Epithelial Sodium Channel Alpha Research Articles

Two-generation exposure to a high-fat diet induces the change of salty taste preference in rats

High-fat diet (HFD) leads to multiple complications, including taste alteration. This study observed the effect of a two-generation exposure to an HFD on the peripheral taste system in offspring. Ten pregnant Wistar rats were assigned a standard diet (SD) (n = 5) or HFD (n = 5) from day 7 of pregnancy through the lactation. Thirty-six male and female 3-week-old offspring were measured for body weight and blood glucose level, and the circumvallate papillae were collected. The other twenty-four 3-week-old offspring were weaned on the same diet as their mothers and raised individually. The taste preference behaviors were studied using the two-bottle taste preference test and analyzed five basic tastes (sweet, bitter, umami, sour, and salty). The expressions of epithelial sodium channel alpha subunit (ENaCα) and angiotensin II receptor type 1 (AT1) in the circumvallate papilla were analyzed by immunohistochemical staining and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). We found increased body weight and salty taste preference of offspring from the HFD group in both sexes. Correspondingly, the AT1 level of the taste bud cells significantly increased in 3-week-old female offspring from the HFD group. An increase in AT1 levels may be a risk factor for changes in salty taste preference.

Upregulation of α-ENaC induces pancreatic β-cell dysfunction, ER stress, and SIRT2 degradation.

Islet beta cells (β-cells) produce insulin in response to high blood glucose levels, which is essential for preserving glucose homeostasis. Voltage-gated ion channels in β-cells, including Na +, K +, and Ca 2+ channels, aid in the release of insulin. The epithelial sodium channel alpha subunit (α-ENaC), a voltage-independent sodium ion channel, is also expressed in human pancreatic endocrine cells. However, there is no reported study on the function of ENaC in the β-cells. In the current study, we found that α-ENaC was expressed in human pancreatic glandule and pancreatic islet β-cells. In the pancreas of db/db mice and high-fat diet-induced mice, and in mouse islet β-cells (MIN6 cells) treated with palmitate, α-ENaC expression was increased. When α-ENaC was overexpressed in MIN6 cells, insulin content and glucose-induced insulin secretion were significantly reduced. On the other hand, palmitate injured islet β-cells and suppressed insulin synthesis and secretion, but increased α-ENaC expression in MIN6 cells. However, α-ENaC knockout ( Scnn1a -/-) in MIN6 cells attenuated β-cell disorder induced by palmitate. Furthermore, α-ENaC regulated the ubiquitylation and degradation of sirtuin 2 in β-cells. α-ENaC also modulated β-cell function in correlation with the inositol-requiring enzyme 1 alpha/X-box binding protein 1 (IRE1α/XBP1) and protein kinase RNA-like endoplasmic reticulum kinase/C/EBP homologous protein (PERK/CHOP) endoplasmic reticulum stress pathways. These results suggest that α-ENaC may play a novel role in insulin synthesis and secretion in the β-cells, and the upregulation of α-ENaC promotes islet β-cell dysfunction. In conclusion, α-ENaC may be a key regulator involved in islet β-cell damage and a potential therapeutic target for type 2 diabetes mellitus.

ALTERED EXPRESSION OF LUNG EPITHELIAL ION AND FLUID TRANSPORTERS DURING PROGRESSION OF PULMONARY HYPERTENSION IN THE MONOCROTALINE MODEL

