Activation of the HMGB1‐TLR4 pathway impacts the functionality of bone marrow mesenchymal stem cells and disrupts macrophage polarization in immune thrombocytopenia

Summary Recent evidence suggests that immune thrombocytopenia (ITP), a common bleeding disorder, is linked to an imbalance in macrophage polarization and impaired bone marrow mesenchymal stem cells (BMSCs). However, the relationship between macrophage polarization imbalance and functional defects in BMSCs, as well as the involvement of associated molecules in BMSCs' defects, is not well understood. This study aimed to investigate the regulatory effects of high mobility group protein 1 (HMGB1) on the physiological functions of BMSCs, specifically in relation to macrophage polarization imbalance. Patients with ITP showed dysregulation in monocyte/macrophage polarization and impaired BMSCs function. HMGB1 was found to have a negative impact on the ability of BMSCs to regulate the imbalance in macrophage polarization, especially when inflammatory factors are present. The MyD88‐dependent pathway downstream of BMSCs was found to be significantly enhanced with HMGB1 treatment. Furthermore, treatment with toll‐like receptor 4 (TLR4) inhibitors successfully restored the regulatory capacity of BMSCs in ameliorating macrophage polarization imbalance and effectively inhibited the activation of the MyD88‐dependent pathway. Meanwhile, infusion of si‐TLR4‐BMSCs reversed HMGB1‐induced platelet dysfunction and reduced over‐polarization to M1‐like macrophages in the ITP mouse model. Consequently, targeting the HMGB1‐TLR4 pathway could be a potential approach to restore the immunoregulatory function of BMSCs.