Rac1 deficiency impairs postnatal development of the renal papilla.

Development of the renal medulla continues after birth to form mature renal papilla and obtain urine-concentrating ability. Here, we found that a small GTPase, Rac1, plays a critical role in the postnatal development of renal papilla. Mice with distal tubule-specific deletion of Rac1 reached adulthood but showed polydipsia and polyuria with an impaired ability to concentrate urine. The elongation of renal papilla that occurs in the first weeks after birth was impaired in the Rac1-deficient infants, resulting in shortening and damage of the renal papilla. Moreover, the osmoprotective signaling mediated by nuclear factor of activated T cells 5, which is a key molecule of osmotic response to osmotic stress in renal medulla, was significantly impaired in the kidneys of the Rac1-deficient infants. These results demonstrate that Rac1 plays an important role in the development of renal papilla in the postnatal period, and suggested a potential link between Rac1 and osmotic response.

Activation of Rac1-Mineralocorticoid Receptor Pathway Contributes to Renal Injury in Salt-Loaded db/db Mice.

[Figure: see text].

Role of Rho in Salt-Sensitive Hypertension.

A high amount of salt in the diet increases blood pressure (BP) and leads to salt-sensitive hypertension in individuals with impaired renal sodium excretion. Small guanosine triphosphatase (GTP)ase Rho and Rac, activated by salt intake, play important roles in the pathogenesis of salt-sensitive hypertension as key switches of intracellular signaling. Focusing on Rho, high salt intake in the central nervous system increases sodium concentrations of cerebrospinal fluid in salt-sensitive subjects via Rho/Rho kinase and renin-angiotensin system activation and causes increased brain salt sensitivity and sympathetic nerve outflow in BP control centers. In vascular smooth muscle cells, Rho-guanine nucleotide exchange factors and Rho determine sensitivity to vasoconstrictors such as angiotensin II (Ang II), and facilitate vasoconstriction via G-protein and Wnt pathways, leading to increased vascular resistance, including in the renal arteries, in salt-sensitive subjects with high salt intake. In the vascular endothelium, Rho/Rho kinase inhibits nitric oxide (NO) production and function, and high salt amounts further augment Rho activity via asymmetric dimethylarginine, an endogenous inhibitor of NO synthetase, causing aberrant relaxation and increased vascular tone. Rho-associated mechanisms are deeply involved in the development of salt-sensitive hypertension, and their further elucidation can help in developing effective protection and new therapies.

Kidney and epigenetic mechanisms of salt-sensitive hypertension.

Dietary salt intake increases blood pressure (BP) but the salt sensitivity of BP differs between individuals. The interplay of ageing, genetics and environmental factors, including malnutrition and stress, contributes to BP salt sensitivity. In adults, obesity is often associated with salt-sensitive hypertension. The children of women who experience malnutrition during pregnancy are at increased risk of developing obesity, diabetes and salt-sensitive hypertension as adults. Similarly, the offspring of mice that are fed a low-protein diet during pregnancy develop salt-sensitive hypertension in association with aberrant DNA methylation of the gene encoding type 1A angiotensin II receptor (AT1AR) in the hypothalamus, leading to upregulation of hypothalamic AT1AR and renal sympathetic overactivity. Ageing is also associated with salt-sensitive hypertension. In aged mice, promoter methylation leads to reduced kidney production of the anti-ageing factor Klotho and a decrease in circulating soluble Klotho. In the setting of Klotho deficiency, salt-induced activation of the vascular Wnt5a-RhoA pathway leads to ageing-associated salt-sensitive hypertension, potentially as a result of reduced renal blood flow and increased peripheral resistance. Thus, kidney mechanisms and aberrant DNA methylation of certain genes are involved in the development of salt-sensitive hypertension during fetal development and old age. Three distinct paradigms of epigenetic memory operate on different timescales in prenatal malnutrition, obesity and ageing.

Methylation pattern of urinary DNA as a marker of kidney function decline in diabetes.

