Tsukuba Hypertensive Mice Research Articles

Is the anti-aging effect of ACE2 due to its role in the renin-angiotensin system?-Findings from a comparison of the aging phenotypes of ACE2-deficient, Tsukuba hypertensive, and Mas-deficient mice.

Angiotensin converting enzyme 2 (ACE2) functions as an enzyme that produces angiotensin 1-7 (A1-7) from angiotensin II (AII) in the renin-angiotensin system (RAS). We evaluated aging phenotypes, especially skeletal muscle aging, in ACE2 systemically deficient (ACE2 KO) mice and found that ACE2 has an antiaging function. The characteristic aging phenotype observed in ACE2 KO mice was not reproduced in mice deficient in the A1-7 receptor Mas or in Tsukuba hypertensive mice, a model of chronic AII overproduction, suggesting that ACE2 has a RAS-independent antiaging function. In this review, the results we have obtained and related studies on the aging regulatory mechanism mediated by RAS components will be presented and summarized. We evaluated the aging phenotype of ACE2 systemically deficient (ACE2 KO) mice, particularly skeletal muscle aging, and found that ACE2 has an antiaging function. The characteristic aging phenotype observed in ACE2 KO mice was not reproduced in Mas KO mice, angiotensin 1-7 receptor-deficient mice or in Tsukuba hypertensive mice, a model of chronic angiotensin II overproduction, suggesting that the antiaging functions of ACE2 are independent of the renin-angiotensin system (RAS).

Innovation of novel anti-hypertensive drug(s) that inhibit adrenal aldosterone synthase gene (CYP11B2) expression

In Japan, hypertensive patients are speculated to be 40 million, and 30 million among them are poor controlled. Moreover, 20% of them are estimated as "resistant hypertension" those are above their target blood pressure even in the simultaneous use of three different classes anti-hypertensive drugs. Recently, aldosterone is recognized as one of the main causes of the etiology of "resistant hypertension." Therefore, it is important to discover novel drugs that inhibit the synthesis and secretion of aldosterone. We recently generated a stable H295R cell line expressing aldosterone synthase gene (CYP11B2) promoter (-1521~+2)/luciferase cDNA chimeric reporter construct. We thereafter established a high-throughput screening (HTS) system for the discovery of novel anti-hypertensive drugs that inhibit angiotensin II-induced CYP11B2 expression using the cell line. After confirmation of its validation (Z' score > 0.5), we performed HTS using Core Library (9,600 chemical compounds) and Validated Compound Library (1,979 chemical compounds) obtained from Drug Discovery Initiative (The University of Tokyo), and Tohoku University Chemical Library (5,562 chemical compounds), respectively. We obtained several hit compounds from each library, and focused on one compound (bortezomib) obtained from Validated Compound Library. The compound did not affect cell viability by WST-1 assay, and was demonstrated to lower blood pressure of Tsukuba Hypertensive Mice, significantly. The compound may therefore be a potential candidate of novel anti-hypertensive drugs in the future.

Different effects of the deletion of angiotensin converting enzyme 2 and chronic activation of the renin-angiotensin system on muscle weakness in middle-aged mice.

Inhibition of the renin-angiotensin system (RAS) has been shown to alleviate muscle atrophy both under pathological conditions and during physiological aging. We recently reported that the deletion of angiotensin converting enzyme 2 (ACE2), which converts Angiotensin II to Angiotensin-(1-7) in mice, leads to the early manifestation of aging-associated muscle weakness along with the increased expression of p16INK4a, a senescence-associated gene, and increased central nuclei in the tibialis anterior (TA) muscle in middle age. As ACE2 is multifunctional and functions beyond its role in the RAS, we investigated whether activation of the RAS primarily contributes to muscle weakness in ACE2 knockout (KO) mice by comparing these mice to Tsukuba hypertensive (TH) mice that overproduce human angiotensin II. The grip strength of young (6 months) and middle-aged (15 months) TH mice was consistently lower than that of wild-type mice at the same ages. Middle-aged TH mice were continuously lean with extremely reduced adiposity. Central nuclei in the gastrocnemius (GM) muscle were increased in ACE2KO mice, while no apparent morphological change was observed in the GM muscles of TH mice. Increased expression of p16INK4a along with alterations in the expression of several sarcopenia-associated genes were observed in the GM muscles of ACE2KO mice but not TH mice. These findings suggest that chronic overactivation of the RAS does not primarily contribute to the early aging phenotypes of skeletal muscle in ACE2KO mice.

