Aldosterone, SGK1, and ion channels in the kidney

SGK1 promotes the lipid accumulation via regulating the transcriptional activity of FOXO1 in bovine

OBJECTIVES

Serum/glucocorticoid-inducible kinase 1 (SGK1) gene encodes a serine/threonine protein kinase that plays an essential role in cellular stress response and regulation of multiple metabolic processes. However, its role in bovine adipogenesis remains unknown. In this study, we aimed to clarify the role of SGK1 in bovine lipid accumulation and improvement of meat quality.

METHODS

Preadipocytes were induced to differentiation to detect the temporal expression pattern of SGK1. Heart, liver, lung, spleen, kidney, muscle and fat tissues were collected to detect its tissue expression profile. Recombinant adenovirus and the lentivirus were packaged for overexpression and knockdown. Oil Red O staining, quantitative real-time PCR, Western blot analysis, Yeast two-hybrid assay, luciferase assay and RNA-seq were performed to study the regulatory mechanism of SGK1.

RESULTS

SGK1 showed significantly higher expression in adipose and significantly induced expression in differentiated adipocytes. Furthermore, overexpression of SGK1 greatly promoted adipogenesis and inhibited proliferation, which could be shown by the remarkable increasement of lipid droplet, and the expression levels of adipogenic marker genes and cell cycle-related genes. Inversely, its knockdown inhibited adipogenesis and facilitated proliferation. Mechanistically, SGK1 regulates the phosphorylation and expression of two critical proteins of FoxO family, FOXO1/FOXO3. Importantly, SGK1 attenuates the transcriptional repression role of FOXO1 for PPARγ via phosphorylating the site S256, then promoting the bovine fat deposition.

CONCLUSIONS

SGK1 is a required epigenetic regulatory factor for bovine preadipocyte proliferation and differentiation, which contributes to a better understanding of fat deposition and meat quality improvement in cattle.

Renal effects and safety between Asian and non-Asian chronic kidney disease and type 2 diabetes treated with nonsteroidal mineralocorticoid antagonists

BACKGROUND

Asians bear a heavier burden of chronic kidney disease (CKD), a common comorbidity of type 2 diabetes mellitus (T2DM), than non-Asians. Nonsteroidal mineralocorticoid receptor antagonists (MRAs) have garnered attention for their potential advantages in renal outcomes. Nevertheless, the impact on diverse ethnic groups remains unknown.

METHODS

The PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang database, and clinical trial registries were searched through August 2023 with the following keywords: nonsteroidal MRAs (finerenone, apararenone, esaxerenone, AZD9977, KBP-5074), CKD, T2DM, and randomized controlled trial (RCT). A random effects model was used to calculate overall effect sizes.

RESULTS

Seven RCTs with 14 997 participants were enrolled. Nonsteroidal MRAs reduced urinary albumin to creatinine ratio (UACR) significantly more in Asians than non-Asians: (weighted mean difference [WMD], -0.59, 95% CI, -0.73 to -0.45, p < .01) vs (WMD, -0.29, 95% CI, -0.32 to -0.27, p < .01), respectively. The average decline of estimated glomerular filtration rate (eGFR) was similar in Asians and non-Asians (p > .05). Regarding systolic blood pressure (SBP), nonsteroidal MRAs had a better antihypertension performance in Asians (WMD, -5.12, 95% CI, -5.84 to -4.41, p < .01) compared to non-Asians (WMD, -3.64, 95% CI, -4.38 to -2.89, p < .01). A higher incidence of hyperkalemia and eGFR decrease ≥30% was found in Asians than non-Asians (p < .01).

CONCLUSIONS

Nonsteroidal MRAs exhibited significant renal benefits by decreasing UACR and lowering SBP in Asian than that of non-Asian patients with CKD and T2DM, without increase of adverse events except hyperkalemia and eGFR decrease ≥30%.

Characterization of transcriptome changes in saline stress adaptation on Leuciscus merzbacheri using PacBio Iso-Seq and RNA-Seq

Leuciscus merzbacheri is a native fish species found exclusively in the Junggar Basin in Xinjiang. It exhibits remarkable adaptability, thriving in varying water conditions such as the saline waters, the semi-saline water, and the freshwater. Despite its significant economic and ecological value, the underlying mechanisms of its remarkable salinity tolerance remain elusive. Our study marks the first time the full-length transcriptome of L. merzbacheri has been reported, utilizing RNA-Seq and PacBio Iso-Seq technologies. We found that the average length of the full-length transcriptome is 1,780 bp, with an N50 length of 2,358 bp. We collected RNA-Seq data from gill, liver, and kidney tissues of L. merzbacheri from both saline water and freshwater environments and conducted comparative analyses across these tissues. Further analysis revealed significant enrichment in several key functional gene categories and signalling pathways related to stress response and environmental adaptation. The findings provide a valuable genetic resource for further investigation into saline-responsive candidate genes, which will deepen our understanding of teleost adaptation to extreme environmental stress. This knowledge is crucial for the future breeding and conservation of native fish species.

Dexamethasone upregulates macrophage PIEZO1 via SGK1, suppressing inflammation and increasing ROS and apoptosis

The side effects of high-dose dexamethasone in anti-infection include increased ROS production and immune cell apoptosis. Dexamethasone effectively activates serum/glucocorticoid-regulated kinase 1 (SGK1), which upregulates various ion channels by activating store-operated calcium entry (SOCE), leading to Ca2+ oscillations. PIEZO1 plays a crucial role in macrophages' immune activity and function, but whether dexamethasone can regulate PIEZO1 by enhancing SOCE via SGK1 activation remains unclear. The effects of dexamethasone were assessed in a mouse model of sepsis, and primary BMDMs and the RAW264.7 were treated with overexpression plasmids, siRNAs, or specific activators or inhibitors to examine the relationships between SGK1, SOCE, and PIEZO1. The functional and phenotypic changes of mouse and macrophage models were detected. The results indicate that high-dose dexamethasone upregulated SGK1 by activating the macrophage glucocorticoid receptor, which enhanced SOCE and subsequently activated PIEZO1. Activation of PIEZO1 resulted in Ca2+ influx and cytoskeletal remodelling. The increase in intracellular Ca2+ mediated by PIEZO1 further increased the activation of SGK1 and ORAI1/STIM1, leading to intracellular Ca2+ peaks. In the context of inflammation, activation of PIEZO1 suppressed the activation of TLR4/NFκB p65 in macrophages. In RAW264.7 cells, PIEZO1 continuous activation inhibited the change in mitochondrial membrane potential, accelerated ROS accumulation, and induced autophagic damage and cell apoptosis in the late stage. CaMK2α was identified as a downstream mediator of TLR4 and PIEZO1, facilitating high-dose dexamethasone-induced macrophage immunosuppression and apoptosis. PIEZO1 is a new glucocorticoid target to regulate macrophage function and activity. This study provides a theoretical basis for the rational use of dexamethasone.

Aldosterone and aldosterone synthase inhibitors in cardiorenal disease

Modulation of the renin-angiotensin-aldosterone system is a foundation of therapy for cardiovascular and kidney diseases. Excess aldosterone plays an important role in cardiovascular disease, contributing to inflammation, fibrosis, and dysfunction in the heart, kidneys, and vasculature through both genomic and mineralocorticoid receptor (MR)-mediated as well as nongenomic mechanisms. MR antagonists have been a key therapy for attenuating the pathologic effects of aldosterone but are associated with some side effects and may not always adequately attenuate the nongenomic effects of aldosterone. Aldosterone is primarily synthesized by the CYP11B2 aldosterone synthase enzyme, which is very similar in structure to other enzymes involved in steroid biosynthesis including CYP11B1, a key enzyme involved in glucocorticoid production. Lack of specificity for CYP11B2, off-target effects on the hypothalamic-pituitary-adrenal axis, and counterproductive increased levels of bioactive steroid intermediates such as 11-deoxycorticosterone have posed challenges in the development of early aldosterone synthase inhibitors such as osilodrostat. In early-phase clinical trials, newer aldosterone synthase inhibitors demonstrated promise in lowering blood pressure in patients with treatment-resistant and uncontrolled hypertension. It is therefore plausible that these agents offer protection in other disease states including heart failure or chronic kidney disease. Further clinical evaluation will be needed to clarify the role of aldosterone synthase inhibitors, a promising class of agents that represent a potentially major therapeutic advance.

