Endogenous angiotensin concentrations in specific intrarenal fluid compartments of the rat

Immunolocalization of the AT-1R Ang II Receptor in Human Kidney Cancer

This study aimed to evaluate AT1-R expression in normal and cancerous human kidneys, how these expressions are modified, and AT1-R functionality. AT-1R mRNA expression, determined by real-time PCR, was detected in all samples. AT-1R mRNA increased in well-differentiated cancer (G1, p < 0.01) and decreased 2.9-fold in undifferentiated cancer (G4, p < 0.001) compared with normal kidney tissues. Immunocytochemistry analysis showed that the AT-1R was expressed in the normal tubular epithelium. The glomerulus was also immunoreactive, and as expected, the smooth muscle cells of the vessel walls also expressed the receptor. A total of 35 out of 42 tumors were AT-1R positive, with the cell tumors showing varying numbers of immunoreactive cells, which were stained in a diffuse cytoplasmic and membranous pattern. Computer-assisted counting of the stained tumor cells showed that the number of AT-1R-positive cells increased in the well-differentiated cancers. The functionality of AT-1R was assessed in primary cultures of kidney epithelial cells obtained from three G3 kidney cancer tissues and corresponding histologically proven non-malignant tissue adjacent to the tumor. Indeed, Ang II stimulated, in a dose-dependent manner, the 24 h proliferation of normal kidney cells and cancer cells in the primary culture and phosphorylated extracellular regulated kinases 1 and 2. In conclusion, Ang II may be involved in the growth or function of neoplastic kidney tissue.

How should we treat acute kidney injury caused by renal congestion?

Decreased kidney function is associated with increased risk of cardiovascular events and mortality, and heart failure (HF) is a wellknown risk factor for renal dysfunction. Acute kidney injury (AKI) in patients with HF often is attributed to prerenal factors, such as renal hypoperfusion and ischemia as a result of decreased cardiac output. Another such factor is reduction of absolute or relative circulating blood volume, with the decrease in renal blood flow leading to renal hypoxia followed by a decrease in the glomerular filtration rate. However, renal congestion is increasingly being recognized as a potential cause of AKI in patients with HF. Increased central venous pressure and renal venous pressure lead to increased renal interstitial hydrostatic pressure and a reduction of the glomerular filtration rate. Both decreased kidney function and renal congestion have been shown to be important prognostic factors of HF, and adequate control of congestion is important for improving kidney function. Loop and thiazide diuretics are recommended as standard therapies to reduce volume overload. However, these agents are associated with worsening renal function even though they are effective for improving congestive symptoms. There is growing interest in tolvaptan, which can improve renal congestion by increasing excretion of free water and decreasing the required dose of loop diuretic, thereby improving kidney function. This review summarizes renal hemodynamics, the pathogenesis of AKI due to renal ischemia and renal congestion, and diagnosis and treatment options for renal congestion.

SARS-CoV-2 triggers pericyte-mediated cerebral capillary constriction

The SARS-CoV-2 receptor, ACE2, is found on pericytes, contractile cells enwrapping capillaries that regulate brain, heart and kidney blood flow. ACE2 converts vasoconstricting angiotensin II into vasodilating angiotensin-(1-7). In brain slices from hamster, which has an ACE2 sequence similar to human ACE2, angiotensin II evoked a small pericyte-mediated capillary constriction via AT1 receptors, but evoked a large constriction when the SARS-CoV-2 receptor binding domain (RBD, original Wuhan variant) was present. A mutated non-binding RBD did not potentiate constriction. A similar RBD-potentiated capillary constriction occurred in human cortical slices, and was evoked in hamster brain slices by pseudotyped virions expressing SARS-CoV-2 spike protein. This constriction reflects an RBD-induced decrease in the conversion of angiotensin II to angiotensin-(1-7) mediated by removal of ACE2 from the cell surface membrane and was mimicked by blocking ACE2. The clinically used drug losartan inhibited the RBD-potentiated constriction. Thus, AT1 receptor blockers could be protective in COVID-19 by preventing pericyte-mediated blood flow reductions in the brain, and perhaps the heart and kidney.

Hypertensive Nephropathy: Unveiling the Possible Involvement of Hemichannels and Pannexons

Hypertension is one of the most common risk factors for developing chronic cardiovascular diseases, including hypertensive nephropathy. Within the glomerulus, hypertension causes damage and activation of mesangial cells (MCs), eliciting the production of large amounts of vasoactive and proinflammatory agents. Accordingly, the activation of AT1 receptors by the vasoactive molecule angiotensin II (AngII) contributes to the pathogenesis of renal damage, which is mediated mostly by the dysfunction of intracellular Ca²⁺ ([Ca²⁺]_i) signaling. Similarly, inflammation entails complex processes, where [Ca²⁺]_i also play crucial roles. Deregulation of this second messenger increases cell damage and promotes fibrosis, reduces renal blood flow, and impairs the glomerular filtration barrier. In vertebrates, [Ca²⁺]_i signaling depends, in part, on the activity of two families of large-pore channels: hemichannels and pannexons. Interestingly, the opening of these channels depends on [Ca²⁺]_i signaling. In this review, we propose that the opening of channels formed by connexins and/or pannexins mediated by AngII induces the ATP release to the extracellular media, with the subsequent activation of purinergic receptors. This process could elicit Ca²⁺ overload and constitute a feed-forward mechanism, leading to kidney damage.

Rho GTPases in kidney physiology and diseases

Rho family GTPases are molecular switches best known for their pivotal role in dynamic regulation of the actin cytoskeleton, but also of cellular morphology, motility, adhesion and proliferation. The prototypic members of this family (RhoA, Rac1 and Cdc42) also contribute to the normal kidney function and play important roles in the structure and function of various kidney cells including tubular epithelial cells, mesangial cells and podocytes. The kidney's vital filtration function depends on the structural integrity of the glomerulus, the proximal portion of the nephron. Within the glomerulus, the architecturally actin-based cytoskeleton podocyte forms the final cellular barrier to filtration. The glomerulus appears as a highly dynamic signalling hub that is capable of integrating intracellular cues from its individual structural components. Dynamic regulation of the podocyte cytoskeleton is required for efficient barrier function of the kidney. As master regulators of actin cytoskeletal dynamics, Rho GTPases are therefore of critical importance for sustained kidney barrier function. Dysregulated activities of the Rho GTPases and of their effectors are implicated in the pathogenesis of both hereditary and idiopathic forms of kidney diseases. Diabetic nephropathy is a progressive kidney disease that is caused by injury to kidney glomeruli. High glucose activates RhoA/Rho-kinase in mesangial cells, leading to excessive extracellular matrix production (glomerulosclerosis). This RhoA/Rho-kinase pathway also seems involved in the post-transplant hypertension frequently observed during treatment with calcineurin inhibitors, whereas Rac1 activation was observed in post-transplant ischaemic acute kidney injury.

Mineralocorticoid Receptor Antagonists in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a major cause of end-stage kidney disease (ESKD) worldwide. Mineralocorticoid receptor (MR) plays an important role in the development of DKD. A series of preclinical studies revealed that MR is overactivated under diabetic conditions, resulting in promoting inflammatory and fibrotic process in the kidney. Clinical studies demonstrated the usefulness of MR antagonists (MRAs), such as spironolactone and eplerenone, on DKD. However, concerns regarding their selectivity for MR and hyperkalemia have remained for these steroidal MRAs. Recently, nonsteroidal MRAs, including finerenone, have been developed. These agents are highly selective and have potent anti-inflammatory and anti-fibrotic properties with a low risk of hyperkalemia. We herein review the current knowledge and future perspectives of MRAs in DKD treatment.

Molecular Mechanisms of Hypertensive Nephropathy: Renoprotective Effect of Losartan through Hsp70

Hypertensive nephrosclerosis is the second most common cause of end-stage renal disease after diabetes. For years, hypertensive kidney disease has been focused on the afferent arterioles and glomeruli damage and the involvement of the renin angiotensin system (RAS). Nonetheless, in recent years, novel evidence has demonstrated that persistent high blood pressure injures tubular cells, leading to epithelial–mesenchymal transition (EMT) and tubulointerstitial fibrosis. Injury primarily determined at the glomerular level by hypertension causes changes in post-glomerular peritubular capillaries that in turn induce endothelial damage and hypoxia. Microvasculature dysfunction, by inducing hypoxic environment, triggers inflammation, EMT with epithelial cells dedifferentiation and fibrosis. Hypertensive kidney disease also includes podocyte effacement and loss, leading to disruption of the filtration barrier. This review highlights the molecular mechanisms and histologic aspects involved in the pathophysiology of hypertensive kidney disease incorporating knowledge about EMT and tubulointerstitial fibrosis. The role of the Hsp70 chaperone on the angiotensin II–induced EMT after angiotensin II type 1 receptor (AT₁R) blockage, as a possible molecular target for therapeutic strategy against hypertensive renal damage is discussed.

