Association of NEDD4L Ubiquitin Ligase With Essential Hypertension

NEDD4 and NEDD4L: Ubiquitin Ligases Closely Related to Digestive Diseases

Protein ubiquitination is an enzymatic cascade reaction and serves as an important protein post-translational modification (PTM) that is involved in the vast majority of cellular life activities. The key enzyme in the ubiquitination process is E3 ubiquitin ligase (E3), which catalyzes the binding of ubiquitin (Ub) to the protein substrate and influences substrate specificity. In recent years, the relationship between the subfamily of neuron-expressed developmental downregulation 4 (NEDD4), which belongs to the E3 ligase system, and digestive diseases has drawn widespread attention. Numerous studies have shown that NEDD4 and NEDD4L of the NEDD4 family can regulate the digestive function, as well as a series of related physiological and pathological processes, by controlling the subsequent degradation of proteins such as PTEN, c-Myc, and P21, along with substrate ubiquitination. In this article, we reviewed the appropriate functions of NEDD4 and NEDD4L in digestive diseases including cell proliferation, invasion, metastasis, chemotherapeutic drug resistance, and multiple signaling pathways, based on the currently available research evidence for the purpose of providing new ideas for the prevention and treatment of digestive diseases.

NEDD4L is a promoter for angiogenesis and cell proliferation in human umbilical vein endothelial cells

Dysregulated angiogenesis leads to neovascularization, which can promote or exacerbate various diseases. Previous studies have proved that NEDD4L plays an important role in hypertension and atherosclerosis. Hence, we hypothesized that NEDD4L may be a critical regulator of endothelial cell (EC) function. This study aimed to define the role of NEDD4L in regulating EC angiogenesis and elucidate their underlying mechanisms. Loss- and gain-of-function of NEDD4L detected the angiogenesis and mobility role in human umbilical vein endothelial cells (HUVECs) using Matrigel tube formation assay, cell proliferation and migration. Pharmacological pathway inhibitors and western blot were used to determine the underlying mechanism of NEDD4L-regulated endothelial functions. Knockdown of NEDD4L suppressed tube formation, cell proliferation and cell migration in HUVECs, whereas NEDD4L overexpression promoted these functions. Moreover, NEDD4L-regulated angiogenesis and cell progression are associated with the phosphorylation of Akt, Erk1/2 and eNOS and the expression of VEGFR2 and cyclin D1 and D3. Mechanically, further evidence was confirmed by using Akt blocker MK-2206, Erk1/2 blocker U0126 and eNOS blocker L-NAME. Overexpression NEDD4L-promoted angiogenesis, cell migration and cell proliferation were restrained by these inhibitors. In addition, overexpression NEDD4L-promoted cell cycle-related proteins cyclin D1 and D3 were also suppressed by Akt blocker MK-2206, Erk1/2 blocker U0126 and eNOS blocker L-NAME. Our results demonstrated a novel finding that NEDD4L promotes angiogenesis and cell progression by regulating the Akt/Erk/eNOS pathways.

NEDD4L intramolecular interactions regulate its auto and substrate NaV1.5 ubiquitination

NEDD4L is a HECT-type E3 ligase that catalyzes the addition of ubiquitin to intracellular substrates such as the cardiac voltage-gated sodium channel, NaV1.5. The intramolecular interactions of NEDD4L regulate its enzymatic activity which is essential for proteostasis. For NaV1.5, this process is critical as alterations in Na+ current is involved in cardiac diseases including arrhythmias and heart failure. In this study, we perform extensive biochemical and functional analyses that implicate the C2 domain and the first WW-linker (1,2-linker) in the autoregulatory mechanism of NEDD4L. Through in vitro and electrophysiological experiments, the NEDD4L 1,2-linker was determined to be important in substrate ubiquitination of NaV1.5. We establish the preferred sites of ubiquitination of NEDD4L to be in the second WW-linker (2,3-linker). Interestingly, NEDD4L ubiquitinates the cytoplasmic linker between the first and second transmembrane domains of the channel (DI-DII) of NaV1.5. Moreover, we design a genetically encoded modulator of Nav1.5 that achieves Na+ current reduction using the NEDD4L HECT domain as cargo of a NaV1.5-binding nanobody. These investigations elucidate the mechanisms regulating the NEDD4 family and furnish a new molecular framework for understanding NaV1.5 ubiquitination.

Nedd4-2 up-regulation is associated with ACE2 ubiquitination in hypertension

AIMS

Angiotensin-converting enzyme 2 (ACE2) is a critical component of the compensatory renin-angiotensin system that is down-regulated during the development of hypertension, possibly via ubiquitination. However, little is known about the mechanisms involved in ACE2 ubiquitination in neurogenic hypertension. This study aimed at identifying ACE2 ubiquitination partners, establishing causal relationships and clinical relevance, and testing a gene therapy strategy to mitigate ACE2 ubiquitination in neurogenic hypertension.

METHODS AND RESULTS

Bioinformatics and proteomics were combined to identify E3 ubiquitin ligases associated with ACE2 ubiquitination in chronically hypertensive mice. In vitro gain/loss of function experiments assessed ACE2 expression and activity to validate the interaction between ACE2 and the identified E3 ligase. Mutation experiments were further used to generate a ubiquitination-resistant ACE2 mutant (ACE2-5R). Optogenetics, blood pressure telemetry, pharmacological blockade of GABAA receptors in mice expressing ACE2-5R in the bed nucleus of the stria terminalis (BNST), and capillary western analysis were used to assess the role of ACE2 ubiquitination in neurogenic hypertension. Ubiquitination was first validated as leading to ACE2 down-regulation, and Neural precursor cell-expressed developmentally down-regulated protein 4-2 (Nedd4-2) was identified as a E3 ligase up-regulated in hypertension and promoting ACE2 ubiquitination. Mutation of lysine residues in the C-terminal of ACE2 was associated with increased activity and resistance to angiotensin (Ang)-II-mediated degradation. Mice transfected with ACE2-5R in the BNST exhibited enhanced GABAergic input to the paraventricular nucleus (PVN) and a reduction in hypertension. ACE2-5R expression was associated with reduced Nedd4-2 levels in the BNST.

CONCLUSION

Our data identify Nedd4-2 as the first E3 ubiquitin ligase involved in ACE2 ubiquitination in Ang-II-mediated hypertension. We demonstrate the pivotal role of ACE2 on GABAergic neurons in the maintenance of an inhibitory tone to the PVN and the regulation of pre-sympathetic activity. These findings provide a new working model where Nedd4-2 could contribute to ACE2 ubiquitination, leading to the development of neurogenic hypertension and highlighting potential novel therapeutic strategies.

Research progress of Nedd4L in cardiovascular diseases

Post-translational modifications (PTMs) are a covalent processing process of proteins after translation. Proteins are capable of playing their roles only after being modified, so as to maintain the normal physiological function of cells. As a key modification of protein post-translational modification, ubiquitination is an essential element, which forms an enzyme-linked reaction through ubiquitin-activating enzyme, ubiquitin binding enzyme, and ubiquitin ligase, aiming to regulate the expression level and function of cellular proteins. Nedd4 family is the largest group of ubiquitin ligases, including 9 members, such as Nedd4-1, Nedd4L (Nedd4-2), WWP1, WWP2, ITCH, etc. They could bind to substrate proteins through their WW domain and play a dominant role in the ubiquitination process, and then participate in various pathophysiological processes of cardiovascular diseases (such as hypertension, myocardial hypertrophy, heart failure, etc.). At present, the role of Nedd4L in the cardiovascular field is not fully understood. This review aims to summarize the progress and mechanism of Nedd4L in cardiovascular diseases, and provide potential perspective for the clinical treatment or prevention of related cardiovascular diseases by targeting Nedd4L.

