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Keul P, van Borren MMGJ, Ghanem A, Müller FU, Baartscheer A, Verkerk AO, Stümpel F, Schulte JS, Hamdani N, Linke WA, van Loenen P, Matus M, Schmitz W, Stypmann J, Tiemann K, Ravesloot JH, Alewijnse AE, Hermann S, Spijkers LJA, Hiller KH, Herr D, Heusch G, Schäfers M, Peters SLM, Chun J, Levkau B. Sphingosine-1-Phosphate Receptor 1 Regulates Cardiac Function by Modulating Ca2+ Sensitivity and Na+/H+ Exchange and Mediates Protection by Ischemic Preconditioning. J Am Heart Assoc 2016; 5:JAHA.116.003393. [PMID: 27207969 PMCID: PMC4889204 DOI: 10.1161/jaha.116.003393] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Background Sphingosine‐1‐phosphate plays vital roles in cardiomyocyte physiology, myocardial ischemia–reperfusion injury, and ischemic preconditioning. The function of the cardiomyocyte sphingosine‐1‐phosphate receptor 1 (S1P1) in vivo is unknown. Methods and Results Cardiomyocyte‐restricted deletion of S1P1 in mice (S1P1αMHCCre) resulted in progressive cardiomyopathy, compromised response to dobutamine, and premature death. Isolated cardiomyocytes from S1P1αMHCCre mice revealed reduced diastolic and systolic Ca2+ concentrations that were secondary to reduced intracellular Na+ and caused by suppressed activity of the sarcolemmal Na+/H+ exchanger NHE‐1 in the absence of S1P1. This scenario was successfully reproduced in wild‐type cardiomyocytes by pharmacological inhibition of S1P1 or sphingosine kinases. Furthermore, Sarcomere shortening of S1P1αMHCCre cardiomyocytes was intact, but sarcomere relaxation was attenuated and Ca2+ sensitivity increased, respectively. This went along with reduced phosphorylation of regulatory myofilament proteins such as myosin light chain 2, myosin‐binding protein C, and troponin I. In addition, S1P1 mediated the inhibitory effect of exogenous sphingosine‐1‐phosphate on β‐adrenergic–induced cardiomyocyte contractility by inhibiting the adenylate cyclase. Furthermore, ischemic precondtioning was abolished in S1P1αMHCCre mice and was accompanied by defective Akt activation during preconditioning. Conclusions Tonic S1P1 signaling by endogenous sphingosine‐1‐phosphate contributes to intracellular Ca2+ homeostasis by maintaining basal NHE‐1 activity and controls simultaneously myofibril Ca2+ sensitivity through its inhibitory effect on adenylate cyclase. Cardioprotection by ischemic precondtioning depends on intact S1P1 signaling. These key findings on S1P1 functions in cardiac physiology may offer novel therapeutic approaches to cardiac diseases.
