Adducin- and ouabain-related gene variants predict the antihypertensive activity of rostafuroxin, part 1: experimental studies

Multiscale photocatalytic proximity labeling reveals cell surface neighbors on and between cells

Proximity labeling proteomics (PLP) strategies are powerful approaches to yield snapshots of protein neighborhoods. Here, we describe a multiscale PLP method with adjustable resolution that uses a commercially available photocatalyst, Eosin Y, which upon visible light illumination activates different photo-probes with a range of labeling radii. We applied this platform to profile neighborhoods of the oncogenic epidermal growth factor receptor and orthogonally validated more than 20 neighbors using immunoassays and AlphaFold-Multimer prediction. We further profiled the protein neighborhoods of cell-cell synapses induced by bispecific T cell engagers and chimeric antigen receptor T cells. This integrated multiscale PLP platform maps local and distal protein networks on and between cell surfaces, which will aid in the systematic construction of the cell surface interactome, revealing horizontal signaling partners and reveal new immunotherapeutic opportunities.

The vascular Na,K-ATPase: clinical implications in stroke, migraine, and hypertension

In the vascular wall, the Na,K-ATPase plays an important role in the control of arterial tone. Through cSrc signaling, it contributes to the modulation of Ca2+ sensitivity in vascular smooth muscle cells. This review focuses on the potential implication of Na,K-ATPase-dependent intracellular signaling pathways in severe vascular disorders; ischemic stroke, familial migraine, and arterial hypertension. We propose similarity in the detrimental Na,K-ATPase-dependent signaling seen in these pathological conditions. The review includes a retrospective proteomics analysis investigating temporal changes after ischemic stroke. The analysis revealed that the expression of Na,K-ATPase α isoforms is down-regulated in the days and weeks following reperfusion, while downstream Na,K-ATPase-dependent cSrc kinase is up-regulated. These results are important since previous studies have linked the Na,K-ATPase-dependent cSrc signaling to futile recanalization and vasospasm after stroke. The review also explores a link between the Na,K-ATPase and migraine with aura, as reduced expression or pharmacological inhibition of the Na,K-ATPase leads to cSrc kinase signaling up-regulation and cerebral hypoperfusion. The review discusses the role of an endogenous cardiotonic steroid-like compound, ouabain, which binds to the Na,K-ATPase and initiates the intracellular cSrc signaling, in the pathophysiology of arterial hypertension. Currently, our understanding of the precise control mechanisms governing the Na,K-ATPase/cSrc kinase regulation in the vascular wall is limited. Understanding the role of vascular Na,K-ATPase signaling is essential for developing targeted treatments for cerebrovascular disorders and hypertension, as the Na,K-ATPase is implicated in the pathogenesis of these conditions and may contribute to their comorbidity.

Multi-scale photocatalytic proximity labeling reveals cell surface neighbors on and between cells

The cell membrane proteome is the primary biohub for cell communication, yet we are only beginning to understand the dynamic protein neighborhoods that form on the cell surface and between cells. Proximity labeling proteomics (PLP) strategies using chemically reactive probes are powerful approaches to yield snapshots of protein neighborhoods but are currently limited to one single resolution based on the probe labeling radius. Here, we describe a multi-scale PLP method with tunable resolution using a commercially available histological dye, Eosin Y, which upon visible light illumination, activates three different photo-probes with labeling radii ranging from ∼100 to 3000 Å. We applied this platform to profile neighborhoods of the oncogenic epidermal growth factor receptor (EGFR) and orthogonally validated >20 neighbors using immuno-assays and AlphaFold-Multimer prediction that generated plausible binary interaction models. We further profiled the protein neighborhoods of cell-cell synapses induced by bi-specific T-cell engagers (BiTEs) and chimeric antigen receptor (CAR)T cells at longer length scales. This integrated multi-scale PLP platform maps local and distal protein networks on cell surfaces and between cells. We believe this information will aid in the systematic construction of the cell surface interactome and reveal new opportunities for immunotherapeutics.

Precision Medicine and the future of Cardiovascular Diseases: A Clinically Oriented Comprehensive Review

Cardiac diseases form the lion's share of the global disease burden, owing to the paradigm shift to non-infectious diseases from infectious ones. The prevalence of CVDs has nearly doubled, increasing from 271 million in 1990 to 523 million in 2019. Additionally, the global trend for the years lived with disability has doubled, increasing from 17.7 million to 34.4 million over the same period. The advent of precision medicine in cardiology has ignited new possibilities for individually personalized, integrative, and patient-centric approaches to disease prevention and treatment, incorporating the standard clinical data with advanced "omics". These data help with the phenotypically adjudicated individualization of treatment. The major objective of this review was to compile the evolving clinically relevant tools of precision medicine that can help with the evidence-based precise individualized management of cardiac diseases with the highest DALY. The field of cardiology is evolving to provide targeted therapy, which is crafted as per the "omics", involving genomics, transcriptomics, epigenomics, proteomics, metabolomics, and microbiomics, for deep phenotyping. Research for individualizing therapy in heart diseases with the highest DALY has helped identify novel genes, biomarkers, proteins, and technologies to aid early diagnosis and treatment. Precision medicine has helped in targeted management, allowing early diagnosis, timely precise intervention, and exposure to minimal side effects. Despite these great impacts, overcoming the barriers to implementing precision medicine requires addressing the economic, cultural, technical, and socio-political issues. Precision medicine is proposed to be the future of cardiovascular medicine and holds the potential for a more efficient and personalized approach to the management of cardiovascular diseases, contrary to the standardized blanket approach.

