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Haywood LMB, Sheahan BJ. A Review of Epithelial Ion Transporters and Their Roles in Equine Infectious Colitis. Vet Sci 2024; 11:480. [PMID: 39453072 DOI: 10.3390/vetsci11100480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2024] [Revised: 09/04/2024] [Accepted: 09/07/2024] [Indexed: 10/26/2024] Open
Abstract
Equine colitis is a devastating disease with a high mortality rate. Infectious pathogens associated with colitis in the adult horse include Clostridioides difficile, Clostridium perfringens, Salmonella spp., Neorickettsia risticii/findlaynesis, and equine coronavirus. Antimicrobial-associated colitis can be associated with the presence of infectious pathogens. Colitis can also be due to non-infectious causes, including non-steroidal anti-inflammatory drug administration, sand ingestion, and infiltrative bowel disease. Current treatments focus on symptomatic treatment (restoring fluid and electrolyte balance, preventing laminitis and sepsis). Intestinal epithelial ion channels are key regulators of electrolyte (especially sodium and chloride) and water movement into the lumen. Dysfunctional ion channels play a key role in the development of diarrhea. Infectious pathogens, including Salmonella spp. and C. difficile, have been shown to regulate ion channels in a variety of ways. In other species, there has been an increased interest in ion channel manipulation as an anti-diarrheal treatment. While targeting ion channels also represents a promising way to manage diarrhea associated with equine colitis, ion channels have not been well studied in the equine colon. This review provides an overview of what is known about colonic ion channels and their known or putative role in specific types of equine colitis due to various pathogens.
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Affiliation(s)
- Lillian M B Haywood
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
| | - Breanna J Sheahan
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
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2
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Walker V. The Intricacies of Renal Phosphate Reabsorption-An Overview. Int J Mol Sci 2024; 25:4684. [PMID: 38731904 PMCID: PMC11083860 DOI: 10.3390/ijms25094684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2024] [Revised: 04/17/2024] [Accepted: 04/19/2024] [Indexed: 05/13/2024] Open
Abstract
To maintain an optimal body content of phosphorus throughout postnatal life, variable phosphate absorption from food must be finely matched with urinary excretion. This amazing feat is accomplished through synchronised phosphate transport by myriads of ciliated cells lining the renal proximal tubules. These respond in real time to changes in phosphate and composition of the renal filtrate and to hormonal instructions. How they do this has stimulated decades of research. New analytical techniques, coupled with incredible advances in computer technology, have opened new avenues for investigation at a sub-cellular level. There has been a surge of research into different aspects of the process. These have verified long-held beliefs and are also dramatically extending our vision of the intense, integrated, intracellular activity which mediates phosphate absorption. Already, some have indicated new approaches for pharmacological intervention to regulate phosphate in common conditions, including chronic renal failure and osteoporosis, as well as rare inherited biochemical disorders. It is a rapidly evolving field. The aim here is to provide an overview of our current knowledge, to show where it is leading, and where there are uncertainties. Hopefully, this will raise questions and stimulate new ideas for further research.
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Affiliation(s)
- Valerie Walker
- Department of Clinical Biochemistry, University Hospital Southampton NHS Foundation Trust, Southampton General Hospital, Southampton S016 6YD, UK
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3
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Yip KP, Ribeiro-Silva L, Cha B, Rieg T, Sham JSK. Epac induces ryanodine receptor-dependent intracellular and inter-organellar calcium mobilization in mpkCCD cells. Front Physiol 2023; 14:1250273. [PMID: 37711462 PMCID: PMC10497751 DOI: 10.3389/fphys.2023.1250273] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Accepted: 08/11/2023] [Indexed: 09/16/2023] Open
Abstract
Arginine vasopressin (AVP) induces an increase in intracellular Ca2+ concentration ([Ca2+]i) with an oscillatory pattern in isolated perfused kidney inner medullary collecting duct (IMCD). The AVP-induced Ca2+ mobilization in inner medullary collecting ducts is essential for apical exocytosis and is mediated by the exchange protein directly activated by cyclic adenosine monophosphate (Epac). Murine principal kidney cortical collecting duct cells (mpkCCD) is the cell model used for transcriptomic and phosphoproteomic studies of AVP signaling in kidney collecting duct. The present study examined the characteristics of Ca2+ mobilization in mpkCCD cells, and utilized mpkCCD as a model to investigate the Epac-induced intracellular and intra-organellar Ca2+ mobilization. Ca2+ mobilization in cytosol, endoplasmic reticulum lumen, and mitochondrial matrix were monitored with a Ca2+ sensitive fluorescent probe and site-specific Ca2+ sensitive biosensors. Fluorescence images of mpkCCD cells and isolated perfused inner medullary duct were collected with confocal microscopy. Cell permeant ligands of ryanodine receptors (RyRs) and inositol 1,4,5 trisphosphate receptors (IP3Rs) both triggered increase of [Ca2+]i and Ca2+ oscillations in mpkCCD cells as reported previously in IMCD. The cell permeant Epac-specific cAMP analog Me-cAMP/AM also caused a robust Ca2+ mobilization and oscillations in mpkCCD cells. Using biosensors to monitor endoplasmic reticulum (ER) luminal Ca2+ and mitochondrial matrix Ca2+, Me-cAMP/AM not only triggered Ca2+ release from ER into cytoplasm, but also shuttled Ca2+ from ER into mitochondria. The Epac-agonist induced synchronized Ca2+ spikes in cytosol and mitochondrial matrix, with concomitant declines in ER luminal Ca2+. Me-cAMP/AM also effectively triggered store-operated Ca2+ entry (SOCE), suggesting that Epac-agonist is capable of depleting ER Ca2+ stores. These Epac-induced intracellular and inter-organelle Ca2+ signals were mimicked by the RyR agonist 4-CMC, but they were distinctly different from IP3R activation. The present study hence demonstrated that mpkCCD cells retain all reported features of Ca2+ mobilization observed in isolated perfused IMCD. It further revealed information on the dynamics of Epac-induced RyR-dependent Ca2+ signaling and ER-mitochondrial Ca2+ transfer. ER-mitochondrial Ca2+ coupling may play a key role in the regulation of ATP and reactive oxygen species (ROS) production in the mitochondria along the nephron. Our data suggest that mpkCCD cells can serve as a renal cell model to address novel questions of how mitochondrial Ca2+ regulates cytosolic Ca2+ signals, inter-organellar Ca2+ signaling, and renal tubular functions.
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Affiliation(s)
- Kay-Pong Yip
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, FL, United States
- Hypertension and Kidney Research Center, Morsani College of Medicine, University of South Florida, Tampa, FL, United States
| | - Luisa Ribeiro-Silva
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, FL, United States
| | - Byeong Cha
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, FL, United States
| | - Timo Rieg
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, FL, United States
- Hypertension and Kidney Research Center, Morsani College of Medicine, University of South Florida, Tampa, FL, United States
- James A. Haley Veterans’ Hospital, Tampa, FL, United States
| | - James S. K. Sham
- Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States
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Slika H, Mansour H, Nasser SA, Shaito A, Kobeissy F, Orekhov AN, Pintus G, Eid AH. Epac as a tractable therapeutic target. Eur J Pharmacol 2023; 945:175645. [PMID: 36894048 DOI: 10.1016/j.ejphar.2023.175645] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2022] [Revised: 02/26/2023] [Accepted: 03/06/2023] [Indexed: 03/09/2023]
Abstract
In 1957, cyclic adenosine monophosphate (cAMP) was identified as the first secondary messenger, and the first signaling cascade discovered was the cAMP-protein kinase A (PKA) pathway. Since then, cAMP has received increasing attention given its multitude of actions. Not long ago, a new cAMP effector named exchange protein directly activated by cAMP (Epac) emerged as a critical mediator of cAMP's actions. Epac mediates a plethora of pathophysiologic processes and contributes to the pathogenesis of several diseases such as cancer, cardiovascular disease, diabetes, lung fibrosis, neurological disorders, and others. These findings strongly underscore the potential of Epac as a tractable therapeutic target. In this context, Epac modulators seem to possess unique characteristics and advantages and hold the promise of providing more efficacious treatments for a wide array of diseases. This paper provides an in-depth dissection and analysis of Epac structure, distribution, subcellular compartmentalization, and signaling mechanisms. We elaborate on how these characteristics can be utilized to design specific, efficient, and safe Epac agonists and antagonists that can be incorporated into future pharmacotherapeutics. In addition, we provide a detailed portfolio for specific Epac modulators highlighting their discovery, advantages, potential concerns, and utilization in the context of clinical disease entities.
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Affiliation(s)
- Hasan Slika
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, P.O. Box 11-0236, Lebanon.
| | - Hadi Mansour
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, P.O. Box 11-0236, Lebanon.
| | | | - Abdullah Shaito
- Biomedical Research Center, Qatar University, Doha, P.O. Box: 2713, Qatar.
| | - Firas Kobeissy
- Department of Neurobiology and Neuroscience, Morehouse School of Medicine, Atlanta, Georgia, USA.
| | - Alexander N Orekhov
- Laboratory of Cellular and Molecular Pathology of Cardiovascular System, Institute of Human Morphology, 3 Tsyurupa Street, Moscow, 117418, Russia; Laboratory of Angiopathology, Institute of General Pathology and Pathophysiology, 8 Baltiiskaya Street, Moscow, 125315, Russia; Institute for Atherosclerosis Research, Skolkovo Innovative Center, Osennyaya Street 4-1-207, Moscow, 121609, Russia.
| | - Gianfranco Pintus
- Department of Biomedical Sciences, University of Sassari, 07100, Sassari, Italy.
| | - Ali H Eid
- Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, P.O. Box 2713, Qatar.
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Mizoguchi M, Takemori H, Furukawa S, Ito M, Asai M, Morino H, Miura T, Yabe D, Shibata T. Increased expression of glucagon-like peptide-1 and cystic fibrosis transmembrane conductance regulator in the ileum and colon in mouse treated with metformin. Endocr J 2023; 70:149-159. [PMID: 36198615 DOI: 10.1507/endocrj.ej22-0260] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Metformin, an oral medication, is prescribed to patients with type 2 diabetes mellitus. Although the efficacy, safety, and low economic burden of metformin on patients have long been recognized, approximately 5% of the patients treated with this drug develop severe diarrhea and discontinue the treatment. We previously reported that 1,000 mg·kg-1·day-1 of metformin induced diarrhea in diabetic obese (db/db) mice and wood creosote (traditional medication for diarrhea) ameliorated the symptoms. In this study, we attempted to elucidate the molecular mechanisms by which metformin induces diarrhea. Cystic fibrosis transmembrane conductance regulator (CFTR) is a key ion (chloride) channel in cyclic adenosine monophosphate (cAMP)-induced diarrhea. Metformin treatment increased bile flow (bile acids and bilirubin) in the ileum of mice. In addition, the treatment was accompanied by an increase in mRNA and protein levels of CFTR in the mucosa of the ileum and colon in both wild-type (C57BL/6J) and db/db mice. Glucagon-like peptide-1 (GLP-1), as well as cholic acid, induces CFTR mRNA expression in human colon carcinoma Caco-2 cells through cAMP signaling. Although wood creosote (10 mg/kg) ameliorated diarrhea symptoms, it did not alter the mRNA levels of Glp-1 or Cftr. Similar to overeating, metformin upregulated GLP-1 and CFTR expression, which may have contributed to diarrhea symptoms in mice. Although we could not identify db/db mouse-specific factors associated with metformin-induced diarrhea, these factors may modulate colon function. Wood creosote may not interact with these factors but ameliorates diarrhea symptoms.
