Apolipoprotein C-III and hepatic triglyceride-rich lipoprotein production

Abstract

A strong positive correlation between plasma apolipoprotein (apo) C-III and triglyceride concentrations has been invariably observed in human and animal studies. The hypertriglyceridemic effect of apo C-III has been conventionally explained by its extracellular roles in inhibiting lipolysis catalysed by lipoprotein lipase and attenuating triglyceride-rich lipoprotein clearance through receptor-dependent and/or independent mechanisms. However, recent experimental evidence suggests that apo C-III may also play an intracellular role in promoting hepatic triglyceride-rich lipoprotein production. Kinetic studies with humans and genetically modified mice have shown that apo C-III is linked with increased production of triglyceride-rich lipoproteins, such as very-low-density lipoprotein 1 (VLDL1). Mutational studies on human apo C-III variants (originally identified in humans with hypotriglyceridemia or hyperalphalipoproteinemia) provide the structure-function analysis of human apo C-III, demonstrating that loss-of-function mutations within human apo C-III impair the assembly and secretion of triglyceride-rich VLDL1 under lipid-rich conditions. The current review summarizes recent experimental evidence for an intrahepatic role of human apo C-III in promoting mobilization and utilization of triglyceride during VLDL1 assembly/secretion. Understanding mechanisms by which hepatic apo C-III expression is regulated under insulin resistance and diabetic conditions will lead to better and more rational strategies for the prevention and treatment of diabetic hypertriglyceridemia that is closely related to premature atherosclerosis.