The adducin saga: pleiotropic genomic targets for precision medicine in human hypertension-vascular, renal, and cognitive diseases

Hypertension is a leading risk factor for stroke, heart disease, chronic kidney disease, vascular cognitive impairment, and Alzheimer's disease. Previous genetic studies have nominated hundreds of genes linked to hypertension, and renal and cognitive diseases. Some have been advanced as candidate genes by showing that they can alter blood pressure or renal and cerebral vascular function in knockout animals; however, final validation of the causal variants and underlying mechanisms has remained elusive. This review chronicles 40 years of work, from the initial identification of adducin (ADD) as an ACTIN-binding protein suggested to increase blood pressure in Milan hypertensive rats, to the discovery of a mutation in ADD1 as a candidate gene for hypertension in rats that were subsequently linked to hypertension in man. More recently, a recessive K572Q mutation in ADD3 was identified in Fawn-Hooded Hypertensive (FHH) and Milan Normotensive (MNS) rats that develop renal disease, which is absent in resistant strains. ADD3 dimerizes with ADD1 to form functional ADD protein. The mutation in ADD3 disrupts a critical ACTIN-binding site necessary for its interactions with actin and spectrin to regulate the cytoskeleton. Studies using Add3 KO and transgenic strains, as well as a genetic complementation study in FHH and MNS rats, confirmed that the K572Q mutation in ADD3 plays a causal role in altering the myogenic response and autoregulation of renal and cerebral blood flow, resulting in increased susceptibility to hypertension-induced renal disease and cerebral vascular and cognitive dysfunction.

Ouabain inhibitor rostafuroxin attenuates dextromethorphan-induced manic potential

Dextromethorphan (DM) abuse produces mania-like symptoms in humans. ERK/Akt signaling activation involved in manic potential can be attenuated by the inhibition of ouabain-like cardiac steroids. In this study, increased phosphorylations of ERK/Akt and hyperlocomotion induced by DM (30 mg/kg, i.p./day × 7) were significantly protected by the ouabain inhibitor rostafuroxin (ROSTA), suggesting that DM induces the manic potential. ROSTA significantly attenuated DM-induced protein kinase C δ (PKCδ) phosphorylation, GluN2B (i.e., MDA receptor subunit) expression, and phospho-PKCδ/GluN2B interaction. DM instantly upregulated the nuclear factor erythroid-2-related factor 2 (Nrf2)-dependent system. However, DM reduced Nrf2 nuclear translocation, Nrf2 DNA binding activity, γ-glutamylcysteine mRNA expression, and subsequent GSH/GSSG level and enhanced oxidative parameters following 1-h of administration. ROSTA, PKCδ inhibitor rottlerin, and GluN2B inhibitor traxoprodil significantly attenuated DM-induced alterations in Nrf2-related redox parameters and locomotor activity induced by DM in wild-type mice. Importantly, in PKCδ knockout mice, DM failed to alter the above parameters. Further, ROSTA and traxoprodil also failed to enhance PKCδ depletion effect, suggesting that PKCδ is a critical target for the anti-manic potential of ROSTA or GluN2B antagonism. Our results suggest that ROSTA inhibits DM-induced manic potential by attenuating ERK/Akt activation, GluN2B/PKCδ signalings, and Nrf2-dependent system.

Antihypertensive treatment guided by genetics: PEARL-HT, the randomized proof-of-concept trial comparing rostafuroxin with losartan

We compared a standard antihypertensive losartan treatment with a pharmacogenomics-guided rostafuroxin treatment in never-treated Caucasian and Chinese patients with primary hypertension. Rostafuroxin is a digitoxigenin derivative that selectively disrupts the binding to the cSrc-SH2 domain of mutant α-adducin and of the ouabain-activated Na-K pump at 10^-11 M. Of 902 patients screened, 172 were enrolled in Italy and 107 in Taiwan. After stratification for country and genetic background, patients were randomized to rostafuroxin or losartan, being the difference in the fall in office systolic blood pressure (OSBP) after 2-month treatment the primary endpoint. Three pharmacogenomic profiles (P) were examined, considering: P1, adding to the gene variants included in the subsequent P2, the variants detected by post-hoc analysis of a previous trial; P2, variants of genes encoding enzymes for endogenous ouabain (EO) synthesis (LSS and HSD3B1), EO transport (MDR1/ABCB1), adducin (ADD1 and ADD3); P3, variants of the LSS gene only. In Caucasians, the group differences (rostafuroxin 50 μg minus losartan 50 mg in OSBP mmHg) were significant both in P2 adjusted for genetic heterogeneity (P2a) and P3 LSS rs2254524 AA [9.8 (0.6-19.0), P = 0.038 and 13.4 (25.4-2.5), P = 0.031, respectively]. In human H295R cells transfected with LSS A and LSS C variants, the EO production was greater in the former (P = 0.038); this difference was abolished by rostafuroxin at 10^-11 M. Chinese patients had a similar drop in OSBP to Caucasians with losartan but no change in OSBP with rostafuroxin. These results show that genetics may guide drug treatment for primary hypertension in Caucasians.

