Angiotensin II type 2 (AT2) receptor is abundantly expressed in vascular smooth muscle cells (VSMC) of the fetal vasculature during late gestation (embryonic day 15–20), during which the blood vessels undergo remodeling. To examine directly the influence of AT2 receptor expression in the developmental biology of VSMC, we studied cultures of VSMC from fetal and postnatal wild-type (Agtr2+) and AT2 receptor null (Agtr2–) mice. Consistent with in vivo data, AT2 receptor binding in cultured Agtr2+ VSMC increased by age, peaking at embryonic day 20, and decreased dramatically after birth. Angiotensin II–induced growth in Agtr2+ VSMC (embryonic day 20) was increased by the AT2 receptor blocker PD123319, indicating that the AT2 receptors are functional and exert an antigrowth effect in Agtr2+ VSMC. Growth of VSMC in response to serum decreased age dependently and was higher in Agtr2– than in Agtr2+, inversely correlating with AT2 receptor expression. However, serum-induced growth in Agtr2+ and Agtr2– VSMC and the exaggerated Agtr2– VSMC growth was maintained even in the presence of PD123319 or losartan, an AT1 receptor blocker. Moreover, Agtr2– VSMC showed greater growth responses to platelet-derived growth factor and basic fibroblast growth factor, indicating that Agtr2– cells exhibit a generalized exaggerated growth phenotype. We studied the mechanism responsible for this phenotype and observed that extracellular signal-regulated kinase (ERK) activity was higher in Agtr2– VSMC at baseline and also in response to serum. ERK kinase inhibitor PD98059 inhibited both growth and ERK phosphorylation dose–dependently, while the regression lines between growth and ERK phosphorylation were identical in Agtr2+ and Agtr2– VSMC, suggesting that increased ERK activity in Agtr2– VSMC is pivotal in the growth enhancement. Furthermore, the difference in ERK phosphorylation between Agtr2+ and Agtr2– was abolished by vanadate but not by okadaic acid, implicating tyrosine phosphatase in the difference in ERK activity. These results suggest that the AT2 receptor expression during the fetal vasculogenesis influences the growth phenotype of VSMC via the modulation of ERK cascade.
We examined the in vivo function of the angiotensin II type 1 receptor (Agtr1) on macrophages in renal fibrosis. Fourteen days after the induction of unilateral ureteral obstruction (UUO), wild-type mice reconstituted with marrow lacking the Agtr1 gene (Agtr1–/–) developed more severe interstitial fibrosis with fewer interstitial macrophages than those in mice reconstituted with Agtr1+/+ marrow. These differences were not observed at day 5 of UUO. The expression of profibrotic genes — including TGF-β1, α1(I) collagen, and α1(III) collagen — was substantially higher in the obstructed kidneys of mice with Agtr1–/– marrow than in those with Agtr1+/+ marrow at day 14 but not at day 5 of UUO. Mice with Agtr1–/– marrow were characterized by reduced numbers of peripheral-blood monocytes and macrophage progenitors in bone marrow. In vivo assays revealed a significantly impaired phagocytic capability in Agtr1–/– macrophages. In vivo treatment of Agtr1+/+ mice with losartan reduced phagocytic capability of Agtr1+/+ macrophages to a level comparable to that of Agtr1–/– macrophages. Thus, during urinary tract obstruction, the Agtr1 on bone marrow–derived macrophages functions to preserve the renal parenchymal architecture, and this function depends in part on its modulatory effect on phagocytosis.
Rodents are the unique species carrying duplicated angiotensin (Ang) type 1 (AT1) receptor genes, Agtr1a and Agtr1b. After separately generating Agtr1a and Agtr1b null mutant mice by gene targeting, we produced double mutant mice homozygous for both Agtr1a and Agtr1b null mutation (Agtr1a-/-; Agtr1b-/-) by mating the single gene mutants. Agtr1a-/-, Agtr1b-/- mice are characterized by normal in utero survival but decreased ex utero survival rate. After birth they are characterized by low body weight gain, marked hypotension, and abnormal kidney morphology including delayed maturity in glomerular growth, hypoplastic papilla, and renal arterial hypertrophy. These abnormal phenotypes are quantitatively similar to those found in mutant mice homozygous for the angiotensinogen gene (Agt-/-), indicating that major biological functions of endogenous Ang elucidated by the abnormal phenotypes of Agt-/- are mediated by the AT1 receptors. Infusion of Ang II, AT1 blockers, or an AT2 blocker was without effect on blood pressure in Agtr1a-/-; Agtr1b-/- mice, indicating that AT2 receptor does not exert acute depressor effects in these mice lacking AT1 receptors. Also, unlike Agt-/- mice, some Agtr1a-/-; Agtr1b-/- mice have a large ventricular septum defect, suggesting that another receptor such as AT2 is functionally activated in Agtr1a-/-, Agtr1b-/- mice.
