AT1 receptor mediated augmentation of intrarenal angiotensinogen in angiotensin II-dependent hypertension

Angiotensin (Ang) II-infused hypertensive rats exhibit increases in renal angiotensinogen mRNA and protein, as well as urinary angiotensinogen excretion in association with increased intrarenal Ang II content. The present study was performed to determine if the augmentation of intrarenal angiotensinogen requires activation of Ang II type 1 (AT1) receptors. Male Sprague-Dawley rats (200 to 220 g) were divided into 3 groups: sham surgery (n=10), subcutaneous infusion of Ang II (80 ng/min, n=11), and Ang II infusion plus AT1 blocker (ARB), olmesartan (5 mg/d, n=12). Ang II infusion progressively increased systolic blood pressure (SBP) compared with sham (178+/-8 mm Hg versus 119+/-4 at day 11). ARB treatment prevented hypertension (113+/-6 at day 11). Twenty-four-hour urine collections were taken at day 12, and plasma and tissue samples were harvested at day 13. The Ang II+ARB group had a significant increase in plasma Ang II compared with Ang II and sham groups (365+/-46 fmol/mL versus 76+/-9 and 45+/-14, respectively). Nevertheless, ARB treatment markedly limited the enhancement of kidney Ang II by Ang II infusion (65+/-17 fmol/g in sham, 606+/-147 in Ang II group, and 288+/-28 in Ang II+ARB group). Ang II infusion significantly increased kidney angiotensinogen compared with sham (1.69+/-0.21 densitometric units versus 1.00+/-0.17). This change was reflected by increased angiotensinogen immunostaining in proximal tubules. ARB treatment prevented this increase (1.14+/-0.12). Urinary angiotensinogen excretion rates were enhanced 4.7x in Ang II group (4.67+/-0.41 densitometric units versus 1.00+/-0.21) but ARB treatment prevented the augmentation of urinary angiotensinogen (0.96+/-0.23). These data demonstrate that augmentation of intrarenal angiotensinogen in Ang II-infused rats is AT1-dependent and provide further evidence that urinary angiotensinogen is closely linked to intrarenal Ang II in Ang II-dependent hypertension.

Protective effects of endogenous adrenomedullin on cardiac hypertrophy, fibrosis, and renal damage

BACKGROUND

Adrenomedullin (AM) is a novel vasodilating peptide thought to have important effects on cardiovascular function. The aim of this study was to assess the activity of endogenous AM in the cardiovascular system using AM knockout mice.

METHODS AND RESULTS

Mice heterozygous for an AM-null mutation (AM+/-) and their wild-type littermates were subjected to aortic constriction or angiotensin II (Ang II) infusion. The resultant cardiovascular stress led to increases in heart weight/body weight ratios, left ventricular wall thickness, and perivascular fibrosis, as well as expression of genes encoding angiotensinogen, ACE, transforming growth factor-beta, collagen type I, brain natriuretic peptide, and c-fos. In addition, renal damage characterized by decreased creatinine clearance with glomerular sclerosis was noted. In all cases, the effects were significantly more pronounced in AM+/- mice. Hearts from adult mice subjected to aortic constriction showed enhanced extracellular signal-regulated kinase (ERK) activation, as did cardiac myocytes from neonates treated acutely with Ang II. Again the effect was more pronounced in AM+/- mice, which showed increases in cardiac myocyte size, protein synthesis, and fibroblast proliferation. ERK activation was suppressed by protein kinase C inhibition to a greater degree in AM+/- myocytes. In addition, treatment of cardiac myocytes with recombinant AM suppressed Ang II-induced ERK activation via a protein kinase A-dependent pathway.

CONCLUSIONS

Endogenous AM exerts a protective effect against stress-induced cardiac hypertrophy via protein kinase C- and protein kinase A-dependent regulation of ERK activation. AM may thus represent a useful new tool for the treatment of cardiovascular disease.

Endogenous angiotensin and pressure modulate brain angiotensinogen and AT1A mRNA expression

In the coarctation hypertension model, we showed both dissociation of plasma renin activity from cardiovascular-induced effects and the reversal of hypertension-induced responses by losartan. In this study, we investigated the effects of hypertension on the expression of brain renin-angiotensin system components and the simultaneous functional responses and effects of long-term angiotensin II (AT) receptor blockade on these responses. Rats were given vehicle or losartan for 9 days and subjected to subdiaphragmatic aortic constriction or sham surgery after 4 days of treatment. On the fifth postsurgical day, pressure and heart rate were measured in the conscious state; the brain was perfused and removed afterward. Sequential slices of brainstem were hybridized with 35S-oligodeoxynucleotide probes for angiotensinogen, AT1A, and AT1B receptors and processed for autoradiography and densitometry. In vehicle-treated rats, hypertension was accompanied by tachycardia and marked increments in angiotensinogen and AT1A mRNA expression in the cardiovascular system-controlling brainstem areas. In the nucleus tractus solitarii, AT1A density was correlated with both pressure and heart rate values (P<0.01), whereas angiotensinogen levels were correlated with pressure only (P<0.05). Losartan did not change the pressure of hypertensive rats (142+/-4 versus 146+/-2 mm Hg, losartan versus vehicle) and the hypertension-induced angiotensinogen mRNA expression but did block both tachycardic response and hypertension-induced AT1A mRNA expression. Hypertension and losartan did not change AT1B mRNA expression. The hypertension-induced positive feedback on angiotensinogen and AT1A mRNA expression supports the concept of a permissive role for brain angiotensin II in orchestrating circulatory responses during the development of hypertension. These data also explain the efficacy of long-term AT1 receptor blockade to reverse hypertension-induced effects.

Insulin-mediated regulation of the endothelial renin???angiotensin system and vascular cell growth

OBJECTIVE

Insulin has a growth-stimulating effect for vascular tissue. At the tissue level, the vascular renin-angiotensin system (RAS) may be involved in the progression of atherosclerosis or vascular hypertrophy. We previously reported that the vascular RAS activity is activated in vascular smooth muscle cells (SMC) by insulin stimulation. However, the effect of insulin on the RAS in endothelial cells (EC) is not fully understood.

METHODS

Cultured human EC were incubated with or without insulin. After incubation for 48 h, cellular angiotensinogen and renin mRNA expression and levels in the cells were quantified by slot-blot hybridization and radioimmunoassay. Angiotensin I converting enzyme (ACE) activity in EC homogenates was measured by modified Cushman and Cheung method. EC growth and SMC with or without EC using co-culture were assessed by 3H-thymidine uptake for evaluation of their growth.

RESULTS

All doses of insulin (10, 100, 1000 microU/ml) decreased angiotensinogen and renin mRNA expression (angiotensinogen: 19.3%, P < 0.05; 25.4%, P < 0.01; 26.2%, P < 0.01, renin: 12.9%, P < 0.05; 21.3%, P < 0.01; 14.3%, P < 0.05, respectively). Both cellular angiotensinogen and renin level were also reduced by high levels of insulin. Neither 10 nor 100 microU/ml insulin increased cellular angiotensin converting enzyme (ACE) activity (2.17 to 3.48-folds, P = 0.077, 0.125, respectively) significantly, but 1000 microU/ml insulin strongly up-regulated ACE activity by 16.67-folds (P = 0.001) in cultured EC. For the co-culture with EC and SMC, 100 microU/ml insulin was not able to induce SMC but 1000 microU/ml insulin accelerated SMC growth in the co-culture. In contrast insulin that was over 100 microU/ml induced SMC growth in the sole culture of SMC.

CONCLUSION

Either low or high levels of insulin suppressed angiotensinogen and renin expression, however, high doses of insulin stimulated ACE activity in cultured human aortic EC. This may indicate that insulin regulates vascular cell growth and endothelial function via bifunctional modification of the vascular angiotensin generation.

Estrogen and enalapril attenuate the development of right ventricular hypertrophy induced by monocrotaline in ovariectomized rats

The present study evaluated the importance of ovarian functions and the renin-angiotensin system in the progression of the right ventricular (RV) hypertrophy. Female Sprague-Dawley rats were bilaterally ovariectomized (Ovx) and injected with monocrotaline (MCT, 60 mg/kg, sc). Four weeks after MCT-treatment, only the male and Ovx female rats showed marked RV hypertrophy. The hypertrophied RV of the male-MCT and Ovx-MCT rats exhibited remarkably elevated renin mRNA levels. Gene expression levels of angiotensinogen, TGF-beta1, and endothelin-1 in the hypertrophied RV also increased, but to the less degree than did the renin mRNA. To investigate beneficial effects of estrogen or enalapril on progression of the pulmonary hypertension and RV hypertrophy, histological changes of the lung and heart were examined. Sham-MCT female rats showed histological changes indicating pulmonary hypertension without RV hypertrophy. In contrast, Ovx-MCT rats showed marked RV hypertrophy with pathological changes, denoting severe pulmonary and myocardial injuries. Estrogen-or enalapril-treated Ovx-MCT rats did not show RV hypertrophy, and showed remarkably ameliorated ultrastructural changes in the lung and RV. These results from this rat model suggest that both estrogen and inhibition of the renin-angiotensin system have protective functions against the development of the pulmonary hypertension and cardiac remodeling.

