Dissertation
Vascular rho-related BTB domain-containing protein 1 (RhoBTB1) in hypertension and aortic stiffness
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2022
DOI: 10.17077/etd.006355
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.
Details
- Title: Subtitle
- Vascular rho-related BTB domain-containing protein 1 (RhoBTB1) in hypertension and aortic stiffness
- Creators
- Shi Fang
- Contributors
- Curt D. Sigmund (Advisor)Frank M Faraci (Committee Member)Isabella Grumbach (Committee Member)Frederick W Quelle (Committee Member)Kamal Rahmouni (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Pharmacology
- Date degree season
- Spring 2022
- DOI
- 10.17077/etd.006355
- Publisher
- University of Iowa
- Number of pages
- xii, 123 pages
- Copyright
- Copyright 2022 Shi Fang
- Language
- English
- Description illustrations
- Illustrations (some color), charts, table
- Description bibliographic
- Includes bibliographical references (pages 114-123).
- Public Abstract (ETD)
This thesis is dedicated to understanding the role of a protein called RhoBTB1 with a focus on hypertension and aortic stiffness.
Globally, cardiovascular disease is the No.1 cause of death. Controlling blood pressure and aortic stiffness will greatly decrease such risk. Since the amount of RhoBTB1 in the blood vessels was decreased in hypertension and aortic stiffness, we wondered if we could reverse the disease by restoring the level of RhoBTB1.
First, we restored RhoBTB1 in a hypertension model mediated by a single genetic mutation in blood vessels. Interestingly, we completely lowered the blood pressure, decreased aortic stiffness, and improved vascular function by restoring RhoBTB1 in blood vessels. We later found out that RhoBTB1 did these by targeting another protein called PDE5, which degrades the substance needed for vasodilation.
Next, we restored RhoBTB1 in a hypertension model established by infusing a hypertension-causing hormone called Ang-II into the whole body. This time, we found that restoring RhoBTB1 in the blood vessels only rescued the aortic stiffness but not the blood pressure. Additionally, we studied how RhoBTB1 decreased aortic stiffness and found that RhoBTB1 changed the organization of the cytoskeleton, a class of substances that maintains the shape and mechanical strength of the cells.
In summary, the protective effects of RhoBTB1 are exerted through different mechanisms to various degrees depending on the cause of the disease. Such knowledge will help us target cardiovascular disease more accurately and effectively.
- Academic Unit
- Neuroscience and Pharmacology
- Record Identifier
- 9984271355102771
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