Knockdown of RIPK1 markedly exacerbates murine immune-mediated liver injury through massive apoptosis of hepatocytes, independent of necroptosis and …

J Suda, L Dara, L Yang, M Aghajan, Y Song… - The Journal of …, 2016 - journals.aai.org
J Suda, L Dara, L Yang, M Aghajan, Y Song, N Kaplowitz, ZX Liu
The Journal of Immunology, 2016journals.aai.org
Receptor-interacting protein kinase (RIPK) 1 has an essential role in the signaling pathways
triggered by death receptors through activation of NF-κB and regulation of caspase-
dependent apoptosis and RIPK3/mixed lineage kinase domain-like protein (MLKL)-
mediated necroptosis. We examined the effect of RIPK1 antisense knockdown on immune-
mediated liver injury in C57BL/6 mice caused by α-galactosylceramide (αGalCer), a specific
activator for invariant NKT cells. We found that knockdown of RIPK1 markedly exacerbated …
Abstract
Receptor-interacting protein kinase (RIPK) 1 has an essential role in the signaling pathways triggered by death receptors through activation of NF-κB and regulation of caspase-dependent apoptosis and RIPK3/mixed lineage kinase domain-like protein (MLKL)-mediated necroptosis. We examined the effect of RIPK1 antisense knockdown on immune-mediated liver injury in C57BL/6 mice caused by α-galactosylceramide (αGalCer), a specific activator for invariant NKT cells. We found that knockdown of RIPK1 markedly exacerbated αGalCer-mediated liver injury and induced lethality. This was associated with increased hepatic inflammation and massive apoptotic death of hepatocytes, as indicated by TUNEL staining and caspase-3 activation. Pretreatment with zVAD. fmk, a pan-caspase inhibitor, or neutralizing Abs against TNF, almost completely protected against the exacerbated liver injury and lethality. Primary hepatocytes isolated from RIPK1-knockdown mice were sensitized to TNF-induced cell death that was completely inhibited by adding zVAD. fmk. The exacerbated liver injury was not due to impaired hepatic NF-κB activation in terms of IκBα phosphorylation and degradation in in vivo and in vitro studies. Lack of RIPK1 kinase activity by pretreatment with necrostatin-1, a RIPK1 kinase inhibitor, or in the RIPK1 kinase-dead knock-in (RIPK1 D138N) mice did not exacerbate αGalCer-mediated liver injury. Furthermore, RIPK3-knockout and MLKL-knockout mice behaved similarly as wild-type control mice in response to αGalCer, with or without knockdown of RIPK1, excluding a switch to RIPK3/MLKL-mediated necroptosis. Our findings reveal a critical kinase-independent platform role for RIPK1 in protecting against TNF/caspase-dependent apoptosis of hepatocytes in immune-mediated liver injury.
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