Function and Regulation of the Epithelial Na+ Channel ENaC

The Epithelial Na⁺ Channel, ENaC, comprised of 3 subunits (αβγ, or sometimes δβγENaC), plays a critical role in regulating salt and fluid homeostasis in the body. It regulates fluid reabsorption into the blood stream from the kidney to control blood volume and pressure, fluid absorption in the lung to control alveolar fluid clearance at birth and maintenance of normal airway surface liquid throughout life, and fluid absorption in the distal colon and other epithelial tissues. Moreover, recent studies have also revealed a role for sodium movement via ENaC in nonepithelial cells/tissues, such as endothelial cells in blood vessels and neurons. Over the past 25 years, major advances have been made in our understanding of ENaC structure, function, regulation, and role in human disease. These include the recently solved three-dimensional structure of ENaC, ENaC function in various tissues, and mutations in ENaC that cause a hereditary form of hypertension (Liddle syndrome), salt-wasting hypotension (PHA1), or polymorphism in ENaC that contributes to other diseases (such as cystic fibrosis). Moreover, great strides have been made in deciphering the regulation of ENaC by hormones (e.g., the mineralocorticoid aldosterone, glucocorticoids, vasopressin), ions (e.g., Na⁺ ), proteins (e.g., the ubiquitin-protein ligase NEDD4-2, the kinases SGK1, AKT, AMPK, WNKs & mTORC2, and proteases), and posttranslational modifications [e.g., (de)ubiquitylation, glycosylation, phosphorylation, acetylation, palmitoylation]. Characterization of ENaC structure, function, regulation, and role in human disease, including using animal models, are described in this article, with a special emphasis on recent advances in the field. © 2021 American Physiological Society. Compr Physiol 11:1-29, 2021.

Genome-Wide Methylation of Mild Cognitive Impairment in Mexican Americans Highlights Genes Involved in Synaptic Transport, Alzheimer's Disease-Precursor Phenotypes, and Metabolic Morbidities

The Mexican American population is among the fastest growing aging population and has a younger onset of cognitive decline. This group is also heavily burdened with metabolic conditions such as hypertension, diabetes, and obesity. Unfortunately, limited research has been conducted in this group. Understanding methylation alterations, which are influenced by both genetic and lifestyle factors, is key to identifying and addressing the root cause for mild cognitive impairment, a clinical precursor for dementia. We conducted an epigenome-wide association study on a community-based Mexican American population using the Illumina EPIC array. Following rigorous quality control measures, we identified 10 CpG sites to be differentially methylated between normal controls and individuals with mild cognitive impairment annotated to PKIB, KLHL29, SEPT9, OR2C3, CPLX3, BCL2L2-PABPN1, and CCNY. We found four regions to be differentially methylated in TMEM232, SLC17A8, ALOX12, and SEPT8. Functional gene-set analysis identified four gene-sets, RIN3, SPEG, CTSG, and UBE2L3, as significant. The gene ontology and pathway analyses point to neuronal cell death, metabolic dysfunction, and inflammatory processes. We found 1,450 processes to be enriched using empirical Bayes gene-set enrichment. In conclusion, the functional overlap of differentially methylated genes associated with cognitive impairment in Mexican Americans implies cross-talk between metabolically-instigated systemic inflammation and disruption of synaptic vesicular transport.

Pharmacogenomics of Hypertension Treatment

Hypertension is one of the strongest modifiable cardiovascular risk factors, affecting an increasing number of people worldwide. Apart from poor medication adherence, the low efficacy of some therapies could also be related to inter-individual genetic variability. Genetic studies of families revealed that heritability accounts for 30% to 50% of inter-individual variation in blood pressure (BP). Genetic factors not only affect blood pressure (BP) elevation but also contribute to inter-individual variability in response to antihypertensive treatment. This article reviews the recent pharmacogenomics literature concerning the key classes of antihypertensive drugs currently in use (i.e., diuretics, β-blockers, ACE inhibitors, ARB, and CCB). Due to the numerous studies on this topic and the sometimes-contradictory results within them, the presented data are limited to several selected SNPs that alter drug response. Genetic polymorphisms can influence drug responses through genes engaged in the pathogenesis of hypertension that are able to modify the effects of drugs, modifications in drug–gene mechanistic interactions, polymorphisms within drug-metabolizing enzymes, genes related to drug transporters, and genes participating in complex cascades and metabolic reactions. The results of numerous studies confirm that genotype-based antihypertension therapies are the most effective and may help to avoid the occurrence of major adverse events, as well as decrease the costs of treatment. However, the genetic heritability of drug response phenotypes seems to remain hidden in multigenic and multifactorial complex traits. Therefore, further studies are required to analyze all associations and formulate final genome-based treatment recommendations.

Flaming the fight against cancer cells: the role of microRNA-93

There have been attempts to develop novel anti-tumor drugs in cancer therapy. Although satisfying results have been observed at a consequence of application of chemotherapeutic agents, the cancer cells are capable of making resistance into these agents. This has forced scientists into genetic manipulation as genetic alterations are responsible for generation of a high number of cancer cells. MicroRNAs (miRs) are endogenous, short non-coding RNAs that affect target genes at the post-transcriptional level. Increasing evidence reveals the potential role of miRs in regulation of biological processes including angiogenesis, metabolism, cell proliferation, cell division, and cell differentiation. Abnormal expression of miRs is associated with development of a number of pathologic events, particularly cancer. MiR-93 plays a significant role in both physiological and pathological mechanisms. At the present review, we show how this miR dually affects the proliferation and invasion of cancer cells. Besides, we elucidate the oncogenesis or oncosuppressor function of miR-93.

Pharmacogenomics of amlodipine and hydrochlorothiazide therapy and the quest for improved control of hypertension: a mini review

Blood pressure (BP) is a complex trait that is regulated by multiple physiological pathways and include but is not limited to extracellular fluid volume homeostasis, cardiac contractility, and vascular tone through renal, neural, or endocrine systems. Uncontrolled hypertension (HTN) has been associated with an increased mortality risk. Therefore, understanding the genetics that underpins and influence BP regulation will have a major impact on public health. Moreover, uncontrolled HTN has been linked to inter-individual variation in the drugs’ response and this has been associated with an individual’s genetics architecture. However, the identification of candidate genes that underpin the genetic basis of HTN remains a major challenge. To date, few variants associated with inter-individual BP regulation have been identified and replicated. Research in this field has accelerated over the past 5 years as a direct result of on-going genome-wide association studies (GWAS) and the progress in the identification of rare gene variants and mutations, epigenetic markers, and the regulatory pathways involved in the pathophysiology of BP. In this review we describe and enhance our current understanding of how genetic variants account for the observed variability in BP response in patients on first-line antihypertensive drugs, amlodipine and hydrochlorothiazide.

A Variant in the NEDD4L Gene Associates With Hypertension in Chronic Kidney Disease in the Southeastern Han Chinese Population

BACKGROUND

"Neuronal precursor cell expressed developmentally down-regulated 4-like" (NEDD4L) is considered a candidate gene for hypertension-both functionally and genetically-through the regulation of the ubiquitination of the epithelial sodium channel (ENaC). This study explores the relationship between genetic variation in NEDD4L and hypertension with chronic kidney disease (CKD) in the southeastern Han Chinese population.

