Background: Sepsis remains a leading cause of death in critically ill patients. It is well known that mesenchymal stem cells (MSCs) are a promising therapy partly due to their paracrine-mediated immunoregulatory function. Previous study demonstrated that transforming growth factor-beta1 (TGF-β1) is an important cytokine secreted by MSCs and that it participates in MSC-mediated macrophage phenotype switch from pro-inflammatory to pro-resolution. In addition, the transformation of macrophage phenotype may be a potential treatment for sepsis. However, the therapeutic effect of overexpressing TGF-β1 in MSCs (MSC-TGF-β1) on sepsis is not well understood. Therefore, this study aimed to evaluate the effects of TGF-β1 overexpressing MSCs on organ injury in cecal ligation and puncture (CLP)-induced septic mice and to detect the changes in macrophage phenotype during this process.
Methods: Mouse MSCs stably transfected with TGF-β1 were constructed and injected into CLP-induced septic mice via tail vein. After 24 h, the mice were sacrificed; then, the histopathology of the organ was evaluated by hematoxylin-eosin (H&E) staining. Inflammatory cytokines were detected by ELISA. Macrophage infiltration and phenotype transformation in the tissues were determined by immunohistochemistry and flow cytometry. In addition, we performed adoptive transfer of mouse peritoneal macrophage pretreated with TGF-β1 overexpressing MSCs in septic mice.
Results: We found that infusion of TGF-β1 overexpressing MSCs attenuated the histopathological impairment of the organ, decreased the pro-inflammatory cytokine levels and inhibited macrophage infiltration in tissues. TGF-β1 overexpressing MSCs induced macrophage phenotypes changed from pro-inflammatory to pro-resolution in inflammatory environment. The adoptive transfer of mouse peritoneal macrophages pretreated with TGF-β1 overexpressing MSCs also relieved organ damage in CLP-induced septic mice.
Conclusion: Under septic conditions, TGF-β1 overexpressing MSCs can enhance the therapeutic effects of MSCs on organ injury and inflammation as a result of reduced macrophage infiltration and induced macrophages transformation, the adoptive transfer of macrophages treated with TGF-β1 overexpressing MSCs also relieved organ damage. This will provide new hope for the treatment of sepsis.
Keywords: Macrophage activation; Mesenchymal stem cells; Sepsis; Transforming growth factor-β1.