INTRODUCTION: Renal tubular injury contributes to the decline in kidney function in patients with diabetes. Cell type-specific DNA methylation patterns have been used to calculate proportions of particular cell types. In this study, we developed a method to detect renal tubular injury in patients with diabetes by detecting exfoliated tubular cells shed into the urine based on tubular cell-specific DNA methylation patterns. RESEARCH DESIGN AND METHODS: We identified DNA methylation patterns specific for human renal proximal tubular cells through compartment-specific methylome analysis. We next determined the methylation levels of proximal tubule-specific loci in urine sediment of patients with diabetes and analyzed correlation with clinical variables. RESULTS: We identified genomic loci in SMTNL2 and G6PC to be selectively unmethylated in human proximal tubular cells. The methylation levels of SMTNL2 and G6PC in urine sediment, deemed to reflect the proportion of exfoliated proximal tubular cells due to injury, correlated well with each other. Methylation levels of SMTNL2 in urine sediment significantly correlated with the annual decline in estimated glomerular filtration rate. Moreover, addition of urinary SMTNL2 methylation to a model containing known risk factors significantly improved discrimination of patients with diabetes with faster estimated glomerular filtration rate decline. CONCLUSIONS: This study demonstrates that patients with diabetes with continual loss in kidney function may be stratified by a specific DNA methylation signature through epigenetic urinalysis and provides further evidence at the level of exfoliated cells in the urine that injury of proximal tubular cells may contribute to pathogenesis of diabetic kidney disease.

Salt causes aging-associated hypertension via vascular Wnt5a under Klotho deficiency.

Aging is associated with a high prevalence of hypertension due to elevated susceptibility of BP to dietary salt, but its mechanism is unknown. Serum levels of Klotho, an anti-aging factor, decline with age. We found that high salt (HS) increased BP in aged mice and young heterozygous Klotho-knockout mice and was associated with increased vascular expression of Wnt5a and p-MYPT1, which indicate RhoA activity. Not only the Wnt inhibitor LGK974 and the Wnt5a antagonist Box5 but Klotho supplementation inhibits HS-induced BP elevation, similarly to the Rho kinase inhibitor fasudil, associated with reduced p-MYPT1 expression in both groups of mice. In cultured vascular smooth muscle cells, Wnt5a and angiotensin II (Ang II) increased p-MYPT1 expression but knockdown of Wnt5a with siRNA abolished Ang II-induced upregulation of p-MYPT1, indicating that Wnt5a is indispensable for Ang II-induced Rho/ROCK activation. Notably, Klotho inhibited Wnt5a- and Ang II-induced upregulation of p-MYPT1. Consistently, Klotho supplementation ameliorated HS-induced augmentation of reduced renal blood flow (RBF) response to intra-arterial infusion of Ang II and the thromboxane A2 analog U46619, which activated RhoA in both groups of mice and were associated with the inhibition of BP elevation, suggesting that abnormal response of RBF to Ang II contributes to HS-induced BP elevation. Thus, Klotho deficiency underlies aging-associated salt-sensitive hypertension through vascular non-canonical Wnt5a/RhoA activation.

PGI2 Analog Attenuates Salt-Induced Renal Injury through the Inhibition of Inflammation and Rac1-MR Activation.

Renal inflammation is known to be involved in salt-induced renal damage, leading to end-stage renal disease. This study aims to evaluate the role of inflammation in anti-inflammatory and renoprotective effects of beraprost sodium (BPS), a prostaglandin I2 (PGI2) analog, in Dahl salt-sensitive (DS) rats. Five-week-old male DS rats were fed a normal-salt diet (0.5% NaCl), a high-salt diet (8% NaCl), or a high-salt diet plus BPS treatment for 3 weeks. BPS treatment could inhibit marked proteinuria and renal injury in salt-loaded DS rats with elevated blood pressure, accompanied by renal inflammation suppression. Notably, high salt increased renal expression of active Rac1, followed by increased Sgk1 expressions, a downstream molecule of mineralocorticoid receptor (MR) signal, indicating salt-induced activation of Rac1-MR pathway. However, BPS administration inhibited salt-induced Rac1-MR activation as well as renal inflammation and damage, suggesting that Rac1-MR pathway is involved in anti-inflammatory and renoprotective effects of PGI2. Based upon Rac1 activated by inflammation, moreover, BPS inhibited salt-induced activation of Rac1-MR pathway by renal inflammation suppression, resulting in the attenuation of renal damage in salt-loaded DS rats. Thus, BPS is efficacious for the treatment of salt-induced renal injury.

