Angiotensin II stimulates the synthesis of angiotensinogen in hepatocytes by inhibiting adenylylcyclase activity and stabilizing angiotensinogen mRNA

Dysfunction of the renin-angiotensin-aldosterone system in human septic shock

Sepsis and septic shock are global healthcare problems associated with mortality rates of up to 40% despite optimal standard-of-care therapy and constitute the primary cause of death in intensive care units worldwide. Circulating biomarkers of septic shock severity may represent a clinically relevant approach to individualize those patients at risk for worse outcomes early in the course of the disease, which may facilitate early and more precise interventions to improve the clinical course. However, currently used septic shock biomarkers, including lactate, may be non-specific and have variable impact on prognosis and/or disease management. Activation of the renin-angiotensin-aldosterone system (RAAS) is likely an early event in septic shock, and studies suggest that an elevated level of renin, the early and committed step in the RAAS cascade, is a better predictor of worse outcomes in septic shock, including mortality, than the current standard-of-care measure of lactate. Despite a robust increase in renin, other elements of the RAAS, including endogenous levels of Ang II, may fail to sufficiently increase to maintain blood pressure, tissue perfusion, and protective immune responses in septic shock patients. We review the current clinical literature regarding the dysfunction of the RAAS in septic shock and potential therapeutic approaches to improve clinical outcomes.

Martin J, Pringle KG. The interacting physiology of COVID-19 and the renin-angiotensin-aldosterone system: Key agents for treatment

SARS‐CoV‐2 interacting with its receptor, angiotensin‐converting enzyme 2 (ACE2), turns the host response to viral infection into a dysregulated uncontrolled inflammatory response. This is because ACE2 limits the production of the peptide angiotensin II (Ang II) and SARS‐CoV‐2, through the destruction of ACE2, allows the uncontrolled production of Ang II. Recovery from trauma requires activation of both a tissue response to injury and activation of a whole‐body response to maintain tissue perfusion. Tissue and circulating renin‐angiotensin systems (RASs) play an essential role in the host response to infection and injury because of the actions of Ang II, mediated via its AT₁ receptor. Both tissue and circulating arms of the renin angiotensin aldosterone system's (RAAS) response to injury need to be regulated. The effects of Ang II and the steroid hormone, aldosterone, on fluid and electrolyte homeostasis and on the circulation are controlled by elaborate feedback networks that respond to alterations in the composition and volume of fluids within the circulatory system. The role of Ang II in the tissue response to injury is however, controlled mainly by its metabolism and conversion to Ang‐(1‐7) by the enzyme ACE2. Ang‐(1‐7) has effects that are contrary to Ang II‐AT₁R mediated effects. Thus, destruction of ACE2 by SARS‐CoV‐2 results in loss of control of the pro‐inflammatory actions of Ang II and tissue destruction. Therefore, it is the response of the host to SARS‐CoV‐2 that is responsible for the pathogenesis of COVID‐19.

Angiotensin and mineralocorticoid receptor antagonism attenuates cardiac oxidative stress in angiotensin II-infused rats

Angiotensin II (Ang II) and aldosterone contribute to hypertension, oxidative stress and cardiovascular damage, but the contributions of aldosterone during Ang II-dependent hypertension are not well defined because of the difficulty to assess each independently. To test the hypothesis that during Ang II infusion, oxidative and nitrosative damage is mediated through both the mineralocorticoid receptor (MR) and angiotensin type 1 receptor (AT1), five groups of Sprague-Dawley rats were studied: (i) control; (ii) Ang II infused (80 ng/min × 28 days); (iii) Ang II + AT1 receptor blocker (ARB; 10 mg losartan/kg per day × 21 days); (iv) Ang II + mineralocorticoid receptor (MR) antagonist (Epl; 100 mg eplerenone/day × 21 days); and (v) Ang II + ARB + Epl (Combo; × 21 days). Both ARB and combination treatments completely alleviated the Ang II-induced hypertension, whereas eplerenone treatment only prolonged the onset of the hypertension. Eplerenone treatment exacerbated the Ang II-mediated increase in plasma and heart aldosterone 2.3- and 1.8-fold, respectively, while ARB treatment reduced both. Chronic MR blockade was sufficient to ameliorate the AT1-mediated increase in oxidative damage. All treatments normalized protein oxidation (nitrotyrosine) levels; however, only ARB and Combo treatments completely reduced lipid peroxidation (4-hydroxynonenal) to control levels. Collectively, these data suggest that receptor signalling, and not the elevated arterial blood pressure, is the principal culprit in the oxidative stress-associated cardiovascular damage in Ang II-dependent hypertension.

Cytologic atypia in the contralateral unaffected breast is related to parity and estrogen-related genes

PURPOSE

The contralateral unaffected breast (CUB) of women with unilateral breast cancer provides a model for the study of breast tissue-based risk factors. Using random fine needle aspiration (rFNA), we have investigated hormonal and gene expression patterns related to atypia in the CUBs of newly diagnosed breast cancer patients.

METHODS

83 women underwent rFNA of the CUB. Cytologic analysis was performed using the Masood Score (MS), atypia was defined as MS > 14. RNA was extracted using 80% of the sample. The expression of 20 hormone related genes was quantified using Taqman Low Density Arrays. Statistical analysis was performed using 2-tailed t tests and linear regression.

RESULTS

Cytological atypia was more frequent in multiparous women (P = 0.0392), and was not associated with any tumor-related features in the affected breast. Masood Score was higher with shorter interval since last pregnancy (R = 0.204, P = 0.0417), higher number of births (R = 0.369, P = 0.0006), and estrogen receptor (ER) negativity of the index cancer (R = -0.203, P = 0.065). Individual cytologic features were associated with aspects of parity. Specifically, anisonucleosis was correlated with shorter interval since last pregnancy (R = 0.318, P = 0.0201), higher number of births (R = 0.382, P = 0.0004), and ER status (R = -0.314, P = 0.0038). Eight estrogen-regulated genes were increased in atypical samples (P < 0.005), including TFF1, AGT, PDZK1, PGR, GREB1, PRLR, CAMK2B, and CCND1.

CONCLUSIONS

Cytologic atypia, and particularly anisonucleosis, is associated with recent and multiple births and ER negative status of the index tumor. Atypical samples showed increased expression of estrogen-related genes, consistent with the role of estrogen exposure in breast cancer development.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Synergistic co-operation of signal transducer and activator of transcription 5B with activator protein 1 in angiotensin II-induced angiotensinogen gene activation in vascular smooth muscle cells

The binding sequences for signal transducer and activator of transcription (STAT) and activator protein 1 have been found in the promoter region of the angiotensinogen gene. We examined whether the elements for activator protein 1 and STAT5B function in angiotensinogen gene activation induced by angiotensin II in vascular smooth muscle cells. Stimulation with angiotensin II increased the level of angiotensinogen mRNA by 2.1-fold in vascular smooth muscle cells. The increased level of angiotensinogen mRNA occurred with concurrent elevations in the levels of STAT5B and c-Jun phosphorylation after stimulation with angiotensin II. Likewise, angiotensin II resulted in similar enhancements of the DNA-binding activity of STAT5B and c-Jun in angiotensin II-induced angiotensinogen expression. Notably, the STAT5B-DNA complex interacted with the c-Jun-DNA complex by forming a stable quaternary complex in angiotensin II-induced angiotensinogen expression. Our findings support a model in which co-operative interaction of STAT5B and activator protein 1 bound to the the promoter region provides maximal activation of angiotensinogen expression by angiotensin II in vascular smooth muscle cells.

