This article is available online at http://www.jlr.org triglyceride (TG)-rich lipoproteins (i.e., VLDLs and chylomicrons) (2-4). In normolipidemic individuals, plasma concentrations of apoC-III are 80-100 g/ml, with approximately 60% of apoC-III associated with HDL, 20% with LDL, 20% with the TG-rich lipoproteins, and very little free in plasma (5). In the hypertriglyceridemic state, plasma apoC3 levels increase to >300 g/ml, and the percentage on TG-rich lipoproteins increases from 20% to upward of 60% (5-7). In fact, animal and human studies have established a strong, positive correlation between elevated plasma apoC-III levels and TG levels, which are an independent risk factor for atherosclerotic CVD (1, 8). The overexpression of human apoC-III in mice promoted the development of atherosclerosis and was associated with elevated TG levels, but low HDL cholesterol levels, in plasma (9). In contrast, targeted disruption of apoC-III in mice was associated with the rapid catabolism of TG-rich lipoproteins and a 70% decrease in fasting TG levels (10).Beyond these mouse models, clinical studies established the importance of apoC-III as a predictor of CVD outcomes. Increased serum apoC-III levels were associated with elevated serum TG and, in turn, insulin resistance, CVD, and type II diabetes (11-13). Plasma levels of apoC-III independently predicted risk for coronary heart disease, even after control for blood lipids (12,14). Further indicating a crucial role of apoC-III in regulating lipid metabolism, subjects with gain-of-function mutations in the apoC-III gene exhibited hypertriglyceridemia that was associated with elevated plasma apoC-III protein levels (15, 16). In contrast, subjects with loss-of-function mutations in the apoC-III gene exhibited reduced TG and apoC-III levels (17-21), which had a cardioprotective effect. apoC-III is a small (79 amino acid), O-glycosylated, secretory protein that is synthesized in the liver and intestine (1). ApoC-III is the most abundant apoC in humans and circulates in plasma as a component of HDLs and the
Abstract