Abstract P347: Retinol-binding Protein 7 (RBP7) is Required for PPARG-mediated Endothelial Protection via Adiponectin

Abstract

PPARγ protects against endothelial dysfunction by regulation of unknown target genes. One such target, RBP7, an intracellular fatty acid-binding protein, exhibits endothelium-specific expression, but its effect on vascular function remain unknown. We hypothesize that RBP7 is endothelial protective. We examined vascular responses in basilar artery (pressurized myograph) of RBP7-knockout (KO) and wild type (WT) mice fed normal chow (ND) or high fat diet (HFD) for 8 wks. Endothelium-dependent acetylcholine (ACh)-induced relaxation was significantly impaired in HFD-fed KO mice (ACh, 100μM: 33±7% KO vs 83±10% WT, p<0.05), but not in ND-fed groups. This response was ameliorated by pre-incubation with superoxide scavenger tempol (1mM) or PEG-superoxide dismutase (100 U/ml). Mean arterial pressure (measured by radiotelemetry), body weight, hepatic steatosis, fasting glucose, glucose tolerance, and insulin sensitivity were similar in HFD-fed KO and WT mice. To identify targets downstream of RBP7, RNA-Sequencing was performed on carotid arteries from 8-week HFD-fed WT and KO mice as well as ND-fed age-matched littermates. Adiponectin (AdipoQ), a PPARγ target, was increased ~6-fold in HFD-fed WT mice, a response that was markedly blunted in KO mice. RNA sequencing was confirmed by qPCR. There was no difference in plasma AdipoQ. AdipoQ protein is expressed in endothelial cells of carotid arteries and its level of expression was increased in HFD-fed WT but not KO mice (AdipoQ/CD31: 1.14±0.1 WT-HFD vs 0.82±0.1 WT-ND, p<0.05; 0.79±0.1 KO-HFD vs 0.81±0.04 KO-ND). This led us to hypothesize that AdipoQ is involved in RBP7-mediated endothelial protection. Incubation of basilar artery with mouse full-length AdipoQ protein (5 μg/mL, 4 hours) significantly ameliorated endothelial dysfunction (ACh, 100 μM: 56±6% AdipoQ+KO vs 26±3% KO, p<0.05) and blunted carotid artery superoxide production in HFD-fed KO mice. AdipoQ also protects against endothelial dysfunction caused by subpressor Ang-II in KO mice. We conclude that RBP7 protects the endothelium from oxidative stress-induced dysfunction through an AdipoQ-dependent mechanism. Our evidence suggests RBP7 is an essential cofactor for activation of some PPARγ target genes in the endothelium.