Activation and functional significance of the renin-angiotensin system in mice with cardiac restricted overexpression of tumor necrosis factor

BACKGROUND

The functional significance of cross-regulation between the renin-angiotensin system (RAS) and tumor necrosis factor (TNF) has been established in nonmyocyte cell types; however, the degree and functional significance of the interaction between RAS and TNF has not been characterized in the heart.

METHODS AND RESULTS

We examined the expression of components of the RAS in a line of transgenic mice (MHCsTNF) with cardiac restricted overexpression of TNF. When examined at 4, 8, and 12 weeks of age, the MHCsTNF mice had increased activation of myocardial RAS, as shown by an increase in ACE mRNA level and ACE activity and increased angiotensin II peptide levels. Furthermore, myocardial angiotensin receptor mRNA and protein levels were reduced in the MHCsTNF mice, consistent with homologous desensitization of the receptors. However, expression of renin and angiotensinogen was not increased in MHCsTNF mice compared with littermate controls. To determine the functional significance of RAS activation in the MHCsTNF mice, we treated the mice with an angiotensin type I receptor antagonist, losartan (30 mg/kg), or diluent from 4 to 8 weeks of age. Analysis of cardiac structure with MRI showed that treatment with losartan normalized left ventricular mass and wall thickness. Furthermore, treatment with losartan reduced myocardial collagen content and reduced the incidence of myocyte apoptosis.

CONCLUSIONS

Taken together, these results show that there are functionally significant interactions between RAS and TNF in the heart and that these interactions play an important role in the development and progression of left ventricular remodeling.

Local and systemic impact of transcriptional up-regulation of 11beta-hydroxysteroid dehydrogenase type 1 in adipose tissue in human obesity

In idiopathic obesity circulating cortisol levels are not elevated, but high intraadipose cortisol concentrations have been implicated. 11beta-Hydroxysteroid dehydrogenase type 1 (11HSD1) catalyzes the conversion of inactive cortisone to active cortisol, thus amplifying glucocorticoid receptor (GR) activation. In cohorts of men and women, we have shown increased ex vivo 11HSD1 activity in sc adipose tissue associated with in vivo obesity and insulin resistance. Using these biopsies, we have now validated this observation by measuring 11HSD1 and GR mRNA and examined the impact on intraadipose cortisol concentrations, putative glucocorticoid regulated adipose target gene expression (angiotensinogen and leptin), and systemic measurements of cortisol metabolism. From aliquots of sc adipose biopsies from 16 men and 16 women we extracted RNA for real-time PCR and steroids for immunoassays. Adipose 11HSD1 mRNA was closely related to 11HSD1 activity [standardized beta coefficient (SBC) = 0.58; P < 0.01], and both were positively correlated with parameters of obesity (e.g. for BMI, SBC = 0.48; P < 0.05 for activity, and SBC = 0.63; P < 0.01 for mRNA) and insulin sensitivity (log fasting plasma insulin; SBC = 0.44; P < 0.05 for activity, and SBC = 0.33; P = 0.09 for mRNA), but neither correlated with urinary cortisol/cortisone metabolite ratios. Adipose GR-alpha and angiotensinogen mRNA levels were not associated with obesity or insulin resistance, but leptin mRNA was positively related to 11HSD1 activity (SBC = 0.59; P < 0.05) and tended to be associated with parameters of obesity (BMI: SBC = 0.40; P = 0.09), fasting insulin (SBC = 0.65; P < 0.05), and 11HSD1 mRNA (SBC = 0.40; P = 0.15). Intraadipose cortisol (142 +/- 30 nmol/kg) was not related to 11HSD1 activity or expression, but was positively correlated with plasma cortisol. These data confirm that idiopathic obesity is associated with transcriptional up-regulation of 11HSD1 in adipose, which is not detected by conventional in vivo measurements of urinary cortisol metabolites and is not accompanied by dysregulation of GR. Although this may drive a compensatory increase in leptin synthesis, whether it has an adverse effect on intraadipose cortisol concentrations and GR-dependent gene regulation remains to be established.

Enhancement of intrarenal angiotensinogen in Dahl salt-sensitive rats on high salt diet

This study was performed to examine whether there is an inappropriate regulation of intrarenal angiotensinogen in Dahl-salt sensitive rats (DS) fed a high salt diet (HS). Dahl salt-resistant rats (DR) and DS were maintained on HS (8% NaCl) or low salt diet (LS, 0.3% NaCl) for 4 weeks. Systolic blood pressure (SBP), measured by tail-cuff plethysmography, was unaltered in DR (DR+HS, 127+/-3 mm Hg, n=5; DR+LS, 126+/-3, n=5); however, SBP was significantly increased in DS+HS (208+/-7, n=9) compared with DS+LS (134+/-2, n=5). HS suppressed plasma renin activity in both strains (0.7+/-0.2 ng of angiotensin I/mL per hour in DS+HS, 3.1+/-0.5 in DS+LS, 0.8+/-0.2 in DR+HS, 5.1+/-0.7 in DR+LS). Plasma angiotensinogen levels, measured by Western blot analysis, were also suppressed by HS in both strains (36 919+/-2170 integrated densitometric unit in DS+HS, 53 028+/-2752 in DS+LS, 44 722+/-1721 in DR+HS, 55782+/-3785 in DR+LS). However, kidney angiotensinogen levels were significantly increased in DS+HS (75 850+/-4171, integrated densitometric unit) compared with DS+LS (47 232+/-3470), DR+HS (44 748+/-8236), and DR+LS (42 504+/-4052). Urinary excretion of angiotensinogen, measured by radioimmunoassay of angiotensin I after incubation with excess renin, had a similar profile. Urinary excretion of angiotensinogen was significantly increased in DS+HS (2958+/-531 pmol/d) compared with DS+LS (56+/-4), DR+HS (31+/-12), and DR+LS (21+/-7). These data indicate that intrarenal angiotensinogen is enhanced in DS+HS, which is reflected by the increased urinary excretion of angiotensinogen. The results suggest that DS on HS have an inappropriate augmentation of intrarenal angiotensinogen, which may contribute to impaired sodium excretion during a high salt diet and the development of hypertension in this strain.

Physiological significance of two common haplotypes of human angiotensinogen using gene targeting in the mouse

Angiotensinogen (AGT) was the first gene to be genetically linked to hypertension in humans. Analysis of the gene sequence identified a number of polymorphisms, several of which were reported associated with increased blood pressure (BP) or other cardiovascular diseases. One haplotype of the human AGT (hAGT) gene consisting of an allele at the -6 (A vs. G) position in the promoter and the sequence encoding amino acid 235 (Thr vs. Met) attracted the most attention and has been the subject of numerous association studies. In this report, we addressed the physiological relevance of alleles at these two positions using an experimental mouse model system. Transgenic mice were generated by targeting each haplotype [-6G/235Met (GM) and -6A/235Thr (AT)] as a single copy transgene to the mouse hypoxanthine phosphoribosyl transferase locus, allowing direct comparison of the two transgenes in vivo. Our results indicate that both transgenes exhibit the same transcriptional activity and produce similar levels of hAGT protein in the plasma of the transgenic mice. BP analysis was performed in double transgenic mice generated by breeding each hAGT line to mice expressing a human renin gene. A small but significant increase in BP and relative heart weight was demonstrated by mice carrying the GM haplotype. Moreover, compensatory downregulation of endogenous renin expression was more pronounced in mice containing the GM variant. Our findings suggest that the AT and GM haplotypes of the hAGT gene have no effect on gene expression, but may affect the cardiovascular system and the regulation of BP differently.

Release of preformed Ang II from myocytes mediates angiotensinogen and ET-1 gene overexpression in vivo via AT1 receptor

The role of angiotensin II in pressure overload is still debated because notwithstanding its effects on myocyte contractility angiotensin II is not an obligatory factor for the development of hypertrophy. To define the role of angiotensin II in acute pressure overload we studied the effects of AT1 blockade (valsartan 80mg per day) on myocardial contractility, cardiac growth factor gene expression, and myocardial hypertrophy in aortic banded (60mmHg) pigs. Acute pressure overload caused an abrupt reduction of myocardial contractility, measured by the end-systolic stiffness constant, and a sharp increase in end-systolic stress which rapidly normalized (within 12h) in the placebo group. In AT1-blocked animals end-systolic stiffness constant remained significantly depressed up to 24h and end-systolic stress was still elevated up to 48h (both P<0.05 vs placebo). In both groups confocal microscopy revealed that granular staining of angiotensin II in cardiomyocyte cytoplasm disappeared after 30min of pressure overload. AT1 blockade abolished following cardiac overexpression of angiotensinogen and endothelin-1 genes as shown in RT-PCR studies and the consequent angiotensin II and endothelin-1 release in the coronary circulation. Conversely, insulin-like growth factor-I and ACE mRNA overexpression, as well as the onset of left ventricular mass increase, were not significantly affected by AT1 blockade.

