Protective effect of mesenchymal stem cell-conditioned medium on hepatic cell apoptosis after acute liver injury

The aim of this study was to investigate the role of Mesenchymal Stem Cell (MSC) conditioned medium (CM(MSC)) on apoptosis of cultured mouse primary hepatocytes after in vivo carbon tetrachloride (CCl4)-induced acute liver injury. The acute liver injury was induced by injecting CCl4 intraperitoneally in C57/BL6 mice. Hepatocytes were isolated by liver perfusion, cultured in a defined medium to maintain their differentiation and characterized by reverse transcriptase polymerase chain reaction (RT-PCR) using the hepatic cell specific genes albumin, hepatocyte nuclear factor 4 (HNF4) and cytokeratin 18 (CK18). CM(MSC) was generated from cultured bone marrow-derived MSCs (BM-MSCs). BM-MSCs were positive for CD73, CD90, CD44 by flow cytometry and able to differentiate into chondrocytes, adipocytes and osteocytes. Apoptosis was evaluated by both annexin V. CM(MSC) were examined by flow cytometry to detect MSC-derived annexin V- and CD54/CD44-positive microparticles (MPs). In the CCl4-CM(MSC) treated hepatocytes, interleukin-6 (IL-6) was increased on the first day of culture compared to control and CCl4 and was followed by upregulation of fibroblast-like-protein (FGL1) expression after 48 hrs. This was associated with a significant decrease of annexin V positive CCl4-CM(MSC) treated hepatocytes at day 3 post plating. Recombinant IL-6 was induced FGL1 expression in hepatocytes derived from CCl4-treated mice suggesting that CM(MSC), which is enriched also in microparticles, attenuates CCl4-induced early apoptosis in hepatocytes through activation of FGL1.