Objective: Recent studies have evaluated a significant incidence of pleural effusions in patients with idiopathic and heritable pulmonary arterial hypertension (PAH) co-diagnosed with isolated right-sided heart failure (RHF). Coincidence of pleural effusions and RHF in these patients significantly increased mortality rate during follow-up. However, mechanism of pleural effusions formation has not been fully explained. Therefore, we examined expression of lung epithelial ion and fluid transporters responsible for alveolar fluid clearance (AFC), which may contribute to lung fluid accumulation under pathological conditions and potentially formation of pleural effusions. Design and method: 12-weeks old male Wistar rats were subcutaneously injected with monocrotaline (60 mg/kg, MCT) or vehicle (CON). The relative expression of AFC transporters: Na+/K+-ATPase alpha1, alpha2, beta1, beta3 subunits, epithelial sodium channel (ENaC) alpha, beta, gama subunits, cystic fibrosis transmembrane conductance regulator (CFTR) were determined by RT-qPCR 1, 2, 4 weeks after MCT application and also in end-stage disease (animals sacrificed after acute health deterioration, ∼ 4 weeks after MCT application) where pleural effusions were observed. Results: Increase in lung weight was observed from second week after MCT application and was more profound in end-stage disease (by 26 % compared to fourth week, p < 0.05). A downregulation of all three pore-forming subunits of ENaC was observed in end-stage disease, accompanied by downregulation of small beta3 subunit of Na+/K+-ATPase. Expression of catalytic alpha2 subunit of Na+/K+-ATPase gradually decreased with disease progression from first week after MCT (-80% in end-stage vs. CON, p < 0.05). On the other hand, we observed upregulation of CFTR (by 80%) and beta1 subunit of Na+/K+ATPase (by 79% vs. CON, p < 0.05) mainly in end-stage disease. Conclusions: Downregulation of lung epithelial ion and fluid transporters contributing to AFC is predominantly limited to higher stages of PH with a marked downregulation in end-stage. These expression alterations may contribute to overall lung weight increase observed in end-stage disease. However, observed early alpha2 subunit of Na+/K+-ATPase downregulation could participate on the pathogenesis of PH while upregulation of beta1 subunit and CFTR in end-stage disease could represent a compensatory mechanism.

Cofilin participates in regulating alpha-epithelial sodium channel by interaction with 14-3-3 isoforms.

Renal epithelial sodium channel (ENaC) plays a crucial role in maintaining homeostasis and sodium absorption. While insulin participates in controlling sodium transport across the renal epithelium, the underlying molecular mechanism remain unclear. In this study, we found that insulin increased the expression and function of alpha-epithelial sodium channel (α-ENaC) as well as phosphorylation of cofilin, a family of actin-binding proteins which disassembles actin filaments, in mouse cortical collecting duct (mpkCCDc14) cells. The wild-type (WT) cofilin and its constitutively phosphorylated form (S3D), but not its constitutively non-phosphorylable form (S3A), contributed to the elevated expression on α-ENaC. Overexpression of 14-3-3ε, β, or γ increased the expression of α-ENaC and cofilin phosphorylation, which was blunted by knockdown of 14-3-3ε, β, or γ. Moreover, it was found that insulin increased the interaction between cofilin and 14-3-3 isoforms, which indicated relevance of 14-3-3 isoforms with cofilin. Furthermore, LIMK1/SSH1 pathway was involved in regulation of cofilin and α-ENaC expression by insulin. The results from this work indicate that cofilin participates in the regulation of α-ENaC by interaction with 14-3-3 isoforms.

Decreased decidual epithelial sodium channel (ENaC) alpha and gamma subunits in recurrent pregnancy loss (RPL).

Decreased decidual epithelial sodium channel (ENaC) alpha and gamma subunits in recurrent pregnancy loss (RPL).

Leptin‐Induced Endothelial Dysfunction is Mediated by Endothelial Mineralocorticoid Receptor Epithelial Sodium Channel Activation in Female Mice

