Differential Activation of ER Stress Signal Pathways Contributes to Palmitate-Induced Hepatocyte Lipoapoptosis

Saturated free fatty acids-induced hepatocyte lipoapoptosis plays a pivotal role in non-alcoholic steatohepatitis. The activation of endoplasmic reticulum (ER) stress is involved in hepatocyte lipoapoptosis induced by the saturated free fatty acid palmitate (PA). However, the underlying mechanisms of the role of ER stress in hepatocyte lipoapoptosis remain largely unclear. In this study, we showed that PA and tunicamycin (Tun), a classic ER stress inducer, resulted in differential activation of ER stress pathways. Our data revealed that PA induced chronic and persistent ER stress response, but Tun induced acute and transient ER stress response. Compared with Tun treatment, PA induced much lower glucose-regulated protein 78 (GRP78), a central regulator of ER homeostasis, accumulation. It is noteworthy that GRP78 over-expression not only inhibited PA-induced ER stress but also decreased PA-induced apoptosis. Taken together, our data suggest that the differential activation of ER stress signal plays an important role in PA-induced hepatocyte lipoapoptosis. More detailed studies on the mechanisms of PA in repressing the accumulation of GRP78 will contribute to the understanding of molecular mechanisms of lipoapoptosis.