T-cells regulate albuminuria but not hypertension, renal histology, or the medullary transcriptome in the Dahl SSCD247+/+ rat.

In the current study, we took advantage of the loss of protection from hypertension in SSCD247-/- rats to characterize the pathological effects of renal T-cells in isolation from the confounding effects of elevated renal perfusion pressure. Male SSCD247-/- and SSCD247+/+ littermates were fed 4.0% NaCl (high salt) diet to induce hypertension. Blood pressure was assessed continuously throughout the time course with radiotelemetry. Urine albumin and protein excretion were assessed on the final day of high salt. Renal injury and medullary transcriptome were assessed after completion of the high salt protocol. In contrast to previous studies, mean arterial pressure was not significantly different between SSCD247-/- and SSCD247+/+ rats. Despite this lack of pressure difference, urinary albumin was significantly lower in SSCD247-/- rats than their wild-type littermates. In the outer medulla, substantially more transcriptomic changes were found to correlate with endpoint blood pressure than with the absence of presence of renal T-cells. We also demonstrated that renal histological damage was driven by elevated renal perfusion pressure rather than the presence of renal T-cells. In conclusion, using the loss of protection from hypertension in SSCD247-/- rats, we demonstrated that renal perfusion pressure has more profound pathological effects on the kidney than renal T-cells. However, renal T-cells, independently of blood pressure, modulate the progression of albuminuria.NEW & NOTEWORTHY In vivo studies in a T-cell-deficient rat model of salt-sensitive hypertension (SSCD247-/- rats) were used to evaluate the role of T-cells on the development of hypertension and renal damage. Detailed physiological and transcriptomic analysis demonstrated no difference in blood pressure between rats with (SSCD247+/+) or without (SSCD247-/-) T-cells. Despite this, albuminuria was significantly lower in SSCD247-/- rats than SSCD247+/+ rats.

Regulating distal tubule functions and salt sensitivity.

This review highlights the molecular basis of salt sensitivity in hypertension, with a focus on the regulation of sodium transport in the distal nephron. Sodium reabsorption in this region is often linked to the actions of aldosterone, although in recent years numerous findings have been reported on the aldosterone-independent pathway of acquiring salt sensitivity by potassium deficiency or potassium loading. The key to this discussion is the interplay, through extracellular potassium concentration, between the first part of the tubules expressing the Na+-Cl- cotransporter (NCC) and the second part expressing the epithelial sodium channel (ENaC). The molecular pathways such as WNK-SPAK/OSR1 signaling, KLHL3-CUL3 complex, protein phosphatases and mTORC2-Nedd4L pathway are described as the mechanism by which salt sensitivity on blood pressure is acquired in response to changes in physiological conditions including potassium depletion or loading. This review highlights the potential for targeting these molecular pathways to develop novel therapeutic strategies for the treatment of salt-sensitive hypertension, the mechanism of which remains to be elucidated.

Sex differences in dietary sodium evoked NCC regulation and blood pressure in male and female Sprague-Dawley, Dahl salt-resistant, and Dahl salt-sensitive rats.