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Affiliation(s)
- Momoka Mizoguchi
- Department of Life Science and Chemistry, Graduate School of Natural Science and Technology, Gifu University, Gifu 501-1193, Japan
| | - Hiroshi Takemori
- Department of Life Science and Chemistry, Graduate School of Natural Science and Technology, Gifu University, Gifu 501-1193, Japan
- United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, Gifu 501-1193, Japan
| | - Saho Furukawa
- Department of Life Science and Chemistry, Graduate School of Natural Science and Technology, Gifu University, Gifu 501-1193, Japan
| | - Masafumi Ito
- Taiko Pharmaceutical Co., Ltd., Osaka 550-0005, Japan
| | - Mutsumi Asai
- Taiko Pharmaceutical Co., Ltd., Osaka 550-0005, Japan
| | | | | | - Daisuke Yabe
- Department of Diabetes, Endocrinology and Metabolism/Department of Rheumatology and Clinical Nutrition, Gifu University Graduate School of Medicine, Gifu 501-1193, Japan
| | - Takashi Shibata
- Taiko Pharmaceutical Co., Ltd., Osaka 550-0005, Japan
- Strategic Global Partnership Cross-Innovation Initiative, Graduate School of Medicine, Osaka University Hospital, Osaka 565-0871, Japan
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Hunter K, Larsen JA, Love HD, Evans RC, Roy S, Zent R, Harris RC, Wilson MH, Fissell WH. Inhibition of Transforming Growth Factor-β Improves Primary Renal Tubule Cell Differentiation in Long-Term Culture. Tissue Eng Part A 2023; 29:102-111. [PMID: 36274231 PMCID: PMC10081716 DOI: 10.1089/ten.tea.2022.0147] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Accepted: 10/19/2022] [Indexed: 11/19/2022] Open
Abstract
Patient-oriented applications of cell culture include cell therapy of organ failure like chronic renal failure. Clinical deployment of a cell-based device for artificial renal replacement requires qualitative and quantitative fidelity of a cultured cell to its in vivo counterpart. Active specific apicobasal ion transport reabsorbs 90-99% of the filtered load of salt and water in the kidney. In a bioengineered kidney, tubular transport concentrates wastes and eliminates the need for hemodialysis, but renal tubule cells in culture transport little or no salt and water due to dedifferentiation that mammalian cells undergo in vitro thereby losing important cell-type specific functions. We previously identified transforming growth factor-β (TGF-β) as a signaling pathway necessary for in vitro differentiation of renal tubule cells. Inhibition of TGF-β receptor-1 led to active and inhibitable electrolyte and water transport by primary human renal tubule epithelial cells in vitro. Addition of metformin increased transport, in the context of a transient effect on 5'-AMP-activated kinase phosphorylation. These data motivated us to examine whether increased transport was an idiosyncratic effect of SB431542, probe pathways downstream of TGF-β receptors possibly responsible for the improved differentiation, evaluate whether TGF-β inhibition induced a range of differentiated tubule functions, and to explore crosstalk between the effects of SB431542 and metformin. In this study, we use multiple small-molecule inhibitors of canonical and noncanonical pathways to confirm that inhibition of canonical TGF-β signaling caused the increased apicobasal transport. Hallmarks of proximal tubule cell function, including sodium reabsorption, para-amino hippurate excretion, and glucose uptake increased with TGF-β inhibition, and the specificity of the response was shown using inhibitors of each transport protein. We did not find any evidence of crosstalk between metformin and SB431542. These data suggest that the TGF-β signaling pathway governs multiple features of differentiation in renal proximal tubule cells in vitro. Inhibition of TGF-β by pharmacologic or genome engineering approaches may be a viable approach to enhancing differentiated function of tubule cells in vitro. Impact statement Cell therapy of renal failure requires qualitative and quantitative fidelity between in vitro and in vivo phenotypes, which has been elusive. We show that control of transforming growth factor-β signaling can promote differentiation of renal tubule cells grown in artificial environments. This is a key enabling step for cell therapy of renal failure.
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Affiliation(s)
- Kuniko Hunter
- Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
| | - Jaclyn A. Larsen
- School of Medicine, University of Utah, Salt Lake City, Utah, USA
| | - Harold D. Love
- Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Rachel C. Evans
- Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Shuvo Roy
- Bioengineering and Therapeutic Sciences, University of California, San Francisco, California, USA
| | - Roy Zent
- Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Raymond C. Harris
- Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Matthew H. Wilson
- Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - William H. Fissell
- Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee, USA
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7
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Puri NM, Romano GR, Lin TY, Mai QN, Irannejad R. The organic cation Transporter 2 regulates dopamine D1 receptor signaling at the Golgi apparatus. eLife 2022; 11:75468. [PMID: 35467530 PMCID: PMC9098220 DOI: 10.7554/elife.75468] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Accepted: 04/22/2022] [Indexed: 11/13/2022] Open
Abstract
Dopamine is a key catecholamine in the brain and kidney, where it is involved in a number of physiological functions such as locomotion, cognition, emotion, endocrine regulation, and renal function. As a membrane-impermeant hormone and neurotransmitter, dopamine is thought to signal by binding and activating dopamine receptors, members of the G protein coupled receptor (GPCR) family, only on the plasma membrane. Here, using novel nanobody-based biosensors, we demonstrate for the first time that the dopamine D1 receptor (D1DR), the primary mediator of dopaminergic signaling in the brain and kidney, not only functions on the plasma membrane but becomes activated at the Golgi apparatus in the presence of its ligand. We present evidence that activation of the Golgi pool of D1DR is dependent on organic cation transporter 2 (OCT2), a dopamine transporter, providing an explanation for how the membrane-impermeant dopamine accesses subcellular pools of D1DR. We further demonstrate that dopamine activates Golgi-D1DR in murine striatal medium spiny neurons, and this activity depends on OCT2 function. We also introduce a new approach to selectively interrogate compartmentalized D1DR signaling by inhibiting Gαs coupling using a nanobody-based chemical recruitment system. Using this strategy, we show that Golgi-localized D1DRs regulate cAMP production and mediate local protein kinase A activation. Together, our data suggest that spatially compartmentalized signaling hubs are previously unappreciated regulatory aspects of D1DR signaling. Our data provide further evidence for the role of transporters in regulating subcellular GPCR activity.
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Affiliation(s)
- Natasha M Puri
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
| | - Giovanna R Romano
- Biochemistry Department, Weill Cornell Medicine, New York, United States
| | - Ting-Yu Lin
- Cardiovascular Research Institute, University of California, San Francisco, San Francisco, United States
| | - Quynh N Mai
- Cardiovascular Research Institute, University of California, San Francisco, San Francisco, United States
| | - Roshanak Irannejad
- Cardiovascular Research Institute, University of California, San Francisco, San Francisco, United States
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8
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Verta R, Gurrieri M, Borga S, Benetti E, Pollicino P, Cavalli R, Thurmond RL, Chazot PL, Pini A, Rosa AC, Grange C. The Interplay between Histamine H 4 Receptor and the Kidney Function: The Lesson from H 4 Receptor Knockout Mice. Biomolecules 2021; 11:biom11101517. [PMID: 34680152 PMCID: PMC8533779 DOI: 10.3390/biom11101517] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 09/30/2021] [Accepted: 10/13/2021] [Indexed: 01/15/2023] Open
Abstract
Previous studies implicated the histamine H4 receptor in renal pathophysiology. The aim here is to elucidate the role of this receptor on renal function using H4 receptor knockout mice (H4R-/-). Healthy and diabetic H4R-/- mice compared to their C57BL/6J wild-type counterpart for renal function and the expression of crucial tubular proteins. H4R-/- and wild-type mice, matched for ages, showed comparable weight gain curves reaching similar median weight at the end of the study. However, H4R-/- mice displayed a higher basal glycemia. H4R-/- mice showed a lower urine 24 h outflow, and albumin-to-creatinine ratio (ACR) compared to wild-type mice. Consistently, H4R-/- mice presented a higher expression of megalin and a lower basal expression of the sodium-hydrogen exchanger (NHE)3 and aquaporin (AQP)2. According to these basal differences, diabetic H4R-/- mice developed more severe hyperglycemia and a higher 24 h urine volume, but a lower increase in ACR and decrease in urine pH were observed. These events were paralleled by a reduced NHE3 over-expression and megalin loss in diabetic H4R-/- mice. The AQP1 and AQP7 patterns were also different between H4R-/- and wild-type diabetic mice. The collected results highlight the role of the histamine H4 receptor in the control of renal reabsorption processes, particularly albumin uptake.
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Affiliation(s)
- Roberta Verta
- Department of Biotechnology and Health Sciences, University of Turin, C.So Dogliotti 14, 10126 Turin, Italy;
| | - Maura Gurrieri
- Department of Scienza e Tecnologia del Farmaco, University of Turin, Via P. Giuria 9, 10125 Turin, Italy; (M.G.); (S.B.); (E.B.); (R.C.)
| | - Sara Borga
- Department of Scienza e Tecnologia del Farmaco, University of Turin, Via P. Giuria 9, 10125 Turin, Italy; (M.G.); (S.B.); (E.B.); (R.C.)
| | - Elisa Benetti
- Department of Scienza e Tecnologia del Farmaco, University of Turin, Via P. Giuria 9, 10125 Turin, Italy; (M.G.); (S.B.); (E.B.); (R.C.)
| | - Paolo Pollicino
- Direzione Ricerca e Terza Missione, University of Turin, Via Bogino 9 Torino, 10123 Turin, Italy;
| | - Roberta Cavalli
- Department of Scienza e Tecnologia del Farmaco, University of Turin, Via P. Giuria 9, 10125 Turin, Italy; (M.G.); (S.B.); (E.B.); (R.C.)
| | - Robin L. Thurmond
- Janssen Research & Development, LLC, 3210 Merryfield Row, San Diego, CA 92121, USA;
| | - Paul L. Chazot
- Department of Biosciences and Wolfson Research Institute, Durham University, South Road, Durham DH1 3LE, UK;
| | - Alessandro Pini
- Department of Clinical and Experimental Medicine, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy;
| | - Arianna Carolina Rosa
- Department of Scienza e Tecnologia del Farmaco, University of Turin, Via P. Giuria 9, 10125 Turin, Italy; (M.G.); (S.B.); (E.B.); (R.C.)
- Correspondence: ; Tel.: +39-011-6707955
| | - Cristina Grange
- Department of Medical Sciences, University of Turin, C.So Dogliotti 14, 10126 Turin, Italy;
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Tomilin VN, Pochynyuk O. A peek into Epac physiology in the kidney. Am J Physiol Renal Physiol 2019; 317:F1094-F1097. [PMID: 31509013 DOI: 10.1152/ajprenal.00373.2019] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
cAMP is a critical second messenger of numerous endocrine signals affecting water-electrolyte transport in the renal tubule. Exchange protein directly activated by cAMP (Epac) is a relatively recently discovered downstream effector of cAMP, having the same affinity to the second messenger as protein kinase A, the classical cAMP target. Two Epac isoforms, Epac1 and Epac2, are abundantly expressed in the renal epithelium, where they are thought to regulate water and electrolyte transport, particularly in the proximal tubule and collecting duct. Recent characterization of renal phenotype in mice lacking Epac1 and Epac2 revealed a critical role of the Epac signaling cascade in urinary concentration as well as in Na+ and urea excretion. In this review, we aim to critically summarize current knowledge of Epac relevance for renal function and to discuss the applicability of Epac-based strategies in the regulation of systemic water-electrolyte homeostasis.