Rising rates of hypertension are significantly associated with rising rates of obesity. While the mechanisms of obesity‐associated hypertension have been heavily investigated, these studies have overwhelmingly favored men and male rodents as research subjects. Therefore, the sex‐specific mechanisms of obesity‐associated hypertension require investigation. Our lab has previously shown that the adipocyte‐derived hormone leptin, whose levels are drastically increased in obesity, is required for hypertension and endothelial dysfunction in obese female mouse models, the development of which is dependent on leptin‐induced aldosterone secretion and subsequent mineralocorticoid receptor (MR) activation. The epithelial sodium channel alpha (ENaC), whose transcription is directly upregulated by MR activation, has also been implicated in endothelial dysfunction in female mice. We therefore sought to test the hypothesis that endothelial MR activation mediates leptin‐induced endothelial dysfunction via increased activation of ENaC. To test that endothelial MR activation, specifically, is required for leptin‐induced endothelial dysfunction we infused female endothelial cell‐specific MR knockout mice (ECMR KO) with leptin (0.9 mg/kg/day) via subcutaneous osmotic minipump. Wild‐type mice (WT) developed endothelial dysfunction, as assessed by vascular (aortic rings) relaxation to acetylcholine (10−9 M–10−5 M, nonlinear fit curve), in response to leptin infusion (P<0.05, two‐way ANOVA, n=4–6). However, ECMR KO female mice infused with leptin were protected from endothelial dysfunction (n=6–7), indicating that endothelial MR activation mediates leptin‐induced endothelial dysfunction in female mice. In contrast, no effect of leptin nor endothelial MR deletion was observed on endothelial function in male WT and ECMR KO mice (n=2–5). To assess if MR‐mediated ENaC activation plays a role in leptin‐induced endothelial dysfunction, leptin‐infused female mice were treated with amiloride (ENaC antagonist, 100 ug/day in drinking water) which ablated endothelial dysfunction in female leptin‐infused mice (P<0.05, two‐way ANOVA, n=4), indicating that leptin‐induced endothelial dysfunction requires ENaC activation. In addition, we sought to assess the potential for leptin to upregulate endothelial cell ENaC expression in female mice. Isolated endothelial cells, which were obtained from the aorta via CD31‐specific magnetic bead sorting, were extracted from female Agouti hyperleptinemic obese mice and RT‐PCR analysis for mRNA expression of ENaC demonstrated elevated ENaC expression in hyperleptinemic mice (10.8±0.5‐fold change from lean control female mice, n=2–3). These elevations in endothelial ENaC mRNA expression are associated with elevated plasma aldosterone in hyperleptinemic female mice, indicating that leptin‐induced aldosterone induces endothelial dysfunction via increased MR activation, which ultimately leads to elevated ENaC expression and activation. Therefore, MR‐stimulated ENaC upregulation may play a crucial role in the development of leptin‐mediated cardiovascular diseases in obese females.Support or Funding InformationThis work was supported by the following: NIH 1R01HL130301‐01, AHA 16IRG27770047, NIH 5F32HL136191‐0This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

High salt loading induces urinary storage dysfunction via upregulation of epithelial sodium channel alpha in the bladder epithelium in Dahl salt-sensitive rats

We aimed to investigate whether high salt intake affects bladder function via epithelial sodium channel (ENaC) by using Dahl salt-resistant (DR) and salt-sensitive (DS) rats. Bladder weight of DR + high-salt diet (HS, 8% NaCl) and DS + HS groups were significantly higher than those of DR + normal-salt diet (NS, 0.3% NaCl) and DS + NS groups after one week treatment. We thereafter used only DR + HS and DS + HS group. Systolic and diastolic blood pressures were significantly higher in DS + HS group than in DR + HS group after the treatment period. Cystometrogram showed the intercontraction intervals (ICI) were significantly shorter in DS + HS group than in DR + HS group during infusion of saline. Subsequent infusion of amiloride significantly prolonged ICI in DS + HS group, while no intra-group difference in ICI was observed in DR + HS group. No intra- or inter-group differences in maximum intravesical pressure were observed. Protein expression levels of ENaCα in the bladder were significantly higher in DS + HS group than in DR + HS group. ENaCα protein was localized at bladder epithelium in both groups. In conclusion, high salt intake is considered to cause urinary storage dysfunction via upregulation of ENaC in the bladder epithelium with salt-sensitive hypertension, suggesting that ENaC might be a candidate for therapeutic target for urinary storage dysfunction.

Arginyl dipeptides increase the frequency of NaCl-elicited responses via epithelial sodium channel alpha and delta subunits in cultured human fungiform taste papillae cells

Salty taste is one of the five basic tastes and is often elicited by NaCl. Because excess sodium intake is associated with many health problems, it could be useful to have salt taste enhancers that are not sodium based. In this study, the regulation of NaCl-induced responses was investigated in cultured human fungiform taste papillae (HBO) cells with five arginyl dipeptides: Ala-Arg (AR), Arg-Ala (RA), Arg-Pro (RP), Arg-Glu (RE), and Glu-Arg (ER); and two non-arginyl dipeptides: Asp-Asp (DD) and Glu-Asp (ED). AR, RA, and RP significantly increased the number of cell responses to NaCl, whereas no effect was observed with RE, ER, DD, or ED. We also found no effects with alanine, arginine, or a mixture of both amino acids. Pharmacological studies showed that AR significantly increased responses of amiloride-sensitive but not amiloride-insensitive cells. In studies using small interfering RNAs (siRNAs), responses to AR were significantly decreased in cells transfected with siRNAs against epithelial sodium channel ENaCα or ENaCδ compared to untransfected cells. AR dramatically increased NaCl-elicited responses in cells transfected with NHE1 siRNA but not in those transfected with ENaCα or ENaCδ siRNAs. Altogether, AR increased responses of amiloride-sensitive cells required ENaCα and ENaCδ.