A15762 Comparison of skeletal muscle aging between ACE2 deficient mice and Tsukuba hypertensive mice with over-activation of the renin-angiotensin system

A15762 Comparison of skeletal muscle aging between ACE2 deficient mice and Tsukuba hypertensive mice with over-activation of the renin-angiotensin system

Activation of the renin-angiotensin system in mice aggravates mechanical loading-induced knee osteoarthritis.

Epidemiological studies have shown an association between hypertension and knee osteoarthritis (OA). The purpose of this study was to investigate whether activation of the renin–angiotensin system (RAS) can aggravate mechanical loading-induced knee OA in mice. Eight-week-old male Tsukuba hypertensive mice (THM) and C57BL/6 mice were divided into four groups: i) running THM group, ii) running C57BL/6 mice group, iii) non-running THM group, and iv) non-running C57BL/6 mice group. Mice in the running group were forced to run (25 m/min, 30 min/day, 5 days/week) on a treadmill. All mice in the four groups (n=10 in each group) were euthanized after 0, 2, 4, 6, or 8 weeks of running or natural breeding. Cartilage degeneration in the left knees was histologically evaluated using the modified Mankin score. Expression of Col X, MMP-13, angiotensin type 1 receptor (AT1R), and AT2R was examined immunohistochemically. To study the effects of stimulation of the AT1R in chondrocytes by mechanical loading and/or Angiotensin II (AngII) on transduction of intracellular signals, phosphorylation levels of JNK and Src were measured in bovine articular chondrocytes cultured in three-dimensional agarose scaffolds. After 4 weeks, the mean Mankin score for the lateral femoral condylar cartilage was significantly higher in the THM running group than in the C57BL/6 running group and non-running groups. AT1R and AT2R expression was not detected at 0 weeks in any group but was noted after 4 weeks in the THM running group. AT1R expression was also noted at 8 weeks in the C57BL/6 running group. The expression levels of AT1R, COL X, and MMP-13 in chondrocytes were significantly higher in the THM running group than in the control groups. Positive significant correlations were noted between the Mankin score and the rate of AT1R-immunopositive cells, between the rates of AT1R- and Col X-positive cells, and between the rates of AT1Rand AT2R-positive cells. The phosphorylation level of JNK was increased by cyclic compression loading or addition of AngII to the cultured chondrocytes and was reversed by pretreatment with an AT1R blocker. A synergistic effect on JNK phosphorylation was observed between compression loading and AngII addition. Transgene activation of renin and angiotensinogen aggravated mechanical load-induced knee OA in mice. These findings suggest that AT1R expression in chondrocytes is associated with early knee OA and plays a role in the progression of cartilage degeneration. The RAS may be a common molecular mechanism involved in the pathogenesis of hypertension and knee OA.

Sleep/Wake Behaviors in Mice During Pregnancy and Pregnancy-Associated Hypertensive Mice.

