The renin-angiotensin system is a major regulator of blood pressure and has been implicated in the pathogenesis of hypertension. Angiotensinogen (AGT), the initiating substrate of the system has been genetically linked to hypertension. Two AGT gene variants in the promoter region of the gene have been associated with hypertension and hypertension sequelae. Both variants A-20C and G-217A exhibit increased transcriptional activity in cultured angiotensinogen-expressing cells. We provide compelling preliminary data suggesting that these two variants are functional and physiologically significant. We also provide compelling preliminary data implicating the differential binding of specific transcription factors to the -20 and -217 polymorphisms as the mechanistic explanation for differences in transcriptional activity. In this competitive renewal, we will test the hypothesis that the level of human AGT expression in liver and extra-hepatic tissues, in particular adipose tissue, is dictated by differential transcription factor binding to polymorphic sites in the AGT promoter. We further hypothesize that differential expression of AGT in tissues plays an important role in the regulation of arterial pressure, water and electrolyte homeostasis. We proposed four specific aims to test these novel hypotheses.
Aim 1 is to directly test the hypothesis that mice carrying the -20C allele of AGT when compared to mice carrying the -20A allele exhibit increased expression of AGT, increased recruitment of USF1/2 to the AGT promoter in chromatin, higher levels of circulating AGT and Ang-II, all resulting in elevated arterial pressure.
Aim 2 will test the hypothesis that AGT expression is regulated by the differential binding of USF1/2 to A-20C, and C/EBP? and GR to G-217A, recruitment of these factors to the AGT promoter in chromatin, association with transcriptional co-activators, and by modifications to histone proteins which control the conformation and transcriptional state of chromatin.
Aim 3 will test the hypotheses that the level of mouse AGT expression is decreased in USF1-deficient and USF-2 deficient mice, the levels of -20C AGT are reduced to a greater degree than -20A AGT in USF1- and USF2-deficient mice, and the normal induction of AGT expression in response to a high fat diet in adipose tissue is blunted in USF1-deficient mice. Finally, in aim 4 we will add a new and exciting translational component to test the hypothesis that the level of AGT expression in human adipose tissue correlates with enhanced transcription factor binding to the A-20C and G-217A alleles in chromatin. These studies will allow us to address fundamental mechanisms by which polymorphisms linked to hypertension cause differential expression of AGT in cells and tissues;will provide novel and unique data on the mechanism of AGT regulation in an important and accessible human tissue (i.e. adipose tissue), and will examine the importance of allele-specific AGT production on arterial pressure.
The aims are based on our productivity, generation of robust preliminary data supporting both methods and hypotheses, and the realization of powerful genetic reagents to manipulate the human and endogenous mouse RAS in vivo.

Public Health Relevance

The Angiotensinogen gene is the initiating substrate of the renin-angiotensin system and a major regulator of blood pressure. Angiotensinogen has been implicated in the pathogenesis of hypertension, and has been genetically linked to human essential hypertension. In this proposal, we will define the molecular mechanisms by which two variants in the angiotensinogen gene cause hypertension through studies of human cell lines, transgenic mouse models and human tissues.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL061446-14
Application #
8299969
Study Section
Hypertension and Microcirculation Study Section (HM)
Program Officer
OH, Youngsuk
Project Start
1999-07-15
Project End
2014-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
14
Fiscal Year
2012
Total Cost
$363,439
Indirect Cost
$111,471
Name
University of Iowa
Department
Pharmacology
Type
Schools of Medicine
DUNS #
062761671
City
Iowa City
State
IA
Country
United States
Zip Code
52242
Jo, Fusakazu; Jo, Hiromi; Hilzendeger, Aline M et al. (2015) Brain endoplasmic reticulum stress mechanistically distinguishes the saline-intake and hypertensive response to deoxycorticosterone acetate-salt. Hypertension 65:1341-8
Sequeira-Lopez, Maria Luisa S; Lin, Eugene E; Li, Minghong et al. (2015) The earliest metanephric arteriolar progenitors and their role in kidney vascular development. Am J Physiol Regul Integr Comp Physiol 308:R138-49
Jin, Hong; Gebska, Milena A; Blokhin, Ilya O et al. (2015) Endothelial PPAR-γ protects against vascular thrombosis by downregulating P-selectin expression. Arterioscler Thromb Vasc Biol 35:838-44
Coble, Jeffrey P; Grobe, Justin L; Johnson, Alan Kim et al. (2015) Mechanisms of brain renin angiotensin system-induced drinking and blood pressure: importance of the subfornical organ. Am J Physiol Regul Integr Comp Physiol 308:R238-49
De Silva, T Michael; Ketsawatsomkron, Pimonrat; Pelham, Christopher et al. (2015) Genetic interference with peroxisome proliferator-activated receptor γ in smooth muscle enhances myogenic tone in the cerebrovasculature via A Rho kinase-dependent mechanism. Hypertension 65:345-51
Sequeira-Lopez, Maria Luisa S; Nagalakshmi, Vidya K; Li, Minghong et al. (2015) Vascular versus tubular renin: role in kidney development. Am J Physiol Regul Integr Comp Physiol 309:R650-7
Ketsawatsomkron, Pimonrat; Sigmund, Curt D (2015) Molecular mechanisms regulating vascular tone by peroxisome proliferator activated receptor gamma. Curr Opin Nephrol Hypertens 24:123-30
De Silva, T Michael; Modrick, Mary L; Ketsawatsomkron, Pimonrat et al. (2014) Role of peroxisome proliferator-activated receptor-γ in vascular muscle in the cerebral circulation. Hypertension 64:1088-93
Coble, Jeffrey P; Johnson, Ralph F; Cassell, Martin D et al. (2014) Activity of protein kinase C-α within the subfornical organ is necessary for fluid intake in response to brain angiotensin. Hypertension 64:141-8
Carrillo-Sepulveda, Maria Alicia; Keen, Henry L; Davis, Deborah R et al. (2014) Role of vascular smooth muscle PPARγ in regulating AT1 receptor signaling and angiotensin II-dependent hypertension. PLoS One 9:e103786

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