Retinol Binding Protein 7 Mediates an Anti‐oxidant Response to Cardiovascular Stressors by Regulating PPARγ Activity and Adiponectin in Endothelium
Authors: Hu Chunyan , Keen Henry L , Lu Ko‐Ting , Liu Xuebo , Davis Deborah R , Wu Jing , Vogel Silke , Quelle Frederick W , Sigmund Curt D 
Published: November 2023

The transcription factor peroxisome proliferator‐activated receptor‐γ (PPARγ) regulates vascular function and protects against endothelial dysfunction by regulation of target genes. Retinol binding protein 7 (RBP7) is a PPARγ target gene that is specifically expressed in endothelial cells (ECs), but its function remains unknown. We hypothesize that RBP7 plays a protective role in endothelium. RBP7 deficient mice and their control littermates were treated with either a high fat diet (HFD, 8 or 20 weeks) or a subpressor dose of angiotensin‐II (Ang‐II, 120 ng/kg/min, 2 weeks), and basilar and carotid artery function were evaluated with pressure and wire myograph, respectively. RBP7 deletion did not alter endothelium‐dependent acetylcholine (ACh)‐induced relaxation in the absence of HFD or Ang‐II. However, ACh‐induced relaxation was significantly impaired in HFD‐ or Ang‐II‐treated RBP7 deficient mice, but not in control mice (p<0.05, n=5–9). This was not due to elevated blood pressure, excess weight gain, impaired glucose homeostasis or hepatosteatosis. Moreover, pre‐incubation with superoxide scavenger tempol (1 mM) or PEG‐superoxide dismutase (100 U/ml) significantly ameliorated the dysfunction (p<0.05, n=5–7). RNA‐Sequencing on DMSO‐ or rosiglitazone‐incubated carotid arteries from control and RBP7 deficient mice revealed that RBP7 was required for the induction of many PPARγ target genes including adiponectin (AdipoQ). AdipoQ was robustly induced by rosiglitazone in carotid artery from control but not RBP7 deficient mice (n=3–4), which was validated by qPCR (n=6–8). These data suggest that RBP7 plays a role in regulating PPARγ transcriptional activity and that AdipoQ might be a potential downstream target of RBP7 in the endothelium. We next used magnetic activated cell sorting to show that AdipoQ mRNA was induced by rosiglitazone specifically in aortic CD31+ ECs from control mice, but not CD31− non‐ECs (p<0.05, n=7–9). This response in ECs was blunted by deletion of RBP7. A similar result was observed for AdipoQ protein in aortic endothelium (using dual immunofluorescence staining). To further investigate the functional importance of AdipoQ, carotid artery from subpressor dose of Ang‐II or vehicle treated C57BL/6J mice was incubated with anti‐AdipoQ antibody (anti‐Adn, 5 μg/ml, 12 hr) to neutralize endogenous AdipoQ. ACh‐induced relaxation was significantly impaired by anti‐Adn in carotid artery from Ang‐II‐infused mice, but not vehicle‐treated mice (p<0.05, n=6). Consistent with an endothelial protective role for AdipoQ, incubation with AdipoQ protein (5 μg/ml) significantly improved ACh‐induced relaxation in basilar and carotid artery from HFD‐ or Ang‐II‐treated RBP7 deficient mice (p<0.05, n=5–8). Mechanistically, AdipoQ reduced aortic superoxide production (dihydroethidium fluorescence) in response to HFD or Ang‐II in RBP7 deficient mice (p<0.05, n=4–8). Thus, we conclude that RBP7 is endothelial protective and is required for the protective action of PPARγ via a mechanism involving AdipoQ.

Support or Funding Information

Grants from the NIH and AHA, research support from the Roy J. Carver Trust.