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Affiliation(s)
- Viktor N Tomilin
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas
| | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas
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10
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Crajoinas RO, Polidoro JZ, Girardi ACC. The potential role of myosin motor proteins in mediating the subcellular distribution of NHE3 in the renal proximal tubule. Am J Physiol Renal Physiol 2019; 316:F986-F992. [PMID: 30864843 DOI: 10.1152/ajprenal.00577.2018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Isoform 3 of the Na+/H+ exchanger (NHE3) is responsible for the majority of the reabsorption of NaCl, NaHCO3, and, consequently, water in the renal proximal tubule. As such, this transporter plays an essential role in acid-base balance and extracellular fluid volume homeostasis and determining systemic arterial blood pressure levels. NHE3 activity is modulated by a number of mechanisms, including the redistribution of the transporter between the body of the microvilli (where NHE3 is active) and the base of the microvilli (where NHE3 is less active). Although the physiological, pathophysiological, and pharmacological importance of the subcellular distribution of NHE3 has been well established, the exact mechanism whereby NHE3 is translocated along microvilli microdomains of the proximal tubule apical membrane is unknown. Nonmuscle myosin IIA and unconventional myosin VI move cargoes in anterograde and retrograde directions, respectively, and are known to redistribute along with NHE3 in the proximal tubule in response to a variety of natriuretic and antinatriuretic stimuli, including stimulation or inhibition of the renin-angiotensin system, high dietary Na+ intake, and high blood pressure. Therefore, this review aims to discuss the current evidence that suggests a potential role of myosin IIA and myosin VI in mediating the subcellular distribution of NHE3 along the kidney proximal tubule microvilli and their possible contribution in modifying NHE3-mediated Na+ reabsorption under both physiological and pathophysiological conditions.
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Affiliation(s)
- Renato O Crajoinas
- Heart Institute (InCor), University of São Paulo Medical School , São Paulo , Brazil
| | - Juliano Z Polidoro
- Heart Institute (InCor), University of São Paulo Medical School , São Paulo , Brazil
| | - Adriana C C Girardi
- Heart Institute (InCor), University of São Paulo Medical School , São Paulo , Brazil
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11
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Gonzalez-Vicente A, Saez F, Monzon CM, Asirwatham J, Garvin JL. Thick Ascending Limb Sodium Transport in the Pathogenesis of Hypertension. Physiol Rev 2019; 99:235-309. [PMID: 30354966 DOI: 10.1152/physrev.00055.2017] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The thick ascending limb plays a key role in maintaining water and electrolyte balance. The importance of this segment in regulating blood pressure is evidenced by the effect of loop diuretics or local genetic defects on this parameter. Hormones and factors produced by thick ascending limbs have both autocrine and paracrine effects, which can extend prohypertensive signaling to other structures of the nephron. In this review, we discuss the role of the thick ascending limb in the development of hypertension, not as a sole participant, but one that works within the rich biological context of the renal medulla. We first provide an overview of the basic physiology of the segment and the anatomical considerations necessary to understand its relationship with other renal structures. We explore the physiopathological changes in thick ascending limbs occurring in both genetic and induced animal models of hypertension. We then discuss the racial differences and genetic defects that affect blood pressure in humans through changes in thick ascending limb transport rates. Throughout the text, we scrutinize methodologies and discuss the limitations of research techniques that, when overlooked, can lead investigators to make erroneous conclusions. Thus, in addition to advancing an understanding of the basic mechanisms of physiology, the ultimate goal of this work is to understand our research tools, to make better use of them, and to contextualize research data. Future advances in renal hypertension research will require not only collection of new experimental data, but also integration of our current knowledge.
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Affiliation(s)
| | - Fara Saez
- Department of Physiology and Biophysics, Case Western Reserve University , Cleveland, Ohio
| | - Casandra M Monzon
- Department of Physiology and Biophysics, Case Western Reserve University , Cleveland, Ohio
| | - Jessica Asirwatham
- Department of Physiology and Biophysics, Case Western Reserve University , Cleveland, Ohio
| | - Jeffrey L Garvin
- Department of Physiology and Biophysics, Case Western Reserve University , Cleveland, Ohio
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12
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Cherezova A, Tomilin V, Buncha V, Zaika O, Ortiz PA, Mei F, Cheng X, Mamenko M, Pochynyuk O. Urinary concentrating defect in mice lacking Epac1 or Epac2. FASEB J 2019; 33:2156-2170. [PMID: 30252533 PMCID: PMC6338637 DOI: 10.1096/fj.201800435r] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Accepted: 08/27/2018] [Indexed: 11/11/2022]
Abstract
cAMP is a universal second messenger regulating a plethora of processes in the kidney. Two downstream effectors of cAMP are PKA and exchange protein directly activated by cAMP (Epac), which, unlike PKA, is often linked to elevation of [Ca2+]i. While both Epac isoforms (Epac1 and Epac2) are expressed along the nephron, their relevance in the kidney remains obscure. We combined ratiometric calcium imaging with quantitative immunoblotting, immunofluorescent confocal microscopy, and balance studies in mice lacking Epac1 or Epac2 to determine the role of Epac in renal water-solute handling. Epac1-/- and Epac2-/- mice developed polyuria despite elevated arginine vasopressin levels. We did not detect major deficiencies in arginine vasopressin [Ca2+]i signaling in split-opened collecting ducts or decreases in aquaporin water channel type 2 levels. Instead, sodium-hydrogen exchanger type 3 levels in the proximal tubule were dramatically reduced in Epac1-/- and Epac2-/- mice. Water deprivation revealed persisting polyuria, impaired urinary concentration ability, and augmented urinary excretion of Na+ and urea in both mutant mice. In summary, we report a nonredundant contribution of Epac isoforms to renal function. Deletion of Epac1 and Epac2 decreases sodium-hydrogen exchanger type 3 expression in the proximal tubule, leading to polyuria and osmotic diuresis.-Cherezova, A., Tomilin, V., Buncha, V., Zaika, O., Ortiz, P. A., Mei, F., Cheng, X., Mamenko, M., Pochynyuk, O. Urinary concentrating defect in mice lacking Epac1 or Epac2.
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Affiliation(s)
- Alena Cherezova
- Department of Physiology, Medical College of Georgia, Augusta University, Augusta, Georgia, USA
| | - Viktor Tomilin
- Department of Integrative Biology and Pharmacology The University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Vadym Buncha
- Department of Physiology, Medical College of Georgia, Augusta University, Augusta, Georgia, USA
| | - Oleg Zaika
- Department of Integrative Biology and Pharmacology The University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Pablo A. Ortiz
- Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan, USA; and
| | - Fang Mei
- Department of Integrative Biology and Pharmacology The University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Xiaodong Cheng
- Department of Integrative Biology and Pharmacology The University of Texas Health Science Center at Houston, Houston, Texas, USA
- Texas Therapeutics Institute, The University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Mykola Mamenko
- Department of Physiology, Medical College of Georgia, Augusta University, Augusta, Georgia, USA
| | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology The University of Texas Health Science Center at Houston, Houston, Texas, USA
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13
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Hernando N. NaPi-IIa interacting partners and their (un)known functional roles. Pflugers Arch 2018; 471:67-82. [PMID: 30022249 DOI: 10.1007/s00424-018-2176-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Accepted: 06/26/2018] [Indexed: 01/14/2023]
Abstract
The sorting and stabilization of proteins at specific subcellular domains depend upon the formation of networks build up by specific protein-protein interactions. In addition, protein networks also ensure the specificity of many regulatory processes by bringing together regulatory molecules with their targets. Whereas the success on the identification of protein-protein interactions is (up to a point) technology-driven, the assignment of functional roles to specific partners remains a major challenge. This review summarizes the work that led to the identification of partners of the Na+/phosphate cotransporter NaPi-IIa as well as the effects of the interactions in the expression and/or regulation of the cotransporter.
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Affiliation(s)
- Nati Hernando
- Institute of Physiology, University Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
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14
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Hernando N, Wagner CA. Mechanisms and Regulation of Intestinal Phosphate Absorption. Compr Physiol 2018; 8:1065-1090. [PMID: 29978897 DOI: 10.1002/cphy.c170024] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
States of hypo- and hyperphosphatemia have deleterious consequences including rickets/osteomalacia and renal/cardiovascular disease, respectively. Therefore, the maintenance of appropriate plasma levels of phosphate is an essential requirement for health. This control is executed by the collaborative action of intestine and kidney whose capacities to (re)absorb phosphate are regulated by a number of hormonal and metabolic factors, among them parathyroid hormone, fibroblast growth factor 23, 1,25(OH)2 vitamin D3 , and dietary phosphate. The molecular mechanisms responsible for the transepithelial transport of phosphate across enterocytes are only partially understood. Indeed, whereas renal reabsorption entirely relies on well-characterized active transport mechanisms of phosphate across the renal proximal epithelia, intestinal absorption proceeds via active and passive mechanisms, with the molecular identity of the passive component still unknown. The active absorption of phosphate depends mostly on the activity and expression of the sodium-dependent phosphate cotransporter NaPi-IIb (SLC34A2), which is highly regulated by many of the factors, mentioned earlier. Physiologically, the contribution of NaPi-IIb to the maintenance of phosphate balance appears to be mostly relevant during periods of low phosphate availability. Therefore, its role in individuals living in industrialized societies with high phosphate intake is probably less relevant. Importantly, small increases in plasma phosphate, even within normal range, associate with higher risk of cardiovascular disease. Therefore, therapeutic approaches to treat hyperphosphatemia, including dietary phosphate restriction and phosphate binders, aim at reducing intestinal absorption. Here we review the current state of research in the field. © 2017 American Physiological Society. Compr Physiol 8:1065-1090, 2018.
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Affiliation(s)
- Nati Hernando
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
| | - Carsten A Wagner
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
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15
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Robichaux WG, Cheng X. Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development. Physiol Rev 2018; 98:919-1053. [PMID: 29537337 PMCID: PMC6050347 DOI: 10.1152/physrev.00025.2017] [Citation(s) in RCA: 141] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 09/05/2017] [Accepted: 09/06/2017] [Indexed: 12/13/2022] Open
Abstract
This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.
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Affiliation(s)
- William G Robichaux
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center , Houston, Texas
| | - Xiaodong Cheng
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center , Houston, Texas
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16
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Differential regulation of the Na +-Ca 2+ exchanger 3 (NCX3) by protein kinase PKC and PKA. Cell Calcium 2017; 65:52-62. [PMID: 28233567 DOI: 10.1016/j.ceca.2017.02.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 02/09/2017] [Accepted: 02/09/2017] [Indexed: 11/21/2022]
Abstract
Isoform 3 of the Na+-Ca2+ exchanger (NCX3) participates in the Ca2+ fluxes across the plasma membrane. Among the NCX family, NCX3 carries out a peculiar role due to its specific functions in skeletal muscle and the immune system and to its neuroprotective effect under stress exposure. In this context, proper understanding of the regulation of NCX3 is primordial to consider its potential use as a drug target. In this study, we demonstrated the regulation of NCX3 by protein kinase A (PKA) and C (PKC). Disparity in regulation has been previously reported among the splice variants of NCX3 therefore the activity of Ca2+ uptake and extrusion of the two murine variants was measured using fura-2-based Ca2+ imaging and revealed that both variants are similarly regulated. PKC stimulation diminished the Ca2+ uptake performed by NCX3 in the reverse mode, triggered by a rise in [Ca2+]i or [Na+]i, whereas an opposite response was observed upon PKA stimulation, with a significant increase of the Ca2+ uptake after a rise in [Ca2+]i. The latter stimulation affected similarly the efflux capacity of NCX3 whereas Ca2+ extrusion capacity remained unaffected under activation of PKC. Next, using site-directed mutagenesis, the sensitivity of NCX3 to PKC was abolished by singly mutating its predicted phosphorylation sites T529 or S695. The sensitivity to PKC might be due to the influence of T529 phosphorylation on the Ca2+-binding domain 1. Additionally, we showed that stimulation of NCX3 by PKA occurred through residue S524. This effect may well participate in the fight-or-flight response in skeletal muscle and the long-term potentiation in hippocampus.
