Vascular rho-related BTB domain-containing protein 1 (RhoBTB1) in hypertension and aortic stiffness
Year: 2022
Type: dissertation
Abstract: Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcription factor that controls the transactivation of hundreds of target genes including RHOBTB1. Both genetic and pharmacological evidence suggested that PPARγ exerts cardioprotection and can lower arterial blood pressure but the target genes that mediate the anti-hypertensive effect of PPARγ remain unclear. Rho-related BTB domain-containing protein 1 (RhoBTB1) is an atypical Rho GTPase whose function is obscure. Notably, two genome-wide association studies (GWAS) reported association between RHOBTB1 with blood pressure. To understand whether RhoBTB1 mediates the anti-hypertensive effect of PPARγ, we first utilized S-P467L mice which express a dominant-negative PPARγ mutation (P467L) specifically in smooth muscle. The P467L mutation in PPARγ causes human hypertension. As a transcriptional target of PPARγ, RhoBTB1 was significantly lowered in the aorta of S-P467L mice. Remarkably, restoration of RhoBTB1 in the vasculature by genetic complementation reversed hypertension, aortic stiffness, and impaired vasodilation in the S-P467L mice. Further mechanistic studies showed that RhoBTB1 downregulated the activity of phosphodiesterase 5 (PDE5) which is a negative regulator of the vasodilation pathway mediated by nitric oxide/cGMP. Moreover, RhoBTB1 increased the ubiquitination of PDE5 in a Cullin-3-dependent manner, suggesting that RhoBTB1 might serve as a substrate adaptor for Cullin-3-RING E3 ubiquitin ligase. Next, we studied the role of RhoBTB1 in angiotensin II (Ang-II)-mediated hypertension because the renin-angiotensin system is an important determinant in clinical hypertension and inhibitors of the renin-angiotensin system are widely used in human patients to control their hypertension. Systemic infusion of Ang-II in mice led to hypertension, increased aortic stiffness, impaired vascular reactivity, and decreased RhoBTB1 expression in the aorta. Restoring RhoBTB1 in the vasculature in mice with pre-established Ang-II hypertension attenuated the aortic stiffness but did not lower the blood pressure or improve vascular function. To understand how RhoBTB1 lowered aortic stiffness, we employed RNA-seq along with various biochemical assays to interrogate individual mechanistic contributors to aortic stiffness. Interestingly, RhoBTB1 showed no profound effect on several classical aortic stiffness contributors such as collagen deposition, elastin abundance, vascular wall area, among others. Instead, restoration of RhoBTB1 abolished the increase of actin polymerization caused by Ang-II. Additionally, in response to RhoBTB1 restoration, changes in the protein levels of two actin polymerization regulators, Cofilin and vasodilator-stimulated phosphoprotein (VASP), were consistent with the changes in actin polymerization. Collectively, our studies revealed distinct physiological and molecular functions of RhoBTB1 in the vasculature.
DOI: 10.17077/etd.006355
Authors: Shi Fang, Frederick W Quelle, Kamal Rahmouni, Curt D. Sigmund, Frank M Faraci, Isabella Grumbach
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W4300598900