Modulation of the rat angiotensin type 1a receptor by an upstream short open reading frame

The rat angiotensin type 1a receptor (AT_1aR) is a peptide hormone G protein-coupled receptor (GPCR) that plays a key role in electrolyte homeostasis and blood pressure control. There is a highly conserved short open reading frame (sORF) in exon 2 (E2) that is downstream from exon 1 (E1) and upstream of the AT_1aR coding region located in exon 3 (E3). To determine the role of this E2 sORF in AT_1aR signaling, human embryonic kidney-293 (HEK293) cells were transfected with plasmids containing AT_1aR cDNA with either an intact or disrupted E2 sORF. The intact sORF attenuated the efficacy of angiotensin (Ang) II (p < 0.001) and sarcosine¹,Ile⁴,Ile⁸-Ang II (SII), (p < 0.01) to activate AT_1aR signaling through extracellular signal-related kinases 1/2 (ERK1/2). A time-course showed agonist-induced AT_1aR-mediated ERK1/2 activation was slower in the presence of the intact compared to the disrupted sORF [Ang II: p < 0.01 and SII: p < 0.05]. Ang II-induced ERK1/2 activation was completely inhibited by the protein kinase C (PKC) inhibitor Ro 31-8220 regardless of whether the sORF was intact or disrupted. Flow cytometric analyses suggested the intact sORF improved cell survival; the percentage of live cells increased (p < 0.05) while the percentage of early apoptotic cells decreased (p < 0.01) in cells transfected with the AT_1aR plasmid containing the intact sORF. These findings have implications for the regulation of AT₁Rs in physiological and pathological conditions and warrant investigation of sORFs in the 5' leader sequence (5'LS) of other GPCRs.

Effect of sodium bicarbonate supplementation on the renin-angiotensin system in patients with chronic kidney disease and acidosis: a randomized clinical trial

Background

Acidosis-induced kidney injury is mediated by the intrarenal renin-angiotensin system, for which urinary renin is a potential marker. Therefore, we hypothesized that sodium bicarbonate supplementation reduces urinary renin excretion in patients with chronic kidney disease (CKD) and metabolic acidosis.

Methods

Patients with CKD stage G4 and plasma bicarbonate 15–24 mmol/l were randomized to receive sodium bicarbonate (3 × 1000 mg/day, ~ 0.5 mEq/kg), sodium chloride (2 × 1,00 mg/day), or no treatment for 4 weeks (n = 15/arm). The effects on urinary renin excretion (primary outcome), other plasma and urine parameters of the renin-angiotensin system, endothelin-1, and proteinuria were analyzed.

Results

Forty-five patients were included (62 ± 15 years, eGFR 21 ± 5 ml/min/1.73m², plasma bicarbonate 21.7 ± 3.3 mmol/l). Sodium bicarbonate supplementation increased plasma bicarbonate (20.8 to 23.8 mmol/l) and reduced urinary ammonium excretion (15 to 8 mmol/day, both P < 0.05). Furthermore, a trend towards lower plasma aldosterone (291 to 204 ng/L, P = 0.07) and potassium (5.1 to 4.8 mmol/l, P = 0.06) was observed in patients receiving sodium bicarbonate. Sodium bicarbonate did not significantly change the urinary excretion of renin, angiotensinogen, aldosterone, endothelin-1, albumin, or α1-microglobulin. Sodium chloride supplementation reduced plasma renin (166 to 122 ng/L), and increased the urinary excretions of angiotensinogen, albumin, and α1-microglobulin (all P < 0.05).

Conclusions

Despite correction of acidosis and reduction in urinary ammonium excretion, sodium bicarbonate supplementation did not improve urinary markers of the renin-angiotensin system, endothelin-1, or proteinuria. Possible explanations include bicarbonate dose, short treatment time, or the inability of urinary renin to reflect intrarenal renin-angiotensin system activity.

Graphic abstract

Salt-sensitive hypertension in chronic kidney disease: distal tubular mechanisms

Chronic kidney disease (CKD) causes salt-sensitive hypertension that is often resistant to treatment and contributes to the progression of kidney injury and cardiovascular disease. A better understanding of the mechanisms contributing to salt-sensitive hypertension in CKD is essential to improve these outcomes. This review critically explores these mechanisms by focusing on how CKD affects distal nephron Na+ reabsorption. CKD causes glomerulotubular imbalance with reduced proximal Na+ reabsorption and increased distal Na+ delivery and reabsorption. Aldosterone secretion further contributes to distal Na+ reabsorption in CKD and is not only mediated by renin and K+ but also by metabolic acidosis, endothelin-1, and vasopressin. CKD also activates the intrarenal renin-angiotensin system, generating intratubular angiotensin II to promote distal Na+ reabsorption. High dietary Na+ intake in CKD contributes to Na+ retention by aldosterone-independent activation of the mineralocorticoid receptor mediated through Rac1. High dietary Na+ also produces an inflammatory response mediated by T helper 17 cells and cytokines increasing distal Na+ transport. CKD is often accompanied by proteinuria, which contains plasmin capable of activating the epithelial Na+ channel. Thus, CKD causes both local and systemic changes that together promote distal nephron Na+ reabsorption and salt-sensitive hypertension. Future studies should address remaining knowledge gaps, including the relative contribution of each mechanism, the influence of sex, differences between stages and etiologies of CKD, and the clinical relevance of experimentally identified mechanisms. Several pathways offer opportunities for intervention, including with dietary Na+ reduction, distal diuretics, renin-angiotensin system inhibitors, mineralocorticoid receptor antagonists, and K+ or H+ binders.

The renal antioxidative effect of losartan involves heat shock protein 70 in proximal tubule cells

Angiotensin II exerts a cardinal role in the pathogenesis of hypertension and renal injury via action of angiotensin II type 1 (AT1) receptors. Local renin-angiotensin system (RAS) activity is essential for the mechanisms mediating pathophysiological functions. Proximal tubular angiotensinogen and tubular AT1 receptors are augmented by intrarenal angiotensin II. Caveolin 1 plays an important role as a regulatory molecule for the compartmentalization of redox signaling events through angiotensin II-induced NADPH oxidase activation in the kidney. A role for the renin-angiotensin system in the development and/or maintenance of hypertension has been demonstrated in spontaneously hypertensive rats (SHRs). Many effects of angiotensin II are dependent on the AT1 stimulation of reactive oxygen species (ROS) production by NADPH oxidase. Angiotensin II upregulation stimulates oxidative stress in proximal tubules from SHR. The NADPH oxidase 4 (Nox4) is abundantly expressed in kidney proximal tubule cells. Induction of the stress response includes synthesis of heat shock protein 70, a molecular chaperone that has a critical role in the recovery of cells from stress and in cytoprotection, guarding cells from subsequent insults. HSP70 chaperones function in part by driving the molecular triage decision, which determines whether proteins enter the productive folding pathway or result in client substrate ubiquitination and proteasomal degradation. This review examines regulation of losartan-mediated antioxidative stress responses by the chaperone HSP70 in proximal tubule cells of spontaneously hypertensive rats.

Renal functional effects of the highly selective AT2R agonist, β-Pro7 Ang III, in normotensive rats

Recently, we designed a group of peptides by sequential substitution of the naturally occurring α-amino acid throughout the Ang III peptide sequence with the corresponding β-amino acid. β-Amino acid substitution at the proline residue of Ang III (β-Pro⁷-Ang III) resulted in a highly selective AT₂R ligand, demonstrating remarkable selectivity for the AT₂R in both binding and functional studies. To provide additional functional evidence for the suitability of β-Pro⁷ Ang III as a novel AT₂R agonist, we tested effects of acute systemic administration of β-Pro⁷-Ang III on renal hemodynamic and excretory function in anesthetized normotensive male and female rats. We also compared the natriuretic effects of acute intrarenal administration of native Ang III and β-Pro⁷-Ang III in the presence of systemic AT₁R blockade in anesthetized female rats to allow for the differentiation of systemic versus direct intrarenal natriuretic actions of β-Pro⁷-Ang III. In both male and female rats, acute systemic administration of β-Pro⁷-Ang III elicited renal vasodilatation and natriuresis. Notably, greater renal vasodilatory effects were observed in female versus male rats at the highest dose of β-Pro⁷-Ang III administered. Moreover, intra-renal administration of β-Pro⁷-Ang III produced significant natriuretic effects in female rats and, like Ang III, evoked AT₂R translocation to the apical plasma membrane in renal proximal tubular cells. Taken together, our findings support the use of β-Pro⁷-Ang III as a novel AT₂R agonist and experimental tool for exploring AT₂R function and its potential as a therapeutic target. Furthermore, our findings provide further evidence of a sex-specific influence of AT₂R stimulation on renal function.