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Affiliation(s)
- Petra Keul
- Institute for Pathophysiology, Westdeutsches Herz- und Gefäßzentrum, Universitätsklinikum Essen, Essen, Germany
| | | | - Alexander Ghanem
- Department of Cardiology, Universitätsklinikum Bonn, Bonn, Germany
| | | | | | - Arie O Verkerk
- Heart Failure Research Center, AMC, University of Amsterdam, The Netherlands
| | - Frank Stümpel
- Institute for Pharmakology und Toxikology, Münster, Germany
| | | | - Nazha Hamdani
- Department of Cardiovascular Physiology, Ruhr University Bochum, Bochum, Germany
| | - Wolfgang A Linke
- Department of Cardiovascular Physiology, Ruhr University Bochum, Bochum, Germany
| | - Pieter van Loenen
- Department of Pharmacology & Pharmacotherapy, AMC, University of Amsterdam, The Netherlands
| | - Marek Matus
- Institute for Pharmakology und Toxikology, Münster, Germany Department of Pharmacology and Toxicology, Comenius University, Bratislava, Slovakia
| | | | - Jörg Stypmann
- Medizinische Klinik und Poliklinik C, Universitätsklinikum Münster, Münster, Germany
| | - Klaus Tiemann
- Medizinische Klinik und Poliklinik C, Universitätsklinikum Münster, Münster, Germany
| | | | - Astrid E Alewijnse
- Department of Pharmacology & Pharmacotherapy, AMC, University of Amsterdam, The Netherlands
| | - Sven Hermann
- European Institute for Molecular Imaging, Münster, Germany
| | - Léon J A Spijkers
- Department of Pharmacology & Pharmacotherapy, AMC, University of Amsterdam, The Netherlands
| | - Karl-Heinz Hiller
- MRB Forschungszentrum Magnet-Resonanz-Bayern e.V., Würzburg, Germany
| | - Deron Herr
- Department of Molecular Biology, Scripps Research Institute, La Jolla, CA
| | - Gerd Heusch
- Institute for Pathophysiology, Westdeutsches Herz- und Gefäßzentrum, Universitätsklinikum Essen, Essen, Germany
| | | | - Stephan L M Peters
- Department of Pharmacology & Pharmacotherapy, AMC, University of Amsterdam, The Netherlands
| | - Jerold Chun
- Department of Molecular Biology, Scripps Research Institute, La Jolla, CA
| | - Bodo Levkau
- Institute for Pathophysiology, Westdeutsches Herz- und Gefäßzentrum, Universitätsklinikum Essen, Essen, Germany
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Weeks KL, Avkiran M. Exchanging cardiac phenotype: Is AKT-mediated NHE1 inhibition a permissive switch in physiological hypertrophy? J Mol Cell Cardiol 2014; 77:175-7. [PMID: 25451172 DOI: 10.1016/j.yjmcc.2014.10.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Revised: 10/14/2014] [Accepted: 10/15/2014] [Indexed: 11/26/2022]
Affiliation(s)
- Kate L Weeks
- Cardiovascular Division, King's College London British Heart Foundation Centre, London SE1 7EH, UK
| | - Metin Avkiran
- Cardiovascular Division, King's College London British Heart Foundation Centre, London SE1 7EH, UK.
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Lan A, Du J. Potential role of Akt signaling in chronic kidney disease. Nephrol Dial Transplant 2014; 30:385-94. [PMID: 24891436 DOI: 10.1093/ndt/gfu196] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Renal fibrosis, particularly tubulointerstitial fibrosis, is the common final outcome of almost all chronic kidney diseases. However, the mechanisms involved in the development of renal fibrosis are poorly understood. The Akt (also known as protein kinase B, PKB) family is serine/threonine protein kinases that play critical roles in regulating growth, proliferation, survival, metabolism and other cellular activities. Cytokines, high-glucose medium, transforming growth factor-β1 or advanced glycation end-products activate Akt in different renal cells. Increased Akt activation has been found in experimental tubulointerstitial fibrosis. In addition, Akt activation is also an important node in diverse signaling cascades involved in kidney damage. These data give evidence for a role for Akt in renal fibrosis, but no reviews are available on the role of Akt in the process. Thus, our aim is to review the role of Akt activation and signaling in renal fibrosis.