IN CONCLUSION

(1) mechanical stress releases preformed angiotensin II from myocyte in vivo; (2) the AT1 blockade abolishes cardiac angiotensin II and endothelin-1 production with delayed recovery of myocardial contractility; whereas (3) the overexpression of insulin-like growth factor-I gene and the development of myocardial hypertrophy are not angiotensin II-mediated effects.

Interplay between the cardiac renin angiotensin system and JAK-STAT signaling: role in cardiac hypertrophy, ischemia/reperfusion dysfunction, and heart failure

Recent studies have shown that the JAK-STAT signaling pathway plays a central role in cardiac pathophysiology. JAK-STAT signaling has been implicated in pressure overload-induced cardiac hypertrophy and remodeling, ischemic preconditioning, and ischemia/reperfusion-induced cardiac dysfunction. The different STAT family members expressed in cardiac myocytes appear to be linked to different, and at times, opposite responses, such as cell growth/survival and apoptosis. Thus, differential activation and/or selective inhibition of the STAT proteins by agonists for G-protein coupled receptors, such as angiotensin II, may contribute to cardiac dysfunction during ischemia and heart failure. In addition, JAK-STAT signaling may represent one limb of an autocrine loop for angiotensin II generation, that serves to amplify the actions of angiotensin II on cardiac muscle. The purpose of this article is to provide an overview of recent findings that have been made for JAK-STAT signaling in cardiac myocytes and to highlight some unresolved issues for future investigation. The central focus of this review is on recent studies suggesting that modulation or activation of JAK-STAT signaling by ANG II has pathological consequences for heart function.

Guanylyl cyclase-A inhibits angiotensin II type 1A receptor-mediated cardiac remodeling, an endogenous protective mechanism in the heart

BACKGROUND

Guanylyl cyclase (GC)-A, a natriuretic peptide receptor, lowers blood pressure and inhibits the growth of cardiac myocytes and fibroblasts. Angiotensin II (Ang II) type 1A (AT1A), an Ang II receptor, regulates cardiovascular homeostasis oppositely. Disruption of GC-A induces cardiac hypertrophy and fibrosis, suggesting that GC-A protects the heart from abnormal remodeling. We investigated whether GC-A interacts with AT1A signaling in the heart by target deletion and pharmacological blockade or stimulation of AT1A in mice.

METHODS AND RESULTS

We generated double-knockout (KO) mice for GC-A and AT1A by crossing GC-A-KO mice and AT1A-KO mice and blocked AT1 with a selective antagonist, CS-866. The cardiac hypertrophy and fibrosis of GC-A-KO mice were greatly improved by deletion or pharmacological blockade of AT1A. Overexpression of mRNAs encoding atrial natriuretic peptide, brain natriuretic peptide, collagens I and III, transforming growth factors beta1 and beta3, were also strongly inhibited. Furthermore, stimulation of AT1A by exogenous Ang II at a subpressor dose significantly exacerbated cardiac hypertrophy and dramatically augmented interstitial fibrosis in GC-A-KO mice but not in wild-type animals.

CONCLUSIONS

These results suggest that cardiac hypertrophy and fibrosis of GC-A-deficient mice are partially ascribed to an augmented cardiac AT1A signaling and that GC-A inhibits AT1A signaling-mediated excessive remodeling.

Effects of chronic hypoxia on the circulating and pancreatic renin-angiotensin system

INTRODUCTION

The circulating renin-angiotensin system (RAS) plays a crucial role in the regulation of blood pressure, electrolytes, and fluid homeostasis. In contrast to the circulating RAS, the presence of an intrinsic RAS has been demonstrated in different tissues/organs, which may affect both local and global functions of a biologic system. Our previous studies provided solid evidence of the existence of a local RAS in rat pancreas. Our further investigation showed that such a pancreatic RAS could be activated by experimental models of chronic hypoxia and chemically induced pancreatitis. These previous findings formed the basis for the current study.

METHODOLOGY

Adult Sprague-Dawley rats were exposed to isobaric hypoxia (10% O2), and the effects on the circulating and pancreatic RAS were documented.

RESULTS

The current study shows that exposure of rats to isobaric hypoxia caused a time-dependent increase in plasma renin activity. The activation of circulating RAS by hypoxia was associated with a parallel upregulation of local RAS components, including the mRNA expression of angiotensinogen and angiotensin II receptor types I and II in the pancreas.

CONCLUSION

The upregulation of local pancreatic RAS, along with its counterpart circulating RAS, may be responsible for both physiologic and pathophysiologic aspects of a biologic system under chronic hypoxic stress.

A locally generated angiotensin system in rat carotid body

Previous studies have shown the existence of functional angiotensin II receptors in rat carotid body, which directly alters the carotid chemoreceptor afferent nerve activity. Moreover, chronic hypoxia could result in an enhanced sensitivity of chemoreceptor afferent activity via an AT(1) receptor-mediated calcium signaling in the carotid body. In the present study, the localization and expression of angiotensinogen, the obligatory component for an intrinsic, angiotensin-generating system, were investigated by in situ hybridization histochemistry, immunohistochemistry, RT-PCR, Western blot and Northern blot analysis. In situ hybridization showed the expression of angiotensinogen within the glomus cells of the carotid body. Double immunostaining of angiotensinogen and tyrosine hydroxylase, an immunohistochemical marker for type I glomus cells, elucidated that angiotensinogen protein was specifically localized to the lobules of type I cells. Consistently, RT-PCR and Western blot analysis confirmed the expression of angiotensinogen mRNA and protein, respectively. On the other hand, renin mRNA was not detected using RT-PCR and Northern blot analysis whereas angiotensin-converting enzyme (ACE) mRNA was detected in the carotid body. These data suggest that a locally generated angiotensin system is operated in the carotid body, which might be linked to a renin-independent biosynthetic pathway. Such an intrinsic, angiotensin-generating system and its local regulation by chronic hypoxia should be important in the modulation of cardiopulmonary adaptation in the hypoxic ventilatory response and the electrolyte as well as water homeostasis.

Neuron-specific expression of human angiotensinogen in brain causes increased salt appetite

The brain renin-angiotensin system (RAS) has an important role in the regulation of cardiovascular function. In the brain, angiotensinogen (AGT) is expressed mainly in astrocytes (glia) and in some neurons in regions controlling cardiovascular activities. Because of the inability to dissect the functional role of astrocyte- vs. neuron-derived AGT in vivo by pharmacological approaches, the exact role of neuron-derived AGT in the regulation of blood pressure (BP) and fluid and electrolyte balance remains unclear. Therefore, we generated a transgenic mouse model overexpressing human AGT under the control of a neuron-specific (synapsin I) promoter (SYN-hAGT). These mice exhibited high-level expression of human AGT mRNA in the brain, with lower expression in the kidney and heart. Human AGT was not detected in plasma, but in the brain it was expressed exclusively in neurons. Intracerebroventricular (30 ng) but not intravenous (500 ng) injection of purified human renin (hREN) caused a pressor response, which was prevented by intracerebroventricular preinjection of the angiotensin II type 1 receptor antagonist losartan, indicating an AT(1) receptor-dependent functional role of neuron-derived AGT in the regulation of BP in response to exogenous REN. Double transgenic mice expressing both the hREN gene and SYN-hAGT transgene exhibited normal BP and water intake but had an increased preference for salt. These data suggest that neuronal AGT may play an important role in regulating salt intake and salt appetite.

Urinary excretion of angiotensinogen reflects intrarenal angiotensinogen production

BACKGROUND

In rats maintained on a high salt diet (H/S) to suppress basal renal angiotensinogen levels, angiotensin II (Ang II) infusion for 13 days increased renal angiotensinogen mRNA and protein, thus providing a mechanism for further augmentation of intrarenal Ang II levels. The present study tested the hypothesis that enhanced intrarenal angiotensinogen formation during Ang II infusion is reflected by secretion into the tubular fluid leading to increased urinary excretion of angiotensinogen (UAGT).

METHODS

The effects of chronic Ang II infusion were examined on kidney and plasma Ang II levels and UAGT in male Sprague-Dawley rats maintained on an 8% salt diet for three weeks (N=10). Following one week on the H/S diet, Ang II (40 ng/min) was administered for two weeks via an osmotic minipump to one group (H/S + Ang II, N=5), while the remaining rats were sham-operated (H/S + Sham, N=5). Additionally, a control group was prepared with normal salt diet and sham-operation (N/S + Sham, N=5).

