and chemokines, while other species did not. Microglial transcriptome analysis yielded that all polymorphs commonly induce toll-like receptor (TLR) signaling cascade despite differential transcriptomic phenotypes. Among structurally distinct a-synuclein polymorphs, live cell TLR reporter assay showed that kinetically stable a-synuclein oligomers induce the activities of TLR2 and 4, and sonicated a-synuclein preformed fibril TLR4, relative to the control. These results suggest that structurally distinct a-synuclein polymorphs have likewise distinct neuroinflammatory properties.