Abstract P123: Retinol-Binding Protein 7 (RBP7) Regulates Endothelial Function via an Adiponectin-Dependent Mechanism in Angiotensin II-Infused Mice

Abstract

The transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) regulates vascular function and protects against endothelial dysfunction. We reported that mice expressing dominant-negative PPARγ in endothelium exhibit an enhanced pressor response to angiotensin II (Ang II). Given that RBP7 is a PPARγ target expressed in endothelium, we hypothesized that loss of RBP7 would augment endothelial dysfunction caused by Ang II. Using osmotic minipumps, RBP7 knockout (KO) mice and wild type (WT) littermates were infused with subpressor Ang II (120 ng/kg/min, 2 weeks) or saline. Systolic blood pressure (by tail cuff) was not different between KO and WT mice and was not altered by infusion of saline or Ang II. Acetylcholine (ACh, 30 μM) mediated relaxation of carotid arteries was not different between groups during saline infusion, but was selectively impaired in KO mice during Ang II (44±5% in KO vs 71±3% in WT, p<0.05). Aortic superoxide, assessed by hydroethidine staining, was higher after Ang II in KO compared with WT mice. Pre-incubation of carotid arteries with a superoxide scavenger Tempol (1 mM, 30 min) restored ACh-induced relaxation in Ang II-infused KO mice (74±6% in Tempol-KO vs 46±8% in KO). To identify molecular mechanisms, RNA Sequencing was performed using carotid arteries from WT and KO mice fed high fat diet (HFD) or normal chow for 8 weeks. Adiponectin (Adipo), a known PPARγ target gene, was increased ~6-fold in HFD-fed WT mice, a response that was markedly blunted in KO mice. Immunohistochemistry revealed that Adipo was expressed specifically in endothelial cells (co-immunostaining with endothelial specific CD31). Rosiglitazone, a PPARγ ligand, increased carotid artery Adipo protein in WT, but not KO mice. To test the importance of Adipo, carotid arteries from Ang II-infused WT and KO mice were incubated with vehicle or full-length Adipo (5 μg/mL) for 12 hrs. Adipo incubation ameliorated Ang II-induced endothelial dysfunction in KO mice (ACh, 30 μM: 86±3% Adipo-KO vs 58±8% KO) while having no effect in WT mice (ACh, 30 μM: 83±1% Adipo-WT vs 87±3% WT). In conclusion, RBP7 protects the endothelium from oxidative stress-induced dysfunction caused by Ang II. Our data suggest an important role for Adipo in mediating this protective response.