Esm-1 mediates transcriptional polarization associated with diabetic kidney disease.

Esm-1, endothelial cell-specific molecule-1, is a susceptibility gene for diabetic kidney disease (DKD) and is a secreted proteoglycan, with notable expression in kidney, which attenuates inflammation and albuminuria. However, little is known about Esm1 expression in mature tissues in the presence or absence of diabetes. We utilized publicly available single-cell RNA sequencing data to characterize Esm1 expression in 27,786 renal endothelial cells (RECs) obtained from three mouse and four human databases. We validated our findings using bulk transcriptome data from 20 healthy subjects and 41 patients with DKD and using RNAscope. In both mice and humans, Esm1 is expressed in a subset of all REC types and represents a minority of glomerular RECs. In patients, Esm1(+) cells exhibit conserved enrichment for blood vessel development genes. With diabetes, these cells are fewer in number and shift expression toward chemotaxis pathways. Esm1 correlates with a majority of genes within these pathways, delineating a glomerular transcriptional polarization reflected by the magnitude of Esm1 deficiency. Diabetes correlates with lower Esm1 expression and with changes in the functional characterization of Esm1(+) cells. Thus, Esm1 appears to be a marker for glomerular transcriptional polarization in DKD.NEW & NOTEWORTHY Esm-1 is primarily expressed in glomerular endothelium in humans. Cells expressing Esm1 exhibit a high degree of conservation in the enrichment of genes related to blood vessel development. In the context of diabetes, these cells are reduced in number and show a significant transcriptional shift toward the chemotaxis pathway. In diabetes, there is a transcriptional polarization in the glomerulus that is reflected by the degree of Esm1 deficiency.

Underdiagnosis of Primary Aldosteronism: A Review of Screening and Detection.

A clinical condition may be missed due to its higher-than-recognized prevalence or inadequate diagnostic screening. Both factors apply to primary aldosteronism, which is woefully underdiagnosed as a cause of hypertension and end-organ damage. Screening tests should be strongly considered for diseases that pose significant morbidity or mortality if left untreated, that have a high prevalence, and that have treatments that lead to improvement or cure. In this review we present the evidence for each of these points. We outline studies that estimate the prevalence of primary aldosteronism in different at-risk populations and how its recognition has changed over time. We also evaluate myriad studies of screening rates for primary aldosteronism and what factors do and do not influence current screening practices. We discuss the ideal conditions for screening, measuring the aldosterone to renin ratio in different populations that use plasma renin activity or direct renin concentration, and the steps for diagnostic workup of primary aldosteronism. Finally, we conclude with potential strategies to implement higher rates of screening and diagnosis of this common, consequential, and treatable disease.

Testing for Primary Aldosteronism and Mineralocorticoid Receptor Antagonist Use Among U.S. Veterans : A Retrospective Cohort Study.

BACKGROUND: Primary aldosteronism is a common cause of treatment-resistant hypertension. However, evidence from local health systems suggests low rates of testing for primary aldosteronism. OBJECTIVE: To evaluate testing rates for primary aldosteronism and evidence-based hypertension management in patients with treatment-resistant hypertension. DESIGN: Retrospective cohort study. SETTING: U.S. Veterans Health Administration. PARTICIPANTS: Veterans with apparent treatment-resistant hypertension (n = 269 010) from 2000 to 2017, defined as either 2 blood pressures (BPs) of at least 140 mm Hg (systolic) or 90 mm Hg (diastolic) at least 1 month apart during use of 3 antihypertensive agents (including a diuretic), or hypertension requiring 4 antihypertensive classes. MEASUREMENTS: Rates of primary aldosteronism testing (plasma aldosterone-renin) and the association of testing with evidence-based treatment using a mineralocorticoid receptor antagonist (MRA) and with longitudinal systolic BP. RESULTS: 4277 (1.6%) patients who were tested for primary aldosteronism were identified. An index visit with a nephrologist (hazard ratio [HR], 2.05 [95% CI, 1.66 to 2.52]) or an endocrinologist (HR, 2.48 [CI, 1.69 to 3.63]) was associated with a higher likelihood of testing compared with primary care. Testing was associated with a 4-fold higher likelihood of initiating MRA therapy (HR, 4.10 [CI, 3.68 to 4.55]) and with better BP control over time. LIMITATIONS: Predominantly male cohort, retrospective design, susceptibility of office BPs to misclassification, and lack of confirmatory testing for primary aldosteronism. CONCLUSION: In a nationally distributed cohort of veterans with apparent treatment-resistant hypertension, testing for primary aldosteronism was rare and was associated with higher rates of evidence-based treatment with MRAs and better longitudinal BP control. The findings reinforce prior observations of low adherence to guideline-recommended practices in smaller health systems and underscore the urgent need for improved management of patients with treatment-resistant hypertension. PRIMARY FUNDING SOURCE: National Institutes of Health.