Serum Glucocorticoid-Regulated Kinase-1 in Ischemia-Reperfusion Injury: Blessing or Curse

The family of serum-glucocorticoid-regulated kinase (SGK) consists of three paralogs, SGK-1, SGK-2, and SGK-3, with SGK-1 being the better studied. Indeed, recognition of the role of SGK-1 in regulation of cell survival and proliferation has led to introduction of a number of small-molecule inhibitors for some types of cancer. In addition, SGK-1 regulates major physiologic effects, such as renal solute transport, and contributes to the pathogenesis of non-neoplastic conditions involving major organs including the heart and the kidney. These observations raise the prospect for therapeutic modulation of SGK-1 to reduce the burden of such diseases as myocardial infarction and acute kidney injury. Following a brief description of the structure and function of SGK family of proteins, the present review is primarily focused on our current understanding of the role of SGK-1 in pathologies related to ischemia-reperfusion injury involving several organs (e.g., heart, kidney). The essential role of the mitochondrial permeability transition pore in cell death coupled with the pro-survival function of SGK-1 raise the prospect that its therapeutic modulation could beneficially impact conditions associated with ischemia-reperfusion injury. SIGNIFICANCE STATEMENT: Since the discovery of serum glucocorticoid-regulated kinase (SGK)-1, extensive research has unraveled its role in cancer biology and, thus, its therapeutic targeting. Increasingly, it is also becoming clear that SGK-1 is a major determinant of the outcome of ischemia-reperfusion injury to various organs. Thus, evaluation of existing information should help identify gaps in our current knowledge and also determine whether and how its therapeutic modulation could impact the outcome of ischemia-reperfusion injury.

Construction of a prediction model for prognosis of bladder cancer based on the expression of ion channel-related genes

OBJECTIVES

To construct a prediction model for the prognosis of bladder cancer patients based on the expression of ion channel-related genes (ICRGs).

METHODS

ICRGs were obtained from the existing researches. The clinical information and the expression of ICRGs mRNA in breast cancer patients were obtained from the Cancer Genome Atlas database. Cox regression analysis, minimum absolute shrinkage and selection operator regression analysis were used to screen breast cancer prognosis related genes, which were verified by immunohistochemistry and qRT-PCR. The risk scoring equation for predicting the prognosis of patients with bladder cancer was constructed, and the patients were divided into high-risk group and low-risk group according to the median risk score. Immune cell infiltration was compared between the two groups. Kaplan-Meier survival curve and receiver operating characteristic (ROC) curve were used to evaluate the accuracy and clinical application value of the risk scoring equation. The factors related to the prognosis of bladder cancer patients were analyzed by univariate and multivariate Cox regression, and a nomogram for predicting the prognosis of bladder cancer patients was constructed.

RESULTS

By comparing the expression levels of ICRGs in bladder cancer tissues and normal bladder tissues, 73 differentially expressed ICRGs were dentified, of which 11 were related to the prognosis of bladder cancer patients. Kaplan-Meier survival curve suggested that the risk score based on these 11 genes was negatively correlated with the prognosis of patients. The area under the ROC curve of the risk score for predicting the prognosis of patients at 1, 3 and 5 year was 0.634, 0.665 and 0.712, respectively. Stratified analysis showed that the ICRGs-based risk score performed well in predicting the prognosis of patients with American Joint Committee on Cancer (AJCC) stage Ⅲ-Ⅳ bladder cancer (P<0.05), while it had a poor value in predicting the prognosis of patients with AJCC stage Ⅰ-Ⅱ (P>0.05). There were significant differences in the infiltration of plasma cells, activated natural killer cells, resting mast cells and M2 macrophages between the high-risk group and the low-risk group. Cox regression analysis showed that risk score, smoking, age and AJCC stage were independently associated with the prognosis of patients with bladder cancer (P<0.05). The nomogram constructed by combining risk score and clinical parameters has high accuracy in predicting the 1, 3 and 5 year overall survival rate of bladder cancer patients.

CONCLUSIONS

The study shows the potential value of ICRGs in the prognostic risk assessment of bladder cancer patients. The constructed prognostic nomogram based on ICRGs risk score has high accuracy in predicting the prognosis of bladder cancer patients.

Role of epithelial sodium channel-related inflammation in human diseases

The epithelial sodium channel (ENaC) is a heterotrimer and is widely distributed throughout the kidneys, blood vessels, lungs, colons, and many other organs. The basic role of the ENaC is to mediate the entry of Na+ into cells; the ENaC also has an important regulatory function in blood pressure, airway surface liquid (ASL), and endothelial cell function. Aldosterone, serum/glucocorticoid kinase 1 (SGK1), shear stress, and posttranslational modifications can regulate the activity of the ENaC; some ion channels also interact with the ENaC. In recent years, it has been found that the ENaC can lead to immune cell activation, endothelial cell dysfunction, aggravated inflammation involved in high salt-induced hypertension, cystic fibrosis, pseudohypoaldosteronism (PHA), and tumors; some inflammatory cytokines have been reported to have a regulatory role on the ENaC. The ENaC hyperfunction mediates the increase of intracellular Na+, and the elevated exchange of Na+ with Ca2+ leads to an intracellular calcium overload, which is an important mechanism for ENaC-related inflammation. Some of the research on the ENaC is controversial or unclear; we therefore reviewed the progress of studies on the role of ENaC-related inflammation in human diseases and their mechanisms.

Unlocking SGK1 inhibitor potential of bis-[1-N,7-N, pyrazolo tetraethoxyphthalimido{-4-(3,5-Dimethyl-4-(spiro-3-methylpyazolo)-1,7-dihydro-1H-dipyrazolo[3,4-b;4',3'-e]pyridin-8-yl)}]p-disubstituted phenyl compounds: a computational study

SGK1 (Serum and Glucocorticoid Regulated Kinase 1), a serine/threonine kinase that is activated by various stimuli, including serum and glucocorticoids. It controls inflammation, apoptosis, hormone release, neuro-excitability and cell proliferation, all of which play an important role in cancer progression and metastasis. SGK1 was recently proposed as a potential drug target for cancer, diabetes, and neurodegenerative diseases. In this study, molecular docking, physiochemical, toxicological properties and molecular dynamic simulation of the Bis-[1-N,7-N, Pyrazolo tetraethoxyphthalimido{-4-(3,5-Dimethyl-4-(spiro-3-methylpyazolo)-1,7-dihydro-1H-dipyrazolo[3,4-b;4',3'-e]pyridin-8-yl)}]p-disubstituted phenyl compoundsand reference EMD638683 against new SGK1 target protein. Compared to the reference inhibitor EMD638683, we choose the best compounds (series 2-6) based on the binding energy (in the range from -11.0 to -10.6 kcal/mol). With the exception of compounds 2 and 6, none of the compounds posed a risk for AMES toxicity or carcinogenicity due to their toxicological properties. 100 ns MD simulation accompanied by MM/PBSA energy calculations and PCA. According to MD simulation results, the binding of compounds 3, 4 and 5 stabilizes the SGK1 structure and causes febrile conformational changes compared to EMD638683. As a result of this research, the final selected compounds 3, 4 and 5 can be used as scaffolds to develop promising SGK1 inhibitors for the treatment of related diseases such as cancer.Communicated by Ramaswamy H. Sarma.