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17
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Lewis AE, Aesoy R, Bakke M. Role of EPAC in cAMP-Mediated Actions in Adrenocortical Cells. Front Endocrinol (Lausanne) 2016; 7:63. [PMID: 27379015 PMCID: PMC4904129 DOI: 10.3389/fendo.2016.00063] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Accepted: 05/30/2016] [Indexed: 12/31/2022] Open
Abstract
Adrenocorticotropic hormone regulates adrenal steroidogenesis mainly via the intracellular signaling molecule cAMP. The effects of cAMP are principally relayed by activating protein kinase A (PKA) and the more recently discovered exchange proteins directly activated by cAMP 1 and 2 (EPAC1 and EPAC2). While the intracellular roles of PKA have been extensively studied in steroidogenic tissues, those of EPACs are only emerging. EPAC1 and EPAC2 are encoded by the genes RAPGEF3 and RAPGEF4, respectively. Whereas EPAC1 is ubiquitously expressed, the expression of EPAC2 is more restricted, and typically found in endocrine tissues. Alternative promoter usage of RAPGEF4 gives rise to three different isoforms of EPAC2 that vary in their N-termini (EPAC2A, EPAC2B, and EPAC2C) and that exhibit distinct expression patterns. EPAC2A is expressed in the brain and pancreas, EPAC2B in steroidogenic cells of the adrenal gland and testis, and EPAC2C has until now only been found in the liver. In this review, we discuss current knowledge on EPAC expression and function with focus on the known roles of EPAC in adrenal gland physiology.
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Affiliation(s)
- Aurélia E. Lewis
- Department of Molecular Biology, University of Bergen, Bergen, Norway
- *Correspondence: Aurélia E. Lewis,
| | - Reidun Aesoy
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Marit Bakke
- Department of Biomedicine, University of Bergen, Bergen, Norway
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18
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He Q, Zhu Y, Corbin BA, Plagge A, Bastepe M. The G protein α subunit variant XLαs promotes inositol 1,4,5-trisphosphate signaling and mediates the renal actions of parathyroid hormone in vivo. Sci Signal 2015; 8:ra84. [PMID: 26307011 DOI: 10.1126/scisignal.aaa9953] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
GNAS, which encodes the stimulatory G protein (heterotrimeric guanine nucleotide-binding protein) α subunit (Gαs), also encodes a large variant of Gαs termed extra-large α subunit (XLαs), and alterations in XLαs abundance or activity are implicated in various human disorders. Although XLαs, like Gαs, stimulates generation of the second messenger cyclic adenosine monophosphate (cAMP), evidence suggests that XLαs and Gαs have opposing effects in vivo. We investigated the role of XLαs in mediating signaling by parathyroid hormone (PTH), which activates a G protein-coupled receptor (GPCR) that stimulates both Gαs and Gαq/11 in renal proximal tubules to maintain phosphate and vitamin D homeostasis. At postnatal day 2 (P2), XLαs knockout (XLKO) mice exhibited hyperphosphatemia, hypocalcemia, and increased serum concentrations of PTH and 1,25-dihydroxyvitamin D. The ability of PTH to reduce serum phosphate concentrations was impaired, and the abundance of the sodium phosphate cotransporter Npt2a in renal brush border membranes was reduced in XLKO mice, whereas PTH-induced cAMP excretion in the urine was modestly increased. Basal and PTH-stimulated production of inositol 1,4,5-trisphosphate (IP3), which is the second messenger produced by Gαq/11 signaling, was repressed in renal proximal tubules from XLKO mice. Crossing of XLKO mice with mice overexpressing XLαs specifically in renal proximal tubules rescued the phenotype of the XLKO mice. Overexpression of XLαs in HEK 293 cells enhanced IP3 generation in unstimulated cells and in cells stimulated with PTH or thrombin, which acts through a Gq/11-coupled receptor. Together, our findings suggest that XLαs enhances Gq/11 signaling to mediate the renal actions of PTH during early postnatal development.
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Affiliation(s)
- Qing He
- Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Yan Zhu
- Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Braden A Corbin
- Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Antonius Plagge
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine University of Liverpool, Liverpool L69 3BX, UK
| | - Murat Bastepe
- Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
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19
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Zhang Y, Wang H, Guo Q, Li X, Gao J, Liu Y, Yang C, Niu L, Yang J. PI3K is involved in P2Y receptor-regulated cAMP /Epac/Kv channel signaling pathway in pancreatic β cells. Biochem Biophys Res Commun 2015; 465:714-8. [PMID: 26296468 DOI: 10.1016/j.bbrc.2015.08.057] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 08/13/2015] [Indexed: 12/20/2022]
Abstract
P2Y receptors (P2YR) are a family of purinergic G protein-coupled receptors, which could be stimulated by extracellular nucleotides. In pancreatic β cells, activation of P2YR has long been shown to stimulate insulin secretion in a glucose-dependent manner. Previously, we reported that P2YR-modulated insulin secretion is mediated by a cAMP/Epac/Kv channel pathway. However, the interaction between Epac and the Kv channel in P2YR-modulated insulin secretion remains unclear. In this study, we used patch-clamp technique and insulin secretion assay to investigate the potential molecules that may link Epac to Kv channel inhibition induced by P2YR activation. We identified that phosphatidylinositide 3-kinase, which mediates P2YR-regulated insulin secretion, is a critical mediator between Epac and the Kv channel.
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Affiliation(s)
- Yi Zhang
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Hui Wang
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Qing Guo
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Xiaodong Li
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Jingying Gao
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Yunfeng Liu
- Department of Endocrinology, The First Hospital of Shanxi Medical University, Shanxi Medical University, Taiyuan, China.
| | - Caihong Yang
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Longgang Niu
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Jing Yang
- Department of Endocrinology, The First Hospital of Shanxi Medical University, Shanxi Medical University, Taiyuan, China.
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20
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Abstract
The H(+) concentration in human blood is kept within very narrow limits, ~40 nmol/L, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: (i) reabsorb HCO3(-) that is filtered through the glomeruli to prevent its excretion in the urine; (ii) generate a sufficient quantity of new HCO3(-) to compensate for the loss of HCO3(-) resulting from dietary metabolic H(+) loads and loss of HCO3(-) in the urea cycle; and (iii) excrete HCO3(-) (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ~60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level.
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Affiliation(s)
- Ira Kurtz
- Division of Nephrology, David Geffen School of Medicine, Los Angeles, CA; Brain Research Institute, UCLA, Los Angeles, CA
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21
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Banerjee U, Cheng X. Exchange protein directly activated by cAMP encoded by the mammalian rapgef3 gene: Structure, function and therapeutics. Gene 2015; 570:157-67. [PMID: 26119090 PMCID: PMC4556420 DOI: 10.1016/j.gene.2015.06.063] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2015] [Accepted: 06/23/2015] [Indexed: 01/08/2023]
Abstract
Mammalian exchange protein directly activated by cAMP isoform 1 (EPAC1), encoded by the RAPGEF3 gene, is one of the two-membered family of cAMP sensors that mediate the intracellular functions of cAMP by acting as guanine nucleotide exchange factors for the Ras-like Rap small GTPases. Extensive studies have revealed that EPAC1-mediated cAMP signaling is highly coordinated spatiotemporally through the formation of dynamic signalosomes by interacting with a diverse array of cellular partners. Recent functional analyses of genetically engineered mouse models further suggest that EPAC1 functions as an important stress response switch and is involved in pathophysiological conditions of cardiac stresses, chronic pain, cancer and infectious diseases. These findings, coupled with the development of EPAC specific small molecule modulators, validate EPAC1 as a promising target for therapeutic interventions. Human gene RAPGEF3 encodes for EPAC1 protein. Along with PKA, CNG & HCN, EPAC is an important cAMP sensor. Selective modulators of EPAC1 have been developed for use as pharmacological probes. Formation of EPAC1 signalosomes allows spatiotemporal control of cAMP signaling. EPAC1 is implicated in major pathophysiological conditions and is an attractive therapeutic target.
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Affiliation(s)
- Upasana Banerjee
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, University of Health Science Center, Houston, TX 77030, United States
| | - Xiaodong Cheng
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, University of Health Science Center, Houston, TX 77030, United States.
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22
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Ferreira AF, França FD, Rossoni JV, Viana PHL, Moraes KCM, Gomes DA, Costa DC, Tagliati CA, Chaves MM. Cyclic adenosine monophosphate protects renal cell lines against amphotericin B toxicity in a PKA-independent manner. Drug Chem Toxicol 2015; 39:28-34. [PMID: 25690107 DOI: 10.3109/01480545.2015.1012210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Amphotericin B is the "gold standard" agent in the management of serious systemic fungal infections. However, this drug can cause nephrotoxicity, which contributes up to 25% of all acute kidney injuries in critically ill patients. Cyclic adenosine monophosphate can protect kidney cells from death due to injury or drug exposure in some cases. Hence, the objective of this work was to evaluate if cAMP could prevent cell death that occurs in renal cell lines subjected to AmB treatment and, if so, to assess the involvement of PKA in the transduction of this signal. Two different renal cell lines (LLC-PK1 and MDCK) were used in this study. MTT and flow cytometry assays showed increased cell survival when cells were exposed to cAMP in a PKA-independent manner, which was confirmed by western blot. This finding suggests that cAMP (db-cAMP) may prevent cell death caused by exposure to AmB. This is the first time this effect has been identified when renal cells are exposed to AmB's nephrotoxic potential.
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Affiliation(s)
- A F Ferreira
- a Departamento de Bioquímica e Imunologia , Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais , Belo Horizonte , MG , Brazil
| | - F D França
- a Departamento de Bioquímica e Imunologia , Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais , Belo Horizonte , MG , Brazil
| | - J V Rossoni
- b Departamento de Ciências Biológicas , Instituto de Ciências Exatas e Biológicas, Universidade Federal de Ouro Preto , Mouro Preto , MG , Brazil
| | - P H L Viana
- a Departamento de Bioquímica e Imunologia , Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais , Belo Horizonte , MG , Brazil
| | - K C M Moraes
- c Departamento de Biologia , Universidade Estadual Paulista "Júlio de Mesquita Filho", Instituto de Biociências , Rio Claro , SP , Brazil , and
| | - D A Gomes
- a Departamento de Bioquímica e Imunologia , Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais , Belo Horizonte , MG , Brazil
| | - D C Costa
- b Departamento de Ciências Biológicas , Instituto de Ciências Exatas e Biológicas, Universidade Federal de Ouro Preto , Mouro Preto , MG , Brazil
| | - C A Tagliati
- d Departamento de Análises Clinicas e Toxicológicas , Faculdade de Farmácia, Universidade Federal de Minas Gerais , Bioquímica, Belo Horizonte , Brazil
| | - M M Chaves
- a Departamento de Bioquímica e Imunologia , Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais , Belo Horizonte , MG , Brazil
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23
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Gildea JJ, Shah IT, Van Sciver RE, Israel JA, Enzensperger C, McGrath HE, Jose PA, Felder RA. The cooperative roles of the dopamine receptors, D1R and D5R, on the regulation of renal sodium transport. Kidney Int 2014; 86:118-26. [PMID: 24552847 PMCID: PMC4077925 DOI: 10.1038/ki.2014.5] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2013] [Revised: 11/27/2013] [Accepted: 12/12/2013] [Indexed: 02/07/2023]
Abstract
Determining the individual roles of the two dopamine D1-like receptors (D1R and D5R) on sodium transport in the human renal proximal tubule has been complicated by their structural and functional similarity. Here we used a novel D5R-selective antagonist (LE-PM436) and D1R or D5R-specific gene silencing to determine second messenger coupling pathways and heterologous receptor interaction between the two receptors. D1R and D5R co-localized in renal proximal tubule cells and physically interact, as determined by co-immunoprecipitation and FRET microscopy. Stimulation of renal proximal tubule cells with fenoldopam (D1R/D5R agonist) led to both adenylyl cyclase and phospholipase C (PLC) activation using real-time FRET biosensors ICUE3 and CYPHR, respectively. Fenoldopam increased cAMP accumulation and PLC activity and inhibited both NHE3 and NaKATPase activities. LE-PM436 and D5R siRNA blocked the fenoldopam-stimulated PLC pathway but not cAMP accumulation, while D1R siRNA blocked both fenoldopam-stimulated cAMP accumulation and PLC signaling. Either D1R or D5R siRNA, or LE-PM436 blocked the fenoldopam dependent inhibition of sodium transport. Further studies using the cAMP-selective D1R/D5R agonist SKF83822 and PLC-selective D1R/D5R agonist SKF83959 confirmed the cooperative influence of the two pathways on sodium transport. Thus, D1R and D5R interact in the inhibition of NHE3 and NaKATPase activity, the D1R primarily by cAMP, while the D1R/D5R heteromer modulates the D1R effect through a PLC pathway.