Two Mineralocorticoid Receptor-Mediated Mechanisms of Pendrin Activation in Distal Nephrons.

BACKGROUND: Regulation of sodium chloride transport in the aldosterone-sensitive distal nephron is essential for fluid homeostasis and BP control. The chloride-bicarbonate exchanger pendrin in ß-intercalated cells, along with sodium chloride cotransporter (NCC) in distal convoluted tubules, complementarily regulate sodium chloride handling, which is controlled by the renin-angiotensin-aldosterone system. METHODS: Using mice with mineralocorticoid receptor deletion in intercalated cells, we examined the mechanism and roles of pendrin upregulation via mineralocorticoid receptor in two different models of renin-angiotensin-aldosterone system activation. We also used aldosterone-treated NCC knockout mice to examine the role of pendrin regulation in salt-sensitive hypertension. RESULTS: Deletion of mineralocorticoid receptor in intercalated cells suppressed the increase in renal pendrin expression induced by either exogenous angiotensin II infusion or endogenous angiotensin II upregulation via salt restriction. When fed a low-salt diet, intercalated cell-specific mineralocorticoid receptor knockout mice with suppression of pendrin upregulation showed BP reduction that was attenuated by compensatory activation of NCC. In contrast, upregulation of pendrin induced by aldosterone excess combined with a high-salt diet was scarcely affected by deletion of mineralocorticoid receptor in intercalated cells, but depended instead on hypokalemic alkalosis through the activated mineralocorticoid receptor-epithelial sodium channel cascade in principal cells. In aldosterone-treated NCC knockout mice showing upregulation of pendrin, potassium supplementation corrected alkalosis and inhibited the pendrin upregulation, thereby lowering BP. CONCLUSIONS: In conjunction with NCC, the two pathways of pendrin upregulation, induced by angiotensin II through mineralocorticoid receptor activation in intercalated cells and by alkalosis through mineralocorticoid receptor activation in principal cells, play important roles in fluid homeostasis during salt depletion and salt-sensitive hypertension mediated by aldosterone excess.

Mineralocorticoid receptor blockade suppresses dietary salt-induced ACEI/ARB-resistant albuminuria in non-diabetic hypertension: a sub-analysis of evaluate study.

Excessive dietary salt intake can counteract the renoprotective effects of renin-angiotensin system (RAS) blockade in hypertensive patients with chronic kidney disease (CKD). In rodents, salt loading induces hypertension and renal damage by activating the mineralocorticoid receptor (MR) independently of plasma aldosterone levels. Thus, high salt-induced resistance to RAS blockade may be mediated by MR activation. To test this, a post hoc analysis of the Eplerenone Combination Versus Conventional Agents to Lower Blood Pressure on Urinary Antialbuminuric Treatment Effect (EVALUATE) trial was conducted. Thus, 304 non-diabetic hypertensive patients on RAS-blocking therapy were divided into tertiles according to salt intake (estimated 24-h urinary sodium excretion at baseline) and compared in terms of percent reduction in urinary albumin-to-creatinine ratio (UACR) at 52 weeks relative to baseline. The eplerenone-treated patients in the highest sodium excretion tertile exhibited significantly greater reduction in UACR than the placebo subjects in the same tertile (-22.5% vs. +21.8%, p = 0.02). This disparity was not observed in the lowest (-10.2% vs. -0.84%, p = 0.65) or middle (-19.5% vs. +9.5%, p = 0.22) tertiles. Similar systolic blood pressure changes were observed. In the whole cohort, reduction in UACR correlated positively with reduction in systolic blood pressure (r2 = 0.04, p = 0.02). These results support the hypothesis that excessive salt intake can enhance resistance to RAS blockade by activating MR. They also suggest that eplerenone plus RAS blockade may be effective for CKD in hypertensive patients, especially those with excessive salt intake.

