1
|
Lombari P, Mallardo M, Petrazzuolo O, Amruthraj Nagoth J, Fiume G, Scanni R, Iervolino A, Damiano S, Coppola A, Borriello M, Ingrosso D, Perna AF, Zacchia M, Trepiccione F, Capasso G. miRNA-23a modulates sodium-hydrogen exchanger 1 expression: studies in medullary thick ascending limb of salt-induced hypertensive rats. Nephrol Dial Transplant 2023; 38:586-598. [PMID: 35921220 DOI: 10.1093/ndt/gfac232] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND The kidney is the main organ in the pathophysiology of essential hypertension. Although most bicarbonate reabsorption occurs in the proximal tubule, the medullary thick ascending limb (mTAL) of the nephron also maintains acid-base balance by contributing to 25% of bicarbonate reabsorption. A crucial element in this regulation is the sodium-hydrogen exchanger 1 (NHE1), a ubiquitous membrane protein controlling intracellular pH, where proton extrusion is driven by the inward sodium flux. MicroRNA (miRNA) expression of hypertensive patients significantly differs from that of normotensive subjects. The aim of this study was to determine the functional role of miRNA alterations at the mTAL level. METHODS By miRNA microarray analysis, we identified miRNA expression profiles in isolated mTALs from high sodium intake-induced hypertensive rats (HSD) versus their normotensive counterparts (NSD). In vitro validation was carried out in rat mTAL cells. RESULTS Five miRNAs involved in the onset of salt-sensitive hypertension were identified, including miR-23a, which was bioinformatically predicted to target NHE1 mRNA. Data demonstrated that miRNA-23a is downregulated in the mTAL of HSD rats while NHE1 is upregulated. Consistently, transfection of an miRNA-23a mimic in an mTAL cell line, using a viral vector, resulted in NHE1 downregulation. CONCLUSION NHE1, a protein involved in sodium reabsorption at the mTAL level and blood pressure regulation, is upregulated in our model. This was due to a downregulation of miRNA-23a. Expression levels of this miRNA are influenced by high sodium intake in the mTALs of rats. The downregulation of miRNA-23a in humans affected by essential hypertension corroborate our data and point to the potential role of miRNA-23a in the regulation of mTAL function following high salt intake.
Collapse
Affiliation(s)
- Patrizia Lombari
- Department of Precision Medicine, University of Campania "L. Vanvitelli", Naples, Italy.,Division of Nephrology, Department of Translational Medical Sciences, University of Campania "L. Vanvitelli", Naples, Italy
| | - Massimo Mallardo
- Department of Molecular Medicine and Medical Biotechnology, University of Naples "Federico II", Naples, Italy
| | - Oriana Petrazzuolo
- Division of Nephrology, Department of Translational Medical Sciences, University of Campania "L. Vanvitelli", Naples, Italy
| | - Joseph Amruthraj Nagoth
- Division of Nephrology, Department of Translational Medical Sciences, University of Campania "L. Vanvitelli", Naples, Italy
| | - Giuseppe Fiume
- Departments of Experimental and Clinical Medicine, University Magna Graecia of Catanzaro, Catanzaro, Italy
| | - Roberto Scanni
- Division of Nephrology, Department of Translational Medical Sciences, University of Campania "L. Vanvitelli", Naples, Italy
| | - Anna Iervolino
- Biogem, Institute of Molecular Biology and Genetics, Ariano Irpino, Italy
| | - Sara Damiano
- Department of Veterinary Medicine and Animal Production, University of Naples "Federico II", Naples, Italy
| | - Annapaola Coppola
- Department of Precision Medicine, University of Campania "L. Vanvitelli", Naples, Italy
| | - Margherita Borriello
- Department of Precision Medicine, University of Campania "L. Vanvitelli", Naples, Italy
| | - Diego Ingrosso
- Department of Precision Medicine, University of Campania "L. Vanvitelli", Naples, Italy
| | - Alessandra F Perna
- Division of Nephrology, Department of Translational Medical Sciences, University of Campania "L. Vanvitelli", Naples, Italy
| | - Miriam Zacchia
- Division of Nephrology, Department of Translational Medical Sciences, University of Campania "L. Vanvitelli", Naples, Italy
| | - Francesco Trepiccione
- Division of Nephrology, Department of Translational Medical Sciences, University of Campania "L. Vanvitelli", Naples, Italy.,Biogem, Institute of Molecular Biology and Genetics, Ariano Irpino, Italy
| | - Giovambattista Capasso
- Division of Nephrology, Department of Translational Medical Sciences, University of Campania "L. Vanvitelli", Naples, Italy.,Biogem, Institute of Molecular Biology and Genetics, Ariano Irpino, Italy
| |
Collapse
|
2
|
Li J, He Q, Li Q, Huang R, Wei X, Pan X, Wu W. Decreased expression of Na+-H+ exchanger isoforms 1 and 3 in denervated spontaneously hypertensive rat kidney. Clin Exp Hypertens 2018; 41:235-243. [PMID: 29787310 DOI: 10.1080/10641963.2018.1469639] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Jianling Li
- Department of Cardiology, First Affiliated Hospital of Guangxi Medical University, Nanning, China
| | - Qiaoling He