Serum and glucocorticoid-regulated kinase 1: Structure, biological functions, and its inhibitors

Serum and glucocorticoid-regulated kinase 1 (SGK1) is a serine/threonine kinase belonging to the protein kinase A, G, and C (AGC) family. Upon initiation of the phosphoinositide 3-kinase (PI3K) signaling pathway, mammalian target of rapamycin complex 2 (mTORC2) and phosphoinositide-dependent protein kinase 1 (PDK1) phosphorylate the hydrophobic motif and kinase domain of SGK1, respectively, inducing SGK1 activation. SGK1 modulates essential cellular processes such as proliferation, survival, and apoptosis. Hence, dysregulated SGK1 expression can result in multiple diseases, including hypertension, cancer, autoimmunity, and neurodegenerative disorders. This review provides a current understanding of SGK1, particularly in sodium transport, cancer progression, and autoimmunity. In addition, we summarize the developmental status of SGK1 inhibitors, their structures, and respective potencies evaluated in pre-clinical experimental settings. Collectively, this review highlights the significance of SGK1 and proposes SGK1 inhibitors as potential drugs for treatment of clinically relevant diseases.

Aldosterone-stimulated endothelial epithelial sodium channel (EnNaC) plays a role in cold exposure–induced hypertension in rats

Background: Previous studies have demonstrated that activated endothelial epithelial sodium channel (EnNaC) impairs vasodilatation, which contributes to salt-sensitive hypertension. Here, we investigate whether mesenteric artery (MA) EnNaC is involved in cold exposure–induced hypertension (CIH) and identify the underlying mechanisms in SD rats.

Methods: One group of rats was housed at room temperature and served as control. Three groups of rats were kept in a 4°C cold incubator for 10 h/day; among which two groups were administrated with either benzamil (EnNaC blocker) or eplerenone (mineralocorticoid receptor antagonist, MR). Blood pressure (BP), vasodilatation, and endothelial function were measured with tail-cuff plethysmography, isometric myograph, and Total Nitric Oxide (NO) Assay kit, respectively. A cell-attached patch-clamp technique, in split-open MA, was used to determine the role of EnNaC in CIH rats. Furthermore, the plasma aldosterone levels were detected using an ELISA kit; and Western blot analysis was used to examine the relative expression levels of Sgk1 and Nedd4-2 proteins in the MA of SD rats.

Results: We demonstrated that cold exposure increased BP, impaired vasodilatation, and caused endothelial dysfunction in rats. The activity of EnNaC significantly increased, concomitant with an increased level of plasma aldosterone and activation of Sgk1/Nedd4-2 signaling. Importantly, CIH was inhibited by either eplerenone or benzamil. It appeared that cold-induced decrease in NO production and impairment of endothelium-dependent relaxation (EDR) were significantly ameliorated by either eplerenone or benzamil in MA of CIH rats. Moreover, treatment of MAs with aldosterone resulted in an activation of EnNaC, a reduction of NO, and an impairment of EDR, which were significantly inhibited by either eplerenone or GSK650394 (Sgk1 inhibitor) or benzamil.

Conclusion: Activation of EnNaC contributes to CIH; we suggest that pharmacological inhibition of the MR/Sgk1/Nedd4-2/EnNaC axis may be a potential therapeutic strategy for CIH.

The Post-Translational Modification Networking in WNK-Centric Hypertension Regulation and Electrolyte Homeostasis

The with-no-lysine (WNK) kinase family, comprising four serine-threonine protein kinases (WNK1-4), were first linked to hypertension due to their mutations in association with pseudohypoaldosteronism type II (PHAII). WNK kinases regulate crucial blood pressure regulators, SPAK/OSR1, to mediate the post-translational modifications (PTMs) of their downstream ion channel substrates, such as sodium chloride co-transporter (NCC), epithelial sodium chloride (ENaC), renal outer medullary potassium channel (ROMK), and Na/K/2Cl co-transporters (NKCCs). In this review, we summarize the molecular pathways dysregulating the WNKs and their downstream target renal ion transporters. We summarize each of the genetic variants of WNK kinases and the small molecule inhibitors that have been discovered to regulate blood pressure via WNK-triggered PTM cascades.

Glucocorticoids Promote Na+ Excretion in the Renal Epithelia of Heart Failure Rats by Suppressing Transporter Proteins Involved in Acute Sodium Loading

ABSTRACT

Glucocorticoid receptors are essential for normal development and stress responses. Their role in H 2 O and Na + metabolism, especially in chronic heart failure (CHF), is not well defined. In a previous study, we found that glucocorticoids potentiate urination in CHF and promote H 2 O excretion by inhibiting the vasopressin receptor 2 pathway. The present study examines the effect of glucocorticoids on renal Na + excretion and the underlying mechanisms in CHF rats with acute sodium loading. CHF was induced by left coronary artery ligation for 8 weeks. Rats were randomly assigned to 5 groups: control, CHF, dexamethasone (DEX)-administered CHF, DEX-administered CHF treated with RU486 (mifepristone, a glucocorticoid receptor antagonist), and RU486-treated CHF. An acute sodium loading test was performed 6 hours after DEX administration. Blood and urine samples were collected, and hemodynamics were measured. The expression and localization of Na + transporter proteins were determined by immunoblotting and immunohistochemistry. DEX increased the urine volume and urinary sodium and improved cardiac function and the estimated glomerular filtration rate in CHF rats. The upregulation of the epithelial sodium channel β and γ subunits, Na-K-2Cl cotransporter, serum glucocorticoid-regulated kinase 1 (SGK1), and Na + /K + -ATPase in the renal epithelium of CHF rats was downregulated by DEX. These beneficial effects were abolished by RU486. The expression of natriuretic peptide receptor A was opposite that of the above proteins. Glucocorticoids might induce profound natriuresis in CHF rats during acute sodium loading, which is associated with downregulating some Na + transporter proteins in the renal epithelium and improving intrarenal hemodynamics.

Potassium homeostasis: sensors, mediators, and targets

Transmembrane potassium (K) gradients are key determinants of membrane potential that can modulate action potentials, control muscle contractility, and influence ion channel and transporter activity. Daily K intake is normally equal to the amount of K in the entire extracellular fluid (ECF) creating a critical challenge - how to maintain ECF [K] and membrane potential in a narrow range during feast and famine. Adaptations to maintain ECF [K] include sensing the K intake, sensing ECF [K] vs. desired set-point and activating mediators that regulate K distribution between ECF and ICF, and regulate renal K excretion. In this focused review, we discuss the basis of these adaptions, including (1) potential mechanisms for rapid feedforward signaling to kidney and muscle after a meal (before a rise in ECF [K]), (2) how skeletal muscles sense and respond to changes in ECF [K], (3) effects of K on aldosterone biosynthesis, and (4) how the kidney responds to changes in ECF [K] to modify K excretion. The concepts of sexual dimorphisms in renal K handling adaptation are introduced, and the molecular mechanisms that can account for the benefits of a K-rich diet to maintain cardiovascular health are discussed. Although the big picture of K homeostasis is becoming more clear, we also highlight significant pieces of the puzzle that remain to be solved, including knowledge gaps in our understanding of initiating signals, sensors and their connection to homeostatic adjustments of ECF [K].

The Ion Channel-Related Gene Signatures Correlated With Diagnosis, Prognosis, and Individualized Treatment in Patients With Clear Cell Renal Cell Carcinoma

Background: Early detection and precise prognostic evaluation of clear cell renal cell carcinoma (ccRCC) are crucial for patient life expectancy. Ion channel-related genes (ICRGs) are of great diagnostic and prognostic value as components that maintain the normal structure of the kidney. Therefore, we systematically explored the diagnostic, prognostic, and therapeutic value of ICRGs in ccRCC using the multi-database.

Methods: RNA transcriptome profiles and clinical data of ccRCC patients were extracted and integrated from public databases including The Cancer Genome Atlas, ICGC, GEO, and E-MTAB databases. Ion channel-related genes were obtained from the literature collection. The diagnostic signature was performed using the LASSO and SVM-REF analyses. Meanwhile, the prognostic signature was conducted using the LASSO analyses. Molecular subtyping was performed using the ConsensusClusterPlus and the corresponding therapeutic targets were evaluated using the pRRophetic package. In addition, a prognostic nomogram was constructed based on the results of cox regression analyses.