Aberrant DNA methylation of hypothalamic angiotensin receptor in prenatal programmed hypertension.

Maternal malnutrition, which causes prenatal exposure to excessive glucocorticoid, induces adverse metabolic programming, leading to hypertension in offspring. In offspring of pregnant rats receiving a low-protein diet or dexamethasone, a synthetic glucocorticoid, mRNA expression of angiotensin receptor type 1a (Agtr1a) in the paraventricular nucleus (PVN) of the hypothalamus was upregulated, concurrent with reduced expression of DNA methyltransferase 3a (Dnmt3a), reduced binding of DNMT3a to the Agtr1a gene, and DNA demethylation. Salt loading increased BP in both types of offspring, suggesting that elevated hypothalamic Agtr1a expression is epigenetically modulated by excessive glucocorticoid and leads to adult-onset salt-sensitive hypertension. Consistent with this, dexamethasone treatment of PVN cells upregulated Agtr1a, while downregulating Dnmt3a, and decreased DNMT3a binding and DNA demethylation at the Agtr1a locus. In addition, Dnmt3a knockdown upregulated Agtr1a independently of dexamethasone. Hypothalamic neuron-specific Dnmt3a-deficient mice exhibited upregulation of Agtr1a in the PVN and salt-induced BP elevation without dexamethasone treatment. By contrast, dexamethasone-treated Agtr1a-deficient mice failed to show salt-induced BP elevation, despite reduced expression of Dnmt3a. Thus, epigenetic modulation of hypothalamic angiotensin signaling contributes to salt-sensitive hypertension induced by prenatal glucocorticoid excess in offspring of mothers that are malnourished during pregnancy.

Aberrant DNA methylation of Tgfb1 in diabetic kidney mesangial cells.

Epigenetic modulation may underlie the progression of diabetic nephropathy (DN). Involvement of TGFB1 in mesangial fibrosis of DN led us to hypothesize that Tgfb1 DNA demethylation contributes to progression of DN. In primary mesangial cells from diabetic (db/db) mouse kidneys, demethylation of Tgfb1 DNA and upregulation of Tgfb1 mRNA progressed simultaneously. USF1 binding site in Tgfb1 promoter region were demethylated, and binding of USF1 increased, with decreased binding of DNMT1 in db/db compared with control. Given downregulation of Tgfb1 expression by folic acid, antioxidant Tempol reversed DNA demethylation, with increased and decreased recruitment of DNMT1 and USF1 to the promoter, resulting in decreased Tgfb1 expression in db/db mice. Addition of H2O2 to mesangial cells induced DNA demethylation and upregulated Tgfb1 expression. Finally, Tempol attenuated mesangial fibrosis in db/db mice. We conclude that aberrant DNA methylation of Tgfb1 due to ROS overproduction play a key to mesangial fibrosis during DN progression.

Aberrant DNA methylation of pregnane X receptor underlies metabolic gene alterations in the diabetic kidney.

Epigenetic abnormalities have been suggested to mediate metabolic memory observed in diabetic complications. We have shown that epigenetic alterations may induce persistent phenotypic changes in the proximal tubules of the diabetic kidneys. In this study, we show that pregnane X receptor (PXR), a xenobiotic nuclear receptor, is epigenetically altered and upregulated and may have a possible function in the diabetic kidney. PXR has been shown to play a critical role in metabolic changes in obesity and diabetes; however, its distribution and function in the kidney are unknown. In the normal kidney, Pxr was selectively expressed in the proximal tubular cells with demethylation in the promoter DNA. In db/db mice, significant increases in Pxr mRNA, further demethylation of DNA, and stimulatory histone marks in the promoter were observed. Epigenetic changes are likely to play a causative role in PXR induction, since a DNA methyltransferase inhibitor increased PXR mRNA in cultured human proximal tubular cells. Administration of a PXR agonist increased mRNA levels of solute carrier organic anion transporter family member 2B1 ( Slco2b1), a xenobiotic transporter; response gene to complement 32 ( Rgc32), a molecule known to exert fibrotic effects in the kidney; and phosphoenolpyruvate carboxykinase 1 ( Pck1), a gluconeogenic enzyme in the kidney. The expressions of these genes were inhibited by PXR small interfering RNA in cultured proximal tubular cells. Increased mRNA levels of Slco2b1, Rgc32, and Pck1 were also observed in the kidney of db/db mice. These data indicate that PXR is upregulated in the diabetic kidney with aberrant epigenetic modifications and may modulate the course of diabetic kidney disease through the activation of these genes.

