Sphingosine-1-phosphate Prevents Egress of Hematopoietic Stem Cells From Liver to Reduce Fibrosis

Abstract Background & Aims There is growing interest in the use of bone marrow cells to treat liver fibrosis, however little is known about their anti-fibrotic efficacy or the identity of their effector cell(s). Sphingosine-1-phosphate (S1P) mediates egress of immune cells from the lymphoid organs into the lymphatic vessels; we investigated its role in the response of hematopoietic stem cells (HSC) to liver fibrosis in mice. Methods Purified (c-kit+/sca1+/lin-) hematopoietic stem cells (HSC) were repeatedly infused into mice undergoing fibrotic liver injury. Chronic liver injury was induced in BoyJ mice by injection of carbon tetrachloride (CCl4) or placement on methionine/choline deficient (MCD) diets. Some mice were irradiated and given transplants of bone marrow cells from C57BL6 mice, with or without the S1P antagonist FTY720; we then studied HSC mobilization and localization. Migration of HSC cell lines was quantified in trans-well assays. Levels of S1P in liver, bone marrow and lymph fluid were measured using an ELISA. Liver tissues were collected and analyzed by immunohistochemical, quantitative PCR and sphingosine kinase activity assays. We performed quantitative PCR analyses of expression of sphingosine kinase 1 and 2 (SphK), sphingosine-1-phosphate lyase 1 (SGPL1), and sphingosine-1-phosphate phosphatase 1 (SGPP1) in normal human liver and cirrhotic liver from patients with alcohol related liver disease (n=6). Results Infusions of HSC into mice with liver injury reduced liver scarring based on picrosirius red staining (49.7% reduction in mice given HSC vs control mice; P