Common genetic variation in the angiotensinogen (AGT) gene predisposes to essential hypertension (EH) and increased plasma AGT in humans. Gene titration experiments by Smithies and colleagues have confirmed this inference in mouse, with limited further characterization. Various rodent experimental models demonstrate a relation between marked activation of the renin-angiotensin system (RAS) and hypertension through either systemic or renal mechanisms. Whether and how a primary increase in AGT expression alone, with normal homeostasis at play, mediates EH raises several questions. These include the relative contributions of systemic or renal increases in AGT expression to phenotypic manifestation at various stages of EH. Our central hypothesis is that AGT overexpression can, without artificial concomitant increase in renin expression, contributes to disease initiation and progression (a) through either or both systemic and tubular mechanisms and (b) that duration of disease, genetic background, gender, and exposures such as diet and lifestyle modulate clinical manifestation and progression. This application is intended to fill specific gaps in knowledge, spelled out in II.13, about the relationship between primary, homospecific alterations in AGT gene expression and phenotypic manifestation in AGT- mediated hypertension, with a particular focus on the relative contributions of systemic and tubular AGT changes in gene expression in early and late stages of EH development. In the studies proposed here, analysis will be restricted to male animals of the sodium-sensitive genetic background, the C57BL/6J strain. We have generated animals that overexpress mouse (m) AGT either in liver (L) or in proximal tubule (PT). We have validated our L-mAGT model and found that phenotypic expression varies with genetic background. We have also developed and validated a new PT-mAGT model where we have altered the KAP gene by homologous recombination (gene targeting) to insert mAGT downstream from the KAP promoter in its natural genomic environment. This model relies on physiologic, natural regulation of endogenous mouse renin. Our new preliminary data document a significant effect of targeted overexpression in PT in response to 2- week sodium loading in young animals (III.1). The purpose of this final, 1-year resubmission is to achieve minimal objectives on long-term, very valuable investment made over years of both NIH and limited bridge funding from the University of Utah to test (1) the relative contributions of homospecific AGT overexpression in either liver, kidney or at both sites in blood pressure regulation and the pathogenesis of AGT-mediated hypertension, (2) the extent to which chronic dietary intake and/or duration of disease or aging account for EH and its progression in these models . The proposed experiments will clarify the manner in which primary, sustained expression of AGT predisposes to EH in humans, with attendant implications for clinical and therapeutic management.
Over 50% of the population of the United States have essential hypertension, or high blood pressure of unknown cause, by the time they reach 65 years of age, and only a fraction of these patients have their blood pressure under control. The renin-angiotensin system (RAS) is a major controller of blood pressure and of its relationship to dietary salt, but its function is complex because it involves overlapping circulating and tissue systems. We have shown that common genetic variants in the angiotensinogen gene (AGT), a component of the RAS, lead to increased plasma levels of the protein and predisposes to EH. As a result of its expression at multiple sites, AGT is involved in both systemic and renal function. We will use transgenic mice to manipulate expression of the gene at two major sites, namely the liver and the kidney, and test the relative significance of these two sources as a function of genetic background, gender, dietary salt, aging and renin regulation. Our goal is to advance the specificity of clinical management and treatment of EH.
| Ramkumar, Nirupama; Stuart, Deborah; Rees, Sara et al. (2014) Collecting duct-specific knockout of renin attenuates angiotensin II-induced hypertension. Am J Physiol Renal Physiol 307:F931-8 |
| Ramkumar, Nirupama; Stuart, Deborah; Ying, Jian et al. (2013) A possible interaction between systemic and renal angiotensinogen in the control of blood pressure. Am J Hypertens 26:473-80 |
| Ramkumar, Nirupama; Kohan, Donald E (2013) Proximal tubule angiotensinogen modulation of arterial pressure. Curr Opin Nephrol Hypertens 22:32-6 |
| Ying, Jian; Stuart, Deborah; Hillas, Elaine et al. (2012) Overexpression of mouse angiotensinogen in renal proximal tubule causes salt-sensitive hypertension in mice. Am J Hypertens 25:684-9 |