Mitochondrial angiotensin II receptors regulate oxygen consumption in kidney mitochondria from healthy and type 1 diabetic rats

Exaggerated activation of the renin-angiotensin-aldosterone system (RAAS) is a key feature in diseases such as hypertension, diabetes, and chronic kidney disease. Recently, an intracellular RAAS was demonstrated with angiotensin II (ANG II) type 1 (AT1) and type 2 (AT2) receptors expressed in nuclei and mitochondria. Diabetes is associated with both mitochondrial dysfunction and increased intracellular ANG II concentration in the kidney cortex. The present study investigated the role of ANG II signaling in kidney cortex mitochondria isolated from control and streptozotocin-induced diabetic rats. Mitochondrial oxygen consumption was evaluated after addition of ANG II alone or after preincubation with candesartan (AT1 receptor antagonist), PD-123319 (AT2 receptor antagonist), or the two in combination. ANG II binds to only mitochondrial AT2 receptors in control rats and both AT1 receptors and AT2 receptors in diabetic rats. ANG II decreased oxygen consumption in mitochondria from both control and diabetic rats. ANG II response was reversed to increased oxygen consumption by the nitric oxide synthase inhibitor N-nitro-l-arginine methyl ester. AT1 receptor inhibition did not affect the response to ANG II, whereas AT2 receptor inhibition abolished the response in mitochondria from control rats and reversed the response to increased oxygen consumption through superoxide-induced mitochondrial uncoupling in mitochondria from diabetic rats. ANG II decrease mitochondrial respiration via AT2 receptor-mediated nitric oxide release in both control and diabetic rats. AT1 receptors do not regulate mitochondria function in control rats, whereas ANG II via AT1 receptors increase mitochondria leak respiration in diabetic animals.

Blockade of myeloid differentiation 2 attenuates diabetic nephropathy by reducing activation of the renin-angiotensin system in mouse kidneys

BACKGROUND AND PURPOSE

Both innate immunity and the renin-angiotensin system (RAS) play important roles in the pathogenesis of diabetic nephropathy (DN). Myeloid differentiation factor 2 (MD2) is a co-receptor of toll-like receptor 4 (TLR4) in innate immunity. While TLR4 is involved in the development of DN, the role of MD2 in DN has not been characterized. It also remains unclear whether the MD2/TLR4 signalling pathway is associated with RAS activation in diabetes.

EXPERIMENTAL APPROACH

MD2 was blocked using siRNA or the low MW inhibitor, L6H9, in renal proximal tubular cells (NRK-52E cells) exposed to high concentrations of glucose (HG). In vivo, C57BL/6 and MD2-/- mice were injected with streptozotocin to induce Type 1 diabetes and nephropathy.

KEY RESULTS

Inhibition of MD2 by genetic knockdown or the inhibitor L6H9 suppressed HG-induced expression of ACE and angiotensin receptors and production of angiotensin II in NRK-52E cells, along with decreased fibrosis markers (TGF-β and collagen IV). Inhibition of the MD2/TLR4-MAPKs pathway did not affect HG-induced renin overproduction. In vivo, using the streptozotocin-induced diabetic mice, MD2 was overexpressed in diabetic kidney. MD2 gene knockout or L6H9 attenuated renal fibrosis and dysfunction by suppressing local RAS activation and inflammation.

CONCLUSIONS AND IMPLICATIONS

Hyperglycaemia activated the MD2/TLR4-MAPKs signalling cascade to induce renal RAS activation, leading to renal fibrosis and dysfunction. Pharmacological inhibition of MD2 may be considered as a therapeutic approach to mitigate DN and the low MW inhibitor L6H9 could be a candidate for such therapy.

Effects of Sleeve Gastrectomy on Blood Pressure and the Renal Renin-Angiotensin System in Rats with Diet-Induced Obesity

OBJECTIVE

Sleeve gastrectomy (SG) has been reported to decrease blood pressure (BP), although the reason has not been revealed. The present study aimed to establish the reason why SG decreases BP.

METHODS

Male Sprague-Dawley rats were subjected to surgical (sham operation or SG) and dietary interventions (fed a normal diet or high-fat diet ad libitum or fed by pair-feeding [PF]). Systolic BP (SBP), urinary sodium excretion, and endocrine parameters were examined 4 weeks after surgery.

RESULTS

Both SG and PF rats had reduced body weight compared with SO rats fed normal diet or high-fat diet ad libitum. SG rats exhibited a reduction in SBP compared with PF, which was associated with a reduction in renal renin, angiotensin II, and catechol-O-methyltransferase levels (P < 0.01 for each). SG increased plasma cholecystokinin (CCK) levels compared with PF (P < 0.0001 for each), whereas glucagon-like peptide 1 and peptide YY were not changed in fasting. Exogenous administration of CCK reduced renal catechol-O-methyltransferase (P = 0.0233), renin (P < 0.0001), and angiotensin II (P < 0.0001) levels and SBP (P = 0.0053).

CONCLUSIONS

SG reduced SBP, at least in part, through suppression of sympathetic nerve action by elevation of CCK, which was followed by suppression of the intrarenal renin-angiotensin system.

Electrolyte transport in the renal collecting duct and its regulation by the renin-angiotensin-aldosterone system

Distal nephron of the kidney plays key roles in fluid volume and electrolyte homeostasis by tightly regulating reabsorption and excretion of Na⁺, K⁺, and Cl^- Studies to date demonstrate the detailed electrolyte transport mechanisms in principal cells of the cortical collecting duct, and their regulation by renin-angiotensin-aldosterone system (RAAS). In recent years, however, accumulating data indicate that intercalated cells, another cell type that is present in the cortical collecting duct, also play active roles in the regulation of blood pressure. Notably, pendrin in β-intercalated cells not only controls acid/base homeostasis, but is also one of the key components controlling salt and K⁺ transport in distal nephron. We have recently shown that pendrin is regulated by the co-ordinated action of angiotensin II (AngII) and aldosterone, and at the downstream of AngII, mammalian target of rapamycin (mTOR) signaling regulates pendrin through inhibiting the kinase unc51-like-kinase 1 and promoting dephosphorylation of mineralocorticoid receptor (MR). In this review, we summarize recent advances in the current knowledge on the salt transport mechanisms in the cortical collecting duct, and their regulation by the RAAS.

High Salt Enhances Reactive Oxygen Species and Angiotensin II Contractions of Glomerular Afferent Arterioles From Mice With Reduced Renal Mass

High salt, Ang II (angiotensin II), and reactive oxygen species enhance progression of chronic kidney disease. We tested the hypothesis that a high salt intake generates specific reactive oxygen species to enhance Ang II contractions of afferent arterioles from mice with reduced renal mass (RRM). C57BL/6 mice were subjected to surgical RRM or sham operations and received 6% or 0.4% NaCl salt diet for 3 months. Ang II contractions were measured in perfused afferent arterioles and superoxide (O2-) and hydrogen peroxide (H2O2) by fluorescence microscopy. RRM enhanced the afferent arteriolar gene expression for p47phox and neutrophil oxidase (NOX) 2 and high salt intake in RRM mice enhanced gene expression for angiotensin type 1 receptors, POLDIP2 and NOX4 and reduced catalase. High salt in mice with RRM enhanced arteriolar O2- and H2O2 generation and maximal contractions to Ang II (10-6 mol/L) that were dependent on O2- because they were prevented by gene deletion of p47phox and on H2O2 because they were prevented by transgenic smooth muscle cell expression of catalase (tgCAT-SMC) and POLDIP2 gene deletion. Three months of tempol normalized arteriolar reactive oxygen species and Ang II contractions. However, arteriolar contractions to lower concentrations of Ang II (10-8 to 10-11 mol/L) were paradoxically inhibited by H2O2 and POLDIP2. In conclusion, both O2- from p47phox/NOX2 and H2O2 from NOX4/POLDIP2 enhance maximal arteriolar Ang II contractions from RRM mice during high salt, but H2O2 and NOX4/POLDIP2 reduce the sensitivity to lower concentrations of Ang II by >100-fold. Tempol prevents all of these changes in function.

