The bile acid-activated phosphatidylinositol 8-kinase pathway inhibits fas apoptosis upstream of bid in rodent hepatocytes

<(Background & Aims)>: Bile acids differentially modulate hepatocyte injury in cholestasis, Although glycochenode-oxycholate (GCDC) induces Fas-mediated hepatocyte apoptosis, taurochenodeoxycholate (TCDC) simultaneously activates a phosphatidylinositol 3-kinase (PI 3-K)-mediated survival pathway blocking Fas apoptosis, In this study, the mechanisms by which the TCDC/PI 3-K survival signal disrupts Fas signaling were examined. (Methods) under bar: Studies were performed in primary cultures of mouse hepatocytes and the bile-salt-transporting Mc-Ntcp.24 rat hepatoma cell line. (Results) under bar: GCDC, but not TCDC, resulted in cytochrome c release demonstrating that TCDC blocked apoptosis upstream of mitochondria. In contrast, both GCDC and TCDC treatment resulted in Fas aggregation and recruitment of a dominant-negative FADD green fluorescent protein (GFP) and C360S pro-caspase 8-GFP to the plasma membrane. Despite recruitment of procaspase 8 to the plasma membrane by both bile acids, only GCDC resulted in increases of caspase 8 activity and Bid-GFP mitochondrial translocation, However, when PI-3K was inhibited with wortmannin or dominant-negative PI 3-K, TCDC-induced Bid-GFP mitochondrial translocation and cytochrome c release. (Conclusions) under bar: The TCDC/PI 3-K survival signal blocks Fas-mediated apoptosis by preventing caspase 8 activation and Bid mitochondrial translocation, Potentiation of this survival pathway in cholestasis has the potential to attenuate liver injury.