Aldosterone Is Essential for Angiotensin II-Induced Upregulation of Pendrin.

The renin-angiotensin-aldosterone system has an important role in the control of fluid homeostasis and BP during volume depletion. Dietary salt restriction elevates circulating angiotensin II (AngII) and aldosterone levels, increasing levels of the Cl-/HCO3- exchanger pendrin in ß-intercalated cells and the Na+-Cl- cotransporter (NCC) in distal convoluted tubules. However, the independent roles of AngII and aldosterone in regulating these levels remain unclear. In C57BL/6J mice receiving a low-salt diet or AngII infusion, we evaluated the membrane protein abundance of pendrin and NCC; assessed the phosphorylation of the mineralocorticoid receptor, which selectively inhibits aldosterone binding in intercalated cells; and measured BP by radiotelemetry in pendrin-knockout and wild-type mice. A low-salt diet or AngII infusion upregulated NCC and pendrin levels, decreased the phosphorylation of mineralocorticoid receptor in ß-intercalated cells, and increased plasma aldosterone levels. Notably, a low-salt diet did not alter BP in wild-type mice, but significantly decreased BP in pendrin-knockout mice. To dissect the roles of AngII and aldosterone, we performed adrenalectomies in mice to remove aldosterone from the circulation. In adrenalectomized mice, AngII infusion again upregulated NCC expression, but did not affect pendrin expression despite the decreased phosphorylation of mineralocorticoid receptor. By contrast, AngII and aldosterone coadministration markedly elevated pendrin levels in adrenalectomized mice. Our results indicate that aldosterone is necessary for AngII-induced pendrin upregulation, and suggest that pendrin contributes to the maintenance of normal BP in cooperation with NCC during activation of the renin-angiotensin-aldosterone system by dietary salt restriction.

Renal Dysfunction Induced by Kidney-Specific Gene Deletion of Hsd11b2 as a Primary Cause of Salt-Dependent Hypertension.

Genome-wide analysis of renal sodium-transporting system has identified specific variations of Mendelian hypertensive disorders, including HSD11B2 gene variants in apparent mineralocorticoid excess. However, these genetic variations in extrarenal tissue can be involved in developing hypertension, as demonstrated in former studies using global and brain-specific Hsd11b2 knockout rodents. To re-examine the importance of renal dysfunction on developing hypertension, we generated kidney-specific Hsd11b2 knockout mice. The knockout mice exhibited systemic hypertension, which was abolished by reducing salt intake, suggesting its salt-dependency. In addition, we detected an increase in renal membrane expressions of cleaved epithelial sodium channel-α and T53-phosphorylated Na+-Cl- cotransporter in the knockout mice. Acute intraperitoneal administration of amiloride-induced natriuresis and increased urinary sodium/potassium ratio more in the knockout mice compared with those in the wild-type control mice. Chronic administration of amiloride and high-KCl diet significantly decreased mean blood pressure in the knockout mice, which was accompanied with the correction of hypokalemia and the resultant decrease in Na+-Cl- cotransporter phosphorylation. Accordingly, a Na+-Cl- cotransporter blocker hydrochlorothiazide significantly decreased mean blood pressure in the knockout mice. Chronic administration of mineralocorticoid receptor antagonist spironolactone significantly decreased mean blood pressure of the knockout mice along with downregulation of cleaved epithelial sodium channel-α and phosphorylated Na+-Cl- cotransporter expression in the knockout kidney. Our data suggest that kidney-specific deficiency of 11ß-HSD2 leads to salt-dependent hypertension, which is attributed to mineralocorticoid receptor-epithelial sodium channel-Na+-Cl- cotransporter activation in the kidney, and provides evidence that renal dysfunction is essential for developing the phenotype of apparent mineralocorticoid excess.

