Lars2 Deficiency-Induced Mitochondrial Dysfunction Drives the Emergence of a Pro-Inflammatory Stroke-Specific Microglial Subpopulation

Stroke significantly alters microglial immune status beyond the traditional M1/M2 classification. We analyzed single-cell RNA sequencing data from the striatum of hemorrhagic, ischemic, and control mice, revealing activation of mitochondrial autophagy and assembly processes after stroke. Gene Ontology functional enrichment analysis indicated that stroke-associated genes predominantly regulate mitochondrial maintenance, with leucyl-tRNA synthetase 2 (Lars2) markedly upregulated in post-stroke microglia. A distinct microglial subset (Mc) was identified with notably low Lars2 expression. In vitro, Lars2 overexpression enhanced mitochondrial function, reduced pro-inflammatory cytokine release, and suppressed Mc marker gene expression. Cell-cell communication analysis revealed Mc as the most interactive microglial subset following stroke, particularly engaging with neurons. Among neuron-Mc signaling pairs, the neurotrophic factor pleiotrophin-syndecan-4 (PTN-SDC4) ligand-receptor pair emerged as a key mediator. Conditioned media from stressed microglia upregulated neuronal Ptn expression, likely recruiting microglia, as exogenous PTN promoted microglial migration. These findings identify Mc as a stroke-induced microglial population with low Lars2 expression and pro-inflammatory features. The lack of compensatory mitochondrial repair in Mc contributes to pro-inflammatory polarization, positioning Lars2 as a mitochondrial checkpoint linking stroke-induced microglial reprogramming to neuroinflammation.