Role of γ-adducin in actin cytoskeleton rearrangements in podocyte pathophysiology

We recently reported that the enhanced susceptibility to chronic kidney disease (CKD) in the fawn-hooded hypertensive (FHH) rat is caused, at least in part, by a mutation in γ-adducin (ADD3) that attenuates renal vascular function. The present study explored whether Add3 contributes to the modulation of podocyte structure and function using FHH and FHH.Add3 transgenic rats. The expression of ADD3 on the membrane of primary podocytes isolated from FHH was reduced compared with FHH.Add3 transgenic rats. We found that F-actin nets, which are typically localized in the lamellipodia, replaced unbranched stress fibers in conditionally immortalized mouse podocytes transfected with Add3 Dicer-substrate short interfering RNA (DsiRNA) and primary podocytes isolated from FHH rats. There were increased F/G-actin ratios and expression of the Arp2/3 complexes throughout FHH podocytes in association with reduced synaptopodin and RhoA but enhanced Rac1 and CDC42 expression in the renal cortex, glomeruli, and podocytes of FHH rats. The expression of nephrin at the slit diaphragm and the levels of focal adhesion proteins integrin-α3 and integrin-β1 were decreased in the glomeruli of FHH rats. Cell migration was enhanced and adhesion was reduced in podocytes of FHH rats as well as in immortalized mouse podocytes transfected with Add3 DsiRNA. Mean arterial pressures were similar in FHH and FHH.Add3 transgenic rats at 16 wk of age; however, FHH rats exhibited enhanced proteinuria associated with podocyte foot process effacement. These results demonstrate that reduced ADD3 function in FHH rats alters baseline podocyte pathophysiology by rearrangement of the actin cytoskeleton at the onset of proteinuria in young animals.

The Na/K-ATPase α1 and c-Src form signaling complex under native condition: A crosslinking approach

The protein-protein interactions amongst the Na/K-ATPase α1 subunit, c-Src, and caveolin-1 (cav-1) are essential for the Na/K-ATPase signaling functions. However, there are arguments concerning the interaction model. The present study aims to clarify the interactions amongst the endogenous native proteins in live cells under native resting condition. Under native condition, Blue Native-PAGE and Blue Native-PAGE/SDS-PAGE 2D analyses demonstrated co-existence of the α1 subunit and c-Src in same protein complex, as well as a direct interaction between the α1 subunit and c-Src. By comparison of cleavable and non-cleavable cysteine-cysteine crosslinked samples, capillary immunoblotting analysis demonstrated that depletion of Src kinase family members (c-Src, Yes, and Fyn) or cav-1 clearly reduced the interactions of the α1 subunit with proteins, but depletion of cav-1 did not affect the interaction of c-Src with the α1 subunit. The data indicated that there are direct interactions between the α1 subunit and c-Src as well as between the α1 subunit and cav-1, but argued about the interaction between c-Src and cav-1 under the condition. Furthermore, the data also indicated the existence of different protein complexes containing the α1 subunit and c-Src, which might have different signaling functions.

A Review of the Epidemiological Evidence for Adducin Family Gene Polymorphisms and Hypertension

Hypertension is one of the most common cardiovascular diseases that seriously endangers human health and has become a significant public health problem worldwide. In the vast majority of patients, the cause of hypertension is unknown, called essential hypertension (EH), accounting for more than 95% of total hypertension. Epidemiological and genetic studies of humans and animals provide strong evidence of a causal relationship between high salt intake and hypertension. Adducin is one of the important candidate genes for essential hypertension. Adducin is a heterodimeric or heterotetrameric protein that consists of α, β, and γ subunits; the three subunits are encoded by genes (ADD1, ADD2, and ADD3) that map to three different chromosomes. Animal model experiments and clinical studies suggest that changes in single-nucleotide polymorphisms (SNPs) at part of the adducin family gene increase the Na⁺-K⁺-ATPase activity of the renal tubular basement membrane and increase the reabsorption of Na⁺ by renal tubular epithelial cells, which may cause hypertension. This review makes a summary on the structure, function, and mechanism of adducin and the role of adducin on the onset of EH, providing a basis for the early screening, prevention, and treatment of EH.

Endogenous ouabain and aldosterone are coelevated in the circulation of patients with essential hypertension

OBJECTIVE

In the setting of normal sodium (Na) intake, many patients with hypertension have inappropriately elevated plasma aldosterone (Aldo) levels and may be at increased risk for tissue damage. Moreover, other adrenocortical steroids, including endogenous ouabain can stimulate tissue damage. As endogenous ouabain is often elevated in chronically Na-loaded states, is a vasoconstrictor, raises blood pressure (BP), and also promotes tissue fibrosis, we investigated the extent to which plasma Aldo and endogenous ouabain were coelevated among naïve hypertensive patients (NHP). We also investigated the impact of an acute salt load on these steroids, BP, and renal function.

METHODS

NHP (590) were grouped in tertiles based on their baseline plasma Aldo (mean ± SEM first 7.59 ± 0.18, versus third 24.15 ± 0.31 ng/dl). Baseline plasma renin activity (2.4 ± 0.1 versus 1.2 ± 0.1 ng/ml per h, P < 0.001), endogenous ouabain (268 ± 14.9 pmol/l versus 239.0 ± 13.6 pmol, P < 0.01) and DBP (91.9 ± 0.76 versus 89.6 ± 0.71 mmHg, P = 0.017) were higher in NHP in the third versus the first Aldo tertile, respectively.