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Affiliation(s)
- John J Gildea
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Ishan T Shah
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Robert E Van Sciver
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Jonathan A Israel
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Christoph Enzensperger
- Institut für Pharmazie, Lehrstuhl für Pharmazeutische/Medizinische Chemie, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Helen E McGrath
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Pedro A Jose
- University of Maryland School of Medicine, Departments of Medicine and Physiology, Baltimore, Maryland, USA
| | - Robin A Felder
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
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24
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Xie P, Joladarashi D, Dudeja P, Sun L, Kanwar YS. Modulation of angiotensin II-induced inflammatory cytokines by the Epac1-Rap1A-NHE3 pathway: implications in renal tubular pathobiology. Am J Physiol Renal Physiol 2014; 306:F1260-74. [PMID: 24553435 DOI: 10.1152/ajprenal.00069.2014] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Besides the glomerulus, the tubulointerstitium is often concomitantly affected in certain diseases, e.g., diabetic nephropathy, and activation of the renin-angiotensin system, to a certain extent, worsens its outcome because of perturbations in hemodynamics and possibly tubuloglomerular feedback. Certain studies suggest that pathobiology of the tubulointerstitium is influenced by small GTPases, e.g., Rap1. We investigated the effect of ANG II on inflammatory cytokines, while at the same time focusing on upstream effector of Rap1, i.e., Epac1, and some of the downstream tubular transport molecules, i.e., Na/H exchanger 3 (NHE3). ANG II treatment of LLC-PK1 cells decreased Rap1a GTPase activity in a time- and dose-dependent manner. ANG II treatment led to an increased membrane translocation of NHE3, which was reduced with Epac1 and PKA activators. ANG II-induced NHE3 translocation was notably reduced with the transfection of Rap1a dominant positive mutants, i.e., Rap1a-G12V or Rap1a-T35A. Transfection of cells with dominant negative Rap1a mutants, i.e., Rap1a-S17A, or Epac1 mutant, i.e., EPAC-ΔcAMP, normalized ANG II-induced translocation of NHE3. In addition, ANG II treatment led to an increased expression of inflammatory cytokines, i.e., IL-1β, IL-6, IL-8, and TNF-α, which was reduced with Rap1a-G12V or Rap1a-T35A transfection, while it reverted to previous comparable levels following transfection of Rap1a-S17A or EPAC-ΔcAMP. ANG II-induced expression of cytokines was reduced with the treatment with NHE3 inhibitor S3226 or with Epac1 and PKA activators. These data suggest that this novel Epac1-Rap1a-NHE3 pathway conceivably modulates ANG II-induced expression of inflammatory cytokines, and this information may yield the impetus for developing strategies to reduce tubulointertstitial inflammation in various renal diseases.
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Affiliation(s)
- Ping Xie
- Departments of Pathology and Medicine, Northwestern University, Chicago, Illinois; and
| | | | - Pradeep Dudeja
- Department of Medicine, University of Illinois, Chicago, Illinois
| | - Lin Sun
- Departments of Pathology and Medicine, Northwestern University, Chicago, Illinois; and
| | - Yashpal S Kanwar
- Departments of Pathology and Medicine, Northwestern University, Chicago, Illinois; and
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Abstract
Urea and urea transporters (UT) are critical to the production of concentrated urine and hence in maintaining body fluid balance. The UT-A1 urea transporter is the major and most important UT isoform in the kidney. Native UT-A1, expressed in the terminal inner medullary collecting duct (IMCD) epithelial cells, is a glycosylated protein with two glycoforms of 117 and 97 kDa. Vasopressin is the major hormone in vivo that rapidly increases urea permeability in the IMCD through increases in phosphorylation and apical plasma-membrane accumulation of UT-A1. The cell signaling pathway for vasopressin-mediated UT-A1 phosphorylation and activity involves two cAMP-dependent signaling pathways: protein kinase A (PKA) and exchange protein activated by cAMP (Epac). In this chapter, we will discuss UT-A1 regulation by phosphorylation, ubiquitination, and glycosylation.
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Affiliation(s)
- Guangping Chen
- Department of Physiology, and Renal Division Department of Medicine, Emory University School of Medicine, Whitehead Research Building Room 605N, 615 Michael Street, Atlanta, GA, 30322, USA,
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26
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Abstract
UT-A and UT-B families of urea transporters consist of multiple isoforms that are subject to regulation of both acutely and by long-term measures. This chapter provides a brief overview of the expression of the urea transporter forms and their locations in the kidney. Rapid regulation of UT-A1 results from the combination of phosphorylation and membrane accumulation. Phosphorylation of UT-A1 has been linked to vasopressin and hyperosmolality, although through different kinases. Other acute influences on urea transporter activity are ubiquitination and glycosylation, both of which influence the membrane association of the urea transporter, again through different mechanisms. Long-term regulation of urea transport is most closely associated with the environment that the kidney experiences. Low-protein diets may influence the amount of urea transporter available. Conditions of osmotic diuresis, where urea concentrations are low, will prompt an increase in urea transporter abundance. Although adrenal steroids affect urea transporter abundance, conflicting reports make conclusions tenuous. Urea transporters are upregulated when P2Y2 purinergic receptors are decreased, suggesting a role for these receptors in UT regulation. Hypercalcemia and hypokalemia both cause urine concentration deficiencies. Urea transporter abundances are reduced in aging animals and animals with angiotensin-converting enzyme deficiencies. This chapter will provide information about both rapid and long-term regulation of urea transporters and provide an introduction into the literature.
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Affiliation(s)
- Janet D Klein
- Renal Division, Department of Medicine and Department of Physiology, Emory University School of Medicine, WMB Room 3319B, 1639 Pierce Drive, NE, Atlanta, GA, 30322, USA,
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Bruzzone A, Saulière A, Finana F, Sénard JM, Lüthy I, Galés C. Dosage-dependent regulation of cell proliferation and adhesion through dual β2-adrenergic receptor/cAMP signals. FASEB J 2013; 28:1342-54. [PMID: 24308976 DOI: 10.1096/fj.13-239285] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The role of β-adrenergic receptors (β-ARs) remains controversial in normal and tumor breast. Herein we explore the cAMP signaling involved in β-AR-dependent control of proliferation and adhesion of nontumor human breast cell line MCF-10A. Low concentrations of a β-agonist, isoproterenol (ISO), promote cell adhesion (87.5% cells remaining adherent to the plastic dishes following specific detachment vs. 35.0% in control, P<0.001), while increasing concentrations further engages an additional 36% inhibition of Erk1/2 phosphorylation (p-Erk1/2)-dependent cell proliferation (P<0.01). Isoproterenol dose response on cell adhesion was fitted to a 2-site curve (EC50(1): 16.5±11.5 fM, EC50(2): 4.08±3.09 nM), while ISO significantly inhibited p-Erk1/2 according to a 1-site model (EC50: 0.25±0.13 nM). Using β-AR-selective agonist/antagonists and cAMP analogs/inhibitors, we identified a dosage-dependent signaling in which low ISO concentrations target a β2-AR population localized in raft microdomains and stimulate a Gs/cAMP/Epac/adhesion-signaling module, while higher concentrations engage a concomitant activation of another β2-AR population outside rafts and inhibit the proliferation by a Gs/cAMP/PKA-dependent signaling module. Our data provide a new molecular basis for the dose-dependent switch of β-AR signaling. This study also sheds light on a new cAMP pathway core mechanism with a single receptor triggering dual cAMP signaling controlled by PKA or Epac but with different cellular outputs.
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Affiliation(s)
- Ariana Bruzzone
- 2Inserm U1048, Institut des Maladies Métaboliques et Cardiovasculaires, I2MC, 1, avenue Jean-Poulhès, BP84225, 31432 Toulouse Cedex 4, France.
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28
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Kumai Y, Kwong RWM, Perry SF. The role of cAMP-mediated intracellular signaling in regulating Na+ uptake in zebrafish larvae. Am J Physiol Regul Integr Comp Physiol 2013; 306:R51-60. [PMID: 24259461 DOI: 10.1152/ajpregu.00317.2013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the current study, the role of cAMP in stimulating Na(+) uptake in larval zebrafish was investigated. Treating larvae at 4 days postfertilization (dpf) with 10 μM forskolin or 1 μM 8-bromo cAMP significantly increased Na(+) uptake by three-fold and twofold, respectively. The cAMP-dependent stimulation of Na(+) uptake was probably unrelated to protein trafficking via microtubules because pretreatment with 200 μM colchicine or 30 μM nocodazole did not attenuate the magnitude of the response. Na(+) uptake was stimulated markedly following acute (2 h) exposure to acidic water. The acid-induced increase in Na(+) uptake was accompanied by a twofold elevation in whole body cAMP levels and attenuated by inhibiting PKA with 10 μM H-89. Knockdown of Na(+)-H(+) exchanger 3b (NHE3b) attenuated, but did not abolish, the stimulation of Na(+) uptake during forskolin treatment. In glial cell missing 2 morphants, in which the role of NHE3b in Na(+) uptake is diminished and the Na(+)-Cl(-) cotransporter (NCC) becomes the predominant route of Na(+) entry, forskolin treatment continued to increase Na(+) uptake. These data suggest that at least NHE3b and NCC are targeted by cAMP in zebrafish larvae. Staining of larvae with fluorescent forskolin and propranolol revealed the presence of transmembrane adenylyl cyclase within multiple subtypes of ionocytes expressing β-adrenergic receptors. Taken together, results of the present study demonstrate that cAMP-mediated intracellular signaling may regulate multiple Na(+) transporters and plays an important role in regulating Na(+) uptake in zebrafish larvae during acute exposure to an acidic environment.
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Affiliation(s)
- Yusuke Kumai
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
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Dërmaku-Sopjani M, Almilaji A, Pakladok T, Munoz C, Hosseinzadeh Z, Blecua M, Sopjani M, Lang F. Down-regulation of the Na+-coupled phosphate transporter NaPi-IIa by AMP-activated protein kinase. Kidney Blood Press Res 2013; 37:547-56. [PMID: 24356547 DOI: 10.1159/000355735] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/25/2013] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND/AIMS The Na(+)-coupled phosphate transporter NaPi-IIa is the main carrier accomplishing renal tubular phosphate reabsorption. It is driven by the electrochemical Na(+) gradient across the apical cell membrane, which is maintained by Na(+) extrusion across the basolateral cell membrane through the Na(+)/K(+) ATPase. The operation of NaPi-IIa thus requires energy in order to avoid cellular Na(+) accumulation and K(+) loss with eventual decrease of cell membrane potential, Cl(-) entry and cell swelling. Upon energy depletion, early inhibition of Na(+)-coupled transport processes may delay cell swelling and thus foster cell survival. Energy depletion is sensed by the AMP-activated protein kinase (AMPK), a serine/threonine kinase stimulating several cellular mechanisms increasing energy production and limiting energy utilization. The present study explored whether AMPK influences the activity of NAPi-IIa. METHODS cRNA encoding NAPi-IIa was injected into Xenopus oocytes with or without additional expression of wild-type AMPK (AMPK(α1)-HA+AMPK(β1)-Flag+AMPK(γ1)-HA), of inactive AMPK(αK45R) (AMPK(α1K45R)+AMPK(β1)-Flag+AMPK(γ1)-HA) or of constitutively active AMPK(γR70Q) (AMPK(α1)-HA+AMPK(β1)-Flag+AMPKγ1(R70Q)). NaPi-IIa activity was estimated from phosphate-induced current in dual electrode voltage clamp experiments. RESULTS In NaPi-IIa-expressing, but not in water-injected Xenopus oocytes, the addition of phosphate (1 mM) to the extracellular bath solution generated a current (Ip), which was significantly decreased by coexpression of wild-type AMPK and of AMPK(γR70Q) but not of AMPK(αK45R). The phosphate-induced current in NaPi-IIa- and AMPK-expressing Xenopus ooocytes was significantly increased by AMPK inhibitor Compound C (20 µM). Kinetic analysis revealed that AMPK significantly decreased the maximal transport rate. CONCLUSION The AMP-activated protein kinase AMPK is a powerful regulator of NaPi-IIa and thus of renal tubular phosphate transport. © 2013 S. Karger AG, Basel.
