The mineralocorticoid hormone, aldosterone, classically acts via the Mineralocorticoid Receptor (MR) to promote sodium transport in aldosterone target tissues, such as the kidney, thereby controlling long-term electrolyte homeostasis and blood pressure (BP). Aldosterone biosynthesis by the adrenal gland is regulated by a negative feedback loop called the Renin Angiotensin Aldosterone System (RAAS). The glucocorticoid cortisol (corticosterone in rodents), which has a very similar structure to aldosterone, shares with aldosterone an equal affinity for the MR. Typically, plasma cortisol levels are approximately 1000-fold higher than plasma aldosterone, and so the ligand specificity for aldosterone must be imposed on MR by other, non-structural, means. This specificity is important in order to retain electrolyte and BP balance within the control of the RAAS. The co-localisation of the enzyme 11β-Hydroxysteroid Dehydrogenase Type 2 (11β-HSD2) with the MR in aldosterone target tissues provides the MR with the aldosterone specificity it inherently lacks. 11β-HSD2 achieves this by converting active cortisol to its inactive 11-keto metabolite, cortisone (dehydrocorticosterone in rodents). In humans with the monogenetic Syndrome of Apparent Mineralocorticoid Excess (SAME), inactivating mutations in the HSD11B2 gene allows cortisol unregulated access to the MR. Resultant symptoms include severe hypertension and life-threatening hypokalemia. Individuals heterozygous for SAME display no overt phenotypes. However, some studies have associated SAME heterozygosity and loss-of-function polymorphisms within the HSD11B2 gene with essential and/or salt-sensitive hypertension in the general population. Targeted disruption of the Hsd11b2 gene in mice (Hsd11b2-/-) faithfully reproduces with all the major phenotypes of SAME patients. Mice heterozygote for the targeted gene (Hsd11b2+/-) have no phenotype and display a normal BP. In the present study, Hsd11b2+/- mice were used to explore the relationship between reduced 11β-HSD2 enzyme activity and salt-sensitive hypertension. On a high salt diet, Hsd11b2+/- mice were found to have increased BP and impaired natriuresis, compared to wild-type controls (Hsd11b2+/+). Further studies used pharmacological blockade of the Epithelial Sodium Channel (ENaC) and MR to ascertain the contributions of these pathways towards the observed phenotypes. These identified a deregulation of ENaC activity pertaining to an inability to regulate sodium appropriately. Investigations into the contributions of the RAAS and the Hypothalamus Pituitary Adrenal (HPA) axis have revealed valuable insights into their roles in this model. There is an implication that the RAAS has increased sensitivity in Hsd11b2+/-, further exacerbated by increased dietary sodium, and that the regulation of corticosteroids may also be altered. Novel observations have suggested that oxidative stress in response to a high salt diet could also be involved, as a study administering an antioxidant drug in conjunction with a high salt diet prevented the manifestation of a phenotype in Hsd11b2+/-. Finally, the generation of a floxed Hsd11b2 targeting construct for tissue-specific deletion of 11β-HSD2 will allow future studies into the contributions of specific 11β-HSD2 expression sites (such as the kidney) towards the phenotypes of both homozygous and heterozygous mice.

Class of 2012 Abstract / Specific Aims: The epithelial sodium channels (ENaC) found on the apical membranes of epithelial cells including those lining the respiratory tract are the rate limiting step of the absorption of excess fluid from the airspace of the alveoli. ENaC function is modulated by the effects of various physiologic signals such as the adrenergic and purinergic pathways, in addition to other local channels which control the flow of negatively charged ions such as the cystic fibrosis transmembrane conductance regulator (CFTR). We sought to determine the influence of genetic variation on the alpha subunit of ENaC at amino acid position 663 on baseline exhaled ions and pulmonary function in patients with CF. Methods: We assessed pulmonary function ( forced vital capacity[FVC], forced expiratory volume in one second [FEV1], forced expiratory flow maximum[FEFmax]) using a Medical Graphics cardiopulmonary testing device (Minneapolis, MN). Measures of exhaled sodium (Na+) and chloride (Cl-) were obtained using exhaled breathe condensate