Bone marrow endothelial progenitor cells activate hepatic stellate cells and aggravate carbon tetrachloride induced liver fibrosis in mice via paracrine factors

Objectives: Bone marrow derived endothelial progenitor cells (BM-EPCs) are increased in chronic liver disease (CLD). Their role in hepatic fibrosis and regeneration remains an area of intense studies. We investigated the migration and secretory functions of BM-EPCs in fibrotic mice liver. Materials and methods: Bone marrow cells from C57BL6-GFP mice were transplanted into the femur of irradiated C57BL6 mice, followed by CCl4 doses for 8 weeks, to develop hepatic fibrosis (n = 36). Transplanted C57BL6 mice without CCl4 treatment were used as controls. EPCs were analyzed in BM, blood and liver by flow cytometry and immunofluorescence. VEGF and TGF-beta were analysed in the hepatic stellate cells (HSCs) and BM-EPCs co-cultures using ELISAs. Results: There was a significant migration of EPCs from BM to blood and to the liver (P <= 0.01). Percentage of GFP(+)CD31(+) EPCs and collagen proportionate area was substantially increased in the liver at 4th week of CCl4 dosage compared to the controls (19.8% vs 1.9%, P <= 0.05). Levels of VEGF (533.6 pg/ml) and TGF-beta (327.44 pg/ml) also increased significantly, when HSCs were treated with the EPC conditioned medium, as compared to controls (25.66 pg/ml and 5.87 pg/ml, respectively; P <= 0.001). Conclusions: Present findings suggest that BM-EPCs migrate to the liver during CCl4-induced liver injury and contribute to fibrosis.