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30
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Tang X, Zhang J, Sun J, Wang Y, Wu J, Zhang L. Caged nucleotides/nucleosides and their photochemical biology. Org Biomol Chem 2013; 11:7814-24. [PMID: 24132515 DOI: 10.1039/c3ob41735b] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Nucleotides and nucleosides are not only key units of DNA/RNA that store genetic information, but are also the regulators of many biological events of our lives. By caging the key functional groups or key residues of nucleotides with photosensitive moieties, it will be possible to trigger biological events of target nucleotides with spatiotemporal resolution and amplitude upon light activation or photomodulate polymerase reactions with the caged nucleotide analogues for next-generation sequencing (NGS) and bioorthogonal labeling. This review highlights three different caging strategies for nucleotides and demonstrates the photochemical biology of these caged nucleotides.
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Affiliation(s)
- Xinjing Tang
- State Key Laboratory of Natural and Biomimetic Drugs, the School of Pharmaceutical Sciences, Peking University, No. 38, Xueyuan Rd., Beijing 100191, China.
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31
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Abstract
The kidney plays a fundamental role in maintaining body salt and fluid balance and blood pressure homeostasis through the actions of its proximal and distal tubular segments of nephrons. However, proximal tubules are well recognized to exert a more prominent role than distal counterparts. Proximal tubules are responsible for reabsorbing approximately 65% of filtered load and most, if not all, of filtered amino acids, glucose, solutes, and low molecular weight proteins. Proximal tubules also play a key role in regulating acid-base balance by reabsorbing approximately 80% of filtered bicarbonate. The purpose of this review article is to provide a comprehensive overview of new insights and perspectives into current understanding of proximal tubules of nephrons, with an emphasis on the ultrastructure, molecular biology, cellular and integrative physiology, and the underlying signaling transduction mechanisms. The review is divided into three closely related sections. The first section focuses on the classification of nephrons and recent perspectives on the potential role of nephron numbers in human health and diseases. The second section reviews recent research on the structural and biochemical basis of proximal tubular function. The final section provides a comprehensive overview of new insights and perspectives in the physiological regulation of proximal tubular transport by vasoactive hormones. In the latter section, attention is particularly paid to new insights and perspectives learnt from recent cloning of transporters, development of transgenic animals with knockout or knockin of a particular gene of interest, and mapping of signaling pathways using microarrays and/or physiological proteomic approaches.
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Affiliation(s)
- Jia L Zhuo
- Laboratory of Receptor and Signal Transduction, Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson, Mississippi, USA.
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32
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Sulfatides are required for renal adaptation to chronic metabolic acidosis. Proc Natl Acad Sci U S A 2013; 110:9998-10003. [PMID: 23716689 DOI: 10.1073/pnas.1217775110] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Urinary ammonium excretion by the kidney is essential for renal excretion of sufficient amounts of protons and to maintain stable blood pH. Ammonium secretion by the collecting duct epithelia accounts for the majority of urinary ammonium; it is driven by an interstitium-to-lumen NH3 gradient due to the accumulation of ammonium in the medullary and papillary interstitium. Here, we demonstrate that sulfatides, highly charged anionic glycosphingolipids, are important for maintaining high papillary ammonium concentration and increased urinary acid elimination during metabolic acidosis. We disrupted sulfatide synthesis by a genetic approach along the entire renal tubule. Renal sulfatide-deficient mice had lower urinary pH accompanied by lower ammonium excretion. Upon acid diet, they showed impaired ammonuria, decreased ammonium accumulation in the papilla, and chronic hyperchloremic metabolic acidosis. Expression levels of ammoniagenic enzymes and Na(+)-K(+)/NH4(+)-2Cl(-) cotransporter 2 were higher, and transepithelial NH3 transport, examined by in vitro microperfusion of cortical and outer medullary collecting ducts, was unaffected in mutant mice. We therefore suggest that sulfatides act as counterions for interstitial ammonium facilitating its retention in the papilla. This study points to a seminal role of sulfatides in renal ammonium handling, urinary acidification, and acid-base homeostasis.
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33
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Astrocyte-specific overexpression of Nrf2 delays motor pathology and synuclein aggregation throughout the CNS in the alpha-synuclein mutant (A53T) mouse model. J Neurosci 2013; 32:17775-87. [PMID: 23223297 DOI: 10.1523/jneurosci.3049-12.2012] [Citation(s) in RCA: 135] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Alpha synuclein (SYN) is a central player in the pathogenesis of sporadic and familial Parkinson's disease (PD). SYN aggregation and oxidative stress are associated and enhance each other's toxicity. It is unknown whether the redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) plays a role against the toxicity of SYN. To examine this, mice selectively overexpressing Nrf2 in astrocytes (GFAP-Nrf2) were crossed with mice selectively expressing human mutant SYN (hSYN(A53T)) in neurons. Increased astrocytic Nrf2 delayed the onset and extended the life span of the hSYN(A53T) mice. This correlated with increased motor neuron survival, reduced oxidative stress, and attenuated gliosis in the spinal cord, as well as a dramatic decrease in total hSYN(A53T) and phosphorylated (Ser129) hSYN(A53T) in Triton-insoluble aggregates. Furthermore, Nrf2 in astrocytes delayed chaperone-mediated autophagy and macroautophagy dysfunction observed in the hSYN(A53T) mice. Our data suggest that Nrf2 in astrocytes provides neuroprotection against hSYN(A53T)-mediated toxicity by promoting the degradation of hSYN(A53T) through the autophagy-lysosome pathway in vivo. Thus, activation of the Nrf2 pathway in astrocytes is a potential target to develop therapeutic strategies for treating pathologic synucleinopathies including PD.
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Yang SK, Xiao L, Li J, Liu F, Sun L, Kanwar YS. Role of guanine-nucleotide exchange factor Epac in renal physiology and pathophysiology. Am J Physiol Renal Physiol 2013; 304:F831-9. [PMID: 23364803 PMCID: PMC3625846 DOI: 10.1152/ajprenal.00711.2012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 01/28/2013] [Indexed: 12/13/2022] Open
Abstract
Exchange proteins directly activated by cAMP [Epac(s)] were discovered more than a decade ago as new sensors for the second messenger cAMP. The Epac family members, including Epac1 and Epac2, are guanine nucleotide exchange factors for the Ras-like small GTPases Rap1 and Rap2, and they function independently of protein kinase A. Given the importance of cAMP in kidney homeostasis, several molecular and cellular studies using specific Epac agonists have analyzed the role and regulation of Epac proteins in renal physiology and pathophysiology. The specificity of the functions of Epac proteins may depend upon their expression and localization in the kidney as well as their abundance in the microcellular environment. This review discusses recent literature data concerning the involvement of Epac in renal tubular transport physiology and renal glomerular cells where various signaling pathways are known to be operative. In addition, the potential role of Epac in kidney disorders, such as diabetic kidney disease and ischemic kidney injury, is discussed.
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Affiliation(s)
- Shi-kun Yang
- Department of Nephrology, The Second Xiangya Hospital, Kidney Institute of Nephrology, Central South University, Changsha, Hunan Province, China
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Ezrin is required for the functional regulation of the epithelial sodium proton exchanger, NHE3. PLoS One 2013; 8:e55623. [PMID: 23405179 PMCID: PMC3566197 DOI: 10.1371/journal.pone.0055623] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Accepted: 12/31/2012] [Indexed: 11/19/2022] Open
Abstract
The sodium hydrogen exchanger isoform 3 (NHE3) mediates absorption of sodium, bicarbonate and water from renal and intestinal lumina. This activity is fundamental to the maintenance of a physiological plasma pH and blood pressure. To perform this function NHE3 must be present in the apical membrane of renal tubular and intestinal epithelia. The molecular determinants of this localization have not been conclusively determined, although linkage to the apical actin cytoskeleton through ezrin has been proposed. We set out to evaluate this hypothesis. Functional studies of NHE3 activity were performed on ezrin knockdown mice (Vil2kd/kd) and NHE3 activity similar to wild-type animals detected. Interpretation of this finding was difficult as other ERM (ezrin/radixin/moesin) proteins were present. We therefore generated an epithelial cell culture model where ezrin was the only detectable ERM. After knockdown of ezrin expression with siRNA, radixin and moesin expression remained undetectable. Consistent with the animal ultrastructural data, cells lacking ezrin retained an epithelial phenotype but had shortened and thicker microvilli. NHE3 localization was identical to cells transfected with non-targeting siRNA. The attachment of NHE3 to the apical cytoskeleton was unaltered as assessed by fluorescent recovery after photobleaching (FRAP) and the solubility of NHE3 in Triton X-100. Baseline NHE3 activity was unaltered, however, cAMP-dependent inhibition of NHE3 was largely lost even though NHE3 was phosphorylated at serines 552 and 605. Thus, ezrin is not necessary for the apical localization, attachment to the cytoskeleton, baseline activity or cAMP induced phosphrylation of NHE3, but instead is required for cAMP mediated inhibition.
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Chen H, Tsalkova T, Mei FC, Hu Y, Cheng X, Zhou J. 5-Cyano-6-oxo-1,6-dihydro-pyrimidines as potent antagonists targeting exchange proteins directly activated by cAMP. Bioorg Med Chem Lett 2012; 22:4038-43. [PMID: 22607683 DOI: 10.1016/j.bmcl.2012.04.082] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Revised: 04/16/2012] [Accepted: 04/17/2012] [Indexed: 12/21/2022]
Abstract
Exchange proteins directly activated by cAMP (Epac) are a family of guanine nucleotide exchange factors that regulate a wide variety of intracellular processes in response to second messenger cAMP. To explore the structural determinants for Epac antagonist properties of high throughput screening (HTS) hit ESI-08, pyrimidine 1, a series of 5-cyano-6-oxo-1,6-dihydro-pyrimidine analogues have been synthesized and evaluated for their activities for Epac inhibition. Structure-activity relationship (SAR) analysis led to the identification of three more potent Epac antagonists (6b, 6g, and 6h). These inhibitors may serve as valuable pharmacological probes for further elucidation of the physiological functions and mechanisms of Epac regulation. Our SAR results and molecular docking studies have also revealed that further optimization of the moieties at the C-6 position of pyrimidine scaffold may allow us to discover more potent Epac-specific antagonists.