We have developed chimeric mice carrying 'regional' null mutation of the angiotensin type 1A (AT1A) receptor, the AT1 receptor subtype exclusively present in mouse juxtaglomerular (JG) cells. The chimeric mouse (Agtr1a -/- <--> +/+) is made up of wild-type (Agtr1a +/+) cells or cells homozygous for Agtr1a deletion (Agtr1a -/-). In the latter, the AT1A coding exon was replaced with a reporter gene, lacZ. In Agtr1a -/- <--> +/+ mice, these two clones of cells are found to be clustered and display patchy distributions in the kidney and heart. Tracking of lacZ activities in hetero- (Agtr1a +/-) and homozygous (Agtr1a -/-) deletion mutant offspring from Agtr1a -/- <--> +/+ mice revealed that the promoter activity of Agtr1a is localized in JG cells, afferent arteriolar walls, glomerular mesangial region and endothelial cells, and apical and basolateral proximal tubule membranes. The JG apparatuses of Agtr1a -/- mice are markedly enlarged with intense expression of renin mRNA and protein. In Agtr1a -/- <--> +/+ mice, these changes were proportional to the degree of chimerism. Within a given Agtr1a -/- <--> +/+ mouse, however, the degree of JG hypertrophy/hyperplasia and the expression of renin mRNA and protein were identical between Agtr1a +/+ and Agtr1a -/- cells. Thus, in the in vivo condition tested, the local interaction between angiotensin and the AT1 receptor on the JG cells has little functional contribution to the feedback regulation of JG renin synthesis.
Longevity phenotype in humans results from the influence of environmental and genetic factors. Few gene polymorphisms have been identified so far with a modest effect on lifespan leaving room for the search of other players in the longevity game. It has been recently demonstrated that targeted disruption of the mouse homolog of the human angiotensin II type 1 receptor (AT1R) gene (AGTR1) translates into marked prolongation of animal lifespan (Benigni et al., J Clin Invest 119(3):524–530, 2009). Based on the above study in mice, here we sought to search for AGTR1 variations associated to reduced AT1 receptor protein levels and to prolonged lifespan in humans. AGTR1 was sequenced in 173 Italian centenarians and 376 younger controls. A novel non-synonymous mutation was detected in a centenarian. Two polymorphisms in AGTR1 promoter, rs422858 and rs275653, in complete linkage disequilibrium, were significantly associated with the ability to attain extreme old age. We then replicated the study of rs275653 in a large independent cohort of Japanese origin (598 centenarians and semi-supercentenarians, 422 younger controls) and indeed confirmed its association with exceptional old age. In combined analyses, rs275653 was associated to extreme longevity either at recessive model (P = 0.007, odds ratio (OR) 3.57) or at genotype level (P = 0.015). Significance was maintained after correcting for confounding factors. Fluorescence activated cell sorting analysis revealed that subjects homozygous for the minor allele of rs275653 had less AT1R-positive peripheral blood polymorphonuclear cells. Moreover, rs275653 was associated to lower blood pressure in centenarians. These findings highlight the role of AGTR1 as a possible candidate among longevity-enabling genes.
Electronic supplementary material
The online version of this article (doi:10.1007/s11357-012-9408-8) contains supplementary material, which is available to authorized users.
Angiotensin II type I receptor; Genetic polymorphism; Centenarians; Human longevity
gestational protein restriction affects the renin-angiotensin system (RAS) in uterine artery remains unknown. In this study, we hypothesized that gestational protein restriction
alters the expression of RAS components in uterine artery. In study one, time-scheduled pregnant Sprague Dawley rats were fed a normal or low-protein (LP) diet from Day 3 of pregnancy until they were killed at Days 19 and 22. The uterine arteries were collected and used for gene expression of Ace, Ace2, Agtr1a, Agtr1b, Agtr2, Esr1, and Esr2 by quantitative real-time PCR and/or Western blotting. LP increased plasma levels of angiotensin II in pregnant rats. In the uterine artery, the expressions of Agtr1a, Agtr1b, and Esr1 were increased by LP at Days 19 and 22 of pregnancy, whereas the abundance of AGTR1 and AGTR2 was increased by LP at Day 19 of pregnancy. The expression of Ace2 was not detectable in rat uterine artery. In study two, virgin female rats were ovariectomized and implanted with either 17beta-estradiol (E2), progesterone (P4), both E2 and P4, or placebo pellets until they were killed 7 days later. In rat uterine artery, E2 and P4 reduced the expression of Agtr1a, and E2 increased the expression of Agtr1b and Agtr2, but neither E2 nor P4 regulated the expression of Ace. These results indicate that gestational protein restriction induces an increase in Agtr1 expression in uterine artery, and thus may exacerbate the vasoconstriction to elevated angiotensin II present in maternal circulation, and that female sex hormones also play a role in this process.
Gestational protein restriction increases plasma levels of angiotensin II and AGTR1 and AGTR2 protein levels in late pregnancy; estrogen plays a role in regulating the expression of angiotensin II receptors in rat uterine artery.
angiotensin I converting enzyme; angiotensin II/angiotensin II receptor; developmental origins of health and disease; gestational protein restriction; nutrition; pregnancy; rat; uterine artery
Transforming growth factor beta (TGFβ), a multifunctional cytokine, plays a crucial role in the accumulation of extracellular matrix components in lung fibrosis, where lung fibroblasts are considered to play a major role. Even though the effects of TGFβ on the gene expression of several proteins have been investigated in several lung fibroblast cell lines, the global pattern of response to this cytokine in adult lung fibroblasts is still unknown.
