Tetramethylpyrazine promotes spinal cord injury repair by modulating macrophage M1/M2 polarization via inhibition of the IL-6/JAK2/STAT3 pathway.

Spinal cord injury (SCI) induces a detrimental secondary inflammatory cascade driven largely by pro-inflammatory M1 macrophages, which impedes neural repair. Tetramethylpyrazine (TMP), a bioactive alkaloid from Ligusticum chuanxiong, has shown promise in modulating neuroinflammation. In this study, Sprague-Dawley rats subjected to thoracic contusion SCI received daily intraperitoneal TMP at 60 mg/kg or 80 mg/kg for 7 days. TMP treatment significantly improved hindlimb motor function, as evidenced by higher Basso-Beattie-Bresnahan (BBB) locomotor scores from day 7 through day 28 post-injury and increased motor evoked potential (MEP) amplitudes at day 28, confirming enhanced motor pathway conduction. Histological analyses (HE and Nissl staining) revealed reductions in lesion cavitation, preservation of neuronal architecture, and attenuated glial scar formation in TMP-treated groups. Immunofluorescence demonstrated increased NeuN, MAP2, and NF200 and decreased GFAP expression, while double staining for iNOS/CCR2 and Arg1/CCR2 indicated a shift from M1 to M2 macrophage polarization. ELISA showed significant reductions in IL-6 and TNF-α and elevation of IL-10, and both WB and RT-qPCR confirmed TMP-mediated suppression of IL-6/JAK2/STAT3 phosphorylation and gene transcription. In vitro, TMP reversed LPS-induced M1/M2 polarization imbalance in RAW 264.7 cells, meanwhile suppressing IL-6/JAK2/STAT3 phosphorylation and gene transcription, reduced pro-inflammatory cytokine release in TMP groups. Furthermore, rescue experiments demonstrated that co-treatment with recombinant IL-6 reversed TMP-mediated suppression of JAK2/STAT3 phosphorylation and M1-to-M2 polarization shift, confirming the IL-6/JAK2/STAT3 pathway as a direct mechanistic target of TMP. These results indicate that TMP fosters histopathological and functional recovery after SCI by reshaping macrophage polarization via inhibition of the IL-6/JAK2/STAT3 pathway, highlighting its potential as an anti-inflammatory neuroprotective therapy.