In humans and other mammals, sleep is altered during pregnancy. However, no studies have been conducted on sleep/wakefulness during pregnancy in mice. In this study, we examined sleep/wakefulness in female C57BL/6 mice during pregnancy. We also examined sleep/wake behaviors in an animal model of preeclampsia, pregnancy-associated hypertensive (PAH) mice, in which increased angiotensin causes hypertension. Sleep/wake behaviors of female C57BL/6 and PAH mice were examined based on electroencephalogram (EEG) or electromyogram recordings before, during, and after pregnancy. To examine whether high blood pressure disrupts the integrity of the blood-brain barrier in PAH mice, Evans blue dye was injected intravenously. Angiotensin II receptor blocker (olmesartan)-administered PAH mice and female Tsukuba hypertensive mice were also examined. C57BL/6 mice showed a decreased total wake time and increased nonrapid eye movement (NREM) sleep time during late pregnancy. Rapid eye movement (REM) sleep time did not change during the course of pregnancy. PAH mice exhibited a general slowing of EEG during late pregnancy and subsequently returned to apparently normal sleep/wakefulness after delivery. All PAH mice exhibited multiple focal leakages of Evans blue dye in the brain. Spike-and-wave discharges were observed in 50% of PAH mice. Olmesartan-administered PAH mice did not show general slowing of EEG. Tsukuba hypertensive mice showed a normal time spent in wakefulness and NREM sleep and a decreased total REM sleep time. This study showed pregnant-stage-specific changes in sleep/wakefulness in C57BL/6 mice. Furthermore, PAH mice may be useful as an animal model for eclampsia.

Suppressive effects of RXR agonist PA024 on adrenal CYP11B2 expression, aldosterone secretion and blood pressure.

The effects of retinoids on adrenal aldosterone synthase gene (CYP11B2) expression and aldosterone secretion are still unknown. We therefore examined the effects of nuclear retinoid X receptor (RXR) pan-agonist PA024 on CYP11B2 expression, aldosterone secretion and blood pressure, to elucidate its potential as a novel anti-hypertensive drug. We demonstrated that PA024 significantly suppressed angiotensin II (Ang II)-induced CYP11B2 mRNA expression, promoter activity and aldosterone secretion in human adrenocortical H295R cells. Human CYP11B2 promoter functional analyses using its deletion and point mutants indicated that the suppression of CYP11B2 promoter activity by PA024 was in the region from -1521 (full length) to -106 including the NBRE-1 and the Ad5 elements, and the Ad5 element may be mainly involved in the PA024-mediated suppression. PA024 also significantly suppressed the Ang II-induced mRNA expression of transcription factors NURR1 and NGFIB that bind to and activate the Ad5 element. NURR1 overexpression demonstrated that the decrease of NURR1 expression may contribute to the PA024-mediated suppression of CYP11B2 transcription. PA024 also suppressed the Ang II-induced mRNA expression of StAR, HSD3β2 and CYP21A2, a steroidogenic enzyme group involved in aldosterone biosynthesis. Additionally, the PA024-mediated CYP11B2 transcription suppression was shown to be exerted via RXRα. Moreover, the combination of PPARγ agonist pioglitazone and PA024 caused synergistic suppressive effects on CYP11B2 mRNA expression. Finally, PA024 treatment significantly lowered both the systolic and diastolic blood pressure in Tsukuba hypertensive mice (hRN8-12 x hAG2-5). Thus, RXR pan-agonist PA024 may be a candidate anti-hypertensive drugs that acts via the suppression of aldosterone synthesis and secretion.

Long-Range Control of Renin Gene Expression in Tsukuba Hypertensive Mice.

Renin, a rate-limiting enzyme in the renin–angiotensin system, is regulated to maintain blood pressure homeostasis: renin gene expression in the kidney is suppressed in a hypertensive environment. We found that expression of a 15-kb human RENIN (hREN) transgene was aberrantly upregulated (>4.2-fold), while the endogenous mouse renin (mRen) gene was suppressed (>1.7-fold) in Tsukuba hypertensive mice (THM), a model for genetically induced hypertension. We then generated transgenic mice using a 13-kb mRen gene fragment that was homologous to the 15-kb hREN transgene and found that its expression was also upregulated (>3.1-fold) in THM, suggesting that putative silencing elements of the renin genes were distally located in the loci. We next examined the possible role of a previously identified mouse distal enhancer (mdE) located outside of the 13-kb mRen gene fragment. Deletion of the mdE in the context of a 156-kb mRen transgene did not affect its transcriptional repression in THM, implying that although the silencing element of the mRen gene is located within the 156-kb fragment tested, it is distinct from the mdE. Consistent with these results, deletion of the 63-kb region upstream of the mdE from the endogenous mRen gene locus abrogated its transcriptional repression in THM. We finally tested whether dysregulation of the short renin transgenes also occurred in the fetal or neonatal kidneys of THM and found that their expression was not aberrantly upregulated, demonstrating that aberrant regulation of short renin transgenes commences sometime between neonate and adult periods.