The Role of Aldosterone in Obesity-Related Hypertension.

Obese subjects often have hypertension and related cardiovascular and renal diseases, and this has become a serious worldwide health problem. In obese subjects, impaired renal-pressure natriuresis causes sodium retention, leading to the development of salt-sensitive hypertension. Physical compression of the kidneys by visceral fat and activation of the sympathetic nervous system, renin-angiotensin systems (RAS), and aldosterone/mineralocorticoid receptor (MR) system are involved in this mechanism. Obese subjects often exhibit hyperaldosteronism, with increased salt sensitivity of blood pressure (BP). Adipose tissue excretes aldosterone-releasing factors, thereby stimulating aldosterone secretion independently of the systemic RAS, and aldosterone/MR activation plays a key role in the development of hypertension and organ damage in obesity. In obese subjects, both salt sensitivity of BP, enhanced by obesity-related metabolic disorders including aldosterone excess, and increased dietary sodium intake are closely related to the incidence of hypertension. Some salt sensitivity-related gene variants affect the risk of obesity, and together with salt intake, its combination is possibly associated with the development of hypertension in obese subjects. With high salt levels common in modern diets, salt restriction and weight control are undoubtedly important. However, not only MR blockade but also new diagnostic modalities and therapies targeting and modifying genes that are related to salt sensitivity, obesity, or RAS regulation are expected to prevent obesity and obesity-related hypertension.

Rac1-Mediated Activation of Mineralocorticoid Receptor in Pressure Overload-Induced Cardiac Injury.

There is increasing evidence for a crucial role of aberrant mineralocorticoid receptor (MR) activation in heart failure, with clinical studies showing beneficial effects of MR blockade. However, the mechanisms of MR activation in heart failure remain unclear. In this study, we observed that the small GTPase Rac1 contributes to myocardial MR activation, whereas Rac1-MR pathway activation leads to cardiac dysfunction. Mouse hearts subjected to chronic pressure overload induced by transverse aortic constriction showed Rac1 activation and increased nuclear accumulation of MR and expression of MR target genes, suggesting MR activation. Pharmacological inhibition of Rac1 and heterozygous deletion of Rac1 in cardiomyocytes suppressed Rac1-induced MR signaling and reduced NADPH oxidase 4 gene induction and reactive oxygen species overproduction, which attenuated transverse aortic constriction-induced cardiac hypertrophy and dysfunction. Consistently, treatment with the selective MR antagonist eplerenone blocked transverse aortic constriction-induced MR signaling and NADPH oxidase 4 gene upregulation, which improved cardiac hypertrophy and dysfunction. These findings suggest that Rac1-MR pathway activation in the myocardium is involved in development of heart failure induced by pressure load via recruitment of the responsible isoform of NADPH oxidase. Thus, the cardiac Rac1-MR-NADPH oxidase 4 pathway may be a therapeutic target for treatment of the pressure-overloaded heart.

Diabetes Induces Aberrant DNA Methylation in the Proximal Tubules of the Kidney.

Epigenetic mechanisms may underlie the progression of diabetic kidney disease. Because the kidney is a heterogeneous organ with different cell types, we investigated DNA methylation status of the kidney in a cell type-specific manner. We first identified genes specifically demethylated in the normal proximal tubules obtained from control db/m mice, and next delineated the candidate disease-modifying genes bearing aberrant DNA methylation induced by diabetes using db/db mice. Genes involved in glucose metabolism, including Sglt2, Pck1, and G6pc, were selectively hypomethylated in the proximal tubules in control mice. Hnf4a, a transcription factor regulating transporters for reabsorption, was also selectively demethylated. In diabetic mice, aberrant hypomethylation of Agt, Abcc4, Cyp4a10, Glut5, and Met and hypermethylation of Kif20b, Cldn18, and Slco1a1 were observed. Time-dependent demethylation of Agt, a marker of diabetic kidney disease, was accompanied by histone modification changes. Furthermore, inhibition of DNA methyltransferase or histone deacetylase increased Agt mRNA in cultured human proximal tubular cells. Aberrant DNA methylation and concomitant changes in histone modifications and mRNA expression in the diabetic kidney were resistant to antidiabetic treatment with pioglitazone. These results suggest that an epigenetic switch involving aberrant DNA methylation causes persistent mRNA expression of select genes that may lead to phenotype changes of the proximal tubules in diabetic kidney disease.