RESULTS

Acute Na loading showed that the BP of the third Aldo tertile NHP was especially salt-sensitive (slope of pressure-natriuresis relationship 0.015 ± 0.002 versus 0.003 ± 0.001 μEq/mmHg per min, P = 0.00024 after adjustment for sex, BMI, and age). Regression analyses showed that plasma Aldo and endogenous ouabain were linearly related (β = 0.181, P = 0.0003).

CONCLUSION

Among patients with essential hypertension, circulating endogenous ouabain and Aldo are typically coelevated and their BP is salt-sensitive. In conditions where Aldo is inappropriately elevated, both Aldo and endogenous ouabain may contribute to adverse cardiovascular and renal outcomes.

Protein Interaction and Na/K-ATPase-Mediated Signal Transduction

The Na/K-ATPase (NKA), or Na pump, is a member of the P-type ATPase superfamily. In addition to pumping ions across cell membrane, it is engaged in assembly of multiple protein complexes in the plasma membrane. This assembly allows NKA to perform many non-pumping functions including signal transduction that are important for animal physiology and disease progression. This article will focus on the role of protein interaction in NKA-mediated signal transduction, and its potential utility as target for developing new therapeutics.

Ouabain Contributes to Kidney Damage in a Rat Model of Renal Ischemia-Reperfusion Injury

Warm renal ischemia performed during partial nephrectomy has been found to be associated with kidney disease. Since endogenous ouabain (EO) is a neuro-endocrine hormone involved in renal damage, we evaluated the role of EO in renal ischemia-reperfusion injury (IRI). We measured plasma and renal EO variations and markers of glomerular and tubular damage (nephrin, KIM-1, Kidney-Injury-Molecule-1, α1 Na-K ATPase) and the protective effect of the ouabain inhibitor, rostafuroxin. We studied five groups of rats: (1) normal; (2) infused for eight weeks with ouabain (30 µg/kg/day, OHR) or (3) saline; (4) ouabain; or (5) saline-infused rats orally treated with 100 µg/kg/day rostafuroxin for four weeks. In group 1, 2-3 h after IRI, EO increased in ischemic kidneys while decreased in plasma. Nephrin progressively decreased and KIM-1 mRNA increased starting from 24 h. Ouabain infusion (group 2) increased blood pressure (from 111.7 to 153.4 mmHg) and ouabain levels in plasma and kidneys. In OHR ischemic kidneys at 120 h from IRI, nephrin, and KIM-1 changes were greater than those detected in the controls infused with saline (group 3). All these changes were blunted by rostafuroxin treatment (groups 4 and 5). These findings support the role of EO in IRI and suggest that rostafuroxin pre-treatment of patients before partial nephrectomy with warm ischemia may reduce IRI, particularly in those with high EO.

Personalized Therapy of Hypertension: the Past and the Future

During the past 20 years, the studies on genetics or pharmacogenomics of primary hypertension provided interesting results supporting the role of genetics, but no actionable finding ready to be translated into personalized medicine. Two types of approaches have been applied: a "hypothesis-driven" approach on the candidate genes, coding for proteins involved in the biochemical machinery underlying the regulation of BP, and an "unbiased hypothesis-free" approach with GWAS, based on the randomness principles of frequentist statistics. During the past 10-15 years, the application of the latter has overtaken the application of the former leading to an enlargement of the number of previously unknown candidate loci or genes but without any actionable result for the therapy of hypertension. In the present review, we summarize the results of our hypothesis-driven approach based on studies carried out in rats with genetic hypertension and in humans with essential hypertension at the pre-hypertensive and early hypertensive stages. These studies led to the identification of mutant adducin and endogenous ouabain as candidate genetic-molecular mechanisms in both species. Rostafuroxin has been developed for its ability to selectively correct Na(+) pump abnormalities sustained by the two abovementioned mechanisms and to selectively reduce BP in rats and in humans carrying the gene variants underlying the mutant adducin and endogenous ouabain (EO) effects. A clinical trial is ongoing to substantiate these findings. Future studies should apply both the candidate gene and GWAS approaches to fully exploit the potential of genetics in optimizing the personalized therapy.

Do Src Kinase and Caveolin Interact Directly with Na,K-ATPase?

Much evidence points to a role of Na,K-ATPase in ouabain-dependent signal transduction. Based on experiments with different cell lines and native tissue membranes, a current hypothesis postulates direct interactions between the Na,K-ATPase and Src kinase (non-receptor tyrosine kinase). Na,K-ATPase is proposed to bind Src kinase and inhibit its activity, whereas ouabain, the specific Na,K-ATPase inhibitor, binds and stabilizes the E2 conformation, thus exposing the Src kinase domain and its active site Tyr-418 for activation. Ouabain-dependent signaling is thought to be mediated within caveolae by a complex consisting of Na,K-ATPase, caveolin, and Src kinase. In the current work, we have looked for direct interactions utilizing purified recombinant Na,K-ATPase (human α1β1FXYD1 or porcine α1D369Nβ1FXYD1) and purified human Src kinase and human caveolin 1 or interactions between these proteins in native membrane vesicles isolated from rabbit kidney. By several independent criteria and techniques, no stable interactions were detected between Na,K-ATPase and purified Src kinase. Na,K-ATPase was found to be a substrate for Src kinase phosphorylation at Tyr-144. Clear evidence for a direct interaction between purified human Na,K-ATPase and human caveolin was obtained, albeit with a low molar stoichiometry (1:15-30 caveolin 1/Na,K-ATPase). In native renal membranes, a specific caveolin 14-5 oligomer (95 kDa) was found to be in direct interaction with Na,K-ATPase. We inferred that a small fraction of the renal Na,K-ATPase molecules is in a ∼1:1 complex with a caveolin 14-5 oligomer. Thus, overall, whereas a direct caveolin 1/Na,K-ATPase interaction is confirmed, the lack of direct Src kinase/Na,K-ATPase binding requires reassessment of the mechanism of ouabain-dependent signaling.

