Glucocorticoid induction of rat angiotensin II type 1A receptor gene promoter

Hypertension in Patients with Cardiac Transplantation

Hypertension is a common complication among post cardiac transplant recipients affecting more than 95% of patients. Increased blood pressure poses a significant cardiovascular morbidity and mortality in these patients; it should be identified quickly and needs to be managed appropriately. Understanding the pathophysiology and contributing factors to this disease in these complex and unique patients is the key to appropriate treatment selection.

High sucrose intake during gestation increases angiotensin II type 1 receptor-mediated vascular contractility associated with epigenetic alterations in aged offspring rats

Accruing evidence have confirmed that the fetal programming in response to adverse environmental in utero factors plays essential roles in the pathogenesis of hypertension in later life. High sugar intake has been accepted worldwide in everyday life diet and becomes the critical public health issue. Our previous studies indicated that intake of high sucrose (HS) during pregnancy could change the vascular reactivity and dipsogenic behavior closely associated with abnormal renin-angiotensin system (RAS), to increase the risk of hypertension in adult offspring. In the present study, we tested the hypothesis that maternal HS intake in pregnancy may further deteriorate the Ang II-induced cardiovascular responses in the aged offspring. HS intake was provided to pregnant rats throughout the gestation. Blood pressure (BP) in conscious state and vascular contractility in vitro were measured in 22-month-old aged offspring rats. In addition, mRNA and protein expressions and epigenetic changes of Ang II type 1 receptor (AT₁R) gene in blood vessels were determined with the methods of real-time RT-PCR, Western blotting, and Chromatin Immunoprecipitation Assay (CHIP). Results showed that, in the aged offspring, maternal HS intake during gestation would cause the elevation of basal BP which could be diminished by losartan. Although the circulatory Ang II was not changed, levels of local Ang II were significantly increased in blood vessels. In addition, prenatal HS exposure would significantly enhance the AT₁R-mediated vasoconstrictions in both aorta and mesenteric arteries of the aged offspring. Moreover, in the aged offspring of prenatal HS exposure, mRNA and protein expressions of AT₁R gene in both large and small blood vessels were significantly increased, which should be closely associated with the changes of epigenetic mechanisms such as histone modifications. Collectively, we proposed that maternal HS intake during gestation would cause abnormal BP responses mediated via the enhancement of vascular RAS, together with the increased expression of AT₁R gene related to the its epigenetic changes, which would actually lead to the overt phenotype of hypertension in the aged offspring.

Interactions of the gasotransmitters contribute to microvascular tone (dys)regulation in the preterm neonate

BACKGROUND & AIMS

Hydrogen sulphide (H2S), nitric oxide (NO), and carbon monoxide (CO) are involved in transitional microvascular tone dysregulation in the preterm infant; however there is conflicting evidence on the interaction of these gasotransmitters, and their overall contribution to the microcirculation in newborns is not known. The aim of this study was to measure the levels of all 3 gasotransmitters, characterise their interrelationships and elucidate their combined effects on microvascular blood flow.

METHODS

90 preterm neonates were studied at 24h postnatal age. Microvascular studies were performed by laser Doppler. Arterial COHb levels (a measure of CO) were determined through co-oximetry. NO was measured as nitrate and nitrite in urine. H2S was measured as thiosulphate by liquid chromatography. Relationships between levels of the gasotransmitters and microvascular blood flow were assessed through partial correlation controlling for the influence of gestational age. Structural equation modelling was used to examine the combination of these effects on microvascular blood flow and derive a theoretical model of their interactions.

RESULTS

No relationship was observed between NO and CO (p = 0.18, r = 0.18). A positive relationship between NO and H2S (p = 0.008, r = 0.28) and an inverse relationship between CO and H2S (p = 0.01, r = -0.33) exists. Structural equation modelling was used to examine the combination of these effects on microvascular blood flow. The model with the best fit is presented.