Cardiorenal Protection With the Newer Antidiabetic Agents in Patients With Diabetes and Chronic Kidney Disease: A Scientific Statement From the American Heart Association.

Chronic kidney disease (CKD) with type 2 diabetes (T2D) is a major public health problem, resulting in significant cardiovascular and kidney adverse outcomes worldwide. Despite the widespread use of standard-of-care therapies for CKD with T2D over the past few decades, rates of progression to end-stage kidney disease remain high with no beneficial impact on its accompanying burden of cardiovascular disease. The advent of the newer classes of antihyperglycemic agents, including SGLT2 (sodium glucose cotransporter 2) inhibitors and GLP-1 (glucagon-like peptide-1) receptor agonists, has changed the landscape of therapeutic options for patients with CKD with T2D, with demonstration of significant reductions in cardiovascular adverse events and progression to end-stage kidney disease. Several potential mechanisms exist through which these beneficial effects are achieved in both drug classes, which may be independent of their antihyperglycemic effects. This scientific statement summarizes the current literature on the cardiorenal protective effects with SGLT2 inhibitors and GLP-1 receptor agonists in patients with CKD and T2D. It reviews potential mechanistic pathways that may drive these benefits and summarizes the literature on adverse effects in patients with CKD and T2D at risk for or with established cardiovascular disease. Last, it provides practical guidance on a proposed collaborative care model bridging cardiologists, nephrologists, endocrinologists, and primary care physicians to facilitate the prompt and appropriate integration of these therapeutic classes in the management of patients with T2D and CKD.

Aldosterone sensitivity: an opportunity to explore the pathogenesis of hypertension.

Aldosterone sensitivity is defined as an outcome variable for a given circulating level of aldosterone. In basic and translational studies, aldosterone sensitivity has been measured in differential tissue responses, e.g., lower urine sodium and higher urine potassium, as an index of the renal response; in clinical studies, aldosterone sensitivity has been measured in differential blood pressure responses. The concept of aldosterone sensitivity disrupts the conventional wisdom of the renin-angiotensin-aldosterone system and has the potential to uncover novel mechanisms of hypertension. Here, we review basic and translational science studies that uncovered differential renal responses to aldosterone and connect this earlier work to more recent observational studies and randomized trials that have demonstrated differential blood pressure responses for a given level of aldosterone in healthy and hypertensive persons. Black race and older age are associated with higher aldosterone sensitivity and blood pressure. We also discuss gaps in the field and how future basic and clinical studies might inform mechanisms of differential sensitivity.

Cardiorenal Syndrome: Classification, Pathophysiology, Diagnosis, and Treatment Strategies: A Scientific Statement From the American Heart Association.

Cardiorenal syndrome encompasses a spectrum of disorders involving both the heart and kidneys in which acute or chronic dysfunction in 1 organ may induce acute or chronic dysfunction in the other organ. It represents the confluence of heart-kidney interactions across several interfaces. These include the hemodynamic cross-talk between the failing heart and the response of the kidneys and vice versa, as well as alterations in neurohormonal markers and inflammatory molecular signatures characteristic of its clinical phenotypes. The mission of this scientific statement is to describe the epidemiology and pathogenesis of cardiorenal syndrome in the context of the continuously evolving nature of its clinicopathological description over the past decade. It also describes diagnostic and therapeutic strategies applicable to cardiorenal syndrome, summarizes cardiac-kidney interactions in special populations such as patients with diabetes mellitus and kidney transplant recipients, and emphasizes the role of palliative care in patients with cardiorenal syndrome. Finally, it outlines the need for a cardiorenal education track that will guide future cardiorenal trials and integrate the clinical and research needs of this important field in the future.

AMPK phosphorylation of the ß1Pix exchange factor regulates the assembly and function of an ENaC inhibitory complex in kidney epithelial cells.