collected on a Jaeger Ecoscreen condenser unit (Cardinal Health, Yorba Linda, CA) with Na+ quantification using an atomic absorption spectrophotometer (Analyst 100; Perkin Elmer, Norwalk, CT) and Cl- anion quantification using a Dionex AS11 HC column. Healthy n=31 (n=18[58%], 9[29%], and 4[13%] subjects; Body mass index (BMI)=23±1, 25±2, and 25±2kg/ m2 for AA, AT and TT groups respectively). CF n= 42 (n=33[79%], 7[16%], and 2[5%] subjects; BMI equals 23±7, 19±0.4, and 20±2.2kg/m2 for AA, AT and TT groups respectively). Main Results: We found that the distribution of genotypes in CF differed from healthy subjects, with the AA genotype in 80% of CF and 59% in healthy. No significant difference were demonstrated in healthy subjects between genotype groups for pulmonary function and exhaled chloride while the genotypes did differ in exhaled Na (Na=2.9±0.4, 1.7±0.3, and 3.7±1.1mmol/L for AA, AT, and TT respectively, ANOVA p=0.07). CF subjects with the AA genotype had a higher baseline exhaled Cl-, FEV1, and FEFmax than those in the AA group (Cl=0.125±0.038,0.0 27±0.007, and 0.033±0.02 mmol/L ; FEV1=71±5, 68±11, and 40±22L; FEFmax=86±4, 72±7, and 44±24L/sec; for AA, AT, and TT respectively, ANOVA p<0.05, Tukey [AA vs. TT] p<0.05) while exhaled Na+ and FVC were similar between genotypes. Conclusions: Our results suggest that CF subjects with the AA genotype of the alpha subunit of the ENaC have a higher baseline exhaled Cl- and a resulting increase in pulmonary function when compared to the overactive TT groupCF patients with the TT αENaC genotype are likely candidates for early identification and treatment with inhaled ENaC inhibitors or other modulators of this pathway in order to improve survival.

Doctor of Philosophy / Department of Anatomy and Physiology / Bruce D. Schultz / The first aim of this project is to define the cellular mechanisms that account for the low Na[superscript]+ concentration in human milk. MCF10A cells, which were derived from human mammary epithelium and grown on permeable supports, exhibit amiloride- and benzamil-sensitive short circuit current (I[subscript]sc), suggesting activity of the epithelial Na[superscript]+ channel, ENaC. When cultured in the presence of cholera toxin (Ctx), MCF10A cells exhibit greater amiloride sensitive I[subscript]sc at all time points tested, an effect that is not reduced with Ctx washout for 12 hours or by cytosolic pathways inhibitors. Ctx increases the abundance of both beta and gamma-ENaC in the apical membrane and increases its monoubiquitination but without changing total protein and mRNA levels. Additionally, Ctx increases the levels of both the phosphorylated and the nonphosphorylated forms of Nedd4-2, a ubiquitin-protein ligase that regulates ENaC degradation. The results reveal a novel mechanism in human mammary gland epithelia by which Ctx regulates ENaC-mediated Na[superscript]+ transport. The second project aim is to develop a protocol to isolate mammary gland epithelia for subsequent in vitro culture. Caprine (1[superscript]0CME) and bovine mammary epithelia (1[superscript]0BME) were isolated and cultured on permeable supports to study hormone- and neurotransmitter-sensitive ion transport. Both 1[superscript]0CME and 1[superscript]0BME cells were passed for multiple subcultures and all passages formed electrically tight barriers. 1[superscript]0CME were cultured in the presence of hydrocortisone and exhibited high electrical resistance and amiloride-sensitive I[subscript]sc, suggesting the presence of ENaC-mediated Na[superscript]+ transport. 1[superscript]0BME were grown in a complex media in the presence or absence of dexamethasone. In contrast to 1[superscript]0CME, 1[superscript]0BME exhibited no detectable amiloride-sensitive I[subscript]sc in either culture condition. However, 1[superscript]0BME monolayers responded to an adrenergic agonist, norepinephrine, and a cholinergic agonist, carbamylcholine, with rapid increases in I[subscript]sc. Thus, this protocol for isolation and primary cell culture can be used for future studies that focus on mammary epithelial cell regulation and functions. In conclusion, the results from these projects demonstrate that mammary epithelial cells form electrically tight monolayers and can exhibit neurotransmitter- and/or hormone-induced net ion transport. The mechanisms that regulate Na[superscript]+ transport across mammary gland may provide clues to prevent or treat mastitis.