METHODS

We recruited 623 CKD patients and measured ambulatory blood pressure monitoring (ABPM), and the rs4149601 and rs2288774 polymorphisms in NEDD4L were genotyped using quantitative polymerase chain reaction.

RESULTS

For rs4149601, significant differences in genotype frequencies in an additive model (GG vs. GA vs. AA) were observed between normotensive patients and hypertensive patients when hypertension was classified into ambulatory hypertension, clinical hypertension, and ambulatory systolic hypertension (P = 0.038, 0.005, and 0.006, respectively). In a recessive model (GG + GA vs. AA), the frequency of the AA genotype of rs4149601 in the hypertension groups was all higher than that in the normotensive groups. The genotype distribution of rs2288774 did not differ significantly between the normotensive and hypertensive patients. In both the full cohort and the propensity score matching (PSM) cohort, the AA genotype of rs4149601 (compared with the GG + GA genotype group) was independently correlated with ambulatory hypertension, clinical hypertension, and ambulatory systolic hypertension by multivariate logistic regression analysis.

CONCLUSIONS

The present study indicates that the AA genotype of rs4149601 associates with hypertension in CKD. Consequently, the rs4149601 A allele might be a risk factor for hypertension with CKD.

Pharmacogenomics And Hypertension: Current Insights

Hypertension is a multifactorial disease that affects approximately one billion subjects worldwide and is a major risk factor associated with cardiovascular events, including coronary heart disease and cerebrovascular accidents. Therefore, adequate blood pressure control is important to prevent these events, reducing premature mortality and disability. However, only one third of patients have the effective control of blood pressure, despite several classes of antihypertensive drugs available. These disappointing outcomes may be at least in part explained by interpatient variability in drug response due to genetic polymorphisms. To address the effects of genetic polymorphisms on blood pressure responses to the antihypertensive drug classes, studies have applied candidate genes and genome wide approaches. More recently, a third approach that considers gene-gene interactions has also been applied in hypertension pharmacogenomics. In this article, we carried out a comprehensive review of recent findings on the pharmacogenomics of antihypertensive drugs, including diuretics, β-blockers, angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers, and calcium channel blockers. We also discuss the limitations and inconsistences that have been found in hypertension pharmacogenomics and the challenges to implement this valuable approach in clinical practice.

Ubiquitin Ligases Involved in the Regulation of Wnt, TGF-β, and Notch Signaling Pathways and Their Roles in Mouse Development and Homeostasis

The Wnt, TGF-β, and Notch signaling pathways are essential for the regulation of cellular polarity, differentiation, proliferation, and migration. Differential activation and mutual crosstalk of these pathways during animal development are crucial instructive forces in the initiation of the body axis and the development of organs and tissues. Due to the ability to initiate cell proliferation, these pathways are vulnerable to somatic mutations selectively producing cells, which ultimately slip through cellular and organismal checkpoints and develop into cancer. The architecture of the Wnt, TGF-β, and Notch signaling pathways is simple. The transmembrane receptor, activated by the extracellular stimulus, induces nuclear translocation of the transcription factor, which subsequently changes the expression of target genes. Nevertheless, these pathways are regulated by a myriad of factors involved in various feedback mechanisms or crosstalk. The most prominent group of regulators is the ubiquitin-proteasome system (UPS). To open the door to UPS-based therapeutic manipulations, a thorough understanding of these regulations at a molecular level and rigorous confirmation in vivo are required. In this quest, mouse models are exceptional and, thanks to the progress in genetic engineering, also an accessible tool. Here, we reviewed the current understanding of how the UPS regulates the Wnt, TGF-β, and Notch pathways and we summarized the knowledge gained from related mouse models.

The correlation between NEDD4L and HIF-1α levels as a gastric cancer prognostic marker

NEDD4L (neural precursor cell expressed developmentally down-regulated 4-like) protein is a member of ubiquitin ligases Nedd4 family. Although studies have shown that Nedd4L may act as a tumor suppressor in various cancers, including gastric cancer (GC), its clinical significance and the diagnostic value in GC is not well defined. HIF-1α (hypoxia inducible factor family of transcription factors) is actively involved in the metabolism of many tumors, although the relationship between its expression levels and clinical significance in GC still need to be established. In this study, the level of HIF-1α and NEDD4L mRNA and protein in 25 freshly frozen GC- and matched normal-tissues were determined by western blot and quantitative PCR (qPCR). Additionally, immunohistochemistry assay was performed to measure the protein level of NEDD4L and HIF-1α in 124 GC and 25 normal control tissues. We observed that the NEDD4L mRNA and protein levels decreased significantly (P < 0.001) in GC tissues, while that of HIF-1α increased (P < 0.001), and they both were associated with a poor prognosis, as was the case in patients with lower NEDD4L and higher HIF-1α expression (P < 0.001). On correlation analysis, a significantly negative relationship (r = 0.288, P < 0.01) was revealed between NEDD4L and HIF-1α expressions. Multivariate analysis revealed that co-expression of NEDD4L (P < 0.05) and HIF-1α (P < 0.001) were independent predictors of GC prognosis. Thus, the correlation of NEDD4L and HIF-1α levels may act as a prognostic marker of GC.

Pharmacogenomic studies of hypertension: paving the way for personalized antihypertensive treatment

Introduction

Increasing clinical evidence supports the implementation of genotyping for anti-hypertensive drug dosing and selection. Despite robust evidence gleaned from clinical trials, the translation of genotype guided therapy into clinical practice faces significant challenges. Challenges to implementation include the small effect size of individual variants and the polygenetic nature of antihypertensive drug response, a lack of expert consensus on dosing guidelines even without genetic information, and proper definition of major antihypertensive drug toxicities. Balancing clinical benefit with cost, while overcoming these challenges, remains crucial.

Areas covered

This review presents the most impactful clinical trials and cohorts which continue to inform and guide future investigation. Variants were selected from among those identified in the Pharmacogenomic Evaluation of Antihypertensive Responses (PEAR), the Genetic Epidemiology of Responses to Antihypertensives study (GERA), the Genetics of Drug Responsiveness in Essential Hypertension (GENRES) study, the SOPHIA study, the Milan Hypertension Pharmacogenomics of hydro-chlorothiazide (MIHYPHCTZ), the Campania Salute Network, the International Verapamil SR Trandolapril Study (INVEST), the Nordic Diltiazem (NORDIL) Study, GenHAT, and others.

Expert Commentary

The polygenic nature of antihypertensive drug response is a major barrier to clinical implementation. Further studies examining clinical effectiveness are required to support broad-based implementation of genotype-based prescribing in medical practice.

Personalized medicine-a modern approach for the diagnosis and management of hypertension

The main goal of treating hypertension is to reduce blood pressure to physiological levels and thereby prevent risk of cardiovascular disease and hypertension-associated target organ damage. Despite reductions in major risk factors and the availability of a plethora of effective antihypertensive drugs, the control of blood pressure to target values is still poor due to multiple factors including apparent drug resistance and lack of adherence. An explanation for this problem is related to the current reductionist and ‘trial-and-error’ approach in the management of hypertension, as we may oversimplify the complex nature of the disease and not pay enough attention to the heterogeneity of the pathophysiology and clinical presentation of the disorder. Taking into account specific risk factors, genetic phenotype, pharmacokinetic characteristics, and other particular features unique to each patient, would allow a personalized approach to managing the disease. Personalized medicine therefore represents the tailoring of medical approach and treatment to the individual characteristics of each patient and is expected to become the paradigm of future healthcare. The advancement of systems biology research and the rapid development of high-throughput technologies, as well as the characterization of different –omics, have contributed to a shift in modern biological and medical research from traditional hypothesis-driven designs toward data-driven studies and have facilitated the evolution of personalized or precision medicine for chronic diseases such as hypertension.