Antinatriuretic phenomena seen in children with acute pyelonephritis may be related to the activation of intrarenal RAAS

We investigated whether antinatriuretic phenomena [decreases in urinary sodium (uNa) and fractional excretion of sodium (FENa)] seen in children with acute pyelonephritis (APN) are associated with the renin-angiotensin-aldosterone system (RAAS).We examined 114 children experiencing their first episode of febrile urinary tract infection (fUTI) consecutively admitted to our hospital from July 2012 to June 2014. Blood tests [C-reactive protein, white blood cell count, erythrocyte sedimentation rate, and aldosterone (Aldo)] and urine tests [uNa, urine potassium (uK) and FENa] were performed upon admission. All enrolled children underwent a 99m-dimercaptosuccinic acid renal scanning (DMSA) at admission. Areas with cortical defects (AreaCD) and uptake counts (UptakeCD) on their DMSA scans were calculated. Data were compared between children with positive DMSA results (APN), lower urinary tract infection (L-UTI), and controls; and between children with high and low Aldo levels.uNa, uNa/K, and FENa negatively correlated with AreaCD%, UptakeCD, and Aldo; were significantly lower in APN patients than in LUTIs and controls regardless of Aldo level; were lower in the high Aldo group than in the low Aldo group. However, there is no difference in AreaCD% and UptakeCD between APN children with the high and low Aldo level.Decreases in uNa, uNa/K, and FENa in children with APN may result from an antinatriuretic effect of RAAS and be related to the activation of the intrarenal RAAS.

Plasma renin activity in patients with heart failure and reduced ejection fraction on optimal medical therapy

Background:

Renin-angiotensin-aldosterone system (RAAS) activation in heart failure with reduced ejection fraction (HFREF) is detrimental through promotion of ventricular remodeling and salt and water retention.

Aims:

The aims of this article are to describe RAAS activity in distinct HFREF populations and to assess its prognostic impact.

Methods:

Venous blood samples were prospectively obtained in 76 healthy volunteers, 72 patients hospitalized for acute decompensated HFREF, and 78 ambulatory chronic HFREF patients without clinical signs of congestion. Sequential measurements were performed in patients with acute decompensated HFREF.

Results:

Plasma renin activity (PRA) was significantly higher in ambulatory chronic HFREF (7.6 ng/ml/h (2.2; 18.1)) compared to patients with acute decompensated HFREF (1.5 ng/ml/h (0.8; 5.7)) or healthy volunteers (1.4 ng/ml/h (0.6; 2.3)) (all p < 0.05). PRA was significantly associated with arterial blood pressure and renin-angiotensin system blocker dose. A progressive rise in PRA (+4 ng/ml/h (0.4; 10.9); p < 0.001) was observed in acute decompensated HFREF patients after three consecutive days of decongestive treatment. Only in acute HFREF were PRA levels associated with increased cardiovascular mortality or HF readmissions (p = 0.035).

Conclusion:

PRA is significantly elevated in ambulatory chronic HFREF patients but is not associated with worse outcome. In contrast, in acute HFREF patients, PRA is associated with cardiovascular mortality or HF readmissions.

Independent regulation of renin-angiotensin-aldosterone system in the kidney

Renin-angiotensin-aldosterone system (RAAS) plays important roles in regulating renal hemodynamics and functions, as well as in the pathophysiology of hypertension and renal disease. In the kidney, angiotensin II (Ang II) production is controlled by independent multiple mechanisms. Ang II is compartmentalized in the renal interstitial fluid with much higher concentrations than those existing in the circulation. Inappropriate activation of the intrarenal RAAS is an important contributor to the pathogenesis of hypertension and renal injury. It has been revealed that intrarenal Ang II levels are predominantly regulated by angiotensinogen and therefore, urinary angiotensinogen could be a biomarker for intrarenal Ang II generation. In addition, recent studies have demonstrated that aldosterone contributes to the progression of renal injury via direct actions on glomerular podocytes, mesangial cells, proximal tubular cells and tubulo-interstitial fibroblasts through the activation of locally expressed mineralocorticoid receptor. Thus, it now appears that intrarenal RAAS is independently regulated and its inappropriate activation contributes to the pathogenesis of the development of hypertension and renal disease. This short review article will focus on the independent regulation of the intrarenal RAAS with an emphasis on the specific role of angiotensinogen.

Role of renal sympathetic nerve activity in prenatal programming of hypertension

Prenatal insults, such as maternal dietary protein deprivation and uteroplacental insufficiency, lead to small for gestational age (SGA) neonates. Epidemiological studies from many different parts of the world have shown that SGA neonates are at increased risk for hypertension and early death from cardiovascular disease as adults. Animal models, including prenatal administration of dexamethasone, uterine artery ligation and maternal dietary protein restriction, result in SGA neonates with fewer nephrons than controls. These models are discussed in this educational review, which provides evidence that prenatal insults lead to altered sodium transport in multiple nephron segments. The factors that could result in increased sodium transport are discussed, focusing on new information that there is increased renal sympathetic nerve activity that may be responsible for augmented renal tubular sodium transport. Renal denervation abrogates the hypertension in programmed rats but has no effect on control rats. Other potential factors that could cause hypertension in programmed rats, such as the renin-angiotensin system, are also discussed.

Dopaminergic Immunofluorescence Studies in Kidney Tissue

The kidney is a highly integrated system of specialized differentiated cells that are responsible for fluid and electrolyte balance in the body. While much of today's research focuses on isolated nephron segments or cells from nephron segments grown in tissue culture, an often overlooked technique that can provide a unique view of many cell types in the kidney is slice culture. Here, we describe techniques that use freshly excised kidney tissue from rats to perform a variety of experiments shortly after isolating the tissue. By slicing the rat kidney in a "bread loaf" format, multiple studies can be performed on slices from the same tissue in parallel. Cryosectioning and staining of the tissue allow for the evaluation of physiological or biochemical responses in a wide variety of specific nephron segments. The procedures described within this chapter can also be extended to human or mouse kidney tissue.

Associations between glycaemic control and activation of the renin-angiotensin-aldosterone system in participants with type 2 diabetes mellitus and hypertension

Introduction

Hyperglycaemia increases succinate concentrations and succinate receptor activation in the kidney resulting in renin release. The aim of our study was to determine if there is an association between glycaemic control as evidenced by glycated haemoglobin values and activation of the renin-angiotensin-aldosterone system in patients with type 2 diabetes mellitus and hypertension.

Methods

A cross-sectional study was conducted at Galway University Hospitals between December 2014 and March 2015. Participants ( n = 66) were identified following interrogation of the electronic database for patients with type 2 diabetes mellitus. Baseline clinical demographics, aldosterone, plasma renin activity, direct renin concentration, urea and electrolytes, glycated haemoglobin, cholesterol, urine sodium and albumin creatinine ratio were recorded.

Results

There was a significant positive linear correlation between glycated haemoglobin and renin (both plasma renin activity [ P = 0.002] and direct renin concentration [ P = 0.008]) and between serum creatinine and aldosterone measured using both radioimmunoassay ( P = 0.008) and immunochemiluminometric assay ( P = 0.008). A significant negative linear correlation was demonstrated between serum sodium and plasma renin activity ( P = 0.005) and direct renin concentration ( P = 0.015) and between estimated glomerular filtration rate and aldosterone measured using radioimmunoassay ( P = 0.02) and immunochemiluminometric assay ( P = 0.016). A significant negative linear correlation existed between urine sodium and plasma renin activity ( P = 0.04) and aldosterone measured using radioimmunoassay ( P = 0.045).

Conclusions

There is a direct positive association between glycaemic control and renin. We advocate for renin measurement to be part of the diabetologist's armamentarium to assess, guide and optimize therapeutic strategies in patients with diabetes.

Effect of renal denervation on urine angiotensinogen excretion in prenatally programmed rats

Prenatal programming results in an increase in blood pressure in adult offspring. We have shown that compared to control adult offspring whose mothers were fed a 20% protein diet, programmed adults whose mothers were fed a 6% protein diet during the last half of pregnancy have an increase in renal sympathetic nerve activity and urinary angiotensinogen/creatinine levels. We hypothesized that the increase in urinary angiotensinogen was mediated by renal sympathetic nerve activity in programmed rats. In this study performed in 3 month old rats, renal denervation resulted in normalization of blood pressure in the 6% programmed group (150 ± 3 Hg in 6% sham vs. 121 ± 4 Hg in 6% denervated, P < 0.001), and a reduction in blood pressure in the 20% group (126 ± 2 Hg 20% sham vs. 113 ± 4 Hg 20% denervated (P < 0.05). We confirm that the intrarenal renin–angiotensin system assessed by urinary angiotensinogen/creatinine is upregulated in offspring of rats fed a 6% protein diet rats compared to 20% controls. To determine if sympathetic nerve activity was mediating the increase in urinary angiotensinogen in programmed rats, we compared denervated to sham‐operated control and programmed rats. Renal denervation had no effect on urinary angiotensinogen/creatinine ratio in the 20% group and no effect on the increased urinary angiotensinogen/creatinine ratio found in programmed rats. This study demonstrates that the increase in urinary angiotensinogen in programmed rats is not mediated by renal sympathetic nerve activity.

