Smek1 deficiency exacerbates experimental autoimmune encephalomyelitis by activating proinflammatory microglia and suppressing the IDO1-AhR pathway

Ruo-Nan Duan,Wen-Jie Sun,Jiang-Xia Li,Chuan-Zhu Yan,Tong Du,Qi-Ji Liu,Xi Li,Ai Liu,An-Ran Wang,Chun-Lin Yang

doi:10.1186/s12974-021-02193-0

Abstract

BackgroundExperimental autoimmune encephalomyelitis (EAE) is an animal disease model of multiple sclerosis (MS) that involves the immune system and central nervous system (CNS). However, it is unclear how genetic predispositions promote neuroinflammation in MS and EAE. Here, we investigated how partial loss-of-function of suppressor of MEK1 (SMEK1), a regulatory subunit of protein phosphatase 4, facilitates the onset of MS and EAE.MethodsC57BL/6 mice were immunized with myelin oligodendrocyte glycoprotein 35-55 (MOG35-55) to establish the EAE model. Clinical signs were recorded and pathogenesis was investigated after immunization. CNS tissues were analyzed by immunostaining, quantitative polymerase chain reaction (qPCR), western blot analysis, and enzyme-linked immunosorbent assay (ELISA). Single-cell analysis was carried out in the cortices and hippocampus. Splenic and lymph node cells were evaluated with flow cytometry, qPCR, and western blot analysis.ResultsHere, we showed that partial Smek1 deficiency caused more severe symptoms in the EAE model than in controls by activating myeloid cells and that Smek1 was required for maintaining immunosuppressive function by modulating the indoleamine 2,3-dioxygenase (IDO1)-aryl hydrocarbon receptor (AhR) pathway. Single-cell sequencing and an in vitro study showed that Smek1-deficient microglia and macrophages were preactivated at steady state. After MOG35-55 immunization, microglia and macrophages underwent hyperactivation and produced increased IL-1β in Smek1-/+ mice at the peak stage. Moreover, dysfunction of the IDO1-AhR pathway resulted from the reduction of interferon γ (IFN-γ), enhanced antigen presentation ability, and inhibition of anti-inflammatory processes in Smek1-/+ EAE mice.ConclusionsThe present study suggests a protective role of Smek1 in autoimmune demyelination pathogenesis via immune suppression and inflammation regulation in both the immune system and the central nervous system. Our findings provide an instructive basis for the roles of Smek1 in EAE and broaden the understanding of the genetic factors involved in the pathogenesis of autoimmune demyelination.

Highlights

Protein phosphatase 4 (PP4), a highly conserved serine/ threonine phosphatase, is a protein complex composed of catalytic subunits and regulatory subunits
Our findings provide an instructive basis for the roles of Suppressor of MEK1 (Smek1) in EAE and broaden the understanding of the genetic factors involved in the pathogenesis of autoimmune demyelination
We identified a novel cluster of proinflammatory colony-stimulating factor 1positive (Csf1+) microglia that highly express interleukin 1β (IL-1β) and chemokines in Smek1-/- mice

Summary

Introduction

Protein phosphatase 4 (PP4), a highly conserved serine/ threonine phosphatase, is a protein complex composed of catalytic subunits and regulatory subunits. Suppressor of MEK1 (SMEK1), a regulatory subunit of the PP4 enzyme, regulates the activity of the PP4 catalytic subunits, leading to dephosphorylation of its target substrates via an unknown mechanism. Recent findings suggest that PP4 is an essential modulator of T cell proliferation and immune responses by dephosphorylating adenosine monophosphate activated protein kinase (AMPK) [2]. Experimental autoimmune encephalomyelitis (EAE) is an animal disease model of multiple sclerosis (MS) that involves the immune system and central nervous system (CNS). It is unclear how genetic predispositions promote neuroinflammation in MS and EAE. We investigated how partial loss-of-function of suppressor of MEK1 (SMEK1), a regulatory subunit of protein phosphatase 4, facilitates the onset of MS and EAE

Methods

Results

Discussion

Conclusion