Abstract 529: Treatment With Telmisartan Inhibits Kidney Injury in High Salt-loading Tsukuba Hypertensive Mice With Attenuation of Sympathetic Nervous System

Objective: It is well known that excessive salt intake and/or activation of renin-angiotensin system (RAS) increases blood pressure in part via an increase in sympathetic nerve activity. To further examine the interaction of these factors, we employed transgenic mice carrying both the human renin and angiotensinogen genes (Tsukuba hypertensive mice) and studied the effects of high salt loading and telmisartan on mortality, blood pressure and kidney functions. Design and Method: Ten-week-old male Tsukuba hypertensive mice (TH) were administrated control chow or the chow containing 8% NaCl with or without telmisartan (1 mg/kg/day) and PPAR-γ antagonist, GW9662, in drinking water for 8 weeks. Blood pressure was assessed by radio telemetry method. Urine samples were obtained before and after salt-loading. Concentrations of urinary adrenalin and noradrenalin were measured by ELISA. Expressions of ENaC-α, P47 and p67-phox mRNA in the kidney were measured by RT-PCR. Results: Survival rate 8 weeks after treatment was decreased in salt-loading TH (sTH) mice compared with control TH (cTH). This decrease was improved by the treatment with telmisartan. Blood pressure in sTH mice was significantly higher compared with cTH mice and the treatment with telmisartan mice decreased blood pressure. Urinary sodium concentration was higher in sTH mice compared with cTH mice and treatment with telmisartan further increased urinary sodium concentration in sTH mice. Expression of ENaC-α in did not between sTH mice and cTH mice. Treatment with telmisartan decreased expression of ENaC-α. Urinary adrenalin and noradrenalin concentrations were higher in sTH mice compared with cTH mice. These increases were attenuated by treatment with telmisartan. Expressions of p47 and p67-phox in sTH mice were increased more markedly compared with cTH mice. These increase were also attenuated by treatment with telmisartan. However, these possible protective effects of telmisartan were not influenced by the co-treatment with GW9662. Conclusion: These results suggested that salt-loading enhanced an increase in blood pressure, superoxide anion production, sympathetic activity and mortality in concert with activated RAS.

Renin inhibition ameliorates renal damage through prominent suppression of both angiotensin I and II in human renin angiotensinogen transgenic mice with high salt loading

The renin-angiotensin-aldosterone system (RAAS) plays pivotal roles in the pathogenesis of chronic kidney disease (CKD) progression. Aliskiren, a direct renin inhibitor, inhibits the rate-limiting step of the RAAS without any alternative pathway. It is proven to reduce albuminuria in CKD patients treated with angiotensin blockade. However, there are few reports which evaluate the advantage of aliskiren as the first-line drug against CKD progression in RAAS-activated hypertensive patients. Tsukuba hypertensive mice (THM), double transgenic mice carrying both the human renin and human angiotensinogen genes, were fed a high-salt diet and treated with hydraladine, ramipril and aliskiren for 10weeks. Blood pressure and urinary albumin excretion were measured every 2weeks during the experimental period. We evaluated renal histological changes and gene expression. Plasma angiotensin concentration was measured to evaluate the RAAS inhibitory effect. High-salt-loaded THM showed severe hypertension and renal injury. All antihypertensive drugs suppressed blood pressure and prevented renal disease progression. RAAS blockade showed a higher renoprotective effect than hydraladine despite an equivalent blood pressure lowering effect. Aliskiren exhibited even stronger renoprotection than ramipril. Plasma angiotensin concentration was increased in THM fed both normal salt and high salt. Hydraladine did not alter the plasma angiotensin concentration. Ramipril significantly decreased angiotensin II concentration. Aliskiren treatment almost completely suppressed angiotensin I and resulted in lower angiotensin II concentration than ramipril treatment. Aliskiren prevents renal disease progression by suppressing both angiotensin I and II in RAAS-activated pathology. Our data suggest the application of a renin inhibitor for preventing kidney disease progression in CKD patients.

