Gain-of-function mutant of angiotensin II receptor, type 1A, causes hypertension and cardiovascular fibrosis in mice

Abstract

The role of the renin-angiotensin system has been investigated by overexpression or inactivation of its different genes in animals. However, there is no data concerning the effect of the constitutive activation of any component of the system. A knockin mouse model has been constructed with a gain-of-function mutant of the Ang II receptor, type 1A (AT 1A ), associating a constitutively activating mutation (N111S) with a C-terminal deletion, which impairs receptor internalization and desensitization. In vivo consequences of this mutant receptor expression in homozygous mice recapitulate its in vitro characteristics: the pressor response is more sensitive to Ang II and longer lasting. These mice present with a moderate (~20 mmHg) and stable increase in BP. They also develop early and progressive renal fibrosis and cardiac fibrosis and diastolic dysfunction. However, there was no overt cardiac hypertrophy. The hormonal parameters (lowrenin and inappropriately normal aldosterone productions) mimic those of low-renin human hypertension. This new model reveals that a constitutive activation of AT 1A leads to cardiac and renal fibrosis in spite of a modest effect on BP and will be useful for investigating the role of Ang II in target organs in a model similar to some forms of human hypertension. IntroductionThe Ang II receptor, type 1 (AT 1 ), is a G protein-coupled receptor (GPCR) that transduces the main physiological actions of the renin-angiotensin system (RAS) in target cells. The major signaling events following agonist binding to this receptor are activation of phospholipase C via a Gq protein, mobilization of the calcium intracellular stores, and activation of protein kinase C. MAP kinase and Jak/STAT pathways are also activated and may participate in the hypertrophic actions of Ang II (1). There are 2 AT 1 subtypes in rodents, AT 1A and AT 1B (2, 3); the tissue distribution of the 2 subtypes (4) and knockout experiments in mice (5-7) indicate that cardiovascular, renal, and adrenal actions of Ang II are mainly mediated by AT 1A . The unambiguous role of AT 1 in controlling BP is evidenced in numerous animal models. For example, the knockout of AT 1A in mouse reduces BP (5, 6), and its overexpression by gene duplication increases BP in female mice (8). This role contrasts with the absence of clear involvement of renin angiotensin genes in genetic forms of human hypertension (9).The concept of constitutive activation is an important breakthrough in the understanding of GPCR molecular functions: point mutations stabilize the receptor in an active conformation independent of ligand, resulting in a permanent activation of the

Agonist-Independent Constitutive Activity of Angiotensin II Receptor Promotes Cardiac Remodeling in Mice

“…In several GPCRs, gain-of-function mutations are causative of diseases, but any activating mutations in the coding region of the AT 1 receptor gene have not been identified in hypertension or primary hyperaldosteronism. 9,10 Although knock-in mice with a constitutively activating mutation (substitution of Asn 111 to Ser with a C-terminal deletion) showed low-renin hypertension and progressive fibrosis in kidney and heart, 11 it remains unclear whether constitutive activity of the native AT 1 receptor leads to some phenotypic abnormalities even under circumstances where the production of Ang II is genetically inhibited.…”

Determination of the Exact Molecular Requirements for Type 1 Angiotensin Receptor Epidermal Growth Factor Receptor Transactivation and Cardiomyocyte Hypertrophy

“…13 Moreover, AT 1 R G-protein coupling is sufficient to trigger cardiomyocyte hypertrophy, as seen with [N111G]AT 1A R. This observation is consistent with a recent knock-in study using N111S/⌬329 AT 1 R, which found that mice had significantly larger heart weight/body weight ratios and elevated brain natriuretic peptide levels, although the more profound phenotype was that of hypertension and cardiac fibrosis. 34 Although G␣ q/11 is the obvious candidate for mediating the G protein-dependent effects described herein, it is important to note that other G-protein subunits can be activated by the AT 1 R in both cardiomyocytes and vascular smooth muscle cells. 35 Functional selectivity also describes the ability of ␤-arrestins to act as ligand-regulated scaffolds.…”

Genetics in endocrinology: Genetics of mineralocorticoid excess: an update for clinicians

“…Mice expressing a constitutively active AT1A receptor develop renal and cardiac fibrosis and diastolic dysfunction and present with a moderate and stable increase in blood pressure. This hypertension is associated with a low plasma renin concentration and a normal aldosterone concentration, leading to an increase in plasma ARR (65). These results suggest that, in humans, modifications or defects in the RAS may contribute to the high-aldosterone, low-renin form of hypertension and, in extreme cases, to mineralocorticoid excess.…”

“…The role of the RAS has been investigated in numerous experimental mouse models (63,64,65). Mice lacking the AngII receptor type 1A (AT1A receptor) have low blood pressure (63), whereas female mice overexpressing AT1A receptor display high blood pressure (64).…”