Inhibition of Sirpα expression enhances microglial phagocytic clearance of myelin debris and reduces neuronal PANoptosis after spinal cord injury

Background: Spinal cord injury (SCI) is a devastating neurological disorder that leads to significant morbidity and mortality. Myelin debris clearance is a crucial step in the recovery process after SCI. Microglial phagocytosis plays a vital role in this process, but the underlying regulatory mechanisms are still poorly understood. This study investigates the role of signal regulatory protein alpha (Sirpα) in myelin debris clearance and neuronal survival after SCI.

Method: Gene Set Enrichment Analysis (GSEA) to analyze genes that inhibit microglial phagocytosis in the GSE196928 dataset. Using siRNA-mediated Sirpα knockdown, we observed a significant increase in phagocytic uptake of myelin debris, as quantified by flow cytometry, immunofluorescence, and Enzyme-linked immunosorbent assay. Moreover, inhibition of Sirpα expression by siRNA promotes debris clearance and reduces PANoptosis of neurons after SCI, as shown by Western Blot and immunofluorescence.

Results: Sirpα is the core gene that negatively regulates the phagocytosis of microglia after SCI. Myelin debris induces the occurrence of PANoptosis in neurons. Mechanistically, inhibition of Sirpα expression enhanced the phagocytosis of myelin debris through the activation of Spleen Tyrosine Kinase (Syk)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway. Pharmacological inhibition of PI3K or Syk reversed the pro-phagocytic effects in Sirpα-knockdown microglia. In addition, overexpression of NOD-like receptors family pyrin domain containing 12 (NLRP12) reversed the reduction of neuronal PANoptosis in co-cultured Sirpα-knockdown microglia.

Conclusions: We have demonstrated that inhibition of Sirpα expression enhances myelin debris clearance by microglia through the activation of the Syk/PI3K/Akt pathway and suppresses NLRP12-mediated PANoptosis of neurons, effectively reducing neuronal death and promoting neurological recovery after SCI. Our findings provide novel insights into the therapeutic potential of targeting Sirpα for SCI treatment.

PANoptosis; Sirpα; microglia; myelin debris; spinal cord injury.