Hypertension affects approximately one in two United States adults and sex plays an important role in the pathogenesis of hypertension. The Na+-Cl- cotransporter (NCC), regulated by a kinase network including with-no-lysine kinase (WNK)1 and WNK4, STE20/SPS1-related proline alanine-rich kinase (SPAK), and oxidative stress response 1 (OxSR1), is critical to Na+ reabsorption and blood pressure regulation. Dietary salt differentially modulates NCC in salt-sensitive and salt-resistant rats, in part by modulation of WNK/SPAK/OxSR1 signaling. In this study, we tested the hypothesis that sex-dependent differences in NCC regulation contribute to the development of the salt sensitivity of blood pressure using male and female Sprague-Dawley (SD), Dahl salt-resistant (DSR), and Dahl salt-sensitive (DSS) rats. In normotensive salt-resistant SD and DSR rats, a high-salt diet evoked significant decreases in NCC activity, expression, and phosphorylation. In males, these changes were associated with no change in WNK1 expression, a decrease in WNK4 levels, and suppression of SPAK/OxSR1 expression and phosphorylation. In contrast, in females, there was decreased NCC activity associated with suppression of SPAK/OxSR1 expression and phosphorylation. In hypertensive DSS rats, the ability of females to suppress NCC (in opposition to males) via a SPAK/OxSR1 mechanism likely contributes to their lower magnitude of salt-sensitive hypertension. Collectively, our findings support the existence of sex differences in male versus female rats with NCC regulation during dietary salt intake involving suppression of WNK4 expression in male rats only and the involvement of SPAK/OxSR1 signaling in both males and females.NEW & NOTEWORTHY NCC regulation is sex dependent. In normotensive male and female Sprague-Dawley and Dahl salt-resistant rats, which exhibit dietary Na+-evoked NCC suppression, male rats exhibit decreased WNK4 expression and decreased SPAK and OxSR1 levels, whereas female rats only suppress SPAK and OxSR1. In hypertensive Dahl salt-sensitive rats, the ability of females to suppress NCC (in opposition to males) via a SPAK/OxSR1 mechanism likely contributes to their lower magnitude of salt-sensitive hypertension.

High sodium, rather than high blood pressure, induces immune cell activation and renal infiltration in ovariectomized adult Wistar rats.

We used an animal model of salt-sensitive hypertension (SSH) in which ovariectomized (oVx) rats developed hypertension with high salt (HS) intake. Hypertension is accompanied by changes in the percentage of CD4+ T lymphocytes, immune CD45+ cell infiltration into renal tissue, and changes in Na+, K+- ATPase (NKA) expression in both renal tissue and peripheral blood mononuclear cells (PBMCs). To determine whether the observed changes resulted from HS intake, high blood pressure, or both, hydralazine (HDZ) was used to lower blood pressure. The oVx HS rats received two HDZ schedules either to prevent or to treat hypertension. NKA was overexpressed in the kidneys of all oVx groups and in PBMCs of oVx HS rats. This pattern was not altered with HDZ treatment. Changes in CD4+ T lymphocytes and renal infiltration of CD45+ cells were not reversed either. High salt, but not high blood pressure, induces immune cell activation and renal infiltration. Overexpressed NKA is the primary event, and HS is the perturbation to the system in this model of SSH, which resembles the postmenopausal state.

Na/K-ATPase signaling tonically inhibits sodium reabsorption in the renal proximal tubule.

Through its classic ATP-dependent ion-pumping function, basolateral Na/K-ATPase (NKA) generates the Na+ gradient that drives apical Na+ reabsorption in the renal proximal tubule (RPT), primarily through the Na+ /H+ exchanger (NHE3). Accordingly, activation of NKA-mediated ion transport decreases natriuresis through activation of basolateral (NKA) and apical (NHE3) Na+ reabsorption. In contrast, activation of the more recently discovered NKA signaling function triggers cellular redistribution of RPT NKA and NHE3 and decreases Na+ reabsorption. We used gene targeting to test the respective contributions of NKA signaling and ion pumping to the overall regulation of RPT Na+ reabsorption. Knockdown of RPT NKA in cells and mice increased membrane NHE3 and Na+ /HCO3 - cotransporter (NBCe1A). Urine output and absolute Na+ excretion decreased by 65%, driven by increased RPT Na+ reabsorption (as indicated by decreased lithium clearance and unchanged glomerular filtration rate), and accompanied by elevated blood pressure. This hyper reabsorptive phenotype was rescued upon crossing with RPT NHE3-/- mice, confirming the importance of NKA/NHE3 coupling. Hence, NKA signaling exerts a tonic inhibition on Na+ reabsorption by regulating key apical and basolateral Na+ transporters. This action, lifted upon NKA genetic suppression, tonically counteracts NKA's ATP-driven function of basolateral Na+ reabsorption. Strikingly, NKA signaling is not only physiologically relevant but it also appears to be functionally dominant over NKA ion pumping in the control of RPT reabsorption.

VEGFC ameliorates salt-sensitive hypertension and hypertensive nephropathy by inhibiting NLRP3 inflammasome via activating VEGFR3-AMPK dependent autophagy pathway.