Prostaglandin E2 (PGE2), a metabolite of arachidonic acid, plays a role in water and sodium reabsorption in the collecting duct of the kidney. The collecting duct is responsible for the fine tuning of water and electrolytes. Only a small fraction of the filtered water and sodium is reabsorbed in the collecting duct, a fraction crucial to the regulation of water and electrolyte balance. This current study addresses the role of EP1, one of four PGE2 receptors, in the collecting duct. It is well documented that PGE2 inhibits sodium and water reabsorption in the collecting duct, however the exact mechanism is still debated. To determine whether the EP1 receptor mitigates AngII renal effects, an in vivo study was performed with EP1-/- mice. Global EP1-/- knockout mice were crossed with a renin overexpressing mouse line (herein denoted as “Ren”) and subjected to a high salt (HS) and low salt (LS) diet. Ren mice displayed an 11mmHg increase in systolic blood pressure (BP) on a HS diet and a decrease in BP of 14mmHg on a LS diet compared to the normal salt (NS) diet. Ren EP1-/- mice did not display a significant increase or decrease in BP on a HS or LS diet. On a LS diet, Ren EP1-/- displayed a drop in urine osmolarity (1641 mOsm/ kgH2O) vs. wild type (WT) mice (2107 mOsm/ kgH2O), consistent with increased sodium reabsorption. Narrowing in on the collecting duct, Ren EP1-/- mice had enhanced αENaC levels compared to Ren mice. In ex vivo microperfusion experiments, EP1-/- tubules show no response to PGE2 in the presence of AVP, whereas PGE2 inhibits AVP induced water reabsorption in WT mice. An increase in αENaC membrane accumulation due to EP1 gene ablation results in increased sodium reabsorption subsequently leading to a rise in BP. This contributes to the lack of salt sensitivity in EP1-/- mice. Overall, the EP1 receptor in the collecting duct represents a potential therapeutic target for the treatment of hypertension.

Class of 2012 Abstract / Specific Aims: The epithelial sodium channels (ENaC) found on the apical membranes of epithelial cells including those lining the respiratory tract are the rate limiting step of the absorption of excess fluid from the airspace of the alveoli. ENaC function is modulated by the effects of various physiologic signals such as the adrenergic and purinergic pathways, in addition to other local channels which control the flow of negatively charged ions such as the cystic fibrosis transmembrane conductance regulator (CFTR). We sought to determine the influence of genetic variation on the alpha subunit of ENaC at amino acid position 663 on baseline exhaled ions and pulmonary function in patients with CF. Methods: We assessed pulmonary function ( forced vital capacity[FVC], forced expiratory volume in one second [FEV1], forced expiratory flow maximum[FEFmax]) using a Medical Graphics cardiopulmonary testing device (Minneapolis, MN). Measures of exhaled sodium (Na+) and chloride (Cl-) were obtained using exhaled breathe condensate collected on a Jaeger Ecoscreen condenser unit (Cardinal Health, Yorba Linda, CA) with Na+ quantification using an atomic absorption spectrophotometer (Analyst 100; Perkin Elmer, Norwalk, CT) and Cl- anion quantification using a Dionex AS11 HC column. Healthy n=31 (n=18[58%], 9[29%], and 4[13%] subjects; Body mass index (BMI)=23±1, 25±2, and 25±2kg/ m2 for AA, AT and TT groups respectively). CF n= 42 (n=33[79%], 7[16%], and 2[5%] subjects; BMI equals 23±7, 19±0.4, and 20±2.2kg/m2 for AA, AT and TT groups respectively). Main Results: We found that the distribution of genotypes in CF differed from healthy subjects, with the AA genotype in 80% of CF and 59% in healthy. No significant difference were demonstrated in healthy subjects between genotype groups for pulmonary function and exhaled chloride while the genotypes did differ in exhaled Na (Na=2.9±0.4, 1.7±0.3, and 3.7±1.1mmol/L for AA, AT, and TT respectively, ANOVA p=0.07). CF subjects with the AA genotype had a higher baseline exhaled Cl-, FEV1, and FEFmax than those in the AA group (Cl=0.125±0.038,0.0 27±0.007, and 0.033±0.02 mmol/L ; FEV1=71±5, 68±11, and 40±22L; FEFmax=86±4, 72±7, and 44±24L/sec; for AA, AT, and TT respectively, ANOVA p<0.05, Tukey [AA vs. TT] p<0.05) while exhaled Na+ and FVC were similar between genotypes. Conclusions: Our results suggest that CF subjects with the AA genotype of the alpha subunit of the ENaC have a higher baseline exhaled Cl- and a resulting increase in pulmonary function when compared to the overactive TT groupCF patients with the TT αENaC genotype are likely candidates for early identification and treatment with inhaled ENaC inhibitors or other modulators of this pathway in order to improve survival.