Pharmacogenomics considerations in the control of hypertension

The response to antihypertensive therapy is very heterogeneous and the need by the physicians to account for it has driven much interest in pharmacogenomics of antihypertensive drugs. The Human Genome Project and the initiatives in genomics that followed, generated a huge number of genetic data that furnished the tools to explore the genotype-phenotype association in candidate genes and at genome-wide level. In spite of the efforts and the great number of publications, pharmacogenomics of antihypertensive drugs is far from being used in clinical practice. In this review, we analyze the main findings available in PubMed from 2010 to 2015, in relation to the major classes of antihypertensive drugs. We also describe a new Phase II drug that targets two specific hypertension predisposing mechanisms.

Rostafuroxin ameliorates endothelial dysfunction and oxidative stress in resistance arteries from deoxycorticosterone acetate-salt hypertensive rats: the role of Na+K+-ATPase/ cSRC pathway

AIMS

Endogenous ouabain is elevated in patients and experimental models of hypertension and is associated with elevated mortality. In this context, it is reasonable to assume that a new antihypertensive drug that inhibits the deleterious effects of endogenous ouabain may be a specific pharmacological tool for hypertension treatment. Here, we investigated the effects of rostafuroxin (ROSTA), an ouabain inhibitor, on SBP, endothelial dysfunction and oxidative stress in deoxycorticosterone acetate (DOCA)-salt rats.

METHODS AND RESULTS

A hypertensive model was established in uninephrectomized Wistar rats using DOCA-salt. After SBP stabilization, DOCA-salt rats were divided into two groups: DOCA-salt (control) and DOCA-salt treatment with ROSTA (1 mg/kg per day gavage, 3 weeks). The SBP was measured using the tail-cuff method, and vascular function was assessed in mesenteric-resistance arteries (MRAs) using a wire myograph. Nitric oxide and reactive oxygen species production were investigated. Western blot was performed to quantify protein expression. Our results indicated that ROSTA treatment decreased SBP, improved acetylcholine-induced relaxation via enhanced nitric oxide synthesis and bioavailability, decreased superoxide anion generation from NAD(P)H oxidase and cyclooxygenase-2 and reduced cytoplasmic tyrosine kinase Src phosphorylation without changes in NaKATPase activity in MRA from DOCA-salt rats.

CONCLUSION

This study reports the critical role of endogenous ouabain in volume-dependent hypertension. In MRA from DOCA-salt rats, the binding of endogenous ouabain to NaK-ATPase results in downstream c-SRC activation, oxidative stress and endothelial dysfunction. Endogenous ouabain is a putative target for the treatment of hypertension, and ROSTA may represent a novel therapeutic approach.

Rostafuroxin protects from podocyte injury and proteinuria induced by adducin genetic variants and ouabain

Glomerulopathies are important causes of morbidity and mortality. Selective therapies that address the underlying mechanisms are still lacking. Recently, two mechanisms, mutant β-adducin and ouabain, have been found to be involved in glomerular podocytopathies and proteinuria through nephrin downregulation. The main purpose of the present study was to investigate whether rostafuroxin, a novel antihypertensive agent developed as a selective inhibitor of Src-SH2 interaction with mutant adducin- and ouabain-activated Na,K-ATPase, may protect podocytes from adducin- and ouabain-induced effects, thus representing a novel pharmacologic approach for the therapy of podocytopathies and proteinuria caused by the aforementioned mechanisms. To study the effect of rostafuroxin on podocyte protein changes and proteinuria, mice carrying mutant β-adducin and ouabain hypertensive rats were orally treated with 100 μg/kg per day rostafuroxin. Primary podocytes from congenic rats carrying mutant α-adducin or β-adducin (NB) from Milan hypertensive rats and normal rat podocytes incubated with 10(-9) M ouabain were cultured with 10(-9) M rostafuroxin. The results indicated that mutant β-adducin and ouabain caused podocyte nephrin loss and proteinuria in animal models. These alterations were reproduced in primary podocytes from NB rats and normal rats incubated with ouabain. Treatment of animals, or incubation of cultured podocytes with rostafuroxin, reverted mutant β-adducin- and ouabain-induced effects on nephrin protein expression and proteinuria. We conclude that rostafuroxin prevented podocyte lesions and proteinuria due to mutant β-adducin and ouabain in animal models. This suggests a potential therapeutic effect of rostafuroxin in patients with glomerular disease progression associated with these two mechanisms.

cGMP-dependent protein kinase 1 polymorphisms underlie renal sodium handling impairment