CONCLUSIONS

The relationships between NO and H2S, and CO and H2S may be of importance in the preterm newborn, particularly as NO levels in males are associated with higher H2S levels and higher microvascular blood flow and CO in females appears to convey protection against vascular dysregulation. Here we present a theoretical model of these interactions and their overall effects on microvascular flow in the preterm newborn, upon which future mechanistic studies may be based.

Nephron-specific expression of components of the renin-angiotensin-aldosterone system in the mouse kidney

INTRODUCTION

The renin-angiotensin-aldosterone system (RAAS) plays an integral role in the regulation of blood pressure, electrolyte and fluid homeostasis in mammals. The capability of the different nephron segments to form components of the RAAS is only partially known. This study therefore aimed to characterize the nephron-specific expression of RAAS components within the mouse kidney.

MATERIALS AND METHODS

Defined nephron segments of adult C57B/16 mice were microdissected after collagenase digestion. The gene expression of renin, angiotensinogen (AGT), angiotensin-converting enzyme (ACE), angiotensin II receptors 1a (AT1a), 1b (AT1b), and 2 (AT2) was assessed by reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

Renin mRNA was present in glomeruli, in proximal tubules, in distal convoluted tubules (DCT) and cortical collecting ducts (CCD). AGT mRNA was found in proximal tubules, descending thin limb of Henle's loop (dTL) and in the medullary part of the thick ascending limb (mTAL). ACE mRNA was not detectable in microdissected mouse nephron segments. AT1a, AT1b and AT2 mRNA was detected in glomeruli and proximal convoluted tubules.

CONCLUSIONS

Our data demonstrate a nephron-specific distribution of RAAS components. All components of the local RAAS - except ACE - are present in proximal convoluted tubules, emphasizing their involvement in sodium and water handling.

Interplay between miR-155, AT1R A1166C polymorphism, and AT1R expression in young untreated hypertensives

BACKGROUND

A silent polymorphism (+1166 A/C single-nucleotide polymorphism) localized in the 3'-UTR (untranslated region) of the human angiotensin II type-1 receptor (AT1R) has been associated with hypertension and cardiovascular complications. The +1166 A/C is recognized by a specific microRNA-155 (miR-155), which is base-pairing complementary with the +1166 A-allele but not with the mutant +1166 C allele. Aim of our study was to investigate the interplay between miR-155 and AT1R protein expression.

METHODS

Sixty-four subjects were selected for the +1166 A/C from the cohort of hypertensives (n = 573) of the Hypertension and Ambulatory Recording Venetia Study (HARVEST): 25 were homozygous for the 1166 A allele, 20 heterozygous, and 19 homozygous for the 1166 C allele.

RESULTS

miR-155 expression was significantly decreased in subjects with CC genotype in comparison to AA and AC genotype. AT1R protein expression was significantly increased in the CC group in comparison to AA and AC (P < 0.01) although AT1R mRNA expression was not significantly different in the three groups. AT1R protein expression was positively correlated with systolic and diastolic blood pressure and negatively correlated with miR-155 expression level. Plasma transforming growth factor-β1 (TGF-β1) may have a modulator role in the interplay between miR-155 and AT1R protein expression as it was correlated negatively with miR-155 expression and positively with AT1R protein expression in subjects with CC genotype.

CONCLUSION

The interplay between miR-155 expression, +1166C polymorphism, and AT1R protein expression may have a role in the regulation of blood pressure.

Angiotensin II receptors and drug discovery in cardiovascular disease

Hypertension is one of the cardiovascular diseases that might cause cardiovascular remodeling and endothelial dysfunction besides high blood pressure. Angiotensin II (Ang II) receptors are implicated in hypertension. Genetic and epigenetic manipulations of the Ang II receptors play a crucial part in the programming of cardiovascular diseases, and certain variants of the Ang II type 1 and Ang II type 2 receptors are constitutively predisposed to higher cardiovascular risk and hypertension. In this review, we focus on the expression, mode of action of Ang II receptors, and their role in programming the cardiovascular diseases in utero. In addition, we discuss possible therapeutic interventions of Ang II stimulation. Collectively, this information might lead us to new drug designs against cardiovascular diseases.

