Tumor necrosis factor-inducible gene 6 promotes liver regeneration in mice with acute liver injury

Introduction: Tumor necrosis factor-inducible gene 6 protein (TSG-6), one of the cytokines released by human mesenchymal stem/stromal cells (hMSC), has an anti-inflammatory effect and alleviates several pathological conditions; however, the hepatoprotective potential of TSG-6 remains unclear. We investigated whether TSG-6 promoted liver regeneration in acute liver failure. Methods: The immortalized hMSC (B10) constitutively over-expressing TSG-6 or empty plasmid (NC: Negative Control) were established, and either TSG-6 or NC-conditioned medium (CM) was intraperitoneally injected into mice with acute liver damage caused by CCl4. Mice were sacrificed at 3 days post-CM treatment. Results: Higher expression and the immunosuppressive activity of TSG-6 were observed in CM from TSG-6-hMSC. The obvious histomorphological liver injury and increased level of liver enzymes were shown in CCl4-treated mice with or without NC-CM, whereas those observations were markedly ameliorated in TSG-6-CM-treated mice with CCl4. Ki67-positive hepatocytic cells were accumulated in the liver of the CCl4 + TSG-6 group. RNA analysis showed the decrease in both of inflammation markers, tnfa, il-1 beta, cxcl1 and cxcl2, and fibrotic markers, tgf-beta 1, alpha-sma and collagen a1, in the CCl4 + TSG-6 group, compared to the CCl4 or the CCl4 + NC group. Protein analysis confirmed the lower expression of TGF-beta 1 and alpha-SMA in the CCl4 + TSG-6 than the CCl4 or the CCl4 + NC group. Immunostaining for a-SMA also revealed the accumulation of the activated hepatic stellate cells in the livers of mice in the CCl4 and CCl4 + NC groups, but not in the livers of mice from the CCl4 + TSG-6 group. The cultured LX2 cells, human hepatic stellate cell line, in TSG-6-CM showed the reduced expression of fibrotic markers, tgf-beta 1, vimentin and collagen a1, whereas the addition of the TSG-6 antibody neutralized the inhibitory effect of TSG-6 on the activation of LX2 cells. In addition, cytoplasmic lipid drops, the marker of inactivated hepatic stellate cell, were detected in TSG-6-CM-cultured LX2 cells, only. The suppressed TSG-6 activity by TSG-6 antibody attenuated the restoration process in livers of TSG-6-CM-treated mice with CCl4. Conclusions: These results demonstrated that TSG-6 contributed to the liver regeneration by suppressing the activation of hepatic stellate cells in CCl4-treated mice, suggesting the therapeutic potential of TSG-6 for acute liver failure.