Local mineralocorticoid receptor activation and the role of Rac1 in obesity-related diabetic kidney disease.

BACKGROUND/AIMS: Obesity and diabetes are intimately interrelated, and are independent risk factors for kidney disease. Overactivation of mineralocorticoid receptor (MR) is implicated in end organ damage of both pathologies. But the underlying mechanism of MR activation in kidney remains uncertain. We explored the involvement of Rac1, which we previously identified as a ligand-independent MR activator, in renal MR activation in vitro and in vivo. METHODS: We evaluated the MR activity and Rac1 activity under high-glucose stimulation using luciferase reporter system and glutathione S-transferase pull-down assay in cultured mesangial cells. To elucidate the role of Rac1 in vivo, we employed KKA(y), a mouse model of obesity-related type 2 diabetes, which spontaneously developed massive albuminuria and distinct glomerular lesions accompanied by increased plasma aldosterone concentration. RESULTS: High-glucose stimulation increased Rac1 activity and MR transcriptional activity in cultured mesangial cells. Overexpression of constitutively active Rac1 activated MR, and glucose-induced MR activation was suppressed by overexpression of dominant negative Rac1 or Rac inhibitor EHT1864. In KKA(y), renal Rac1 was activated, and nuclear MR was increased. EHT1864 treatment suppressed renal Rac1 and MR activity and mitigated renal pathology of KKA(y) without changing plasma aldosterone concentration. CONCLUSION: Our results suggest that MR activation plays an important role in the nephropathy of KKA(y) mice, and that glucose-induced Rac1 activation, in addition to hyperaldosteronemia, contributes to their renal MR activation. Along with MR blockade, Rac inhibition may potentially be a preferred option in the treatment of nephropathy in obesity-related diabetic patients.

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

BACKGROUND: 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. METHODS: 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 10 weeks. Blood pressure and urinary albumin excretion were measured every 2 weeks during the experimental period. We evaluated renal histological changes and gene expression. Plasma angiotensin concentration was measured to evaluate the RAAS inhibitory effect. RESULTS: 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. CONCLUSION: 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.

Aberrant Rac1-mineralocorticoid receptor pathways in salt-sensitive hypertension.

According to Guyton's model, impaired renal sodium excretion plays a key role in the increased salt sensitivity of blood pressure (BP). Several factors contribute to impaired renal sodium excretion, including the sympathetic nervous system, the renin-angiotensin system and aldosterone. Accumulating evidence suggests that abnormalities in aldosterone and its receptor (i.e. the mineralocorticoid receptor (MR)) are involved in the development of salt-sensitive (SS) hypertension. Patients with metabolic syndrome often exhibit hyperaldosteronism and are susceptible to SS hypertension. Aldosterone secretion from the adrenal glands is not suppressed in obese hypertensive rats fed a high-salt diet because of the abundant production of adipocyte-derived aldosterone-releasing factors, which are independent of the negative feedback regulation of aldosterone secretion by the renin-angiotensin-aldosterone system. Increased plasma aldosterone levels lead to SS hypertension via MR activation in the kidney. Renal MR activity is increased in Dahl salt-sensitive rats fed a high-salt diet, despite the appropriate suppression of plasma aldosterone levels. In this rat strain, activation of MR in the distal nephron causes salt-induced hypertension. This paradoxical response of the MR to salt loading can be attributed to activation of Rac1, a small GTPase. In the presence of aldosterone, activated Rac1 synergistically and directly activates MR in a ligand-independent manner. Thus, Rac1 activation in the kidney determines the salt sensitivity of BP. Together, the available evidence suggests that the aberrant Rac1-MR pathway plays a key role in the development of SS hypertension.