Abstract 504: Muscle Regeneration is Impaired in Diabetic Mice

Background Sarcopenia is the degenerative loss of skeletal muscle mass which impaired quality of life in the elderly. On the other hand, sarcopenic obesity which is a loss of muscle and a concomitant increase in fat is reported to increase in life-style related diseases. Especially the prevalence of sarcopenia is greater in patients with type-2 diabetes mellitus (T2DM) than in non-diabetic subjects. However, the detailed mechanism of such muscle degeneration has not been well established. Here, we investigated muscle regeneration using muscle-injured models in life-style related disease mouse model such as angiotensin II overexpression mice for hypertension and obese diabetic mice for diabetes. Methods Male eight-week-old wild-type mice (C57BL6), Tsukuba hypertensive mice (transgenic mice carrying human renin and angiotensinogen genes) and T2DM mice (KKAy) were undergone intramuscular injection of cardiotoxin (Ctx) (100uL/10uM) into tibia. After two weeks, muscle were removed and stained with hematoxylin and eosin. KKAy replaced by bone marrow prepared from GFP-transgenic mice were generated by 8 Gy whole body X-ray irradiation. Results Treatment with Ctx showed increased muscle satellite cells where nucleuses were observed in the center of cells. In Tsukuba hypertensive mice, inflammatory cells were significantly accumulated in muscle compared with C57BL6, but muscle regeneration was not significantly impaired. KKAy mice exhibited impaired muscle regeneration. Tibia weight was a half in Ctx-injected KKAy compared with Ctx non-injected KKAy, and Ctx-injected and non-injected C57BL6 tibia. Moreover, remarkable fat deposition was observed in Ctx-treated muscle of KKAy. Such change was also observed in another diabetic mouse model, db/db, but not in streptozocin-induced diabetic mice. Fat deposition was remarkably increased in aged KKAy (6-month-old) compared with younger mice (8-week-old). In GFP-chimeric mice, fat tissue showed highly GFP-positive indicating that fat tissue was generated from marrow cells. Conclusion Diabetic mice showed significantly impaired muscle regeneration with fat deposition, suggesting that diabetes enhanced sarcopenic obesity possibly due to inhibitory effect of marrow cell differentiation.

Effects of aging and uninephrectomy on renal changes in Tsukuba hypertensive mice

Renal dysfunction is accelerated by various factors such as hypertension, aging and diabetes. Glomerular hyper-filtration, considered one of the major risk factors leading to diabetic nephropathy, is often encountered in diabetic patients. However, the interrelationship of these risk factors during the course and development of renal dysfunction has not been fully elucidated. In this study, the effects of aging and uninephrectomy (UNx)-induced hyperfiltration on renal changes were investigated in Tsukuba hypertensive mice (THM) carrying both human renin and angiotensinogen genes. In THM, the urinary albumin/creatinine (Alb/Cr) ratio was elevated with age without a concomitant increase in the plasma Cr concentration. Moreover, the urinary neutrophil gelatinase-associated lipocalin/Cr (NGAL/Cr) ratio, the renal monocyte chemoattractant protein-1 (MCP-1) mRNA expression and the renal collagen type I α 2 (COL1A2) mRNA expression were also increased with age. Age-related albuminuria in THM is likely caused by renal tubular damage, enhanced inflammatory response and tubulointerstitial fibrosis. Furthermore, following UNx, the urinary Alb/Cr ratio and the plasma Cr concentration were increased in THM. The urinary NGAL/Cr ratio and the renal MCP-1 and COL1A2 mRNA expression were not affected by UNx. These results suggested that UNx-induced albuminuria in THM was caused by glomerular dysfunction, rather than renal tubular injury. In conclusion, this study demonstrated for the first time the effects of aging and UNx on renal changes in THM. These findings strongly reinforce the significance of applying a diversity of therapeutic approaches to the management of renal dysfunction.