Deletion of Nedd4-2 results in progressive kidney disease in mice

NEDD4-2 (NEDD4L), a ubiquitin protein ligase of the Nedd4 family, is a key regulator of cell surface expression and activity of the amiloride-sensitive epithelial Na⁺ channel (ENaC). While hypomorphic alleles of Nedd4-2 in mice show salt-sensitive hypertension, complete knockout results in pulmonary distress and perinatal lethality due to increased cell surface levels of ENaC. We now show that Nedd4-2 deficiency in mice also results in an unexpected progressive kidney injury phenotype associated with elevated ENaC and Na⁺Cl⁻ cotransporter expression, increased Na⁺ reabsorption, hypertension and markedly reduced levels of aldosterone. The observed nephropathy is characterized by fibrosis, tubule epithelial cell apoptosis, dilated/cystic tubules, elevated expression of kidney injury markers and immune cell infiltration, characteristics reminiscent of human chronic kidney disease. Importantly, we demonstrate that the extent of kidney injury can be partially therapeutically ameliorated in mice with nephron-specific deletions of Nedd4-2 by blocking ENaC with amiloride. These results suggest that increased Na⁺ reabsorption via ENaC causes kidney injury and establish a novel role of NEDD4-2 in preventing Na⁺-induced nephropathy. Contrary to some recent reports, our data also indicate that ENaC is the primary in vivo target of NEDD4-2 and that Nedd4-2 deletion is associated with hypertension on a normal Na⁺ diet. These findings provide further insight into the critical function of NEDD4-2 in renal pathophysiology.

Ubiquitination and the Regulation of Membrane Proteins

Newly synthesized transmembrane proteins undergo a series of steps to ensure that only the required amount of correctly folded protein is localized to the membrane. The regulation of protein quality and its abundance at the membrane are often controlled by ubiquitination, a multistep enzymatic process that results in the attachment of ubiquitin, or chains of ubiquitin to the target protein. Protein ubiquitination acts as a signal for sorting, trafficking, and the removal of membrane proteins via endocytosis, a process through which multiple ubiquitin ligases are known to specifically regulate the functions of a number of ion channels, transporters, and signaling receptors. Endocytic removal of these proteins through ubiquitin-dependent endocytosis provides a way to rapidly downregulate the physiological outcomes, and defects in such controls are directly linked to human pathologies. Recent evidence suggests that ubiquitination is also involved in the shedding of membranes and associated proteins as extracellular vesicles, thereby not only controlling the cell surface levels of some membrane proteins, but also their potential transport to neighboring cells. In this review, we summarize the mechanisms and functions of ubiquitination of membrane proteins and provide specific examples of ubiquitin-dependent regulation of membrane proteins.

Mechanisms and pharmacogenetic signals underlying thiazide diuretics blood pressure response

Thiazide (TZD) diuretics are among the most commonly prescribed antihypertensives globally; however their chronic blood pressure (BP) lowering mechanism remains unclear. Herein we discuss the current evidence regarding specific mechanisms regulating the antihypertensive effects of TZDs, suggesting that TZDs act via multiple complex and interacting mechanisms, including natriuresis with short term use and direct vasodilatory effects chronically. Additionally, we review pharmacogenomics signals that have been associated with TZDs BP-response in several cohorts (i.e. NEDD4L, PRKCA, EDNRA-GNAS, and YEATS4) and discuss how these genes might be related to TZD BP-response mechanism. Understanding the association between these genes and TZD BP mechanism might facilitate the development of new drugs and therapeutic approaches based on a deeper understanding of the determinants of BP-response.

Hypertension pharmacogenomics: in search of personalized treatment approaches

Cardiovascular and renal diseases are associated with many risk factors, of which hypertension is one of the most prevalent. Worldwide, blood pressure control is only achieved in ∼50% of those treated for hypertension, despite the availability of a considerable number of antihypertensive drugs from different pharmacological classes. Although many reasons exist for poor blood pressure control, a likely contributor is the inability to predict to which antihypertensive drug an individual is most likely to respond. Hypertension pharmacogenomics and other 'omics' technologies have the potential to identify genetic signals that are predictive of response or adverse outcome to particular drugs, and guide selection of hypertension treatment for a given individual. Continued research in this field will enhance our understanding of how to maximally deploy the various antihypertensive drug classes to optimize blood pressure response at the individual level. This Review summarizes the available literature on the most convincing genetic signals associated with antihypertensive drug responses and adverse cardiovascular outcomes. Future research in this area will be facilitated by enhancing collaboration between research groups through consortia such as the International Consortium for Antihypertensives Pharmacogenomics Studies, with the goal of translating replicated findings into clinical implementation.

Recent Advances in the Genetics of Hypertension

Hypertension is a silent killer worldwide, caused by both genetic and environmental factors. Until now, genetic and genomic association studies of hypertension are reporting different degree of association on hypertension. Hence, it is essential to gather all the available information on the reported genetic loci and to determine if any biomarker(s) is/are significantly associated with hypertension. Current review concluded the potential biomarkers for hypertension, with regards to electrolyte and fluid transports, as well as sodium/potassium ions homeostasis, which are supported by the results of case-controls and meta-analyses.

miR-93 promotes TGF-β-induced epithelial-to-mesenchymal transition through downregulation of NEDD4L in lung cancer cells

The level of microRNA-93 (miR-93) in tumors has been recently reported to be negatively correlated with survival of lung cancer patients. Considering that the most devastating aspect of lung cancer is metastasis, which can be promoted by transforming growth factor-β (TGF-β)-induced epithelial-to-mesenchymal transition (EMT), we sought to determine whether miR-93 is involved in this process. Here, we report that a previously unidentified target of miR-93, neural precursor cell expressed developmentally downregulated gene 4-like (NEDD4L), is able to mediate TGF-β-mediated EMT in lung cancer cells. miR-93 binds directly to the 3'-UTR of the NEDD4L messenger RNA (mRNA), leading to a downregulation of NEDD4L expression at the protein level. We next demonstrated that the downregulation of NEDD4L enhanced, while overexpression of NEDD4L reduced TGF-β signaling, reflected by increased phosphorylation of SMAD2 in the lung cancer cell line after TGF-β treatment. Furthermore, overexpression of miR-93 in lung cancer cells promoted TGF-β-induced EMT through downregulation of NEDD4L. The analysis of publicly available gene expression array datasets indicates that low NEDD4L expression correlates with poor outcomes among patients with lung cancer, further supporting the oncogenic role of miR-93 in lung tumorigenesis and metastasis.

