Homing of bone marrow mesenchymal stem cells mediated by sphingosine 1-phosphate contributes to liver fibrosis

Background/Aims: Myofibroblasts play a central role in the pathogenesis of liver fibrosis. Myofibroblasts of bone marrow (BM) origin have recently been identified in fibrotic liver. However, little is known about the mechanism that controls their mobilization in vivo. Here we confirmed that BM mesenchymal stem cells (BMSCs) can migrate to the damaged liver and differentiate into myofibroblasts. We also investigated the mechanism underlying the homing of BMSCs after liver injury. Methods: ICR mice were lethally irradiated and received BM transplants from enhanced green fluorescent protein transgenic mice. Carbon tetrachloride or bile duct ligation was used to induce liver fibrosis. The fibrotic liver tissue was examined by immunofluorescent staining to identify BM-derived myofibroblasts. Results: BMSCs contributed significantly to myofibroblast population in fibrotic liver. Moreover, analysis in vivo and in vitro suggested that homing of BMSCs to the damaged liver was in response to sphingosine 1-phosphate (S1P) gradient between liver and BM. Furthermore, S1P receptor type 3 (S1P(3)) was required for migration of BMSCs triggered by S1P. Conclusions: S1P mediates liver fibrogenesis through homing of BMSCs via S1P(3) receptor, which may represent a novel therapeutic target in liver fibrosis through inhibiting S1P formation and/or receptor activation. (C) 2009 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.