Angiotensin II- and Salt-Induced Kidney Injury through Rac1-Mediated Mineralocorticoid Receptor Activation

Experiments with hyperaldosteronemic animals suggest that, despite lowering plasma aldosterone, salt worsens renal injury by paradoxical activation of the mineralocorticoid receptor (MR). Salt and aldosterone synergistically contribute to renal impairment through Rac1-mediated activation of the MR, but whether angiotensin II also promotes renal injury through this mechanism is unknown. Here, we placed angiotensin II-overproducing double transgenic Tsukuba hypertensive mice on a low- or high-salt intake for 6 weeks and treated some animals with adrenalectomy, the MR antagonist eplerenone, the Rac inhibitor EHT1864, or hydralazine. High-salt intake, but not low-salt intake, led to hypertension and prominent kidney injury. Adrenalectomy prevented angiotensin II/salt-induced nephropathy in mice receiving high-salt intake, which was recapitulated by aldosterone supplementation, suggesting the involvement of aldosterone/MR signaling. Plasma aldosterone levels, however, were lower in high- than low-salt conditions. Instead, angiotensin II/salt-evoked MR activation associated with Rac1 activation and was not dependent on plasma aldosterone level. Both EHT1864 and eplerenone repressed the augmented MR signaling and mitigated kidney injury with partial but significant reduction in BP with high-salt intake. Hydralazine similarly reduced BP, but it neither suppressed the Rac1-MR pathway nor ameliorated the nephropathy. Taken together, these results show that angiotensin II and salt accelerate kidney injury through Rac1-mediated MR activation. Rac inhibition may be a promising strategy for the treatment of CKD.

Aldosterone blockade by Spironolactone improves the hypertensive vascular hypertrophy and remodeling in angiotensin II overproducing transgenic mice

Objectives and backgroundRecent evidence has revealed that aldosterone (ALDO) is produced in the vasculature, and acts directly in the cardiovascular system. This study was designed to examine the role of ALDO in the process of long-term renin–angiotensin system (RAS) induced vascular remodeling. Material and methodHypertensive transgenic mice that overproduce angiotensin II (AngII), i.e., Tsukuba-Hypertensive-Mice (THM), were given tap water or 1% salt water and treated with or without Spironolactone (SPRL: 20mg/kg/day) for 4 weeks. We also employed A7r5 cells and investigated the effect of SPRL on the AngII mediated signal transduction in the vascular smooth muscle cells. ResultsIntimal hyperplasia, medial hypertrophy and degradation of medial elastic laminae were observed in the abdominal aorta, independent of blood pressure. Taking 1% salt water markedly enhanced these changes. In contrast, SPRL-treated THM showed almost complete disappearance of these intimal hyperplasia and medial hypertrophy. Osteopontin (OPN) was markedly up-regulated in the intima and media. However, it was inhibited by SPRL treatment in spite of high level of AngII. In A7r5 cells, AngII (10−7μM) induced OPN expression and pretreatment with MEK, PI3K, and EGFR inhibitor suppressed it. SPRL pretreatment also inhibited AngII-induced ERK and AKT phosphorylation, and resulted in the suppression of AngII-induced OPN expression. ConclusionsALDO blockade by SPRL restores the vascular remodeling caused by the long-term RAS enhancement even in the high level of AngII, independent of blood pressure. Blocking AngII alone may not be sufficient, and direct ALDO blockade is also important to prevent vascular disease.