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Affiliation(s)
- Aiping Lan
- The Key Laboratory of Remodeling-related Cardiovascular Diseases, Ministry of Education, Beijing An Zhen Hospital, Institute of Heart Lung and Blood Vessel Diseases, Capital Medical University, Beijing 100029, China
| | - Jie Du
- The Key Laboratory of Remodeling-related Cardiovascular Diseases, Ministry of Education, Beijing An Zhen Hospital, Institute of Heart Lung and Blood Vessel Diseases, Capital Medical University, Beijing 100029, China
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Pakladok T, Hosseinzadeh Z, Lebedeva A, Alesutan I, Lang F. Upregulation of the Na⁺-coupled phosphate cotransporters NaPi-IIa and NaPi-IIb by B-RAF. J Membr Biol 2013; 247:137-45. [PMID: 24258620 DOI: 10.1007/s00232-013-9616-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Accepted: 11/08/2013] [Indexed: 01/11/2023]
Abstract
B-RAF, a serine/threonine protein kinase, contributes to signaling of insulin-like growth factor IGF1. Effects of IGF1 include stimulation of proximal renal tubular phosphate transport, accomplished in large part by Na⁺-coupled phosphate cotransporter NaPi-IIa. The related Na⁺-coupled phosphate cotransporter NaPi-IIb accomplishes phosphate transport in intestine and tumor cells. The present study explored whether B-RAF influences protein abundance and/or activity of type II Na⁺-coupled phosphate cotransporters NaPi-IIa and NaPi-IIb. cRNA encoding wild-type NaPi-IIa and wild-type NaPi-IIb was injected into Xenopus oocytes with or without additional injection of cRNA encoding wild-type B-RAF, and electrogenic phosphate transport determined by dual-electrode voltage clamp. NaPi-IIa protein abundance in Xenopus oocyte cell membrane was visualized by confocal microscopy and quantified by chemiluminescence. Moreover, in HEK293 cells, the effect of B-RAF inhibitor PLX-4720 on NaPi-IIa cell surface protein abundance was quantified utilizing biotinylation of cell surface proteins and western blotting. In NaPi-IIa-expressing Xenopus oocytes, but not in oocytes injected with water, addition of phosphate to extracellular bath generated a current (I P), which was significantly increased following coexpression of B-RAF. According to kinetic analysis, coexpression of B-RAF enhanced the maximal IP. Coexpression of B-RAF further enhanced NaPi-IIa protein abundance in the Xenopus oocyte cell membrane. Treatment of HEK293 cells for 24 h with PLX-4720 significantly decreased NaPi-IIa cell membrane protein abundance. Coexpression of B-RAF, further significantly increased IP in NaPi-IIb-expressing Xenopus oocytes. Again, B-RAF coexpression enhanced the maximal IP. In conclusion, B-RAF is a powerful stimulator of the renal and intestinal type II Na⁺-coupled phosphate cotransporters NaPi-IIa and NaPi-IIb, respectively.
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Affiliation(s)
- Tatsiana Pakladok
- Department of Physiology I, University of Tübingen, Gmelinstr. 5, 72076, Tübingen, Germany
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Aiello EA, De Giusti VC. Regulation of the cardiac sodium/bicarbonate cotransporter by angiotensin II: potential Contribution to structural, ionic and electrophysiological myocardial remodelling. Curr Cardiol Rev 2013; 9:24-32. [PMID: 23116057 PMCID: PMC3584305 DOI: 10.2174/157340313805076340] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Revised: 08/15/2012] [Accepted: 09/13/2012] [Indexed: 12/15/2022] Open
Abstract
The sodium/ bicarbonate cotransporter (NBC) is, with the Na+/H+ exchanger (NHE), an important alkalinizing mechanism that maintains cellular intracellular pH (pHi). In the heart exists at least three isoforms of NBC, one that promotes the co-influx of 1 molecule of Na+ per 1molecule of HCO3-(electroneutral isoform; nNBC) and two others that generates the co-influx of 1 molecule of Na+ per 2 molecules of HCO3- (electrogenic isoforms; eNBC). In addition, the eNBC generates an anionic repolarizing current that modulate the cardiac action potential (CAP), adding to such isoforms the relevance to modulate the electrophysiological function of the heart. Angiotensin II (Ang II) is one of the main hormones that regulate cardiac physiology. The alkalinizing mechanisms (NHE and NBC) are stimulated by Ang II, increasing pHi and intracellular Na+ concentration, which indirectly, due to the stimulation of the Na+/Ca2+ exchanger (NCX) operating in the reverse form, leads to an increase in the intracellular Ca2+ concentration. Interestingly, it has been shown that Ang II exhibits an opposite effect on NBC isoforms: it activates the nNBC and inhibits the eNBC. This inhibition generates a CAP prolongation, which could directly increase the intracellular Ca2+ concentration. The regulation of the intracellular Na+ and Ca2+ concentrations is crucial for the cardiac cellular physiology, but these ions are also involved in the development of cardiac hypertrophy and the damage produced by ischemia-reperfusion, suggesting a potential role of NBC in cardiac diseases.
