Abstract-We cloned a novel molecule interacting with angiotensin II type 1 receptor, which we named ATRAP (for angiotensin II type 1 receptor-associated protein). Previous in vitro studies showed that ATRAP significantly promotes constitutive internalization of the angiotensin II type 1 receptor and further attenuates angiotensin II-mediated hypertrophic responses in cardiomyocytes. The present study was designed to investigate the putative functional role of ATRAP in cardiac hypertrophy by angiotensin II infusion in vivo. We first examined the effect of angiotensin II infusion on endogenous ATRAP expression in the heart of C57BL/6J wild-type mice. The angiotensin II treatment promoted cardiac hypertrophy, concomitant with a significant decrease in cardiac ATRAP expression, but without significant change in cardiac angiotensin II type 1 receptor expression. We hypothesized that a downregulation of the cardiac ATRAP to angiotensin II type 1 receptor ratio is involved in the pathogenesis of cardiac hypertrophy. To examine this hypothesis, we next generated transgenic mice expressing ATRAP specifically in cardiomyocytes under control of the ␣-myosin heavy chain promoter. In cardiac-specific ATRAP transgenic mice, the development of cardiac hypertrophy, activation of p38 mitogen-activated protein kinase, and expression of hypertrophy-related genes in the context of angiotensin II treatment were completely suppressed, in spite of there being no significant difference in blood pressure on radiotelemetry between the transgenic mice and littermate control mice. These results demonstrate that cardiomyocyte-specific overexpression of ATRAP in vivo abolishes the cardiac hypertrophy provoked by chronic angiotensin II infusion, thereby suggesting ATRAP to be a novel therapeutic target in cardiac hypertrophy. (Hypertension. 2010;55:1157-1164.)Key Words: basic science Ⅲ receptors Ⅲ gene expression/regulation Ⅲ hypertrophy/remodeling Ⅲ angiotensin receptors E vidence suggests that the activation of angiotensin II (Ang II) type 1 receptor (AT 1 R) through the tissue renin-angiotensin system may play an important role in the development of cardiac hypertrophy. The carboxyl-terminal portion of AT 1 R is involved in the control of AT 1 R internalization independent of G protein coupling, and it plays an important role in linking receptor-mediated signal transduction to the specific biological response to Ang II. 1,2 We previously cloned a novel AT 1 R-associated protein (ATRAP) that specifically interacts with the carboxylterminal domain of AT 1 R. [3][4][5][6] We showed that ATRAP is broadly expressed in many tissues, as is AT 1 R, and suppresses Ang II-mediated pathological responses in cardiomyocytes and vascular smooth muscle cells by promoting the constitutive internalization of AT 1 R. 7-9 However, the function of ATRAP in cardiac hypertrophy in vivo still remains to be demonstrated. Thus, the present study was carried out to investigate whether there is a role for ATRAP in the cardiac hypertrophy induced by chronic Ang II ...

BackgroundMetabolic disorders with visceral obesity have become a major medical problem associated with the development of hypertension, type 2 diabetes, and dyslipidemia and, ultimately, life‐threatening cardiovascular and renal diseases. Adipose tissue dysfunction has been proposed as the cause of visceral obesity‐related metabolic disorders, moving the tissue toward a proinflammatory phenotype.Methods and ResultsHere we first report that adipose tissues from patients and mice with metabolic disorders exhibit decreased expression of ATRAP/Agtrap, which is a specific binding modulator of the angiotensin II type 1 receptor, despite its abundant expression in adipose tissues from normal human and control mice. Subsequently, to examine a functional role of ATRAP in the pathophysiology of metabolic disorders, we produced homozygous ATRAP deficient (Agtrap−/−) mice, which exhibited largely normal physiological phenotype at baseline. Under dietary high fat loading, Agtrap−/− mice displayed systemic metabolic dysfunction, characterized by an increased accumulation of pad fat, hypertension, dyslipidemia, and insulin resistance, along with adipose tissue inflammation. Conversely, subcutaneous transplantation of donor fat pads overexpressing ATRAP derived from Agtrap transgenic mice to Agtrap−/− recipient mice improved the systemic metabolic dysfunction.ConclusionsThese results demonstrate that Agtrap−/− mice are an effective model of metabolic disorders with visceral obesity and constitute evidence that ATRAP plays a protective role against insulin resistance, suggesting a new therapeutic target in metabolic disorders. Identification of ATRAP as a novel receptor binding modulator of adipose tissue inflammation not only has cardiovascular significance but may have generalized implication in the regulation of tissue function.