We used Affymetrix oligonucleotide microarrays U95v2, containing approximately 12,000 human genes, to study the transcriptional profile in response to a four hour treatment with TGFβ in control lung fibroblasts and in fibroblasts from patients with idiopathic and scleroderma-associated pulmonary fibrosis. A combination of the Affymetrix change algorithm (Microarray Suite 5) and of analysis of variance models was used to identify TGFβ-regulated genes. Additional criteria were an average up- or down- regulation of at least two fold.
Exposure of fibroblasts to TGFβ had a profound impact on gene expression, resulting in regulation of 129 transcripts. We focused on genes not previously found to be regulated by TGFβ in lung fibroblasts or other cell types, including nuclear co-repressor 2, SMAD specific E3 ubiquitin protein ligase 2 (SMURF2), bone morphogenetic protein 4, and angiotensin II receptor type 1 (AGTR1), and confirmed the microarray results by real time-PCR. Western Blotting confirmed induction at the protein level of AGTR1, the most highly induced gene in both control and fibrotic lung fibroblasts among genes encoding for signal transduction molecules.
Upregulation of AGTR1 occurred through the MKK1/MKK2 signalling pathway. Immunohistochemical staining showed AGTR1 expression by lung fibroblasts in fibroblastic foci within biopsies of idiopathic pulmonary fibrosis.
This study identifies several novel TGFβ targets in lung fibroblasts, and confirms with independent methods the induction of angiotensin II receptor type 1, underlining a potential role for angiotensin II receptor 1 antagonism in the treatment of lung fibrosis.
Both BRCA1 and angiotensin II type 1 receptor (AGTR1) play a critical role in ovarian cancer progression. However, the crosstalk between BRCA1 and AGTR1 signaling pathways remains largely unknown.
BRCA1 promoter methylation was analyzed by bisulfite sequence using primers focused on the core promoter region. Expression levels of BRCA1 and AGTR1 were assessed by immunohistochemistry and real-time PCR. Regression analysis was used to examine the possible relationship between BRCA1 and AGTR1 protein levels. Knockdown or overexpression of BRCA1 was achieved by using a lentiviral vector in 293 T cells and SKOV3 ovarian carcinoma cells, and primary non-mutated and BRCA1-mutated ovarian cancer cells.
BRCA1 dysfunction (BRCA1 mutation or hypermethylated BRCA1 promoter) ovarian cancer showed decreased AGTR1 levels compared to normal tissue. In contrast, AGTR1 expression was increased in non-BRCA1-mutated ovarian cancer. Notably, BRCA1 activation was an effective way to induce AGTR1 expression in primary ovarian cancer cells and a positive correlation exists between BRCA1 and AGTR1 expression in human ovarian cancer specimens.
These results indicate that BRCA1 may be a potential trigger involved in the transcriptional regulation of AGTR1 in the development of ovarian cancer.
BRCA1; Angiotensin II type 1 receptor; Ovarian cancer
To characterize the mode of action of angiotensin II (Ang II) in cardiac remodeling, we generated chimeric mice that are made of both homozygous Ang II receptor type 1A gene (Agtr1a) null mutant cells and Agtr1a intact cells expressing the lacZ gene (ROSA26). Both Agtr1a null and intact myocytes and interstitial cells independently form areas that are randomly distributed throughout the heart. The distribution of ROSA26 cardiomyocytes overlaps completely with that of Ang II binding, indicating that the majority of Ang II receptors reside on cardiomyocytes. When Ang II (1 ng/g body weight/min) was infused for 2 weeks, mice developed mild to moderate hypertension. The proliferating cardiac fibroblasts identified by bromodeoxyuridine staining were present predominantly in the areas surrounded by Agtr1a intact cardiomyocytes. When control chimeric mice made of wild-type cells and ROSA26 cells (i.e., both carrying intact Agtr1a) were infused with Ang II, fibroblast proliferation was found equally in these cardiomyocyte types. When compared with Agtr1a null mutant chimeras, the control chimeras had more extensive cardiac fibrosis, most prominently in perivascular regions. Therefore, in response to Ang II, cardiac fibroblasts proliferate through both the local and systemic action of Ang II. Importantly, the former is determined by the Ang II receptor of neighboring cardiomyocytes, indicating that a communication between myocytes and fibroblasts plays an important role during Ang II–dependent cardiac remodeling.