Kidney-specific enhancement of ANG II stimulates endogenous intrarenal angiotensinogen in gene-targeted mice

This study was performed in transgenic mice to test the hypothesis that the selective intrarenal overproduction of ANG II increases intrarenal mouse (m) angiotensinogen (AGT) expression. We used the following three groups: 1) single transgenic mice (group A, n = 14) expressing human (h) AGT only in the kidney, 2) double-transgenic mice (group D, n = 13) expressing human renin systemically in addition to hAGT only in the kidney, and 3) wild-type (group W, n = 12) mice. Exogenous hAGT protein is inactive in group A because endogenous mouse renin cannot cleave hAGT to ANG I because of a high species specificity. All mice were monitored from 12 to 18 wk of age. Systolic blood pressure progressively increased from 116 +/- 5 mmHg (12 wk) to 140 +/- 7 (18 wk) in group D. This increase was not observed in groups A or W. Intrarenal hAGT levels were similar in groups A and D; however, hAGT was not detectable in kidneys of group W. Kidney ANG II levels were increased in group D (216 +/- 43 fmol/g) compared with groups A (117 +/- 16) and W (118 +/- 17). However, plasma ANG II concentrations were similar among the three groups. Endogenous renal mAGT mRNA was increased significantly in group D (1.46 +/- 0.19, ratio) compared with groups A (0.97 +/- 0.12) and W (1.00 +/- 0.08). Endogenous renal mAGT protein was also significantly increased in group D compared with groups A and W. Interstitial collagen-positive area, interstitial macrophage/monocyte infiltration, and afferent arteriolar wall thickness were increased significantly in group D compared with groups A and W. These data indicate for the first time that the selective stimulation of intrarenal production of ANG II from hAGT augments endogenous intrarenal mAGT mRNA and protein expression.

Urinary angiotensinogen as a marker of intrarenal angiotensin II activity associated with deterioration of renal function in patients with chronic kidney disease

In chronic kidney disease (CKD), enhanced intrarenal angiotensin II (AngII) is involved in deterioration of renal function, but it is difficult to measure it. For assessment of the potential of urinary angiotensinogen as a marker of intrarenal AngII activity, the correlation of plasma and urinary renin-angiotensin system components, including angiotensinogen, with deterioration of renal function was investigated in 80 patients who had CKD and were not treated with AngII blocking agents. Changes that were induced by 14 d of losartan treatment (25 mg/d) were also measured in 28 patients. Angiotensinogen was measured by RIA of AngI after incubation with renin. Urinary angiotensinogen levels were greater in patients with low estimated GFR and elevated urinary protein and type IV collagen and correlated with renal AngII and type I collagen immunostaining intensities. The risk for deterioration of renal function (i.e., estimated GFR decline of >2.5 ml/min per yr) during a mean follow-up period of 23 mo (maximum 43 mo) was associated with urinary angiotensinogen of >3.0 nmol AngI equivalent per 1 g of urinary creatinine (AngI Eq/g Cre) at enrollment (hazard ratio 3.52). The event-free survival for deterioration of renal function was better in patients with urinary angiotensinogen <3.0 nmol AngI Eq/g Cre than those >3.0 nmol AngI Eq/g Cre. Losartan reduced urinary and plasma angiotensinogen, urinary protein and type IV collagen, and systolic BP, despite concomitant increases in plasma renin and AngII. These data suggest that urinary angiotensinogen is a potentially suitable marker of intrarenal AngII activity associated with increased risk for deterioration of renal function in patients with CKD.

Expression of constitutively active angiotensin receptors in the rostral ventrolateral medulla increases blood pressure

Angiotensin type 1A (AT(1A)) receptors are expressed within the rostral ventrolateral medulla, and microinjections of angiotensin II into this region increase sympathetic vasomotor tone. To determine the effect of sustained increases in AT(1A) receptor density or activity in rostral ventrolateral medulla, we used radiotelemetry to monitor blood pressure in conscious rats before and after bilateral microinjection into the rostral ventrolateral medulla of adenoviruses encoding the wild-type AT(1A) receptor or a constitutively active version of the receptor (Asn111Gly, [N111G]AT(1A)). The constitutively active receptor signals in the absence of angiotensin II. Adenovirus-directed receptor expression was extensively characterized both in vitro and in vivo. We established that adenoviral infection was limited to the rostral ventrolateral medulla and that receptor expression was sustained for > or =10 days; we also observed that adenoviral transgene expression occurs in glia, with no transgene expression observed in neurons of the rostral ventrolateral medulla. Rats receiving the wild-type AT(1A) receptor showed no change in blood pressure, whereas animals receiving the [N111G]AT(1A) receptor displayed an increase in blood pressure that persisted for 3 to 4 days before returning to basal levels. These data indicate that increased AT(1A) receptor activity (not just overexpression) is a primary determinant of efferent drive from rostral ventrolateral medulla and reveal counterregulatory processes that moderate AT(1A) receptor actions at this crucial relay point. More importantly, they imply that constitutive receptor signaling in glia of the rostral ventrolateral medulla can modulate the activity of adjacent neurons to change blood pressure.

Enhanced intrarenal angiotensinogen contributes to early renal injury in spontaneously hypertensive rats

This study was performed to determine whether augmented intrarenal angiotensinogen may contribute to the enhanced renal angiotensin II (Ang II) and associated tissue injury in spontaneously hypertensive rats (SHR). SHR and Wistar-Kyoto rats (WKY) were maintained on a normal diet and killed at either 7 or 14 wk of age. Two groups of SHR received either an Ang II type 1 receptor blocker (ARB; olmesartan, 5 mg/d) or a triple therapy (hydralazine 7.5 mg/d, reserpine 0.15 mg/d, and hydrochlorothiazide 3 mg/d [HRH]) during weeks 7 through 14. Systolic BP and renal Ang II were significantly increased in SHR-14 (n = 8) compared with WKY-7, WKY-14, and SHR-7 (n = 8 each), and ARB treatment prevented these increases (n = 8). However, whereas HRH treatment prevented the development of hypertension in SHR, this combination therapy failed to decrease renal Ang II (n = 8). With the use of urine samples or fixed renal sections, renal injuries in rats were quantified in a semiautomated manner by the following six parameters: (1) urinary excretion rate of total protein, (2) glomerular sclerosis, (3) interstitial expansion, (4) and (5) numbers of monocytes/macrophages in interstitium or glomeruli, and (6) arterial proliferation. Angiotensinogen mRNA and protein levels in kidney cortex, measured by real-time reverse transcriptase-PCR and Western blot analysis, respectively, and all six parameters of renal damage were changed in parallel, and ARB treatment also prevented these increases. However, HRH treatment failed to prevent these increases. These results indicate that SHR have enhanced intrarenal angiotensinogen production that contributes to increased Ang II levels leading to the development of hypertension and renal injury in this strain.

Importance of the renin-angiotensin system in the regulation of arterial blood pressure in conscious mice and rats

AIM

The present experiments were designed to determine the mechanism(s) for increased sensitivity to blockade of the renin-angiotensin system in mice in comparison with rats.

