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SGK1 dependence of insulin induced hypokalemia. Pflugers Arch 2008; 457:955-61. [PMID: 18665390 DOI: 10.1007/s00424-008-0559-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 06/23/2008] [Accepted: 07/11/2008] [Indexed: 12/23/2022]
Abstract
Insulin stimulates cellular K+ uptake leading to hypokalemia. Cellular K+ uptake is accomplished by parallel stimulation of Na+/H+ exchange, Na+,K+,2Cl- co-transport, and Na+/K+ ATPase and leads to cell swelling, a prerequisite for several metabolic effects of the hormone. Little is known about underlying signaling. Insulin is known to activate the serum and glucocorticoid-inducible kinase SGK1, which in turn enhances the activity of all three transport proteins. The present study thus explored the contribution of SGK1 to insulin-induced hypokalemia. To this end, gene-targeted mice lacking SGK1 (sgk1-/-) and their wild-type littermates (sgk1+/+) have been infused with insulin (2 mU kg(-1) min(-1)) and glucose at rates leaving the plasma glucose concentration constant. Moreover, isolated liver perfusion experiments have been performed to determine stimulation of cellular K+ uptake by insulin (100 nM). As a result, combined glucose and insulin infusion significantly decreased plasma K+ concentration despite a significant decrease of urinary K+ excretion in sgk1+/+ but not in sgk1-/- mice. Accordingly, the plasma K+ concentration was within 60 min significantly lower in sgk1+/+ than in sgk1-/- mice. In isolated liver perfusion experiments, cellular K+ uptake was stimulated by insulin (100 nM), an effect blunted by 72% in sgk1-/- mice as compared to sgk1+/+ mice. Accordingly, insulin-induced cell hydration was 63% lower in sgk1-/- mice than in sgk1+/+ mice. Moreover, volume regulatory K+ release was 31% smaller in sgk1-/- mice than in sgk1+/+ mice. In conclusion, the serum and glucocorticoid-inducible kinase SGK1 participates in the signaling mediating the hypokalemic effect of insulin.
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Schwab M, Lupescu A, Mota M, Mota E, Frey A, Simon P, Mertens PR, Floege J, Luft F, Asante-Poku S, Schaeffeler E, Lang F. Association of SGK1 gene polymorphisms with type 2 diabetes. Cell Physiol Biochem 2008; 21:151-60. [PMID: 18209482 DOI: 10.1159/000113757] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/30/2007] [Indexed: 11/19/2022] Open
Abstract
The serum and glucocorticoid inducible kinase SGK1 is genomically upregulated by glucocorticoids and in turn stimulates a variety of carriers and channels including the renal epithelial Na(+) channel ENaC and the intestinal Na(+) glucose transporter SGLT1. Twin studies disclosed an association of a specific SGK1 haplotype with moderately enhanced blood pressure in individuals who are carrying simultaneously a homozygous genotype for a variant in intron 6 [I6CC] and a homozygous or heterozygous genotype for the C allele of a polymorphism in exon 8 [E8CC/CT] of the SGK1 gene. A subsequent study confirmed the impact of this risk haplotype on blood pressure. SGK1 knockout mice are resistant to the insulin and high salt induced increase of blood pressure, glucocorticoid induced increase of electrogenic glucose transport, and glucocorticoid induced suppression of insulin release. The present study explored whether the I6CC/E8CC/CT haplotype impacts on the prevalence of type 2 diabetes. The prevalence of the I6CC genotype was 3.1% in a healthy German, 2.4 % in a healthy Romanian and 11.6 % in a healthy African population from Ghana (p=0.0006 versus prevalence in Caucasians). Comparison of genotype frequencies between type 2 diabetic patients and the respective control groups revealed significant differences for the intron 6 T>C variant. Carriers of at least one T allele were protected against type 2 diabetes (Romanians: p=0.023; OR 0.29; 95% CI 0.09-0.89; Germans: p=0.01; OR 0.37; 95% CI 0.17-0.81). The SGK1 risk haplotype (I6CC/E8CC/CT) was significantly (p=0.032; OR 4.31, 95% CI 1.19-15.58) more frequent in diabetic patients (7.2 %) than in healthy volunteers from Romania (1.8%). The observations support the view that SGK-1 may participate in the pathogenesis of metabolic syndrome.
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Affiliation(s)
- Matthias Schwab
- Dr Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany
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Lack of the serum and glucocorticoid-inducible kinase SGK1 attenuates the volume retention after treatment with the PPARgamma agonist pioglitazone. Pflugers Arch 2008; 456:425-36. [PMID: 18172605 DOI: 10.1007/s00424-007-0401-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2007] [Revised: 11/06/2007] [Accepted: 11/14/2007] [Indexed: 10/22/2022]
Abstract
PPARgamma-agonists enhance insulin sensitivity and improve glucose utilization in diabetic patients. Adverse effects of PPARgamma-agonists include volume retention and edema formation. Recent observations pointed to the ability of PPARgamma 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 PPARgamma agonists. To test this hypothesis, food containing the PPARgamma 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 distribution, pioglitazone increased plasma volume only in sgk1+/+ mice (from 50.9+/-3.9 to 63.7+/-2.5 microl/g bw) but not in sgk-/- mice (from 46.8+/-3.8 to 48.3+/-5.2 microl/g bw). Pioglitazone decreased aldosterone plasma levels and blood pressure and increased leptin plasma levels in both genotypes. We conclude that SGK1 contributes to but does not fully account for the volume retention during treatment with the PPARgamma agonist pioglitazone.
