The concentration of tumor necrosis factor-α determines its protective or damaging effect on liver injury by regulating Yap activity.

Previous studies have shown that tumor necrosis factor (TNF)-α is a mediator of hepatotoxicity in liver injury. Moreover, TNF-α has also been reported to have a protective effect in liver regeneration, yet the function of TNF-α during liver injury remains controversial. Here, we report that the concentration of TNF-α determines its functions. High concentrations of TNF-α could aggravate LPS-induced liver injury. However, the TNF-α level was unchanged during APAP-induced liver injury, which exerted a protective effect. We expected that the concentration of TNF-α may affect its function. To test this hypothesis, TNF-α ^-/- rats or hepatocyte cells were treated with different concentrations of TNF-α. We found low TNF-α could reduce the levels of ALT and AST in the plasma of TNF-α ^-/- rats and promote the proliferation of hepatocyte cells. However, the levels of ALT and AST increased gradually with increasing TNF-α concentration after reaching the lowest value. Moreover, we showed that TNF-α affects the cell proliferation and cell death of hepatocytes by regulating Yap activity. Low TNF-α promoted Yap1 nuclear translocation, triggering the proliferation of hepatocytes. However, high TNF-α triggered the phosphorylation and inactivation of Yap1, preventing its nuclear import and consequently promoting cell death. Collectively, our findings provide novel evidence that the concentration of TNF-α is an important factor affecting its function in liver injury, which may provide a reference for the clinical treatment of liver injury.