miR-99b-5p Targets AKT1 to Modulate Microglial Polarization: A Prognostic Biomarker for Spinal Cord Injury

Study design: Cross-sectional study. Objectives This study aimed to investigate the mechanism by which miR-99b-5p regulates microglial polarization via targeting AKT1, and to evaluate its potential as a prognostic biomarker and therapeutic target for spinal cord injury (SCI). Setting: The study was conducted at Wuhan Hankou Hospital and Nedong District People's Hospital, China. Methods A total of 90 individuals with SCI and 70 healthy controls were enrolled. Serum levels of miR-99b-5p, inflammatory cytokines, and microglial polarization markers were quantified. Functional outcomes were assessed using the AIS, FIM, SCIM-III, and WISCI-II scales. In vitro investigations included cell transfection, LPS-induced polarization, co-culture, and dual-luciferase reporter assays. Results Serum miR-99b-5p was significantly elevated in SCI individuals (AUC = 0.872) and positively correlated with AIS grade and functional outcomes (FIM, SCIM-III, WISCI-II). The miR-99b-5p mimic selectively inhibited M1 polarization in microglia, downregulating markers such as iNOS and TNF-α, while exhibiting no significant effect on macrophages. AKT1 was identified as a direct target of miR-99b-5p, and its overexpression reversed the inhibitory effect of miR-99b-5p on microglial polarization. Furthermore, miR-99b-5p alleviated neuronal inflammation and apoptosis, as evidenced by decreased Bax and increased Bcl-2 expression, through its regulatory action on microglia. Conclusion miR-99b-5p targets AKT1 to suppress microglial M1 polarization, thereby alleviating neuroinflammation and neuronal damage in SCI. Its serum level serves as a promising prognostic biomarker and potential therapeutic target.