Abstract 068: Role for the Rho-GAP Graf3 in the Pathogenesis of Human Hypertension
Activation of RhoA in vascular smooth muscle cells (SMC) has been linked to vasoconstrictor-induced hypertension (HTN), but the relevance of this pathway to human disease was undetermined. We identified GRAF3 as a RhoA-GAP expressed specifically in SMC in mice and humans and reported that global GRAF3-deficient mice exhibited significant basal HTN (+ 25 mm Hg) that was fully reversed by treatment with a Rho-kinase inhibitor (Nature Comm. 2013;4:2910). Importantly, we recently created a tamoxifen inducible SMC-GRAF3 re-expression model which resulted in a near complete reversal of MAP (from 123 mmHg to 95 mm Hg), indicating that GRAF3's ability to limit RhoA activity in SMC is required for the maintenance of normal BP. Given that a BP-associated locus within the GRAF3 gene was identified by Genome Wide Association, we next sought to characterize the mechanisms that control GRAF3 expression. Through the use of a series of siRNA-dependent approaches in cultured SMC, we found that SMC-specific expression of GRAF3 is mediated by the RhoA/MRTF-A/SRF-signaling axis. Interestingly, RhoA is known to be activated by mechanical forces and we found that GRAF3 expression was significantly increased (8-fold) in vessels subjected to pathological stress. The finding that GRAF3 expression was significantly increased in two separate hypertensive animal models relative to their littermate controls provides further evidence that GRAF3 expression is regulated as part of an auto-regulatory negative feedback loop to inhibit RhoA activity and SMC tone. Interestingly, the BP associated locus maps to the 80Kb first intron of the GRAF3 gene and we found that the minor GRAF3 allele that decreases BP was associated with a significant increase in GRAF3 mRNA in human tibial artery samples (3-fold increase; N=123; p=1e-10 ). We have identified regulatory elements within the hypertensive locus that exhibit SMC-selective transcriptional activity and have shown that a minor allele variation within one of these elements significantly increased transcriptional activity. Our studies add significantly to our understanding of the development and pathophysiologic consequences of hypertension and may lead to novel and perhaps individualized approaches to its treatment.
Author Disclosures: X. Bai: None. K. Mangum: None. C. Mack: None. J.M. Taylor: None.
This research has received full or partial funding support from the American Heart Association, Mid-Atlantic Affiliate (Maryland, North Carolina, South Carolina, Virginia & Washington, DC).
- © 2015 by American Heart Association, Inc.