The metabolic sensor AMP-activated protein kinase (AMPK) inhibits the epithelial Na+ channel (ENaC), a key regulator of salt reabsorption by the kidney and thus total body volume and blood pressure. Recent studies have suggested that AMPK promotes the association of p21-activated kinase-interacting exchange factor-ß1 ß1Pix, 14-3-3 proteins, and the ubiquitin ligase neural precursor cell expressed developmentally downregulated protein (Nedd)4-2 into a complex that inhibits ENaC by enhancing Nedd4-2 binding to ENaC and ENaC degradation. Functional ß1Pix is required for ENaC inhibition by AMPK and promotes Nedd4-2 phosphorylation and stability in mouse kidney cortical collecting duct cells. Here, we report that AMPK directly phosphorylates ß1Pix in vitro. Among several AMPK phosphorylation sites on ß1Pix detected by mass spectrometry, Ser71 was validated as functionally significant. Compared with wild-type ß1Pix, overexpression of a phosphorylation-deficient ß1Pix-S71A mutant attenuated ENaC inhibition and the AMPK-activated interaction of both ß1Pix and Nedd4-2 to 14-3-3 proteins in cortical collecting duct cells. Similarly, overexpression of a ß1Pix-Δ602-611 deletion tract mutant unable to bind 14-3-3 proteins decreased the interaction between Nedd4-2 and 14-3-3 proteins, suggesting that 14-3-3 binding to ß1Pix is critical for the formation of a ß1Pix/Nedd4-2/14-3-3 complex. With expression of a general peptide inhibitor of 14-3-3-target protein interactions (R18), binding of both ß1Pix and Nedd4-2 to 14-3-3 proteins was reduced, and AMPK-dependent ENaC inhibition was also attenuated. Altogether, our results demonstrate the importance of AMPK-mediated phosphorylation of ß1Pix at Ser71, which promotes 14-3-3 interactions with ß1Pix and Nedd4-2 to form a tripartite ENaC inhibitory complex, in the mechanism of ENaC regulation by AMPK.

Improved protocols for the study of urinary electrolyte excretion and blood pressure in rodents: use of gel food and stepwise changes in diet composition.

Many experimental protocols in rodents require the comparison of groups that are fed different diets. Changes in dietary electrolyte and/or fat content can influence food intake, which can potentially introduce bias or confound the results. Unpalatable diets slow growth or cause weight loss, which is exacerbated by housing the animals in individual metabolic cages or by surgery. For balance studies in mice, small changes in body weight and food intake and low urinary flow can amplify these challenges. Powder food can be administered as gel with the addition of a desired amount of water, electrolytes, drugs (if any), and a small amount of agar. We describe here how the use of gel food to vary water, Na, K, and fat content can reduce weight loss and improve reproducibility of intake, urinary excretion, and blood pressure in rodents. In addition, mild food restriction reduces the interindividual variability and intergroup differences in food intake and associated variables, thus improving the statistical power of an experiment. Finally, we also demonstrate the advantages of using gel food for weight-based drug dosing. These protocols can improve the accuracy and reproducibility of experimental data where dietary manipulations are needed and are especially advisable in rodent studies related to water balance, obesity, and blood pressure.

Regulation of the Water Channel Aquaporin-2 via 14-3-3θ and -ζ.

The 14-3-3 family of proteins are multifunctional proteins that interact with many of their cellular targets in a phosphorylation-dependent manner. Here, we determined that 14-3-3 proteins interact with phosphorylated forms of the water channel aquaporin-2 (AQP2) and modulate its function. With the exception of σ, all 14-3-3 isoforms were abundantly expressed in mouse kidney and mouse kidney collecting duct cells (mpkCCD14). Long-term treatment of mpkCCD14 cells with the type 2 vasopressin receptor agonist dDAVP increased mRNA and protein levels of AQP2 alongside 14-3-3ß and -ζ, whereas levels of 14-3-3η and -θ were decreased. Co-immunoprecipitation (co-IP) studies in mpkCCD14 cells uncovered an AQP2/14-3-3 interaction that was modulated by acute dDAVP treatment. Additional co-IP studies in HEK293 cells determined that AQP2 interacts selectively with 14-3-3ζ and -θ. Use of phosphatase inhibitors in mpkCCD14 cells, co-IP with phosphorylation deficient forms of AQP2 expressed in HEK293 cells, or surface plasmon resonance studies determined that the AQP2/14-3-3 interaction was modulated by phosphorylation of AQP2 at various sites in its carboxyl terminus, with Ser-256 phosphorylation critical for the interactions. shRNA-mediated knockdown of 14-3-3ζ in mpkCCD14 cells resulted in increased AQP2 ubiquitylation, decreased AQP2 protein half-life, and reduced AQP2 levels. In contrast, knockdown of 14-3-3θ resulted in increased AQP2 half-life and increased AQP2 levels. In conclusion, this study demonstrates phosphorylation-dependent interactions of AQP2 with 14-3-3θ and -ζ. These interactions play divergent roles in modulating AQP2 trafficking, phosphorylation, ubiquitylation, and degradation.

Molecular Mechanisms of Sodium-Sensitive Hypertension in the Metabolic Syndrome.