DDB2 modulates TGF-β signal transduction in human ovarian cancer cells by downregulating NEDD4L

The expression of DNA damage-binding protein 2 (DDB2) has been linked to the prognosis of ovarian cancer and its underlying transcription regulatory function was proposed to contribute to the favorable treatment outcome. By applying gene microarray analysis, we discovered neural precursor cell expressed, developmentally downregulated 4-Like (NEDD4L) as a previously unidentified downstream gene regulated by DDB2. Mechanistic investigation demonstrated that DDB2 can bind to the promoter region of NEDD4L and recruit enhancer of zeste homolog 2 histone methyltransferase to repress NEDD4L transcription by enhancing histone H3 lysine 27 trimethylation (H3K27me3) at the NEDD4L promoter. Given that NEDD4L plays an important role in constraining transforming growth factor β signaling by targeting activated Smad2/Smad3 for degradation, we investigated the role of DDB2 in the regulation of TGF-β signaling in ovarian cancer cells. Our data indicate that DDB2 enhances TGF-β signal transduction and increases the responsiveness of ovarian cancer cells to TGF-β-induced growth inhibition. The study has uncovered an unappreciated regulatory mode that hinges on the interaction between DDB2 and NEDD4L in human ovarian cancer cells. The novel mechanism proposes the DDB2-mediated fine-tuning of TGF-β signaling and its downstream effects that impinge upon tumor growth in ovarian cancers.

Proteomics analysis of EV71-infected cells reveals the involvement of host protein NEDD4L in EV71 replication

Enterovirus 71 (EV71) is a human enterovirus that has seriously affected the Asia-Pacific area for the past two decades. EV71 infection can result in mild hand-foot-and-mouth disease and herpangina and may occasionally lead to severe neurological complications in children. However, the specific biological processes that become altered during EV71 infection remain unclear. To further explore host responses upon EV71 infection, we identified proteins differentially expressed in EV71-infected human glioblastoma SF268 cells using isobaric mass tag (iTRAQ) labeling coupled with multidimensional liquid chromatography-mass spectrometry (LC-MS/MS). Network analysis of proteins altered in cells infected with EV71 revealed that the changed biological processes are related to protein and ion transport, regulation of protein degradation, and homeostatic processes. We confirmed that the levels of NEDD4L and PSMF1 were increased and reduced, respectively, in EV71-infected cells compared to mock-infected control cells. To determine the physiological relevance of our findings, we investigated the consequences of EV71 infection in cells with NEDD4L or PSMF1 depletion. We found that the depletion of NEDD4L significantly reduced the replication of EV71, whereas PSMF1 knockdown enhanced EV71 replication. Collectively, our findings provide the first evidence of proteome-wide dysregulation by EV71 infection and suggest a novel role for the host protein NEDD4L in the replication of this virus.

NEDD4-2 (NEDD4L): the ubiquitin ligase for multiple membrane proteins

NEDD4-2 (also known as NEDD4L, neural precursor cell expressed developmentally down-regulated 4-like) is a ubiquitin protein ligase of the Nedd4 family which is known to bind and regulate a number of membrane proteins to aid in their internalization and turnover. Several of the NEDD4-2 substrates include ion channels, such as the epithelial and voltage-gated sodium channels. Given the critical function of NEDD4-2 in regulating membrane proteins, this ligase is essential for the maintenance of cellular homeostasis. In this article we review the biology and function of this important ubiquitin-protein ligase and discuss its pathophysiological significance.

Two genomic regions of chromosomes 1 and 18 explain most of the stroke susceptibility under salt loading in stroke-prone spontaneously hypertensive rat/Izm

To clarify the genetic mechanisms of stroke susceptibility in the stroke-prone spontaneously hypertensive rat (SHRSP), a quantitative trait locus (QTL) analysis was performed. Using 295 F2 rats of a cross between SHRSP/Izm and SHR/Izm, 2 major QTLs for stroke latency under salt loading were identified on chromosomes (chr) 1 and 18. Evaluation of 6 reciprocal single and double congenic rats for these QTLs showed that substitution of the SHRSP for the SHR fragment at the chr 1 and 18 QTLs increased the relative risk for stroke by 8.4 and 5.0, respectively. The combined effect of the 2 QTLs was 10× greater than that of the background genome (by Cox hazard model). Blood pressure monitoring by radio telemetry indicated that the combination of the 2 QTLs had a clear effect on the salt-dependent blood pressure increase, suggesting an important role for the salt-sensitive blood pressure increase in the susceptibility of SHRSP to stroke. A haplotype analysis of 11 substrains of SHRSP and SHR using 340 simple sequence repeat markers in the chr 1 QTL suggested that the 7-Mbp fragment between D1Rat260 and D1Rat178 was most likely to harbor the responsible gene(s), which was confirmed by a study of additional subcongenic strains. This study indicated a major role for 2 QTLs on chr 1 and 18 in stroke susceptibility in SHRSP under salt loading. The salt-sensitive blood pressure increase was implied to play a key role in the stroke susceptibility.

A functional variant of NEDD4L is associated with obesity and related phenotypes in a Han population of Southern China

NEDD4L is a candidate gene for hypertension, both functionally and genetically. Recently, studies showed evidence for the association of NEDD4L with obesity, a key intermediate phenotype in hypertension. To further investigate the relationship between NEDD4L and body mass-related phenotypes, we genotyped three common variants (rs2288774, rs3865418 and rs4149601) in a population-based study of 892 unrelated Han Cantonese using the Sequenom MALDI-TOF-MS platform. Allele frequencies and genotype distribution were calculated in lean controls and overweight/obese cases and analyzed for association by the Chi-squared test and Logistic regression. Linear regression analysis was used to analyze the effect of individual genotypes on quantitative traits. Multivariate analyses demonstrated that the minor allele of rs4149601(A = 20.9%) was associated with a 2.60 kg, 2.78 cm and 0.97 kg/m² decrease per allele copy in weight, waist and BMI, respectively. Carriers of this allele also had a significant lower risk of overweight/obesity (p < 0.0001, OR = 0.52, 95% CI: 0.37–0.74) as compared to non-carriers. However, no significant association between genotypes at rs2288774 and rs3865418 and covariate-adjusted overweight/obesity or any related phenotypes was observed. These results suggested that the functional variant of NEDD4L, rs4149601, may be associated with obesity and related phenotypes, and further genetic and functional studies are required to understand its role in the manifestation of obesity.

Advancing management of hypertension through pharmacogenomics

Hypertension is the most common, chronic disease in the world, and there are many effective pharmacological agents available for its treatment. Despite the plethora of treatment options, data across the globe suggest that blood pressure control rates are < 50%, a fact likely influenced in part by the inability to predict the antihypertensive drug likely to be most effective for an individual patient. Pharmacogenomics in hypertension holds the promise of identifying genetic biomarkers for antihypertensive drug response, which might be used in the future in treatment selection. Research in the field is also likely to enhance our understanding of hypertension and the mechanisms by which the various drugs produce efficacy. There are several examples in the literature of genes with relatively strong data on associations of genetic polymorphisms with antihypertensive response; the data on ADRB1, CACNB2, and NEDD4L are detailed as examples. Substantial additional data in hypertension pharmacogenomics are expected to be forthcoming from recently completed genome-wide association studies. Increased collaboration among research groups will help insure successful discoveries from these large-scale studies. The next decade should clearly define the potential clinical implications of the research in hypertension pharmacogenomics that is currently in progress.