Results: We successfully constructed diagnostic signatures for five ICRGs and prognostic signatures for 10 ICRGs with AUC values greater than 0.7, showing good predictive performance. Based on the median risk score, we found that high-risk patients had a significantly worse prognosis. We also divided ccRCC patients into two clusters according to prognostic ICRGs, and there was a significant survival outcome between the two clusters and different sensitivity to diverse clinical therapeutic strategies. Meanwhile, we constructed a nomogram based on clinical molecules and signatures, and its predictive efficacy was better than the signature or the present tumor-node-metastasis staging system.

Conclusion: In this study, we established useful signatures for early detection, prognosis evaluation, and individualized treatment for ccRCC. Moreover, KCNJ16 deserves to be explored comprehensively in the future.

Kidney-specific KO of the circadian clock protein PER1 alters renal Na+ handling, aldosterone levels, and kidney/adrenal gene expression

PERIOD 1 (PER1) is a circadian clock transcription factor that is regulated by aldosterone, a hormone that increases blood volume and Na+ retention to increase blood pressure. Male global Per1 knockout (KO) mice develop reduced night/day differences in Na+ excretion in response to a high-salt diet plus desoxycorticosterone pivalate treatment (HS + DOCP), a model of salt-sensitive hypertension. In addition, global Per1 KO mice exhibit higher aldosterone levels on a normal-salt diet. To determine the role of Per1 in the kidney, male kidney-specific Per1 KO (KS-Per1 KO) mice were generated using Ksp-cadherin Cre recombinase to remove exons 2-8 of Per1 in the distal nephron and collecting duct. Male KS-Per1 KO mice have increased Na+ retention but have normal diurnal differences in Na+ excretion in response to HS + DOCP. The increased Na+ retention is associated with altered expression of glucocorticoid and mineralocorticoid receptors, increased serum aldosterone, and increased medullary endothelin-1 compared with control mice. Adrenal gland gene expression analysis revealed that circadian clock and aldosterone synthesis genes have altered expression in KS-Per1 KO mice compared with control mice. These results emphasize the importance of the circadian clock not only in maintaining rhythms of physiological functions but also for adaptability in response to environmental cues, such as HS + DOCP, to maintain overall homeostasis. Given the prevalence of salt-sensitive hypertension in the general population, these findings have important implications for our understanding of how circadian clock proteins regulate homeostasis.NEW & NOTEWORTHY For the first time, we show that knockout of the circadian clock transcription factor PERIOD 1 using kidney-specific cadherin Cre results in increased renal Na+ reabsorption, increased aldosterone levels, and changes in gene expression in both the kidney and adrenal gland. Diurnal changes in renal Na+ excretion were not observed, demonstrating that the clock protein PER1 in the kidney is important for maintaining homeostasis and that this effect may be independent of time of day.

Transient early-childhood hyperkalaemia without salt wasting, pathophysiological approach of three cases

Two types of early childhood hyperkalemia had been recognized, according to the presence or absence of urinary salt wasting. This condition was attributed to a maturation disorder of aldosterone receptors and is characterized by sustained hyperkalemia, hyperchloremic metabolic acidosis (MA) due to reduced ammonium urinary excretion and bicarbonate loss, and normal creatinine with growth delay. We present 3 patients of the type without salt wasting, which we will call transient early-childhood hyperkalemia (TECHH) without salt wasting, and discuss its physiopathology according to new insights into sodium and potassium handling by the aldosterone in distal nephron. In 3 children from 30 to 120-day-old admitted with bronchiolitis and growth delay hyperkalemia was found in routine laboratory. Further studies revealed a normal creatinine with inappropriately normal or low fractional excretion (FE) of potassium, accompanied by inadequately normal serum aldosterone and plasma renin activity for their higher plasma potassium levels, but without urine salt wasting. They also presented hyperchloremic MA with FE of bicarbonate 0.58%-2.2%, positive urinary anion gap during MA and normal ability to acidify the urine. Based on these findings a diagnosis of TECHH without salt wasting was made and they were treated sodium bicarbonate and hydrochlorothiazide with favorable response. The condition was transient in all cases leading to treatment discontinuation. Given that TECCH without salt wasting is a tubular disorder of transient nature with mild symptoms; it must be keep in mind in the differential diagnosis of hyperkalemia in young children.

Low-salt diet increases mRNA expression of aldosterone-regulated transporters in the intermediate portion of the endolymphatic sac

The endolymphatic sac is a small sac-shaped organ at the end of the membranous labyrinth of the inner ear. The endolymphatic sac absorbs the endolymph, in which the ion balance is crucial for inner ear homeostasis. Of the three sections of the endolymphatic sac, the intermediate portion is the center of endolymph absorption, particularly sodium transport, and is thought to be regulated by aldosterone. Disorders of the endolymphatic sac may cause an excess of endolymph (endolymphatic hydrops), a histological observation in Meniere's disease. A low-salt diet is an effective treatment for Meniere's disease, and is based on the assumption that the absorption of endolymph in the endolymphatic sac abates endolymphatic hydrops through a physiological increase in aldosterone level. However, the molecular basis of endolymph absorption in each portion of the endolymphatic sac is largely unknown because of difficulties in gene expression analysis, resulting from its small size and intricate structure. The present study combined reverse transcription-quantitative polymerase chain reaction and laser capture microdissection techniques to analyze the difference of gene expression of the aldosterone-controlled epithelial Na⁺ channel, thiazide-sensitive Na⁺-Cl^- cotransporter, and Na⁺, K⁺-ATPase genes in the three individual portions of the endolymphatic sac in a rat model. A low-salt diet increased the expression of aldosterone-controlled ion transporters, particularly in the intermediate portion of the endolymphatic sac. Our findings will contribute to the understanding of the physiological function of the endolymphatic sac and the pathophysiology of Meniere's disease.

Regulation of distal tubule sodium transport: mechanisms and roles in homeostasis and pathophysiology

Regulated Na⁺ transport in the distal nephron is of fundamental importance to fluid and electrolyte homeostasis. Further upstream, Na⁺ is the principal driver of secondary active transport of numerous organic and inorganic solutes. In the distal nephron, Na⁺ continues to play a central role in controlling the body levels and concentrations of a more select group of ions, including K⁺, Ca⁺⁺, Mg⁺⁺, Cl^-, and HCO₃^-, as well as water. Also, of paramount importance are transport mechanisms aimed at controlling the total level of Na⁺ itself in the body, as well as its concentrations in intracellular and extracellular compartments. Over the last several decades, the transporters involved in moving Na⁺ in the distal nephron, and directly or indirectly coupling its movement to that of other ions have been identified, and their interrelationships brought into focus. Just as importantly, the signaling systems and their components-kinases, ubiquitin ligases, phosphatases, transcription factors, and others-have also been identified and many of their actions elucidated. This review will touch on selected aspects of ion transport regulation, and its impact on fluid and electrolyte homeostasis. A particular focus will be on emerging evidence for site-specific regulation of the epithelial sodium channel (ENaC) and its role in both Na⁺ and K⁺ homeostasis. In this context, the critical regulatory roles of aldosterone, the mineralocorticoid receptor (MR), and the kinases SGK1 and mTORC2 will be highlighted. This includes a discussion of the newly established concept that local K⁺ concentrations are involved in the reciprocal regulation of Na⁺-Cl^- cotransporter (NCC) and ENaC activity to adjust renal K⁺ secretion to dietary intake.

Postnatal glucocorticoid use impacts renal function in VLBW neonates

BACKGROUND

Preterm neonates often require glucocorticoids to manage refractory hypotension, prevent, and treat bronchopulmonary dysplasia. We have investigated the effect of cumulative dose and duration of glucocorticoids on blood pressure and renal function in VLBW infants.