RESULTS

H/S alone did not alter systolic blood pressure (BP) (103 +/- 2 vs. 104 +/- 2 mm Hg), while Ang II infusion to H/S rats significantly increased systolic BP from 103 +/- 2 to 154 +/- 2 after two weeks. Intrarenal Ang II content in H/S + Ang II was significantly greater than H/S + Sham (435 +/- 153 vs. 65 +/- 14 fmol/g). Ang II infusion significantly increased UAGT (4.0 +/- 0.5 vs. 1.0 +/- 0.2 nmol Ang I/day by radioimmunoassay of generated Ang I; 57 +/- 15 vs. 14 +/- 2 densitometric units by Western blotting analysis) compared to Sham. UAGT by radioimmunoassay was highly correlated with kidney Ang II content (r=0.79); but not with plasma Ang II concentration (r=0.20).

CONCLUSIONS

These data demonstrate that chronic Ang II infusion increases urinary excretion rate of angiotensinogen, and suggest that UAGT provides a specific index of intrarenal angiotensinogen production in Ang II-dependent hypertension.

Elevated blood pressure in transgenic mice with brain-specific expression of human angiotensinogen driven by the glial fibrillary acidic protein promoter

In addition to the circulatory renin (REN)-angiotensin system (RAS), a tissue RAS having an important role in cardiovascular function also exists in the central nervous system. In the brain, angiotensinogen (AGT) is expressed in astrocytes and in some neurons important to cardiovascular control, but its functional role remains undefined. We generated a transgenic mouse encoding the human AGT (hAGT) gene under the control of the human glial fibrillary acidic protein (GFAP) promoter to experimentally dissect the role of brain versus systemically derived AGT. This promoter targets expression of transgene products to astrocytes, the most abundant cell type expressing AGT in brain. All transgenic lines exhibited hAGT mRNA expression in brain, with variable expression in other tissues. In one line examined in detail, transgene expression was high in brain and low in tissues outside the central nervous system, and the level of plasma hAGT was not elevated over baseline. In the brain, hAGT protein was mainly localized in astrocytes, but was present in neurons in the subfornical organ. Intracerebroventricular (ICV) injection of human REN (hREN) in conscious unrestrained mice elicited a pressor response, which was abolished by ICV preinjection of losartan. Double-transgenic mice expressing the hREN gene and the GFAP-hAGT transgene exhibited a 15-mm Hg increase in blood pressure and an increased preference for salt. Blood pressure in the hREN/GFAP-hAGT mice was lowered after ICV, but not intravenous losartan. These studies suggest that AGT synthesis in the brain has an important role in the regulation of blood pressure and electrolyte balance.

Antisense inhibition of brain renin-angiotensin system decreased blood pressure in chronic 2-kidney, 1 clip hypertensive rats

The systemic renin-angiotensin system (RAS) plays an important role in blood pressure (BP) regulation during the development of 2-kidney, 1 clip (2K1C) hypertension. Its contributions decrease with time after constriction of the renal artery. During the chronic phase, the peripheral RAS returns to normal, but the hypertension is sustained for months. We hypothesized that in this phase the brain RAS contributes to the maintenance of high BP. To test the hypothesis, we studied the role of brain RAS by decreasing the synthesis of angiotensinogen (AGT) and the angiotensin II (Ang II) type 1a receptor (AT(1)R) with intracerebroventricular injections of antisense oligonucleotides (AS-ODNs). The response of systolic BP (SBP) to AS-ODNs to AGT mRNA was studied in 2K1C rats at 6 months after clipping, and the response to AS-ODNs to AT(1)R mRNA was studied at 10 months after clipping. Intracerebroventricular injection of AS-ODN-AGT (200 microgram/kg, n=5) significantly decreased SBP (-22+/-6 mm Hg, P<0.05) compared with the sense ODN (n=5) and saline (n=3) groups. Intracerebroventricular injection of AS-ODN-AGT reduced the elevated hypothalamic Ang II level. The hypothalamic Ang II content in sense ODN and saline groups was significantly (P<0.05) higher than in the nonclipped group. Compared with inverted ODN, intracerebroventricular injection of AS-ODN-AT(1)R (250 microgram/kg, n=6) significantly decreased SBP (-26+/-8 mm Hg, P<0.05) for 3 days after injection. This was a brain effect because intravenous AS-ODN-AT(1)R at a dose of 250 to 500 microgram/kg did not affect SBP. These results suggest that the brain RAS plays an important role in maintaining the elevated SBP in chronic 2K1C hypertension.

Rat epididymal fat tissue express all components of the renin-angiotensin system

In the present study the gene expression of components of the renin-angiotensin system was investigated in fat tissue of rats. mRNAs for angiotensinogen, renin, angiotensin-converting enzyme and type I (AT1) angiotensin II receptor were detected in the stromal-vascular fraction of the fat tissue and the same mRNAs, with the exception of the angiotesin-converting enzyme, in the adipocyte fraction. Renin and angiotensin-converting enzyme activity was measured. The main source of renin activity was found in adipocytes and some minor activity in the stromal-vascular fraction, while the majority of the angiotensin-converting enzyme activity was in the stromal-vascular fraction. The present data provide evidence for the presence of the active renin-angiotensin system in rat adipose tissue.

Insulin and insulin-like growth factor-I promotes angiotensinogen production and growth in vascular smooth muscle cells

BACKGROUND

Circulating insulin and insulin-like growth factor-I (IGF-I) levels are increased in patients with hypertension and insulin resistance. Since both hormones are known to have cell growth-promoting effects, they may contribute to the progression of vascular hypertrophy in patients with insulin resistance. Insulin-mediated activation of the vascular renin-angiotensin system (RAS) stimulates growth in cultured rat vascular smooth muscle cells (VSMC).

OBJECTIVE

In order to evaluate the role of IGF-I-mediated activation of components of the tissue RAS, we examined the effect of IGF-I receptor stimulation on cell proliferation, and production of angiotensinogen in cultured VSMC.

STUDY DESIGN

Aortic VSMC were derived from male Sprague-Dawley rats. IGF-I and insulin-mediated DNA synthesis were estimated by 3H-thymidine uptake (3H-TdR) with or without the angiotensin I converting enzyme inhibitor, captopril. Moreover, angiotensinogen released by the cells to the culture medium was determined by radioimmunoassay with or without the anti-IGF-I receptor antibody alphaIR3 or captopril.

RESULTS

Both IGF-I and insulin increased 3H-TdR uptake by cultured rat VSMC (P < 0.05). Captopril blocked IGF-I and insulin-mediated 3H-TdR uptake (-34.4 +/- 1.9% and -32.7 +/- 1.8%, P < 0.05, respectively). IGF-I increased the angiotensinogen level in the medium by 30.6 +/- 2.9% (P < 0.01). Insulin also stimulated angiotensinogen synthesis by 26.3 +/- 2.2% (P < 0.01). Captopril and alphaIR3 significantly suppressed angiotensinogen production stimulated by both IGF-I and insulin.

CONCLUSIONS

These results indicate that IGF-I as well as insulin stimulates angiotensinogen production and growth in VSMC. Thus, both hormones may independently play a role in progression of the vascular hypertrophy and atherosclerosis in patients with hypertension and insulin resistance through activation of the tissue RAS.

Appropriate tissue- and cell-specific expression of a single copy human angiotensinogen transgene specifically targeted upstream of the HPRT locus by homologous recombination

Development of experimental models by genetic manipulation in mice has proven to be very useful in determining the significance of particular genes in the development of or susceptibility to hypertension. Advances in molecular genetics, transgenic mouse technology, and physiological measurements in mice provided an opportunity to go a step further and develop models to analyze the physiological significance of specific gene variants potentially causing hypertension. In this report, we describe the development of a human angiotensinogen transgenic mouse model generated by targeting the human angiotensinogen gene upstream of the mouse HPRT locus by homologous recombination. The main benefit of this transgenic mouse model is that the human angiotensinogen gene is inserted into the mouse genome as a single copy at a predefined locus and in a specific orientation-a process that can be repeated utilizing other variants of this gene. We establish the validity of this approach by showing that the hAGT(hprt) mice have normal tissue- and cell-specific expression of the human angiotensinogen gene and normally produce and process the hAGT protein at physiological levels.

Differences in mRNA expression of the proteins secreted by the adipocytes in human subcutaneous and visceral adipose tissues

We have investigated the difference in gene expression of six proteins secreted by adipocytes in paired biopsies from visceral and abdominal subcutaneous adipose tissue in nine individuals with various degrees of obesity. The mRNAs levels of leptin, TNFalpha, angiotensinogen, acylation stimulating protein (ASP), cholesterol ester transfer protein (CETP) and phospholipid transfer protein (PLTP) were quantified by RT-competitive PCR. ASP and angiotensinogen mRNA levels were higher in the visceral fat, whereas the mRNA levels of leptin and CETP were higher in the subcutaneous depot. TNFalpha mRNA expression was similar in the two sites. For angiotensinogen, the difference was more pronounced in the subjects with body mass index (BMI) lower than 30 kg/m(2) whereas for ASP, CETP and leptin, the difference was observed regardless the BMI of the subjects. PLTP mRNA levels in subcutaneous, but not in the visceral, adipose tissue were positively related to the BMI of the subjects. These results strongly suggest that visceral and subcutaneous adipocytes may have different properties in the production of bioactive molecules.

