SGK1 as a determinant of kidney function and salt intake in response to mineralocorticoid excess

Aldosterone and endothelin-1 (ET-1) act on collecting duct cells of the kidney and are important regulators of renal sodium transport and cardiovascular physiology. We recently identified the ET-1 gene (edn1) as a novel aldosterone-induced transcript. However, aldosterone action on edn1 has not been characterized at the present time. In this report, we show that aldosterone stimulated edn1 mRNA in acutely isolated rat inner medullary collecting duct cells ex vivo and ET-1 peptide in rat inner medulla in vivo. Aldosterone induction of edn1 mRNA occurred in cortical, outer medullary, and inner medullary collecting duct cells in vitro. Inspection of the edn1 promoter revealed two putative hormone response elements. Levels of heterogeneous nuclear RNA synthesis demonstrated that edn1 mRNA stimulation occurred at the level of transcription. RNA knockdowns corroborated pharmacological studies and demonstrated both mineralocorticoid receptor and glucocorticoid receptor participated in this response. Aldosterone resulted in dose-dependent nuclear translocation and binding of mineralocorticoid receptor and glucocorticoid receptor to the edn1 hormone response elements. Hormone receptors mediated the association of chromatin remodeling complexes, histone modification, and RNA polymerase II at the edn1 promoter. Direct interaction between aldosterone and ET-1 has important implications for renal and cardiovascular function.The steroid hormone aldosterone is critical for sodium homeostasis and blood pressure control. Aldosterone works by modulating the fine regulation of sodium reabsorption in the distal nephron and collecting duct of the kidney. Classic aldosterone action is mediated through the mineralocorticoid receptor (MR), 3 a member of the nuclear receptor family of proteins that function as ligand-dependent transcription factors (1). MR acts on cells of the distal nephron and collecting duct to stimulate transcription of genes involved in transepithelial sodium transport, including the epithelial sodium channel ␣ subunit (scnn1a, ␣ENaC), the sodium, potassium-ATPase ␣1 subunit (atp1a1), and the serum-and glucocorticoid-regulated kinase-1 (sgk1) (2). The increase in expression of genes involved in sodium transport results in net sodium reabsorption followed by in increase in extracellular fluid volume and a consequent increase in blood pressure. Indeed, MR antagonists such as spironolactone and eplerenone are used clinically as diuretic and anti-hypertensive agents (3). The mechanism of MR action is consistent with a classic steroid receptor mechanism (4). Prior to activation MR resides in the cytosol. Ligand binding induces a conformational change that releases chaperone proteins and reveals a nuclear localization signal. Nuclear MR binds directly to DNA at hormone response elements (HREs) in target genes to modulate their transcription. A typical HRE for MR consists of two receptor binding half-sites with the consensus sequence 5Ј-TGTTCT-3Ј, arranged as an inverted palindrome (1, 5). These HREs facilitate binding of...

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“…1A). The observed stimulation in edn1 exceeded the 28 Ϯ 5% increase in the mRNA of the well established aldosterone response gene sgk1 (48,49).…”

Section: Aldosterone Stimulates Et-1 Inmentioning

confidence: 82%

Aldosterone Modulates Steroid Receptor Binding to the Endothelin-1 Gene (edn1)

Stow

Gumz

Lynch

et al. 2009

Journal of Biological Chemistry

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“…SGK1 does not only participate in electrolyte balance by its influence on renal elimination, but mediates at least, in part, the effect of mineralocorticoids on salt appetite [41]. Thus, SGK1 plays a dual role in mineralocorticoidregulated NaCl homeostasis.…”

Section: Discussionmentioning

confidence: 99%

Lack of the serum and glucocorticoid-inducible kinase SGK1 attenuates the volume retention after treatment with the PPARγ agonist pioglitazone

Artunc

Sandulache

Nasir

et al. 2008

Pflugers Arch - Eur J Physiol

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PPARγ-agonists enhance insulin sensitivity and improve glucose utilization in diabetic patients. Adverse effects of PPARγ-agonists include volume retention and edema formation. Recent observations pointed to the ability of PPARγ agonists to enhance transcription of the serum and glucocorticoid-inducible kinase SGK1, a kinase that is genomically upregulated by mineralocorticoids and stimulates various renal channels and transporters including the renal epithelial Na + channel ENaC. SGK1 has been proposed to mediate the volume retention after treatment with PPARγ agonists. To test this hypothesis, food containing the PPARγ agonist pioglitazone (0.02%, i.e., approximately 25 mg/kg bw/day) was administered to gene-targeted mice lacking SGK1 (sgk1 −/− , n=12) and their wild-type littermates (sgk1 +/+ , n=12). According to in situ hybridization, quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunofluorescence, treatment with pioglitazone significantly increased renal SGK1 mRNA and protein expression in sgk1 +/+ mice. The treatment increased body weight significantly in both, sgk1 +/+ mice (+2.2±0.3 g) and sgk −/− mice (+1.3±0.2 g), and decreased hematocrit significantly in sgk1 +/+ mice (−6.5±1.0%) and sgk1 −/− mice (−3.1±0.6%). Both effects were significantly (p<0.05) more pronounced in sgk1 +/+ mice. According to Evans Blue