Genetic analysis of diabetic nephropathy on chromosome 18 in African Americans: linkage analysis and dense SNP mapping

Genetic studies in Turkish, Native American, European American, and African American (AA) families have linked chromosome 18q21.1-23 to susceptibility for diabetes-associated nephropathy. In this study, we have carried out fine linkage mapping in the 18q region previously linked to diabetic nephropathy in AAs by genotyping both microsatellite and single nucleotide polymorphisms (SNPs) for linkage analysis in an expanded set of 223 AA families multiplexed for type 2 diabetes associated ESRD (T2DM-ESRD). Several approaches were used to evaluate evidence of linkage with the strongest evidence for linkage in ordered subset analysis with an earlier age of T2DM diagnosis compared to the remaining pedigrees (LOD 3.9 at 90.1 cM, ΔP = 0.0161, NPL P value = 0.00002). Overall, the maximum LODs and LOD-1 intervals vary in magnitude and location depending upon analysis. The linkage mapping was followed up by performing a dense SNP map, genotyping 2,814 SNPs in the refined LOD-1 region in 1,029 AA T2DM-ESRD cases and 1,027 AA controls. Of the top 25 most associated SNPs, 10 resided within genic regions. Two candidate genes stood out: NEDD4L and SERPINB7. SNP rs512099, located in intron 1 of NEDD4L, was associated under a dominant model of inheritance [P value = 0.0006; Odds ratio (95% Confidence Interval) OR (95% CI) = 0.70 (0.57-0.86)]. SNP rs1720843, located in intron 2 of SERPINB7, was associated under a recessive model of inheritance [P value = 0.0017; OR (95% CI) = 0.65 (0.50-0.85)]. Collectively, these results suggest that multiple genes in this region may influence diabetic nephropathy susceptibility in AAs.

Intracellular ubiquitylation of the epithelial Na+ channel controls extracellular proteolytic channel activation via conformational change

The epithelial Na(+) channel ENaC is a key player in the maintenance of whole body Na(+) balance, and consequently of blood pressure. It is tightly regulated by numerous signaling pathways including ubiquitylation via the ubiquitin-protein ligase Nedd4-2. This mechanism is itself under the control of several kinases, which phosphorylate Nedd4-2, thereby interfering with ENaC/Nedd4-2 interaction, or by Usp2-45, which binds to and deubiquitylates ENaC. Another, different regulatory mechanism concerns the proteolytic activation of ENaC, during which the channel is cleaved on its luminal side by intracellular convertases such as furin, and further activated by extracellular proteases such as CAP-1. This process is regulated as well but the underlying mechanisms are not understood. Previously, evidence was provided that the ubiquitylation status of ENaC may affect the cleavage of the channel. When ubiquitylation of ENaC was reduced, either by co-expressing Usp2-45, or mutating either the ENaC PY-motifs (i.e. the binding sites for Nedd4-2) or intracellular lysines (i.e. ubiquitylation sites), the level of channel cleavage was increased. Here we demonstrate that lysine-mutated ENaC channels are not ubiquitylated at the cell surface, are preferentially cleaved, and Usp2-45 does not affect their cleavage efficiency. We further show by limited proteolysis that the intracellular ubiquitylation status of ENaC affects the extracellular conformation of αENaC, by demonstrating that non-ubiquitylated channels are more efficiently cleaved when treated with extracellularly added trypsin or chymotrypsin. These results present a new paradigm in which an intracellular, post-translational modification (e.g. ubiquitylation) of a transmembrane protein can affect its extracellular conformation.

Identification of candidate genes for dyslexia susceptibility on chromosome 18

BACKGROUND

Six independent studies have identified linkage to chromosome 18 for developmental dyslexia or general reading ability. Until now, no candidate genes have been identified to explain this linkage. Here, we set out to identify the gene(s) conferring susceptibility by a two stage strategy of linkage and association analysis.

METHODOLOGY/PRINCIPAL FINDINGS

Linkage analysis: 264 UK families and 155 US families each containing at least one child diagnosed with dyslexia were genotyped with a dense set of microsatellite markers on chromosome 18. Association analysis: Using a discovery sample of 187 UK families, nearly 3000 SNPs were genotyped across the chromosome 18 dyslexia susceptibility candidate region. Following association analysis, the top ranking SNPs were then genotyped in the remaining samples. The linkage analysis revealed a broad signal that spans approximately 40 Mb from 18p11.2 to 18q12.2. Following the association analysis and subsequent replication attempts, we observed consistent association with the same SNPs in three genes; melanocortin 5 receptor (MC5R), dymeclin (DYM) and neural precursor cell expressed, developmentally down-regulated 4-like (NEDD4L).

CONCLUSIONS

Along with already published biological evidence, MC5R, DYM and NEDD4L make attractive candidates for dyslexia susceptibility genes. However, further replication and functional studies are still required.

Genetic architecture of complex traits predisposing to nephropathy: hypertension

Blood pressure and hypertension have significant genetic underpinnings that may be age-dependent. The age-dependency, significant contributions from environmental factors such as diet and exercise, and inherent moment-to-moment variability complicate the identification of the genes contributing to the development of hypertension. Although genetic abnormalities may have moderate effects, the physiologic pathways involving these genes have redundant compensating mechanisms to bring the system back into equilibrium. This has the effect of reducing or completely masking the initial genetic defects, one of the hypothesized reasons for the small genetic effects found by the recent genome-wide association studies. This review article discusses the concept of initiators versus compensators in the context of finding genes related to hypertension development. A brief review is provided of some key genes found to be associated with hypertension, including the genes identified from the nine genome-wide association studies published to date.

Calcium activates Nedd4 E3 ubiquitin ligases by releasing the C2 domain-mediated auto-inhibition

Nedd4 E3 ligases are members of the HECT E3 ubiquitin ligase family and regulate ubiquitination-mediated protein degradation. In this report, we demonstrate that calcium releases the C2 domain-mediated auto-inhibition in both Nedd4-1 and Nedd4-2. Calcium disrupts binding of the C2 domain to the HECT domain. Consistent with this, calcium activates the E3 ubiquitin ligase activity of Nedd4. Elevation of intracellular calcium by ionomycin treatment, or activation of acetylcholine receptor or epidermal growth factor receptor by carbachol or epidermal growth factor stimulation induced activation of endogenous Nedd4 in vivo evaluated by assays of either Nedd4 E3 ligase activity or ubiquitination of Nedd4 substrate ENaC-beta. The activation effect of calcium on Nedd4 E3 ligase activity was dramatically enhanced by a membrane-rich fraction, suggesting that calcium-mediated membrane translocation through the C2 domain might be an activation mechanism of Nedd4 in vivo. Our studies have revealed an activation mechanism of Nedd4 E3 ubiquitin ligases and established a connection of intracellular calcium signaling to regulation of protein ubiquitination.

Genetic variation of NEDD4L is associated with essential hypertension in female Kazakh general population: a case-control study

Background

Hypertension affects > 18.8% of adults in China. Indeed, hypertension is the most prevalent risk factor for cardiovascular morbidity and mortality worldwide. Genetic variation is thought to contribute to the etiology of hypertension. NEDD4L is a candidate gene for hypertension, both functionally and genetically. The purpose of the current study was to investigate the relationship between the variation in NEDD4L and essential hypertension in Kazakh, which is a relatively isolated population with a pure genetic background and is an ideal population to study genetic mechanisms of hypertension.

Methods

We screened the promoter and exons of NEDD4L in 94 Kazakh hypertensive individuals to identify representative variations. Then, by genotyping the representative variations in the Kazakh general population, a case-control study was conducted.

