The epithelial Na+ channel (ENaC) constitutes the rate-limiting step for Na+ transport across tight epithelia and is the principal target of hormonal regulation, particularly by insulin and mineralocorticoids. Recently, the serine-threonine kinase (SGK) was identified as a rapidly mineralocorticoid-responsive gene, the product of which stimulates ENaC-mediated Na+ transport. Like its close relative, protein kinase B (also called Akt), SGK's kinase activity is dependent on phosphatidylinositol 3-kinase (PI3K), a key mediator of insulin signaling. In our study we show that PI3K is required for SGK-dependent stimulation of ENaC-mediated Na+ transport as well as for the production of the phosphorylated form of SGK. In A6 kidney cells, mineralocorticoid induction of the phosphorylated form of SGK preceded the increase in Na+ transport, and specific inhibition of PI3K inhibited both phosphorylation of SGK and mineralocorticoid-induced Na+ transport. Insulin both augmented SGK phosphorylation and synergized with mineralocorticoids in stimulating Na+ transport. In a Xenopus laevis oocyte coexpression assay, SGK-stimulated ENaC activity was also markedly reduced by PI3K inhibition. Finally, in vitro-translated SGK specifically interacted with the ENaC subunits expressed in Escherichia coli as glutathione S-transferase fusion proteins. These data suggest that SGK is a PI3K-dependent integrator of insulin and mineralocorticoid actions that interacts with ENaC subunits to control Na+ entry into kidney collecting duct cells.

Aldosterone regulates volume homeostasis and blood pressure by enhancing sodium reabsorption in the kidney's distal nephron (DN). On the apical surface of these renal epithelia, aldosterone increases expression and activity of the thiazide-sensitive Na-Cl cotransporter (NCC) and the epithelial sodium channel (ENaC). While the cellular mechanisms by which aldosterone regulates ENaC have been well characterized, the molecular mechanisms that link aldosterone to NCC-mediated Na + /Cl -reabsorption remain elusive. The serine/threonine kinase with-no-lysine 4 (WNK4) has previously been shown to reduce cell surface expression of NCC. Here we measured sodium uptake in a Xenopus oocyte expression system and found that serum and glucocorticoid-induced kinase 1 (SGK1), an aldosterone-responsive gene expressed in the DN, attenuated the inhibitory effect of WNK4 on NCC activity. In addition, we showed -both in vitro and in a human kidney cell line -that SGK1 bound and phosphorylated WNK4. We found one serine located within an established SGK1 consensus target sequence, and the other within a motif that was, to our knowledge, previously uncharacterized. Mutation of these target serines to aspartate, in order to mimic phosphorylation, attenuated the effect of WNK4 on NCC activity in the Xenopus oocyte system. These data thus delineate what we believe to be a novel mechanism for aldosterone activation of NCC through SGK1 signaling of WNK4 kinase.

Objectives To compare the health-related quality of life (HRQoL) of children with CKD and short stature (SS) to children with CKD and normal height (NH), to evaluate the impact of catch up growth and growth hormone use on HRQoL, and to describe the concordance of perceptions of HRQoL between children with SS and NH and their parents. Study design 483 children and/or parents enrolled in the multicenter CKiD study and had completed the Pediatric Quality of Life Inventory (PedsQL, V4.0) on at least two CKiD study visits comprised this sub-study population. Participants were dichotomized into NH or SS groups. The demographic characteristics that varied at baseline (sex, GFR and parent education) were controlled for in the main analysis evaluating the impact of catch up growth and use of growth hormone on HRQoL. Results Multivariate modeling (controlling for confounding variables) revealed a significant association between both catch up growth and growth hormone usage on parent-proxy reports of child physical functioning (p<.05) and social functioning (p<.05). Older children with CKD (15 to 17 years old) had significantly higher ratings than their parents on PedsQL Physical, Emotional, Social and School Functioning scales compared with younger children (8–14 years old). Conclusion The finding that height gains and growth hormone use are associated with increases in physical and social functioning by parent report provides additional support for interventions to improve height in children with CKD. The importance of evaluating both the parent and child perceptions of HRQoL is supported by our results.