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Affiliation(s)
- Haijun Chen
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX 77555, USA
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37
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Bakouh N, Chérif-Zahar B, Hulin P, Prié D, Friedlander G, Edelman A, Planelles G. Functional interaction between CFTR and the sodium-phosphate co-transport type 2a in Xenopus laevis oocytes. PLoS One 2012; 7:e34879. [PMID: 22514683 PMCID: PMC3325942 DOI: 10.1371/journal.pone.0034879] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Accepted: 03/09/2012] [Indexed: 11/25/2022] Open
Abstract
Background A growing number of proteins, including ion transporters, have been shown to interact with Cystic Fibrosis Transmembrane conductance Regulator (CFTR). CFTR is an epithelial chloride channel that is involved in Cystic Fibrosis (CF) when mutated; thus a better knowledge of its functional interactome may help to understand the pathophysiology of this complex disease. In the present study, we investigated if CFTR and the sodium-phosphate co-transporter type 2a (NPT2a) functionally interact after heterologous expression of both proteins in Xenopus laevis oocytes. Methodology/Findings NPT2a was expressed alone or in combination with CFTR in X. laevis oocytes. Using the two-electrode voltage-clamp technique, the inorganic phosphate-induced current (IPi) was measured and taken as an index of NPT2a activity. The maximal IPi for NPT2a substrates was reduced when CFTR was co-expressed with NPT2a, suggesting a decrease in its expression at the oolemna. This was consistent with Western blot analysis showing reduced NPT2a plasma membrane expression in oocytes co-expressing both proteins, whereas NPT2a protein level in total cell lysate was the same in NPT2a- and NPT2a+CFTR-oocytes. In NPT2a+CFTR- but not in NPT2a-oocytes, IPi and NPT2a surface expression were increased upon PKA stimulation, whereas stimulation of Exchange Protein directly Activated by cAMP (EPAC) had no effect. When NPT2a-oocytes were injected with NEG2, a short amino-acid sequence from the CFTR regulatory domain that regulates PKA-dependent CFTR trafficking to the plasma membrane, IPi values and NPT2a membrane expression were diminished, and could be enhanced by PKA stimulation, thereby mimicking the effects of CFTR co-expression. Conclusion/Perspectives We conclude that when both CFTR and NPT2a are expressed in X. laevis oocytes, CFTR confers to NPT2a a cAMPi-dependent trafficking to the membrane. This functional interaction raises the hypothesis that CFTR may play a role in phosphate homeostasis.
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Affiliation(s)
- Naziha Bakouh
- Inserm UMRS-845, Paris, France
- Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, Paris, France
| | - Baya Chérif-Zahar
- Inserm UMRS-845, Paris, France
- Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, Paris, France
| | - Philippe Hulin
- Inserm UMRS-845, Paris, France
- Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, Paris, France
| | - Dominique Prié
- Inserm UMRS-845, Paris, France
- Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, Paris, France
| | - Gérard Friedlander
- Inserm UMRS-845, Paris, France
- Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, Paris, France
| | - Aleksander Edelman
- Inserm UMRS-845, Paris, France
- Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, Paris, France
| | - Gabrielle Planelles
- Inserm UMRS-845, Paris, France
- Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, Paris, France
- * E-mail:
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Qin Y, Stokman G, Yan K, Ramaiahgari S, Verbeek F, de Graauw M, van de Water B, Price LS. cAMP signalling protects proximal tubular epithelial cells from cisplatin-induced apoptosis via activation of Epac. Br J Pharmacol 2012; 165:1137-50. [PMID: 21745194 PMCID: PMC3346244 DOI: 10.1111/j.1476-5381.2011.01594.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 06/03/2011] [Accepted: 06/23/2011] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Nephrotoxicity is the principal dose-limiting factor for cisplatin chemotherapy and is primarily associated with proximal tubular epithelial cells, including disruption of cell adhesions and induction of apoptosis. Cell adhesion and survival is regulated by, amongst other factors, the small GTPase Rap and its activator, the exchange protein directly activated by cAMP (Epac). Epac is particularly enriched in renal tubule epithelium. This study investigates the cytoprotective effects of cAMP-Epac-Rap signalling in a model of cisplatin-induced renal cell injury. EXPERIMENTAL APPROACH The Epac-selective cAMP analogue 8-pCPT-2'-O-Me-cAMP was used to activate the Epac-Rap signalling pathway in proximal tubular epithelial cells. Cells were exposed to cisplatin, in the presence or absence of 8-pCPT-2'-O-Me-cAMP, and nephrotoxicity was determined by monitoring cell-cell junctions and cell apoptosis. KEY RESULTS Activation of Epac-Rap signalling preserves cell-cell junctions and protects against cell apoptosis of mouse proximal tubular cells during cisplatin treatment. Activation with the Epac-selective cAMP analogue 8-pCPT-2'-O-Me-cAMP or receptor-mediated induction of cAMP both induced cytoprotection against cisplatin, whereas a PKA-selective cAMP analogue was not cytoprotective. 8-pCPT-2'-O-Me-cAMP mediated cytoprotection was blocked by RNAi-mediated silencing of Epac-Rap signalling in these cells. In contrast, 8-pCPT-2'-O-Me-cAMP did not protect against cisplatin-induced cell death of cancer cells that lacked Epac1 expression. CONCLUSIONS AND IMPLICATIONS Our study identifies activation of Epac-Rap signalling as a potential strategy for reducing the nephrotoxicity associated with cisplatin treatments and, as a result, broadens the therapeutic window of this chemotherapeutic agent.
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Affiliation(s)
- Yu Qin
- Division of Toxicology, Leiden/Amsterdam Center for Drug Research, Leiden UniversityLeiden, the Netherlands
| | - Geurt Stokman
- Division of Toxicology, Leiden/Amsterdam Center for Drug Research, Leiden UniversityLeiden, the Netherlands
| | - Kuan Yan
- Section Imaging and Bioinformatics, Leiden Institute of Advanced Computer Science, Leiden UniversityLeiden, the Netherlands
| | - Sreenivasa Ramaiahgari
- Division of Toxicology, Leiden/Amsterdam Center for Drug Research, Leiden UniversityLeiden, the Netherlands
| | - Fons Verbeek
- Section Imaging and Bioinformatics, Leiden Institute of Advanced Computer Science, Leiden UniversityLeiden, the Netherlands
| | - Marjo de Graauw
- Division of Toxicology, Leiden/Amsterdam Center for Drug Research, Leiden UniversityLeiden, the Netherlands
| | - Bob van de Water
- Division of Toxicology, Leiden/Amsterdam Center for Drug Research, Leiden UniversityLeiden, the Netherlands
| | - Leo S Price
- Division of Toxicology, Leiden/Amsterdam Center for Drug Research, Leiden UniversityLeiden, the Netherlands
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Lee YJ, Kim MO, Ryu JM, Han HJ. Regulation of SGLT expression and localization through Epac/PKA-dependent caveolin-1 and F-actin activation in renal proximal tubule cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1823:971-82. [PMID: 22230192 DOI: 10.1016/j.bbamcr.2011.12.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2011] [Revised: 12/07/2011] [Accepted: 12/21/2011] [Indexed: 11/29/2022]
Abstract
This study demonstrated that exchange proteins directly activated by cAMP (Epac) and protein kinase A (PKA) by 8-bromo (8-Br)-adenosine 3',5'-cyclic monophosphate (cAMP) stimulated [(14)C]-α-methyl-D-glucopyranoside (α-MG) uptake through increased sodium-glucose cotransporters (SGLTs) expression and translocation to lipid rafts in renal proximal tubule cells (PTCs). In PTCs, SGLTs were colocalized with lipid raft caveolin-1 (cav-1), disrupted by methyl-β-cyclodextrin (MβCD). Selective activators of Epac or PKA, 8-Br-cAMP, and forskolin stimulated expressions of SGLTs and α-MG uptake in PTCs. In addition, 8-Br-cAMP-induced PKA and Epac activation increased phosphorylation of extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (MAPK), and nuclear factor kappa B (NF-κB), which were involved in expressions of SGLTs. Furthermore, 8-Br-cAMP stimulated SGLTs translocation to lipid rafts via filamentous actin (F-actin) organization, which was blocked by cytochalasin D. In addition, cav-1 and SGLTs stimulated by 8-Br-cAMP were detected in lipid rafts, which were blocked by cytochalasin D. Furthermore, 8-Br-cAMP-induced SGLTs translocation and α-MG uptake were attenuated by inhibition of cav-1 activation with cav-1 small interfering RNA (siRNA) and inhibition of F-actin organization with TRIO and F-actin binding protein (TRIOBP). In conclusion, 8-Br-cAMP stimulated α-MG uptake via Epac and PKA-dependent SGLTs expression and trafficking through cav-1 and F-actin in PTCs.
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Affiliation(s)
- Yu Jin Lee
- Department of Veterinary Physiology, Chonnam National University, Gwangju, Republic of Korea
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40
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Di Sole F, Girardi ACC. Uncovering the pathway of sepsis-induced renal tubular dysfunction. Focus on “Basolateral LPS inhibits NHE3 and HCO3− absorption through TLR4/MyD88-dependent ERK activation in medullary thick ascending limb”. Am J Physiol Cell Physiol 2011; 301:C1290-2. [DOI: 10.1152/ajpcell.00350.2011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Francesca Di Sole
- Department of Internal Medicine and
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas; and
| | - Adriana C. C. Girardi
- Heart Institute (InCor), University of São Paulo Medical School, São Paulo, SP, Brazil
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41
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Sun L, Kondeti VK, Xie P, Raparia K, Kanwar YS. Epac1-mediated, high glucose-induced renal proximal tubular cells hypertrophy via the Akt/p21 pathway. THE AMERICAN JOURNAL OF PATHOLOGY 2011; 179:1706-18. [PMID: 21854750 DOI: 10.1016/j.ajpath.2011.06.035] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2011] [Revised: 05/30/2011] [Accepted: 06/08/2011] [Indexed: 11/17/2022]
Abstract
The mechanisms involved in tubular hypertrophy in diabetic nephropathy are unclear. We investigated the role of exchange protein activated by cAMP 1(Epac1), which activates Rap-family G proteins in cellular hypertrophy. Epac1 is expressed in heart, renal tubules, and in the HK-2 cell line. In diabetic mice, increased Epac1 expression was observed, and under high glucose ambience (HGA), HK-2 cells also exhibited increased Epac1 expression. We isolated a 1614-bp DNA fragment upstream of the initiation codon of Epac1 gene, inclusive of glucose response elements (GREs). HK-2 or COS7 cells transfected with the Epac1 promoter revealed a dose-dependent increase in its activity under HGA. Mutations in GRE motifs resulted in decreased promoter activity. HK-2 cells exhibited a hypertrophic response and increased protein synthesis under HGA, which was reduced by Epac1-siRNA or -mutants, whereas the use of a protein kinase A inhibitor had minimal effect. Epac1 transfection led to cellular hypertrophy and increased protein synthesis, which was accentuated by HGA. HGA increased the proportion of cells in the G0/G1 cell-cycle phase, and the expression of pAkt and the cyclin-dependent kinase inhibitors p21 and p27 was increased while the activity of cyclin-dependent kinase 4 decreased. These effects were reversed following transfection of cells with Epac1-siRNA or -mutants. These data suggest that HGA increases GRE-dependent Epac1 transcription, leading to cell cycle arrest and instigation of cellular hypertrophy.
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Affiliation(s)
- Lin Sun
- Departments of Pathology and Medicine, Northwestern University, Chicago, Illinois 60611, USA
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42
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Rap-linked cAMP signaling Epac proteins: Compartmentation, functioning and disease implications. Cell Signal 2011; 23:1257-66. [DOI: 10.1016/j.cellsig.2011.03.007] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 03/04/2011] [Accepted: 03/04/2011] [Indexed: 12/14/2022]
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Stokman G, Qin Y, Genieser HG, Schwede F, de Heer E, Bos JL, Bajema IM, van de Water B, Price LS. Epac-Rap signaling reduces cellular stress and ischemia-induced kidney failure. J Am Soc Nephrol 2011; 22:859-72. [PMID: 21493776 DOI: 10.1681/asn.2010040423] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Renal ischemia-reperfusion injury is associated with the loss of tubular epithelial cell-cell and cell-matrix interactions which contribute to renal failure. The Epac-Rap signaling pathway is a potent regulator of cell-cell and cell-matrix adhesion. The cyclic AMP analogue 8-pCPT-2'-O-Me-cAMP has been shown to selectively activate Epac, whereas the addition of an acetoxymethyl (AM) ester to 8-pCPT-2'-O-Me-cAMP enhanced in vitro cellular uptake. Here we demonstrate that pharmacological activation of Epac-Rap signaling using acetoxymethyl-8-pCPT-2'-O-Me-cAMP preserves cell adhesions during hypoxia in vitro, maintaining the barrier function of the epithelial monolayer. Intrarenal administration in vivo of 8-pCPT-2'-O-Me-cAMP also reduced renal failure in a mouse model for ischemia-reperfusion injury. This was accompanied by decreased expression of the tubular cell stress marker clusterin-α, and lateral expression of β-catenin after ischemia indicative of sustained tubular barrier function. Our study emphasizes the undervalued importance of maintaining tubular epithelial cell adhesion in renal ischemia and demonstrates the potential of pharmacological modulation of cell adhesion as a new therapeutic strategy to reduce the extent of injury in kidney disease and transplantation.