Kidney‐specific Conditional Knockout of Klotho Gene Impairs Natriuresis and causes hypertension by upregulating Epithelial Sodium Channel alpha

Background and PurposeExcessive reabsorption of sodium by the kidney tubules contributes to renal dysfunction and high blood pressure. Deletion of Klotho leads to hypertension. The purpose of this study is to investigate if renal epithelial sodium channel (ENaC) contributes to klotho deficiency‐induced hypertension.Methods and ResultsWe generated kidney‐specific conditional klotho null (KspKL−/−) mice and found out that renal alpha subunit of ENaC is significantly upregulated compared to wild type (WT) mice. Blood pressure measured by telemetry demonstrated systolic hypertension and elevated pulse pressure suggesting vascular dysfunction in KspKL−/−. Pulse wave velocity, a marker of arterial stiffening was significantly increased in KspKL−/− mice. Amiloride, an ENaC inhibitor, completely prevented systolic hypertension and arterial stiffening in KspKL−/− mice. Ex vivo vascular relaxing responses to acetylcholine were diminished in mesenteric arteries in KspKL−/− group, indicating that klotho deficiency causes vascular endothelial dysfunction. Interestingly, treatment with amiloride abolished Klotho deficiency‐induced vascular endothelial dysfunction. We found that urinary sodium excretion (UNaV) was significantly impaired in KspKL−/− group. Na retention was also associated with a decrease in glomerular filtration rate (GFR), suggesting impaired renal function in KspKL−/− mice. Treatment with amiloride prevented sodium retention and improved GFR in KspKL−/− mice. Total renal nitric oxide bioavailabililty and eNOS activity were significantly decreased in KspKl−/− mice which was ameliorated by amiloride treatment. Histological and morphometric analysis showed glomerular and tubular damage in KspKL−/−, which was improved by amiloride treatment. Western blotting analysis demonstrated a significant decrease in the αγ subunits of ENaC in the kidney cortex following treatment with amiloride.ConclusionThis study demonstrates for the first time that depletion of klotho causes impairment in Na‐excretion and hypertension by affecting ENaCα levels. ENaC may be a promising therapeutic target for klotho deficiency‐induced renal and vascular dysfunction and hypertension.

The role of dexamethasone in scorpion venom-induced deregulation of sodium and water transport in rat lungs.

BackgroundSevere scorpion envenomation can evolve to lung injury and, in some cases, death. The lung injury could be attributed to acute left ventricular failure and increased pulmonary vascular permeability secondary to the release of inflammatory mediators. In clinical practice, corticosteroids have been administered to reduce the early side effects of the anti-venom. We propose to study the effects of Tityus serrulatus venom and dexamethasone on pulmonary expression of sodium and water transporters, as well as on the inflammatory response.MethodsWistar rats were injected intraperitoneally with saline (control group), dexamethasone, and saline (2.0 mg/kg body weight—60 min before saline injection; dexamethasone + saline group), venom (T. serrulatus venom—3.8 mg/kg body weight), or dexamethasone and venom (2.0 mg/kg body weight—60 min before venom injection; dexamethasone + venom group). At 60 min after venom/saline injection, experiments were performed in ventilated and non-ventilated animals. We analyzed sodium transporters, water transporters, and Toll-like receptor 4 (TLR4) by Western blotting, macrophage infiltration by immunohistochemistry, and serum interleukin (IL) by cytokine assay.ResultsIn the lung tissue of non-ventilated envenomed animals, protein expression of the epithelial sodium channel alpha subunit (α-ENaC) and aquaporin 5 (AQP5) were markedly downregulated whereas that of the Na-K-2Cl cotransporter (NKCC1) and TLR4 was elevated although expression of the Na,K-ATPase alpha 1 subunit was unaffected. Dexamethasone protected protein expression of α-ENaC, NKCC1, and TLR4 but not that of AQP5. We found that IL-6, IL-10, and tumor necrosis factor alpha were elevated in the venom and dexamethasone + venom groups although CD68 expression in lung tissue was elevated only in the venom group. Among the ventilated animals, both envenomed groups presented hypotension at 50 min after injection, and the arterial oxygen tension/fraction of inspired oxygen ratio was lower at 60 min than at baseline.ConclusionsOur results suggest that T. serrulatus venom and dexamethasone both regulate sodium transport in the lung and that T serrulatus venom regulates sodium transport via the TLR4 pathway.