In the central nervous system, angiotensin II (AngII) binds to angiotensin type 1 receptors (AT1R) to affect autonomic and endocrine functions as well as learning and memory. However, understanding the function of cells containing AT1Rs has been restricted by limited availability of specific antisera, difficulties discriminating AT1 receptor-immunoreactive cells in many brain regions and, the identification of AT1R-containing neurons for physiological and molecular studies. Here, we demonstrate that an Agtr1a bacterial artificial chromosome (BAC) transgenic mouse line that expresses type A AT1Rs (AT1aRs) identified by enhanced green fluorescent protein (EGFP) overcomes these shortcomings. Throughout the brain, AT1aR-EGFP was detected in the nuclei and cytoplasm of cells, most of which were neurons. EGFP often extended into dendritic processes and could be identified either natively or with immunolabeling of EGFP. The distribution of AT1aR-EGFP cells in brain closely corresponded to that reported for AngII binding and AT1aR protein and mRNA. In particular, AT1aR-EGFP cells were in autonomic regions (e.g., hypothalamic paraventricular nucleus, central nucleus of the amygdala, parabrachial nucleus, nuclei of the solitary tract and rostral ventrolateral medulla) and in regions involved in electrolyte and fluid balance (i.e., subfornical organ) and learning and memory (i.e., cerebral cortex and hippocampus). Additionally, dual label electron microscopic studies in select brain areas demonstrate that cells containing AT1aR-EGFP colocalize with AT1R-immunoreactivity. Assessment of AngII-induced free radical production in isolated EGFP cells demonstrated feasibility of studies investigating AT1aR signaling ex vivo. These findings support the utility of Agtr1a BAC transgenic reporter mice for future studies understanding the role of AT1 receptor containing cells in brain function.
autonomic nuclei; hypothalamus; subfornical organ; amygdala; nucleus of the solitary tract; rostral ventrolateral medulla
Angiotensin converting enzyme (ACE)-related pathways influence arrhythmias and sudden cardiac arrest (SCA) risk.
We investigated whether genetic variation in ACE-related pathways are associated with SCA risk. Because these pathways are sex-dependent and influenced by estrogen, we examined these genotype-SCA associations in the full study population, and tested for interaction with gender.
In a population-based case-control study set in King County WA, we genotyped 211 SCA cases (mean age 59, 80% male) and 730 age- and gender-matched controls of European descent for 47 single nucleotide polymorphisms (SNPs) in eight genes (ACE, AGT, REN, AGTR1, AGTR2, ACE2, KNG1, BDKRB2). We examined association of SNPs and haplotypes with SCA risk using logistic regression.
AGTR1 SNP rs1492099 (allele frequency=15%) was associated with decreased SCA risk (OR=0.62, 95%CI=0.4–0.9). Haplotype variation in AGTR2 was associated with SCA risk (global haplotype test p=0.001), with haplotype 2 (allele frequency=27%) associated with increased risk (OR=1.26, 95%CI=1.1–1.5). There was interaction with gender on SCA risk for variation in KNG1 (interaction p-value range=0.0004–0.017 for 6/8 SNPs). KNG1 SNP rs710448 (allele frequency=42%) was associated with decreased risk (OR=0.44, 95%CI=0.3–0.8) among women but not men. Other SNPs and haplotypes in the eight genes examined were not associated with SCA risk after multiple testing correction.
Variation in AGTR1 and AGTR2 are associated with SCA risk in a population-based case-control study. There was evidence of interaction with gender on SCA risk for variation in KNG1. Our findings, if replicated, suggest that variation in genes in ACE-related pathways influence SCA risk.
sudden death; cardiac arrest; epidemiology; genetics; polymorphism; renin-angiotensin system
Single nucleotide polymorphisms (SNPs) in microRNAs (miRNAs) or their target sites (miR-SNPs) within the 3′-UTR of mRNAs are increasingly thought to play a major role in pathological dysregulation of gene expression. Here, we studied the functional role of miR-SNPs on miRNA-mediated post-transcriptional regulation of gene expression. First, analyses were performed on a SNP located in the miR-155 target site within the 3′-UTR of the Angiotensin II type 1 receptor (AGTR1; rs5186, A > C) mRNA. Second, a SNP in the 3′-UTR of the muscle RAS oncogene homolog (MRAS; rs9818870, C > T) mRNA was studied which is located outside of binding sites of miR-195 and miR-135. Using these SNPs we investigated their effects on local RNA structure, on local structural accessibility and on functional miRNA binding, respectively. Systematic computational RNA folding analyses of the allelic mRNAs in either case predicted significant changes of local RNA structure in the vicinity of the cognate miRNA binding sites. Consistently, experimental in vitro probing of RNA showing differential cleavage patterns and reporter gene-based assays indicated functional differences of miRNA-mediated regulation of the two AGTR1 and MRAS alleles. In conclusion, we describe a novel model explaining the functional influence of 3′-UTR-located SNPs on miRNA-mediated control of gene expression via SNP-related changes of local RNA structure in non-coding regions of mRNA. This concept substantially extends the meaning of disease-related SNPs identified in non protein-coding transcribed sequences within or close to miRNA binding sites.
