RIPK1 protects hepatocytes from death in Fas-induced hepatitis

Aveline Filliol,Mathieu J. M. Bertrand,Valentine Genet,Marie-Thérèse Dimanche-Boitrel,Claire Piquet-Pellorce,Peter Vandenabeele,Muhammad Farooq,Jacques Le Seyec,Michel Samson

doi:10.1038/s41598-017-09789-8

Abstract

Hepatocyte death is a central event during liver disease progression, in which immune cells play key roles by activating members of the Tumor Necrosis Factor Receptor Superfamily (TNFRSF), including TNFR1 (TNFRSF1A), Fas (TNFRSF6) and TRAIL-R2 (TNFRSF10B). Receptor Interacting Protein Kinase 1 (RIPK1) emerged as a signaling node downstream of these receptors. In the case of TNFR1, RIPK1 has been demonstrated to paradoxically serve as a scaffold to promote the survival of hepatocytes and as a kinase to kill them. To evaluate whether RIPK1 also protects hepatocytes from death in response to FasL or TRAIL, we took advantage of liver parenchymal cell-specific Ripk1 knockout mice (Ripk1LPC-KO). We found that Ripk1LPC-KO mice, as well as primary hepatocytes derived from them, were more susceptible to Fas-mediated apoptosis than their respective WT counterparts. Fas-induced hepatocyte death was independent of TNF-α signaling. Interestingly, while TRAIL administration did not induce hepatitis in Ripk1LPC-KO mice or in their WT counterparts, its combination with IFN-γ only induced TNF-α dependent apoptosis in the Ripk1LPC-KO mice. Together, our data demonstrate the protective role of RIPK1 downstream of Fas and highlight the general protective function of RIPK1 in hepatocytes exposed to inflammatory conditions, where TNF-α, FasL and/or TRAIL are present.

Highlights

The intravenous injection of the plant lectin Concanavalin A (ConA) is a widely used experimental model for acute immune-mediated hepatitis in mice
We have described that Receptor Interacting Protein Kinase 1 (RIPK1) deficiency in liver parenchymal cells sensitizes mice (Ripk1LPC-KO) to TNF-α- and by consequence to ConA-induced liver injury[30, 32]
While Ripk1LPC-KO mice challenged with ConA developed severe acute hepatitis that sometimes led to death (4 out of the 12 enrolled animals), a co-treatment with Etanercept (ETA), a TNF-α decoy receptor, significantly reduced liver injury and prevented any death

Summary

Results and Discussion

We have described that RIPK1 deficiency in liver parenchymal cells sensitizes mice (Ripk1LPC-KO) to TNF-α- and by consequence to ConA-induced liver injury[30, 32]. Whereas single injections of TRAIL or IFN-γ did not induce hepatolysis in Ripk1fl/fl or in Ripk1LPC-KO mice, their co-injection was able to trigger hepatocyte apoptosis but only in Ripk1LPC-KO mice, as assessed by the levels of serum transaminases, and appearance of necrotic and cleaved caspase-3 positive cells in the liver of these mice (Fig. 5) Our data showed that in hepatocytes RIPK1 is able to limit the hepatic injuries initiated during Fas pathway activation which is independent of TNF-α This suggested that the remaining hepatolysis observed in Ripk1LPC-KO mice treated with ETA and ConA (Fig. 1a) was most likely dependent on FasL. Protective role of RIPK1 in dysimmune hepatitis and highlight the risks of potential defects in the RIPK1 scaffolding function that would sensitize hepatocytes to death, risking to worsen hepatitis and even to increase HCC onset

Methods

Author Contributions

Additional Information