Defective pressure-natriuresis related to abnormalities in the natriuretic response has been associated with hypertension development. A major signaling pathway mediating pressure natriuresis involves the cGMP-dependent protein kinase 1 (PRKG1) that, once activated by Src kinase, inhibits renal Na(+) reabsorption via a direct action on basolateral Na-K ATPase and luminal Na-H exchanger type 3, as shown in renal tubuli of animals. Because a clear implication of PRKG1 in humans is still lacking, here we addressed whether PRKG1 polymorphisms affect pressure-natriuresis in patients. Naive hypertensive patients (n = 574), genotyped for PRKG1 rs1904694, rs7897633, and rs7905063 single nucleotide polymorphisms (SNPs), underwent an acute Na(+) loading, and the slope of the pressure-natriuresis relationship between blood pressure and Na(+) excretion was calculated. The underlying molecular mechanism was investigated by immunoblotting protein quantifications in human kidneys. The results demonstrate that the PRKG1 risk haplotype GAT (rs1904694, rs7897633, rs7905063, respectively) associates with a rightward shift of the pressure-natriuresis curve (0.017 ± 0.004 μEq/mm Hg per minute) compared with the ACC (0.0013 ± 0.003 μEq/mm Hg per minute; P = 0.001). In human kidneys, a positive correlation of protein expression levels between PRKG1 and Src (r = 0.83; P<0.001) or α1 Na-K ATPase (r = 0.557; P<0.01) and between α1 Na-K ATPase and Na-H exchanger type 3 (r = 0.584; P<0.01) or Src (r = 0.691; P<0.001) was observed in patients carrying PRKG1 risk GAT (n = 23) but not ACC (n = 14) variants. A functional signaling complex among PRKG1, α1 Na-K ATPase, and Src was shown by immunoprecipitation from human renal caveolae. These findings indicate that PRKG1 risk alleles associate with salt-sensitivity related to a loss of the inhibitory control of renal Na(+) reabsorption, suggestive of a blunt pressure-natriuresis response.

Genome sequencing reveals loci under artificial selection that underlie disease phenotypes in the laboratory rat

Large numbers of inbred laboratory rat strains have been developed for a range of complex disease phenotypes. To gain insights into the evolutionary pressures underlying selection for these phenotypes, we sequenced the genomes of 27 rat strains, including 11 models of hypertension, diabetes, and insulin resistance, along with their respective control strains. Altogether, we identified more than 13 million single-nucleotide variants, indels, and structural variants across these rat strains. Analysis of strain-specific selective sweeps and gene clusters implicated genes and pathways involved in cation transport, angiotensin production, and regulators of oxidative stress in the development of cardiovascular disease phenotypes in rats. Many of the rat loci that we identified overlap with previously mapped loci for related traits in humans, indicating the presence of shared pathways underlying these phenotypes in rats and humans. These data represent a step change in resources available for evolutionary analysis of complex traits in disease models.

Diagnostic tools for hypertension and salt sensitivity testing

PURPOSE OF REVIEW

One-third of the world's population has hypertension and it is responsible for almost 50% of deaths from stroke or coronary heart disease. These statistics do not distinguish salt-sensitive from salt-resistant hypertension or include normotensives who are salt-sensitive even though salt sensitivity, independent of blood pressure, is a risk factor for cardiovascular and other diseases, including cancer. This review describes new personalized diagnostic tools for salt sensitivity.

RECENT FINDINGS

The relationship between salt intake and cardiovascular risk is not linear, but rather fits a J-shaped curve relationship. Thus, a low-salt diet may not be beneficial to everyone and may paradoxically increase blood pressure in some individuals. Current surrogate markers of salt sensitivity are not adequately sensitive or specific. Tests in the urine that could be surrogate markers of salt sensitivity with a quick turn-around time include renal proximal tubule cells, exosomes, and microRNA shed in the urine.

SUMMARY

Accurate testing of salt sensitivity is not only laborious but also expensive, and with low patient compliance. Patients who have normal blood pressure but are salt-sensitive cannot be diagnosed in an office setting and there are no laboratory tests for salt sensitivity. Urinary surrogate markers for salt sensitivity are being developed.

Na(+),K (+)-ATPase as a docking station: protein-protein complexes of the Na(+),K (+)-ATPase

The Na(+),K(+)-ATPase, or sodium pump, is well known for its role in ion transport across the plasma membrane of animal cells. It carries out the transport of Na(+) ions out of the cell and of K(+) ions into the cell and thus maintains electrolyte and fluid balance. In addition to the fundamental ion-pumping function of the Na(+),K(+)-ATPase, recent work has suggested additional roles for Na(+),K(+)-ATPase in signal transduction and biomembrane structure. Several signaling pathways have been found to involve Na(+),K(+)-ATPase, which serves as a docking station for a fast-growing number of protein interaction partners. In this review, we focus on Na(+),K(+)-ATPase as a signal transducer, but also briefly discuss other Na(+),K(+)-ATPase protein-protein interactions, providing a comprehensive overview of the diverse signaling functions ascribed to this well-known enzyme.

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.

Traditional Chinese medicine as dual guardians against hypertension and cancer?

This study utilizes the comprehensive traditional Chinese medicine database TCM Database@Taiwan ( http://tcm.cmu.edu.tw/ ) in conjunction with structure-based and ligand-based drug design to identify multi-function Src inhibitors. The three potential TCM candidates identified as having suitable docking conformations and bioactivity profiles were Angeliferulate, (3R)-2'-hydroxy-3',4'-dimethoxyisoflavan-7-O-beta-D-glucoside (HMID), and 3-[2',6-dihydroxy-5'-(2-propenyl)[1,1'-biphenyl]3-yl]-(E)-2-propenoic acid (3PA). Molecular dynamics simulation demonstrated that the TCM candidates have more stable interactions with the cleft and in complex with Src kinase compared to Saracatinib. Angeliferulate and HMID, both originated from Angelica sinensis, not only interact with Lys298 and amino acids from different loops in the cleft, but also with Asp407 located on the activation loop. These interactions are important to reduce the opening of the activation loop due to phosphorylation, hence stabilize the Src kinase cleft structure and inhibit activation. The TCM candidates also exhibited high affinity to other cancer-related target proteins (EGFR, HER2, and HSP90). Our observations suggest that the TCM candidates might have multi-targeting effects in hypertension and cancer.