METHODS

Mice and rats, with indwelling femoral arterial and venous catheters, were chronically administered angiotensin II or pharmacological inhibitors of the renin-angiotensin system as sodium intake was altered.

RESULTS

Increasing sodium intake led to suppression of circulating renin, angiotensin II, and aldosterone in rats and mice in the absence of alterations in arterial blood pressure. Additional experiments demonstrated that continuous intravenous infusion of angiotensin II (20 ng kg(-1) min(-1)) significantly increased arterial blood pressure by approximately 35 mmHg in conscious rats at all levels of sodium intake (n = 6). In contrast, arterial pressure was unaffected by angiotensin II infusion in conscious mice under conditions of low sodium intake, although arterial pressure was increased by 16 mmHg when mice were administered a high sodium intake while infused with angiotensin II (n = 6). In comparison, blockade of the endogenous renin-angiotensin system led to significantly greater effects on arterial pressure in mice than rats. Continuous infusion of captopril (30 microg kg(-1) min(-1)) or losartan (100 microg kg(-1) min(-1)) resulted in a 55-90% greater fall in blood pressure in conscious mice in comparison with conscious rats.

CONCLUSION

The present studies indicate that arterial pressure in mice is more dependent upon the endogenous renin-angiotensin system than it is in rats, but mice are more resistant to the hypertensive effects of exogenous angiotensin II.

Antisense oligodeoxynucleotides directed against a novel angiotensinogen mRNA-stabilizing protein reduce blood pressure in spontaneously hypertensive rats

We have previously reported that hypertension in the young spontaneously hypertensive rat (SHR) is associated with an elevation in tissue angiotensinogen and a novel polysomal protein known to stabilize angiotensinogen mRNA. In our current study we determined the role of the mRNA-stabilizing protein in the regulation of tissue angiotensinogen expression and mean arterial pressure (MAP) in the SHR utilizing antisense oligodeoxynucleotide (AON) inhibition. Three AONs (RNASTAAS1, position 31-50; RNASTAAS2, position 21-40; RNASTAAS3, position 143-162 of the cDNA coding for the polysomal protein) were administered intravenously (dose 450, 900, and 1,800 microg/kg; 1 dosage/day over 3 days) in conscious, chronically instrumented male SHRs at the age of 7 wk. Control SHRs received corresponding scrambled oligodeoxynucleotide sequences (SCR1, SCR2, SCR3). Each animal received the increasing dose schedule. RNASTAAS2 resulted in a reduced expression of the polysomal protein to 21% (liver), 12% (brain), 27% (heart), 18% (renal cortex), and 22% (renal medulla) of control. Angiotensinogen expression was inhibited to 54% (liver), 41% (brain), 68% (heart), 52% (renal cortex), and 74% (renal medulla) compared with control SHRs. Decreases in plasma concentrations of angiotensinogen and plasma renin activities were associated with a significant decrease in MAP from 147 +/- 6 mmHg (after SCR2) to 106 +/- 4 mmHg after RNASTAAS2. The effects of the two other AONs on MAP were less (RNASTAAS1, -31 mmHg; RNASTAAS3, -16 mmHg) with corresponding decreases in mRNAs coding for angiotensinogen and the polysomal protein. A significant decrease in intracellular concentrations of the polysomal protein accompanied AON inhibition. The magnitude of effects (-15 to -41 mmHg) was comparable to the effects of captopril (100 mg x kg(-1) x day(-1) for 3 days: -32 mmHg) and an AT(1) receptor antagonist (L-158809, 1.5 mg x kg(-1) x day(-1) for 3 days: -36 mmHg). These data suggest an important role of the mRNA-stabilizing protein for hepatic and extrahepatic angiotensinogen expression and MAP in the SHR.

cAMP-positive regulation of angiotensinogen gene expression and protein secretion in rat adipose tissue

The adipose renin-angiotensin system (RAS) has been assigned to participate in the control of adipose tissue development and in the pathogenesis of obesity-related hypertension. In adipose cells, the biological responses to beta-adrenergic stimulation are mediated by an increase in intracellular cAMP. Because cAMP is known to promote adipogenesis and because an association exists between body fat mass, hypertension, and increased sympathetic stimulation, we examined the influence of cAMP on angiotensinogen (ATG) expression and secretion in rat adipose tissue. Exposure of primary cultured differentiated preadipocytes to the cAMP analog 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) or cAMP-stimulating agents (forskolin and IBMX) results in a significant increase in ATG mRNA levels. In adipose tissue fragments, 8-BrcAMP also increases ATG mRNA levels and protein secretion, but not in the presence of the protein kinase A inhibitor H89. The addition of isoproterenol, known to stimulate the synthesis of intracellular cAMP via beta-adrenoreceptors, had the same stimulatory effect on ATG expression and secretion. These results indicate that cAMP in vitro upregulates ATG expression and secretion in rat adipose tissue via the protein kinase A-dependent pathway. Further studies are required to determine whether this regulatory pathway is activated in human obesity, where increased sympathetic tone is frequently observed, and to elucidate the importance of adipose ATG to the elevated blood pressure observed in this pathological state.

Local renin-angiotensin systems: the unanswered questions

The concept of local renin-angiotensin systems has been introduced almost 20 years ago to explain the beneficial blood pressure-independent effects of ACE inhibitors and AT(1) receptor antagonists in cardiovascular diseases. In the past decade, research has focussed on the local effects of angiotensin II rather than on the mechanism(s) of its local generation. This review addresses several of the unanswered questions with regard to tissue angiotensin II generation, focussing in particular on the heart and vascular wall: (1) what is the origin of the renin that is required to generate angiotensin II locally, (2) where does tissue angiotensin generation occur (intra- versus extracellular), (3) what is the importance of alternative (non-renin, non-ACE) angiotensin-generating enzymes, (4) do ACE inhibitors and AT(1) receptor antagonists exert local effects that are renin-angiotensin system independent (thereby incorrectly leading to the conclusion that they interfere with the local generation or effects of angiotensin II), and (5) to what degree do differences in tissue angiotensin generation underlie the association between cardiovascular diseases and renin-angiotensin system gene polymorphisms?

Effects of chronic ethanol treatment on the angiotensin II-mediated p42/p44 mitogen-activated protein kinase and phosphorylase a activation in rat hepatocytes

We have demonstrated previously that 24 h of ethanol treatment potentiates angiotensin II (ANG II)-stimulated p42/p44 mitogen-activated protein kinase (MAPK) activity in hepatocytes. This potentiation of p42/p44 MAPK by ethanol exhibited agonist selectivity. To compare the effects of acute (24 h) versus chronic (6 weeks) ethanol treatment, ANG II-induced intracellular signaling was examined in (1) rat hepatocytes treated with ethanol for 24 h and (2) hepatocytes obtained from rats fed ethanol for 6 weeks. In hepatocytes obtained from rats fed ethanol for 6 weeks, ANG II-stimulated phosphorylase a was reduced, and this activity was calcium dependent and p42/p44 MAPK independent. Surprisingly, ANG II-stimulated p42/p44 MAPK activation was not affected in hepatocytes obtained from rats fed ethanol chronically (6 weeks). However, chronic (6 weeks) ethanol treatment decreased ethanol potentiation of p42/p44 MAPK by about 56.3% +/- 3.6% for p42 MAPK and 61.3% +/- 11.7% for p44 MAPK. Furthermore, ethanol had no effect on the expression of angiotensinogen and c-myc mRNA in hepatocytes. A decrease in ANG II-activated phosphorylase a, but not in p42/p44 MAPK activation, after chronic (6 weeks) ethanol treatment leads to the conclusion that they may not be dependent on each other.