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Affiliation(s)
- Geurt Stokman
- Division of Toxicology, Leiden/Amsterdam Center for Drug Research, Leiden University, Leiden, The Netherlands
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Liu Z, Segawa H, Aydin C, Reyes M, Erben RG, Weinstein LS, Chen M, Marshansky V, Fröhlich LF, Bastepe M. Transgenic overexpression of the extra-large Gsα variant XLαs enhances Gsα-mediated responses in the mouse renal proximal tubule in vivo. Endocrinology 2011; 152:1222-33. [PMID: 21303955 PMCID: PMC3060637 DOI: 10.1210/en.2010-1034] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
XLαs, a variant of the stimulatory G protein α-subunit (Gsα), can mediate receptor-activated cAMP generation and, thus, mimic the actions of Gsα in transfected cells. However, it remains unknown whether XLαs can act in a similar manner in vivo. We have now generated mice with ectopic transgenic expression of rat XLαs in the renal proximal tubule (rptXLαs mice), where Gsα mediates most actions of PTH. Western blots and quantitative RT-PCR showed that, while Gsα and type-1 PTH receptor levels were unaltered, protein kinase A activity and 25-hydroxyvitamin D 1-α-hydroxylase (Cyp27b1) mRNA levels were significantly higher in renal proximal tubules of rptXLαs mice than wild-type littermates. Immunohistochemical analysis of kidney sections showed that the sodium-phosphate cotransporter type 2a was modestly reduced in brush border membranes of male rptXLαs mice compared to gender-matched controls. Serum calcium, phosphorus, and 1,25 dihydroxyvitamin D were within the normal range, but serum PTH was ∼30% lower in rptXLαs mice than in controls (152 ± 16 vs. 222 ± 41 pg/ml; P < 0.05). After crossing the rptXLαs mice to mice with ablation of maternal Gnas exon 1 (E1(m-/+)), male offspring carrying both the XLαs transgene and maternal Gnas exon 1 ablation (rptXLαs/E1(m-/+)) were significantly less hypocalcemic than gender-matched E1(m-/+) littermates. Both E1(m-/+) and rptXLαs/E1(m-/+) offspring had higher serum PTH than wild-type littermates, but the degree of secondary hyperparathyroidism tended to be lower in rptXLαs/E1(m-/+) mice. Hence, transgenic XLαs expression in the proximal tubule enhanced Gsα-mediated responses, indicating that XLαs can mimic Gsα in vivo.
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Affiliation(s)
- Zun Liu
- Endocrine Unit, Department of Medicine, Massachusetts General Hospital, 50 Blossom Street, Thier 10, Boston, Massachusetts 02114, USA
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Abstract
Urea transport proteins were initially proposed to exist in the kidney in the late 1980s when studies of urea permeability revealed values in excess of those predicted by simple lipid-phase diffusion and paracellular transport. Less than a decade later, the first urea transporter was cloned. Currently, the SLC14A family of urea transporters contains two major subgroups: SLC14A1, the UT-B urea transporter originally isolated from erythrocytes; and SLC14A2, the UT-A group with six distinct isoforms described to date. In the kidney, UT-A1 and UT-A3 are found in the inner medullary collecting duct; UT-A2 is located in the thin descending limb, and UT-B is located primarily in the descending vasa recta; all are glycoproteins. These transporters are crucial to the kidney's ability to concentrate urine. UT-A1 and UT-A3 are acutely regulated by vasopressin. UT-A1 has also been shown to be regulated by hypertonicity, angiotensin II, and oxytocin. Acute regulation of these transporters is through phosphorylation. Both UT-A1 and UT-A3 rapidly accumulate in the plasma membrane in response to stimulation by vasopressin or hypertonicity. Long-term regulation involves altering protein abundance in response to changes in hydration status, low protein diets, adrenal steroids, sustained diuresis, or antidiuresis. Urea transporters have been studied using animal models of disease including diabetes mellitus, lithium intoxication, hypertension, and nephrotoxic drug responses. Exciting new animal models are being developed to study these transporters and search for active urea transporters. Here we introduce urea and describe the current knowledge of the urea transporter proteins, their regulation, and their role in the kidney.
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Affiliation(s)
- Janet D Klein
- Renal Division, Department of Medicine, Emory University, Atlanta, Georgia, USA
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Champeris Tsaniras S. Generating Mature β-Cells From Embryonic Stem Cells. STEM CELL REGULATORS 2011; 87:79-92. [DOI: 10.1016/b978-0-12-386015-6.00025-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Sarker R, Valkhoff VE, Zachos NC, Lin R, Cha B, Chen TE, Guggino S, Zizak M, de Jonge H, Hogema B, Donowitz M. NHERF1 and NHERF2 are necessary for multiple but usually separate aspects of basal and acute regulation of NHE3 activity. Am J Physiol Cell Physiol 2010; 300:C771-82. [PMID: 21191106 DOI: 10.1152/ajpcell.00119.2010] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Na(+)/H(+) exchanger 3 (NHE3) is expressed in the brush border (BB) of intestinal epithelial cells and accounts for the majority of neutral NaCl absorption. It has been shown that the Na(+)/H(+) exchanger regulatory factor (NHERF) family members of multi-PDZ domain-containing scaffold proteins bind to the NHE3 COOH terminus and play necessary roles in NHE3 regulation in intestinal epithelial cells. Most studies of NHE3 regulation have been in cell models in which NHERF1 and/or NHERF2 were overexpressed. We have now developed an intestinal Na(+) absorptive cell model in Caco-2/bbe cells by expressing hemagglutinin (HA)-tagged NHE3 with an adenoviral infection system. Roles of NHERF1 and NHERF2 in NHE3 regulation were determined, including inhibition by cAMP, cGMP, and Ca(2+) and stimulation by EGF, with knockdown (KD) approaches with lentivirus (Lenti)-short hairpin RNA (shRNA) and/or adenovirus (Adeno)-small interfering RNA (siRNA). Stable infection of Caco-2/bbe cells by NHERF1 or NHERF2 Lenti-shRNA significantly and specifically reduced NHERF protein expression by >80%. NHERF1 KD reduced basal NHE3 activity, while NHERF2 KD stimulated NHE3 activity. siRNA-mediated (transient) and Lenti-shRNA-mediated (stable) gene silencing of NHERF2 (but not of NHERF1) abolished cGMP- and Ca(2+)-dependent inhibition of NHE3. KD of NHERF1 or NHERF2 alone had no effect on cAMP inhibition of NHE3, but KD of both simultaneously abolished the effect of cAMP. The stimulatory effect of EGF on NHE3 was eliminated in NHERF1-KD but occurred normally in NHERF2-KD cells. These findings show that both NHERF2 and NHERF1 are involved in setting NHE3 activity. NHERF2 is necessary for cGMP-dependent protein kinase (cGK) II- and Ca(2+)-dependent inhibition of NHE3. cAMP-dependent inhibition of NHE3 activity requires either NHERF1 or NHERF2. Stimulation of NHE3 activity by EGF is NHERF1 dependent.
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Affiliation(s)
- Rafiquel Sarker
- Gastroenterology and Hepatology Division, Department of Medicine, Johns Hopkins Univ. School of Medicine, Baltimore, MD 21205-2195, USA
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Spatial regulation of cyclic AMP-Epac1 signaling in cell adhesion by ERM proteins. Mol Cell Biol 2010; 30:5421-31. [PMID: 20855527 DOI: 10.1128/mcb.00463-10] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Epac1 is a guanine nucleotide exchange factor for the small G protein Rap and is involved in membrane-localized processes such as integrin-mediated cell adhesion and cell-cell junction formation. Cyclic AMP (cAMP) directly activates Epac1 by release of autoinhibition and in addition induces its translocation to the plasma membrane. Here, we show an additional mechanism of Epac1 recruitment, mediated by activated ezrin-radixin-moesin (ERM) proteins. Epac1 directly binds with its N-terminal 49 amino acids to ERM proteins in their open conformation. Receptor-induced activation of ERM proteins results in increased binding of Epac1 and consequently the clustered localization of Epac1 at the plasma membrane. Deletion of the N terminus of Epac1, as well as disruption of the Epac1-ERM interaction by an interfering radixin mutant or small interfering RNA (siRNA)-mediated depletion of the ERM proteins, impairs Epac1-mediated cell adhesion. We conclude that ERM proteins are involved in the spatial regulation of Epac1 and cooperate with cAMP- and Rap-mediated signaling to regulate adhesion to the extracellular matrix.
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49
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Hernando N, Gisler SM, Reining SC, Déliot N, Capuano P, Biber J, Murer H. NaPi-IIa interacting proteins and regulation of renal reabsorption of phosphate. ACTA ACUST UNITED AC 2010; 38:271-6. [PMID: 20665015 DOI: 10.1007/s00240-010-0304-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Accepted: 07/08/2010] [Indexed: 11/29/2022]
Abstract
Control of phosphate (P(i)) homeostasis is essential for many biologic functions and inappropriate low levels of P(i) in plasma have been suggested to associate with several pathological states, including renal stone formation and stone recurrence. P(i) homeostasis is achieved mainly by adjusting the renal reabsorption of P(i) to the body's requirements. This task is performed to a major extent by the Na/Pi cotransporter NaPi-IIa that is specifically expressed in the brush border membrane of renal proximal tubules. While the presence of tight junctions in epithelial cells prevents the diffusion and mixing of the apical and basolateral components, the location of a protein within a particular membrane subdomain (i.e., the presence of NaPi-IIa at the tip of the apical microvilli) often requires its association with scaffolding elements which directly or indirectly connect the protein with the underlying cellular cytoskeleton. NaPi-IIa interacts with the four members of the Na(+)/H(+) exchanger regulatory factor family as well as with the GABA(A)-receptor associated protein . Here we will discuss the most relevant findings regarding the role of these proteins on the expression and regulation of the cotransporter, as well as the impact that their absence has in P(i) homeostasis.
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Affiliation(s)
- Nati Hernando
- Institute of Physiology and Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Winterthurerstr. 190, 8057 Zurich, Switzerland.
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50
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Mechanisms of the regulation of the intestinal Na+/H+ exchanger NHE3. J Biomed Biotechnol 2010; 2010:238080. [PMID: 20011065 PMCID: PMC2789519 DOI: 10.1155/2010/238080] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Accepted: 09/11/2009] [Indexed: 01/25/2023] Open
Abstract
A major of Na+ absorptive process in the proximal part of intestine and kidney is electroneutral exchange of Na+ and H+ by Na+/H+ exchanger type 3 (NHE3). During the past decade, significant advance has been achieved in the mechanisms of NHE3 regulation. A bulk of the current knowledge on Na+/H+ exchanger regulation is based on heterologous expression of mammalian Na+/H+ exchangers in Na+/H+ exchanger deficient fibroblasts, renal epithelial, and intestinal epithelial cells. Based on the reductionist's approach, an understanding of NHE3 regulation has been greatly advanced. More recently, confirmations of in vitro studies have been made using animals deficient in one or more proteins but in some cases unexpected findings have emerged. The purpose of this paper is to provide a brief overview of recent progress in the regulation and functions of NHE3 present in the luminal membrane of the intestinal tract.
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