Salt-inducible kinase 1 regulates E-cadherin expression and intercellular junction stability

The protein kinase liver kinase B1 (LKB1) regulates cell polarity and intercellular junction stability. Also, LKB1 controls the activity of salt-inducible kinase 1 (SIK1). The role and relevance of SIK1 and its downstream effectors in linking the LKB1 signals within these processes are partially understood. We hypothesize that SIK1 may link LKB1 signals to the maintenance of epithelial junction stability by regulating E-cadherin expression. Results from our studies using a mouse lung alveolar epithelial (MLE-12) cell line or human renal proximal tubule (HK2) cell line transiently or stably lacking the expression of SIK1 (using SIK1 siRNAs or shRNAs), or with its expression abrogated (sik1(+/+) vs. sik1(-/-) mice), indicate that suppression of SIK1 (∼40%) increases the expression of the transcriptional repressors Snail2 (∼12-fold), Zeb1 (∼100%), Zeb2 (∼50%), and TWIST (∼20-fold) by activating cAMP-response element binding protein. The lack of SIK1 and activation of transcriptional repressors decreases the availability of E-cadherin (mRNA and protein expression by ∼100 and 80%, respectively) and the stability of intercellular junctions in epithelia (decreases in transepithelial resistance). Furthermore, LKB1-mediated increases in E-cadherin expression are impaired in cells where SIK1 has been disabled. We conclude that SIK1 is a key regulator of E-cadherin expression, and thereby contributes to the stability of intercellular junctions.

In silico investigation of potential SRC kinase ligands from traditional Chinese medicine

Src kinase is an attractive target for drug development based on its established relationship with cancer and possible link to hypertension. The suitability of traditional Chinese medicine (TCM) compounds as potential drug ligands for further biological evaluation was investigated using structure-based, ligand-based, and molecular dynamics (MD) analysis. Isopraeroside IV, 9alpha-hydroxyfraxinellone-9-O-beta-D-glucoside (9HFG) and aurantiamide were the top three TCM candidates identified from docking. Hydrogen bonds and hydrophobic interactions were the primary forces governing docking stability. Their stability with Src kinase under a dynamic state was further validated through MD and torsion angle analysis. Complexes formed by TCM candidates have lower total energy estimates than the control Sacaratinib. Four quantitative-structural activity relationship (QSAR) in silico verifications consistently suggested that the TCM candidates have bioactive properties. Docking conformations of 9HFG and aurantiamide in the Src kinase ATP binding site suggest potential inhibitor-like characteristics, including competitive binding at the ATP binding site (Lys295) and stabilization of the catalytic cleft integrity. The TCM candidates have significantly lower ligand internal energies and are estimated to form more stable complexes with Src kinase than Saracatinib. Structure-based and ligand-based analysis support the drug-like potential of 9HFG and aurantiamide and binding mechanisms reveal the tendency of these two candidates to compete for the ATP binding site.

Polymorphisms, hypertension and thiazide diuretics

It is 10 years since the discovery of the human genome; however, the study of the influence of genetic variants on drug effect - pharmacogenomics - has so far failed to create a major impact on day-to-day prescription practices. In the present article we analyze the main findings in candidate gene variants, gene combinations and whole-genome scans in relation to diuretic treatment. A critical analysis of the main reasons for some contrasting results will be discussed. The hypertension phases, in clinical trials dealing with genes and related pathophysiological mechanisms, may account for these inconsistent findings. The use of previously untreated versus treated patients is addressed. Finally, a positive study with a new genetic molecular strategy is described.

Increased arterial smooth muscle Ca2+ signaling, vasoconstriction, and myogenic reactivity in Milan hypertensive rats

The Milan hypertensive strain (MHS) rats are a genetic model of hypertension with adducin gene polymorphisms linked to enhanced renal tubular Na(+) reabsorption. Recently we demonstrated that Ca(2+) signaling is augmented in freshly isolated mesenteric artery myocytes from MHS rats. This is associated with greatly enhanced expression of Na(+)/Ca(2+) exchanger-1 (NCX1), C-type transient receptor potential (TRPC6) protein, and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2) compared with arteries from Milan normotensive strain (MNS) rats. Here, we test the hypothesis that the enhanced Ca(2+) signaling in MHS arterial smooth muscle is directly reflected in augmented vasoconstriction [myogenic and phenylephrine (PE)-evoked responses] in isolated mesenteric small arteries. Systolic blood pressure was higher in MHS (145 ± 1 mmHg) than in MNS (112 ± 1 mmHg; P < 0.001; n = 16 each) rats. Pressurized mesenteric resistance arteries from MHS rats had significantly augmented myogenic tone and reactivity and enhanced constriction to low-dose (1-100 nM) PE. Isolated MHS arterial myocytes exhibited approximately twofold increased peak Ca(2+) signals in response to 5 μM PE or ATP in the absence and presence of extracellular Ca(2+). These augmented responses are consistent with increased vasoconstrictor-evoked sarcoplasmic reticulum (SR) Ca(2+) release and increased Ca(2+) entry, respectively. The increased SR Ca(2+) release correlates with a doubling of inositol 1,4,5-trisphosphate receptor type 1 and tripling of SERCA2 expression. Pressurized MHS arteries also exhibited a ∼70% increase in 100 nM ouabain-induced vasoconstriction compared with MNS arteries. These functional alterations reveal that, in a genetic model of hypertension linked to renal dysfunction, multiple mechanisms within the arterial myocytes contribute to enhanced Ca(2+) signaling and myogenic and vasoconstrictor-induced arterial constriction. MHS rats have elevated plasma levels of endogenous ouabain, which may initiate the protein upregulation and enhanced Ca(2+) signaling. These molecular and functional changes provide a mechanism for the increased peripheral vascular resistance (whole body autoregulation) that underlies the sustained hypertension.