Effects of placental insufficiency on the ovine fetal renin-angiotensin system

We postulated that chronic placental insufficiency would be associated with reduced expression of renal renin and angiotensinogen genes in the fetal sheep. Placental development was restricted in ewes by removing the majority of caruncles prior to mating (placentally restricted (PR) group). The weights of PR fetuses were significantly reduced (P < 0.05, 2.98 +/- 0.33 kg) compared to control fetuses (4.20 +/- 0.30 kg). Kidney weights were also significantly reduced in the PR fetuses (P < 0.05, 8.4 +/- 0.9 g) compared with control fetuses (12.2 +/- 1.3 g). The ratios of renal renin/-actin mRNA levels were significantly reduced in PR fetuses (P < 0.001, 0.35 +/- 0.02) when compared to control animals (0.98 +/- 0.13). The renal angiotensinogen mRNA/18S rRNA ratio was significantly lower (P < 0.05, 0.28 +/- 0.13) in PR fetuses compared with control fetuses (0.72 +/- 0.10), while hepatic angiotensinogen was unaffected. There was a positive correlation between renal renin mRNA and renal angiotensinogen mRNA levels (r = 0.65, P < 0.05, n = 12). It is unlikely that these changes in renal angiotensinogen and renin mRNA were due to the small increment in plasma cortisol levels (< 5 nmol l-1). There was, however, a positive correlation between arterial PO2 and renal renin mRNA (r2 = 0.77, P < 0.01). Plasma renin levels were not different between the two groups. Thus, restriction of nutrient and oxygen supply throughout fetal life was associated with suppression of renal renin and renal angiotensinogen gene expression, with no effect on hepatic angiotensinogen mRNA levels. This specific suppression of fetal renal renin and angiotensinogen expression could alter the activity of the intrarenal RAS and so affect growth and development of the kidney.

Hypertension in unilaterally nephrectomized rats induced by single-kidney transfection with angiotensinogen cDNA

Plasmid expression vectors containing angiotensinogen (ATG) cDNA were complexed to cationic liposomes and injected into the renal artery of unilaterally nephrectomized rats to evaluate the effect of intrarenal ATG cDNA on arterial blood pressure and the renin-angiotensin system. Systolic blood pressures measured by tail cuff on days 12, 16, and 18 after transfection were significantly higher in rats that received ATG cDNA than in control rats that received the lac Z reporter gene. Plasma renin activity and plasma ATG concentration were unchanged. These results provide direct evidence that the availability of intrarenal ATG may be instrumental in the development of systemic hypertension.

The paradox of the low-renin state in diabetic nephropathy

Although diabetic nephropathy is often a low renin state, the renin system appears to be implicated in its pathogenesis. In this study, it was hypothesized that the low plasma renin activity (PRA) is misleading, masking and perhaps reflecting an activated intrarenal renin system. PRA and renal vascular responses (inulin and para-aminohippurate clearance) to graded doses of an angiotensin II (AngII) antagonist, irbesartan, were assessed in eight healthy volunteers and 12 patients with type 2 diabetes mellitus and nephropathy on a 10 mmol Na intake, to activate the renin system. Basal PRA was suppressed in type 2 diabetes mellitus compared with the healthy subjects (0.58 +/- 0.14 versus 1.58 +/- 0.28 ng/L per s, mean +/- SEM; P < 0.01). Despite the low PRA, renal perfusion rose more in response to irbesartan in type 2 diabetes mellitus (714 +/- 83 to 931 +/- 116 ml/min; P = 0.002) than normal (624 +/- 29 to 772 +/- 49 ml/min; P = 0.008). The youngest patients were hyperfiltrating and showed the largest rise in renal plasma flow in response to irbesartan, whereas renal plasma flow rose less and GFR fell in patients with low basal GFR. PRA rose in response to irbesartan more gradually in the patients with type 2 diabetes mellitus, but ultimately matched the normal response. To account for the apparent paradox of a heightened renal hemodynamic response to an AngII antagonist in the face of a low PRA in type 2 diabetes mellitus, and the rise in PRA following the AngII antagonist, it is proposed that there is increased intrarenal AngII production in type 2 diabetes mellitus. This increase could account for suppressed circulating renin, the exaggerated renal vasodilator response to irbesartan, and the therapeutic effectiveness of interrupting the renin system in diabetic nephropathy.

Effect of renal perfusion pressure on renal function, renin release and renin and angiotensinogen gene expression in rats

1. A study was undertaken to examine the influence of acute renal perfusion pressure (RPP) reduction on renin release, renal renin and angiotensinogen gene expression and the role played by angiotensin II in these responses. 2. In chloralose-urethane anaesthetised rats, reduction of RPP to 60 mmHg for 3 h in vehicle or losartan-treated (5 days at 10 mg kg-1 bis in die (b.i.d.)) rats decreased renal blood flow by 46 and 29 % (both P < 0.001), respectively, glomerular filtration rate by 45 and 57 % (both P < 0.001), respectively, and sodium excretion by 96 and 98 % (both P < 0.01). 3. Chloralose-urethane anaesthesia and surgery caused a rise in plasma renin activity but was associated with a suppression of renal renin (50 %, P < 0.01) and angiotensinogen (40 %, P < 0.05) gene expression. Following reduction of RPP to 60 mmHg for 3 h, plasma renin activity was increased more than 7-fold (P < 0.001) and renal renin gene expression about 2-fold (P < 0.05). 4. Chronic (5 days) blockade of angiotensin II receptors with losartan elevated plasma renin activity some 29-fold (P < 0.001) and caused a marked increase (30-fold, P < 0.05) in renal renin gene expression, compatible with angiotensin II exerting a negative feedback control on renin release and gene expression. Reduction of RPP to 60 mmHg for 3 h in these animals had little effect on renal renin gene expression. 5. From these findings it can be concluded that (a) chloralose-urethane anaesthesia and surgery had a stimulatory effect on renin release but suppressed basal levels of renal renin and angiotensinogen gene expression; (b) acute reduction of RPP for 3 h could stimulate renin gene expression in the renin producing cells; and (c) the negative feedback control of angiotensin II on renin release and synthesis which was evident following chronic losartan treatment was not apparent during short-term reduction of RPP.

Gestational changes in fetal renal and hepatic angiotensinogen mRNA and protein

The aim of the study was to determine the amount of angiotensinogen expression and its protein product in fetal sheep liver and kidney in the last third of gestation. Angiotensinogen mRNA was measured by RNase protection assay and its protein levels were measured by radioimmunoassay. Levels were measured at 80, 95, 111, 125 and 139 days. Angiotensinogen mRNA was present in all fetal liver and kidney samples tested. The ratio of hepatic angiotensinogen mRNA/18 S rRNA increased by 100% (P < 0.001) and angiotensinogen levels increased by 33% (P < 0.001) in fetal sheep from 80 to 139 d. Over the same period the ratio of renal angiotensinogen mRNA/18 S rRNA increased by 170% (P < 0.001) and renal angiotensinogen protein increased by 41% (P < 0.001). The levels of angiotensinogen mRNA and its protein in the adult kidney were less than in kidneys of 139 d old fetuses (P < 0.01). There was a direct relationship between levels of angiotensinogen mRNA and its protein in the liver (r = 0.53, P < 0.01, n = 25) and in the kidney (r = 0.75, P < 0.0001, n = 24). These findings demonstrate that there is a significant increase in both hepatic and renal angiotensinogen gene expression in the last third of gestation in the fetal sheep and that this increase is associated with an increase of angiotensinogen levels in both tissues. This increase in angiotensinogen in late gestation could influence the activity of both the intrarenal and circulating renin angiotensin systems.

Angiotensinogen gene-activating elements regulate blood pressure in the brain

Although the angiotensinogen gene is a possible candidate as a determinant of hypertension, the molecular mechanisms of tissue angiotensinogen gene regulation have yet to be clarified. We identified essential transcription regulators of angiotensinogen production in the central nervous system using synthetic double-stranded oligodeoxynucleotides (ODNs) as "decoy" cis elements to block the binding of nuclear factors to promoter regions of the targeted gene. Using a gel mobility shift assay, angiotensinogen gene-activating element (AGE) 2 binding protein was detected in the brain nuclear extracts of both spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto rats (WKYs). Importantly, the binding activity of AGE 2 and angiotensinogen mRNA level were significantly higher in the brain of SHRs than in that of WKYs. Using the decoy approach, we demonstrated a significant decrease in the blood pressure of SHRs by transfection of AGE 2 decoy, but not mismatched, ODNs into the lateral cerebroventricle, accompanied by a significant decrease in brain angiotensinogen concentration and mRNA, and angiotensin II level. That these effects, demonstrated herein, are due to central effects is confirmed by the fact that no changes in circulating levels of angiotensinogen or angiotensin II concentrations were observed. Notably, AGE 2 decoy ODNs did not decrease the blood pressure of WKYs. We conclude that the abnormal expression of AGE 2 binding protein in the central nervous system plays a crucial role in high blood pressure of a genetically hypertensive rat model.