Salt-sensitivity hypertension (SSHTN) is an independent predictor for cardiovascular mortality. VEGFC has been reported to be a protective role in SSHTN and hypertensive kidney injury. However, the underlying mechanisms remain largely unclear. The current study aimed to explore the protective effects and mechanisms of VEGFC against SSHTN and hypertensive nephropathy. Here, we reported that VEGFC attenuated high blood pressure as well as protected against renal inflammation and fibrosis in SSHTN mice. Moreover, VEGFC suppressed the activation of renal NLRP3 inflammasome in SSHTN mice. In vitro, we found VEGFC inhibited NLRP3 inflammasome activation, meanwhile, upregulated autophagy in high-salt-induced macrophages, while these effects were reversed by an autophagy inhibitor 3MA. Furthermore, in vivo, 3MA pretreatment weakened the protective effects of VEGFC on SSHTN and hypertensive nephropathy. Mechanistically, VEGF receptor 3 (VEGFR3) kinase domain activated AMPK by promoting the phosphorylation at Thr183 via binding to AMPK, thus enhancing autophagy activity in the context of high-salt-induced macrophages. These findings indicated that VEGFC inhibited NLRP3 inflammasome activation by promoting VEGFR3-AMPK-dependent autophagy pathway in high-salt-induced macrophages, which provided a mechanistic basis for the therapeutic target in SSHTN and hypertensive kidney injury.

Profiling Cell Heterogeneity and Fructose Transporter Expression in the Rat Nephron by Integrating Single-Cell and Microdissected Tubule Segment Transcriptomes.

Single-cell RNA sequencing (scRNAseq) is a crucial tool in kidney research. These technologies cluster cells based on transcriptome similarity, irrespective of the anatomical location and order within the nephron. Thus, a transcriptome cluster may obscure the heterogeneity of the cell population within a nephron segment. Elevated dietary fructose leads to salt-sensitive hypertension, in part, through fructose reabsorption in the proximal tubule (PT). However, the organization of the four known fructose transporters in apical PTs (SGLT4, SGLT5, GLUT5, and NaGLT1) remains poorly understood. We hypothesized that cells within each subsegment of the proximal tubule exhibit complex, heterogeneous fructose transporter expression patterns. To test this hypothesis, we analyzed rat kidney transcriptomes and proteomes from publicly available scRNAseq and tubule microdissection databases. We found that microdissected PT-S1 segments consist of 81% ± 12% cells with scRNAseq-derived transcriptional characteristics of S1, whereas PT-S2 express a mixture of 18% ± 9% S1, 58% ± 8% S2, and 19% ± 5% S3 transcripts, and PT-S3 consists of 75% ± 9% S3 transcripts. The expression of all four fructose transporters was detectable in all three PT segments, but key fructose transporters SGLT5 and GLUT5 progressively increased from S1 to S3, and both were significantly upregulated in S3 vs. S1/S2 (Slc5a10: 1.9 log2FC, p < 1 × 10-299; Scl2a5: 1.4 log2FC, p < 4 × 10-105). A similar distribution was found in human kidneys. These data suggest that S3 is the primary site of fructose reabsorption in both humans and rats. Finally, because of the multiple scRNAseq transcriptional phenotypes found in each segment, our findings also imply that anatomical labels applied to scRNAseq clusters may be misleading.

A nationwide cohort study comparing the effectiveness of diuretics and calcium channel blockers on top of renin-angiotensin system inhibitors on chronic kidney disease progression and mortality.