METHODS

In this retrospective cohort study, medical records of infants (GA ≤ 35 weeks) born January 2015 to December 2019 were reviewed to extract demographic and clinical characteristics, dose and duration of steroids, blood pressure (BP), and creatinine at the time of discharge from the neonatal intensive care unit.

RESULTS

Two hundred and eighty-three neonates with average GA (28 ± 3 weeks) and birthweight (1060±381 g). Twenty-eight percent (33/116) of infants who received postnatal steroids developed hypertension versus 16% (27/167) of controls (OR = 2.0, p = 0.011). There was a correlation between the cumulative dosage of postnatal steroids and systolic BP (R² = 0.06, p < 0.001). With increasing steroid dose and total steroid days, there was a significant increase in creatinine clearance at the time of discharge (R² = 0.13, p < 0.001; R² = 0.13, p < 0.001, respectively).

CONCLUSIONS

Cumulative dose of postnatal steroids and duration of use is associated with increased systolic BP in premature infants. Postnatal steroids should be used prudently to prevent long-term cardiovascular and renal morbidity.

IMPACT

Preterm neonates are exposed to a high dose of glucocorticoids during their neonatal intensive care stay. The dose and duration of use of postnatal glucocorticoids was associated with significant increase in blood pressure at the time of discharge in preterm neonates. Postnatal glucocorticoid use is associated with improved creatinine clearance likely due to a state of hyperfiltration and may lead to chronic kidney disease later in life. Postnatal glucocorticoids should be used prudently in this highly vulnerable population.

Salt sensitivity of volume and blood pressure in a mouse with globally reduced ENaC γ-subunit expression

The epithelial Na+ channel (ENaC) promotes the absorption of Na+ in the aldosterone-sensitive distal nephron, colon, and respiratory epithelia. Deletion of genes encoding subunits of ENaC results in early postnatal mortality. Here, we present the initial characterization of a mouse with dramatically suppressed expression of the ENaC γ-subunit. We used this hypomorphic (γmt) allele to explore the importance of this subunit in homeostasis of electrolytes and body fluid volume. At baseline, γ-subunit expression in γmt/mt mice was markedly suppressed in the kidney and lung, whereas electrolytes resembled those of littermate controls. Aldosterone levels in γmt/mt mice exceeded those seen in littermate controls. Quantitative magnetic resonance measurement of body composition revealed similar baseline body water, lean tissue mass, and fat tissue mass in γmt/mt mice and controls. γmt/mt mice exhibited a more rapid decline in body water and lean tissue mass in response to a low-Na+ diet than the controls. Replacement of drinking water with 2% saline selectively and transiently increased body water and lean tissue mass in γmt/mt mice relative to the controls. Lower blood pressures were variably observed in γmt/mt mice on a high-salt diet compared with the controls. γmt/mt also exhibited reduced diurnal blood pressure variation, a "nondipping" phenotype, on a high-Na+ diet. Although ENaC in the renal tubules and colon works to prevent extracellular fluid volume depletion, our observations suggest that ENaC in other tissues may participate in regulating extracellular fluid volume and blood pressure.NEW & NOTEWORTHY A mouse with globally suppressed expression of the epithelial Na+ channel γ-subunit showed enhanced sensitivity to dietary salt, including a transient increase in total body fluid, reduced blood pressure, and reduced diurnal blood pressure variation when given a dietary NaCl challenge. These results point to a role for the epithelial Na+ channel in regulating body fluid and blood pressure beyond classical transepithelial Na+ transport mechanisms.

Role of mTOR Signaling for Tubular Function and Disease

The mechanistic target of rapamycin (mTOR) forms two distinct intracellular multiprotein complexes that control a multitude of intracellular processes linked to metabolism, proliferation, actin cytoskeleton, and survival. Recent studies have identified the importance of these complexes for transport regulation of ions and nutrients along the entire nephron. First reports could link altered activity of these complexes to certain disease entities, i.e. diabetic nephropathy, acute kidney injury or hyperkalemia.

Serum- and glucocorticoid-inducible kinase 1 promotes insulin resistance in adipocytes via degradation of insulin receptor substrate 1

AIMS

Accumulating evidence indicates that serum- and glucocorticoid-inducible kinase 1 (SGK1) plays a role in the development of metabolic syndrome via a poorly understood mechanism. This study aimed to investigate the direct effect of SGK1 on insulin sensitivity in adipose tissue.

MATERIALS AND METHODS

We ectopically expressed or silenced SGK1 in adipocytes via lentiviral transfection, measured glucose uptake and evaluated insulin signalling using western blotting. In vivo insulin resistance was measured at the whole-body and adipose tissue levels in db/db mice treated with an inhibitor of SGK1.

RESULTS

After 8 weeks of SGK1 inhibitor treatment, the serum insulin level and homeostasis model assessment of insulin resistance index were significantly decreased, and AKT phosphorylation in adipose tissue was enhanced in db/db mice. Overexpression of constitutively active SGK1 in adipocytes in vitro decreased AKT phosphorylation and insulin-stimulated glucose uptake. Dexamethasone and oleic acid increased SGK1 expression and decreased AKT phosphorylation and insulin receptor substrate expression in adipocytes. Administration of an inhibitor of SGK1 or Lv-shSGK1 reversed the suppression of insulin signalling induced by dexamethasone and oleic acid. SGK1 overexpression increased FoxO1 phosphorylation, and administration of Lv-shSGK1 reversed an increase in FoxO1 phosphorylation induced by dexamethasone and oleic acid.

CONCLUSIONS

Thus, SGK1 mediates the effect of glucocorticoids and high-fat feeding and induces insulin resistance in adipocytes. Our data suggest that SGK1 is a possible therapeutic target for metabolic syndrome and related complications.

Transient early-childhood hyperkalemia without salt wasting, physiopathological approach of three cases

Two types of early-childhood hyperkalemia had been recognized, according to the presence or absence of urinary salt wasting. This condition was attributed to a maturation disorder of aldosterone receptors and is characterized by sustained hyperkalemia, hyperchloremic metabolic acidosis due to reduced ammonium urinary excretion and bicarbonate loss, and normal creatinine with growth delay. We present three patients of the type without salt wasting, which we will call transient early-childhood hyperkalemia without salt wasting, and discuss its physiopathology according to new insights into sodium and potassium handling by the aldosterone in distal nephron. In three children from 30 to 120-day-old admitted with bronchiolitis and growth delay hyperkalemia was found in routine laboratory. Further studies revealed a normal creatinine with inappropriately normal or low fractional excretion of potassium, accompanied by inadequately normal serum aldosterone and plasma renin activity for their higher plasma potassium levels, but without urine salt wasting. They also presented hyperchloremic metabolic acidosis with fractional excretion of bicarbonate 0.58-2.2%, positive urinary anion gap during metabolic acidosis and normal ability to acidify the urine. Based on these findings a diagnosis of transient early-childhood hyperkalemia without salt wasting was made and they were treated sodium bicarbonate and hydrochlorothiazide with favorable response. The condition was transient in all cases leading to treatment discontinuation. Given that transient early-childhood hyperkalemia without salt wasting is a tubular disorder of transient nature with mild symptoms; it must be keep in mind in the differential diagnosis of hyperkalemia in young children.

Oxidative Stress and Hypertension

A link between oxidative stress and hypertension has been firmly established in multiple animal models of hypertension but remains elusive in humans. While initial studies focused on inactivation of nitric oxide by superoxide, our understanding of relevant reactive oxygen species (superoxide, hydrogen peroxide, and peroxynitrite) and how they modify complex signaling pathways to promote hypertension has expanded significantly. In this review, we summarize recent advances in delineating the primary and secondary sources of reactive oxygen species (nicotinamide adenine dinucleotide phosphate oxidases, uncoupled endothelial nitric oxide synthase, endoplasmic reticulum, and mitochondria), the posttranslational oxidative modifications they induce on protein targets important for redox signaling, their interplay with endogenous antioxidant systems, and the role of inflammasome activation and endoplasmic reticular stress in the development of hypertension. We highlight how oxidative stress in different organ systems contributes to hypertension, describe new animal models that have clarified the importance of specific proteins, and discuss clinical studies that shed light on how these processes and pathways are altered in human hypertension. Finally, we focus on the promise of redox proteomics and systems biology to help us fully understand the relationship between ROS and hypertension and their potential for designing and evaluating novel antihypertensive therapies.