Activation of Renin-Angiotensin System Induces Osteoporosis Independently of Hypertension

Hypertension and osteoporosis are two major age-related disorders; however, the underlying molecular mechanism for this comorbidity is not known. The renin-angiotensin system (RAS) plays a central role in the control of blood pressure and has been an important target of antihypertensive drugs. Using a chimeric RAS model of transgenic THM (Tsukuba hypertensive mouse) expressing both the human renin and human angiotensinogen genes, we showed in this study that activation of RAS induces high turnover osteoporosis with accelerated bone resorption. Transgenic mice that express only the human renin gene were normotensive and yet exhibited a low bone mass, suggesting that osteoporosis occurs independently of the development of hypertension per se. Ex vivo cultures showed that angiotensin II (AngII) acted on osteoblasts and not directly on osteoclast precursor cells and increased osteoclastogenesis-supporting cytokines, RANKL and vascular endothelial growth factor (VEGF), thereby stimulating the formation of osteoclasts. Knockdown of AT2 receptor inhibited the AngII activity, whereas silencing of the AT1 receptor paradoxically enhanced it, suggesting a functional interaction between the two AngII receptors on the osteoblastic cell surface. Finally, treatment of THM mice with an ACE inhibitor, enalapril, improved osteoporosis and hypertension, whereas treatment with losartan, an angiotensin receptor blockers specific for AT1, resulted in exacerbation of the low bone mass phenotype. Thus, blocking the synthesis of AngII may be an effective treatment of osteoporosis and hypertension, especially for those afflicted with both conditions.

Absence of Peroxisome Proliferator-Activated Receptor-α Abolishes Hypertension and Attenuates Atherosclerosis in the Tsukuba Hypertensive Mouse

Peroxisome proliferator-activated receptor-alpha is widely distributed in the vasculature where it is believed to exert pleiotropic antiatherogenic effects. Its role in the regulation of blood pressure is still unresolved; however, some evidence suggests that it may affect the renin-angiotensin system. We investigated its role in angiotensin II-induced hypertension in the Tsukuba hypertensive mouse (THM). This is a model of hypertension and atherosclerosis because of high angiotensin II and aldosterone levels as a result of the transgenic expression of the entire human renin-angiotensin system. Making the THM animals deficient in Peroxisome proliferator-activated receptor-alpha (THM/PPARKO) totally abolished hypertension and myocardial hypertrophy. This was accompanied by a reduction in plasma human active renin in THM/PPARKO mice compared with THM animals from 3525+/-128 mU/L to 1910+/-750 mU/L (P<0.05) and by a normalization of serum aldosterone (1.6+/-0.29 nmol/L versus 3.4+/-0.69 nmol/L; P=0.003). In the THM/PPARKO mice, the extent of atherosclerosis at the aortic sinus after a 12-week period on an atherogenic diet was decreased by >80%. In addition, the spontaneous formation of foam cells from peritoneal macrophages, a blood pressure-independent event, was reduced by 92% in the THM/PPARKO mice, suggesting protection from the usual oxidative stress in these animals, possibly because of lower prevailing angiotensin II levels. Finally, chronic fenofibrate treatment further elevated blood pressure in THM animals but not in THM/PPARKO animals. Taken together, these data indicate that peroxisome proliferator-activated receptor-alpha may regulate the renin-angiotensin system. They raise the possibility that its activation may aggravate hypertension and hasten atherosclerosis in the context of an activated renin-angiotensin system.

