Search

Apolipoprotein A5 has recently been identified as a crucial determinant of plasma triglyceride levels. Our results showed that RORa up-regulates human APOA5 but has no effect on mouse apoa5 promoter. These data suggest an additional important physiological role for RORa in the regulation of genes involved in plasma triglyceride homeostasis in human and probably in the development of atherosclerosis

Several epidemiological studies have established that elevated plasma triglyceride concentrations constitute an independent risk factor for cardiovascular diseases. In addition, systemic inflammation is associated with severe hypertriglyceridemia and previous studies have demonstrated that cytokines such as tumor necrosis factor alpha (TNFalpha;) and interleukin-1 (IL-1) can elevate plasma triglyceride levels. Recently, we identified a new apolipoprotein, APOA5, selectively expressed in the liver and showed that this gene is a crucial determinant of plasma triglyceride levels. In this study, we sought to determine whether inflammatory cytokines regulate APOA5 and consequently influence plasma triglyceride levels. We found initially that treatment of human hepatocytes with TNFalpha; or IL-1 reduced the expression of APOA5 mRNA. Subsequent, we demonstrated through transient transfection experiments that both TNFalpha; and IL-1 down-regulate human APOA5 at the transcriptional level. Further deletion analyses of the APOA5 promoter and binding assays revealed the presence of a promoter sequence, containing a PPARalpha; Response Element, responsive to cytokine stimulation. In vivo, treatment of hAPOA5 transgenic mice with TNFalpha; down-regulated the hAPOA5 gene expression in hepatocytes. In patients displaying systemic inflammation, plasma concentrations of triglycerides and ApoAV were inversely correlated. These findings demonstrate that APOA5 is an inflammatory responsive gene and constitutes a link between inflammation and triglyceride-associated cardiovascular risk.

The apolipoprotein A5 (APOA5) gene has been shown to be important in lowering plasma triglyceride levels. Since several studies have shown that hyperinsulinemia is associated with hypertriglyceridemia, we sought to determine whether APOA5 gene is regulated by insulin. We show here that cell and mouse treatments with insulin down-regulated APOA5 expression in a dose-dependent manner. Furthermore, we determined that insulin decreases APOA5 promoter activity and subsequent deletion analyses revealed an E-box-containing fragment. We showed that Upstream Stimulatory Factors, USF1/USF2, bind to the identified E-box in the APOA5 promoter. Moreover, in cotransfection studies, USF1 stimulates APOA5 promoter activity. The treatment with insulin reduces the binding of USF1/USF2 to APOA5 promoter. The inhibition of PI3K pathway with wortmannin abolished the insulin s effect on APOA5 gene transcription. Using oligoprecipitation method of USF from nuclear extracts, we demontrated that phosphorylated USF1 failed to bind to APOA5 promoter. This indicates that the APOA5 gene transrepression by insulin involves a phosphorylation of USF through PI3K, that modulate their binding to APOA5 promoter and results in APOA5 down-regulation. The effect of exogenous hyperinsulinemia in healthy men shows a decrease of the plasma ApoAV level. These data suggest a potential mechanism involving APOA5 gene in hypertriglyceridemia associated with hyperinsulinemia.

Recently, we reported that apoAV plays key role in triglycerides lowering. Here, we attempted to determine the mechanism underlying this hypotriglyceridemic effect. We showed that triglyceride turnover is faster in hAPOA5 transgenic compared to wild type mice. Moreover, both apoB and apoCIII are decreased and LPL activity is increased in postheparin plasma of hAPOA5 transgenic mice. These data suggest a decrease in size and number of VLDL. To further investigate the mechanism of hAPOA5 in hyperlipidemic background, we intercrossed hAPOA5 and hAPOC3 transgenic mice. The effect resulted in a marked decreased of VLDL triglyceride, cholesterol, apolipoproteins B and CIII. In postprandial state, the triglyceride response is abolished in hAPOA5 transgenic mice. We demonstrated that in response to the fat load in hAPOA5XhAPOC3 mice, apoAV shifted from HDL to VLDL, probably to limite the elevation of triglycecrides. In vitro, apoAV activates lipoprotein lipase. However, apoAV does not interact with LPL but interacts physically with apoCIII. This interaction does not seem to displace apoCIII from VLDL but may induce conformational change in apoCIII and consequently change in its function leading the activation of lipoprotein lipase.

Both the apolipoprotein A5 and C3 genes have repeatedly been shown to play an important role in determining plasma triglyceride concentrations in humans and mice. In mice, transgenic and knockout experiments indicate that plasma triglyceride levels are negatively and positively correlated with APOA5 and APOC3 expression, respectively. In humans, common polymorphisms in both genes have also been associated with plasma triglyceride concentrations. The evolutionary relationship among these two apolipoprotein genes and their close proximity on human chromosome 11q23 have largely precluded the determination of their relative contribution to altered Both the apolipoprotein A5 and C3 genes have repeatedly been shown to play an important role in determining plasma triglyceride concentrations in humans and mice. In mice, transgenic and knockout experiments indicate that plasma triglyceride levels are negatively and positively correlated with APOA5 and APOC3 expression, respectively. In humans, common polymorphisms in both genes have also been associated with plasma triglyceride concentrations. The evolutionary relationship among these two apolipoprotein genes and their close proximity on human chromosome 11q23 have largely precluded the determination of their relative contribution to altered triglycerides. To overcome these confounding factors and address their relationship, we generated independent lines of mice that either over-expressed ("double transgenic") or completely lacked ("double knockout") both apolipoprotein genes. We report that both "double transgenic" and "double knockout" mice display intermedia tetriglyceride concentrations compared to over-expression or deletion of either gene alone. Furthermore, we find that human ApoAV plasma protein levels in the "double transgenic" mice are approximately 500-fold lower than human ApoCIII levels, supporting ApoAV is a potent triglyceride modulator despite its low concentration. Together, these data indicate that APOA5 and APOC3 independently influence plasma triglyceride concentrations but in an opposing manner.

The relationship between the frequency of major cardiovascular events and HDL cholesterol levels in coronary heart disease patients treated with statins analyzed from the TNT trial examination is described. HDL cholesterol levels were observed to be predictive even among patients with LDL cholesterol levels below 70 mg per deciliter.

An investigation to assess whether very intensive satin therapy could regress coronary atherosclerosis as determined by intravascular ultrasound (IVUS) imaging is conducted. Results reveal that very high-intensity statin therapy using rosuvastatin 40mg/d achieved an average LDL-C of 60.8 mg/dL and increased HDL-C by 14.7%, resulting in significant regression of atherosclerosis for all 3 prespecified IVUS measures of disease burden.

Lowering low-density lipoprotein (LDL) cholesterol levels below recommended levels is beneficial in patients with acute coronary syndromes. Intensive lipid-lowering therapy with 80mg of atorvastatin per day in patients with stable coronary heart disease (CHD) provides significant clinical benefit beyond that afforded by treatment with 10mg of atorvastatin per day.