PROGRESSION OF SEVERE ATHEROSCLEROSIS AND INCREASED ARTERIAL PULSE PRESSURE IN THE NEWLY DEVELOPED HERITABLE MIXED HYPERLIPIDAEMIC RABBITS

Mining the genome for lipid genes

Mining of the genome for lipid genes has since the early 1970s helped to shape our understanding of how triglycerides are packaged (in chylomicrons), repackaged (in very low density lipoproteins; VLDL), and hydrolyzed, and also how remnant and low-density lipoproteins (LDL) are cleared from the circulation. Gene discoveries have also provided insights into high-density lipoprotein (HDL) biogenesis and remodeling. Interestingly, at least half of these key molecular genetic studies were initiated with the benefit of prior knowledge of relevant proteins. In addition, multiple important findings originated from studies in mouse, and from other types of non-genetic approaches. Although it appears by now that the main lipid pathways have been uncovered, and that only modulators or adaptor proteins such as those encoded by LDLRAP1, APOA5, ANGPLT3/4, and PCSK9 are currently being discovered, genome wide association studies (GWAS) in particular have implicated many new loci based on statistical analyses; these may prove to have equally large impacts on lipoprotein traits as gene products that are already known. On the other hand, since 2004 - and particularly since 2010 when massively parallel sequencing has become de rigeur - no major new insights into genes governing lipid metabolism have been reported. This is probably because the etiologies of true Mendelian lipid disorders with overt clinical complications have been largely resolved. In the meantime, it has become clear that proving the importance of new candidate genes is challenging. This could be due to very low frequencies of large impact variants in the population. It must further be emphasized that functional genetic studies, while necessary, are often difficult to accomplish, making it hazardous to upgrade a variant that is simply associated to being definitively causative. Also, it is clear that applying a monogenic approach to dissect complex lipid traits that are mostly of polygenic origin is the wrong way to proceed. The hope is that large-scale data acquisition combined with sophisticated computerized analyses will help to prioritize and select the most promising candidate genes for future research. We suggest that at this point in time, investment in sequence technology driven candidate gene discovery could be recalibrated by refocusing efforts on direct functional analysis of the genes that have already been discovered. This article is part of a Special Issue entitled: From Genome to Function.

Aldosterone synthase (CYP11B2) C-344T polymorphism affects the association of age-related changes of the serum C-reactive protein

Aldosterone participates in vascular and myocardial inflammation either directly or indirectly through blood pressure (BP). Aldosterone synthase (CYP11B2) C-344T polymorphism may influence the severity of systemic inflammation. A total of 398 Japanese Americans (152 men and 246 women, age 19-92 years) from the Hawaii-Los Angeles-Hiroshima study were enrolled. BP and serum levels of C-reactive protein (CRP) were measured, and the CYP11B2 C-344T polymorphism, rs1799998, was determined. No influence of the polymorphism on baseline characteristics such as systolic, diastolic and mean BP, pulse pressure or serum CRP levels was observed. In all genotypes, systolic BP showed a significantly positive correlation with age (TT (n=178): r=0.283, P<0.001; TC (n=164): r=0.213, P=0.006; and CC (n=56): r=0.289, P=0.031). However, the regression coefficients of systolic BP with age were not different across genotypes. According to the results of univariate and multivariate analyses with adjustment for BP, the serum CRP level increased with age only in subjects with the CC genotype (P=0.027 and P=0.004, respectively), and elevation of serum CRP was mainly observed in the elderly population (aged >or=60 years). Moreover, the regression coefficient of CRP levels with age was significantly steeper in subjects with the CC genotype than in those with the TC or TT genotype (P=0.028). The CC genotype of the CYP11B2 C-344T polymorphism was associated with an age-dependent increase in the serum CRP level independent of BP, and may contribute to a cardiovascular phenotype by promoting vascular inflammation.

Endothelial arginase II: a novel target for the treatment of atherosclerosis

Oxidized low-density lipoproteins increase arginase activity and reciprocally decrease endothelial NO in human aortic endothelial cells. Here, we demonstrate that vascular endothelial arginase activity is increased in atherogenic-prone apolipoprotein E-null (ApoE(-/-)) and wild-type mice fed a high cholesterol diet. In ApoE(-/-) mice, selective arginase II inhibition or deletion of the arginase II gene (Arg II(-/-) mice) prevents high-cholesterol diet-dependent decreases in vascular NO production, decreases endothelial reactive oxygen species production, restores endothelial function, and prevents oxidized low-density lipoprotein-dependent increases in vascular stiffness. Furthermore, arginase inhibition significantly decreases plaque burden. These data indicate that arginase II plays a critical role in the pathophysiology of cholesterol-mediated endothelial dysfunction and represents a novel target for therapy in atherosclerosis.