It is unknown whether initiating diuretics on top of renin-angiotensin system inhibitors (RASi) is superior to alternative antihypertensive agents such as calcium channel blockers (CCBs) in patients with chronic kidney disease (CKD). For this purpose, we emulated a target trial in the Swedish Renal Registry 2007-2022 that included nephrologist-referred patients with moderate-advanced CKD and treated with RASi, who initiated diuretics or CCB. Using propensity score-weighted cause-specific Cox regression, we compared risks of major adverse kidney events (MAKE; composite of kidney replacement therapy [KRT], experiencing over a 40% eGFR decline from baseline, or an eGFR under 15 ml/min per 1.73m2), major cardiovascular events (MACE; composite of cardiovascular death, myocardial infarction or stroke), and all-cause mortality. We identified 5875 patients (median age 71 years, 64% men, median eGFR 26 ml/min per 1.73m2), of whom 3165 started a diuretic and 2710 a CCB. After a median follow-up of 6.3 years, 2558 MAKE, 1178 MACE and 2299 deaths occurred. Compared to CCB, diuretic use was associated with a lower risk of MAKE (weighted hazard ratio 0.87 [95% confidence interval: 0.77-0.97]), consistent across single components (KRT: 0.77 [0.66-0.88], over 40% eGFR decline: 0.80 [0.71-0.91] and eGFR under 15ml/min/1.73m2: 0.84 [0.74-0.96]). The risks of MACE (1.14 [0.96-1.36]) and all-cause mortality (1.07 [0.94-1.23]) did not differ between therapies. Results were consistent when modeling the total time drug exposure, across sub-groups and a broad range of sensitivity analyses. Thus, our observational study suggests that in patients with advanced CKD, using a diuretic rather than a CCB on top of RASi may improve kidney outcomes without compromising cardioprotection.

Role of Female Sex Hormones and Immune Response in Salt-Sensitive Hypertension Development: Evidence from Experimental Models.

PURPOSEOF REVIEW: Female sex hormones have systemic effects unrelated to their reproductive function. We describe experiences of different research groups and our own, on aspects related to the importance of female sex hormones on blood pressure (BP) regulation and salt-sensitivity-mediated BP response and salt sensitivity without alterations in BP, as well as renal sodium handling and interactions with the immune system. RECENT FINDINGS: Changes in sodium intake in normotensive premenopausal women cause more BP variations than in men. After menopause, women often develop arterial hypertension (HT) with a profile of sodium sensitivity. Besides, experimental results have shown that in adult rat models resembling the postmenopausal hormonal state induced by ovariectomy, controlling BP is not enough to avoid renal and other tissue infiltration with immune cells, which does not occur when sodium intake is low or normal. Therefore, excess sodium promotes an inflammatory state with the involvement of immune cells. The evidence of activation of adaptive immunity, besides changes in T cell subpopulations, includes changes in sodium transporters and receptors. More studies are needed to evaluate the particular sodium sensitivity of women and its meaning. Changes in lifestyle and sodium intake reduction are the main therapeutic steps. However, to face the actual burden of salt-sensitive HT in postmenopausal women and its associated inflammatory/immune changes, it seems reasonable to work on immune cell activity by considering the peripheral blood mononuclear cell phenotypes of molecules and transport proteins related to sodium handle, both to screen for and treat cell activation.

The circadian clock protein PER1 is important in maintaining endothelin axis regulation in Dahl salt-sensitive rats.

Endothelin-1 (ET-1) is a peptide hormone that acts on its receptors to regulate sodium handling in the kidney's collecting duct. Dysregulation of the endothelin axis is associated with various diseases, including salt-sensitive hypertension and chronic kidney disease. Previously, our lab has shown that the circadian clock gene PER1 regulates ET-1 levels in mice. However, the regulation of ET-1 by PER1 has never been investigated in rats. Therefore, we used a novel model where knockout of Per1 was performed in Dahl salt-sensitive rat background (SS Per1 -/-) to test a hypothesis that PER1 regulates the ET-1 axis in this model. Here, we show increased renal ET-1 peptide levels and altered endothelin axis gene expression in several tissues, including the kidney, adrenal glands, and liver in SS Per1 -/- compared with control SS rats. Edn1 antisense lncRNA Edn1-AS, which has previously been suggested to be regulated by PER1, was also altered in SS Per1 -/- rats compared with control SS rats. These data further support the hypothesis that PER1 is a negative regulator of Edn1 and is important in the regulation of the endothelin axis in a tissue-specific manner.

Effects of Exercise Training on Mitochondrial Fatty Acid ß-Oxidation in the Kidneys of Dahl Salt-Sensitive Rats.