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Affiliation(s)
- Ernesto Alejandro Aiello
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Calle 60 y 120, 1900, La Plata, Argentina.
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Anzawa R, Seki S, Nagoshi T, Taniguchi I, Feuvray D, Yoshimura M. The role of Na+/H+ exchanger in Ca2+ overload and ischemic myocardial damage in hearts from type 2 diabetic db/db mice. Cardiovasc Diabetol 2012; 11:33. [PMID: 22490613 PMCID: PMC3366908 DOI: 10.1186/1475-2840-11-33] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2011] [Accepted: 04/11/2012] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND A higher increase in intracellular Na(+) via Na(+)/H(+) exchanger (NHE) during ischemia has been reported in type 2 diabetic mouse hearts. We investigated the role of NHE in inducing changes in cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and alterations in ventricular function during ischemia-reperfusion in type 2 diabetic mouse hearts. METHODS Hearts from male type 2 diabetic db/db (12-15 weeks old) and age-matched control db/+ mice were subjected to Langendorff perfusion and loaded with 4 μM of the Ca(2+) indicator fura-2. The hearts were exposed to no-flow ischemia for 15 minutes and then reperfused. [Ca(2+)](i) was measured by monitoring fura-2 fluorescence at 500 nm (excitation wavelengths of 340 and 380 nm), while left ventricular (LV) pressure was simultaneously measured. RESULTS db/db hearts exhibited a lower recovery of LV developed pressure than db/+ hearts during reperfusion following ischemia. Diastolic [Ca(2+)](i) was increased to a greater level in diabetic hearts than in the control hearts during ischemia and reperfusion. Such an increase in cytoplasmic Ca(2+) overload during ischemia-reperfusion in diabetic hearts was markedly reduced in the presence of the NHE inhibitor cariporide. This was accompanied by a significantly improved recovery of ventricular function on reperfusion, as shown by a lower increase in diastolic pressure and increased recovery of developed pressure. CONCLUSION NHE plays a key role in enhancing cytoplasmic Ca(2+) overload during ischemia-reperfusion and severely impairing post-ischemic cardiac function in hearts from type 2 diabetic db/db mice.
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Affiliation(s)
- Ryuko Anzawa
- Division of Cardiology, Department of Internal Medicine, The Jikei University School of Medicine, 3-25-8 Nishi-Shimbashi, Minato-ku, Tokyo 105-8461, Japan.
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Translocation of the Na+/H+ exchanger 1 (NHE1) in cardiomyocyte responses to insulin and energy-status signalling. Biochem J 2011; 432:515-23. [PMID: 20868366 PMCID: PMC2995423 DOI: 10.1042/bj20100717] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The Na+/H+ exchanger NHE1 is a highly regulated membrane protein that is required for pH homoeostasis in cardiomyocytes. The activation of NHE1 leads to proton extrusion, which is essential for counteracting cellular acidity that occurs following increased metabolic activity or ischaemia. The activation of NHE1 intrinsic catalytic activity has been well characterized and established experimentally. However, we have examined in the present study whether a net translocation of NHE1 to the sarcolemma of cardiomyocytes may also be involved in the activation process. We have determined the distribution of NHE1 by means of immunofluorescence microscopy and cell-surface biotinylation. We have discovered changes in the distribution of NHE1 that occur when cardiomyocytes are stimulated with insulin that are PI3K (phosphoinositide 3-kinase)-dependent. Translocation of NHE1 also occurs when cardiomyocytes are challenged by hypoxia, or inhibition of mitochondrial oxidative metabolism or electrically induced contraction, but these responses occur through a PI3K-independent process. As the proposed additional level of control of NHE1 through translocation was unexpected, we have compared this process with the well-established translocation of the glucose transporter GLUT4. In immunofluorescence microscopy comparisons, the translocation of NHE1 and GLUT4 to the sarcolemma that occur in response to insulin appear to be very similar. However, in basal unstimulated cells the two proteins are mainly located, with the exception of some co-localization in the perinuclear region, in distinct subcellular compartments. We propose that the mechanisms of translocation of NHE1 and GLUT4 are linked such that they provide spatially and temporally co-ordinated responses to cardiac challenges that necessitate re-adjustments in glucose transport, glucose metabolism and cell pH.