Co-expression of renin-angiotensin system genes in human adipose tissue

OBJECTIVE

The renin-angiotensin system plays a central role in blood pressure regulation, both by affecting renal function and by modulating vascular tone and structure. Recent studies in rodents demonstrated the existence of several components of this system in adipose tissue. The activity of the renin-angiotensin system appears to be regulated by food intake, suggesting that it may be involved in obesity-associated hypertension. Few data are available on the presence of renin-angiotensin system components in human adipose tissue.

MATERIALS AND METHODS

In order to explore the expression of renin-angiotensin system genes in human adipose tissue and adipocytes, total RNA was isolated from whole adipose tissue (subcutaneous and omental) or cultured adipocytes (mammary) and subjected to reverse-transcriptase polymerase chain reaction with primers specific for human angiotensinogen, renin, renin-binding protein, angiotensin converting enzyme, chymase and type 1 and type 2 angiotensin receptors.

RESULTS

Angiotensinogen, angiotensin converting enzyme and type 1 angiotensin receptor genes were widely expressed, both in human adipose tissue and in cultured human adipocytes. Furthermore, we found expression of the chymase and renin-binding protein genes in these samples.

CONCLUSIONS

Our findings suggest the presence of a local renin -angiotensin system in human adipose tissue, with adipocytes being an important part of this system, and prompt speculation that this local renin-angiotensin system may be involved in obesity-related disorders, including hypertension and the metabolic syndrome.

Orphan receptor Arp-1 binds to the nucleotide sequence located between TATA box and transcriptional initiation site of the human angiotensinogen gene and reduces estrogen induced promoter activity

Human angiotensinogen gene contains a C/A polymorphism at 20 bases upstream from the transcriptional initiation site. This sequence binds to the estrogen receptor when nucleoside A is present at this site and reporter constructs containing human angiotensinogen gene promoter with nucleoside A at -20 are transactivated on co-transfection of estrogen receptor in HepG2 cells followed by estrogen treatment. We show here that orphan receptor, Arp-1, which belongs to the COUP family of transcription factors also binds to this sequence. Co-transfection of Arp-1 reduces estrogen induced promoter activity of reporter constructs containing human angiotensinogen gene promoter. On the other hand co-transfection of Arp-1 does not have a significant effect on estrogen induced promoter activity of reporter constructs containing rat angiotensinogen gene promoter. Our data suggests that human and rat angiotensinogen genes are regulated in a different manner by estrogens.

Effects of mineralocorticoid receptor gene disruption on the components of the renin-angiotensin system in 8-day-old mice

Targeted disruption of mineralocorticoid receptor (MR) gene results in pseudohypoaldosteronism type I with failure to thrive, severe dehydration, hyperkalemia, hyponatremia, and high plasma levels of renin, angiotensin II, and aldosterone. In this study, mRNA expression of the different components of the renin-angiotensin system (RAS) were evaluated in liver, lung, heart, kidney and adrenal gland to assess their response to a state of extreme sodium depletion. Angiotensinogen, renin, angiotensin-I converting enzyme, and angiotensin II receptor (AT1 and AT2) mRNA expressions were determined by Northern blot and RT-PCR analysis. Furthermore, in situ hybridization and immunohistochemistry allowed us to identify the cell types involved in the variation of the RAS component expression. In the heterozygous mice (MR+/-), compared with wild-type mice (MR+/+), there was no significant variation of any mRNA of the RAS components. In MR knockout mice (MR-/-), compared with wild-type mice, there were significant increases in the expression level of several RAS components. In the liver, angiotensinogen and AT1 receptor mRNA expressions were moderately stimulated. In the kidney, renin mRNA was increased up to 10-fold and in situ hybridization showed a marked recruitment of renin-producing cells; however, the levels of angiotensin-I converting enzyme mRNA and AT1 mRNA were not changed. Interestingly, in adrenal gland, renin expression was also strongly up-regulated in a thickened zona glomerulosa, whereas AT1 mRNA expression remained unchanged. Altogether, these results demonstrate that in the MR knockout mice model, RAS component expressions are differentially altered, renin being the most stimulated component. Angiotensinogen and AT1 in the liver are also increased, but the other elements of the RAS are not affected.

Appropriate regulation of renin and blood pressure in 45-kb human renin/human angiotensinogen transgenic mice

The renin-angiotensin system is normally subject to servo control mechanisms that suppress plasma renin levels in response to increased blood pressure and increase plasma renin levels when blood pressure falls. In most species, renin is rate limiting, and angiotensinogen circulates at a concentration close to the Km, so varying the concentration of either can affect the rate of angiotensin formation. However, only the plasma renin level responds to changes in blood pressure and sodium balance to maintain blood pressure homeostasis. Therefore, the high plasma human renin levels and the hypertension of mice and rats containing both human renin and angiotensinogen transgenes indicate inappropriate regulation of renin and blood pressure. These anomalies led us to develop new lines of transgenic mice with a longer human renin gene fragment (45 kb) than earlier lines (13 to 15 kb). Unlike their predecessors, the 45-kb hREN mice secrete human renin only from the kidneys, and both the human and mouse renins respond appropriately to physiological stimuli. To determine whether blood pressure is also regulated appropriately, we crossed these new 45-kb hREN mice with mice containing the human angiotensinogen gene. All doubly transgenic mice were normotensive like their singly transgenic and nontransgenic littermates. Moreover, among doubly transgenic mice, both human and mouse plasma renin concentrations were suppressed relative to the singly transgenic 45-kb hREN mice. These findings demonstrate the importance of appropriate cell and tissue specificity of gene expression in constructing transgenic models and affirm the pivotal role played by renal renin secretion in blood pressure control.

The renin-angiotensin system in the vessel wall

The behavior of the circulating renin-angiotensin system is well known; however, the actions of renin and the generation of angiotensin (ANG) II at the tissue level are less appreciated. We have used rat models to study this issue. We examined the cleavage of human angiotensinogen to ANG I by human renin and its inhibition by a human renin inhibitor in an isolated perfused hindlimb preparation from rats which express the human angiotensinogen gene. With this model, we were able to show that renin acts at the site of the vascular wall, rather than in the lumen, to generate ANG I, which is subsequently converted to ANG II. Furthermore, the cleavage is specifically dependent on renin and not on other lysosomal proteases. The renin gene is present in the vascular wall; however, whether or not renin is generated locally to act locally, or whether renin is taken up from the circulation to act locally was not clear. We used the same strain of transgenic rats to test this issue and showed that renin can be taken up by cardiac or coronary vasculature tissue and induces long-lasting local ANG II generation. Locally formed ANG I was converted to ANG II more effectively than infused ANG I. We did additional studies to examine the conversion step from ANG I to ANG II in the vessel wall. We perfused hindlimbs from Sprague-Dawley rats with ANG I and observed ANG II production, which was linear over a 10,000-fold concentration range of ANG I. However, when we increased angiotensin converting enzyme (ACE) gene expression in the vascular bed, which also increased ACE tissue concentrations, we were nevertheless able to demonstrate increased ANG II production with ACE upregulation. Taken together, these results demonstrate (1) the cleavage of local angiotensinogen to ANG I within the vascular wall by renin, (2) renin uptake from the circulation to evoke that local effect, and (3) a potential regulatory effect by vascular tissue ACE on ANG II production in the vessel wall. The findings support the notion of localized renin-angiotensin system-related effects on vascular function and structure.

Human adipose tissue expresses angiotensinogen and enzymes required for its conversion to angiotensin II

Angiotensin II regulates blood pressure and may affect adipogenesis and adipocyte metabolism. Angiotensin II is produced by cleavage of angiotensinogen by renin and angiotensin-converting enzyme in the circulation. In addition, angiotensin II may be produced in various tissues by enzymes of the renin-angiotensin system (RAS) or the nonrenin-angiotensin system (NRAS). We have analyzed the expression of angiotensinogen and enzymes required for its conversion to angiotensin II in human adipose tissue. Northern blot demonstrated angiotensinogen expression in adipose tissue from nine obese subjects. Western blot revealed a distinct band of expected size of the angiotensinogen protein (61 kDa) in isolated adipocytes. RT-PCR, followed by Southern blot, demonstrated renin expression in human adipose tissue. Angiotensin-converting enzyme messenger RNA was detected by RT-PCR, and the identity of the PCR products was verified by restriction enzyme cleavage. Transcripts for cathepsin D and cathepsin G, components of the NRAS, were detected by RT-PCR, verified by restriction enzyme cleavage. We conclude that human adipose tissue expresses angiotensinogen and enzymes of RAS and NRAS. This opens the possibility that angiotensinogen-derived peptides, produced in adipose tissue itself, may affect adipogenesis and play a role in the pathogenesis of obesity.