Cystic Fibrosis (CF) is a degenerative disorder that is often associated with chronic lung disease. CF is caused by mutations in the gene encoding the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) chloride channel, which lead to defective chloride and sodium ion movement across epithelia. Subsequent dehydration of the airway surface liquid (ASL) on airway epithelia, is associated with poor mucociliary clearance and chronic lung infection. The monogenic nature of CF, along with the accessibility of the lung, makes the disease amenable to gene replacement therapy. Gene therapy clinical trials have focused on replacing the mutated CFTR with a functional copy, which has led to improved chloride transport, but has shown no significant effects on sodium transport. An alternative strategy for CF gene therapy therefore, could be to reduce the expression of the epithelial sodium channel (ENaC) in the lung, using RNA interference (RNAi), combined with CFTR delivery. Developing a dual-function gene transfer vector could potentially restore chloride and sodium levels in the ASL and help alleviate CF lung disease. The aim of this thesis was to develop a recombinant lentivirus delivery system capable of simultaneously delivering CFTR expression and knocking down ENaC expression in the airways. A modular HIV vector genome plasmid was developed to allow simple insertion of various promoter elements, transgenes and knockdown sequences, for subsequent virus production. Insertion of the CFTR transgene and a short-hairpin RNA (shRNA) sequence targeting the ENaC alpha subunit (ENaC&alpha;) resulted in significant knockdown of human ENaC&alpha; and simultaneous expression of CFTR in A549 (human lung carcinoma) cell culture. Replacement of the ENaC&alpha; shRNA with an shRNA targeting the transcription factor BACH1 resulted in target gene knockdown and concomitant HMOX1 up-regulation, confirming specific knockdown effects, and demonstrating that the dual-function rLV vector could mediate target gene knockdown irrespective of the target. Attempts were made to knock down BACH1 in primary cultures of human bronchial epithelial cells grown at the air-liquid interface (ALI), but improved transduction efficiencies from the apical surface will be required to generate successful knockdown in this experimental model. These studies provide proof-of-principle for the utility of this versatile dual-function prototype virus. The dual function vector not only has the potential for treatment of CF lung disease, but could be readily altered to target other lung diseases where combinations of prolonged target gene knockdown and gene expression/up-regulation could collectively provide an appropriate therapy. In conclusion, the focus on the rational design of gene transfer vectors for specific therapeutic effects will aid the development and translation of gene therapy approaches to human studies.

Le transport actif de sodium par les cellules épithéliales alvéolaires est le principal mécanisme impliqué dans la régulation du niveau de liquide dans le poumon distal. Le canal épithélial sodique (ENaC) exprimé par les cellules épithéliales alvéolaires est essentiel à la résorption du liquide des poumons à la naissance ainsi que la résolution de l'œdème pulmonaire chez l'adulte. L'activité et l'expression du canal ENaC sont modulées par de nombreux stress pathophysiologiques. L'inflammation pulmonaire constitue un facteur important dans l'inhibition de l'expression du canal ENaC et pourrait favoriser la formation d'œdème pulmonaire. Nous avons précédemment démontré que différentes cytokines pro-inflammatoires, ainsi que les lipopolysaccharides (LPS) de Pseudomonas aeruginosa, inhibent l'expression de l'ARNm αENaC par des mécanismes de régulation transcriptionnelle et post-transcriptionnelle. Ces résultats suggèrent que les mécanismes qui modulent la stabilité des ARNm αENaC pourraient jouer un rôle important dans la régulation du niveau d’expression du transcrit en condition inflammatoire. Le principal objectif de mes travaux était de caractériser les mécanismes de modulation de l’ARNm αENaC dans les cellules épithéliales alvéolaires lors de différents stress pathophysiologiques et déterminer si cette modulation pouvait s’expliquer en partie par une régulation de la stabilité du transcrit. Mes travaux montrent que les LPS et la cycloheximide inhibent l’expression de l’ARNm αENaC de façon similaire via l’activation des voies de signalisation des MAPK ERK1/2 et p38. Cependant, les mécanismes de modulation de l’expression de l'ARNm αENaC sont différents puisque les LPS répriment la transcription du gène, alors que la cycloheximide diminuerait la stabilité du transcrit via des mécanismes post-transcriptionnels impliquant la région 3' non traduite (3'UTR) de l'ARNm αENaC. Pour mieux étudier le rôle du 3'UTR dans ce processus, nous avons développé un modèle Tet-Off nous permettant de mesurer la demi-vie de l’ARNm αENaC indépendamment de l’utilisation d’un inhibiteur de la transcription comme l'actinomycine D (Act. D). Nous avons montré que la demi-vie de l’ARNm αENaC était de 100min, un temps beaucoup plus court que celui rapporté dans la littérature. Nous avons démontré que l’Act. D