Altered expression of renal aquaporins and α-adducin polymorphisms may contribute to the establishment of salt-sensitive hypertension

Exploring the therapeutic effect of core components in Xuanshen Yishen mixture on hypertension through network pharmacology

OBJECTIVE

This study aims to elucidate the mechanism of action and impact of the "Xuanshen Yishen Mixture" (XYM) on hypertension.

METHODS

Active components were identified and potential targets were predicted using the Traditional Chinese Medicine Systems Pharmacology database. Hypertension-related targets were collected from GeneCards, DRUGBANK, OMIM, TTD, and PharmaGKB databases. Intersections of disease and drug targets were visualized using the R package "VennDiagram". A protein-protein interaction network was established via the STRING database. GO function enrichment and KEGG pathway analyses were conducted using "clusterProfiler", while "Cytoscape" was used to construct a "drug-component-target" network. Additionally, data from 60 patients with essential hypertension from the Affiliated Hospital of Shandong University of Traditional Chinese Medicine were retrospectively analyzed. Patients were divided into a control group (n = 30) and an XYM group (n = 30) based on treatment regimen.

RESULTS

Sixty active ingredients and 98 related targets were identified from Uncaria, Radix Scrophulariae, and Epimedium in hypertension treatment. Key active components such as quercetin, kaempferol, yohimbine, and beta-sitosterol were pinpointed, with PTGS2, PTGS1, AR, DPP4, and F2 as crucial targets. KEGG pathway analysis highlighted significant pathways including IL-17 signaling, TNF signaling, Relaxin signaling, and HIF-1 signaling. Clinical data indicated that XYM's therapeutic effects are comparable to those of valsartan, which significantly reduced diastolic and systolic blood pressure and demonstrated good biosafety.

CONCLUSIONS

Uncaria, Radix Scrophulariae, and Epimedium effectively mitigate hypertension through multiple components, targets, and pathways. Additionally, DPP4, IL-17, and TNF-α are identified as potential therapeutic targets for traditional Chinese medicine preparations in hypertension treatment. This study provides a foundation for further investigation into XYM's mechanisms in hypertension management.

Genetic imputation of kidney transcriptome, proteome and multi-omics illuminates new blood pressure and hypertension targets

Genetic mechanisms of blood pressure (BP) regulation remain poorly defined. Using kidney-specific epigenomic annotations and 3D genome information we generated and validated gene expression prediction models for the purpose of transcriptome-wide association studies in 700 human kidneys. We identified 889 kidney genes associated with BP of which 399 were prioritised as contributors to BP regulation. Imputation of kidney proteome and microRNAome uncovered 97 renal proteins and 11 miRNAs associated with BP. Integration with plasma proteomics and metabolomics illuminated circulating levels of myo-inositol, 4-guanidinobutanoate and angiotensinogen as downstream effectors of several kidney BP genes (SLC5A11, AGMAT, AGT, respectively). We showed that genetically determined reduction in renal expression may mimic the effects of rare loss-of-function variants on kidney mRNA/protein and lead to an increase in BP (e.g., ENPEP). We demonstrated a strong correlation (r = 0.81) in expression of protein-coding genes between cells harvested from urine and the kidney highlighting a diagnostic potential of urinary cell transcriptomics. We uncovered adenylyl cyclase activators as a repurposing opportunity for hypertension and illustrated examples of BP-elevating effects of anticancer drugs (e.g. tubulin polymerisation inhibitors). Collectively, our studies provide new biological insights into genetic regulation of BP with potential to drive clinical translation in hypertension.