Results

By systemically screening variations of NEDD4L, we did not identify any functional mutations in NEDD4L. A new common variation (296921-296923delTTG), which is not found in the NCBI database, was identified. Three representative variations (296921-296923delTTG, rs2288774, and rs2288775) were successfully genotyped in the Kazakh general population. The distribution of the dominant model (AA vs. AG+GG) of rs2288775, the additive model, and the recessive model (II+ID vs. DD) of 296921-296923delTTG differed significantly between the cases and controls in females (P = 0.040, P = 0.024, and P = 0.007, respectively). After adjusting for confounding factors, logistic regression analysis showed that rs2288775 (in the dominant model) and 296921-296923delTTG (in the recessive model) were significantly associated with hypertension (rs2288775: OR = 1.479, 95% CI = 1.011-2.064, p = 0.044; and 296921-296923delTTG: OR = 1.908, 95% CI = 1.020-3.568, p = 0.043) in females. The frequency of the D-C-G haplotype was significantly higher for cases than for controls in females (P = 0.020). There was a significant interaction between the NEDD4L genotype and gender (P for interaction: 0.045 for rs2288775 and 0.064 for 296921-296923delTTG), but there was no significant interaction between the NEDD4L genotype and smoking (P for interaction: 0.616 for rs2288775 and 0.447 for 296921-296923delTTG). For females and total participants, the urinary Na excretion rate was significantly lower in the DD than the I/I+I/D individuals (P = 0.032 and P = 0.027 respectively).

Conclusion

The genetic variations of NEDD4L may be associated with essential hypertension in females in the Kazakh general population.

Ubiquitin ligase Nedd4L targets activated Smad2/3 to limit TGF-beta signaling

TGF-beta induces phosphorylation of the transcription factors Smad2 and Smad3 at the C terminus as well as at an interdomain linker region. TGF-beta-induced linker phosphorylation marks the activated Smad proteins for proteasome-mediated destruction. Here, we identify Nedd4L as the ubiquitin ligase responsible for this step. Through its WW domain, Nedd4L specifically recognizes a TGF-beta-induced phosphoThr-ProTyr motif in the linker region, resulting in Smad2/3 polyubiquitination and degradation. Nedd4L is not interchangeable with Smurf1, a ubiquitin ligase that targets BMP-activated, linker-phosphorylated Smad1. Nedd4L limits the half-life of TGF-beta-activated Smads and restricts the amplitude and duration of TGF-beta gene responses, and in mouse embryonic stem cells, it limits the induction of mesoendodermal fates by Smad2/3-activating factors. Hierarchical regulation is provided by SGK1, which phosphorylates Nedd4L to prevent binding of Smad2/3. Previously identified as a regulator of renal sodium channels, Nedd4L is shown here to play a broader role as a general modulator of Smad turnover during TGF-beta signal transduction.

PepT1 oligopeptide transporter (SLC15A1) gene polymorphism in inflammatory bowel disease

BACKGROUND

Human polymorphisms affecting gut epithelial barrier and interactions with bacteria predispose to the inflammatory bowel diseases (IBD) Crohn's disease (CD) and ulcerative colitis (UC). The intestinal transporter PepT1, encoded by the SLC15A1 gene, mediates intracellular uptake of bacterial products that can induce inflammation and NF-kappaB activation upon binding to NOD2, a protein often mutated in CD. Hence, we tested SLC15A1 polymorphisms for association with IBD.

METHODS

Twelve SLC15A1 single nucleotide polymorphisms (SNPs) were genotyped in 1783 individuals from 2 cohorts of Swedish and Finnish IBD patients and controls. An in vitro system was set up to evaluate the potential impact of SLC15A1 polymorphism on PepT1 transporter function by quantification of NOD2-mediated activation of NF-kappaB.

RESULTS

The common allele (C) of a coding polymorphism (rs2297322, Ser117Asn) was associated with CD susceptibility both in Sweden and in Finland, but with genetic effects in opposite directions (risk and protection, respectively). The best evidence of association was found in both populations when the analysis was performed on individuals not carrying NOD2 common risk alleles (Sweden allelic P = 0.0007, OR 1.97, 95% confidence interval [CI] 1.34-2.92; Finland genotype P = 0.0013, OR 0.63, 95% CI 0.44-0.90). The PepT1 variant encoded by the C allele (PepT1-Ser117) was associated with reduced signaling downstream of NOD2 (P < 0.0001 compared to Pept1-Asn117).

CONCLUSIONS

A functional polymorphism in the SLC15A1 gene might be of relevance to inflammation and antibacterial responses in IBD. Whether this polymorphism truly contributes to disease susceptibility needs to be further addressed, and should stimulate additional studies in other populations.

A human polymorphism affects NEDD4L subcellular targeting by leading to two isoforms that contain or lack a C2 domain

Background

Ubiquitination serves multiple cellular functions, including proteasomal degradation and the control of stability, function, and intracellular localization of a wide variety of proteins. NEDD4L is a member of the HECT class of E3 ubiquitin ligases. A defining feature of NEDD4L protein isoforms is the presence or absence of an amino-terminal C2 domain, a class of subcellular, calcium-dependent targeting domains. We previously identified a common variant in human NEDD4L that generates isoforms that contain or lack a C2 domain.

Results

To address the potential functional significance of the NEDD4L common variant on NEDD4L subcellular localization, NEDD4L isoforms that either contained or lacked a C2 domain were tagged with enhanced green fluorescent protein, transfected into Xenopus laevis kidney epithelial cells, and imaged by performing confocal microscopy on live cells. We report that the presence or absence of this C2 domain exerts differential effects on the subcellular distribution of NEDD4L, the ability of C2 containing and lacking NEDD4L isoforms to mobilize in response to a calcium stimulus, and the intracellular transport of subunits of the NEDD4L substrate, ENaC. Furthermore, the ability of the C2-containing isoform to influence β-ENaC mobilization from intracellular pools involves the NEDD4L active site for ubiquitination. We propose a model to account for the potential impact of this common genetic variant on protein function at the cellular level.

Conclusion

NEDD4L isoforms that contain or lack a C2 domain target different intracellular locations. Additionally, whereas the C2-containing NEDD4L isoform is capable of shuttling between the plasma membrane and intracellular compartments in response to calcium stimulus the C2-lacking isoform can not. The C2-containing isoform differentially affects the mobilization of ENaC subunits from intracellular pools and this trafficking step requires NEDD4L ubiquitin ligase activity. This observation suggests a new mechanism for the requirement for the PY motif in cAMP-mediated exocytosis of ENaC. We have elucidated how a common genetic variant can underlie significant functional diversity in NEDD4L at the cellular level. We propose a model that describes how that functional variation may influence blood pressure. Moreover, our observations regarding differential function of the NEDD4L isoforms may impact other aspects of physiology that involve this ubiquitin ligase.

Physiologic regulation of the epithelial sodium channel by phosphatidylinositides

PURPOSE OF REVIEW

Epithelial sodium channel (ENaC) activity is limiting for sodium reabsorption in the distal nephron. Humans regulate blood pressure by fine-tuning sodium balance through control of ENaC. ENaC dysfunction causes some hypertensive and renal salt wasting diseases. Thus, it is critical to understand the cellular mechanisms controlling ENaC activity.

RECENT FINDINGS

ENaC is sensitive to phosphatidylinositol 4,5-bisphosphate (PIP2), the target of phospholipase C-mediated metabolism, and phosphatidylinositiol 3,4,5-trisphosphate (PIP3), the product of phosphatidylinositide 3-OH kinase (PI3-K). PIP2 is permissive for ENaC gating possibly interacting directly with the channel. Activation of distal nephron P2Y receptors tempers ENaC activity by promoting PIP2 metabolism. This is important because gene deletion of P2Y2 receptors causes hypertension associated with hyperactive ENaC. Aldosterone, the final hormone in a negative-feedback cascade activated by decreases in blood pressure, increases ENaC activity. PIP3 sits at a critical bifurcation in the aldosterone-signaling cascade, increasing ENaC open probability and number. PIP3-effectors mediate increases in ENaC number by suppressing channel retrieval. PIP3 binds ENaC, at a site distinct from that important to PIP2 regulation, to modulate directly open probability.