Increased SGK1 activity potentiates mineralocorticoid/NaCl-induced kidney injury

Serum and glucocorticoid-regulated kinase 1 (SGK1) stimulates aldosterone-dependent renal Na⁺ reabsorption and modulates blood pressure. In addition, genetic ablation or pharmacological inhibition of SGK1 limits the development of kidney inflammation and fibrosis in response to excess mineralocorticoid signaling. In this work, we tested the hypothesis that a systemic increase in SGK1 activity would potentiate mineralocorticoid/salt-induced hypertension and kidney injury. To that end, we used a transgenic mouse model with increased SGK1 activity. Mineralocorticoid/salt-induced hypertension and kidney damage was induced by unilateral nephrectomy and treatment with deoxycorticosterone acetate and NaCl in the drinking water for 6 wk. Our results show that although SGK1 activation did not induce significantly higher blood pressure, it produced a mild increase in glomerular filtration rate, increased albuminuria, and exacerbated glomerular hypertrophy and fibrosis. Transcriptomic analysis showed that extracellular matrix- and immune response-related terms were enriched in the downregulated and upregulated genes, respectively, in transgenic mice. In conclusion, we propose that systemically increased SGK1 activity is a risk factor for the development of mineralocorticoid-dependent kidney injury in the context of low renal mass and independently of blood pressure.NEW & NOTEWORTHY Increased activity of the protein kinase serum and glucocorticoid-regulated kinase 1 may be a risk factor for accelerated renal damage. Serum and glucocorticoid-regulated kinase 1 expression could be a marker for the rapid progression toward chronic kidney disease and a potential therapeutic target to slow down the process.

SGK1 in Human Cancer: Emerging Roles and Mechanisms

Serum and glucocorticoid-induced protein kinase 1 (SGK1) is a member of the "AGC" subfamily of protein kinases, which shares structural and functional similarities with the AKT family of kinases and displays serine/threonine kinase activity. Aberrant expression of SGK1 has profound cellular consequences and is closely correlated with human cancer. SGK1 is considered a canonical factor affecting the expression and signal transduction of multiple genes involved in the genesis and development of many human cancers. Abnormal expression of SGK1 has been found in tissue and may hopefully become a useful indicator of cancer progression. In addition, SGK1 acts as a prognostic factor for cancer patient survival. This review systematically summarizes and discusses the role of SGK1 as a diagnostic and prognostic biomarker of diverse cancer types; focuses on its essential roles and functions in tumorigenesis, cancer cell proliferation, apoptosis, invasion, metastasis, autophagy, metabolism, and therapy resistance and in the tumor microenvironment; and finally summarizes the current understanding of the regulatory mechanisms of SGK1 at the molecular level. Taken together, this evidence highlights the crucial role of SGK1 in tumorigenesis and cancer progression, revealing why it has emerged as a potential target for cancer therapy.

Phosphodiesterase 2A and 3B variants are associated with primary aldosteronism

Familial primary aldosteronism (PA) is rare and mostly diagnosed in early-onset hypertension (HT). However, 'sporadic' bilateral adrenal hyperplasia (BAH) is the most frequent cause of PA and remains without genetic etiology in most cases. Our aim was to investigate new genetic defects associated with BAH and PA. We performed whole-exome sequencing (paired blood and adrenal tissue) in six patients with PA caused by BAH that underwent unilateral adrenalectomy. Additionally, we conducted functional studies in adrenal hyperplastic tissue and transfected cells to confirm the pathogenicity of the identified genetic variants. Rare germline variants in phosphodiesterase 2A (PDE2A) and 3B (PDE3B) genes were identified in three patients. The PDE2A heterozygous variant (p.Ile629Val) was identified in a patient with BAH and early-onset HT at 13 years of age. Two PDE3B heterozygous variants (p.Arg217Gln and p.Gly392Val) were identified in patients with BAH and HT diagnosed at 18 and 33 years of age, respectively. A strong PDE2A staining was found in all cases of BAH in zona glomerulosa and/or micronodules (that were also positive for CYP11B2). PKA activity in frozen tissue was significantly higher in BAH from patients harboring PDE2A and PDE3B variants. PDE2A and PDE3B variants significantly reduced protein expression in mutant transfected cells compared to WT. Interestingly, PDE2A and PDE3B variants increased SGK1 and SCNN1G/ENaCg at mRNA or protein levels. In conclusion, PDE2A and PDE3B variants were associated with PA caused by BAH. These novel genetic findings expand the spectrum of genetic etiologies of PA.

Role of the vascular endothelial sodium channel activation in the genesis of pathologically increased cardiovascular stiffness

Cardiovascular (CV) stiffening represents a complex series of events evolving from pathological changes in individual cells of the vasculature and heart which leads to overt tissue fibrosis. While vascular stiffening occurs naturally with ageing it is accelerated in states of insulin (INS) resistance, such as obesity and type 2 diabetes. CV stiffening is clinically manifested as increased arterial pulse wave velocity and myocardial fibrosis-induced diastolic dysfunction. A key question that remains is how are these events mechanistically linked. In this regard, heightened activation of vascular mineralocorticoid receptors (MR) and hyperinsulinaemia occur in obesity and INS resistance states. Further, a downstream mediator of MR and INS receptor activation, the endothelial cell Na+ channel (EnNaC), has recently been identified as a key molecular determinant of endothelial dysfunction and CV fibrosis and stiffening. Increased activity of the EnNaC results in a number of negative consequences including stiffening of the cortical actin cytoskeleton in endothelial cells, impaired endothelial NO release, increased oxidative stress-meditated NO destruction, increased vascular permeability, and stimulation of an inflammatory environment. Such endothelial alterations impact vascular function and stiffening through regulation of vascular tone and stimulation of tissue remodelling including fibrosis. In the case of the heart, obesity and INS resistance are associated with coronary vascular endothelial stiffening and associated reductions in bioavailable NO leading to heart failure with preserved systolic function (HFpEF). After a brief discussion on mechanisms leading to vascular stiffness per se, this review then focuses on recent findings regarding the role of INS and aldosterone to enhance EnNaC activity and associated CV stiffness in obesity/INS resistance states. Finally, we discuss how coronary artery-mediated EnNaC activation may lead to cardiac fibrosis and HFpEF, a condition that is especially pronounced in obese and diabetic females.

Stimulation of Epithelial Sodium Channels in Endothelial Cells by Bone Morphogenetic Protein-4 Contributes to Salt-Sensitive Hypertension in Rats

Previous studies have shown that high salt induces artery stiffness by causing endothelial dysfunction via increased sodium influx. We used our unique split-open artery technique combined with protein biochemistry and in vitro measurement of vascular tone to test a hypothesis that bone morphogenetic protein 4 (BMP4) mediates high salt-induced loss of vascular relaxation by stimulating the epithelial sodium channel (ENaC) in endothelial cells. The data show that high salt intake increased BMP4 both in endothelial cells and in the serum and that exogenous BMP4 stimulated ENaC in endothelial cells. The data also show that the stimulation is mediated by p38 mitogen-activated protein kinases (p38 MAPK) and serum and glucocorticoid-regulated kinase 1 (Sgk1)/neural precursor cell expressed developmentally downregulated gene 4-2 (Nedd4-2) (Sgk1/Nedd4-2). Furthermore, BMP4 decreased mesenteric artery relaxation in a benzamil-sensitive manner. These results suggest that high salt intake stimulates endothelial cells to express and release BMP4 and that the released BMP4 reduces artery relaxation by stimulating ENaC in endothelial cells. Therefore, stimulation of ENaC in endothelial cells by BMP4 may serve as another pathway to participate in the complex mechanism of salt-sensitive (SS) hypertension.