a un effet stabilisateur important sur l’ARNm αENaC et qu’il ne peut être utilisé pour évaluer la stabilité du transcrit. À l’aide de différents mutants de délétion, nous avons entrepris de déterminer la nature des régions du 3’UTR impliquées dans la modulation de la stabilité du transcrit. Nous avons trouvé que le 3’UTR joue un rôle à la fois de stabilisation (région 3’UTR proximale) et de déstabilisation (région 3’UTR distale) du transcrit. Notre système nous a finalement permis de confirmer que la diminution de l’ARNm αENaC observée en présence de TNF-α s’expliquait en partie par une diminution importante de la stabilité du transcrit induite par cette cytokine. Enfin, nous avons identifié la nature des protéines pouvant se lier au 3’UTR de l’ARNm αENaC et déterminé lesquelles pouvaient moduler la stabilité du transcrit. Des trois protéines candidates trouvées, nous avons confirmé que la surexpression de DHX36 et TIAL1 diminue le niveau de transcrit par un mécanisme impliquant la stabilité du messager. Les travaux présentés ici montrent la complexité des voies de signalisation induites par différents stress sur les cellules épithéliales alvéolaires et montrent comment la stabilité de l’ARNm αENaC et en particulier, les séquences du 3’UTR jouent un rôle important dans la modulation du niveau de transcrit. Le modèle Tet-Off que nous avons développé permet d’estimer le temps de demi-vie réel de l’ARNm αENaC et montre que le 3’UTR du messager joue un rôle complexe dans la stabilisation du messager en condition de base ainsi qu’en condition pro-inflammatoire. Enfin, nous avons identifié deux protéines liant l’ARNm qui pourraient jouer un rôle important dans la modulation de la stabilité du transcrit. / The epithelial sodium channel (ENaC) expressed in alveolar epithelial cells plays a major role for lung liquid clearance at birth and lung edema resorption in adulthood. The expression and activity of ENaC are inhibited by many pathophysiological stress that could have an impact in the clinical outcome of acute respiratory distress syndrome (ARDS). Pulmonary inflammation is an important factor in this inhibition that may promote or sustain pulmonary edema. We have previously shown that pro-inflammatory cytokines and lipopolysaccharide (LPS) from Pseudomonas aeruginosa inhibit αENaC mRNA expression by transcriptional and post-transcriptional mechanisms, suggesting that a modulation of αENaC mRNA stability could play a role in this process. The main objective of the present work was to characterize how different pathophysiological stress affect αENaC mRNA expression in alveolar epithelial cells and determine whether this modulation could be explained in part by regulating the stability of the transcript. Our study shows that LPS and cycloheximide decrease the level of αENaC mRNA with a similar time course and via the activation of the MAPK ERK1/2 and p38 signaling pathways. Despite similarities, there were important differences in the mechanisms involved in the modulation of αENaC mRNA expression. While LPS repress αENaC mRNA transcription, cycloheximide triggers post-transcriptional mechanisms involving the 3' untranslated region (3'UTR) of αENaC mRNA. To further study the role of αENaC 3'UTR in this process, we developed a Tet-Off model that allows us to measure the half-life of αENaC mRNA regardless of the use of a transcription inhibitor such as actinomycin D (Act. D). Using this system, we showed a 100 min half-life for αENaC mRNA, a much shorter time then the one reported for this mRNA using Act. D. We showed that Act. D has an important stabilizing effect on αENaC mRNA and cannot be used to assess the stability of the transcript. Using deletion mutants of the αENaC 3'UTR region, we determined how different portions of 3'UTR were important in modulating stability of the transcript. We found that the 3'UTR has dual functions, with portions important to promote stabilization (proximal 3'UTR) and others that strongly destabilize (distal 3'UTR) the transcript. Our system also allowed us to confirm that the decreased expression of αENaC mRNA induced by TNF-α results in part by a decreased stability of the mRNA. Finally, we identified several RNA-binding proteins that interact specifically with αENaC 3'UTR and determined if these proteins had an impact on transcript stability. Surexpression of two of these proteins in alveolar epithelial cells, DHX36 and TIAL1 was able to decrease the level of αENaC mRNA via a downregulation of mRNA stability. The work presented here shows the complexity of the signal transduction pathways elicited by different pathological stress conditions in alveolar epithelial cells and is the first to show that αENaC mRNA stability elicited by sequences in 3’UTR plays an important role in modulating the level of the transcript. The Tet-Off model that we developed allows to accurately estimate the half-life of αENaC mRNA and shows that the 3’UTR portion of the mRNA plays a complex role in the modulation of transcript stability in basal and pro-inflammatory conditions. Finally, we identified two putative RNA-binding proteins able to specifically recognize αENaC 3’UTR and modulate the transcript stability.

No description available.