SUMMARY

Phosphoinositides play key roles in physiologic control of ENaC and perhaps dysregulation plays a role in disease associated with abnormal renal sodium handling.

Prostasin: a possible candidate gene for human hypertension

BACKGROUND

Prostasin, a serine protease, is suggested to be a novel mechanism regulating the epithelial sodium channel (ENaC) expressed in the distal nephron. This study aimed to evaluate whether the human prostasin gene is a novel candidate gene underlying blood pressure (BP) elevation.

METHODS

In a sample of healthy African-American (AA) and European-American (EA) twin subjects aged 17.6 +/- 3.3 years (n = 920, 45% AAs), race-specific tagging single-nucleotide polymorphisms (tSNPs) were identified to tag all the available SNPs +/- 2 kb up- and downstream of the prostasin gene from HapMap at r2 of 0.8-1.0. Selection yielded four tSNPs in AAs and one in EAs, with one tSNP (rs12597511: C to T) present in both AAs and EAs.

RESULTS

For rs12597511, CT and TT genotypes exhibited higher systolic BP (SBP) than CC genotype (115.9 +/- 1.1 mm Hg vs. 113.7 +/- 0.6 mm Hg, P = 0.025 (AAs); and 110.7 +/- 0.5 mm Hg vs. 109.6 +/- 0.6 mm Hg, P = 0.115 (EAs)). CT and TT genotypes compared with CC genotype showed a significant increase in diastolic BP (DBP) in both racial groups (62.5 +/- 0.7 mm Hg vs. 60.4 +/- 0.4 mm Hg, P = 0.003 (AAs); and 58.2 +/- 0.3 mm Hg vs. 56.7 +/- 0.4 mm Hg, P = 0.007 (EAs)). Furthermore, there was an increase in radial pulse wave velocity (PWV) in subjects with CT and TT genotype as compared with those with CC genotype (6.5 +/- 0.1 vs. 6.1 +/- 0.1 m/s, P < 0.0001) (EAs); and 6.7 +/- 0.1 vs. 6.6 +/- 0.1 m/s, P = 0.354 (AAs)). Analyses combining AAs and EAs consistently demonstrated a statistical significance of rs12597511 on all the phenotypes including SBP/DBP and PWV.

CONCLUSION

Genetic variation of the prostasin gene may be implicated in the development of hypertension in youths..

Physiological Interaction Between α-Adducin and WNK1-NEDD4L Pathways on Sodium-Related Blood Pressure Regulation

The kidney plays an important role in salt and blood pressure (BP) homeostasis. In previous studies, variants in the genes for α-adducin (ADD1), WNK1, and NEDD4L, which all regulate renal sodium absorption, have been associated with increased BP. However, findings have been inconsistent. We tested whether this is because of physiological interactions between the effects of variants in these genes. We assessed the single and combined effects of the ADD1 (Gly460Trp), WNK1 (rs880054 A/G), and NEDD4L (rs4149601 G/A) polymorphisms on renal and BP response to an acute Na load (n=344 subjects), BP decrease after 1 month of treatment with 12.5 mg of hydrochlorothiazide (n=193), and ambulatory 24-hour BP (n=690). Individually, the variants showed modest effects on some of the studied phenotypes. We found the ADD1 Trp allele to be permissive for the effects of variants of the other genes. In combination, the same variants (ADD1 Trp/WNK1 GG/Nedd4L GA+AA) showed a consistent effect on renal Na handling ( P =0.009) and acute BP response to a saline infusion ( P =0.021), BP lowering after thiazide treatment ( P =0.008), and nocturnal systolic BP ( P =0.044). Physiological interaction between the ADD1 and WNK1-NEDD4L pathways influences the effects of variants in these genes on sodium-related BP regulation. Relatively common alleles in the ADD1, WNK1, and NEDD4L genes when present in combination may have significant effects on renal sodium handling, BP, and antihypertensive response to thiazides.

Salt-sensitive hypertension and cardiac hypertrophy in mice deficient in the ubiquitin ligase Nedd4-2

Nedd4-2 has been proposed to play a critical role in regulating epithelial Na+ channel (ENaC) activity. Biochemical and overexpression experiments suggest that Nedd4-2 binds to the PY motifs of ENaC subunits via its WW domains, ubiquitinates them, and decreases their expression on the apical membrane. Phosphorylation of Nedd4-2 (for example by Sgk1) may regulate its binding to ENaC, and thus ENaC ubiquitination. These results suggest that the interaction between Nedd4-2 and ENaC may play a crucial role in Na+ homeostasis and blood pressure (BP) regulation. To test these predictions in vivo, we generated Nedd4-2 null mice. The knockout mice had higher BP on a normal diet and a further increase in BP when on a high-salt diet. The hypertension was probably mediated by ENaC overactivity because 1) Nedd4-2 null mice had higher expression levels of all three ENaC subunits in kidney, but not of other Na+ transporters; 2) the downregulation of ENaC function in colon was impaired; and 3) NaCl-sensitive hypertension was substantially reduced in the presence of amiloride, a specific inhibitor of ENaC. Nedd4-2 null mice on a chronic high-salt diet showed cardiac hypertrophy and markedly depressed cardiac function. Overall, our results demonstrate that in vivo Nedd4-2 is a critical regulator of ENaC activity and BP. The absence of this gene is sufficient to produce salt-sensitive hypertension. This model provides an opportunity to further investigate mechanisms and consequences of this common disorder.

Two polymorphisms in NEDD4L gene and essential hypertension in Chinese Hans - a population-based case-control study

Neural precursor cell expressed developmentally down-regulated 4-like (NEDD4L) gene may play an important role in the development of hypertension by regulating the amiloride-sensitive epithelial sodium channel for sodium reabsorption. Recently, a functional polymorphism located at the last nucleotide of exon 1 (rs4149601) of the NEDD4L gene were found to be associated with hypertension both in African Americans and whites, and a "flip-flop" association with hypertension was found in two white samples for a polymorphism located at intron 13 (rs3865418). In this study, we aimed at examining the role of these two variants on essential hypertension in Chinese Hans. In a population-based association study, we observed significantly higher prevalence of T allelic frequencies (p = 0.023) in hypertensives than normotensives. In logistic regression analysis, the stronger association was found under the additive model with an odds ratio of 1.31 (1.04-1.67) for T allele (p = 0.025). The association remained significant (p = 0.039) with an odds ratio of 1.29 (1.01-3.66) when adjusting for age and sex. We also constructed an ANCOVA factorial model by using clinical parameters as the dependent variable for rs3865418 polymorphisms. A significantly higher diastolic blood pressure was observed at rs3865418 in the dominant model for the T allele (p = 0.009). The positive association still exist after controlling age and sex (p = 0.013). For rs4149601 polymorphism, however, we did not observe a positive association with hypertension by implicating either logistic regression models or ANCOVA models. Thus, our results support rs3865418 but not rs4149601 polymorphism of NEDD4L gene implicated in the prevalence of hypertension in Chinese Hans.