PURPOSE OF REVIEW: We review the known mechanisms of sodium-sensitive hypertension in the metabolic syndrome with a focus on preclinical models, differences between these models, and methodological limitations. We also identify future directions for a better understanding and treatment of this common condition. RECENT FINDINGS: Rigorous methodologies to measure blood pressure in preclinical models may clarify some of the inconsistencies in the literature. Renal, neural, hormonal, and cardiovascular systems are dysregulated and contribute to elevated blood pressure. Local renin-angiotensin systems enhance systemic hormone signaling to increase blood pressure. Since the original description of metabolic syndrome, investigators from many fields have contributed to an increasingly complex and mechanistic understanding of this common condition. These systems integrate to regulate sodium transport in the kidney leading to hypertension and enhanced sodium sensitivity. An array of non-uniform preclinical models are used and support clinical studies to inform which models are pathophysiologically relevant for further mechanistic studies to guide targeted therapy.

New perspective of ClC-Kb/2 Cl- channel physiology in the distal renal tubule.

Since its identification as the underlying molecular cause of Bartter's syndrome type 3, ClC-Kb (ClC-K2 in rodents, henceforth it will be referred as ClC-Kb/2) is proposed to play an important role in systemic electrolyte balance and blood pressure regulation by controlling basolateral Cl(-) exit in the distal renal tubular segments from the cortical thick ascending limb to the outer medullary collecting duct. Considerable experimental and clinical effort has been devoted to the identification and characterization of disease-causing mutations as well as control of the channel by its cofactor, barttin. However, we have only begun to unravel the role of ClC-Kb/2 in different tubular segments and to reveal the regulators of its expression and function, e.g., insulin and IGF-1. In this review we discuss recent experimental evidence in this regard and highlight unexplored questions critical to understanding ClC-Kb/2 physiology in the kidney.

Na+-sensitive elevation in blood pressure is ENaC independent in diet-induced obesity and insulin resistance.

The majority of patients with obesity, insulin resistance, and metabolic syndrome have hypertension, but the mechanisms of hypertension are poorly understood. In these patients, impaired sodium excretion is critical for the genesis of Na(+)-sensitive hypertension, and prior studies have proposed a role for the epithelial Na(+) channel (ENaC) in this syndrome. We characterized high fat-fed mice as a model in which to study the contribution of ENaC-mediated Na(+) reabsorption in obesity and insulin resistance. High fat-fed mice demonstrated impaired Na(+) excretion and elevated blood pressure, which was significantly higher on a high-Na(+) diet compared with low fat-fed control mice. However, high fat-fed mice had no increase in ENaC activity as measured by Na(+) transport across microperfused cortical collecting ducts, electrolyte excretion, or blood pressure. In addition, we found no difference in endogenous urinary aldosterone excretion between groups on a normal or high-Na(+) diet. High fat-fed mice provide a model of metabolic syndrome, recapitulating obesity, insulin resistance, impaired natriuresis, and a Na(+)-sensitive elevation in blood pressure. Surprisingly, in contrast to previous studies, our data demonstrate that high fat feeding of mice impairs natriuresis and produces elevated blood pressure that is independent of ENaC activity and likely caused by increased Na(+) reabsorption upstream of the aldosterone-sensitive distal nephron.

Pemetrexed-Induced Nephrogenic Diabetes Insipidus.

Pemetrexed is an approved antimetabolite agent, now widely used for treating locally advanced or metastatic nonsquamous non-small cell lung cancer. Although no electrolyte abnormalities are described in the prescribing information for this drug, several case reports have noted nephrogenic diabetes insipidus with associated acute kidney injury. We present a case of nephrogenic diabetes insipidus without severely reduced kidney function and propose a mechanism for the isolated finding. Severe hypernatremia can lead to encephalopathy and osmotic demyelination, and our report highlights the importance of careful monitoring of electrolytes and kidney function in patients with lung cancer receiving pemetrexed.

Harvest and primary culture of the murine aldosterone-sensitive distal nephron.

The aldosterone-sensitive distal nephron (ASDN) exhibits axial heterogeneity in structure and function from the distal convoluted tubule to the medullary collecting duct. Ion and water transport is primarily divided between the cortex and medulla of the ASDN, respectively. Transcellular transport in this segment is highly regulated in health and disease and is integrated across different cell types. We currently lack an inexpensive, high-yield, and tractable technique to harvest and culture cells for the study of gene expression and physiological properties of mouse cortical ASDN. To address this need, we harvested tubules bound to Dolichos biflorus agglutinin lectin-coated magnetic beads from the kidney cortex and characterized these cell preparations. We determined that these cells are enriched for markers of distal convoluted tubule, connecting tubule, and cortical collecting duct, including principal and intercalated cells. In primary culture, these cells develop polarized monolayers with high resistance (1,000-1,500 Ω * cm(2)) and maintain expression and activity of key channels. These cells demonstrate an amiloride-sensitive short-circuit current that can be enhanced with aldosterone and maintain measurable potassium and anion secretion. Our method can be easily adopted to study the biology of the ASDN and to investigate phenotypic differences between wild-type and transgenic mouse models.

