Microglial TIA1-mediated stress granules promote neuroinflammation and aggravate neuron loss in mice after ischemic stroke by IGF2 signaling

<b>Rationale:</b> Microglia cells as niche homeostasis monitor with rapid responses to acute ischemic stroke (IS). T-cell intracellular antigen 1 (TIA1), a core component of stress granules (SGs), is involved in cellular stress responses such as hypoxia, but its roles and mechanisms in regulating microglial responses during IS remain unclear. <b>Methods:</b> To evaluate the function of microglial TIA1 in IS, we established a mouse model of IS by using photothrombotic method. Furthermore, conditional knockout (CKO) of <i>Tia1</i> in microglia mice (<i>Tia1</i> ^Cx3cr1-CKO mice) was generated and then <i>Tia1</i> ^Cx3cr1-CKO IS mice and their littermate controls (<i>Tia1</i> ^f/f IS mice) were used as experimental subjects. The behavioral tests, immunostaining, Laser speckle contrast imaging (LSCI), TTC staining, Nissl staining, quantitative real-time PCR (qPCR) and Western blotting were used to assess the effects of microglial <i>Tia1</i> deletion in IS progression. <i>In vitro,</i> we utilized the microglia cell line (HMC3 cells) and primary cultured microglia to establish an OGD model, and generated stable <i>TIA1</i>-knockdown or <i>TIA1</i>-overexpressing HMC3 cell lines, and employed a co-culture system of HMC3 and N2a cells to further explore the roles of microglial <i>Tia1</i> signaling in IS. Through RNA sequencing (RNA-seq) of control HMC3 cells and <i>Tia1</i>-knockdown HMC3 cells, we investigated in depth the role and molecular mechanism of TIA1-mediated insulin-like growth factor 2 (IGF2) signaling pathway in microglia during IS progression. <b>Results:</b> Microglial TIA1 was significantly upregulated in mice during the acute phase of IS. Microglial <i>Tia1</i> knockout suppressed microglial pro-inflammatory responses, enhanced anti-inflammatory responses, promoted phagocytic clearance of infarct debris, alleviated neuronal death, and improved motor deficits in post-IS mice. <i>In vitro</i>, TIA1 promoted pro-inflammatory responses to exacerbate neuronal cell death and inhibited phagocytic ability of microglia cells after OGD. Mechanistically, <i>Tia1</i> deletion in microglia impaired SG formation, reduced sequestration of <i>Igf2</i> mRNA into SGs, upregulated IGF2 expression, and IGF2 signaling enhanced anti-inflammatory responses and phagocytic capacity while suppressing pro-inflammatory activation in microglia. <b>Conclusions:</b> These findings identify a previously unrecognized function of microglial TIA1 in modulating microglia homeostasis and sustaining pro-inflammatory responses via SGs-mediated <i>Igf2</i> mRNA sequestration after IS, providing a novel therapeutic target for IS treatment.