Evaluation of the relationship between T663A polymorphism in the alpha-epithelial sodium channel gene and essential hypertension.

Objectives:To evaluate the relationship between alpha epithelial sodium channel (alpha-ENaC) T663A polymorphism and the risk of essential hypertension.Methods:This meta-analysis was conducted between November 2014 and February 2015 in Shanghai Medical Instrumentation College, Shanghai, China. We collected all published available case-control data (N=12) identified through PubMed, Web of Science, Scopus, and Chinese National Knowledge Infrastructure (CNKI) up to December 2014. The pooled odds ratio (OR) with 95% confidence interval (CI) was calculated using the fixed- or random-effect model.Results:Although subgroup analysis showed that alpha-ENaC T663A polymorphism was associated with essential hypertension in North American individuals (OR=1.55, 95% CI=1.22-1.98, p=0.0003), our meta-analysis results did not confirm such association overall (OR=1.03, 95% CI=0.92-1.15, p=0.62). The lack of association was further confirmed by the non-superiority test (p<0.0001).Conclusion:Alpha-ENaC T663A polymorphism might not be a risk factor for essential hypertension.

A long isoform of the epithelial sodium channel alpha subunit forms a highly active channel

A long isoform of the human Epithelial Sodium Channel (ENaC) α subunit has been identified, but little data exist regarding the properties or regulation of channels formed by α728. The baseline whole cell conductance of oocytes expressing trimeric α728βγ channels was 898.1 ± 277.2 and 49.59 ± 13.2 µS in low and high sodium solutions, respectively, and was 11 and 2 fold higher than the conductances of α669βγ in same solutions. α728βγ channels were also 2 to 5 fold less sensitive to activation by the serine proteases subtilisin and trypsin than α669βγ in low and high Na+ conditions. The long isoform exhibited lower levels of full length and cleaved protein at the plasma membrane and a rightward shifted sensitivity to inhibition by increases of [Na+]i. Both channels displayed similar single channel conductances of 4 pS, and both were activated to a similar extent by reducing temperature, altogether indicating that activation of baseline conductance of α728βγ was likely mediated by enhanced channel activity or open probability. Expression of α728 in native kidneys was validated in human urinary exosomes. These data demonstrate that the long isoform of αENaC forms the structural basis of a channel with different activity and regulation, which may not be easily distinguishable in native tissue, but may underlie sodium hyperabsorption and salt sensitive differences in humans.

Retinal vasculopathy is reduced by dietary salt restriction: involvement of Glia, ENaCα, and the renin-angiotensin-aldosterone system.

Neovascularization and vaso-obliteration are vision-threatening events that develop by interactions between retinal vascular and glial cells. A high-salt diet is causal in cardiovascular and renal disease, which is linked to modulation of the renin-angiotensin-aldosterone system. However, it is not known whether dietary salt influences retinal vasculopathy and if the renin-angiotensin-aldosterone system is involved. We examined whether a low-salt (LS) diet influenced vascular and glial cell injury and the renin-angiotensin-aldosterone system in ischemic retinopathy. Pregnant Sprague Dawley rats were fed LS (0.03% NaCl) or normal salt (0.3% NaCl) diets, and ischemic retinopathy was induced in the offspring. An LS diet reduced retinal neovascularization and vaso-obliteration, the mRNA and protein levels of the angiogenic factors, vascular endothelial growth factor, and erythropoietin. Microglia, which influence vascular remodeling in ischemic retinopathy, were reduced by LS as was tumor necrosis factor-α. Macroglial Müller cells maintain the integrity of the blood-retinal barrier, and in ischemic retinopathy, LS reduced their gliosis and also vascular leakage. In retina, LS reduced mineralocorticoid receptor, angiotensin type 1 receptor, and renin mRNA levels, whereas, as expected, plasma levels of aldosterone and renin were increased. The aldosterone/mineralocorticoid receptor-sensitive epithelial sodium channel alpha (ENaCα), which is expressed in Müller cells, was increased in ischemic retinopathy and reduced by LS. In cultured Müller cells, high salt increased ENaCα, which was prevented by mineralocorticoid receptor and angiotensin type 1 receptor blockade. Conversely, LS reduced ENaCα, angiotensin type 1 receptor, and mineralocorticoid receptor expression. An LS diet reduced retinal vasculopathy, by modulating glial cell function and the retinal renin-angiotensin-aldosterone system.

