Anti-high mobility group box-1 antibody attenuated vascular smooth muscle cell phenotypic switching and vascular remodelling after subarachnoid haemorrhage in rats

Although cerebral vascular smooth muscle cell (VSMC) phenotypic switching is involved in the vascular dysfunction after subarachnoid haemorrhage (SAH), the precise mechanisms are still unclear. High mobility group box-1 (HMGB1) has been identified as a modulator in VSMC proliferation. The purpose of this study was to investigate the potential role of HMGB1 in the VSMC phenotypic switching following SAH. An endovascular perforation SAH model was used in our experiments. The expression levels of HMGB1, alpha smooth muscle actin (alpha-SMA), osteopontin (OPN), smooth muscle myosin heavy chain (SM-MHC), embryonic smooth muscle myosin heavy chain (Smemb), TXA2, PAR-1 and AT1 receptor were evaluated by Western blot analyses. Iba1-positive cells and apoptotic cells were determined by immunofluorescence staining and TUNEL staining, respectively. Vasoconstriction of the isolated basilar artery was stimulated by thrombin and KCl. We found that HMGB1 expression was markedly increased following SAH, and anti-HMGB1 mAb significantly reversed VSMC phenotypic switching and vascular remodelling in rats. However, the effects of HMGB1 on VSMC phenotypic switching were partly blocked in the presence of SC79, a potent activator of phosphatidylinositol-3-kinase-AKT (PI3K/AKT). Furthermore, the enhanced vasoconstriction and decreased cerebral cortical blood flow induced by SAH were reversed by anti-HMGB1 mAb. Finally, we found that anti-HMGB1 mAb attenuated microglial activation and brain oedema, ameliorating neurological dysfunction. These results indicated that HMGB1 is a useful regulator of VSMC phenotypic switching and vascular remodelling following SAH and might be exploited as a novel therapeutic target for delayed cerebral ischaemia.