Effects of a high-salt diet on MAP and expression levels of renal ENaCs and aquaporins in SHR

An increase in blood pressure by a high-salt (HS) diet may change the expression levels of renal epithelial sodium channels (ENaCs) and aquaporins (AQPs). Spontaneously hypertensive rats (SHRs) and Wistar Kyoto (WKY) rats were exposed to HS and regular-salt (RS) diets for 6 weeks. Mean arterial pressure (MAP) and plasma atrial natriuretic peptide (ANP), angiotensin II (Ang II), aldosterone, and arginine vasopressin (AVP) levels were determined. Expression of mRNA levels of ENaCs and AQPs were quantified by real-time PCR. The MAP was higher in SHRs on the HS diet. Plasma Ang II and aldosterone levels were low while plasma ANP level was high in both strains of rats. Renal expression of mRNA levels of α-, β-, and γ-ENaCs was lowered in SHRs on the HS diet. Meanwhile, renal AQP1, AQP2, and AQP7 mRNA expression levels were lowered in both strains of rats on the HS diet. Suppression of mRNA expression levels of ENaC and AQP subunits suggests that the high-salt-induced increase in the MAP of SHR may not be solely due to renal sodium and water retention.

Aquaporins in Urinary System

There are at least eight aquaporins (AQPs) expressed in the kidney. Including AQP1 expressed in proximal tubules, thin descending limb of Henle and vasa recta; AQP2, AQP3, AQP4, AQP5, and AQP6 expressed in collecting ducts; AQP7 expressed in proximal tubules; AQP8 expressed in proximal tubules and collecting ducts; and AQP11 expressed in the endoplasmic reticulum of proximal tubular epithelial cells. Over years, researchers have constructed different AQP knockout mice and explored the effect of AQP knockout on kidney function. Thus, the roles of AQPs in renal physiology are revealed, providing very useful information for addressing fundamental questions about transepithelial water transport and the mechanism of near isoosmolar fluid reabsorption. This chapter introduces the localization and function of AQPs in the kidney and their roles in different kidney diseases to reveal the prospects of AQPs in further basic and clinical studies.

Genetic Variants Associated With Uncontrolled Blood Pressure on Thiazide Diuretic/β-Blocker Combination Therapy in the PEAR (Pharmacogenomic Evaluation of Antihypertensive Responses) and INVEST (International Verapamil-SR Trandolapril Study) Trials

BACKGROUND

The majority of hypertensive individuals require combination antihypertensive therapy to achieve adequate blood pressure (BP) control. This study aimed to identify genetic variants associated with uncontrolled BP on combination therapy with a thiazide diuretic and a β-blocker.

METHODS AND RESULTS

A genome-wide association study of uncontrolled BP on combination therapy was conducted among 314 white participants of the PEAR (Pharmacogenomic Evaluation of Antihypertensive Responses) trial. Multivariable logistic regression analysis was used. Genetic variants meeting a suggestive level of significance (P<1.0E-05) were tested for replication in an external cohort, INVEST (International Verapamil-SR Trandolapril study). We also examined genome-wide variant associations with systolic and diastolic BP response on combination therapy and tested for replication. We discovered a single nucleotide polymorphism, the rs261316 major allele, at chromosome 15 in the gene ALDH1A2 associated with an increased odds of having uncontrolled BP on combination therapy (odds ratio: 2.56, 95% confidence interval, 1.69-3.88, P=8.64E-06). This single nucleotide polymorphism replicated (odds ratio: 1.86, 95% confidence interval, 1.35-2.57, P=0.001) and approached genome-wide significance in the meta-analysis between discovery and replication cohorts (odds ratio: 2.16, 95% confidence interval, 1.63-2.86, P=8.60E-08). Other genes in the region surrounding rs261316 (ALDH1A2) include AQP9 and LIPC.

CONCLUSIONS

A single nucleotide polymorphism in the gene ALDH1A2 may be associated with uncontrolled BP following treatment with a thiazide diuretic/β-blocker combination.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT00246519.

Aquaporins in Urinary System

Several aquaporin (AQP )-type water channels are expressed in kidney: AQP1 in the proximal tubule, thin descending limb of Henle, and vasa recta; AQP2 -6 in the collecting duct; AQP7 in the proximal tubule; AQP8 in the proximal tubule and collecting duct; and AQP11 in the endoplasmic reticulum of proximal tubule cells. AQP2 is the vasopressin-regulated water channel that is important in hereditary and acquired diseases affecting urine-concentrating ability. The roles of AQPs in renal physiology and transepithelial water transport have been determined using AQP knockout mouse models. This chapter describes renal physiologic insights revealed by phenotypic analysis of AQP knockout mice and the prospects for further basic and clinical studies.