Angiotensin II type 1 receptor (AT1R)–associated protein (ATRAP) promotes AT1R internalization along with suppression of pathological activation of tissue AT1R signaling. However, the functional significance of ATRAP in renal sodium handling and blood pressure regulation under pathological stimuli is not fully resolved. Here we show the blood pressure of mice with a gene-targeted disruption of ATRAP was comparable to that of wild-type mice at baseline. However, in ATRAP-knockout mice, angiotensin II–induced hypertension was exacerbated and the extent of positive sodium balance was increased by angiotensin II. Renal expression of the sodium-proton antiporter 3, a major sodium transporter in the proximal tubules, urinary pH, renal angiotensinogen production, and angiotensin II content was unaffected. Stimulation of the renal expression and activity of the epithelial sodium channel (ENaC), a major sodium transporter in the distal tubules, was significantly enhanced by chronic angiotensin II infusion. The circulating and urinary aldosterone levels were comparable. The blood pressure response and renal ENaC expression by aldosterone were not affected. Thus, ATRAP deficiency exacerbated angiotensin II–mediated hypertension by pathological activation of renal tubular AT1R by angiotensin II. This directly stimulates ENaC in the distal tubules and enhances sodium retention in an aldosterone-independent manner.

These results indicate that activation of aortic vascular ATRAP partially inhibits the Nox4/p22(phox)-ROS-p38MAPK/JNK pathway and pathological aortic hypertrophy provoked by Ang II-mediated hypertension, thereby suggesting ATRAP as a novel receptor-binding modulator of vascular pathophysiology.

ATRAP [ANG II type 1 receptor (AT1R)-associated protein] is a molecule which directly interacts with AT1R and inhibits AT1R signaling. The aim of this study was to examine the effects of continuous ANG II infusion on the intrarenal expression and distribution of ATRAP and to determine the role of AT1R signaling in mediating these effects. C57BL/6 male mice were subjected to vehicle or ANG II infusions at doses of 200, 1,000, or 2,500 ng·kg(-1)·min(-1) for 14 days. ANG II infusion caused significant suppression of ATRAP expression in the kidney but did not affect ATRAP expression in the testis or liver. Although only the highest ANG II dose (2,500 ng·kg(-1)·min(-1)) provoked renal pathological responses, such as an increase in the mRNA expression of angiotensinogen and the α-subunit of the epithelial sodium channel, ANG II-induced decreases in ATRAP were observed even at the lowest dose (200 ng·kg(-1)·min(-1)), particularly in the outer medulla of the kidney, based on immunohistochemical staining and Western blot analysis. The decrease in renal ATRAP expression by ANG II infusion was prevented by treatment with the AT1R-specific blocker olmesartan. In addition, the ANG II-mediated decrease in renal ATRAP expression through AT1R signaling occurred without an ANG II-induced decrease in plasma membrane AT1R expression in the kidney. On the other hand, a transgenic model increase in renal ATRAP expression beyond baseline was accompanied by a constitutive reduction of renal plasma membrane AT1R expression and by the promotion of renal AT1R internalization as well as the decreased induction of angiotensinogen gene expression in response to ANG II. These results suggest that the plasma membrane AT1R level in the kidney is modulated by intrarenal ATRAP expression under physiological and pathophysiological conditions in vivo.

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UMIN000003878.

Previous studies have shown increases in ambulatory short-term blood pressure (BP) variability to be related to cardiovascular disease. In this study, we examined whether the angiotensin II type 1 receptor blocker (ARB) would improve ambulatory shortterm BP variability in hypertensive patients with diabetic nephropathy. A total of 30 patients with type II diabetes, along with hypertension and overt nephropathy, were enrolled in this randomized, two-period, crossover trial of 12 weeks of treatment with losartan (50 mg daily) and telmisartan (40 mg daily). At baseline and at the end of each treatment period, 24-h ambulatory BP monitoring with power spectral analysis of heart rate and measurements of proteinuria, estimated glomerular filtration rate and brachial-ankle pulse wave velocity (baPWV) were performed. After 12 weeks of treatment, 24-h, daytime and nighttime shortterm BP variability, assessed on the basis of the coefficient of variation of ambulatory BP, was significantly decreased by telmisartan. Both losartan and telmisartan reduced urinary protein excretion and baPWV. However, compared with losartan, telmisartan significantly decreased urinary protein excretion, baPWV and low-frequency (LF)-to-high-frequency (HF) ratio, an index of sympathovagal balance. Multiple regression analysis showed significant correlations between urinary protein excretion and baPWV, 24-h LF-to-HF ratio, nighttime systolic BP and 24-h short-term systolic BP variability. These results suggest that ARB, particularly telmisartan, is effective in reducing proteinuria in hypertensive patients with overt diabetic nephropathy, partly through inhibitory effects on ambulatory short-term BP variability and sympathetic nerve activity, in addition to its longer duration of action on nighttime BP reduction.