Exercise training (Ex) has anti-hypertensive and renal protective effects. In this study, we investigate the effects of Ex on mitochondrial fatty acid metabolism in the kidneys of Dahl salt-sensitive (Dahl-S) rats fed a high-salt (HS) diet. Eight-week-old, male Dahl-S rats were divided into three groups: (1) normal-salt diet, sedentary (NS-Sed), (2) HS diet, sedentary (HS-Sed), and (3) HS-Ex. The NS and HS groups were fed a diet containing 0.6% and 8% NaCl, respectively. The HS-Ex group performed treadmill running for 8 weeks (5 days/week; 60 min/day at 16-20 m/min, 0% gradient). Renal function and the expression of enzymes and regulators of ß-oxidation and electron transport chain (ETC) complexes were assessed. HS increased systolic blood pressure and proteinuria, and Ex ameliorated these defects. HS also reduced creatinine clearance, and Ex ameliorated it. HS reduced the renal expression of enzymes of ß-oxidation (carnitine palmitoyltransferase type I (CPTI) and acyl-CoA dehydrogenases (CADs)) and the related transcription factors peroxisome proliferator-activated receptor α (PPARα) and PPARγ-coactivator-1α (PGC-1α), and Ex restored this. HS also reduced the renal expression of enzymes in ETC complexes, and Ex restored this expression. Ex ameliorates HS-induced renal damage by upregulating enzymes involved in fatty acid ß-oxidation and ETC complexes via increases in PPAR-α and PGC-1α expressions in the kidneys of Dahl-S rats. These results suggest that Ex may have beneficial effects on HS-induced mitochondrial dysfunction in the kidney.

Inhibition of the epithelial sodium channel (ENaC) by connexin 30 involves stimulation of clathrin-mediated endocytosis.

Mice lacking connexin 30 (Cx30) display increased epithelial sodium channel (ENaC) activity in the distal nephron and develop salt-sensitive hypertension. This indicates a functional link between Cx30 and ENaC, which remains incompletely understood. Here, we explore the effect of Cx30 on ENaC function using the Xenopus laevis oocyte expression system. Coexpression of human Cx30 with human αßγENaC significantly reduced ENaC-mediated whole-cell currents. The size of the inhibitory effect on ENaC depended on the expression level of Cx30 and required Cx30 ion channel activity. ENaC inhibition by Cx30 was mainly due to reduced cell surface ENaC expression resulting from enhanced ENaC retrieval without discernible effects on proteolytic channel activation and single-channel properties. ENaC retrieval from the cell surface involves the interaction of the ubiquitin ligase Nedd4-2 with PPPxY-motifs in the C-termini of ENaC. Truncating the C- termini of ß- or γENaC significantly reduced the inhibitory effect of Cx30 on ENaC. In contrast, mutating the prolines belonging to the PPPxY-motif in γENaC or coexpressing a dominant-negative Xenopus Nedd4 (xNedd4-CS) did not significantly alter ENaC inhibition by Cx30. Importantly, the inhibitory effect of Cx30 on ENaC was significantly reduced by Pitstop-2, an inhibitor of clathrin-mediated endocytosis, or by mutating putative clathrin adaptor protein 2 (AP-2) recognition motifs (YxxФ) in the C termini of ß- or γ-ENaC. In conclusion, our findings suggest that Cx30 inhibits ENaC by promoting channel retrieval from the plasma membrane via clathrin-dependent endocytosis. Lack of this inhibition may contribute to increased ENaC activity and salt-sensitive hypertension in mice with Cx30 deficiency.

SGLT2 inhibition effect on salt-induced hypertension, RAAS, and Na+ transport in Dahl SS rats.