AGTR1; MRAS; RNA secondary structure analysis; SNP; cardiovascular disease; miR-SNP; miRNA
Angiotensin II type 1 receptor (AGTR1) has been reported to play a fibrogenic role in non-alcoholic fatty liver disease (NAFLD). In this study, five variants of the AGTR1 gene (rs3772622, rs3772627, rs3772630, rs3772633, and rs2276736) were examined for their association with susceptibility to NAFLD. Subjects made up of 144 biopsy-proven NAFLD patients and 198 controls were genotyped using TaqMan assays. The liver biopsy specimens were histologically graded and scored according to the method of Brunt. Single locus analysis in pooled subjects revealed no association between each of the five variants with susceptibility to NAFLD. In the Indian ethnic group, the rs2276736, rs3772630 and rs3772627 appear to be protective against NAFLD (p = 0.010, p = 0.016 and p = 0.026, respectively). Haplotype ACGCA is shown to be protective against NAFLD for the Indian ethnic subgroup (p = 0.03). Gene-gene interaction between the AGTR1 gene and the patatin-like phospholipase domain-containing 3 (PNPLA3) gene, which we previously reported as associated with NAFLD in this sample, showed a strong interaction between AGTR1 (rs3772627), AGTRI (rs3772630) and PNPLA3 (rs738409) polymorphisms on NAFLD susceptibility (p = 0.007). Further analysis of the NAFLD patients revealed that the G allele of the AGTR1 rs3772622 is associated with increased fibrosis score (p = 0.003). This is the first study that replicates an association between AGTR1 polymorphism and NAFLD, with further details in histological features of NAFLD. There is lack of evidence to suggest an association between any of the five variants of the AGTR1 gene and NAFLD in the Malays and Chinese. In the Indians, the rs2276736, rs3772630 and rs3772627 appear to protect against NAFLD. We report novel findings of an association between the G allele of the rs3772622 with occurrence of fibrosis and of the gene-gene interaction between AGTR1gene and the much-studied PNPLA3 gene.
Using type 1a angiotensin receptor (AT1a) receptor-deficient (Agtr1a−/−) mice and in vivo autoradiography, we tested the hypothesis that intracellular uptake of ANG II in the kidney and adrenal glands is primarily mediated by AT1a receptors and that the response is regulated by prevailing endogenous ANG II. After pretreatment of wild-type (Agtr1a+/+) and Agtr1a−/− mice (n = 6–9 each group) with or without captopril (25 mg·kg−1 ·day−1) or losartan (10 mg·kg−1 ·day−1) for 2 wk, [125I]Val5-ANG II was infused for 60 min. Intracellular uptake of [125I]Val5-ANG II was determined by quantitative in vivo autoradiography after washout of circulating [125I]Val5-ANG II. Basal intracellular ANG II levels were 65% lower in the kidney (P < 0.001), but plasma ANG II levels were threefold higher, in Agtr1a−/− than wild-type mice (P < 0.01). Although plasma [125I]Val5-ANG II levels were similar, urinary excretion of [125I]Val5-ANG II was fourfold higher in Agtr1a−/− mice (P < 0.001). By contrast, intracellular [125I]Val5-ANG II levels were ~80% lower in the kidney and adrenal glands of Agtr1a−/− mice (P < 0.01). Captopril decreased endogenous plasma and renal ANG II levels (P < 0.01) but increased intracellular uptake of [125I]Val5-ANG II in the kidney and adrenal glands of wild-type and Agtr1a−/− mice (P < 0.01). Losartan largely blocked renal and adrenal uptake of [125I]Val5-ANG II in wild-type and Agtr1a−/− mice. Thus 80% of intracellular ANG II uptake in the kidney and adrenal glands is mediated by AT1a receptors, whereas AT1b receptor- and other non-receptor-mediated mechanisms account for 20% of the response. Our results suggest that AT1a receptor-mediated uptake of extracellular ANG II may play a physiological role in the kidney and adrenal glands.
AT1 receptor-mediated endocytosis; in vivo autoradiography; losartan
The renin–angiotensin system (RAS), mainly associated with the regulation of blood pressure, has been recently investigated in female reproductive organs and the developing foetus. Angiotensin II (Ang II) influences oviductal gamete movements and foetal development, but there is no information about RAS in the early embryo. The aim of this study was to determine whether RAS components are present in the pre-implantation embryo, to determine how early they are expressed and to investigate their putative role at this stage of development. Bovine embryos produced in vitro were used for analysis of RAS transcripts (RT-PCR) and localisation of the receptors AGTR1 and AGTR2 (immunofluorescent labelling). We also investigated the effects of Ang II, Olmesartan (AGTR1 antagonist) and PD123319 (AGTR2 antagonist) on oocyte cleavage, embryo expansion and hatching. Pre-implanted embryos possessed AGTR1 and AGTR2 but not the other RAS components. Both receptors were present in the trophectoderm and in the inner cell mass of the blastocyst. AGTR1 was mainly localised in granular-like structures in the cytoplasm, suggesting its internalisation into clathrin-coated vesicles, and AGTR2 was found mainly in the nuclear membrane and in the mitotic spindle of dividing trophoblastic cells. Treating embryos with PD123319 increased the proportion of hatched embryos compared with the control. These results, the first on RAS in the early embryo, suggest that the pre-implanted embryo responds to Ang II from the mother rather than from the embryo itself. This may be a route by which the maternal RAS influences blastocyst hatching and early embryonic development.