The gene-expression profile of renal medulla in ISIAH rats with inherited stress-induced arterial hypertension

Background

The changes in the renal function leading to a reduction of medullary blood flow can have a great impact on sodium and water homeostasis and on the long-term control of arterial blood pressure. The RNA-Seq approach was used for transcriptome profiling of the renal medulla from hypertensive ISIAH and normotensive WAG rats to uncover the genetic basis of the changes underlying the renal medulla function in the ISIAH rats being a model of the stress-sensitive arterial hypertension and to reveal the genes which possibly may contribute to the alterations in medullary blood flow.

Results

Multiple DEGs specifying the function of renal medulla in ISIAH rats were revealed. The group of DEGs described by Gene Ontology term ‘oxidation reduction’ was the most significantly enriched one. The other groups of DEGs related to response to external stimulus, response to hormone (endogenous) stimulus, response to stress, and homeostatic process provide the molecular basis for integrated responses to homeostasis disturbances in the renal medulla of the ISIAH rats. Several DEGs, which may modulate the renal medulla blood flow, were detected. The reduced transcription of Nos3 pointed to the possible reduction of the blood flow in the renal medulla of ISIAH rats.

Conclusions

The generated data may be useful for comparison with those from different models of hypertension and for identifying the common molecular determinants contributing to disease manifestation, which may be potentially used as new pharmacological targets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0462-6) contains supplementary material, which is available to authorized users.

Rare Variants in NOD1 Associated with Carotid Bifurcation Intima-Media Thickness in Dominican Republic Families

Cardiovascular disorders including ischemic stroke (IS) and myocardial infarction (MI) are heritable; however, few replicated loci have been identified. One strategy to identify loci influencing these complex disorders is to study subclinical phenotypes, such as carotid bifurcation intima-media thickness (bIMT). We have previously shown bIMT to be heritable and found evidence for linkage and association with common variants on chromosome 7p for bIMT. In this study, we aimed to characterize contributions of rare variants (RVs) in 7p to bIMT. To achieve this aim, we sequenced the 1 LOD unit down region on 7p in nine extended families from the Dominican Republic (DR) with strong evidence for linkage to bIMT. We then performed the family-based sequence kernel association test (famSKAT) on genes within the 7p region. Analyses were restricted to single nucleotide variants (SNVs) with population based minor allele frequency (MAF) <5%. We first analyzed all exonic RVs and then the subset of only non-synonymous RVs. There were 68 genes in our analyses. Nucleotide-binding oligomerization domain (NOD1) was the most significantly associated gene when analyzing exonic RVs (famSKAT p = 9.2x10^-4; number of SNVs = 14). We achieved suggestive replication of NOD1 in an independent sample of twelve extended families from the DR (p = 0.055). Our study provides suggestive statistical evidence for a role of rare variants in NOD1 in bIMT. Studies in mice have shown Nod1 to play a role in heart function and atherosclerosis, providing biologic plausibility for a role in bIMT thus making NOD1 an excellent bIMT candidate.

Transcriptome analysis in rat kidneys: importance of genes involved in programmed hypertension

Suboptimal conditions in pregnancy can elicit long-term effects on the health of offspring. The most common outcome is programmed hypertension. We examined whether there are common genes and pathways in the kidney are responsible for generating programmed hypertension among three different models using next generation RNA sequencing (RNA-Seq) technology. Pregnant Sprague-Dawley rats received dexamethasone (DEX, 0.1 mg/kg) from gestational day 16 to 22, 60% high-fructose (HF) diet, or N^G-nitro-l-arginine-methyester (l-NAME, 60 mg/kg/day) to conduct DEX, HF, or l-NAME model respectively. All three models elicited programmed hypertension in adult male offspring. We observed five shared genes (Bcl6, Dmrtc1c, Egr1, Inmt, and Olr1668) among three different models. The identified differential genes (DEGs) that are related to regulation of blood pressure included Aqp2, Ptgs1, Eph2x, Hba-a2, Apln, Guca2b, Hmox1, and Npy. RNA-Seq identified genes in arachidonic acid metabolism are potentially gatekeeper genes contributing to programmed hypertension. In addition, HF and DEX increased expression and activity of soluble epoxide hydrolase (Ephx2 gene encoding protein). Conclusively, the DEGs in arachidonic acid metabolism are potentially gatekeeper genes in programmed hypertension. The roles of DEGs identified by the RNA-Seq in this study deserve further clarification, to develop the potential interventions in the prevention of programmed hypertension.