Loss-of-function and gain-of-function phenotypes of stomatocytosis mutant RhAG F65S

Four patients with overhydrated cation leak stomatocytosis (OHSt) exhibited the heterozygous RhAG missense mutation F65S. OHSt erythrocytes were osmotically fragile, with elevated Na and decreased K contents and increased cation channel-like activity. Xenopus oocytes expressing wild-type RhAG and RhAG F65S exhibited increased ouabain and bumetanide-resistant uptake of Li(+) and (86)Rb(+), with secondarily increased (86)Rb(+) influx sensitive to ouabain and to bumetanide. Increased RhAG-associated (14)C-methylammonium (MA) influx was severely reduced in RhAG F65S-expressing oocytes. RhAG-associated influxes of Li(+), (86)Rb(+), and (14)C-MA were pharmacologically distinct, and Li(+) uptakes associated with RhAG and RhAG F65S were differentially inhibited by NH(4)(+) and Gd(3+). RhAG-expressing oocytes were acidified and depolarized by 5 mM bath NH(3)/NH(4)(+), but alkalinized and depolarized by subsequent bath exposure to 5 mM methylammonium chloride (MA/MA(+)). RhAG F65S-expressing oocytes exhibited near-wild-type responses to NH(4)Cl, but MA/MA(+) elicited attenuated alkalinization and strong hyperpolarization. Expression of RhAG or RhAG F65S increased steady-state cation currents unaltered by bath Li(+) substitution or bath addition of 5 mM NH(4)Cl or MA/MA(+). These oocyte studies suggest that 1) RhAG expression increases oocyte transport of NH(3)/NH(4)(+) and MA/MA(+); 2) RhAG F65S exhibits gain-of-function phenotypes of increased cation conductance/permeability, and loss-of-function phenotypes of decreased and modified MA/MA(+) transport, and decreased NH(3)/NH(4)(+)-associated depolarization; and 3) RhAG transports NH(3)/NH(4)(+) and MA/MA(+) by distinct mechanisms, and/or the substrates elicit distinct cellular responses. Thus, RhAG F65S is a loss-of-function mutation for amine transport. The altered oocyte intracellular pH, membrane potential, and currents associated with RhAG or RhAG F65S expression may reflect distinct transport mechanisms.

The emerging role for rat models in gene discovery

Rat models have been used for many decades to study physiological and pathophysiological mechanisms. Prior to the release of the rat genome and new technologies for targeting gene manipulation, the rat had been the underdog in the genomics era, despite the abundance of physiological data compared to the mouse. The overarching goal of biomedical research is to improve health and advance medical science. Translating human disease gene discovery and validation in the rat, through the use of emerging technologies and integrated tools and databases, is providing power to understand the genetics, environmental influences, and biology of disease. In this review we briefly outline the rat models, bioinformatics tools, and technologies that are changing the landscape of translational research. The strategies used to translate disease traits to genes to function, and, ultimately, to improve human health is discussed. Finally, our perspective on how rat models will continue to positively impact biomedical research is provided.

Adducin- and ouabain-related gene variants predict the antihypertensive activity of rostafuroxin, part 2: clinical studies

Twenty years of genetic studies have not contributed to improvement in the clinical management of primary arterial hypertension. Genetic heterogeneity, epistatic-environmental-biological interactions, and the pathophysiological complexity of hypertension have hampered the clinical application of genetic findings. In the companion article, we furnished data from rodents and human cells demonstrating two hypertension-triggering mechanisms--variants of adducin and elevated concentrations of endogenous ouabain (within a particular range)--and their selective inhibition by the drug rostafuroxin. Here, we have investigated the relationship between variants of genes encoding enzymes for ouabain synthesis [LSS (lanosterol synthase) and HSD3B1 (hydroxy-δ-5-steroid dehydrogenase, 3β- and steroid δ-isomerase 1)], ouabain transport {MDR1/ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1]}, and adducin activity [ADD1 (adducin 1) and ADD3], and the responses to antihypertensive medications. We determined the presence of these variants in newly recruited, never-treated patients. The genetic profile defined by these variants predicted the antihypertensive effect of rostafuroxin (a mean placebo-corrected systolic blood pressure fall of 14 millimeters of mercury) but not that of losartan or hydrochlorothiazide. The magnitude of the rostafuroxin antihypertensive effect was twice that of antihypertensive drugs recently tested in phase 2 clinical trials. One-quarter of patients with primary hypertension display these variants of adducin or concentrations of endogenous ouabain and would be expected to respond to therapy with rostafuroxin. Because the mechanisms that are inhibited by rostafuroxin also underlie hypertension-related organ damage, this drug may also reduce the cardiovascular risk in these patients beyond that expected by the reduction in systolic blood pressure alone.