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Kempe DS, Ackermann TF, Boini KM, Klaus F, Umbach AT, Dërmaku-Sopjani M, Judenhofer MS, Pichler BJ, Capuano P, Stange G, Wagner CA, Birnbaum MJ, Pearce D, Föller M, Lang F. Akt2/PKBbeta-sensitive regulation of renal phosphate transport. Acta Physiol (Oxf) 2010; 200:75-85. [PMID: 20236253 DOI: 10.1111/j.1748-1716.2010.02109.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
AIM The protein kinase B (PKB)/Akt is known to stimulate the cellular uptake of glucose and amino acids. The kinase is expressed in proximal renal tubules. The present study explored the influence of Akt/PKB on renal tubular phosphate transport. METHODS The renal phosphate transporter NaPi-IIa was expressed in Xenopus oocytes with or without PKB/Akt and Na(+) phosphate cotransport determined using dual electrode voltage clamp. Renal phosphate excretion was determined in Akt2/PKBbeta knockout mice (akt2(-/-)) and corresponding wild-type mice (akt2(+/+)). Transporter protein abundance was determined using Western blotting and phosphate transport by (32)P uptake into brush border membrane vesicles. RESULTS The phosphate-induced current in NaPi-IIa-expressing Xenopus oocytes was significantly increased by the coexpression of Akt/PKB. Phosphate excretion [micromol per 24 h per g BW] was higher by 91% in akt2(-/-) than in akt2(+/+) mice. The phosphaturia of akt2(-/-) mice occurred despite normal transport activity and expression of the renal phosphate transporters NaPi-IIa, NaPi-IIc and Pit2 in the brush border membrane, a significantly decreased plasma PTH concentration (by 46%) and a significantly enhanced plasma 1,25-dihydroxyvitamin D(3) concentration (by 46%). Moreover, fractional renal Ca(2+) excretion was significantly enhanced (by 53%) and bone density significantly reduced (by 11%) in akt2(-/-) mice. CONCLUSIONS Akt2/PKBbeta plays a role in the acute regulation of renal phosphate transport and thus contributes to the maintenance of phosphate balance and adequate mineralization of bone.
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Affiliation(s)
- D S Kempe
- Department of Physiology, University of Tübingen, Tübingen, Germany
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De Vito P, Incerpi S, Pedersen JZ, Luly P. Atrial natriuretic peptide and oxidative stress. Peptides 2010; 31:1412-9. [PMID: 20385186 DOI: 10.1016/j.peptides.2010.04.001] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2009] [Revised: 04/01/2010] [Accepted: 04/01/2010] [Indexed: 02/07/2023]
Abstract
Atrial natriuretic peptide (ANP) is a hormone, produced mainly by cardiomyocytes, with a major role in cardiovascular homeostatic mechanisms such as natriuresis and vasodilation, which serve to regulate blood pressure. However, ANP also acts as an autocrine/paracrine factor on other targets such as kidney, lung, thymus, liver and the immune system. ANP participates in the regulation of cell growth and proliferation, and evidence is accumulating that these effects are associated with the generation of reactive oxygen species (ROS). In vascular cells and cardiomyocytes ANP stimulates the antioxidant defense, but in other systems such as hepatoblastoma and macrophages ANP may produce either antioxidant or prooxidant effects, depending on experimental conditions and cell context. At present very little is known on the relationship between ANP and ROS production in the normal homeostatic processes or during the development of cardiovascular diseases and cancer. Our current knowledge of the role of ANP in signaling pathways leading to the generation of intracellular messengers such as diacylglycerol (DAG), and guanosine 3'-5'-cyclic monophosphate has been examined in order to clarify the mechanisms by which the hormone may counteract or contribute to the potentially dangerous effects of free radicals.
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Affiliation(s)
- Paolo De Vito
- Department of Biology, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy.
