Molecular Signatures of Neuroinflammation Induced by αSynuclein Aggregates in Microglial Cells.

Souvarish Sarkar,Emir Malovic,Syed Ali Raza,Srikant Rangaraju,Valerie Joers,Duc Duong,Malú G Tansey,Nicholas Seyfried,Thomas Kukar,Anumantha G Kanthasamy,Abby L Olsen,Tianwen Gao,Hailian Xiao,Eric B Dammer,Danielle L Oliver,Meixiang Huang

doi:10.3389/fimmu.2020.00033

Abstract

Alpha-synuclein (αSynAgg) are pathological hallmarks of Parkinson's disease (PD) and other synucleinopathies that induce microglial activation and immune-mediated neurotoxicity, but the molecular mechanisms of αSynAgg-induced immune activation are poorly defined. We performed quantitative proteomics by mass spectrometry coupled with PCR, immunohistochemical and functional validations studies to define the molecular characteristics of alpha synuclein mediated microglial activation. In mouse microglia, αSynAgg induced robust pro-inflammatory activation (increased expression of 864 genes including Irg1, Ifit1, and Pyhin) and increased nuclear proteins involved in RNA synthesis, splicing, and anti-viral defense mechanisms. Conversely, αSynAgg decreased expression several proteins (including Cdc123, Sod1, and Grn), which were predominantly cytosolic and involved in metabolic, proteasomal and lysosomal mechanisms. Pathway analyses and confirmatory in vitro studies suggested that αSynAgg partly mediates its effects via Stat3 activation. As predicted by our proteomic findings, we verified that αSynAgg induces mitochondrial dysfunction in microglia. Twenty-six proteins differentially expressed by αSynAgg were also identified as PD risk genes in genome-wide association studies (upregulated: Brd2, Clk1, Siglec1; down-regulated: Memo1, Arhgap18, Fyn, and Pgrn/Grn). We validated progranulin (PGRN) as a lysosomal PD-associated protein that is downregulated by αSynAgg in microglia in-vivo and is expressed by microglia in post-mortem PD brain, congruent with our in vitro findings.Conclusion: Together, proteomics approach both reveals novel molecular insights into αSyn-mediated neuroinflammation in PD and other synucleinopathies.

Highlights

Chronic and sustained microglial activation is a key pathophysiological hallmark of multiple neurodegenerative disorders including Parkinson’s disease (PD) [1]
Among the microglial proteins differentially regulated by αSyn forms aggregates (αSynAgg), we identified novel immune roles for PD-risk genes including progranulin (Grn) which appears to be downregulated in microglia in response to αSynAgg
We have previously shown that Mouse microglial cell (MMC) at basal level is in a relatively resting/quiescent state which becomes activated by LPS or αSynAgg treatment to an M1-like state, similar to that seen in primary microglia

Summary

Introduction

Chronic and sustained microglial activation is a key pathophysiological hallmark of multiple neurodegenerative disorders including Parkinson’s disease (PD) [1]. Neuroinflammation has been shown to be a key contributor to loss of dopaminergic neurons in animal models of PD [2, 3] and is observed in striatal and cortical regions of the brain in post-mortem PD studies [4,5,6,7,8]. Various pro-inflammatory factors like tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) have been shown to be upregulated in cerebrospinal fluid (CSF) and in different regions of the brain in PD patients [9]. In animal models of PD, such as the 6-hydroxydopamine (6OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and rotenone models, selective loss of dopaminergic neurons is accompanied by chronic neuroinflammation [10,11,12,13]. Treatment with non-steroidal anti-inflammatory drugs (NSAIDs), like ibuprofen, may be effective against PDrelated inflammation [16] suggesting that neuroinflammation may modify the course of neurodegeneration in PD

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Results

Conclusion