Prorenin uptake in the heart: a prerequisite for local angiotensin generation?

Interference with locally generated angiotensin II most likely underlies the beneficial effects of renin-angiotensin system blockers in cardiac disorders. Since renin is not synthesized in the heart, this enzyme must be sequestered from the circulation in order to allow angiotensin generation at cardiac tissue sites. This review addresses the various ways through which circulating (i.e., kidney-derived) renin may reach cardiac tissue sites, considering in particular the possibility that prorenin, the inactive precursor of renin, is involved in cardiac angiotensin generation, as the plasma concentrations of prorenin are tenfold higher than those of renin. Renin and prorenin diffuse into the cardiac interstitial space and bind to cardiac (pro)renin receptors/renin-binding proteins. One of these receptors is the mannose 6-phosphate/insulin-like growth factor II receptor. This receptor not only binds mannose 6-phosphate-containing ligands like renin and prorenin, it also internalizes these enzymes, and activates prorenin intracellularly. This process possibly represents (pro)renin clearance, since intracellular angiotensin generation could not be demonstrated following (pro)renin uptake by cardiomyocytes. Angiotensin II-mediated myocyte proliferation did occur when incubating cardiomyocytes with prorenin plus angiotensionogen. The effects of prorenin plus angiotensinogen were comparable to those of 100nmol/l angiotensin II, although the angiotensin II levels in the medium during exposure of the cells to prorenin plus angiotensinogen were <1nmol/l. This suggests that cardiac angiotensin II generation by circulating renin occurs predominantly on the cell surface. The presence of ACE and/or renin on the cell membrane, in the microenvironment of angiotensin receptors, would allow maximal efficiency of local angiotensin II generation, i.e., immediate binding of angiotensin II to its receptors with minimal loss into the extracellular space.

Physiological elevation in plasma angiotensinogen increases blood pressure

Hepatic angiotensinogen secretion is controlled by a complex pattern of physiological or pathophysiological mediators. Because plasma concentrations of angiotensinogen are close to the Michaelis-Menten constant, it was hypothesized that changes in circulating angiotensinogen affect the formation rate of ANG I and ANG II and, therefore, blood pressure. To further test this hypothesis, we injected purified rat angiotensinogen intravenously in Sprague-Dawley rats via the femoral vein and measured mean arterial blood pressure after arterial catheterization. In controls, mean arterial pressure was 131 +/- 2 mmHg before and after the injection of vehicle (sterile saline). The injection of 0.8, 1.2, and 2.9 mg/kg angiotensinogen caused a dose-dependent increase in mean arterial blood pressure of 8 +/- 0.4, 19.3 +/- 2.1, and 32 +/- 2.4 mmHg, respectively. In contrast, the injection of a purified rabbit anti-rat angiotensinogen antibody (1.4 mg/kg) resulted in a significant decrease in mean arterial pressure (-33 +/- 3.2 mmHg). Plasma angiotensinogen increased to 769 +/- 32, 953 +/- 42, and 1,289 +/- 79 pmol/ml, respectively, after substrate and decreased by 361 +/- 28 pmol/ml after antibody administration. Alterations in plasma angiotensinogen correlated well with changes in plasma renin activity. In summary, variations in circulating angiotensinogen can result in changes in blood pressure. In contrast to renin, which is known as a tonic regulator for the generation of ANG I, angiotensinogen may be a factor rather important for long-term control of the basal activity of the renin-angiotensin system.

Enhancement of angiotensinogen expression in angiotensin II-dependent hypertension

Chronic infusion of angiotensin (Ang) II leads to the development of hypertension and enhances intrarenal Ang II content to levels greater than can be explained from the circulating concentrations of the peptide. We previously reported that renal angiotensinogen (Ao) mRNA is enhanced in Ang II-dependent hypertension and may contribute to augmented intrarenal Ang II levels, but the Ao protein levels were not significantly increased. Because a high-salt diet (H/S) has been shown to suppress renal expression of Ao mRNA, we examined the effects of chronic Ang II infusion on kidney and liver Ao mRNA and protein levels in male Sprague-Dawley rats (n=12) maintained on an 8% salt diet. Ang II was administered via osmotic minipumps (40 ng/min) to 1 group (n=6) while the remaining rats were sham-operated. A H/S diet alone did not alter systolic blood pressure in sham animals (109+/-6 mm Hg at day 12); however, Ang II infusions to the H/S rats significantly increased systolic blood pressure (167+/-7 at day 12) and intrarenal Ang II content (459+/-107 fmol/g versus 270+/-42) despite a marked suppression of plasma renin activity (0.9+/-0.2 ng Ang I. mL(-1). h(-1) versus 2.8+/-1.3). Ang II infusions significantly increased kidney Ao mRNA compared with the H/S diet alone by 1.9+/-0.1-fold. Western blot analysis of kidney protein extracts showed that the Ang II-infused rats had increased kidney Ao protein levels compared with the H/S diet alone (1.9+/-0.1-fold). Liver Ao mRNA and protein and plasma Ao protein were also significantly increased by Ang II infusions. These data demonstrate the effects of Ang II infusion to stimulate Ao mRNA and protein. Thus, the augmented intrarenal Ang II in Ang II-dependent hypertension may result, in part, by a positive amplification mechanism to activate renal expression of AO:

Expression of angiotensinogen mRNA and protein in angiotensin II-dependent hypertension

Chronic elevations in circulating angiotensin II (AngII) levels produce sustained hypertension and increased intrarenal AngII contents through multiple mechanisms, which may include sustained or increased local production of AngII. This study was designed to test the hypothesis that chronic AngII infusion increases renal angiotensinogen mRNA and protein levels, thus contributing to the increase in intrarenal AngII levels. AngII (80 ng/min) was infused subcutaneously for 13 d into Sprague-Dawley rats, using osmotic minipumps. Control rats underwent sham operations. By day 12, systolic arterial BP increased to 184 +/- 3 mmHg in AngII-treated rats, whereas values for sham-treated rats remained at control levels (125 +/- 1 mmHg). Plasma renin activity was markedly suppressed (0.2 +/- 0.1 versus 5.3 +/- 1.2 ng AngI/ml per h); however, renal AngII contents were significantly increased in AngII-treated rats (273 +/- 29 versus 99 +/- 18 fmol/g). Western blot analyses of plasma and liver protein using a polyclonal anti-angiotensinogen antibody demonstrated two specific immunoreactive bands, at 52 and 64 kD, whereas kidney tissue exhibited one band, at 52 kD. Densitometric analyses demonstrated that AngII infusion did not alter plasma (52- or 64-kD), renal (52-kD), or hepatic (52-kD) angiotensinogen protein levels; however, there was a significant increase in hepatic expression of the highly glycosylated 64-kD angiotensinogen protein, of almost fourfold (densitometric value/control value ratios of 3.79 +/- 1.16 versus 1.00 +/- 0.35). Renal and hepatic expression of angiotensinogen mRNA, which was examined by semiquantitative reverse transcription-PCR, was significantly increased in AngII-treated rats, compared with shamtreated rats (kidney, densitometric value/glyceraldehyde-3-phosphate dehydrogenase mRNA value ratios of 0.82 +/- 0.11 versus 0.58 +/- 0.04; liver, densitometric value/glyceraldehyde-3-phosphate dehydrogenase mRNA value ratios of 2.34 +/- 0.07 versus 1.32 +/- 0.15). These results indicate that increases in circulating AngII levels increase intrarenal angiotensinogen mRNA levels, which may contribute to the sustained renal AngII-generating capacity that paradoxically occurs in AngII-treated hypertensive rats.