angiotensin II; embryo; development; receptor
Adverse events in pregnancy may ‘programme’ offspring for the later development of cardiovascular disease and hypertension. Previously, using a rodent model of programmed hypertension we have demonstrated the role of the renin-angiotensin system in this process. More recently we showed that a maternal low protein diet resulted in undermethylation of the At1b angiotensin receptor promoter and the early overexpression of this gene in the adrenal of offspring. Here, we investigate the hypothesis that maternal glucocorticoid modulates this effect on fetal DNA methylation and gene expression. We investigated whether treatment of rat dams with the 11β-hydroxylase inhibitor metyrapone, could prevent the epigenetic and gene expression changes we observed. Offspring of mothers subjected to a low protein diet in pregnancy showed reduced adrenal Agtr1b methylation and increased adrenal gene expression as we observed previously. Treatment of mothers with metyrapone for the first 14 days of pregnancy reversed these changes and prevented the appearance of hypertension in the offspring at 4 weeks of age. As a control for non-specific effects of programmed hypertension we studied offspring of mothers treated with dexamethasone from day 15 of pregnancy and showed that, whilst they had raised blood pressure, they failed to show any evidence of Agtr1b methylation or increase in gene expression. We conclude that maternal glucocorticoid in early pregnancy may induce changes in methylation and expression of the Agtr1b gene as these are clearly reversed by an 11 beta-hydroxylase inhibitor. However in later pregnancy a converse effect with dexamethasone could not be demonstrated and this may reflect either an alternative mechanism of this glucocorticoid or a stage-specific influence.
Elevated left ventricular mass (LVM) is a strong predictor of negative cardiovascular outcomes, including heart failure, stroke, and sudden cardiac death. A relationship between close (< 50 m compared with > 150 m) residential proximity to major roadways and higher LVM has previously been described, but the mechanistic pathways that are involved in this relationship are not known. Understanding genetic factors that influence susceptibility to these effects may provide insight into relevant mechanistic pathways.
We set out to determine whether genetic polymorphisms in genes affecting vascular and autonomic function, blood pressure, or inflammation influence the relationship between traffic proximity and LVM.
This was a cross-sectional study of 1,376 genotyped participants in the Multi-Ethnic Study of Atherosclerosis, with cardiac magnetic resonance imaging performed between 2000 and 2002. The impact of tagged single-nucleotide polymorphisms (tagSNPs) and inferred haplotypes in 12 candidate genes (ACE, ADRB2, AGT, AGTR1, ALOX15, EDN1, GRK4, PTGS1, PTGS2, TLR4, VEGFA, and VEGFB) on the relationship between residential proximity to major roadways and LVM was analyzed using multiple linear regression, adjusting for multiple potential confounders.
After accounting for multiple testing and comparing homozygotes, tagSNPs in the type 1 angiotensin II receptor (AGTR1, rs6801836) and arachidonate 15-lipoxygenase (ALOX15, rs2664593) genes were each significantly (q < 0.2) associated with a 9–10% difference in the association between residential proximity to major roadways and LVM. Participants with suboptimal blood pressure control demonstrated stronger interactions between AGTR1 and traffic proximity.
Common polymorphisms in genes responsible for vascular function, inflammation, and oxidative stress appear to modify associations between proximity to major roadways and LVM. Further understanding of how genes modify effects of air pollution on CVD may help guide research efforts into specific mechanistic pathways.
AGTR1; ALOX15; cardiac structure; cardiac MRI; gene-environment interactions; left ventricular mass; traffic, air pollution
The renin-angiotensin system (RAS) is implicated in the response to physiological and psychosocial stressors however its role in stress-related psychiatric disorders is poorly understood. We examined if variation in AGTR1, the gene coding for the type 1 angiotensin II receptor (AT1R), is associated with a diagnosis of depression and differences in white matter hyperintensities and frontotemporal brain volumes. 257 depressed and 116 nondepressed elderly Caucasian subjects completed clinical assessments and provided blood samples for genotyping. We utilized a haplotype-tagging single nucleotide polymorphism (htSNP) analysis to test for variation in AGTR1. 1.5T MRI data for measurement of hyperintense lesions were available on 281 subjects, while 70 subjects completed 3T MRI allowing for measurements of the hippocampus and dorsolateral prefrontal cortex (dlPFC). Two htSNPs exhibited statistically significant frequency differences between diagnostic cohorts: rs10935724 and rs12721331. Although hyperintense lesion volume did not significantly differ by any htSNP, dlPFC and hippocampus volume differed significantly for several htSNPs. Intriguingly, for those htSNPs differing significantly for both dlPFC and hippocampus volume, the variant associated with smaller dlPFC volume was associated with larger hippocampal volume. This supports that genetic variation in AGTR1 is associated with depression and differences in frontotemporal morphology.
Geriatrics; renin-angiotensin system; MRI; genetic polymorphisms; hippocampus; amygdala; prefrontal cortex
The renin-angiotensin system plays a role in the etiology of hypertension and the pathophysiology of cardiac and renal diseases in humans. Ang II is the central product of this system and is involved in regulating immune responses, inflammation, cell growth, and proliferation by acting through Ang II type 1 receptors (AT1 and AT2). Here, we show that targeted disruption of the Agtr1a gene that encodes AT1A results in marked prolongation of life span in mice. Agtr1a–/– mice developed less cardiac and vascular injury, and multiple organs from these mice displayed less oxidative damage than wild-type mice. The longevity phenotype was associated with an increased number of mitochondria and upregulation of the prosurvival genes nicotinamide phosphoribosyltransferase (Nampt) and sirtuin 3 (Sirt3) in the kidney. In cultured tubular epithelial cells, Ang II downregulated Sirt3 mRNA, and this effect was inhibited by an AT1 antagonist. These results demonstrate that disruption of AT1 promotes longevity in mice, possibly through the attenuation of oxidative stress and overexpression of prosurvival genes, and suggests that the Ang II/AT1 pathway may be targeted to influence life span in mammals.