Melatonin prevents maternal fructose intake-induced programmed hypertension in the offspring: roles of nitric oxide and arachidonic acid metabolites

Fructose intake has increased globally and is linked to hypertension. Melatonin was reported to prevent hypertension development. In this study, we examined whether maternal high fructose (HF) intake causes programmed hypertension and whether melatonin therapy confers protection against the process, with a focus on the link to epigenetic changes in the kidney using next-generation RNA sequencing (NGS) technology. Pregnant Sprague-Dawley rats received regular chow or chow supplemented with HF (60% diet by weight) alone or with additional 0.01% melatonin in drinking water during the whole period of pregnancy and lactation. Male offspring were assigned to four groups: control, HF, control + melatonin (M), and HF + M. Maternal HF caused increases in blood pressure (BP) in the 12-wk-old offspring. Melatonin therapy blunted the HF-induced programmed hypertension and increased nitric oxide (NO) level in the kidney. The identified differential expressed gene (DEGs) that are related to regulation of BP included Ephx2, Col1a2, Gucy1a3, Npr3, Aqp2, Hba-a2, and Ptgs1. Of which, melatonin therapy inhibited expression and activity of soluble epoxide hydrolase (SEH, Ephx2 gene encoding protein). In addition, we found genes in arachidonic acid metabolism were potentially involved in the HF-induced programmed hypertension and were affected by melatonin therapy. Together, our data suggest that the beneficial effects of melatonin are attributed to its ability to increase NO level in the kidney, epigenetic regulation of genes related to BP control, and inhibition of SEH expression. The roles of DEGs by the NGS in long-term epigenetic changes in the adult offspring kidney require further clarification.

Hypertension-linked mutation of α-adducin increases CFTR surface expression and activity in HEK and cultured rat distal convoluted tubule cells

The CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) activity and localization are influenced by the cytoskeleton, in particular by actin and its polymerization state. In this study we investigated whether the expression of the hypertensive mutations of α-adducin (G460W-S586C in humans, F316Y in rats), an actin capping protein, led to a functional modification of CFTR activity and surface expression. The experiments were performed on HEK293 T cells cotransfected with CFTR and the human wild type (WT) or G460W mutated α-adducin. In whole-cell patch-clamp experiments, both the CFTR chloride current and the slope of current activation after forskolin addition were significantly higher in HEK cells overexpressing the G460W adducin. A higher plasma membrane density of active CFTR channels was confirmed by cell-attached patch-clamp experiments, both in HEK cells and in cultured primary DCT cells, isolated from MHS (Milan Hypertensive Strain, a Wistar rat (Rattus norvegicus) hypertensive model carrying the F316Y adducin mutation), compared to MNS (Milan Normotensive Strain) rats. Western blot experiments demonstrated an increase of the plasma membrane CFTR protein expression, with a modification of the channel glycosylation state, in the presence of the mutated adducin. A higher retention of CFTR protein in the plasma membrane was confirmed both by FRAP (Fluorescence Recovery After Photobleaching) and photoactivation experiments. The present data indicate that in HEK cells and in isolated DCT cells the presence of the G460W-S586C hypertensive variant of adducin increases CFTR channel activity, possibly by altering its membrane turnover and inducing a retention of the channel in the plasmamembrane. Since CFTR is known to modulate the activity of many others transport systems, the increased surface expression of the channel could have consequences on the whole network of transport in kidney cells.