Aldosterone regulates microRNAs in the cortical collecting duct to alter sodium transport.

A role for microRNAs (miRs) in the physiologic regulation of sodium transport in the kidney has not been established. In this study, we investigated the potential of aldosterone to alter miR expression in mouse cortical collecting duct (mCCD) epithelial cells. Microarray studies demonstrated the regulation of miR expression by aldosterone in both cultured mCCD and isolated primary distal nephron principal cells. Aldosterone regulation of the most significantly downregulated miRs, mmu-miR-335-3p, mmu-miR-290-5p, and mmu-miR-1983 was confirmed by quantitative RT-PCR. Reducing the expression of these miRs separately or in combination increased epithelial sodium channel (ENaC)-mediated sodium transport in mCCD cells, without mineralocorticoid supplementation. Artificially increasing the expression of these miRs by transfection with plasmid precursors or miR mimic constructs blunted aldosterone stimulation of ENaC transport. Using a newly developed computational approach, termed ComiR, we predicted potential gene targets for the aldosterone-regulated miRs and confirmed ankyrin 3 (Ank3) as a novel aldosterone and miR-regulated protein. A dual-luciferase assay demonstrated direct binding of the miRs with the Ank3-3' untranslated region. Overexpression of Ank3 increased and depletion of Ank3 decreased ENaC-mediated sodium transport in mCCD cells. These findings implicate miRs as intermediaries in aldosterone signaling in principal cells of the distal kidney nephron.

EditABLE: A Simple Web Application for Designing Genome Editing Experiments.

CRISPR-Cas genome editing is transformative; however, there is no simple tool available for determining the optimal genome editing technology to create specific mutations for experimentation or to correct mutations as a curative therapy for specific diseases. We developed editABLE, an online resource (editable-app.stanford.edu) to provide computationally validated CRISPR editors and guide RNAs based on user provided sequence data. We demonstrate the utility of editABLE by applying it to one of the most common monogenic disorders, autosomal dominant polycystic kidney disease (ADPKD), identifying specific editing tools across the landscape of ADPKD mutations.

Prevalence of Mendelian Kidney Disease Among Patients With High-Risk APOL1 Genotypes Undergoing Commercial Genetic Testing in the United States.

Introduction: Among individuals with high-risk APOL1 genotypes, the lifetime risk of developing kidney failure is ∼15%, indicating that other genetic variants or nongenetic modifiers likely contribute substantially to an individual patient's risk of progressive kidney disease. Here, we estimate the prevalence and distribution of Mendelian kidney diseases among patients with high-risk APOL1 genotypes undergoing commercial genetic testing in the United States. Methods: We analyzed clinical exome sequencing data from 15,181 individuals undergoing commercial genetic testing for Mendelian kidney disease in the United States from 2020 to 2021. We identified patients with high-risk APOL1 genotypes by the presence of G1/G1, G1/G2, or G2/G2 alleles. Patients carrying single risk APOL1 alleles were identified as G1/G0, G2/G0; the remainder of patients were G0/G0. We estimated the prevalence and distribution of Mendelian kidney disease stratified by APOL1 genotype and genetically predicted ancestry. Results: Of 15,181 patients, 3119 had genetic testing results consistent with a molecular diagnosis of Mendelian kidney disease (20.5%). Of 15,181 patients, 1035 (6.8%) had high-risk APOL1 genotypes. Among patients with recent genomic African ancestry, the prevalence of Mendelian kidney diseases was lower in those with high-risk APOL1 genotypes (9.6%; n = 91/944) compared with single risk APOL1 allele carriers (13.6%; n = 198/1453) and those with G0/G0 APOL1 genotypes (16.6%; n = 213/1281). Among patients with Mendelian kidney disease and recent genomic African ancestry, we observed differences in the prevalence of pathogenic/likely pathogenic variants in PKD1 (19.8% in high-risk vs. 30.2% in low-risk genotypes), and COL4A4 (24.2% in high-risk vs. 10.5% in low-risk genotypes). Conclusion: In this selected population of patients undergoing clinical genetic testing, we found evidence of Mendelian kidney disease in ∼10% patients with high-risk APOL1 genotypes.