Na+-glucose cotransporter-2 (SGLT2) inhibitors are the new mainstay of treatment for diabetes mellitus and cardiovascular diseases. Despite the remarkable benefits, the molecular mechanisms mediating the effects of SGLT2 inhibitors on water and electrolyte balance are incompletely understood. The goal of this study was to determine whether SGLT2 inhibition alters blood pressure and kidney function via affecting the renin-angiotensin-aldosterone system (RAAS) and Na+ channels/transporters along the nephron in Dahl salt-sensitive rats, a model of salt-induced hypertension. Administration of dapagliflozin (Dapa) at 2 mg/kg/day via drinking water for 3 wk blunted the development of salt-induced hypertension as evidenced by lower blood pressure and a left shift of the pressure natriuresis curve. Urinary flow rate, glucose excretion, and Na+- and Cl--to-creatinine ratios increased in Dapa-treated compared with vehicle-treated rats. To define the contribution of the RAAS, we measured various hormones. Despite apparent effects on Na+- and Cl--to-creatinine ratios, Dapa treatment did not affect RAAS metabolites. Subsequently, we assessed the effects of Dapa on renal Na+ channels and transporters using RT-PCR, Western blot analysis, and patch clamp. Neither mRNA nor protein expression levels of renal transporters (SGLT2, Na+/H+ exchanger isoform 3, Na+-K+-2Cl- cotransporter 2, Na+-Cl- cotransporter, and α-, ß-, and γ-epithelial Na+ channel subunits) changed significantly between groups. Furthermore, electrophysiological experiments did not reveal any difference in Dapa treatment on the conductance and activity of epithelial Na+ channels. Our data suggest that SGLT2 inhibition in a nondiabetic model of salt-sensitive hypertension blunts the development of salt-induced hypertension by causing glucosuria and natriuresis without changes in the RAAS or the expression or activity of the main Na+ channels and transporters.NEW & NOTEWORTHY The present study indicates that Na+-glucose cotransporter-2 (SGLT2) inhibition in a nondiabetic model of salt-sensitive hypertension blunts the development and magnitude of salt-induced hypertension. Chronic inhibition of SGLT2 increases glucose and Na+ excretion without secondary effects on the expression and function of other Na+ transporters and channels along the nephron and hormone levels in the renin-angiotensin-aldosterone system. These data provide novel insights into the effects of SGLT2 inhibitors and their potential use in hypertension.

Bile acids and salt-sensitive hypertension: a role of the gut-liver axis.

Salt-sensitivity of blood pressure (SSBP) affects 50% of the hypertensive and 25% of the normotensive populations. Importantly, SSBP is associated with increased risk for mortality in both populations independent of blood pressure. Despite its deleterious effects, the pathogenesis of SSBP is not fully understood. Emerging evidence suggests a novel role of bile acids in salt-sensitive hypertension and that they may play a crucial role in regulating inflammation and fluid volume homeostasis. Mechanistic evidence implicates alterations in the gut microbiome, the epithelial sodium channel (ENaC), the farnesoid X receptor, and the G protein-coupled bile acid receptor TGR5 in bile acid-mediated effects on cardiovascular function. The mechanistic interplay between excess dietary sodium-induced alterations in the gut microbiome and immune cell activation, bile acid signaling, and whether such interplay may contribute to the etiology of SSBP is still yet to be defined. The main goal of this review is to discuss the potential role of bile acids in the pathogenesis of cardiovascular disease with a focus on salt-sensitive hypertension.

Molecular Mechanisms of Na-Cl Cotransporter in Relation to Hypertension in Chronic Kidney Disease.

Chronic kidney disease (CKD) is a common clinical disease with an increasing incidence, affecting 10 to 15% of the world's population. Hypertension is the most common and modifiable risk factor for preventing adverse cardiovascular outcomes in patients with CKD. A survey from developed countries shows that 47% of hypertensive patients over the age of 20 have uncontrolled blood pressure (BP), and the control rate is even lower in developing countries. CKD is both a common cause of uncontrolled hypertension and a risk factor for altered sequelae. In particular, studies have demonstrated that abnormal blood-pressure patterns in CKD patients, such as non-dipping-blood-pressure patterns, are associated with a significantly increased risk of cardiovascular (CV) disease. The distal convoluted tubule (DCT) is a region of the kidney, and although only 5-10% of the sodium (Na+) filtered by the glomerulus is reabsorbed by DCT, most studies agree that Na-Cl cotransporter (NCC) in human, rabbit, mouse, and rat kidneys is the most important route of sodium reabsorption across the DCT for maintaining the homeostasis of sodium. The regulation of NCC involves a large and complex network structure, including certain physiological factors, kinases, scaffold proteins, transporter phosphorylation, and other aspects. This regulation network includes various levels. Naturally, cross-talk between the components of this system must occur in order to relay the important signals to the transporter to play its role. Knowledge of the mechanisms regulating NCC activation is critical for understanding and treating hypertension and CKD. Previous studies from our laboratory have investigated the mechanisms through which NCC is activated in several different models. In the following sections, we review the literature on the mechanisms of NCC in relation to hypertension in CKD.

