Abstract 339: Hyperhomocysteinemia Reduces Large HDL Particle and EL Expression via Hypomethylation Related Mechanism in Mice

Abstract

Hyper-homocysteinemia (HHcy) has been identified as an independent risk factors of cardiovascular diseases (CVD). We previous reported HHcy is associated with reduced HDL-cholesterol and decreased large HDL particle in mouse and human CVD. Here, we investigated underlying mechanism of homocysteine (Hcy)-related HDL biosynthesis and degradation. We examined protein/gene expression, activities of four HDL-degradation related lipases including endothelial lipase (EL), lipoprotein lipase (LPL), hepatic lipase (HL), and pancreatic lipase (PL). Severe HHcy (98.4±22 μM) was established in cystathionine betasynthase-gene mutant mice ( Cbs +/- ), moderate HHcy (23.5±5 μM) was also developed in Cbs +/+ mice, both fed a high methionine (HM) diet for 8-week. Moderate and severe HHcy increased protein levels of EL in aorta (204% and 319%), lung (201% and 264%), and decreased LPL in aorta (98% and 34%), lung (99% and 61%), spleen (98% and 51%). HL and PL protein levels were not changed by HHcy. Activities of overall lipases were increased in moderate and severe HHcy in aorta (19.8±5.2 and 27.5±7.1, arbitrary unit), plasma (64.3±5.5 and 126.5±26.2), adipose (147.0±8.9 and 210.9±38.9) and liver (160.5±41.3 and 276.2±51.3). Next, we examined tissue levels of Hcy, and its metabolites (SAM, SAH) in heart, lung, brain, spleen, kidney and liver from wild type mice. Tissue expression profile of Hcy degradation and synthesis-related enzymes were established by database mining analysis. We found that mRNA levels of EL, HL, and PL were positively correlated with Hcy and negatively correlated with SAM/SAH ratio, which indicated of methylation status. In contrast, LPL mRNA levels were negatively correlated with Hcy and positively correlated with SAM/SAH ratio. These data suggest that EL, HL, PL gene expression may be induced by Hcy-related hypomethylation. We identified a large CpG island with 113 CG dinucleotide pairs in human EL promoter region, where four HDL-related single nucleotide polymorphisms (SNPs) was overlapping with CpG containing transcription factor consensus element. Our study suggests that HHcy inhibits HDL biosynthesis, promotes HDL degradation via EL induction and DNA hypomethylation related mechanisms.