Aldosterone up-regulates voltage-gated potassium currents and NKCC1 protein membrane fractions

Na+-K+-2Cl- Cotransporter (NKCC1) is a protein that aids in the active transport of sodium, potassium, and chloride ions across cell membranes. It has been shown that long-term systemic treatment with aldosterone (ALD) can enhance NKCC1 protein expression and activity in the aging cochlea resulting in improved hearing. In the present work, we used a cell line with confirmed NKCC1 expression to demonstrate that in vitro application of ALD increased outward voltage-gated potassium currents significantly, and simultaneously upregulated whole lysate and membrane portion NKCC1 protein expression. These ALD-induced changes were blocked by applying the mineralocorticoid receptor antagonist eplerenone. However, application of the NKCC1 inhibitor bumetanide or the potassium channel antagonist Tetraethyl ammonium had no effect. In addition, NKKC1 mRNA levels remained stable, indicating that ALD modulates NKCC1 protein expression via the activation of mineralocorticoid receptors and post-transcriptional modifications. Further, in vitro electrophysiology experiments, with ALD in the presence of NKCC1, K+ channel and mineralocorticoid receptor inhibitors, revealed interactions between NKCC1 and outward K+ channels, mediated by a mineralocorticoid receptor-ALD complex. These results provide evidence of the therapeutic potential of ALD for the prevention/treatment of inner ear disorders such as age-related hearing loss.

Sodium butyrate ameliorates deoxycorticosterone acetate/salt-induced hypertension and renal damage by inhibiting the MR/SGK1 pathway

Our recent work demonstrates that infusion of sodium butyrate (NaBu) into the renal medulla blunts angiotensin II-induced hypertension and improves renal injury. The present study aimed to test whether oral administration of NaBu attenuates salt-sensitive hypertension in deoxycorticosterone acetate (DOCA)/salt-treated rats. Uninephrectomized male Sprague-Dawley (SD) rats were treated with DOCA pellets (150 mg/rat) plus 1% NaCl drinking water for 2 weeks. Animals received oral administration of NaBu (1 g/kg) or vehicle once per day. Our results showed that NaBu administration significantly attenuated DOCA/salt-increased mean arterial pressure from 156 ± 4 mmHg to 136 ± 1 mmHg. DOCA/salt treatment markedly enhanced renal damage as indicated by an increased ratio of kidney weight/body weight, elevated urinary albumin, extensive fibrosis, and inflammation, whereas kidneys from NaBu-treated rats exhibited a significant reduction in these renal damage responses. Compared to the DOCA/salt group, the DOCA/salt-NaBu group had ~30% less salt water intake and decreased Na⁺ and Cl^- excretion in urine but no alteration in 24-h urine excretion. Mechanistically, NaBu inhibited the protein levels of several sodium transporters stimulated by DOCA/salt in vivo, such as βENaC, γENaC, NCC, and NKCC-2. Further examination showed that NaBu downregulated the expression of mineralocorticoid receptor (MR) and serum and glucocorticoid-dependent protein kinase 1 (SGK1) in DOCA/salt-treated rats or aldosterone-treated human renal tubular duct epithelial cells. These results provide evidence that NaBu may attenuate DOCA/salt-induced hypertension and renal damage by inhibiting the MR/SGK1 pathway.

Interactive Actions of Aldosterone and Insulin on Epithelial Na+ Channel Trafficking

Epithelial Na⁺ channel (ENaC) participates in renal epithelial Na⁺ reabsorption, controlling blood pressure. Aldosterone and insulin elevate blood pressure by increasing the ENaC-mediated Na⁺ reabsorption. However, little information is available on the interactive action of aldosterone and insulin on the ENaC-mediated Na⁺ reabsorption. In the present study, we tried to clarify if insulin would modify the aldosterone action on the ENaC-mediated Na⁺ reabsorption from a viewpoint of intracellular ENaC trafficking. We measured the ENaC-mediated Na⁺ transport as short-circuit currents using a four-state mathematical ENaC trafficking model in renal A6 epithelial cells with or without aldosterone treatment under the insulin-stimulated and -unstimulated conditions. We found that: (A) under the insulin-stimulated condition, aldosterone treatment (1 µM for 20 h) significantly elevated the ENaC insertion rate to the apical membrane (kI) 3.3-fold and the ENaC recycling rate (kR) 2.0-fold, but diminished the ENaC degradation rate (kD) 0.7-fold without any significant effect on the ENaC endocytotic rate (kE); (B) under the insulin-unstimulated condition, aldosterone treatment decreased kE 0.5-fold and increased kR 1.4-fold, without any significant effect on kI or kD. Thus, the present study indicates that: (1) insulin masks the well-known inhibitory action of aldosterone on the ENaC endocytotic rate; (2) insulin induces a stimulatory action of aldosterone on ENaC apical insertion and an inhibitory action of aldosterone on ENaC degradation; (3) insulin enhances the aldosterone action on ENaC recycling; (4) insulin has a more effective action on diminution of ENaC endocytosis than aldosterone.

Virtual Screening Approach to Identify High-Affinity Inhibitors of Serum and Glucocorticoid-Regulated Kinase 1 among Bioactive Natural Products: Combined Molecular Docking and Simulation Studies

Serum and glucocorticoid-regulated kinase 1 (SGK1) is a serine/threonine kinase that works under acute transcriptional control by several stimuli, including serum and glucocorticoids. It plays a significant role in the cancer progression and metastasis, as it regulates inflammation, apoptosis, hormone release, neuro-excitability, and cell proliferation. SGK1 has recently been considered as a potential drug target for cancer, diabetes, and neurodegenerative diseases. In the present study, we have performed structure-based virtual high-throughput screening of natural compounds from the ZINC database to find potential inhibitors of SGK1. Initially, hits were selected based on their physicochemical, absorption, distribution, metabolism, excretion, and toxicity (ADMET), and other drug-like properties. Afterwards, PAINS filter, binding affinities estimation, and interaction analysis were performed to find safe and effective hits. We found four compounds bearing appreciable binding affinity and specificity towards the binding pocket of SGK1. The docking results were complemented by all-atom molecular dynamics simulation for 100 ns, followed by MM/PBSA, and principal component analysis to investigate the conformational changes, stability, and interaction mechanism of SGK1 in-complex with the selected compound ZINC00319000. Molecular dynamics simulation results suggested that the binding of ZINC00319000 stabilizes the SGK1 structure, and it leads to fewer conformational changes. In conclusion, the identified compound ZINC00319000 might be further exploited as a scaffold to develop promising inhibitors of SGK1 for the therapeutic management of associated diseases, including cancer.

Regulation of the Renal NaCl Cotransporter and Its Role in Potassium Homeostasis

Daily dietary potassium (K+) intake may be as large as the extracellular K+ pool. To avoid acute hyperkalemia, rapid removal of K+ from the extracellular space is essential. This is achieved by translocating K+ into cells and increasing urinary K+ excretion. Emerging data now indicate that the renal thiazide-sensitive NaCl cotransporter (NCC) is critically involved in this homeostatic kaliuretic response. This suggests that the early distal convoluted tubule (DCT) is a K+ sensor that can modify sodium (Na+) delivery to downstream segments to promote or limit K+ secretion. K+ sensing is mediated by the basolateral K+ channels Kir4.1/5.1, a capacity that the DCT likely shares with other nephron segments. Thus, next to K+-induced aldosterone secretion, K+ sensing by renal epithelial cells represents a second feedback mechanism to control K+ balance. NCC’s role in K+ homeostasis has both physiological and pathophysiological implications. During hypovolemia, NCC activation by the renin-angiotensin system stimulates Na+ reabsorption while preventing K+ secretion. Conversely, NCC inactivation by high dietary K+ intake maximizes kaliuresis and limits Na+ retention, despite high aldosterone levels. NCC activation by a low-K+ diet contributes to salt-sensitive hypertension. K+-induced natriuresis through NCC offers a novel explanation for the antihypertensive effects of a high-K+ diet. A possible role for K+ in chronic kidney disease is also emerging, as epidemiological data reveal associations between higher urinary K+ excretion and improved renal outcomes. This comprehensive review will embed these novel insights on NCC regulation into existing concepts of K+ homeostasis in health and disease.