Androgen regulation and site specificity of angiotensinogen gene expression and secretion in rat adipocytes

Adipose tissue is an important source of angiotensinogen (ATG), and hypertension is commonly associated with android obesity. Therefore, we tested the hypothesis that androgens may control ATG gene expression and secretion in rat fat cells. In intact male rats, ATG mRNA expression (Northern blot and co-reverse transcription-polymerase chain reaction analysis) and protein secretion were significantly higher in deep intra-abdominal (perirenal and epididymal) than in subcutaneous adipocytes. After castration, ATG mRNA was reduced almost 50% in the three fat deposits, with parallel changes in ATG protein secretion. Conversely, testosterone treatment fully restored the ATG mRNA decrease after castration, whatever the anatomical origin of the adipocytes. Finally, a 24-h in vitro exposure of perirenal fat cells or differentiated preadipocytes from castrated rats to testosterone or dihydrotestosterone (10 nM free hormone concentration) increased ATG mRNA expression by 50-100%, an effect that was prevented by the anti-androgen cyproterone acetate. These data, demonstrating both in vivo and in vitro androgen induction of ATG mRNA expression in rat adipocytes, add further weight to the hypothesis of a link between adipose tissue ATG production, androgens, and android obesity-related hypertension.

Transcriptional regulation of angiotensinogen gene expression

The renin--angiotensin system (RAS) is an extracellular hormonal system implicated in acute, homeostatic control of peripheral vascular resistance and electrolyte homeostasis. In this tightly regulated system, physiological regulators of blood pressure and fluid balance induce the production of the potent vasoactive angiotensin peptides by sequential proteolysis of the angiotensinogen (AGT) prohormone. AGT is the only known precursor of the angiotensin peptides, whose circulating concentrations influence the tonic activity of the RAS. AGT abundance is regulated at the transcriptional level through hormonal and cell-type specific regulators. In this review, we will discuss the identified mechanisms controlling AGT expression separately for the rodent and human genes. The most intensively investigated gene (rodent AGT) is regulated constitutively by multiple positive- and negative-acting cis factors that function in a cell-type dependent fashion. Inducible rodent AGT expression is mediated through a multihormone-inducible enhancer that integrates signals from steroid and cytokine hormones into AGT transcription. We review recent advances in understanding the mechanism of the nuclear factor-kappa B (NF-kappa B) family in mediating cytokine-induced AGT expression and our recent discoveries on the existence of differentially inducible pools of cytoplasmic NF-kappa B. Constitutive control of the human AGT gene will be discussed; there is surprisingly little information on the cis- and trans-acting regulators controlling inducible expression of human AGT. Finally, we will explore some of the recent developments in gene linkage studies where human AGT alleles have been associated with hypertensive phenotypes through a mechanism that may involve enhanced transcription. These studies have provided a molecular explanation for a subset of heritable hypertensive disorders in humans.

Blood pressure reduction and diabetes insipidus in transgenic rats deficient in brain angiotensinogen

Angiotensin produced systemically or locally in tissues such as the brain plays an important role in the regulation of blood pressure and in the development of hypertension. We have established transgenic rats [TGR(ASrAOGEN)] expressing an antisense RNA against angiotensinogen mRNA specifically in the brain. In these animals, the brain angiotensinogen level is reduced by more than 90% and the drinking response to intracerebroventricular renin infusions is decreased markedly compared with control rats. Blood pressure of transgenic rats is lowered by 8 mmHg (1 mmHg = 133 Pa) compared with control rats. Crossbreeding of TGR(ASrAOGEN) with a hypertensive transgenic rat strain exhibiting elevated angiotensin II levels in tissues results in a marked attenuation of the hypertensive phenotype. Moreover, TGR(ASrAOGEN) exhibit a diabetes insipidus-like syndrome producing an increased amount of urine with decreased osmolarity. The observed reduction in plasma vasopressin by 35% may mediate these phenotypes of TGR(ASrAOGEN). This new animal model presenting long-term and tissue-specific down-regulation of angiotensinogen corroborates the functional significance of local angiotensin production in the brain for the central regulation of blood pressure and for the pathogenesis of hypertension.

Angiotensin-converting enzyme is upregulated in the proximal tubules of rats with intense proteinuria

Persistent proteinuria is considered a deleterious prognostic factor in most progressive renal diseases. However, the mechanisms by which proteinuria induces renal damage remain undetermined. Since proximal tubular cells possess all the machinery to generate angiotensin II (Ang II), we approached the hypothesis that proteinuria could elicit the renal activation of the renin-angiotensin system in a model of intense proteinuria and interstitial nephritis induced by protein overload. After uninephrectomy (UNX), Wistar-Kyoto rats received daily injections of 1 g BSA or saline for 8 days. The mean peak of proteinuria was observed at the fourth day (538+/-89 versus 3+/-1 mg/24 h in UNX controls; n=12; P<0.05) and was increased during the whole study period (at the eighth day: 438+/-49 mg/24 h; n=12; P=NS). Morphological examination of the kidneys at the end of the study showed marked tubular lesions (atrophy, vacuolization, dilation, and casts), interstitial infiltration of mononuclear cells, and mesangial expansion. In relation to UNX control rats, renal cortex of BSA-overloaded rats showed an increment in the gene expression of angiotensinogen (2.4-fold) and angiotensin-converting enzyme (ACE) (2.1-fold), as well as a diminution in renin gene expression. No changes were observed in angiotensin type 1 (AT1) receptor mRNA expression in both groups of rats. By in situ reverse transcription-polymerase chain reaction and immunohistochemistry, ACE expression (gene and protein) was mainly localized in proximal and distal tubules and in the glomeruli. By immunohistochemistry, angiotensinogen was localized only in proximal tubules, and AT1 receptor was localized mainly in proximal and distal tubules. In the tubular brush border, an increase in ACE activity was also seen (5. 5+/-0.5 versus 3.1+/-0.7 U/mg protein x10(-4) in UNX control; n=7; P<0.05). Our results show that in the kidney of rats with intense proteinuria, ACE and angiotensinogen were upregulated, while gene expression of renin was inhibited and AT1 was unmodified. On the whole, these data suggest an increase in Ang II intrarenal generation. Since Ang II can elicit renal cell growth and matrix production through the activation of AT1 receptor, this peptide may be responsible for the tubulointerstitial lesions occurring in this model. These results suggest a novel mechanism by which proteinuria may participate in the progression of renal diseases.