, a renally expressed nonselective cation channel of the transient receptor potential (TRP) family, is gated by hypotonicity. Kinases of the WNK family influence expression and function of the thiazide-sensitive Na ϩ -Cl Ϫ cotransporter, and monogenic human hypertension has been linked to mutations in the gene coding for WNK4. Along with TRPV4, WNK isoforms are highly expressed in the distal nephron. We show here that coexpression of WNK4 downregulates TRPV4 function in human embryonic kidney (HEK-293) cells and that this effect is mediated via decreased cell surface expression of TRPV4; total abundance of TRPV4 in whole cell lysates is unaffected. The effect of the related kinase WNK1 on TRPV4 function and surface expression was similar to that of WNK4. Disease-causing point mutations in WNK4 abrogate, but do not eliminate, the inhibitory effect on TRPV4 function. In contrast to wild-type WNK4, a kinase-dead WNK4 point mutant failed to influence TRPV4 trafficking; however, deletion of the entire WNK4 kinase domain did not blunt the effect of WNK4 on localization of TRPV4. Deletion of the extreme COOH-terminal putative coiled-coil domain of WNK4 abolished its effect. In immunoprecipitation experiments, we were unable to detect direct interaction between TRPV4 and either WNK kinase. In aggregate, these data indicate that TRPV4 is functionally regulated by WNK family kinases at the level of cell surface expression. Because TRPV4 and WNK kinases are coexpressed in the distal nephron in vivo and because there is a tendency toward hypercalcemia in TRPV4

Serum and glucocorticoid-regulated kinase-1 (SGK1) is a serine-threonine kinase that is regulated at the transcriptional level by numerous regulatory inputs, including mineralocorticoids, glucocorticoids, follicle-stimulating hormone, and osmotic stress. In the distal nephron, SGK1 is induced by aldosterone and regulates epithelial Na+ channel-mediated transepithelial Na+ transport. In other tissues, including liver and shark rectal gland, SGK1 is regulated by hypertonic stress and is thought to modulate epithelial Na+ channel- and Na+-K+-2Cl- cotransporter-mediated Na+ transport. In this report, we examined the regulation of SGK1 mRNA and protein expression and Na+ currents in response to osmotic stress in A6 cells, a cultured cell line derived from Xenopus laevis distal nephron. We found that in contrast to hepatocytes and rectal gland cells, hypotonic conditions stimulated SGK1 expression and Na+ transport in A6 cells. Moreover, a correlation was found between SGK1 induction and the later phase of activation of Na+ transport in response to hypotonic treatment. When A6 cells were pretreated with an inhibitor of phosphatidylinositol 3-kinase (PI3K), Na+ transport was blunted and only inactive forms of SGK1 were expressed. Surprisingly, these results demonstrate that both hypertonic and hypotonic stimuli can induce SGK1 gene expression in a cell type-dependent fashion. Moreover, these data lend support to the view that SGK1 contributes to the defense of extracellular fluid volume and tonicity in amphibia by mediating a component of the hypotonic induction of distal nephron Na+ transport.

Whether caused by direct toxicity, genetic predisposition, or an as-yet unidentified nephrotoxin, this association between synthetic cannabinoid exposure and acute kidney injury reinforces the need for vigilance to detect new toxicologic syndromes associated with emerging drugs of abuse. Liquid chromatography and time-of-flight mass spectrometry are useful tools in determining the active ingredients in these evolving products and evaluating them for toxic contaminants.

Background Phthalates are associated with increased blood pressure in children. Large exposures to di-(2-ethylhexyl) phthalate (DEHP) among premature infants have been a cause for concern. Methods We conducted a prospective observational cohort study to determine if DEHP exposures are related to systolic blood pressure (SBP) in premature infants, and if this exposure is associated with activation of the mineralocorticoid receptor (MR). Infants were monitored longitudinally for 8 months from birth. Those who developed idiopathic hypertension were compared with normotensive infants for DEHP exposures. Appearance of urinary metabolites after exposure was documented. Linear regression evaluated the relationship between DEHP exposures and SBP index and whether urinary cortisol/cortisone ratio (a surrogate marker for 11β-HSD2 activity) mediated those relationships. Urinary exosomes were quantified for sodium transporter/channel expression and interrogated against SBP index. Results Eighteen patients met the study criteria, nine developed transient idiopathic hypertension at a postmenstrual age of 40.6 ± 3.4 weeks. The presence of urinary DEHP metabolites was associated with prior IV and respiratory tubing DEHP exposures ( p < 0.05). Both IV and respiratory DEHP exposures were greater in hypertensive infants ( p < 0.05). SBP index was related to DEHP exposure from IV fluid ( p = 0.018), but not respiratory DEHP. Urinary cortisol/cortisone ratio was related to IV DEHP and SBP index ( p < 0.05). Sodium transporter/channel expression was also related to SBP index ( p < 0.05). Conclusions Increased blood pressure and hypertension in premature infants are associated with postnatal DEHP exposure. The mechanism of action appears to be activation of the MR through inhibition of 11β-HSD2. Electronic supplementary material The online version of this article (10.1007/s00467-019-04244-4) contains supplementary material, which is available to authorized users.

Premature infants with unexplained hypertension, with and without CLD, presented at a postmenstrual age of 40 weeks with low PRA, transient time course, and a favorable response to spironolactone treatment.