DBP binds to the proximal promoter and regulates liver-specific expression of the human angiotensinogen gene

Angiotensinogen is the glycoprotein precursor of one of the most potent vasoactive hormones, angiotensin-II. It has been shown recently that an ATF like element (ALE) located between bases -102 and -87 of the human angiotensinogen gene plays an important role in liver specific expression of this gene and binds to CREB/ATF family of transcription factors and a novel factor (ALF). We show here that this sequence binds to the liver enriched transcription factor DBP and cotransfection of expression vector CMV-DBP increases the expression of reporter constructs containing this sequence. In addition, we show that transcription factor C/EBP-delta binds to this sequence and an expression vector containing C/EBP-delta coding region increases the expression of reporter constructs containing this sequence. Since DBP is involved in circadian rhythm, our studies suggest that this sequence may be involved in circadian expression of the human angiotensinogen gene.

Developmental changes in expression of angiotensinogen mRNA in rat nephron segments

We studied the localization of angiotensinogen mRNA in rat nephron segments and the differences in angiotensinogen mRNA levels between male Sprague-Dawley rats at 6 and 12 wk of age using reverse transcription and polymerase chain reaction (RT-PCR). Each nephron segment of the rat kidney was microdissected. Total RNA was prepared and used in the following RT-PCR assay. The PCR products were size-fractionated by agarose gel electrophoresis, visualized with ethidium bromide staining, and identified by Southern blot analysis. The relative amounts of products were determined by densitometry. Strong bands corresponding to angiotensinogen mRNA were detected from proximal convoluted and straight tubules, and weaker bands were found in glomeruli. The signals in all tissues in 12-wk-old rats were weaker than those in 6-wk-old rats. Since local angiotensinogen is the unique substrate of the tissue renin-angiotensin system and exerts an autocrine-paracrine influence on renal function, the changes in tubular angiotensinogen may be related to physiological and morphological changes in the rat kidney during development.

Activation of angiotensinogen gene in cardiac myocytes by angiotensin II and mechanical stretch

Circulating and cardiac renin-angiotensin systems (RAS) play important roles in the development of cardiac hypertrophy. Mechanical stretch of cardiac myocytes induces secretion of ANG II and evokes hypertrophic responses. Angiotensinogen is a unique substrate of the RAS. This study was performed to examine the regulation of the angiotensinogen gene in cardiac myocytes in response to ANG II and stretch. ANG II and stretch significantly increased the levels of angiotensinogen mRNA in cardiac myocytes. Actinomycin D completely inhibited ANG II- and stretch-mediated increases in angiotensinogen mRNA. Although CV-11974 abolished ANG II-mediated increases in mRNA level and promoter activity of the angiotensinogen gene, the inhibition of stretch-mediated activation by CV-11974 was significant but not complete. These results indicate that ANG II activates transcription of the angiotensinogen gene exclusively via ANG II type 1-receptor pathway and that stretch activates such transcription mainly via the same pathway in cardiac myocytes. Furthermore, factors other than ANG II may also be involved in stretch-mediated activation of the angiotensinogen gene in cardiac myocytes.

[The relationship between genetic polymorphisms and disease, illustrated by the renin-angiotensin-aldosterone system and cardiovascular disease]

The role of molecular genetics in the pathophysiology of various diseases is becoming clearer and clearer. In the field of cardiovascular diseases, molecular genetic aspects have been shown to play a definite role in the aetiology of these diseases. Several molecular-genetic variations called polymorphisms, occur in the population. The genes encoding the different components of the reninangiotensin-aldosterone system (RAAS), an important system in the regulation of the function and structure of the heart and vascular wall, also display polymorphisms. For some of these polymorphisms associations with various cardiovascular and renal diseases have been described. At present, this is particularly clear for the relation between angiotensin-converting-enzyme (ACE) polymorphism and the incidence of atherosclerotic complications and diabetic nephropathy, and for the relation between so-called M235 T-variant of the angiotensinogen gene and hypertension. Future research will have to show where it is worthwhile to use these and other polymorphisms as a marker for genetic risk. In what way the different RAAS-polymorphisms relate to functional abnormalities is as yet unclear, as are the potential therapeutic implications.

Endothelin-converting enzyme and angiotensin-converting enzyme in failing hearts of rats with myocardial infarction

We have previously reported that production of endothelin (ET)-1 is markedly increased in failing hearts of rats with chronic heart failure (CHF). It was also reported that the production of angiotensin II (Ang II) is increased in the failing heart. In this study we investigated both converting enzymes of the ET-1 system and the angiotensin system. We used left coronary artery-ligated rats as a model of CHF. The peptide level of ET-1 in the left ventricle (LV) was markedly higher in CHF rats than in control rats. In the LV, expression of preproET-1 mRNA was also markedly higher in CHF rats than in controls. The expression of endothelin-converting enzyme (ECE)-1 mRNA in the rats with CHF was similar to that in controls. Therefore, we believed that the increase in ET-1 production in the failing heart originated from an increase in preproET-1 production rather than increase in ECE. The expression of angiotensin-converting enzyme (ACE) mRNA in failing hearts of CHF rats was significantly higher than that of the sham-operated rats. The expression of angiotensinogen mRNA in failing hearts of these CHF rats was slightly higher than that of the sham-operated rats. This study suggests that there is a difference in the role of peptide synthesis between the ECE system and the ACE system in rats with CHF.

Developmental expression of human angiotensinogen in transgenic mice

Transgenic mice containing the human angiotensinogen (HAGT) gene were utilized to determine the developmental regulation of HAGT expression. RNase protection assay on total RNA obtained from whole transgenic fetuses revealed that HAGT expression was first detected at embryonic day 8.5 (E8.5) and was abundant from E9.5 onward. The earliest expression of the HAGT transgene appeared to precede the earliest expression of the endogenous mouse AGT gene by 1-2 days. Northern blot analysis revealed moderate levels of HAGT mRNA in liver and kidney and low levels of HAGT mRNA in heart and brain from E16.5 (day 16.5 of gestation) onward. HAGT mRNA in liver, although abundant during late gestation and in 2-wk-old and adult mice, decreased transiently around birth. In situ hybridization performed on sections from whole fetuses revealed that HAGT mRNA was restricted to the developing liver and heart between E9.5 and E11.5 but became more widespread to include the developing aorta, brain, subcutaneous tissues, and vertebra at E13.5. In situ hybridization analysis on fetal kidneys from late gestation, newborn, and 2-wk-old mice demonstrated a progressive restriction of HAGT mRNA to developing cortical proximal tubular cells. These data illustrate the developmental tissue-specific regulation of HAGT expression and demonstrate that sequences present in the transgene can confer an appropriate developmental expression profile.

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.

Role of AT1 angiotensin II receptors in renal ischemic injury

The present studies determined the effect of renal ischemia/reperfusion on components of the intrarenal renin-angiotensin system in rats and evaluated the effect of AT1 angiotensin (ANG) II receptor blockade on functional recovery. After bilateral renal pedicle occlusion for 60 min, serum creatinine increased, peaking at 72 h, and returned to sham levels after 120 h. ANG II levels in ischemic kidneys were significantly increased 24 h after reperfusion but did not differ from levels in sham kidneys after 120 h. Both renal cortical angiotensinogen mRNA and proximal tubular AT1 receptor mRNA were significantly reduced early after reperfusion, returning to sham levels by 120 and 72 h, respectively. AT2 ANG II receptor mRNA was undetectable in proximal tubules from sham rats but was consistently present in ischemic rats at 120 h. By histoautoradiography, we found that binding of 125I-labeled ANG II was preserved in glomeruli but was decreased in whole cortex and outer medulla early after reperfusion and was completely blocked by the AT1 antagonist losartan. Treatment of rats with losartan (25 mg/kg s.c. daily), starting at the time of reperfusion, had no effect on expression of proliferating cell nuclear antigen in cortical tubules but caused a significant decrease in serum creatinine at 72 h (ischemia: 334 +/- 69 microM vs. ischemia + losartan: 135 +/- 28 microM; P < 0.025, n = 6). These data indicate that renal ischemic injury causes an early increase in intrarenal ANG II levels, associated with reduction of mRNA for angiotensinogen and proximal tubular AT1 receptors, and maintenance of glomerular ANG II binding. Losartan accelerates recovery of renal function, suggesting that activation of AT1 receptors impairs glomerular filtration in the postischemic kidney.

