Abstract 627: The Smooth Muscle-selective RhoGAP Graf3 Is A Critical Regulator Of Vascular Tone And Hypertension
Our ability to effectively treat hypertensive patients is limited by an incomplete understanding of its origin. Activation of RhoA in vascular smooth muscle cells (SMC) has been implicated in the development of vasoconstrictor-induced hypertension (HTN), but until now, the extent that RhoA contributed to basal BP was unknown and the mechanisms that limit RhoA activity in SMC were undetermined. We identified GRAF3 as a RhoA-GAP expressed specifically in SMC in mice and humans and reported that our novel global GRAF3-deficient mice exhibit significant basal HTN (+ 25 mm Hg) that was fully reversed by treatment with a Rho-kinase inhibitor (Nature Comm. 2013;4:2910). One objective of this new study was to test if elevated RhoA-dependent myogenic tone was causal for HTN in global GRAF3-deficient (GRAF3gt/gt) mice. Importantly, normal GRAF3 expression can be permanently restored by Cre recombinase-dependent excision in our model. Thus, we crossed the GRAF3gt/gt mice to the tamoxifen-inducible SM-specific SM MHC- CreERT2 line and measured BP before and after tamoxifen treatment (1mg i.p. for 5 consecutive days). Tamoxifen induced SMC-GRAF3 re-expression and resulted in a complete reversal of MAP (from 123 mmHg to 95 mm Hg). Moreover, RhoA activity and myosin light chain phosphorylation were elevated 2-fold in GRAF3-depleted SMC in vitro and in vivo and isolated vessel segments from GRAF3-deficient mice showed a 2.5 fold increase in Rho kinase-dependent Ang II-induced contractility. Collectively, these findings provide unequivocal evidence that GRAF3 levels in SMC control basal BP homeostasis and that elevated BP in GRAF3gt/gt mice is due to an enhanced, reversible, SMC contractile phenotype. A second objective was to determine whether GRAF3 variations are causally linked to cardiovascular outcomes in hypertensive patients. We found a clear and significant increase in minor allele frequency of a hypertensive GRAF3 locus in patients with HTN and coronary artery disease versus healthy volunteers (0.19 versus 0.30; p<0.05; N=920) and this association was significant regardless of race. Our studies provide a potential mechanism for the hypertensive locus identified within GRAF3 and provide the foundation for the future development of innovative HTN therapies.
Author Disclosures: X. Bai: None. G. Stouffer: None. C. Lee: None. J. Schisler: None. C. Patterson: None. J. Lee: None. A. Oni-Orisan: None. C. Mack: None. J.M. Taylor: None.
- © 2014 by American Heart Association, Inc.