Recent Updates on the Proximal Tubule Renin-Angiotensin System in Angiotensin II-Dependent Hypertension

It is well recognized that the renin-angiotensin system (RAS) exists not only as circulating, paracrine (cell to cell), but also intracrine (intracellular) system. In the kidney, however, it is difficult to dissect the respective contributions of circulating RAS versus intrarenal RAS to the physiological regulation of proximal tubular Na(+) reabsorption and hypertension. Here, we review recent studies to provide an update in this research field with a focus on the proximal tubular RAS in angiotensin II (ANG II)-induced hypertension. Careful analysis of available evidence supports the hypothesis that both local synthesis or formation and AT1 (AT1a) receptor- and/or megalin-mediated uptake of angiotensinogen (AGT), ANG I and ANG II contribute to high levels of ANG II in the proximal tubules of the kidney. Under physiological conditions, nearly all major components of the RAS including AGT, prorenin, renin, ANG I, and ANG II would be filtered by the glomerulus and taken up by the proximal tubules. In ANG II-dependent hypertension, the expression of AGT, prorenin, and (pro)renin receptors, and angiotensin-converting enzyme (ACE) is upregulated rather than downregulated in the kidney. Furthermore, hypertension damages the glomerular filtration barrier, which augments the filtration of circulating AGT, prorenin, renin, ANG I, and ANG II and their uptake in the proximal tubules. Together, increased local ANG II formation and augmented uptake of circulating ANG II in the proximal tubules, via activation of AT1 (AT1a) receptors and Na(+)/H(+) exchanger 3, may provide a powerful feedforward mechanism for promoting Na(+) retention and the development of ANG II-induced hypertension.

Dietary Fructose Enhances the Ability of Low Concentrations of Angiotensin II to Stimulate Proximal Tubule Na⁺ Reabsorption

Fructose-enriched diets cause salt-sensitive hypertension. Proximal tubules (PTs) reabsorb 70% of the water and salt filtered through the glomerulus. Angiotensin II (Ang II) regulates this process. Normally, dietary salt reduces Ang II allowing the kidney to excrete more salt, thereby preventing hypertension. We hypothesized that fructose-enriched diets enhance the ability of low concentrations of Ang II to stimulate PT transport. We measured the effects of a low concentration of Ang II (10⁻¹² mol/L) on transport-related oxygen consumption (QO₂), and Na/K-ATPase and Na/H-exchange (NHE) activities and expression in PTs from rats consuming tap water (Control) or 20% fructose (FRUC). In FRUC-treated PTs, Ang II increased QO₂ by 14.9 ± 1.3 nmol/mg/min (p < 0.01) but had no effect in Controls. FRUC elevated NHE3 expression by 19 ± 3% (p < 0.004) but not Na/K-ATPase expression. Ang II stimulated NHE activity in FRUC PT (Δ + 0.7 ± 0.1 Arbitrary Fluorescent units (AFU)/s, p < 0.01) but not in Controls. Na/K-ATPase activity was not affected. The PKC inhibitor Gö6976 blocked the ability of FRUC to augment the actions of Ang II. FRUC did not alter the inhibitory effect of dopamine on NHE activity. We conclude that dietary fructose increases the ability of low concentrations of Ang II to stimulate PT Na reabsorption via effects on NHE.

The vasoprotective axes of the renin-angiotensin system: Physiological relevance and therapeutic implications in cardiovascular, hypertensive and kidney diseases

The renin-angiotensin system (RAS) is undisputedly one of the most prominent endocrine (tissue-to-tissue), paracrine (cell-to-cell) and intracrine (intracellular/nuclear) vasoactive systems in the physiological regulation of neural, cardiovascular, blood pressure, and kidney function. The importance of the RAS in the development and pathogenesis of cardiovascular, hypertensive and kidney diseases has now been firmly established in clinical trials and practice using renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, type 1 (AT₁) angiotensin II (ANG II) receptor blockers (ARBs), or aldosterone receptor antagonists as major therapeutic drugs. The major mechanisms of actions for these RAS inhibitors or receptor blockers are mediated primarily by blocking the detrimental effects of the classic angiotensinogen/renin/ACE/ANG II/AT₁/aldosterone axis. However, the RAS has expanded from this classic axis to include several other complex biochemical and physiological axes, which are derived from the metabolism of this classic axis. Currently, at least five axes of the RAS have been described, with each having its key substrate, enzyme, effector peptide, receptor, and/or downstream signaling pathways. These include the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor, the ANG II/APA/ANG III/AT₂/NO/cGMP, the ANG I/ANG II/ACE2/ANG (1-7)/Mas receptor, the prorenin/renin/prorenin receptor (PRR or Atp6ap2)/MAP kinases ERK1/2/V-ATPase, and the ANG III/APN/ANG IV/IRAP/AT₄ receptor axes. Since the roles and therapeutic implications of the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor axis have been extensively reviewed, this article will focus primarily on reviewing the roles and therapeutic implications of the vasoprotective axes of the RAS in cardiovascular, hypertensive and kidney diseases.

Luminal ANG II is internalized as a complex with AT1R/AT2R heterodimers to target endoplasmic reticulum in LLC-PK1 cells

ANG II has many biological effects in renal physiology, particularly in Ca²⁺ handling in the regulation of fluid and solute reabsorption. It involves the systemic endocrine renin-angiotensin system (RAS), but tissue and intracrine ANG II are also known. We have shown that ANG II induces heterodimerization of its AT₁ and AT₂ receptors (AT₁R and AT₂R) to stimulate sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) activity. Thus, we investigated whether ANG II-AT₁R/AT₂R complex is formed and internalized, and also examined the intracellular localization of this complex to determine how its effect might be exerted on renal intracrine RAS. Living cell imaging of LLC-PK₁ cells, quantification of extracellular ANG II, and use of the receptor antagonists, losartan and PD123319, showed that ANG II is internalized with AT₁R/AT₂R heterodimers as a complex in a microtubule-dependent and clathrin-independent manner, since colchicine-but not Pitstop2-blocked this process. This result was confirmed by an increase of β-arrestin phosphorylation after ANG II treatment, clathrin-mediated endocytosis being dependent on dephosphorylation of β-arrestin. Internalized ANG II colocalized with an endoplasmic reticulum (ER) marker and increased levels of AT₁R, AT₂R, and PKCα in ER-enriched membrane fractions. This novel evidence suggests the internalization of an ANG II-AT₁/AT₂ complex to target ER, where it might trigger intracellular Ca²⁺ responses.

Effects of Genetic Polymorphisms of the Renin-Angiotensin System in Children with Nephrotic Syndrome

Background. The renin-angiotensin system (RAS) has been considered to be responsible for the pathogenesis or progression of many diseases which may or may not be related to kidney. Genetic polymorphisms of the various components of the RAS have been associated with differences in the clinical course of several disease states in adults and children.

Objectives. The purpose of our study was to investigate RAS gene polymorphisms in patients with steroid resistant primary focal segmental glomerulosclerosis (FSGS) and nephrotic syndrome responding to steroid therapy. Furthermore, we aimed to investigate whether there was an association between polymorphic alleles and responses to steroid therapy, the degree of renal dysfunction, and prevalence of end-stage renal disease (ESRD).

Material and methods. One hundred and fifty-eight children with the diagnosis of nephrotic syndrome were recruited from the Nephrology unit in the Department of Paediatrics of Ege University. Forty-nine of them were classified as renal biopsy-proven FSGS and 102 patients were considered to have response to steroid treatment. Renal functional impairment was detected in 19 subjects with FSGS and end-stage renal insufficiency in 13 patients. The control group consisted of 287 healthy adult subjects. Angiotensin-converting enzyme (ACE), angiotensin II type 1 receptor (AT1R) and angiotensinogen (AGT) gene polymorphisms were determined by the polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) technique. Statistical significance was regarded as p<0.05.

Results. There were no statistically significant differences for the C allele of AT1R or the T allele of AGT genes between the children with nephrotic syndrome and control group, but on the other hand statistically significant differences were detected for D allele of ACE gene. There was no significant relationship detected between the D allele of ACE, the C allele of AT1R or the T allele of AGT genes and response to steroid therapy, extent of renal dysfunction and the progression to ESRD. However, there was a significant relationship between T allele of AGT gene and resistance to steroid treatment (OR; 4,837, 95% CI; 1,723—13,577, p=0.01), renal dysfunction (OR; 3,189, 95% CI; 0,999—10,182, p=0.041) and progression to ESRD (OR; 3,852, 95% CI; 1,057—14,040, p=0.03).

Conclusion. In this study, the angiotensino gene -235T allele was found to be related with steroid resistance, renal dysfunction and progression of ESRD in nephrotic syndrome.

Regulation of renal proximal fluid uptake by luminal and peritubular angiotensin II

Introduction

Angiotensin II (Ang II), when administered to either tubular lumen or peritubular capillary, exerts a biphasic action on proximal fluid uptake rate. At low concentrations, (10-12—10-10M) Ang II stimulates fluid transport, whereas higher doses (> 10-9 M) inhibit. Ang II is secreted into the lumen in the proximal tubule and the concentration of Ang II in the proximal lumen has been reported to be in the nanomolar range, 100—1,000 times higher than in peritubular blood. We investigated the regulation of renal proximal fluid transport by luminal (predominantly locally produced) and peritubular capillary (circulatory) Ang II in anaesthetised rats, using a selective AT1-receptor antagonist, candesartan.