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Zhang W, Xia X, Reisenauer MR, Rieg T, Lang F, Kuhl D, Vallon V, Kone BC. Aldosterone-induced Sgk1 relieves Dot1a-Af9-mediated transcriptional repression of epithelial Na+ channel alpha. J Clin Invest 2007; 117:773-83. [PMID: 17332896 PMCID: PMC1804379 DOI: 10.1172/jci29850] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2006] [Accepted: 01/02/2007] [Indexed: 01/17/2023] Open
Abstract
Aldosterone plays a major role in the regulation of salt balance and the pathophysiology of cardiovascular and renal diseases. Many aldosterone-regulated genes--including that encoding the epithelial Na+ channel (ENaC), a key arbiter of Na+ transport in the kidney and other epithelia--have been identified, but the mechanisms by which the hormone modifies chromatin structure and thus transcription remain unknown. We previously described the basal repression of ENaCalpha by a complex containing the histone H3 Lys79 methyltransferase disruptor of telomeric silencing alternative splice variant a (Dot1a) and the putative transcription factor ALL1-fused gene from chromosome 9 (Af9) as well as the release of this repression by aldosterone treatment. Here we provide evidence from renal collecting duct cells and serum- and glucocorticoid-induced kinase-1 (Sgk1) WT and knockout mice that Sgk1 phosphorylated Af9, thereby impairing the Dot1a-Af9 interaction and leading to targeted histone H3 Lys79 hypomethylation at the ENaCalpha promoter and derepression of ENaCalpha transcription. Thus, Af9 is a physiologic target of Sgk1, and Sgk1 negatively regulates the Dot1a-Af9 repressor complex that controls transcription of ENaCalpha and likely other aldosterone-induced genes.
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Affiliation(s)
- Wenzheng Zhang
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Xuefeng Xia
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Mary Rose Reisenauer
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Timo Rieg
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Florian Lang
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Dietmar Kuhl
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Volker Vallon
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Bruce C. Kone
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
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Lang F, Böhmer C, Palmada M, Seebohm G, Strutz-Seebohm N, Vallon V. (Patho)physiological significance of the serum- and glucocorticoid-inducible kinase isoforms. Physiol Rev 2006; 86:1151-78. [PMID: 17015487 DOI: 10.1152/physrev.00050.2005] [Citation(s) in RCA: 516] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The serum- and glucocorticoid-inducible kinase-1 (SGK1) is ubiquitously expressed and under genomic control by cell stress (including cell shrinkage) and hormones (including gluco- and mineralocorticoids). Similar to its isoforms SGK2 and SGK3, SGK1 is activated by insulin and growth factors via phosphatidylinositol 3-kinase and the 3-phosphoinositide-dependent kinase PDK1. SGKs activate ion channels (e.g., ENaC, TRPV5, ROMK, Kv1.3, KCNE1/KCNQ1, GluR1, GluR6), carriers (e.g., NHE3, GLUT1, SGLT1, EAAT1-5), and the Na+-K+-ATPase. They regulate the activity of enzymes (e.g., glycogen synthase kinase-3, ubiquitin ligase Nedd4-2, phosphomannose mutase-2) and transcription factors (e.g., forkhead transcription factor FKHRL1, beta-catenin, nuclear factor kappaB). SGKs participate in the regulation of transport, hormone release, neuroexcitability, cell proliferation, and apoptosis. SGK1 contributes to Na+ retention and K+ elimination of the kidney, mineralocorticoid stimulation of salt appetite, glucocorticoid stimulation of intestinal Na+/H+ exchanger and nutrient transport, insulin-dependent salt sensitivity of blood pressure and salt sensitivity of peripheral glucose uptake, memory consolidation, and cardiac repolarization. A common ( approximately 5% prevalence) SGK1 gene variant is associated with increased blood pressure and body weight. SGK1 may thus contribute to metabolic syndrome. SGK1 may further participate in tumor growth, neurodegeneration, fibrosing disease, and the sequelae of ischemia. SGK3 is required for adequate hair growth and maintenance of intestinal nutrient transport and influences locomotive behavior. In conclusion, the SGKs cover a wide variety of physiological functions and may play an active role in a multitude of pathophysiological conditions. There is little doubt that further targets will be identified that are modulated by the SGK isoforms and that further SGK-dependent in vivo physiological functions and pathophysiological conditions will be defined.
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Affiliation(s)
- Florian Lang
- Department of Physiology, University of Tuebingen, Tuebingen, Germany.
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