Induction of tolerance against grafted organs is achieved by the immunosuppressive agent cyclosporine, a prominent member of the calcineurin inhibitors. Unfortunately, its lifetime use is associated with hypertension and nephrotoxicity. Several mechanism for cyclosporine induced hypertension have been proposed, i.e. activation of the sympathetic nervous system, endothelin-mediated systemic vasoconstriction, impaired vasodilatation secondary to reduction in prostaglandin and nitric oxide, altered cytosolic calcium translocation, and activation of the renin-angiotensin system (RAS). In this regard the molecular basis for undue RAS activation and an increased signaling of the vasoactive oligopeptide angiotensin II (AngII) remain elusive. Notably, angiotensinogen (AGT) is the precursor of AngII and transcriptional regulation of AGT is controlled by the hepatic nuclear factor HNF4alpha. To better understand the molecular events associated with cyclosporine induced hypertension, we investigated the effect of cyclosporine on HNF4alpha expression and activity and searched for novel HNF4alpha target genes among members of the RAS cascade. Using bioinformatic algorithm and EMSA bandshift assays we identified angiotensin II receptor type 1 (AGTR1), angiotensin I converting enzyme (ACE), and angiotensin I converting enzyme 2 (ACE2) as genes targeted by HNF4alpha. Notably, cyclosporine represses HNF4alpha gene and protein expression and its DNA-binding activity at consensus sequences to AGT, AGTR1, ACE, and ACE2. Consequently, the gene expression of AGT, AGTR1, and ACE2 was significantly reduced as evidenced by quantitative real-time RT-PCR. While RAS is composed of a sophisticated interplay between multiple factors we propose a decrease of ACE2 to enforce AngII signaling via AGTR1 to ultimately result in vasoconstriction and hypertension. Taken collectively we demonstrate cyclosporine to repress HNF4alpha activity through calcineurin inhibitor mediated inhibition of nuclear factor of activation of T-cells (NFAT) which in turn represses HNF4alpha that leads to a disturbed balance of RAS.
the systemic and the uteroplacental renin-angiotensin system (RAS) display dramatic changes during pregnancy. However, whether gestational protein insufficiency affects the expressions of RAS in the placenta remains unknown. In this study, we hypothesized that the expression of Ace2 in the placental labyrinth was reduced by maternal protein restriction. Pregnant Sprague-Dawley rats were fed a normal diet or a low-protein diet (LP) from Day 1 of pregnancy until they were killed at Day 14 or Day 18. The labyrinth zone (LZ) of the placenta was then dissected and snap frozen for expression analysis by quantitative real-time PCR of Ace, Ace2, Agtr1a, Agtr1b, and Agtr2. Formalin-fixed placentas were used for immunohistochemical analysis on ACE and ACE2 proteins. The findings include 1) the expression of Ace2 in rat LZ was reduced by maternal protein restriction in late pregnancy; 2) ACE protein was mainly present in syncytiotrophoblasts, whereas ACE2 protein was found predominantly in fetal mesenchymal tissue and fetal capillaries; 3) Agtr1a was predominant in the rat LZ, and its mRNA levels, but not protein levels, were reduced by LP; 4) expressions of Ace, Ace2, and Agtr1a in the rat LZ and their response to LP occurred in a gender-dependent manner. These results may indicate that a reduced expression of Ace2 and perhaps an associated reduction in angiotensin (1–7) production in the placenta by maternal protein restriction may be responsible for fetal growth restriction and associated programming of adulthood hypertension.
Maternal protein restriction reduces expression of Ace2 and alters expression of Ace and Agtr1 in the rat labyrinth in a gender-specific manner, which may be responsible for the placental programming on adulthood hypertension.
angiotensin I-converting enzyme; labyrinth zone; maternal protein restriction; placenta; pregnancy; rodents; (guinea pigs; mice; rats; voles)
Some studies suggest that polymorphisms in angiotensin-converting enzyme (ACE), angiotensinogen (AGT), angiotensin II type I receptor (AGTR1) and angiotensin II type II receptor (AGTR2) genes may contribute to renal function variation.
Genotyping for single nucleotide polymorphisms (SNPs) in these candidate genes was performed in 2,847 participants from four racial/ethnic groups (African American, Chinese, White and Hispanic) without known cardiovascular disease in the Multi-Ethnic Study of Atherosclerosis. SNP and haplotype analyses were performed to determine associations between genotypes and cross-sectional renal function measurements, including urine albumin excretion (UAE) and estimated glomerular filtration rate (eGFR) using serum creatinine and cystatin C.