Overview of Monogenic Forms of Hypertension Combined With Hypokalemia

Hypertension is an important risk factor in many conditions and creates a heavy burden of disease and mortality globally. Polygenic hypertension is the most common form; however, it is increasingly recognized that monogenic hypertension is not rare, especially in patients with electrolyte disorders. Single genetic alterations are associated with plasma volume expansion and catecholamines/sympathetic excess with simultaneously increased potassium excretion in the urine and potassium intracellular shift. Early-onset refractory hypertension and profound hypokalemia are characteristics of monogenic hypertension. However, accumulated evidence shows the existence of phenotypic heterogeneity in monogenic hypertension meaning that, even for mild symptoms, clinicians cannot easily exclude the possibility of monogenic hypertension. Genetic, epigenetic and non-genetic factors are all possible mechanisms influencing phenotypic diversity. Genetic sequencing is a precise and efficient method that can broaden the mutant gene spectrum of the disease and is very helpful for understanding the pathophysiology of monogenic hypertension. Genetic sequencing, along with biochemical tests and imaging modalities, is essential for the early diagnosis and targeted management of monogenic hypertension to avoid long-term catastrophic complications.

Membrane trafficking pathways regulating the epithelial Na+ channel

Renal Na⁺ reabsorption, facilitated by the epithelial Na⁺ channel (ENaC), is subject to multiple forms of control to ensure optimal body blood volume and pressure through altering both the ENaC population and activity at the cell surface. Here, the focus is on regulating the number of ENaCs present in the apical membrane domain through pathways of ENaC synthesis and targeting to the apical membrane as well as ENaC removal, recycling, and degradation. Finally, the mechanisms by which ENaC trafficking pathways are regulated are summarized.

Association of SGK1 Polymorphisms With Susceptibility to Coronary Heart Disease in Chinese Han Patients With Comorbid Depression

There is a strong link between heart disease and depression, both of which are closely related to lifetime stress exposure. Serum/glucocorticoid-regulated kinase 1 (SGK1) is a stress-responsive gene with a pivotal role in both the heart and brain. To determine the role of SGK1 polymorphisms (rs2758151, rs1743963, rs9493857, rs1763509, rs9376026, and rs9389154) in susceptibility to comorbid coronary heart disease (CHD) and depression, we conducted a hospital-based case–control study involving 257 CHD cases (including 69 cases with depression and 188 cases without depression) and 107 controls in a Chinese Han population. Six single-nucleotide polymorphisms (SNPs) in the SGK1 gene were successfully genotyped by polymerase chain reaction–ligase detection reaction (PCR-LDR) assay. Our results showed no significant differences in SGK1 genetic polymorphisms between CHD patients and controls, whereas significant associations were observed between SGK1 SNPs (rs1743963 and rs1763509) and the development of depression in CHD patients (P = 0.018 by genotype, P = 0.032 by allele; P = 0.017 by genotype, P = 0.003 by allele, respectively). However, none of these associations remained significant after Bonferroni correction (P = 0.054 for rs1743963; P = 0.051 for rs1763509). Interestingly, both the GG genotype of SGK1 rs1743963 and AA genotype of SGK1 rs1763509 were associated with a higher risk of depression in CHD patients; for rs1763509, the Patient Health Questionnaire-9 (PHQ-9) scores in the carriers of the risk genotype for comorbid depression, AA, were significantly higher than in GG and AG carriers (P = 0.008). Notably, haplotype analysis indicated that haplotype GGA significantly increased the risk of depression in CHD patients (P = 0.011, odds ratio (OR) = 1.717, 95% confidence interval (CI) = 1.132–2.605), whereas haplotype AAG may be a protective factor for CHD patients with comorbid depression (P = 0.038, OR = 0.546, 95% CI = 0.307–0.972). It should be noted that only the significance of haplotype GGA survived after Bonferroni adjustment (P = 0.044) and that no significant differences were found for other SGK1 SNPs (rs2758151, rs9493857, rs9376026, and rs9389154) between CHD patients with and without depression. These findings, for the first time, elucidate the important role of SGK1 variants in the comorbidity of CHD and depression.

Renal denervation improves sodium excretion in rats with chronic heart failure: effects on expression of renal ENaC and AQP2

Previously we have shown that increased expression of renal epithelial sodium channels (ENaC) may contribute to the renal sodium and water retention observed during chronic heart failure (CHF). The goal of this study was to examine whether renal denervation (RDN) changed the expressions of renal sodium transporters ENaC, sodium-hydrogen exchanger-3 proteins (NHE3), and water channel aquaporin 2 (AQP2) in rats with CHF. CHF was produced by left coronary artery ligation in rats. Four weeks after ligation surgery, surgical bilateral RDN was performed. The expression of ENaC, NHE3, and AQP2 in both renal cortex and medulla were measured. As a functional test for ENaC activation, diuretic and natriuretic responses to ENaC inhibitor benzamil were monitored in four groups of rats (Sham, Sham+RDN, CHF, CHF+RDN). Western blot analysis indicated that RDN (1 wk later) significantly reduced protein levels of α-ENaC, β-ENaC, γ-ENaC, and AQP2 in the renal cortex of CHF rats. RDN had no significant effects on the protein expression of kidney NHE3 in both Sham and CHF rats. Immunofluorescence studies of kidney sections confirmed the reduced signaling of ENaC and AQP2 in the CHF+RDN rats compared with the CHF rats. There were increases in diuretic and natriuretic responses to ENaC inhibitor benzamil in rats with CHF. RDN reduced the diuretic and natriuretic responses to benzamil in CHF rats. These findings suggest a critical role for renal nerves in the enhanced expression of ENaC and AQP2 and subsequent pathophysiology of renal sodium and water retention associated with CHF.NEW & NOTEWORTHY This is the first study to show in a comprehensive way that renal denervation initiated after a period of chronic heart failure reduces the expression of epithelial sodium channels and aquaporin 2 leading to reduced epithelial sodium channel function and sodium retention.

Lack of Renal Tubular Glucocorticoid Receptor Decreases the Thiazide-Sensitive Na+/Cl- Cotransporter NCC and Transiently Affects Sodium Handling

Chronic glucocorticoid infusion impairs NCC activity and induces a non-dipping profile in mice, suggesting that glucocorticoids are essential for daily blood pressure variations. In this paper, we studied mice lacking the renal tubular glucocorticoid receptor (GR) in adulthood (GR knockouts, Nr3c1^Pax8/LC1). Upon standard salt diet, Nr3c1^Pax8/LC1 mice grow normally, but show reduced NCC activity despite normal plasma aldosterone levels. Following diet switch to low sodium, Nr3c1^Pax8/LC1 mice exhibit a transient but significant reduction in the activity of NCC and expression of NHE3 and NKCC2 accompanied by significant increased Spak activity. This is followed by transiently increased urinary sodium excretion and higher plasma aldosterone concentrations. Plasma corticosterone levels and 11βHSD2 mRNA expression and activity in the whole kidney remain unchanged. High salt diet does not affect whole body Na⁺ and/or K⁺ balance and NCC activity is not reduced, but leads to a significant increase in diastolic blood pressure dipping in Nr3c1^Pax8/LC1 mice. When high sodium treatment is followed by 48 h of darkness, NCC abundance is reduced in knockout mice although activity is not different. Our data show that upon Na⁺ restriction renal tubular GR-deficiency transiently affects Na⁺ handling and transport pathways. Overall, upon standard, low Na⁺ and high Na⁺ diet exposure Na⁺ and K⁺ balance is maintained as evidenced by normal plasma and urinary Na⁺ and K⁺ and aldosterone concentrations.