A critical role for vascular smooth muscle in acute glucocorticoid-induced hypertension

Although glucocorticoid (GC)-induced hypertension has commonly been attributed to promiscuous activation of the mineralocorticoid receptor by cortisol, thereby promoting excess reabsorption of sodium and water, numerous lines of evidence indicate that this is not the only or perhaps even the primary mechanism. GC induce a number of effects on vascular smooth muscle (VSM) in vitro that may be pertinent to hypertension, but their contribution in vivo is unknown. To address this question, a mouse model with a tissue-specific knockout (KO) of the GC receptor in the VSM was created and characterized. Similar to control mice, KO mice exhibited normal baseline BP and, interestingly, showed normal circadian variation in BP. When dexamethasone was administered, however, the acute hypertensive response was markedly attenuated in KO mice, and there was a trend toward a decreased chronic hypertensive response. These data suggest that the GC receptor in VSM plays a critical role in the acute hypertensive response to GC in vivo.

Effects of dexamethasone exposure on rat metanephric development: in vitro and in vivo studies

Maternal administration of dexamethasone (DEX) for 48 h early in rat kidney development results in offspring with a reduced nephron endowment. However, the mechanism through which DEX inhibits nephrogenesis is unknown. In this study, we hypothesized that DEX may indirectly inhibit nephrogenesis by inhibiting ureteric branching morphogenesis. Whole metanephroi from embryonic day 14.5 (E14.5) rat embryos were cultured in the presence of DEX. DEX (10(-5) M) exposure for 2 days significantly inhibited ureteric branching compared with metanephroi grown in control media or DEX (10(-7) M). Culturing metanephroi for a further 3 days (in control media only) reduced total glomerular number in metanephroi previously exposed to DEX (10(-5) M) or (10(-7) M) compared with control cultures. Expression of genes known to regulate ureteric branching morphogenesis was determined by real-time PCR in metanephroi after 2 days in culture. DEX exposure in vitro decreased expression of glial cell line-derived neurotrophic factor (GDNF) and increased expression of bone morphogenetic protein-4 (BMP-4) and transforming growth factor-beta1 (TGF-beta1). Similar gene expression changes were found in E16.5 metanephroi in which the dam had been exposed to 2 days of DEX (0.2 mg.kg(-1).day(-1)) at E14.5/15.5 in vivo. However, in kidneys collected at E20.5 after in vivo exposure for 2 days, GDNF expression was increased and BMP-4 and TGF-beta1 expression decreased suggesting a biphasic response in gene expression to DEX exposure. These results show for the first time that inhibition of ureteric branching morphogenesis may be a key mechanism through which DEX exposure results in a reduced nephron endowment.

Inhibition of catecholamine-induced cardiac fibrosis by an aldosterone antagonist

In heart failure, the renin-angiotensin-aldosterone and the sympathetic systems are overactivated and lead to formation of cardiac fibrosis, which contributes to the aggravation of cardiac function. The aim of the present study was to evaluate the role of aldosterone and angiotensin II on formation of left ventricular fibrosis induced by chronic beta-adrenergic stimulation with isoproterenol (iso) in the rat heart failure model induced by myocardial infarction (MI). Rats were submitted to chronic treatment with either the aldosterone receptor antagonist potassium canrenoate (pc, 20 mg/kg/d) or both aldosterone and angiotensin II receptor antagonists with addition of losartan (los, 10 mg/kg/d). Isoproterenol induced cardiac hypertrophy, which was completely inhibited by potassium canrenoate alone in atria and by potassium canrenoate plus losartan in infarcted ventricles. Isoproterenol also induced cardiac fibrosis, which was completely inhibited in infarcted rats by potassium canrenoate alone in right and left ventricles. In left ventricle, extent of fibrosis was, for control MI, 1.30 +/- 0.34%; MI + iso, 2.50 +/- 0.27%; MI + iso + pc, 0.82 +/- 0.11%; and MI + iso + pc + los, 1.47 +/- 0.31%. The deleterious effects of beta-adrenoceptor stimulation on cardiac fibrosis seem therefore to involve aldosterone action. These results suggest a transregulation between the adrenergic and mineralocorticoid pathways, most likely at the nucleus level, with activation of profibrotic genes.