Angiotensin AT1 receptors in Clone 9 rat liver cells: Ca2+ signaling and c-fos expression

In C9 (Clone 9) liver cells, angiotensin 11 increased the intracellular Ca2+ content, inositol phosphate production and c-fos mRNA expression. Other angiotensins were also active with the order of potency being angiotensin II = angiotensin III >> angiotensin I > angiotensin IV. Losartan, but not PD 123177 (1-(4-amino-3-methyl)-5-diphenylacetyl-4,5,6,7-tetrahydro-1H-imida zo [4,5c]pyridine-6-carboxylic acid), blocked the effects of angiotensin II. Pertussis toxin did not alter these actions of angiotensin II. These data indicate that the effects were mediated through angiotensin AT1 receptors involving pertussis toxin-insensitive G-proteins. Phorbol myristate acetate was also able to increase c-fos mRNA expression. The action of angiotensin II was consistently greater than that of the active phorbol ester. Staurosporine but not genistein inhibited this effect of angiotensin II. Angiotensin II- and phorbol myristate acetate-induced proto-oncogene mRNA expression was attenuated in cells incubated overnight with the active phorbol ester, which suggests a major role of protein kinase C.

Erythropoietin upregulates angiotensin receptors in cultured rat vascular smooth muscle cells

OBJECTIVE

Plasma renin is not elevated in recombinant human erythropoietin (rhEPO)-induced hypertension but angiotensin converting enzyme inhibitors reduce blood pressure in both human and animal studies. Since rhEPO elevates renin and angiotensinogen messenger RNAs in angiotensin II target tissues such as the aorta, we explored the actions of rhEPO on renin-angiotensin system-related gene transcription of cultured rat vascular smooth muscle cells.

DESIGN AND METHODS

To separate direct actions of rhEPO from those mediated secondarily by potential activation of the renin-angiotensin system, vascular smooth muscle cells were cultured with rhEPO and enalapril to inhibit the angiotensin converting enzyme and losartan to inhibit angiotensin II type 1 receptors.

RESULTS

Vascular smooth muscle cells cultured with rhEPO (6-8 units/ml) demonstrated elevations (40-120%) in messenger RNAs of the renin-angiotensin system (renin, angiotensinogen, angiotensin receptor types 1 and 2) and increased levels of several messenger RNAs known to respond to angiotensin II (transforming growth factor-beta, insulin-like growth factor-II, epidermal growth factor, c-fos and platelet-derived growth factor). In contrast, cells cultured in the presence of rhEPO and enalapril or losartan showed elevations of messenger RNA for only the two types of angiotensin II receptor. This increase was higher than that obtained when cells were cultured with rhEPO or either antagonist alone. The increase in specific binding of angiotensin II to cells cultured in the presence of rhEPO and enalapril or rhEPO and losartan paralleled the changes in receptor messenger RNA.

CONCLUSIONS

rhEPO exerts its primary action on vascular smooth muscle cells via an increase in angiotensin receptor messenger RNA, resulting in a parallel increase in angiotensin II receptor expression. We suggest that increased receptor expression secondarily mediates the expression of other renin-angiotensin system messenger RNAs, which leads to angiotensin II-responsive gene transcription. The elevation in angiotensin II receptors, as observed in response to rhEPO, may provide a mechanism by which other forms of renin-dependent hypertension are initiated.

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.

Cell type-specific angiotensin II-evoked signal transduction pathways: critical roles of Gbetagamma subunit, Src family, and Ras in cardiac fibroblasts

Angiotensin II (Ang II) induces hypertrophy of cardiac myocytes and hyperplasia of cardiac fibroblasts. To determine the molecular mechanism by which Ang II displayed different effects on cardiac myocytes and fibroblasts, we examined signal transduction pathways leading to activation of extracellular signal-regulated kinases (ERKs). Ang II-induced ERK activation was abolished by pretreatment with pertussis toxin and by overexpression of the Gbetagamma subunit-binding domain of the beta-adrenergic receptor kinase 1 in cardiac fibroblasts but not in cardiac myocytes. Inhibition of protein kinase C strongly inhibited activation of ERKs by Ang II in cardiac myocytes, whereas inhibitors of tyrosine kinases but not of protein kinase C abolished Ang II-induced ERK activation in cardiac fibroblasts. Overexpression of C-terminal Src kinase (Csk), which inactivates Src family tyrosine kinases, suppressed the activation of transfected ERK in cardiac fibroblasts. Ang II rapidly induced phosphorylation of Shc and association of Shc with Grb2. Cotransfection of the dominant-negative mutant of Ras or Raf-1 kinase abolished Ang II-induced ERK activation in cardiac fibroblasts. Overexpression of Csk or the dominant-negative mutant of Ras had no effects on Ang II-induced ERK activation in cardiac myocytes. These findings suggest that Ang II-evoked signal transduction pathways differ among cell types. In cardiac fibroblasts, Ang II activates ERKs through a pathway including the Gbetagamma subunit of Gi protein, tyrosine kinases including Src family tyrosine kinases, Shc, Grb2, Ras, and Raf-1 kinase, whereas Gq and protein kinase C are important in cardiac myocytes.

Reciprocal change in angiotensinogen mRNA expression in rat myocardium and liver after myocardial infarction

The aim of this study was to analyze sequential change of angiotensinogen (Ao) mRNA expression in rat liver and noninfarcted myocardium after myocardial infarction (MI). Female sprague-Dawley rats were subjected either to left coronary artery occlusion or sham operation. Three weeks after MI, coronary artery ligation resulted in comparable infarct sizes. A hypokinetic thin anterior wall and remarkable dilatation of the left ventricle, as well as decreased contractility (left ventricular end-systolic dimension = 6.0+/-0.4, 3.3+/-0.2, LV end-diastolic dimension = 7.9+/-0.3, 5.9+/-0.2 mm, and fractional shortening = 25.3+/-3.1%, 45.1+/-3.3%) were shown in the MI and sham group, respectively, by echocardiography (P < 0.01). Experimental MI caused a significant fall in systolic blood pressure (MI 90+/-5.0, vs sham 130+/-7.5 mmHg; P< 0.01) and significantly higher left ventricular end-diastolic pressure (MI 21+/-1.5, vs sham 11+/-1.0 mmHg: P < 0.01). At 4, 18, and 24h after MI, liver Ao mRNA levels, as shown by Northern blot analysis, had increased by up to four times (Ao/glyceraldehyde-3-phosphate dehydrogenase (GAPDH) = 1.4+/-0.1 and 6.0+/-0.2 at baseline and 4h after MI, respectively (P < 0.01). After sham surgery, however, the corresponding increase was slight (maximal 1.5-fold). Three days after MI, liver mRNA had returned to the baseline level. In contrast, ATG mRNA expression in noninfarcted myocardium, as shown by reverse transcription-polymerase chain reaction and Southern blotting, decreased transiently during the acute phase. It returned to its baseline level within 3 days, and then increased further (Ao/ GAPDH = 2.9+/-0.6, 0.3+/-0.1, 3.2+/-0.8, and 3.7+/-0.8 at baseline, 24h, 3 days, and 3 weeks after MI, respectively). In conclusion, it can be stated that after MI, the Ao gene contributes, acutely in the liver and chronically in the myocardium, to the maintenance of hemodynamic homeostasis during the acute phase and ventricular remodeling during the chronic phase.