The role of renal water channels in health and disease

Seven members of the aquaporin (AQP) family are expressed in different regions of the kidney. AQP1-4 are localized in plasma membranes of renal epithelial cells and are intimately involved in water reabsorption by the kidney. AQP7 is also localized in the plasma membrane and may facilitate glycerol transport. AQP6 and AQP11 are localized within the cell, with AQP6 involved in anion transport and AQP11 water transport. Mutations in AQP2 can result in diabetes insipidus, whereas mutations in other AQPs have not yet been shown to be disease-associated. Genetic polymorphisms may contribute to the susceptibility to defects in urine concentrating mechanisms associated with some diseases. Most of the AQPs are subject to transcriptional regulation and post-translational modifications by a range of biological modifiers. As a result a number of chronic kidney and systemic diseases produce changes in the abundance of AQPs. The more recent developments in this field are reviewed.

The first discovered water channel protein, later called aquaporin 1: molecular characteristics, functions and medical implications

After a decade of work on the water permeability of red blood cells (RBC) Benga group in Cluj-Napoca, Romania, discovered in 1985 the first water channel protein in the RBC membrane. The discovery was reported in publications in 1986 and reviewed in subsequent years. The same protein was purified by chance by Agre group in Baltimore, USA, in 1988, who called in 1991 the protein CHIP28 (CHannel forming Integral membrane Protein of 28 kDa), suggesting that it may play a role in linkage of the membrane skeleton to the lipid bilayer. In 1992 the Agre group identified CHIP28's water transport property. One year later CHIP28 was named aquaporin 1, abbreviated as AQP1. In this review the molecular structure-function relationships of AQP1 are presented. In the natural or model membranes AQP1 is in the form of a homotetramer, however, each monomer has an independent water channel (pore). The three-dimensional structure of AQP1 is described, with a detailed description of the channel (pore), the molecular mechanisms of permeation through the channel of water molecules and exclusion of protons. The permeability of the pore to gases (CO(2), NH(3), NO, O(2)) and ions is also mentioned. I have also reviewed the functional roles and medical implications of AQP1 expressed in various organs and cells (microvascular endothelial cells, kidney, central nervous system, eye, lacrimal and salivary glands, respiratory apparatus, gastrointestinal tract, hepatobiliary compartments, female and male reproductive system, inner ear, skin). The role of AQP1 in cell migration and angiogenesis in relation with cancer, the genetics of AQP1 and mutations in human subjects are also mentioned. The role of AQP1 in red blood cells is discussed based on our comparative studies of water permeability in over 30 species.

Abnormal increase in urinary aquaporin-2 excretion in response to hypertonic saline in essential hypertension

Background

Dysregulation of the expression/shuttling of the aquaporin-2 water channel (AQP2) and the epithelial sodium channel (ENaC) in renal collecting duct principal cells has been found in animal models of hypertension. We tested whether a similar dysregulation exists in essential hypertension.

Methods

We measured urinary excretion of AQP2 and ENaC β-subunit corrected for creatinine (u-AQP2_CR, u-ENaC_β-CR), prostaglandin E2 (u-PGE₂) and cyclic AMP (u-cAMP), fractional sodium excretion (FE_Na), free water clearance (C_H2O), as well as plasma concentrations of vasopressin (AVP), renin (PRC), angiotensin II (Ang II), aldosterone (Aldo), and atrial and brain natriuretic peptide (ANP, BNP) in 21 patients with essential hypertension and 20 normotensive controls during 24-h urine collection (baseline), and after hypertonic saline infusion on a 4-day high sodium (HS) diet (300 mmol sodium/day) and a 4-day low sodium (LS) diet (30 mmol sodium/day).

Results

At baseline, no differences in u-AQP2_CR or u-ENaC_β-CR were measured between patients and controls. U-AQP2_CR increased significantly more after saline in patients than controls, whereas u-ENaC_β-CR increased similarly. The saline caused exaggerated natriuretic increases in patients during HS intake. Neither baseline levels of u-PGE₂, u-cAMP, AVP, PRC, Ang II, Aldo, ANP, and BNP nor changes after saline could explain the abnormal u-AQP2_CR response.

Conclusions

No differences were found in u-AQP2_CR and u-ENaC_β-CR between patients and controls at baseline. However, in response to saline, u-AQP2_CR was abnormally increased in patients, whereas the u-ENaC_β-CR response was normal. The mechanism behind the abnormal AQP2 regulation is not clarified, but it does not seem to be AVP-dependent.

Clinicaltrial.gov identifier

NCT00345124.