miR-665 Ameliorates Neuroinflammation After Intracerebral Hemorrhage by Modulating Myeloid Cell Polarization via Targeting STAT3

Background Microglia-mediated neuroinflammation contributes to secondary injury after intracerebral hemorrhage (ICH), but the role of miR-665 remains unclear.Methods An ICH rat model was established. A combination of techniques, including Neurological scoring, brain water content measurement, histology and molecular assays were employed to assess miR-665, the STAT3/NF-κB pathway, myeloid polarization and inflammation. Stereotaxic miR-665 agomir/antagomir delivery verified its function. The targeting relationship between miR-665 and STAT3 was confirmed by a dual-luciferase reporter assay. In vitro experiments were performed in Hemin-stimulated BV2 cells with miR-665 mimics/inhibitor, followed by flow cytometry detection of cell polarization and inflammatory factor analysis. Rescue experiments with STAT3 overexpression were conducted both in vivo and in vitro.Results After ICH, miR-665 was downregulated andinduced excessive activation of the STAT3/NF-κB signaling axis in peri-hematomal tissue, accompanied by M1-like/pro-inflammatory myeloid cell polarization and elevated pro-inflammatory cytokines. Upregulation of miR-665 ameliorated neurological function, reduced brain edema, promoted M2-like/repair-associated polarization, and suppressed inflammation, whereas miR-665 downregulation aggravated injury. Dual-luciferase assay confirmed that miR-665 directly targets STAT3. In vitro, miR-665 overexpression inhibited STAT3 phosphorylation and further suppressed the downstream NF-κB signaling, reversing the Hemin-induced M1-like/pro-inflammatory polarization. STAT3 overexpression counteracted the protective effects of miR-665.Conclusion Downregulated miR-665 after ICH exacerbates neuroinflammation by promoting M1-like/pro-inflammatory myeloid cell polarization via disinhibition of STAT3 and subsequent activation of NF-κB signaling. Upregulating miR-665 exerts neuroprotection by inhibiting STAT3 phosphorylation and facilitating M2-like/repair-associated myeloid cell polarization, highlighting the miR-665/STAT3 regulatory cascade as a promising therapeutic target for post-ICH neuroinflammation.