PKC contributes to bile salt-induced apoptosis of hepatocytes

Hepatocyte injury due to elevated bile salt concentrations is a pathogenic mechanism in cholestatic liver diseases. Toxic bile salts cause hepatocyte apoptosis in vitro, a model relevant to cholestatic liver injury. Cell signaling cascades mediate apoptosis by activating effector mechanisms. However, the initial cell signaling mechanisms causing bile salt-induced apoptosis remain unclear. Because protein kinase C mediates apoptosis in other cells and bile salts may activate PKC, we tested the hypothesis that bile salts cause hepatocyte apoptosis through protein kinase C. After 2 hours, 28±5% of cultured hepatocytes treated with the toxic bile salt glycochenodeoxycholate (GCDC), 50 μM, were apoptotic vs. 2±2% of controls. The PKC inhibitors, chelerythrine and Gö 6976, both inhibited GCDC-induced apoptosis in a concentration-dependent manner, with a maximum inhibition of 64±7% with 1 mM Gö 6976 and 78±9% with 2.5 mM chelerythrine. In addition to preventing the morphologic features of apoptosis, both PKC inhibitors also blocked DNA fragmentation. Intracellular activity of cathepsin B, an effector protease in bile salt-induced apoptosis, was increased to 280±47% in GCDC-treated cells; in the presence of PKC inhibitors this increase was prevented. Activation of PKC. by PMA (200 nM) increased apoptosis 1.4-fold and cathepsin B activity to 600% in GCDC-treated cells. Treatment of hepatocytes with GCDC or PMA for 120 min resulted in translocation of PKC ̈, -δ, and -∈ from the cytosol to the membrane fraction on quantitative immunoblot analysis consistent with activation of these isoforms. Conclusion: Our data suggest a PKC-dependent signaling pathway may initiate hepatocyte apoptosis by toxic bile salts.