Increased cystic fibrosis transmembrane conductance regulators expression and decreased epithelial sodium channel alpha subunits expression in early abortion: findings from a mouse model and clinical cases of abortion.

The status of the maternal endometrium is vital in regulating humoral homeostasis and for ensuring embryo implantation. Cystic fibrosis transmembrane conductance regulators (CFTR) and epithelial sodium channel alpha subunits (ENaC-α) play an important role in female reproduction by maintaining humoral and cell homeostasis. However, it is not clear whether the expression levels of CFTR and ENaC-α in the decidual component during early pregnancy are related with early miscarriage. CBA×DBA/2 mouse mating has been widely accepted as a classical model of early miscarriage. The abortion rate associated with this mating was 33.33% in our study. The decidua of abortion-prone CBA female mice (DBA/2 mated) had higher CFTR mRNA and protein expression and lower ENaC-α mRNA and protein expression, compared to normal pregnant CBA mice (BLAB/C mated). Furthermore, increased CFTR expression and decreased ENaC-α expression were observed in the uterine tissue from women with early miscarriage, as compared to those with successful pregnancy. In conclusion, increased CFTR expression and decreased ENaC-α expression in the decidua of early abortion may relate with failure of early pregnancy.

Regulation of the delta and alpha epithelial sodium channel (ENaC) by ubiquitination and Nedd8

The δ epithelial sodium channel (δENaC) is a proton-activated, sodium-selective, amiloride-sensitive ion channel in the ENaC/degenerin family of ion channels involved in blood pressure regulation and mechanosensation. Other ENaC family members are subject to ubiquitin modification leading to internalization from the cell surface, and degradation of the channel. Here, we show that δENaC is also modified by ubiquitin on three intracellular lysine residues. Absence of these lysines abolished ubiquitin modification of δENaC and increased cell surface levels of δENaC. Although the HECT-domain ubiquitin ligase Nedd4-2 reduced amiloride-sensitive current generated by δβγENaC-containing channels, δENaC does not contain a binding site for Nedd4-2; therefore, this effect is probably mediated by the βγENaC subunits. Nedd8, a ubiquitin-like protein that regulates RING-domain E3 ubiquitin ligases, promoted δENaC ubiquitination, decreased both the intracellular and cell surface δENaC populations, and decreased δβγENaC amiloride-sensitive short circuit current (Isc -amiloride) in a mammalian epithelium. Nedd8 also promoted α- and γENaC ubiquitination, decreased the cell surface pools, and decreased αβγENaC Isc -amiloride. Conversely, XIAP, a single subunit RING E3 ligase, decreased ubiquitinated δENaC, increased the δENaC cell surface pool and increased δβγENaC Isc -amiloride. Therefore δ- and α - βγENaC channel function may be influenced by RING-domain E3 ubiquitin ligases.

Reduced Prostasin (CAP1/PRSS8) Activity Eliminates HAI-1 and HAI-2 Deficiency–Associated Developmental Defects by Preventing Matriptase Activation

