Mutations in subunits of the epithelial sodium channel cause salt wasting with hyperkalaemic acidosis, pseudohypoaldosteronism type 1

Dehydration with hyponatremia can occur from a variety of causes and can be potentially fatal to infants. Pseudohypoaldosteronism type 1 (PHA1) is a rare disease that can cause severe dehydration along with hyponatremia and hyperkalemia because of renal tubular unresponsiveness to mineralocorticoids. Autosomal dominant PHA1 (ADPHA1, OMIM #177735) is caused by inactivating mutations in the NR3C2 gene, which encodes the mineralocorticoid receptor, and it can lead to renal salt-wasting, dehydration, and failure to thrive during infancy. Here, we report a case of a 20-day-old female neonate who presented as severe dehydration with hyponatremia and polyuria. We suspected that her diagnosis might be PHA1 based on markedly elevated plasma renin activity and serum aldosterone levels. For the genetic diagnosis of PHA1, we performed targeted exome sequencing of all causative genes of PHA1, but the result was negative. We confirmed by chromosomal microarray that a novel heterozygous microdeletion was found in the 4q31.23 region spanning exons 7–9 of the NR3C2 gene, and the patient was diagnosed with ADPHA1. In conclusion, our patient is a case of ADPHA1 that developed into a salt-wasting crisis in the neonatal period due to a microdeletion of the 4q31.23 region inherited from her father.

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Rac1-mediated NADPH oxidase release of O2− regulates epithelial sodium channel activity in the alveolar epithelium

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00230.2009 ◽

2010 ◽

Vol 298 (4) ◽

pp. L509-L520 ◽

Cited By ~ 34

Author(s):

Yoshizumi Takemura ◽

Preston Goodson ◽

Hui Fang Bao ◽

Lucky Jain ◽

My N. Helms

Keyword(s):

Nadph Oxidase ◽

Sodium Channel ◽

Single Channel ◽

Epithelial Sodium Channel ◽

Alveolar Epithelial Cells ◽

Apical Surface ◽

Alveolar Cells ◽

Open Probability

We examine whether alveolar cells can control release of O2− through regulated NADPH oxidase (NOX) 2 (NOX2) activity to maintain lung fluid homeostasis. Using FACS to purify alveolar epithelial cells, we show that type 1 cells robustly express each of the critical NOX components that catalyze the production of O2− (NOX2 or gp91 phox, p22 phox, p67 phox, p47 phox, and p40 phox subunits) as well as Rac1 at substantially higher levels than type 2 cells. Immunohistochemical labeling of lung tissue shows that Rac1 expression is cytoplasmic and resides near the apical surface of type 1 cells, whereas NOX2 coimmunoprecipitates with epithelial sodium channel (ENaC). Since Rac1 is a known regulator of NOX2, and hence O2− release, we tested whether inhibition or activation of Rac1 influenced ENaC activity. Indeed, 1 μM NSC23766 inhibition of Rac1 decreased O2− output in lung cells and significantly decreased ENaC activity from 0.87 ± 0.16 to 0.52 ± 0.16 [mean number of channels ( N) and single-channel open probability ( Po) ( NPo) ± SE, n = 6; P < 0.05] in type 2 cells. NSC23766 (10 μM) decreased ENaC NPo from 1.16 ± 0.27 to 0.38 ± 0.10 ( n = 6 in type 1 cells). Conversely, 10 ng/ml EGF (a known stimulator of both Rac1 and O2− release) increased ENaC NPo values in both type 1 and 2 cells. NPo values increased from 0.48 ± 0.21 to 0.91 ± 0.28 in type 2 cells ( P < 0.05; n = 10). In type 1 cells, ENaC activity also significantly increased from 0.40 ± 0.15 to 0.60 ± 0.23 following EGF treatment ( n = 7). Sequestering O2− using 2,2,6,6-tetramethylpiperidine- N-oxyl (TEMPO) compound prevented EGF activation of ENaC in both type 1 and 2 cells. In conclusion, we report that Rac1-mediated NOX2 activity is an important component in O2− regulation of ENaC.

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Mineralocorticoid receptor antagonizes Dot1a-Af9 complex to increase αENaC transcription

AJP Renal Physiology ◽

10.1152/ajprenal.00202.2013 ◽

2013 ◽

Vol 305 (10) ◽

pp. F1436-F1444 ◽

Cited By ~ 5

Author(s):

Xi Zhang ◽

Qiaoling Zhou ◽

Lihe Chen ◽

Stefan Berger ◽

Hongyu Wu ◽

...

Keyword(s):

Mrna Expression ◽

Mineralocorticoid Receptor ◽

Collecting Duct ◽

Mrna Levels ◽

Salt Wasting ◽

Molecular Defects ◽

Binding Partner ◽

Medullary Collecting Duct ◽

Pseudohypoaldosteronism Type

Aldosterone is a major regulator of Na+ absorption and acts by activating the mineralocorticoid receptor (MR) to stimulate the epithelial Na+ channel (ENaC). MR −/− mice exhibited pseudohypoaldosteronism type 1 (hyponatremia, hyperkalemia, salt wasting, and high levels of aldosterone) and died around postnatal day 10. However, if and how MR regulates ENaC transcription remain incompletely understood. Our earlier work demonstrated that aldosterone activates αENaC transcription by reducing expression of Dot1a and Af9 and by impairing Dot1a-Af9 interaction. Most recently, we reported identification of a major Af9 binding site in the αENaC promoter and upregulation of αENaC mRNA expression in mouse kidneys lacking Dot1a. Despite these findings, the putative antagonism between the MR/aldosterone and Dot1a-Af9 complexes has never been addressed. The molecular defects leading to PHA-1 in MR −/− mice remain elusive. Here, we report that MR competes with Dot1a to bind Af9. MR/aldosterone and Dot1a-Af9 complexes mutually counterbalance ENaC mRNA expression in inner medullary collecting duct 3 (IMCD3) cells. Real-time RT-quantitative PCR revealed that 5-day-old MR −/− vs. MR +/+ mice had significantly lower αENaC mRNA levels. This change was associated with an increased Af9 binding and H3 K79 hypermethylation in the αENaC promoter. Therefore, this study identified MR as a novel binding partner and regulator of Af9 and a novel mechanism coupling MR-mediated activation with relief of Dot1a-Af9-mediated repression via MR-Af9 interaction. Impaired ENaC expression due to failure to inhibit Dot1a-Af9 may play an important role in the early stages of PHA-1 (before postnatal day 8) in MR −/− mice.

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