Everything we always wanted to know about furosemide but were afraid to ask

Furosemide is a widely used, potent natriuretic drug, which inhibits the Na(+)-K(+)-2Cl(-) cotransporter (NKCC)-2 in the ascending limb of the loop of Henle applied to reduce extracellular fluid volume expansion in heart and kidney disease. Undesirable consequences of furosemide, such as worsening of kidney function and unpredictable effects on sodium balance, led to this critical evaluation of how inhibition of NKCC affects renal and cardiovascular physiology. This evaluation reveals important knowledge gaps, involving furosemide as a drug, the function of NKCC2 (and NKCC1), and renal and systemic indirect effects of NKCC inhibition. Regarding renal effects, renal blood flow and glomerular filtration rate could become compromised by activation of tubuloglomerular feedback or by renin release, particularly if renal function is already compromised. Modulation of the intrarenal renin angiotensin system, however, is ill-defined. Regarding systemic effects, vasodilation followed by nonspecific NKCC inhibition and changes in venous compliance are not well understood. Repetitive administration of furosemide induces short-term (braking phenomenon, acute diuretic resistance) and long-term (chronic diuretic resistance) adaptations, of which the mechanisms are not well known. Modulation of NKCC2 expression and activity in kidney and heart failure is ill-defined. Lastly, furosemide's effects on cutaneous sodium stores and on uric acid levels could be beneficial or detrimental. Concluding, a considerable knowledge gap is identified regarding a potent drug with a relatively specific renal target, NKCC2, and renal and systemic actions. Resolving these questions would increase the understanding of NKCCs and their actions and improve rational use of furosemide in pathophysiology of fluid volume expansion.

Angiotensin III increases monocyte chemoattractant protein-1 expression in cultured human proximal tubular epithelial cells

BACKGROUND/AIMS

We investigated whether angiotensin III (Ang III) is involved in monocyte recruitment through regulation of the chemokine monocyte chemoattractant protein-1 (MCP-1) in cultured human proximal tubular epithelial cells (HK-2 cells).

METHODS

We measured MCP-1 levels in HK-2 cells that had been treated with various concentrations of Ang III and Ang II type-1 (AT1) receptor antagonists at various time points. The phosphorylation states of p38, c-Jun N-terminal kinases (JNK), and extracellular-signal-regulated kinases were measured in Ang III-treated cells to explore the mitogen-activated protein kinase (MAPK) pathway. MCP-1 levels in HK-2 cell-conditioned media were measured after pre-treatment with the transcription factor inhibitors curcumin or pyrrolidine dithiocarbamate.

RESULTS

Ang III increased MCP-1 protein production in dose- and time-dependent manners in HK-2 cells, which was inhibited by the AT1 receptor blocker losartan. p38 MAPK activity increased significantly in HK-2 cells exposed to Ang III for 30 minutes, and was sustained at higher levels after 60 minutes (p < 0.05). Total phosphorylated JNK protein levels tended to increase 20 minutes after stimulation with Ang III. Pre-treatment with a p38 inhibitor, a JNK inhibitor, or curcumin significantly inhibited Ang III-induced MCP-1 production.

CONCLUSIONS

Ang III increases MCP-1 synthesis via stimulation of intracellular p38 and JNK MAPK signaling activity and subsequent activated protein-1 transcriptional activity in HK-2 cells.

Luminal angiotensin II stimulates rat medullary thick ascending limb chloride transport in the presence of basolateral norepinephrine

Angiotensin II (ANG II) is secreted by the proximal tubule resulting in a luminal concentration that is 100- to 1,000-fold greater than that in the blood. Luminal ANG II has been shown to stimulate sodium transport in the proximal tubule and distal nephron. Surprisingly, luminal ANG II inhibits NaCl transport in the medullary thick ascending limb (mTAL), a nephron segment responsible for a significant amount of NaCl absorption from the glomerular ultrafiltrate. We confirmed that addition of 10(-8) M ANG II to the lumen inhibited mTAL chloride transport (220 ± 19 to 165 ± 25 pmol·mm(-1)·min(-1), P < 0.01) and examined whether an interaction with basolateral norepinephrine existed to simulate the in vivo condition of an innervated tubule. We found that in the presence of a 10(-6) M norepinephrine bath, luminal ANG II stimulated mTAL chloride transport from 298 ± 18 to 364 ± 42 pmol·mm(-1)·min(-1) (P < 0.05). Stimulation of chloride transport by luminal ANG II was also observed with 10(-3) M bath dibutyryl cAMP in the bathing solution and bath isoproterenol. A bath of 10(-5) H-89 blocked the stimulation of chloride transport by norepinephrine and prevented the effect of luminal ANG II to either stimulate or inhibit chloride transport. Bath phentolamine, an α-adrenergic agonist, also prevented the decrease in mTAL chloride transport by luminal ANG II. Thus luminal ANG II increases chloride transport with basolateral norepinephrine; an effect likely mediated by stimulation of cAMP. Alpha-1 adrenergic stimulation prevents the inhibition of chloride transport by luminal ANG II.

ANG II-induced hypertension in the VCD mouse model of menopause is prevented by estrogen replacement during perimenopause

Premenopausal females are resistant to the development of hypertension, and this protection is lost after the onset of menopause, resulting in a sharp increase in disease onset and severity. However, it is unknown how a fluctuating ovarian hormone environment during the transition from perimenopause to menopause impacts the onset of hypertension, and whether interventions during perimenopause prevent disease onset after menopause. A gradual transition to menopause was induced by repeated daily injections of 4-vinylcyclohexene diepoxide (VCD). ANG II (800 ng·kg(-1)·min(-1)) was infused into perimenopausal and menopausal female mice for 14 days. A separate cohort of mice received 17β-estradiol replacement during perimenopause. ANG II infusion produced significantly higher mean arterial pressure (MAP) in menopausal vs. cycling females, and 17β-estradiol replacement prevented this increase. In contrast, MAP was not significantly different when ANG II was infused into perimenopausal and cycling females, suggesting that female resistance to ANG II-induced hypertension is intact during perimenopause. ANG II infusion caused a significant glomerular hypertrophy, and hypertrophy was not impacted by hormonal status. Expression levels of aquaporin-2 (AQP2), a collecting duct protein, have been suggested to reflect blood pressure. AQP2 protein expression was significantly downregulated in the renal cortex of the ANG II-infused menopause group, where blood pressure was increased. AQP2 expression levels were restored to control levels with 17β-estradiol replacement. This study indicates that the changing hormonal environment in the VCD model of menopause impacts the severity of ANG II-induced hypertension. These data highlight the utility of the ovary-intact VCD model of menopause as a clinically relevant model to investigate the physiological mechanisms of hypertension that occur in women during the transition into menopause.

Overexpression of heterogeneous nuclear ribonucleoprotein F stimulates renal Ace-2 gene expression and prevents TGF-β1-induced kidney injury in a mouse model of diabetes

AIMS/HYPOTHESIS

We investigated whether heterogeneous nuclear ribonucleoprotein F (hnRNP F) stimulates renal ACE-2 expression and prevents TGF-β1 signalling, TGF-β1 inhibition of Ace-2 gene expression and induction of tubulo-fibrosis in an Akita mouse model of type 1 diabetes.

METHODS

Adult male Akita transgenic (Tg) mice overexpressing specifically hnRNP F in their renal proximal tubular cells (RPTCs) were studied. Non-Akita littermates and Akita mice served as controls. Immortalised rat RPTCs stably transfected with plasmid containing either rat Hnrnpf cDNA or rat Ace-2 gene promoter were also studied.

RESULTS

Overexpression of hnRNP F attenuated systemic hypertension, glomerular filtration rate, albumin/creatinine ratio, urinary angiotensinogen (AGT) and angiotensin (Ang) II levels, renal fibrosis and profibrotic gene (Agt, Tgf-β1, TGF-β receptor II [Tgf-βrII]) expression, stimulated anti-profibrotic gene (Ace-2 and Ang 1-7 receptor [MasR]) expression, and normalised urinary Ang 1-7 level in Akita Hnrnpf-Tg mice as compared with Akita mice. In vitro, hnRNP F overexpression stimulated Ace-2 gene promoter activity, mRNA and protein expression, and attenuated Agt, Tgf-β1 and Tgf-βrII gene expression. Furthermore, hnRNP F overexpression prevented TGF-β1 signalling and TGF-β1 inhibition of Ace-2 gene expression.