Loss of either hepatocyte growth factor activator inhibitor (HAI)-1 or -2 is associated with embryonic lethality in mice, which can be rescued by the simultaneous inactivation of the membrane-anchored serine protease, matriptase, thereby demonstrating that a matriptase-dependent proteolytic pathway is a critical developmental target for both protease inhibitors. Here, we performed a genetic epistasis analysis to identify additional components of this pathway by generating mice with combined deficiency in either HAI-1 or HAI-2, along with genes encoding developmentally co-expressed candidate matriptase targets, and screening for the rescue of embryonic development. Hypomorphic mutations in Prss8, encoding the GPI-anchored serine protease, prostasin (CAP1, PRSS8), restored placentation and normal development of HAI-1–deficient embryos and prevented early embryonic lethality, mid-gestation lethality due to placental labyrinth failure, and neural tube defects in HAI-2–deficient embryos. Inactivation of genes encoding c-Met, protease-activated receptor-2 (PAR-2), or the epithelial sodium channel (ENaC) alpha subunit all failed to rescue embryonic lethality, suggesting that deregulated matriptase-prostasin activity causes developmental failure independent of aberrant c-Met and PAR-2 signaling or impaired epithelial sodium transport. Furthermore, phenotypic analysis of PAR-1 and matriptase double-deficient embryos suggests that the protease may not be critical for focal proteolytic activation of PAR-2 during neural tube closure. Paradoxically, although matriptase auto-activates and is a well-established upstream epidermal activator of prostasin, biochemical analysis of matriptase- and prostasin-deficient placental tissues revealed a requirement of prostasin for conversion of the matriptase zymogen to active matriptase, whereas prostasin zymogen activation was matriptase-independent.

The Effect of Endogenous Angiotensin II on Alveolar Fluid Clearance in Rats with Acute Lung Injury

In acute lung injury (ALI), angiotensin II (Ang II) plays a vital role in the stimulation of pulmonary permeability edema formation through the angiotensin type 1 (AT1) receptor. The effect of Ang II on alveolar fluid clearance (AFC) in ALI remains unknown. Sprague Dawley rats were anesthetized and intratracheally injected with 1 mg⁄kg lipopolysaccharide (LPS), while control rats received saline. The AT1 receptor antagonist ZD7155 was injected intraperitoneally (10 mg⁄kg) 30 min before LPS administration. The lungs were isolated for AFC measurement, and alpha-epithelial sodium channel (ENaC) messenger RNA and protein expression were detected by reverse-transcription polymerase chain reaction and Western blot. LPS-induced ALI caused an increase in Ang II levels in plasma and lung tissue but a decrease in AFC. The time course of Ang II levels paralleled that of AFC. Pretreatment with ZD7155 prevented ALI-induced reduction of AFC. ZD7155 also reversed the ALI-induced reduction of beta-ENaC and gamma-ENaC levels, and further decreased alpha-ENaC levels. These findings suggest that endogenous Ang II inhibits AFC and dysregulates ENaC expression via AT1 receptors, which contribute to alveolar filling and pulmonary edema in LPS-induced ALI.

Study of regulatory effect of insulin on expression of epithelial sodium channel alpha subunit in A549 cells

To observe the effects of insulin on the expression of epithelial sodium channel alpha subunit (ENaC-alpha) in human pulmonary adenocarcinoma cell line (A549 cells) and its impact on apoptosis of the cells. A549 cells were cultured with insulin in a concentration of 30 U/L for 30 minutes or 60 minutes. Then ENaC-alpha, serum and glucocorticoid-inducible kinase-1 (SGK-1) protein and mRNA were determined with Western blotting and reverse transcription-polymerase chain reaction (RT-PCR). Then chelidonii, a blocking agent of protein kinase C (PKC), which could inhibit the effect of SGK-1, was added to the cells culture for 60 minutes, and ENaC-alpha protein was then determined. Cells were cultured in a hypoxia circumstance for 30 minutes, to induce apoptosis, the rate of which was detected with terminal-deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL), in cells cultured with or without insulin. Insulin could up-regulate the protein and mRNA expression of ENaC-alpha and SGK-1 in A549 cells, and there was a significant difference at 30 minutes, and it gradually increased with prolongation of time. When A549 cells were cultured without insulin, the protein expression of A549 cells was 100%. The protein expression of ENaC-alpha and SGK-1 was 124% and 135% at 30 minutes after being cultured with insulin, and 186% and 176% at 60 minutes, respectively (all P<0.05). Insulin also could inhibit apoptosis which was induced by hypoxia (10.3% vs. 21.6%, P<0.05). Insulin can up-regulate expression of the ENaC-alpha in A549 cells via PKC and SGK-1 pathways, also insulin can inhibit hypoxia induced apoptosis. So insulin can be beneficial in the prognosis of acute lung injury/acute respiratory distress syndrome (ALI/ARDS).