Tissue angiotensinogen gene expression induced by lipopolysaccharide in hypertensive rats

There is now convincing evidence that various tissues express their own tissue renin-angiotensin system, which may be regulated independently of the systemic renin-angiotensin system. However, little information is available on the regulation of the tissue renin-angiotensin system. We investigated the regulation of tissue angiotensinogen gene expression with respect to the development of hypertension. We measured basal and lipopolysaccharide-stimulated plasma angiotensinogen concentrations by radioimmunoassay and examined the expression of tissue angiotensinogen by Northern blot analysis in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) at 4 and 13 weeks of age. Basal plasma angiotensinogen concentration in SHR was comparable to that in WKY at 4 weeks of age and was significantly higher than that in WKY at 13 weeks of age. Lipopolysaccharide induced a significant increase in plasma angiotensinogen concentration in both WKY and SHR at 4 and 13 weeks of age. At 4 weeks of age, the basal levels of angiotensinogen mRNA in the liver, fat, adrenal, and aorta were higher in WKY than in SHR. At 13 weeks of age, the basal levels of angiotensinogen mRNA in the fat, adrenal, aorta, spleen, and kidney were higher in WKY than in SHR, while that in the liver did not differ significantly between the two strains. At 4 weeks of age, pretreatment with lipopolysaccharide increased the angiotensinogen mRNA levels in the liver, fat, adrenal, and aorta in both WKY and SHR. At 13 weeks of age, pretreatment with lipopolysaccharide increased the angiotensinogen mRNA levels in the liver, aorta, and adrenal; decreased those in the spleen; and had no effect in the kidney in both WKY and SHR. Interestingly, lipopolysaccharide increased the angiotensinogen mRNA level in fat only in SHR, with no effect in WKY, at 13 weeks of age. Lipopolysaccharide stimulated tumor necrosis factor-a mRNA expression in fat of WKY and SHR, and the increase in tumor necrosis factor-alpha mRNA level in SHR was significantly greater than that in WKY. Therefore, the increased tumor necrosis factor-alpha mRNA expression may be involved in the increased lipopolysaccharide-induced expression of angiotensinogen gene in fat of SHR at 13 weeks of age. These data suggest that the transcriptional and probably posttranscriptional regulation of angiotensinogen mRNA differs between SHR and WKY, that the regulation of angiotensinogen gene expression is tissue-specific, and that the altered expression of the angiotensinogen gene may be involved in the development of hypertension.

Tissue-specific regulation of angiotensinogen gene expression in spontaneously hypertensive rats

Angiotensinogen is expressed in many tissues besides the liver. Recent studies have suggested that abnormalities in the regulation of angiotensinogen gene expression may be involved in the development of hypertension. However, little information is available concerning the functional significance of tissue angiotensinogen. In this study, we measured plasma angiotensinogen concentration by radioimmunoassay and examined the expression of tissue angiotensinogen by Northern blot analysis in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Although plasma angiotensinogen concentration in SHR was comparable to that in WKY at 6 weeks of age, it was increased significantly at 14 weeks of age in SHR and became higher than that in WKY. The levels of hepatic angiotensinogen mRNA were similar in SHR and WKY, and the levels of aortic, adrenal, and renal angiotensinogen mRNAs were lower in SHR than in WKY at both 6 and 14 weeks of age. Brain angiotensinogen expression in SHR was higher than in WKY at 6 weeks of age and was comparable to that in WKY at 14 weeks of age. On the other hand, cardiac and fat angiotensinogen mRNA levels were significantly increased at 14 weeks of age in SHR. These results demonstrate that the expression of tissue angiotensinogen is regulated differently in SHR and WKY and indicate that the development of hypertension is accompanied at least temporally with increases in plasma angiotensinogen concentration as well as cardiac and adipogenic angiotensinogen mRNA in SHR.

Mechanisms for inducible control of angiotensinogen gene transcription

The intravascular renin-angiotensin system is an endocrine system designed to maintain cardiovascular homeostasis in response to hypotension. Under normal conditions, angiotensinogen concentrations circulating in the plasma are rate limiting for the maximum velocity of angiotensin I formation. In the liver, the major site of circulating angiotensinogen synthesis, angiotensinogen expression is under exquisite hormonal control. We review the mechanisms by which hormones effect transcriptional control of angiotensinogen expression. Adrenal-derived glucocorticoids produce the translocation of the glucocorticoid receptor into the nucleus. It in turn binds to two glucocorticoid response elements and stimulates angiotensinogen gene transcription. Inflammation activates angiotensinogen transcription as a result of the macrophage-derived cytokines interleukin-1 and tumor necrosis factor-alpha. These cytokines change the abundance of two transcription factor families that bind a single regulatory site in the angiotensinogen promoter, the acute-phase response element. These proteins include the nuclear factor-kappaB complex and the CCAAT/enhancer binding protein family. Activation of the renin-angiotensin system, through production of angiotensin II, results in feedback stimulation of angiotensinogen synthesis (the "positive feedback loop"). We have discovered that the nuclear factor-kappaB transcription factor is regulated by angiotensin II, a finding that provides a mechanism for the transcriptional component of angiotensinogen gene synthesis in the positive feedback loop. These studies underscore the concept that induction of the angiotensinogen gene by diverse physiological stimuli is mediated through changes in the nuclear abundance of sequence-specific transcription factors. The intracellular convergence of cytokine- and angiotensin II-induced signaling pathways on the nuclear factor-kappaB transcription factor provides a point for "cross talk" between angiotensin- and cytokine-activated second messenger pathways.

Differences in cultured cardiac fibroblast populations isolated from SHR and WKY rats

1. The mechanisms whereby angiotensin converting enzyme inhibitors reverse cardiac remodelling appear to involve angiotensin and/or bradykinin receptors. Previously we reported that cultured rat cardiac fibroblasts express angiotensin II (AII) receptors. In the present study we compared AII receptor binding, gene expression of angiotensinogen and the AII, Subtype 1A (AT1A) receptor, as well as morphological changes induced by selected hormonal treatments in cultured fibroblasts derived from SHRLJ or WKYLJ rats. 2. Fibroblasts were isolated from adult rat left ventricle by either collagenase B or collagenase P digestion. Collagenase B yielded cell preparations from SHRLJ which grew slower than cells from WKYLJ rats and expressed nearly two-fold fewer AII receptors (compared to WKYLJ) while collagenase P yielded SHRLJ cells with similar binding and growth properties to WKYLJ. A good correlation was observed between receptor binding and AII receptor, type 1A (AT1A) mRNA concentrations. In the presence of steroids collagenase B cells showed a higher tendency to transform towards a preadipocyte cell type, estimated by the formation of lipid containing vacuoles/cell, while collagenase P cells, mainly the SHRLJ type, start to differentiate toward a myofibroblast-like cell type in the presence of AII, as calculated by the expression of alpha-smooth muscle actin. 3. From the results obtained in this study it is evident that a subset of fibroblasts can be isolated from the SHRLJ heart using collagenase B or P which differ in growth rates, AII receptor binding, AT1A and angiotensinogen mRNA levels, morphology and steroid responsiveness when compared to fibroblasts isolated from cardiac WKYLJ tissue.

mRNA stability in mammalian cells

This review concerns how cytoplasmic mRNA half-lives are regulated and how mRNA decay rates influence gene expression. mRNA stability influences gene expression in virtually all organisms, from bacteria to mammals, and the abundance of a particular mRNA can fluctuate manyfold following a change in the mRNA half-life, without any change in transcription. The processes that regulate mRNA half-lives can, in turn, affect how cells grow, differentiate, and respond to their environment. Three major questions are addressed. Which sequences in mRNAs determine their half-lives? Which enzymes degrade mRNAs? Which (trans-acting) factors regulate mRNA stability, and how do they function? The following specific topics are discussed: techniques for measuring eukaryotic mRNA stability and for calculating decay constants, mRNA decay pathways, mRNases, proteins that bind to sequences shared among many mRNAs [like poly(A)- and AU-rich-binding proteins] and proteins that bind to specific mRNAs (like the c-myc coding-region determinant-binding protein), how environmental factors like hormones and growth factors affect mRNA stability, and how translation and mRNA stability are linked. Some perspectives and predictions for future research directions are summarized at the end.