CONCLUSIONS/INTERPRETATION

These data demonstrate that hnRNP F stimulates Ace-2 gene transcription, prevents TGF-β1 inhibition of Ace-2 gene transcription and induction of kidney injury in diabetes. HnRNP F may be a potential target for treating hypertension and renal fibrosis in diabetes.

Renin and the (pro)renin receptor in the renal collecting duct: Role in the pathogenesis of hypertension

The intrarenal renin-angiotensin system (RAS) plays a critical role in the pathogenesis and progression of hypertension and kidney disease. In angiotensin (Ang) II-dependent hypertension, collecting duct renin synthesis and secretion are stimulated despite suppression of juxtaglomerular (JG) renin. This effect is mediated by the AngII type I receptor (AT1 R), independent of blood pressure. Although the regulation of JG renin has been extensively studied, the mechanisms by which renin is regulated in the collecting duct remain unclear. The augmentation of renin synthesis and activity in the collecting duct may provide a pathway for additional generation of intrarenal and intratubular AngII formation due to the presence of angiotensinogen substrate and angiotensin-converting enzyme in the nephron. The recently described (pro)renin receptor ((P)RR) binds renin or prorenin, enhancing renin activity and fully activating the biologically inactive prorenin peptide. Stimulation of (P)RR also activates intracellular pathways related to fibrosis. Renin and the (P)RR are augmented in renal tissues of AngII-dependent hypertensive rats. However, the functional contribution of the (P)RR to enhanced renin activity in the collecting duct and its contribution to the development of hypertension and kidney disease have not been well elucidated. This review focuses on recent evidence demonstrating the mechanism of renin regulation in the collecting ducts and its interaction with the (P)RR. The data suggest that renin-(P)RR interactions may induce stimulation of intracellular pathways associated with the development of hypertension and kidney disease.

Roles of collecting duct renin and (pro)renin receptor in hypertension: mini review

In angiotensin (Ang)-II-dependent hypertension, collecting duct renin synthesis and secretion are stimulated despite suppression of juxtaglomerular (JG) renin. This effect is mediated by Ang II type 1 (AT1) receptor independent of blood pressure. Although the regulation of JG renin is known, the mechanisms by which renin is regulated in the collecting duct are not completely understood. The presence of renin activity in the collecting duct may provide a pathway for intratubular Ang II formation since angiotensinogen substrate and angiotensin converting enzyme are present in the distal nephron. The recently named new member of the renin-angiotensin system (RAS), the (pro)renin receptor [(P)RR], is able to bind renin and the inactive prorenin, thus enhancing renin activity and fully activating prorenin. We have demonstrated that renin and (P)RR are augmented in renal tissues from rats infused with Ang II and during sodium depletion, suggesting a physiological role in intrarenal RAS activation. Importantly, (P)RR activation also causes activation of intracellular pathways associated with increased cyclooxygenase 2 expression and induction of profibrotic genes. In addition, renin and (P)RR are upregulated by Ang II in collecting duct cells. Although the mechanisms involved in their regulation are still under study, they seem to be dependent on the intrarenal RAS activation. The complexities of the mechanisms of stimulation also depend on cyclooxygenase 2 and sodium depletion. Our data suggest that renin and (P)RR can interact to increase intratubular Ang II formation and the activation of profibrotic genes in renal collecting duct cells. Both pathways may have a critical role in the development of hypertension and renal disease.

Molecular mechanisms and regulation of urinary acidification

The H(+) concentration in human blood is kept within very narrow limits, ~40 nmol/L, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: (i) reabsorb HCO3(-) that is filtered through the glomeruli to prevent its excretion in the urine; (ii) generate a sufficient quantity of new HCO3(-) to compensate for the loss of HCO3(-) resulting from dietary metabolic H(+) loads and loss of HCO3(-) in the urea cycle; and (iii) excrete HCO3(-) (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ~60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level.

Renin-angiotensin blockade resets podocyte epigenome through Kruppel-like Factor 4 and attenuates proteinuria

Proteinuria is a central component of chronic kidney disease and an independent risk factor for cardiovascular disease. Kidney podocytes have an essential role as a filtration barrier against proteinuria. Kruppel-like Factor 4 (KLF4) is expressed in podocytes and decreased in glomerular diseases leading to methylation of the nephrin promoter, decreased nephrin expression and proteinuria. Treatment with an angiotensin receptor blocker (ARB) reduced methylation of the nephrin promoter in murine glomeruli of an adriamycin nephropathy model with recovery of KLF4 expression and a decrease in albuminuria. In podocyte-specific KLF4 knockout mice, the effect of ARB on albuminuria and the nephrin promoter methylation was attenuated. In cultured human podocytes, angiotensin II reduced KLF4 expression and caused methylation of the nephrin promoter with decreased nephrin expression. In patients, nephrin promoter methylation was increased in proteinuric kidney diseases with decreased KLF4 and nephrin expression. KLF4 expression in ARB-treated patients was higher in patients with than without ARB treatment. Thus, angiotensin II can modulate epigenetic regulation in podocytes and ARB inhibits these actions in part via KLF4 in proteinuric kidney diseases. This study provides a new concept that renin-angiotensin system blockade can exert therapeutic effects through epigenetic modulation of the kidney gene expression.

Crosstalk between (Pro)renin receptor and COX-2 in the renal medulla during angiotensin II-induced hypertension

Angiotensin II (AngII) is an octapeptide hormone that plays a central role in regulation of sodium balance, plasma volume, and blood pressure. Its role in the pathogenesis of hypertension is highlighted by the wide use of inhibitors of the renin-angiotensin system (RAS) as the first-line antihypertensive therapy. However, despite intensive investigation, the mechanism of AngII-induced hypertension is still incompletely understood. Although diverse pathways are likely involved, increasing evidence suggests that the activation of intrarenal RAS may represent a dominant mechanism of AngII-induced hypertension. (Pro)renin receptor (PRR), a potential regulator of intrarenal RAS, is expressed in the intercalated cells of the collecting duct (CD) and induced by AngII, in parallel with increased renin in the principal cells of the CD. Activation of PRR elevated PGE2 release and COX-2 expression in renal inner medullary cells whereas COX-2-derived PGE2via the EP4 receptor mediates the upregulation of PRR during AngII infusion, thus forming a vicious cycle. The mutually stimulatory relationship between PRR and COX-2 in the distal nephron may play an important role in mediating AngII-induced hypertension.

Lack of renoprotective effect of chronic intravenous angiotensin-(1-7) or angiotensin-(2-10) in a rat model of focal segmental glomerulosclerosis

Unopposed angiotensin (Ang) II-mediated cellular effects may lead to progressive glomerulosclerosis. While Ang-II can be locally generated in the kidneys, we previously showed that glomerular podocytes primarily convert Ang-I, the precursor of Ang-II, to Ang-(1-7) and Ang-(2-10), peptides that have been independently implicated in biological actions opposing those of Ang-II. Therefore, we hypothesized that Ang-(1-7) and Ang-(2-10) could be renoprotective in the fawn-hooded hypertensive rat, a model of focal segmental glomerulosclerosis. We evaluated the ability of 8-12 week-long intravenous administration of either Ang-(1-7) or Ang-(2-10) (100-400 ng/kg/min) to reduce glomerular injury in uni-nephrectomized fawn-hooded hypertensive rats, early or late in the disease. Vehicle-treated rats developed hypertension and lesions of focal segmental glomerulosclerosis. No reduction in glomerular damage was observed, as measured by either 24-hour urinary protein excretion or histological examination of glomerulosclerosis, upon Ang-(1-7) or Ang-(2-10) administration, regardless of peptide dose or disease stage. On the contrary, when given at 400 ng/kg/min, both peptides induced a further increase in systolic blood pressure. Content of Ang peptides was measured by parallel reaction monitoring in kidneys harvested at sacrifice. Exogenous administration of Ang-(1-7) and Ang-(2-10) did not lead to a significant increase in their corresponding intrarenal levels. However, the relative abundance of Ang-(1-7) with respect to Ang-II was increased in kidney homogenates of Ang-(1-7)-treated rats. We conclude that chronic intravenous administration of Ang-(1-7) or Ang-(2-10) does not ameliorate glomerular damage in a rat model of focal segmental glomerulosclerosis and may induce a further rise in blood pressure, potentially aggravating glomerular injury.

Susceptibility and progression of end stage renal disease are not associated with angiotensin II type 1 receptor gene polymorphism

CONTEXT

The role of the angiotensin II type 1 receptor (AT1R) gene polymorphism, A1166C, has been shown to be associated with end stage renal disease (ESRD) and its progression. There is also some evidence that HLA class II alleles are associated with ESRD independent of other factors.

OBJECTIVE

To examine the association between AT1R gene polymorphism in the susceptibility and progression to ESRD in patients with chronic renal failure and to investigate if the AT1R genotypes and HLA-DR alleles predict the time to ESRD.