Hsp90 Directly Modulates the Spatial Distribution of AF9/MLLT3 and Affects Target Gene Expression

AF9/MLLT3 contributes to the regulation of the gene encoding the epithelial sodium channel alpha, ENaCalpha, in renal tubular cells. Specifically, increases in AF9 protein lead to a reduction in ENaCalpha expression and changes in AF9 activity appear to be an important component of aldosterone signaling in the kidney. Whereas AF9 is found in the nucleus where it interacts with the histone H3 lysine 79 methyltransferase, Dot1, AF9 is also present in the cytoplasm. Data presented in this report indicate that the heat shock protein Hsp90 directly and specifically interacts with AF9 as part of an Hsp90-Hsp70-p60/Hop chaperone complex. Experimental manipulation of Hsp90 function by the inhibitor novobiocin, but not 17-AAG, results in redistribution of AF9 from a primarily nuclear to cytoplasmic location. Knockdown of Hsp90 with siRNA mimics the effect elicited by novobiocin. As expected, a shift in AF9 from the nucleus to the cytoplasm in response to Hsp90 interference leads to increased ENaCalpha expression. This is accompanied by a decrease in AF9 occupancy at the ENaCalpha promoter. Our data suggest that the interaction of Hsp90, Hsp70, and p60/Hop with AF9 is necessary for the proper subnuclear localization and activity of AF9. AF9 is among a growing number of nuclear proteins recognized to rely on the Hsp90 complex for nuclear targeting.

Relationship between four single nucleotide polymorphisms of epithelial sodium channel alpha subunit gene and essential hypertension of Kazakhs in Xinjiang

To explore the relationship between G2139A,G3091A, T663A, and T3593C single nucleotide polymorphisms (SNPs), which are located at the promoter region,13th exon, and 2nd intron of epithelial sodium channel (ENaC) gene, and their haplotypes with essential hypertension (EH) in Kazakhs in Xinjiang. A case-control study was conducted including 252 EH patients (EH group) and 254 normotensive subjects (NT group) among Kazakhs in Xinjiang. The four genetic polymorphisms were identified by polymerase chain reaction - restriction fragment length polymorphism. The distribution of the genotypes and alleles in all subjects and the different frequency of these four SNPs between EH group and NT group were analyzed. The linkage disequilibrium and haplotypes of these four SNPs were analyzed. These four SNPs of alpha ENaC gene existed in Xinjiang Kazakhs. In all subjects, the distribution frequencies of genotypes AA, AG, and GG at G2139A were 26.2%, 52.3%, and 21.5%, respectively, and those of alleles (A, G) were 52.37% and 47.63%. The distribution frequencies of genotypes AA, AG, and GG at G3091A were 19.0%, 52.5%, and 28.5%, respectively, and those of and alleles (A, G) were 45.56% and 59.44%. The distribution frequencies of genotypes AA, AG, and GG at T663A were 15.6%, 49.9%, and 34.5%, respectively, and those of alleles (A, G) were 40.53% and 59.47%. The distribution frequencies of genotypes TT, TC, and CC at T3593C were 88.5%, 10.5%, and 1.0%, respectively, and those of alleles (T, C) were 93.77% and 6.23%. The distribution of genotypes at these four SNPs were all consistent with Hardy-Weinberg equilibrium in this population (P0.05). The distribution frequencies of genotypes and alleles about these four genetic polymorphisms were not significantly different between the EH group and NT group (P0.05). However, the frequencies of two haplotypes were found to be significantly different between these two groups (P0.05). The haplotype frequency which included 2139G, 3091A, 663G, and 3593T alleles was significantly increased in EH group (P0.01), while the haplotype frequency which included 2139A, 3091A, 663A, and 3593C alleles was significantly increased in NT group (P0.05). The haplotypes that are composed of G2139A, G3091A, T663A, and T3593C polymorphisms of alphaENaC gene may play an important role in the development of EH among Kazakhs in Xinjiang. The haplotypes that are composed of 2139G, 3091A, 663G, and 3593T alleles may aggravate the development of EH. The haplotypes that composed of 2139A, 3091A, 663A, and 3593C alleles may decrease the risk of EH among Kazakhs.