Association of Antihypertensive Effects of Esaxerenone with the Internal Sodium Balance in Dahl Salt-Sensitive Hypertensive Rats.

BACKGROUND: The nonsteroidal mineralocorticoid receptor blocker esaxerenone is effective in reducing blood pressure (BP). OBJECTIVE: In this study, we investigated esaxerenone-driven sodium homeostasis and its association with changes in BP in Dahl salt-sensitive (DSS) hypertensive rats. METHODS: In the different experimental setups, we evaluated BP by a radiotelemetry system, and sodium homeostasis was determined by an approach of sodium intake (food intake) and excretion (urinary excretion) in DSS rats with a low-salt diet (0.3% NaCl), high-salt diet (HSD, 8% NaCl), HSD plus 0.001% esaxerenone (w/w), and HSD plus 0.05% furosemide. RESULTS: HSD-fed DSS rats showed a dramatic increase in BP with a non-dipper pattern, while esaxerenone treatment, but not furosemide, significantly reduced BP with a dipper pattern. The cumulative sodium excretion in the active period was significantly elevated in esaxerenone- and furosemide-treated rats compared with their HSD-fed counterparts. Sodium content in the skin, skinned carcass, and total body tended to be lower in esaxerenone-treated rats than in their HSD-fed counterparts, while these values were unchanged in furosemide-treated rats. Consistently, sodium balance tended to be reduced in esaxerenone-treated rats during the active period. Histological evaluation showed that esaxerenone, but not furosemide, treatment attenuated glomerulosclerosis, tubulointerstitial fibrosis, and urinary protein excretion induced by high salt loading. CONCLUSIONS: Collectively, these findings suggest that an esaxerenone treatment-induced reduction in BP and renoprotection are associated with body sodium homeostasis in salt-loaded DSS rats.

Upregulation of Mineralocorticoid Receptor Contributes to Development of Salt-Sensitive Hypertension after Ischemia-Reperfusion Injury in Rats.

The ischemia-reperfusion injury (IRI) of rat kidneys is used as a model of acute kidney injury. Salt-sensitive hypertension occurs in rats after IRI, and the distal nephrons play important roles in the development of this condition. We investigated the role of the mineralocorticoid receptor (MR) in the progression of IRI-induced salt-sensitive hypertension in rats. Fourteen days after right-side nephrectomy, IRI was induced by clamping the left renal artery, with sham surgery performed as a control. IRI rats were provided with normal water or water with 1.0% NaCl (IRI/NaCl), or they were implanted with an osmotic mini-pump to infuse vehicle or aldosterone (IRI/Aldo). Esaxerenone, a non-steroidal MR blocker (MRB), was administered to IRI/NaCl and IRI/Aldo rats for 6 weeks. MR expression increased by day 7 post-IRI. Blood pressure and urinary protein excretion increased in IRI/NaCl and IRI/Aldo rats over the 6-week period, but these effects were negated by MRB administration. The MRB attenuated the expression of the gamma-epithelial sodium channel (ENaC) and renal damage. The ENaC inhibitor, amiloride, ameliorated hypertension and renal damage in IRI/NaCl and IRI/Aldo rats. Our findings thus showed that MR upregulation may play a pivotal role in ENaC-mediated sodium uptake in rats after IRI, resulting in the development of salt-sensitive hypertension in response to salt overload or the activation of the renin-angiotensin-aldosterone system.

Renal Corin Is Essential for Normal Blood Pressure and Sodium Homeostasis.