Twenty-four ACE SNPs, 10 AGT SNPs, 15 AGTR1 SNPs and 6 AGTR2 SNPs were typed successfully. After adjusting for ancestry, age and gender, 3 SNPs (AGT M235T, AGT rs2148582 and AGTR1 rs2131127) showed associations with an empiric p value <0.05 with the same phenotype in multiple racial/ethnic groups, suggesting replication. The AGT M235T SNP has been shown previously to be associated with diabetic and hypertensive nephropathy. Conclusions: These data suggest that genetic polymorphisms in the renin-angiotensin system are associated with renal phenotypes in the general population, but that many associations differ across racial/ethnic groups.
Renin-angiotensin; ACE; AGT; AGTR1; AGTR2; Albuminuria; Creatinine clearance epidemiology; Genetics
Vascular injury and remodeling are common pathological sequelae of hypertension. Previous studies have suggested that the renin-angiotensin system (RAS) acting through the type I (AT1) angiotensin (AT1)-receptor promotes vascular pathology in hypertension. To study the role of AT1-receptors in this process, we generated mice with cell-specific deletion of AT1-receptors in VSMCs using Cre/Loxp technology. We crossed the SM22α-Cre transgenic mouse line expressing Cre recombinase in smooth muscle cells with a mouse line bearing a conditional allele of the Agtr1a gene (Agtr1a flox), encoding the major murine AT1-receptor isoform (AT1A). In SM22α-Cre+Agtr1a flox/flox (SMKO) mice, AT1A-receptors were efficiently deleted from VSMCs in larger vessels, but not from resistance vessels such as pre-glomerular arterioles. Thus, vasoconstrictor responses to angiotensin II were preserved in SMKOs. To induce hypertensive vascular remodeling, mice were continuously infused with angiotensin II for 4 weeks. During infusion of angiotensin II, blood pressures increased significantly and to a similar extent in SMKOs and controls. In control mice, there was evidence of vascular oxidative stress indicated by enhanced nitrated tyrosine residues in segments of aorta; this was significantly attenuated in SMKOs. Despite these differences in oxidative stress, the extent of aortic medial expansion induced by angiotensin II infusion was virtually identical in both groups. Thus, vascular AT1A-receptors promote oxidative stress in the aortic wall but are not required for remodeling in angiotensin II-dependent hypertension.
angiotensin II; hypertrophy; hyperplasia; aorta; smooth muscle; hypertension
Vascular aging consists of complex and multifaceted processes that may be influenced by genetic polymorphisms of the renin-angiotensin system. A polymorphism in the angiotensin II type 1 receptor gene (AGTR1/rs5186) has been associated with an increased risk for arterial stiffness, hypertension, and ischemic stroke. Despite these identified relationships, the impact of AGTR1 A1166C on white matter integrity and cognition is less clear in a healthy aging population. The present study utilized indices of neuroimaging and neuropsychological assessment to examine the impact of the A1166C polymorphism on subcortical hyperintensities (SH) and cognition in 49 healthy adults between ages 51–85. Using a dominant statistical model (CC + CA (risk) vs. AA), results revealed significantly larger SH volume for individuals with the C1166 variant (p < 0.05, partial eta2 = 0.117) compared with those with the AA genotype. Post hoc analyses indicated that increased SH volume in C allele carriers could not be explained by vascular factors such as pulse pressure or body mass index. In addition, cognitive performance did not differ significantly between groups and was not significantly associated with SH in this cohort. Results suggest that presence of the C1166 variant may serve as a biomarker of risk for suboptimal brain integrity in otherwise healthy older adults prior to changes in cognition.
AGTR1; A1166C; Cerebrovascular aging; Subcortical hyperintensities; Cognition
Analysis of global gene expression in mesenteric control and collateral arteries was used to investigate potential molecules, pathways, and mechanisms responsible for impaired collateral growth in the Spontaneously Hypertensive Rat (SHR). A fundamental difference was observed in overall gene expression pattern in SHR versus Wistar Kyoto (WKY) collaterals; only 6% of genes altered in collaterals were similar between rat strains. Ingenuity® Pathway Analysis (IPA) identified major differences between WKY and SHR in networks and biological functions related to cell growth and proliferation and gene expression. In SHR control arteries, several mechano-sensitive and redox-dependent transcription regulators were downregulated including JUN (−5.2×, P = 0.02), EGR1 (−4.1×, P = 0.01), and NFĸB1 (−1.95×, P = 0.04). Predicted binding sites for NFĸB and AP-1 were present in genes altered in WKY but not SHR collaterals. Immunostaining showed increased NFĸB nuclear translocation in collateral arteries of WKY and apocynin-treated SHR, but not in untreated SHR. siRNA for the p65 subunit suppressed collateral growth in WKY, confirming a functional role of NFkB. Canonical pathways identified by IPA in WKY but not SHR included nitric oxide and renin–angiotensin system signaling. The angiotensin type 1 receptor (AGTR1) exhibited upregulation in WKY collaterals, but downregulation in SHR; pharmacological blockade of AGTR1 with losartan prevented collateral luminal expansion in WKY. Together, these results suggest that collateral growth impairment results from an abnormality in a fundamental regulatory mechanism that occurs at a level between signal transduction and gene transcription and implicate redox-dependent modulation of mechano-sensitive transcription factors such as NFĸB as a potential mechanism.
Arteriogenesis; collateral gene expression; microarray analysis; peripheral vascular disease