The Role of Vascular Smooth Muscle RhoBTB1 in Hypertension

Abstract

Rho‐related BTB domain containing protein 1 (RhoBTB1) is a novel transcriptional target of peroxisome proliferator activated receptor gamma (PPARγ). In a GWAS study of over 1 million subjects, RhoBTB1 was identified as an interacting locus for hypertension. However, the physiological and molecular function of RhoBTB1 is not well‐understood. Previous studies suggest that RhoBTB1 in vascular smooth muscle cells (VSMC) mediates the anti‐hypertensive effect of PPARγ. RhoBTB1 expression was decreased in aortas from mice expressing smooth muscle specific dominant negative PPARγ mutation. Genetic complementation of smooth muscle RhoBTB1 reverses the hypertension, vascular dysfunction and arterial stiffness caused by dominant negative PPARγ mutation. In HEK293 cells, RhoBTB1 interacts with phosphodiesterase 5 (PDE5) and increases PDE5 ubiquitination in a Cullin‐3 dependent manner, suggesting that RhoBTB1 might function as a substrate adaptor for Cullin‐3‐RING ubiquitin ligase and mediate PDE5 turn over.RhoBTB1 expression was also decreased in aortas from mice treated with angiotensin II (Ang‐II, 490ng/kg/min, two weeks). We hypothesized that restoration of VSMC RhoBTB1 will reverse Ang‐II mediated hypertension, vascular dysfunction and arterial stiffness. We treated transgenic mice expressing inducible VSMC specific RhoBTB1 (S‐RhoBTB1 mice) with Ang‐II (490ng/kg/min, six weeks) and activated the transgene with Tamoxifen injections during the third week of Ang‐II infusion. ISM‐Cre mice expressing smooth muscle specific Cre‐recombinase were also treated with Ang‐II and Tamoxifen to serve as control. Blood pressure was measured by radiotelemetry. Ang‐II increased blood pressure in both ISM‐Cre and S‐RhoBTB1 mice to a similar extent. Thus, Ang‐II induced hypertension was not affected by RhoBTB1 transgene expression in VSMC. Carotid artery vasodilation response to acetylcholine and sodium nitroprusside, as well as vasoconstriction response to KCl, serotonin and endothelin‐1 were tested using wire myography. No differences were found in these measures of vascular function between S‐RhoBTB1 mice and ISM‐Cre mice. Arterial stiffness was assessed by pulse wave velocity (PWV). Ang‐II infusion increased PWV to a similar level in ISM‐Cre and S‐RhoBTB1 mice before the transgene induction. PWV of S‐RhoBTB1 mice started to decrease after Tamoxifen whereas PWV of ISM‐Cre mice continued to increase. By the second week after Tamoxifen, RhoBTB1 transgene expression in VSMC significantly attenuated Ang‐II mediated arterial stiffness (ISM‐Cre vs. S‐RhoBTB1 4.21±0.37 vs. 3.17±0.16 mm/ms, p=0.02, n=7–9). This data suggests a potential mechanism where RhoBTB1 improves vascular plasticity independently from blood pressure and is protective against arterial stiffness.Support or Funding InformationNIH R35 HL144807AHA 20PRE35120137