In examining the liver's response to
sepsis, our laboratory has found that septic hepatocytes exhibit a higher degree of
necrosis when compared with septic thymocytes, which typically die through the canonical apoptotic pathway. Recently, an adaptor
protein associated with the Fas/TNF
death receptor pathway, receptor interacting
protein 1 (RIP1), has been shown to be critical for determining whether a cell's death is apoptotic or necrotic. We propose to test the central hypothesis that RIP1 activation by
death receptor (Fas) during
sepsis determines whether the hepatocytes' fate is apoptotic versus necrotic. We approached this problem by delivering RIP1
siRNA in vivo to C57BL/6 mice and observing changes in mortality after septic challenge. Contrary to our hypothesis, RIP1-silenced mice did not survive as long as scrambled sequence injected controls (22.2% vs. 50.0% 14 days after cecal
ligation and
puncture, respectively). When we used a pharmacological/synthetic antagonist of RIP1
kinase, necrostatin 1 (Nec1), and examined the mortality of Nec1-treated mice, there was no difference from the RIP1
siRNA-treated mice (20.0% vs. 22.2%, respectively). Furthermore, we carried out a series of comparative histological studies, which indicated that septic mice pretreated with Nec1 exhibited a preservation of
liver glycogen stores (represented by
periodic acid Schiff
stain) versus
siRNA-treated mice, which exhibit lower
glycogen stores as well as altered morphology. Furthermore, the histological studies also revealed that Nec1 treatment in septic mice increases
caspase 3 activity. We speculate that these contradictatory findings are due to the dual-signaling responsibilities of RIP1, where the RIP1
kinase domain can induce death through Fas
ligation while also initiating prosurvival signaling through nuclear factor κB (NF-κB).