MATERIALS AND METHODS

Genotyping was performed in 50 ESRD patients and 44 control subjects for the AT1R A1166C gene polymorphism using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). ESRD patients were examined for HLA-DRB1 alleles according to a reverse hybridization line probe assay.

RESULTS

Allele and genotype frequencies of the AT1R polymorphism did not differ significantly between ESRD patients and controls. Furthermore, there was no association between the AT1R gene polymorphism or HLA-DRB1 alleles with the time to the occurrence of end stage failure.

DISCUSSION AND CONCLUSION

We concluded that the AT1R genotype does not contribute to the genetic susceptibility of ESRD and is not associated with progression of chronic kidney failure to ESRD.

Renin-angiotensin system in the kidney: What is new?

The renin-angiotensin system (RAS) has been known for more than a century as a cascade that regulates body fluid balance and blood pressure. Angiotensin II(Ang II) has many functions in different tissues; however it is on the kidney that this peptide exerts its main functions. New enzymes, alternative routes for Ang IIformation or even active Ang II-derived peptides have now been described acting on Ang II AT₁ or AT₂ receptors, or in receptors which have recently been cloned, such as Mas and AT₄. Another interesting observation was that old members of the RAS, such as angiotensin converting enzyme (ACE), renin and prorenin, well known by its enzymatic activity, can also activate intracellular signaling pathways, acting as an outside-in signal transduction molecule or on the renin/(Pro)renin receptor. Moreover, the endocrine RAS, now is also known to have paracrine, autocrine and intracrine action on different tissues, expressing necessary components for local Ang II formation. This in situ formation, especially in the kidney, increases Ang II levels to regulate blood pressure and renal functions. These discoveries, such as the ACE2/Ang-(1-7)/Mas axis and its antangonistic effect rather than classical deleterious Ang II effects, improves the development of new drugs for treating hypertension and cardiovascular diseases.

Effects of acid challenges on type 2 angiotensin II receptor-sensitive ammonia production by the proximal tubule

Angiotensin II (ANG II) acting through its type 1 (AT1) receptor stimulates total ammonia (tNH3) production by the proximal tubule. The present studies explored the role of ANG II type 2 (AT2) receptors in modulating the stimulatory effects of ANG II on tNH3 production. Mouse S2 proximal tubule segments derived from 18-h and 7-day acid-loaded mice, and non-acid-loaded controls were dissected and microperfused in vitro. Adding ANG II to the luminal perfusion solution resulted in different increments in tNH3 production rates in tubules derived from 18-h vs. 7-day acid-loaded mice such that the increase in tNH3 production with ANG II was higher in tubules derived from 18-h acid-loaded mice compared with those derived from control and 7-day acid-loaded mice. Adding the AT2 receptor blocker PD123319 with ANG II increased ANG II-stimulated tNH3 production in S2 segments from control and 7-day acid-loaded mice but not in those from 18-h acid-loaded mice, and this increased effect of PD123319 was associated with higher AT2 receptor protein levels in brush-border membranes. Studies in cultured proximal tubule cells demonstrated that 2-h exposure to pH 7.0 reduced the modulating effect of PD123319 on ANG II-simulated tNH3 production and reduced cell surface AT2 receptor levels. We concluded that AT2 receptors reduce the stimulatory effect of ANG II on proximal tubule tNH3 production and that the time-dependent impact of AT2 receptor blockade on the ANG II-stimulated tNH3 production corresponded to time-dependent changes in AT2 receptor cell surface expression in the proximal tubule.

Role of angiotensin-converting enzyme 2 (ACE2) in diabetic cardiovascular complications

Diabetes mellitus results in severe cardiovascular complications, and heart disease and failure remain the major causes of death in patients with diabetes. Given the increasing global tide of obesity and diabetes, the clinical burden of diabetes-induced cardiovascular disease is reaching epidemic proportions. Therefore urgent actions are needed to stem the tide of diabetes which entails new prevention and treatment tools. Clinical and pharmacological studies have demonstrated that AngII (angiotensin II), the major effector peptide of the RAS (renin–angiotensin system), is a critical promoter of insulin resistance and diabetes mellitus. The role of RAS and AngII has been implicated in the progression of diabetic cardiovascular complications and AT1R (AngII type 1 receptor) blockers and ACE (angiotensin-converting enzyme) inhibitors have shown clinical benefits. ACE2, the recently discovered homologue of ACE, is a monocarboxypeptidase which converts AngII into Ang-(1–7) [angiotensin-(1–7)] which, by virtue of its actions on the MasR (Mas receptor), opposes the effects of AngII. In animal models of diabetes, an early increase in ACE2 expression and activity occurs, whereas ACE2 mRNA and protein levels have been found to decrease in older STZ (streptozotocin)-induced diabetic rats. Using the Akita mouse model of Type 1 diabetes, we have recently shown that loss of ACE2 disrupts the balance of the RAS in a diabetic state and leads to AngII/AT1R-dependent systolic dysfunction and impaired vascular function. In the present review, we will discuss the role of the RAS in the pathophysiology and treatment of diabetes and its complications with particular emphasis on potential benefits of the ACE2/Ang-(1–7)/MasR axis activation.

The regulation of NHE₁ and NHE₃ activity by angiotensin II is mediated by the activation of the angiotensin II type I receptor/phospholipase C/calcium/calmodulin pathway in distal nephron cells

Angiotensin II (Ang II), acting via the AT1 receptor, induces an increase in intracellular calcium [Ca(2+)]i that then interacts with calmodulin (CaM). The Ca(2+)/CaM complex directly or indirectly activates sodium hydrogen exchanger 1 (NHE1) and phosphorylates calmodulin kinase II (CaMKII), which then regulates sodium hydrogen exchanger 3 (NHE3) activity. In this study, we investigated the cellular signaling pathways responsible for Ang II-mediated regulation of NHE1 and NHE3 in Madin-Darby canine kidney (MDCK) cells. The NHE1- and NHE3-dependent pHi recovery rates were evaluated by fluorescence microscopy using the fluorescent probe BCECF/AM, messenger RNA was evaluated with the reverse transcription polymerase chain reaction (RT-PCR), and protein expression was evaluated by immunoblot. We demonstrated that treatment with Ang II (1pM or 1 nM) for 30 min induced, via the AT1 but not the AT2 receptor, an equal increase in NHE1 and NHE3 activity that was reduced by the specific inhibitors HOE 694 and S3226, respectively. Ang II (1 nM) did not change the total expression of NHE1, NHE3 or calmodulin, but it induced CaMKII, cRaf-1, Erk1/2 and p90(RSK) phosphorylation. The stimulatory effects of Ang II (1 nM) on NHE1 or NHE3 activity or protein abundance was reduced by ophiobolin-A (CaM inhibitor), KN93 (CaMKII inhibitor) or PD98059 (Mek inhibitor). These results indicate that after 30 min, Ang II treatment may activate G protein-dependent pathways, including the AT1/PLC/Ca(2+)/CaM pathway, which induces CaMKII phosphorylation to stimulate NHE3 and induces cRaf-1/Mek/Erk1/2/p90(RSK) activity to stimulate NHE1.

Angiotensin II-induced hypertension increases plasma membrane Na pump activity by enhancing Na entry in rat thick ascending limbs

Thick ascending limbs (TAL) reabsorb 30% of the filtered NaCl load. Na enters the cells via apical Na-K-2Cl cotransporters and Na/H exchangers and exits via basolateral Na pumps. Chronic angiotensin II (ANG II) infusion increases net TAL Na transport and Na apical entry; however, little is known about its effects on the basolateral Na pump. We hypothesized that in rat TALs Na pump activity is enhanced by ANG II-infusion, a model of ANG II-induced hypertension. Rats were infused with 200 ng·kg(-1)·min(-1) ANG II or vehicle for 7 days, and TAL suspensions were obtained. We studied plasma membrane Na pump activity by measuring changes in 1) intracellular Na (Nai) induced by ouabain; and 2) ouabain-sensitive oxygen consumption (QO2). We found that the ouabain-sensitive rise in Nai in TALs from ANG II-infused rats was 12.8 ± 0.4 arbitrary fluorescent units (AFU)·mg(-1)·min(-1) compared with only 9.9 ± 1.1 AFU·mg(-1)·min(-1) in controls (P < 0.024). Ouabain-sensitive oxygen consumption was 17 ± 5% (P < 0.043) greater in tubules from ANG II-treated than vehicle rats. ANG II infusion did not alter total Na pump expression, the number of Na pumps in the plasma membrane, or the affinity for Na. When furosemide (1.1 mg·kg(-1)·day(-1)) was coinfused with ANG II, no increase in plasma membrane Na pump activity was observed. We concluded that in ANG II-induced hypertension Na pump activity is increased in the plasma membrane of TALs and that this increase is caused by the chronically enhanced Na entry occurring in this model.