Abstract P183: Retinol Binding Protein 7, a PPARγ Target Gene Protects Against Endothelial Dysfunction Induced by Mitochondrial Uncoupling

Abstract

PPARγ is a nuclear receptor that prevents oxidative stress in the endothelium. Endothelium specific PPARγ target gene, retinol binding protein 7 (RBP7) is required for the protective effects of PPARγ. In response to a cardiovascular stressor (high fat diet or Ang II), transgenic mice carrying a dominant-negative mutation in PPARγ in the endothelium (E-V290M) and RBP7 knockout mice (RBP7KO) exhibited increased oxidative stress and endothelial dysfunction. We hypothesize that RBP7 has a protective role against endothelial dysfunction induced by the pro-oxidant effects of mitochondrial uncoupling (MU). Acetylcholine (ACh) and sodium nitroprusside (SNP) induced vasodilation response were evaluated in carotid arteries from 4 and 8 month old RBP7KO mice, infused with either saline or a sub-pressor dose of Ang II (120ng/kg/min) for 2 weeks. Ang II infusion did not alter systolic blood pressure either in wild type (WT) (4 months old: 116.2±4.2 vs 113.9±4.1 mmHg; 8 months old: 111.3±3.8 vs 109.5±2.9 mmHg) or RBP7KO (4 months old: 112.9±1.1 vs 111.8±5.2 mmHg; 8 months old: 112.2±4.2 vs 113.9±4.1 mmHg). Endothelium-dependent relaxation to ACh was not affected by Ang II in either RBP7KO (4 month old: % relaxation - saline, 89.7±1.3 vs Ang II, 93.8±2.0; 8 months old: % relaxation - saline, 80.1±6.8 vs Ang II, 74.6±10.6) or WT littermates (4 months old: % relaxation - saline, 98.1±0.3 vs Ang II, 94.5±1.7; 8 months old: % relaxation - saline, 81.4±4.7 vs Ang II, 78.6±10.4). To test if RBP7 plays a role in MU, the vessels were pre-incubated with the MU carbonyl cyanide m-chlorophenyl hydrazone (CCCP; 1uM for 30 min). Pre-incubation with CCCP did not alter the relaxation responses to ACh in 4 month old mice in all groups. However, in 8 month old mice, there is a trend towards impaired endothelial function in the carotid artery from Ang II-infused RBP7KO compared with genotype-matched saline-treated mice (% relaxation: 51.9±3.8 vs 81.8±5.3, p=0.06) as well as Ang II-treated WT mice (% relaxation: 51.9±3.8 vs 77.1±2.0 p=0.08). In conclusion, Ang II alone was not able to impair vascular function, however, in 8 month old mice, Ang II increased the susceptibility to CCCP-dependent endothelial impairment, and RBP7 was required to mediate vascular protection against mitochondrial uncoupling.