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“…It stimulates Na + reabsorption in aldo-sensitive epithelia in the kidney, colon, and sweat glands and elicits its effects by binding to the mineralocorticoid receptor (MR). The MR acts as a transcription factor controlling expression and activity of proteins either mediating or regulating epithelial Na + transport [2,21,32]. The importance of the MR for Na + homeostasis is underlined by the observation that in humans loss-of-function mutations in the MR cause renal salt wasting and hyperkalemia despite high plasma aldosterone levels (pseudohypoaldosteronism) [8].…”

Section: Introductionmentioning

confidence: 99%

“…Increased plasma levels of aldosterone induced by exogenous aldosterone infusion, dietary Na + restriction or diuretic treatment correlate with an increased abundance and phosphorylation of the thiazide-sensitive NaCl cotransporter (NCC) in the DCT [11,12,34,35]. The stimulatory effect of aldosterone on NCC was also reported to occur in DCT cells in vitro and was suggested to involve the activation of various different kinases including SGK1 [32], WNK4 [34], and SPAK [12] as well as the ubiquitin ligase Nedd4-2 [14,27]. Pharmacological blockade of the MR by spironolactone inhibited, at least part, the effects of aldosterone on the DCT and NCC [16], suggesting that the MR mediated the effects of aldosterone on NCC.…”

Section: Introductionmentioning

confidence: 99%

The mineralocorticoid receptor (MR) regulates ENaC but not NCC in mice with random MR deletion

Czogalla

Vohra

Pentón

et al. 2016

Pflugers Arch - Eur J Physiol

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Aldosterone binds to the mineralocorticoid receptor (MR) and increases renal Na+ reabsorption via up-regulation of the epithelial Na+ channel (ENaC) and the Na+-K+-ATPase in the collecting system (CS) and possibly also via the NaCl cotransporter (NCC) in the distal convoluted tubule (DCT). However, whether aldosterone directly regulates NCC via MR, or indirectly through systemic alterations remains controversial. We used mice with deletion of MR in 20% of renal tubule cells (MR/X mice), in which MR-positive (MRwt) and -negative (MRko) cells can be studied sideby-side in the same physiological context. Adult MR/X mice showed similar mRNA and protein levels of renal ion transport proteins to control mice. In MR/X mice, no differences in NCC abundance and phosphorylation was seen between MRwt and MRko cells and dietary Na+ restriction up-regulated NCC to similar extent in both groups of cells. In contrast, MRko cells in the CS did not show any detectable alpha-ENaC abundance or apical targeting of ENaC neither on control diet nor in response to dietary Na+ restriction. Furthermore, Na+-K+-ATPase expression was unaffected in MRko cells of the DCT, while it was lost in MRko cells of the CS. In conclusion, MR is crucial for ENaC and Na+-K+-ATPase regulation in the CS, but is dispensable for NCC and Na+-K+-ATPase regulation in the DCT. PAEJ-D-16-00005 -NCC regulation is MR independent 2 ACKNOWLEDGEMENTSThe authors would like to thank Günter Schütz and Stefan Berger, Burkhard Becher, Celso E. Gomez-Sanchez, and Eric Feraille for kindly providing us with the MRlox/lox mouse line, the cmv-cre mouse line, the anti-MR antibodies, and the anti-Na + -K + -ATPase antibody, respectively. The expert technical assistance by Monique Carrel and Michèle Heidemeyer is gratefully acknowledged. GRANTS DISCLOSURESThe authors declare no conflict of interest, financial or otherwise. PAEJ-D-16-00005 -NCC regulation is MR independent 3 ABSTRACTAldosterone binds to the mineralocorticoid receptor (MR) and increases renal Na + reabsorption via up-regulation of the epithelial Na + channel (ENaC) and the Na + -K + -ATPase in the collecting system (CS) and possibly also via the NaCl cotransporter (NCC) in the distal convoluted tubule (DCT). However, whether aldosterone directly regulates NCC via MR, or indirectly through systemic alterations remains controversial. We used mice with deletion of MR in ~20% of renal tubule cells (MR/X mice), in which MR-positive (MR wt ) and -negative (MR ko ) cells can be studied sideby-side in the same physiological context. Adult MR/X mice showed similar mRNA and protein levels of renal ion transport proteins to control mice. In MR/X mice, no differences in NCC abundance and phosphorylation was seen between MR wt and MR ko cells and dietary Na + restriction up-regulated NCC to similar extent in both groups of cells. In contrast, MR ko cells in the CS did not show any detectable alphaENaC abundance or apical targeting of ENaC neither on control diet nor in response to dietary Na + restriction. Furtherm...

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SGK1 as a determinant of kidney function and salt intake in response to mineralocorticoid excess

Abstract: . SGK1 as a determinant of kidney function and salt intake in response to mineralocorticoid excess.

Cited by 69 publications

References 65 publications

Aldosterone Modulates Steroid Receptor Binding to the Endothelin-1 Gene (edn1)

Aldosterone Modulates Steroid Receptor Binding to the Endothelin-1 Gene (edn1)

Lack of the serum and glucocorticoid-inducible kinase SGK1 attenuates the volume retention after treatment with the PPARγ agonist pioglitazone

The mineralocorticoid receptor (MR) regulates ENaC but not NCC in mice with random MR deletion

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