Centrally regulated blood pressure response to vasoactive peptides is modulated by corticosterone

To investigate the role of brain glucocorticoid (GR) and mineralocorticoid receptors (MR) in centrally evoked blood pressure responses, the effects of intracerebroventricular (i.c.v.) administration of angiotensin II and vasopressin were studied in adrenalectomized rats with and without corticosterone or aldosterone replacement. Five groups were examined: (i) Adrenalectomy (ADX); (ii) ADX + a subcutaneously implanted 20-mg corticosterone pellet (low corticosterone); (iii) ADX + 100 mg corticosterone pellet (high corticosterone); (iv) ADX + 6 microg/24 h aldosterone via Alzet minipump (Aldo); and (v) Sham adrenalectomy (Sham). Pressor responses to 150 ng angiotensin II and 50 ng vasopressin i.c.v. were determined in freely moving rats using biotelemetry. The results show that, compared to sham rats, ADX rats showed significantly reduced pressor responses. This reduction of the pressor response to angiotensin II could be reversed and even further enhanced by replacement of the ADX rats with high corticosterone concentrations. In contrast, with aldosterone, a depressor type response was observed. Corticosterone replacement could not restore the pressor response to vasopressin. We conclude that the pressor response to centrally administered vasoactive substances is substantially attenuated by removal of the adrenals and that, in the case of angiotensin II, this is due to the lack of high concentrations of circulating corticosterone occupying both MR and GR. However, predominant MR occupancy appears to play an opposite role and attenuates the angiotensin II-induced pressor response.

Regulation of type-2 corticotropin-releasing hormone receptor mRNA in rat heart by glucocorticoids and urocortin

A novel subtype of corticotropin-releasing hormone (CRH) receptor, designated type-2 CRH receptor (CRHR-2), has been cloned by a number of laboratories, and its mRNA has been found to be distributed not only in the brain but in peripheral tissues such as heart and skeletal muscle. To date, however, the regulation of CRHR-2 mRNA is poorly understood. Therefore, we examined the effect of glucocorticoid treatment, adrenalectomy, and systemic administration of urocortin, a possible endogenous ligand for CRHR-2, on heart CRHR-2 mRNA levels in male Wistar rats, using in situ hybridization histochemistry. CRHR-2 mRNA in the heart was significantly decreased 9 h after systemic administration of urocortin (5 microg/kg b.w.). Systemic administration of corticosterone (CORT; 10 mg/rat/day for 12 days) or CORT pellet (200 mg) implant for 7 and 14 days also decreased CRHR-2 mRNA in the heart, whereas it was unchanged 7 days after adrenalectomy. Thus, similar regulation of CRHR-2 mRNA in the rat heart by its ligand and glucocorticoids was observed. The precise mechanism of the regulation of CRHR-2 mRNA in the heart and the physiologic significance of cardiac CRHR-2 remains to be elucidated.

