Heterogeneity of Microglia in Ischemic Stroke from the Perspective of Single-Cell RNA Sequencing: Subset Characteristics, Mechanisms and Therapeutic Potential

Ischemic stroke (IS), a predominant cerebrovascular disorder contributing to global disability and mortality, characterizes by a complex, multi-tiered cascade of pathological processes. As the primary innate immune cells within the central nervous system (CNS), microglia exhibit dual functional characteristics following ischemic injury, switching dynamically between pro-inflammatory detrimental phenotypes and anti-inflammatory reparative phenotypes in response to temporal progression, cellular phenotypic transformation, and changes in the local microenvironment. Consequently, therapeutic strategies targeting microglia have garnered considerable research interest, challenging the traditional neuron-centric therapeutic approaches. Microglia display a wide range of phenotypes, and the traditional M1/M2 classification is overly simplistic, failing to capture the full spectrum of their functional diversity. In contrast, single-cell RNA sequencing (scRNA-seq) technology has surpassed the limitations of bulk sequencing, providing a robust tool for elucidating microglial heterogeneity. Recent studies utilizing animal models of stroke have identified several subsets distinct from the conventional M1/M2-like subsets, including but no limited to ischemic stroke-associated microglia (ISAM), <i>Prdx1</i> ⁺SAM, <i>Spp1</i> ⁺microglia and SAM-foamy. The mechanisms underlying microglial heterogeneity encompass innate programming influenced by genetic background, dynamic remodeling of epigenetic modifications, metabolic reprogramming in response to extrinsic microenvironmental stress, and intercellular interaction networks. This review systematically examines, from the perspective of scRNA-seq, the biological functions of MG, the heterogeneity observed throughout their CNS life cycle development and regional homeostasis, the characteristics and regulatory mechanisms of heterogeneous microglial subpopulations following ischemic stroke, and potential therapeutic strategies and associated challenges. The aim is to provide a reference for the development of precise therapeutic strategies for IS.