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Kempe DS, Siraskar G, Fröhlich H, Umbach AT, Stübs M, Weiss F, Ackermann TF, Völkl H, Birnbaum MJ, Pearce D, Föller M, Lang F. Regulation of renal tubular glucose reabsorption by Akt2/PKBβ. Am J Physiol Renal Physiol 2010; 298:F1113-7. [PMID: 20164156 DOI: 10.1152/ajprenal.00592.2009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Akt/PKB is known to regulate the facilitative glucose carrier GLUT4. Nothing is known, however, of the role of Akt/PKB in the regulation of renal epithelial transport. To explore whether Akt2/PKBβ influences the Na(+)-coupled glucose cotransporter SGLT1, human SGLT1 was expressed in Xenopus laevis oocytes with or without Akt/PKB, and electrogenic glucose transport was determined by dual-electrode voltage clamp. The coexpression of Akt/PKB in SGLT1-expressing oocytes was followed by an increase in glucose-induced currents. To study the functional significance of Akt/PKB-sensitive renal glucose transport, further experiments were performed in gene-targeted mice lacking functional Akt2/PKBβ (akt2(-/-)) and in their wild-type littermates (akt2(+/+)). Plasma glucose concentration was significantly higher in akt2(-/-) mice than in akt2(+/+) mice but was virtually identical to the plasma glucose concentration in fructose-treated akt2(+/+) mice. Urinary glucose excretion was significantly higher in akt2(-/-) mice compared with akt2(+/+) mice with or without fructose treatment. Moreover, the glucose-induced depolarization of proximal tubular cells was significantly smaller in isolated, perfused renal tubules from akt2(-/-) mice than in those from akt2(+/+) mice. In conclusion, Akt2/PKBβ plays a role in the regulation of renal glucose transport.
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Affiliation(s)
- Daniela S Kempe
- Department of Physiology, University of Tübingen, Tübingen, Germany
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Darmellah A, Rücker-Martin C, Feuvray D. ERM proteins mediate the effects of Na+/H+ exchanger (NHE1) activation in cardiac myocytes. Cardiovasc Res 2008; 81:294-300. [PMID: 19028724 DOI: 10.1093/cvr/cvn320] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
AIMS Ezrin, radixin, and moesin (ERM) proteins have been implicated in regulating signalling molecules. The aim of the present study was to investigate the activity and subcellular distribution of ERM proteins in cardiac myocytes from both Wistar and diabetic Goto-Kakizaki (GK) rats, and the role of these proteins in mediating the downstream effects of the cardiac sarcolemmal Na+/H+ exchanger (NHE1) activation in response to cell acidification. METHODS AND RESULTS Immunofluorescence microscopy revealed that activated ERM proteins were localized predominantly at the intercalated disc regions in left ventricular (LV) myocytes of both Wistar and GK rats under basal conditions. After acid loading, profound changes in activated ERM distribution were observed in both groups of myocytes, with immunolabelling detected in regions corresponding to the transverse tubules. This correlated with a marked increase in phospho-ERM levels in both groups, which was higher in GK myocytes and blocked by NHE1 inhibitor treatment. Levels of phospho-Akt paralleled those of phospho-ERM under the various experimental conditions used; in particular, the marked acid-induced increase in both phospho-ERM and phospho-Akt in GK myocytes was abolished by an NHE1 inhibitor treatment. Moreover, the pattern of glycogen synthase kinase-3beta (GSK-3beta) phosphorylation in these myocytes was strikingly similar to that observed for Akt activity under the conditions used. CONCLUSION Activated ERM proteins mediate the effects of acid-induced NHE1 activation in LV myocytes. Akt is a downstream effector in the cascade activated by NHE1-ERM interaction. In addition, GSK-3beta phosphorylation is required for downstream effects of NHE1/ERM-Akt signalling.
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Affiliation(s)
- Amaria Darmellah
- University of Paris-Sud 11 and CNRS UMR 8162, Marie Lannelongue Hospital, 133 avenue de la Résistance, 92350 Le Plessis Robinson, France
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