A-type Natriuretic Peptide Level in Hypertensive Transgenic Mice

A-type (atrial) natriuretic peptide (ANP) levels in heart and plasma were examined by immunohistochemistry, electron microscopy, and radioimmunoassay (RIA) in hypertensive transgenic mice (Tsukuba hypertensive mice; THM). Additionally, the ANP mRNA level in the heart was measured using real-time polymerase chain reaction (PCR) assay. The blood pressure and the ratio of heart weight to body weight in THM was significantly higher than those in the control mice (C57BL/6J). The number of ANP-granules and ANP immunoreactivity in the auricular cardiocytes were significantly lower in THM than in the control. Ultrastructurally, the ventricular cardiocytes in the THM occasionally had ANP-like granules, which were not present in the controls. Using RIA, the plasma, auricular, and ventricular ANP concentrations were significantly higher in THM than in the control, but there was no significant difference in plasma cyclic guanosine monophosphate (GMP) concentration between THM and the control. The ANP mRNA levels of the auricular and ventricular cardiocytes in the THM were siginificantly higher than those in the controls. The present study suggested that the ANP release system of the auricular cardiocytes in these transgenic mice is different from normal (control mice).

Renin, cyclooxygenase-2 and neuronal nitric oxide synthase in the kidneys of transgenic Tsukuba hypertensive mouse.

The transgenic Tsukuba hypertensive mouse (THM), which expresses the human renin and angiotensinogen genes, develops hypertension secondary to increased renin-angiotensin system activity. The aim of the present study was to assess expression of the renin, cyclooxygenase-2 (COX-2), and neuronal nitric oxide synthase (nNOS) proteins in THM kidneys by immunohistochemical stainings. Renin expression was decreased in the THM kidneys when compared to kidneys from heterozygotes or control mice. Although no differences were observed in nNOS expression, overexpression of the COX-2 protein was observed in the macula densa cells in THM kidneys.

Depressor effect induced by dipeptide, Val-Tyr, in hypertensive transgenic mice is due, in part, to the suppression of human circulating renin-angiotensin system.

1. In the present study, the depressor action of the dipeptide Val-Tyr, with an in vivo antihypertensive effect, was investigated in transgenic mice carrying the human renin gene cross-mated with mice bearing the human angiotensinogen gene (Tsukuba Hypertensive Mouse; THM). 2. Single oral administration of Val-Tyr (0.1 mg/g) to 11-week-old THM resulted in a prolonged reduction of blood pressure for up to 9 h. The effect clearly demonstrated that the Val-Tyr absorbed acted on the enhanced human renin-angiotensin system (RAS). 3. After Val-Tyr administration, an approximate eightfold higher increment of plasma Val-Tyr was observed at 1 h (3406 +/- 211 fmol/mL plasma) compared with the level observed at 0 h; plasma concentrations of Val-Tyr returned to baseline levels at 6 h. 4. Transient changes in plasma concentrations of angiotensin (Ang) I and AngII only at 1 h were consistent with plasma Val-Tyr concentrations, suggesting that that the long-lasting reduction in blood pressure was achieved by the latent hypotensive mechanism of Val-Tyr and not by transient suppression of the circulatory RAS. 5. Ageing of the THM greatly affected the depressor action of Val-Tyr, with no significant reduction in blood pressure observed in 18- and 24-week-old THM.

Effect of lisinopril on deposition of iron in renal tissue in Tsukuba hypertensive mice carrying human renin‐angiotensin system genes

SUMMARY:Tsukuba hypertensive mice (THM) are transgenic mice that carry both human renin and angiotensinogen genes and overexpress the human renin‐angiotensin system (RAS). In the present study, the effect of lisinopril on deposition of macromolecular iron in renal tissue in THM was evaluated. Twelve‐week‐old male THM were divided into the following groups: lisinopril dosage group (ACEI group), hydralazine dosage group (hydralazine group), and a no‐drug group (control group). Age‐matched male C57BL/6 mice (wild group) were used as normal controls. Each mouse was treated with a drug for 8 weeks. All mice were euthanised at 20 weeks of age, and their kidneys were fixed and stained with Berlin‐blue. Systolic blood pressure was significantly higher in the control group than in the wild group, and it decreased significantly to similar levels in the ACEI group and the hydralazine group. Iron deposition was observed in proximal renal tubules in the control group and the hydralazine group, but iron deposition was not observed in the ACEI group or the wild group. The results of the study suggest that the RAS plays an important role in the deposition of iron in the proximal renal tubules in THM, and that lisinopril prevents this deposition.