Captopril modifies gene expression in hypertrophied and failing hearts of aged spontaneously hypertensive rats

The spontaneously hypertensive rat (SHR) exhibits a transition from stable compensated left ventricular (LV) hypertrophy to heart failure (HF) at a mean age of 21 months that is characterized by a decrease in alpha-myosin heavy chain (alpha-MHC) gene expression and increases in the expression of the atrial natriuretic factor (ANF), pro-alpha1(III) collagen, and transforming growth factor beta1 (TGF-beta1) genes. We tested the hypotheses that angiotensin-converting enzyme inhibition (ACEI) in SHR would prevent and reverse HF-associated changes in gene expression when administered prior to and after the onset of HF, respectively. We also investigated the effect of ACEI on circulating and cardiac components of the renin-angiotensin system. ACEI (captopril 2 g/L in the drinking water) was initiated at 12, 18, and 21 months of age in SHR without HF and in SHR with HF. Results were compared with those of age-matched normotensive Wistar-Kyoto (WKY) rats, and to untreated SHR with and without evidence of HF. ACEI initiated prior to failure prevented the changes in alpha-MHC, ANF, pro-alpha1(III) collagen, and TGF-beta1 gene expression that are associated with the transition to HF. ACEI initiated after the onset of HF lowered levels of TGF-beta1 mRNA by 50% (P<.05) and elevated levels of alpha-MHC mRNA two- to threefold (P<.05). Circulating levels of renin and angiotensin I were elevated four- to sixfold by ACEI, but surprisingly, plasma levels of angiotensin II were not reduced. ACEI increased LV renin mRNA levels in WKY and SHR by two- to threefold but did not influence LV levels of angiotensinogen mRNA. The results suggest that the anti-HF benefits of ACEI in SHR may be mediated, at least in part, by effects on the expression of specific genes, including those encoding alpha-MHC, ANF, TGF-beta1, pro-alpha1(III) collagen, and renin-angiotensin system components.

Essential hypertension and 5' upstream core promoter region of human angiotensinogen gene

The angiotensinogen (AGT) gene M235T variant is associated with essential hypertension and elevated plasma AGT concentrations, although the underlying mechanisms are unknown. Recent studies have suggested that AGCE 1 (human AGT gene core promoter element 1) located in the 5' upstream core promoter region (position -25 to -1) of the human AGT gene has an important part in the expression of AGT mRNA by binding with transcription factor AGCF 1 (human AGT gene core promoter element binding factor 1), and a mutation at -20 from adenine to cytosine (A-20C) increases the level of expression of this transcript. We therefore examined subjects with this mutation to study the association with increased plasma AGT concentrations and with essential hypertension. One hundred eighty-eight subjects receiving no antihypertensive medication were examined with regard to the correlation between A-20C and plasma AGT concentrations, and 234 subjects were studied with respect to the association between A-20C and essential hypertension. A-20C was determined by polymerase chain reaction-restriction fragment length polymorphism analysis with EcoOR 109I. Multiple regression analysis showed a weak but significant correlation between A-20C and plasma AGT concentrations (P=.047) and essential hypertension (P=.049). The results suggest that A-20C may underlie the increase in plasma AGT concentrations and be involved in the development of essential hypertension.

Nitric oxide and the renin angiotensin system: contributions to blood pressure in the young rat

The present study was designed to investigate the effects of chronic administration of the arginine analogue L-Name (50 mg/kg body weight), the angiotensin converting enzyme inhibitor, perindopril (2 mg/kg body weight), and perindopril (2 mg/kg) plus L-Name (50 mg/kg) on blood pressure, plasma renin activity, plasma angiotensinogen, and hepatic angiotensinogen mRNA levels in young and adult rats. The drugs were given daily from birth to day 21 to puppies and for 15 days to adults. Analytical procedures were performed on day 21 for the puppies and at 10 weeks for the adults. In puppies, blood pressure did not change with L-Name, it decreased to 45% of control values (P < 0.001) with perindopril, and decreased to 77% of control values (P < 0.05) with perindopril plus L-Name. In adults, blood pressure increased to 129% of control values (P < 0.02) with L-Name, decreased to 80% of control values (P < 0.05) with perindopril, and did not change with perindopril plus L-Name. Compared with controls, plasma renin activity was unchanged in puppies and adults with L-Name, undetectable in puppies and slightly increased in adults with perindopril, undetectable in puppies and slightly decreased in adults with perindopril plus L-Name. With L-Name, angiotensinogen mRNA levels were unchanged in puppies and slightly increased in adults, while plasma angiotensinogen levels were decreased (P < 0.05) in puppies and increased (P < 0.01) in adults; with perindopril, angiotensinogen mRNA levels were unchanged in puppies and slightly decreased in adults, while plasma angiotensinogen levels were undetectable in puppies and decreased (P < 0.05) in adults; with perindopril plus L-Name, angiotensinogen mRNA levels were unchanged in puppies while plasma angiotensinogen levels were undetectable in puppies and decreased (P < 0.01) in adults. This study suggests that during the early postnatal period (1) nitric oxide does not exert a basal vasodilator tone but contributes to the hypotensive state induced by perindopril, (2) angiotensin II is essential to maintain blood pressure, (3) and angiotensinogen mRNA levels are not influenced by nitric oxide or angiotensin II.

Stretch-induced proliferation of cultured vascular smooth muscle cells and a possible involvement of local renin-angiotensin system and platelet-derived growth factor (PDGF)

This experiment was designed to investigate the possible involvement of angiotensin II (Ang II) and platelet-derived growth factor (PDGF) in the mechanism underlying stretch-induced proliferation of vascular smooth muscle cells (SMCs). SMCs from the rabbit aortic media were grown on polystyrene rubber-bottomed dishes coated with type I collagen. Cells were stretched cyclically by a vacuum-operated downward flexion of the culture dish bottom. A 1.4- to 1.6-fold increase in proliferation of SMCs was induced by cyclic stretching, as determined by [3H]-thymidine incorporation, in a stretch force-dependent manner in the range of 5% to 15% elongation, 30 cycles/min for 24 h. Expression of PDGF-B chain mRNA was up-regulated in a time-dependent manner in the range of 2 to 24 h, 10% elongation, and 30 cycles/min. Saralasin, a selective antagonist of Ang II, and captopril, an angiotensin I converting enzyme inhibitor, significantly suppressed the stretch-induced proliferation of SMCs. Blockade of angiotensinogen mRNA translation by antisense oligonucleotide inhibited proliferation under the mechanical strain. Stretch-induced proliferation was inhibited by 78% in the presence of anti-PDGF-AB neutralizing antibody. Increased expression of PDGF-B chain mRNA under the mechanical strain was inhibited by treatment with saralasin. Our results indicate that the stretch-induced proliferation of cultured SMCs is mediated at least in part via increased production of Ang II by the local renin-angiotensin system and a subsequent up-regulation of PDGF-B chain mRNA in an autocrine-paracrine manner.

ATF-like element contributes to hepatic activation of human angiotensinogen promoter

Angiotensinogen is the precursor protein of angiotensin II that is involved in regulating blood pressure and electrolyte homeostasis, and it is mainly synthesized in the liver. In the present study, we analyzed the human angiotensinogen proximal promoter region by means of Chloramphenicol acetyltransferase assays, and suggested that the region from -106 to +44 is sufficient for hepatoma cell line (HepG2)-specific expression. Electrophoretic mobility shift assays using ALE (ATF-like element, -102 to -87) fragment identified CREB/ATF family nuclear factors and novel ones, ALF (ALE-binding factor). The deletion and in vivo competition of ALE decreased the human angiotensinogen promoter activity. Furthermore, the heterologous promoter analysis demonstrated that ALE acts as a HepG2-dependent activating element. These results indicate that ALE plays an important role in hepatic expression of human angiotensinogen gene.

Angiotensinogen gene expression in adipose tissue: analysis of obese models and hormonal and nutritional control

Synthesis of angiotensin II (ANG II) has recently been described in adipose cells and has been linked to regulation of adiposity. Angiotensinogen (AGT), the substrate from which ANG II is formed, was previously shown to be elevated in adipose tissue of obese (ob/ob and db/db) mice and regulated by nutritional manipulation. It is unknown, however, whether overexpression of adipose AGT can be extended to other models of obesity and whether hormonal and/or nutritional factors directly regulate AGT expression in adipocytes. We investigated these possibilities by analyzing AGT mRNA levels in adipose tissue of obese Zucker rats, viable yellow (Avy) mice, and humans and by treating 3T3-L1 adipocytes with insulin, glucose, and a beta-adrenergic agonist. We demonstrate that AGT mRNA is decreased by approximately 50 and 80%, respectively, in adipose tissue of obese vs. lean Zucker rats and Avy mice. We also report that AGT is expressed at variable levels in human adipose tissue. Finally, we show that AGT mRNA is upregulated by insulin and downregulated by beta-adrenergic stimulation in adipocytes.