Atrial natriuretic peptide (ANP)-mediated natriuresis is known as a cardiac endocrine function in sodium and body fluid homeostasis. Corin is a protease essential for ANP activation. Here, we studied the role of renal corin in regulating salt excretion and blood pressure. We created corin conditional knockout (cKO), in which the Corin gene was selectively disrupted in the kidney (kcKO) or heart (hcKO). We examined the blood pressure, urinary Na+ and Cl- excretion, and cardiac hypertrophy in wild-type, corin global KO, kcKO, and hcKO mice fed normal- and high-salt diets. We found that on a normal-salt diet (0.3% NaCl), corin kcKO and hcKO mice had increased blood pressure, indicating that both renal and cardiac corin is necessary for normal blood pressure in mice. On a high-salt diet (4% NaCl), reduced urinary Na+ and Cl- excretion, increased body weight, salt-exacerbated hypertension, and cardiac hypertrophy were observed in corin kcKO mice. In contrast, impaired urinary Na+ and Cl- excretion and salt-exacerbated hypertension were not observed in corin hcKO mice. These results indicated that renal corin function is important in enhancing natriuresis upon high salt intakes and that this function cannot be compensated by the cardiac corin function in mice.

Salt, Not Always a Cardiovascular Enemy? A Mini-Review and Modern Perspective.

Dietary salt intake is a long-debated issue. Increased sodium intake is associated with high blood pressure, leading to salt-sensitive hypertension. Excessive salt intake leads to arterial stiffness in susceptible individuals via impaired nitric oxide action and increased endothelin-1 expression, overactivity of the renal sympathetic nervous system and also via aldosterone-independent activation of the mineralocorticoid receptor. Salt restriction in such individuals reduces blood pressure (BP) values. The optimal level of salt restriction that leads to improved cardiovascular outcomes is still under debate. Current BP and dietary guidelines recommend low sodium intake for the general population. However, a specific category of patients does not develop arterial hypertension in response to sodium loading. In addition, recent research demonstrates the deleterious effects of aggressive sodium restriction, even in heart failure patients. This mini review discusses current literature data regarding the advantages and disadvantages of salt restriction and how it impacts the overall health status.

Activation of the kidney sodium chloride cotransporter by the ß2-adrenergic receptor agonist salbutamol increases blood pressure.

The thiazide-sensitive sodium-chloride-cotransporter (NCC) in the kidney distal convoluted tubule (DCT) plays an essential role in sodium and potassium homeostasis. Here, we demonstrate that NCC activity is increased by the ß2-adrenoceptor agonist salbutamol, a drug prevalently used to treat asthma. Relative to ß1-adrenergic receptors, the ß2-adrenergic receptors were greatly enriched in mouse DCT cells. In mice, administration of salbutamol increased NCC phosphorylation (indicating increased activity) within 30 minutes but also caused hypokalemia, which also increases NCC phosphorylation. In ex vivo kidney slices and isolated tubules, salbutamol increased NCC phosphorylation in the pharmacologically relevant range of 0.01-10 µM, an effect observed after 15 minutes and maintained at 60 minutes. Inhibition of the inwardly rectifying potassium channel (Kir) 4.1 or the downstream with-no-lysine kinases (WNKs) and STE20/SPS1-related proline alanine-rich kinase (SPAK) pathway greatly attenuated, but did not prevent, salbutamol-induced NCC phosphorylation. Salbutamol increased cAMP in tubules, kidney slices and mpkDCT cells (model of DCT). Phosphoproteomics indicated that protein phosphatase 1 (PP1) was a key upstream regulator of salbutamol effects. A role for PP1 and the PP1 inhibitor 1 (I1) was confirmed in tubules using inhibitors of PP1 or kidney slices from I1 knockout mice. On normal and high salt diets, salbutamol infusion increased systolic blood pressure, but this increase was normalized by thiazide suggesting a role for NCC. Thus, ß2-adrenergic receptor signaling modulates NCC activity via I1/PP1 and WNK-dependent pathways, and chronic salbutamol administration may be a risk factor for hypertension.