Identification of a cis-acting glucocorticoid responsive element in the rat angiotensin II type 1A promoter

Enhanced vascular responsiveness to angiotensin II at the AT1 receptor has been considered one of the major contributing factors to vascular hypertrophy and high blood pressure. The transcription of the rat angiotensin II type 1A receptor gene is stimulated by glucocorticoids. To clarify the molecular mechanism for glucocorticoid action in rat vascular smooth muscle cells, we investigated the effects of dexamethasone on the promoter activity of the angiotensin II type 1A receptor by using promoter/luciferase reporter gene constructs and heterologous context constructs (containing the thymidine kinase promoter) in transfected vascular smooth muscle cells (< 12 passages). There are three putative glucocorticoid responsive elements (GREs) in the promoter. However, only one GRE was found to respond to dexamethasone (1 mumol/L) and was located at positions -756 to -770 bp upstream from the transcription initiation site. When compared with the consensus sequence of GRE, 9 of 12 bases were identical. RU38486, a glucocorticoid antagonist, completely blocked the induction by dexamethasone, suggesting that the GRE was functional through a specific glucocorticoid receptor. The response to dexamethasone was lost in vascular smooth muscle cells at higher passage numbers (> 8 passages) but was restored when the cells were transfected with a glucocorticoid-receptor expression construct. This finding provided additional support that the response to dexamethasone was mediated by the glucocorticoid receptor. The gel mobility supershift assay showed that the GRE binds in vitro-translated rat glucocorticoid receptors in a specific manner. Compared with the angiotensin II type 1A receptor promoter, no effect by dexamethasone was observed in vascular smooth muscle cells transfected with the angiotensin II type 1B receptor promoter/luciferase reporter gene constructs.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue distribution, hormone regulation and evidence for a human homologue of the estrogen-inducible Xenopus laevis vitellogenin mRNA binding protein

17 beta-estradiol induces the synthesis of massive amounts of the hepatic mRNA encoding the Xenopus laevis egg yolk precursor protein, vitellogenin. Vitellogenin mRNA exhibits a half life of approx. 500 h when 17 beta-estradiol is present, and 16 h after removal of 17 beta-estradiol from the culture medium. We recently reported that Xenopus liver contains a protein, which is induced by 17 beta-estradiol and binds with a high degree of specificity to a binding site in a segment of the 3'-untranslated region (3'-UTR) of vitellogenin mRNA implicated in 17 beta-estradiol stabilization of vitellogenin mRNA. To determine if this mRNA binding protein was specific to this system, or if it was present elsewhere, and regulated by other steroids, we examined the tissue distribution and androgen regulation of this protein. Substantial amounts of the vitellogenin 3'-UTR binding protein were found in several Xenopus tissues including testis, ovary and muscle. In the absence of hormone treatment, lung and intestine contained minimal levels of the mRNA binding protein. Testosterone administration induced the vitellogenin 3'-UTR RNA binding protein in several tissues. Additionally, we found a homologous mRNA binding protein in MCF-7, human breast cancer cells. Although the MCF-7 cell protein was not induced by 17 beta-estradiol, the MCF-7 cell mRNA binding protein appears to be closely related to the Xenopus protein since: (i) the human and Xenopus proteins elicit gel shifted bands with the same electrophoretic mobility using the vitellogenin mRNA 3'-UTR binding site; (ii) The human and Xenopus proteins exhibit similar binding specificity for the vitellogenin 3'-UTR RNA binding site; and (iii) RNA from MCF-7 cells is at least as effective as RNA from control male Xenopus liver in blocking the binding of the Xenopus and human proteins to the vitellogenin mRNA 3'-UTR binding site. Its broad tissue distribution and regulation by both 17 beta-estradiol and testosterone suggests that this mRNA binding protein may play a significant role in steroid hormone regulation of mRNA metabolism in many vertebrate cells.

Steroid hormones upregulate rat angiotensin II type 1A receptor gene: role of glucocorticoid responsive elements in rat angiotensin II type 1A promoter

The transcription of the rat angiotensin II type 1A receptor gene is stimulated by glucocorticoids. To clarify the molecular mechanism for glucocorticoid action in rat vascular smooth muscle cells, we investigated the effects of dexamethasone on the promoter activity of the angiotensin II type 1A receptor by using promoter/luciferase reporter gene constructs and heterologous context constructs (containing the thymidine kinase promoter) in transfected vascular smooth muscle cells. There are three putative glucocorticoid responsive elements in the promoter. However, only one glucocorticoid responsive element was found to respond to dexamethasone (1 microM). The region was located at positions, -756 to -770 bp upstream of the transcription initiation site. A glucocorticoid antagonist, RU38486, completely blocked the induction by dexamethasone, suggesting that the glucocorticoid responsive element was functional through a specific glucocorticoid receptor. Compared with the angiotensin II type 1A receptor promoter, no effect by dexamethasone was observed in vascular smooth muscle cells transfected with the angiotensin II type 1B receptor promoter/luciferase reporter gene constructs. We concluded that the dexamethasone-induced increase in the transcription of the angiotensin II type 1A receptor gene occurred through the binding to GRE up the glucocorticoid-specific receptor.

Transient inhibition of angiotensinogen production in transgenic mice bearing an antisense angiotensinogen gene

Angiotensinogen is the precursor of the biologically active hormone angiotensin II. Enzyme kinetic parameters suggest that concentrations of plasma angiotensinogen are rate limiting in the renin reaction. It is therefore assumed that a decrease in angiotensinogen synthesis in vivo would result in a decrease in angiotensin II plasma levels and then of blood pressure. To test this hypothesis, we generated a transgenic mouse line that carries an inducible antisense angiotensinogen gene. Transient inhibition of angiotensinogen synthesis could be demonstrated in these transgenic animals. However, the amounts of liver angiotensinogen message and plasma angiotensinogen concentrations were rapidly back to levels observed in control animals.

Angiotensinogen: hormonal regulation and relative importance in the generation of angiotensin II

The production of angiotensinogen is controlled mainly by hormones that affect the concentration of its mRNA in tissues. Accordingly, hormones that act upon gene transcription play a prominent role. However, other factors may modulate the transcriptional effects of hormones, and these should be considered to appreciate the final effects of hormones on the secretion of angiotensinogen. The most important role played by hormones in the regulation of angiotensinogen may be to maintain its production in the face of rapid consumption by high levels of renin. However, elevated levels of angiotensinogen may become a risk factor in situations where the normal feedback regulation of renin does not operate normally. Finally, the synthesis of angiotensinogen in tissues may be regulated differentially than that in liver, although the exact importance of these observations is still poorly understood.