Elevated microglial oxidative phosphorylation and phagocytosis stimulate post-stroke brain remodeling and cognitive function recovery in mice

Shanshan Song,Cullen B Young,Mara L G Sullivan,Victoria M Fiesler,Steven J Mullett,Dandan Sun,Md Nabiul Hasan,Donna B Stolz,Satya S Paruchuri,Lauren Yu,Stacy G Wendell

doi:10.1038/s42003-021-02984-4

Abstract

New research shows that disease-associated microglia in neurodegenerative brains present features of elevated phagocytosis, lysosomal functions, and lipid metabolism, which benefit brain repair. The underlying mechanisms remain poorly understood. Intracellular pH (pHi) is important for regulating aerobic glycolysis in microglia, where Na/H exchanger (NHE1) is a key pH regulator by extruding H+ in exchange of Na+ influx. We report here that post-stroke Cx3cr1-CreER+/−;Nhe1flox/flox (Nhe1 cKO) brains displayed stimulation of microglial transcriptomes of rate-limiting enzyme genes for glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation. The other upregulated genes included genes for phagocytosis and LXR/RXR pathway activation as well as the disease-associated microglia hallmark genes (Apoe, Trem2, Spp1). The cKO microglia exhibited increased oxidative phosphorylation capacity, and higher phagocytic activity, which likely played a role in enhanced synaptic stripping and remodeling, oligodendrogenesis, and remyelination. This study reveals that genetic blockade of microglial NHE1 stimulated oxidative phosphorylation immunometabolism, and boosted phagocytosis function which is associated with tissue remodeling and post-stroke cognitive function recovery.

Highlights

New research shows that disease-associated microglia in neurodegenerative brains present features of elevated phagocytosis, lysosomal functions, and lipid metabolism, which benefit brain repair
We report here that the Nhe[1] cKO microglia displayed a stimulated spectrum of energy metabolism, featured with elevated transcriptomes for key rate-limiting enzymes involved in oxidative phosphorylation, as well as the tricarboxylic acid (TCA) cycle and glycolysis
We observed that the post-stroke cKO microglia exhibited increased transcriptome profiles for all processes in phagocytosis, and stimulated liver X receptor-retinoid X receptor (LXR/RXR) pathway activation, a regulatory pathway that stimulates phagocytosis and promote anti-inflammatory responses in microglial cells[19]

Summary

Introduction

New research shows that disease-associated microglia in neurodegenerative brains present features of elevated phagocytosis, lysosomal functions, and lipid metabolism, which benefit brain repair. We report here that post-stroke Cx3cr1-CreER+/−;Nhe1flox/flox (Nhe[1] cKO) brains displayed stimulation of microglial transcriptomes of rate-limiting enzyme genes for glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation. This study reveals that genetic blockade of microglial NHE1 stimulated oxidative phosphorylation immunometabolism, and boosted phagocytosis function which is associated with tissue remodeling and post-stroke cognitive function recovery. The underlying mechanisms of how microglia regulate their energy metabolism to support phagocytic functions remain poorly understood. NHE1-mediated H+ extrusion activity alkalinizes microglial pHi and promotes NADPH oxidase (NOX) function upon lipopolysaccharides (LPS) stimulation[16], or in mouse brains upon NMDA injection or after ischemic stroke[17]. Our recent study of selective deletion of microglial Nhe[1] in the Cx3cr1-CreER+/−;Nhe1flox/flox (cKO) mice demonstrated that loss of microglial NHE1 protein reduced proinflammatory microglial activation in ischemic brains and improved post-stroke motor-sensory functions[18]. To investigate the underlying mechanisms, we conducted transcriptomic analysis of post-stroke wild-type (WT) and Nhe[1]

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Results

Conclusion