Inhibition of the expression of the gene for the angiotensin AT1 receptor by angiotensin II in the rat adrenal gland

The expression of angiotensin AT1A and AT1B receptor mRNA after continuous angiotensin II administration was investigated in the rat adrenal gland. Angiotensin AT1 receptor mRNA detected by Northern blot analysis decreased to 52.7+/-16.1% of control after the administration of angiotensin II (20 microg/h) for 24 h, and to 70.8+/-8.0% after 1 week. A low dose of angiotensin II (0.2 microg/h) also decreased angiotensin AT1 receptor mRNA to 73.0+/-5.5% after 1 week. Competitive reverse transcription and polymerase chain reaction (RT-PCR) experiments revealed that both angiotensin AT1A and AT1B receptor mRNAs decreased after administration of angiotensin II (20 or 0.2 microg/h) for 1 week. Analysis of the angiotensin AT1A promoter by using luciferase-reporter system showed that angiotensin II (up to 1 microM) did not have any effects on the promoter activity (106+/-5.7% after 0.1 microM angiotensin II stimulation) in Y1 cells and cultured vascular smooth muscle cells, although phorbol myristate acetate (PMA) decreased the promoter activity by about 40% compared with control. These results suggest that angiotensin AT1 receptor gene expression in the rat adrenal gland is inhibited by angiotensin II and it may not be due to suppression of promoter activity. Other mechanisms such as destabilization of angiotensin AT1 receptor mRNA or angiotensin II-induced increased blood pressure may be involved in the inhibition.

Regulation of angiotensin II receptor subtypes by dexamethasone in rat mesangial cells

The objective of this study was to examine the role of dexamethasone on the expression of angiotensin II (Ang II) receptors in cultured rat mesangial cells. Dexamethasone caused concentration- and time-dependent decreases in 125I-[Sar1,Ala8]Ang II binding that were prevented by glucocorticoid receptor inhibition with mifepristone. A lag time of 24 hours and a dexamethasone concentration of at least 10 nmol/L were necessary for this effect to occur. Dexamethasone-induced reduction of 125I-[Sar1,Ala8]Ang II binding resulted from decreased Ang II type 1 (AT1) receptor density. No change in the apparent dissociation constant was observed. Dexamethasone also markedly inhibited Ang II-dependent inositol phosphate accumulation. Both reverse transcription-polymerase chain reaction and Northern blot analysis using specific short probes from the 3' noncoding region of the cDNA demonstrated the presence of AT1A and AT1B receptor mRNAs in rat mesangial cells, with a slight predominance of AT1B. Therefore, we studied the effect of dexamethasone on the expression of these two subtypes in rat mesangial cells. Dexamethasone produced a time-dependent decrease of AT1B receptor mRNA that was apparent after 6 hours of incubation, whereas AT1A receptor mRNA did not change. Mifepristone also suppressed the dexamethasone-induced decrease in AT1B receptor mRNA. In conclusion, glucocorticoids diminish Ang II receptor density at the mesangial cell surface through a mechanism that implies successive interaction with the glucocorticoid receptor and specific reduction in AT1B receptor mRNA expression. This differential regulation of both AT1 receptor subtypes might allow glucocorticoids to exert adjusted effects in their various target tissues.

Glucocorticoids regulate V1a vasopressin receptor expression by increasing mRNA stability in vascular smooth muscle cells

Enhancement of vascular responsiveness is considered to be one of the major contributing factors observed in glucocorticoid-induced hypertension. We examined the effects of glucocorticoids on V1a arginine vasopressin receptor mRNA and protein levels in vascular smooth muscle cells. Dexamethasone (1 mumol/L) produced a 1.8-fold increase in V1a receptor density without changing its affinity. Steady-state values of V1a receptor mRNA, analyzed by Northern blotting, increased 2.7-fold after a 12-hour exposure to dexamethasone. This effect of dexamethasone was blocked by the glucocorticoid antagonist RU38486 and did not occur in the presence of the protein synthesis inhibitor cycloheximide. The V1a receptor gene transcription rate, determined by nuclear run-off assays, was unchanged in cells treated with dexamethasone for 12 hours. Dexamethasone increased the half-life of V1a receptor mRNA by 2.2-fold. These findings suggest that dexamethasone upregulates the expression of the V1a receptor by increasing mRNA stability rather than by gene transcription and that de novo protein synthesis is involved in this regulation.