Edaravone Plays Protective Effects on LPS-Induced Microglia by Switching M1/M2 Phenotypes and Regulating NLRP3 Inflammasome Activation

Jiping Li,Xinxiu Li,Liuyi Zhou,Xinping Dai,Dongxiao Pan

doi:10.3389/fphar.2021.691773

Abstract

Parkinson’s disease is a neurodegenerative disorder in which activated microglia may appear prior to motor symptoms, but the specific therapeutic mechanisms remain unclear. This study investigated the potential effects of Edaravone (EDA) on M1/M2 polarization of microglia in rats with dopaminergic neurons damage induced by lipopolysaccharide (LPS) and its mechanism. Rats were randomly grouped as the following (n = 10): Control, EDA alone (10 mg/kg), LPS-model (LPS 5 μg), LPS + EDA (5 mg/kg) and LPS + EDA (10 mg/kg). After intragastric administration of EDA once a day for seven consecutive days, LPS was injected into SN pars unilaterally. Rotarod test, pole test, and traction test were used to analyze the intervention effect of EDA on neurobehavioral function in rats. Protein expression levels of TH, TNF-α, Arg-1, Iba-1, NLRP3 and caspase-1 were measured by immunofluorescence staining and western blot. In vitro, BV-2 cells were treated with LPS (100 ng/ml) before adding different doses of EDA. Levels of inflammatory cytokines in culture medium were detected by ELISA. Western blot and immunofluorescence were used to evaluate microglial activation and polarization. First, rotarod test, pole test, and traction test all showed that EDA mitigated motor dysfunction of PD rats. Second, pathological analysis suggested that EDA inhibited LPS-induced microglial activation and remitted declines of dopaminergic neurons. In addition, EDA shifted M1 pro-inflammatory phenotype of microglia to M2 anti-inflammatory state, while decreased expression of M1 markers (TNF-α and IL-1β) and facilitated expression of M2 markers (Arg-1 and IL-10). EDA suppressed inflammatory responses through inhibiting the expression of pro-inflammatory factors (IL-1β, IL-18 and NO), but the neuroprotective effects were invalid while siRNA NLRP3 existed. In conclusion, these results indicated that EDA could improve neurobehavioral functions and play anti-neuroinflammatory roles in PD rats, possibly by inhibiting NLPR3 inflammasome activation and regulating microglia M1/M2 polarization.

Highlights

Parkinson’s disease (PD) is an age-related neurodegenerative disease around the world, whose pathogenesis is still unclear (Zou et al, 2015)
In order to verify the degree of motor dysfunction in LPSinduced DA neuron damage, a significant clinical symptoms of PD patients, the behavior of rats was analyzed by rotarod test, pole test and traction test after intragastric administration of EDA for 7 days
EDA can inhibit the M1-type polarization of microglia caused by NLRP3 activation, and further inhibit the inflammatory response involved by microglia

Summary

Introduction

Parkinson’s disease (PD) is an age-related neurodegenerative disease around the world, whose pathogenesis is still unclear (Zou et al, 2015). Classical pathological feature is the progressive loss of dopaminergic (DAergic) neurons within the nigrostriatal tract, related to decreased dopamine content in the striatum, which exacerbates motor function damage of patients. According to the clinical and etiological overlaps between PD and inflammation, recent preclinical researches have indicated that there are strong correlations between activated microglia and the progression of PD symptoms. Activated microglia are usually divided into two polarization states, termed “M1” (pro-inflammatory) phenotype and “M2” (anti-inflammatory) phenotype. In patients with neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease, the proportion of M1-polarized microglia increased. M1-phenotype microglia are considered to have pro-inflammatory activity by increasing production of inflammatory cytokines, such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), leading to tissue damage. M2-phenotype microglia exert a neuroprotective effect by upregulating anti-inflammatory mediators and suppressing the pro-inflammatory response. Activated microglia can coexist as single or mixed phenotype, which reflects the complexity of microglia function and the dynamic changes of the environment in vivo (Sica and Mantovani, 2012)

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