- Department of Pharmacology, Affiliated Hospital of Guangxi Medical University, The First people’s Hospital of Nanning, Nanning, China
| | - Qingjie Li
- Department of Cardiology, First Affiliated Hospital of Guangxi Medical University, Nanning, China
| | - Rongjie Huang
- Department of Pharmacology, Affiliated Hospital of Guangxi Medical University, The First people’s Hospital of Nanning, Nanning, China
| | - Xiaoyan Wei
- Department of Pharmacology, Affiliated Hospital of Guangxi Medical University, The First people’s Hospital of Nanning, Nanning, China
| | - Xiaofeng Pan
- Department of Cardiology, First Affiliated Hospital of Guangxi Medical University, Nanning, China
| | - Weifeng Wu
- Department of Cardiology, First Affiliated Hospital of Guangxi Medical University, Nanning, China
| |
Collapse
|
3
|
Watts BA, George T, Badalamenti A, Good DW. High-mobility group box 1 inhibits HCO3- absorption in the medullary thick ascending limb through RAGE-Rho-ROCK-mediated inhibition of basolateral Na+/H+ exchange. Am J Physiol Renal Physiol 2016; 311:F600-13. [PMID: 27358052 DOI: 10.1152/ajprenal.00185.2016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2016] [Accepted: 06/27/2016] [Indexed: 02/07/2023] Open
Abstract
High-mobility group box 1 (HMGB1) is a nuclear protein released extracellularly in response to infection or injury, where it activates immune responses and contributes to the pathogenesis of kidney dysfunction in sepsis and sterile inflammatory disorders. Recently, we demonstrated that HMGB1 inhibits HCO3 (-) absorption in perfused rat medullary thick ascending limbs (MTAL) through a basolateral receptor for advanced glycation end products (RAGE)-dependent pathway that is additive to Toll-like receptor 4 (TLR4)-ERK-mediated inhibition by LPS (Good DW, George T, Watts BA III. Am J Physiol Renal Physiol 309: F720-F730, 2015). Here, we examined signaling and transport mechanisms that mediate inhibition by HMGB1. Inhibition of HCO3 (-) absorption by HMGB1 was eliminated by the Rho-associated kinase (ROCK) inhibitor Y27632 and by a specific inhibitor of Rho, the major upstream activator of ROCK. HMGB1 increased RhoA and ROCK1 activity. HMGB1-induced ROCK1 activation was eliminated by the RAGE antagonist FPS-ZM1 and by inhibition of Rho. The Rho and ROCK inhibitors had no effect on inhibition of HCO3 (-) absorption by bath LPS. Inhibition of HCO3 (-) absorption by HMGB1 was eliminated by bath amiloride, 0 Na(+) bath, and the F-actin stabilizer jasplakinolide, three conditions that selectively prevent inhibition of MTAL HCO3 (-) absorption mediated through NHE1. HMGB1 decreased basolateral Na(+)/H(+) exchange activity through activation of ROCK. We conclude that HMGB1 inhibits HCO3 (-) absorption in the MTAL through a RAGE-RhoA-ROCK1 signaling pathway coupled to inhibition of NHE1. The HMGB1-RAGE-RhoA-ROCK1 pathway thus represents a potential target to attenuate MTAL dysfunction during sepsis and other inflammatory disorders. HMGB1 and LPS inhibit HCO3 (-) absorption through different receptor signaling and transport mechanisms, which enables these pathogenic mediators to act directly and independently to impair MTAL function.
Collapse
Affiliation(s)
- Bruns A Watts
- Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas; and
| | - Thampi George
- Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas; and
| | - Andrew Badalamenti
- Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas; and
| | - David W Good
- Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas; and Department of Neuroscience and Cell Biology, The University of Texas Medical Branch, Galveston, Texas
| |
Collapse
|
4
|
Good DW, George T, Watts BA. High-mobility group box 1 inhibits HCO(3)(-) absorption in medullary thick ascending limb through a basolateral receptor for advanced glycation end products pathway. Am J Physiol Renal Physiol 2015; 309:F720-30. [PMID: 26180239 DOI: 10.1152/ajprenal.00227.2015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Accepted: 07/07/2015] [Indexed: 12/31/2022] Open
Abstract
High-mobility group box 1 (HMGB1) is a damage-associated molecule implicated in mediating kidney dysfunction in sepsis and sterile inflammatory disorders. HMGB1 is a nuclear protein released extracellularly in response to infection or injury, where it interacts with Toll-like receptor 4 (TLR4) and other receptors to mediate inflammation. Previously, we demonstrated that LPS inhibits HCO(3)(-) absorption in the medullary thick ascending limb (MTAL) through a basolateral TLR4-ERK pathway (Watts BA III, George T, Sherwood ER, Good DW. Am J Physiol Cell Physiol 301: C1296-C1306, 2011). Here, we examined whether HMGB1 could inhibit HCO(3)(-) absorption through the same pathway. Adding HMGB1 to the bath decreased HCO(3)(-) absorption by 24% in isolated, perfused rat and mouse MTALs. In contrast to LPS, inhibition by HMGB1 was preserved in MTALs from TLR4(-/-) mice and was unaffected by ERK inhibitors. Inhibition by HMGB1 was eliminated by the receptor for advanced glycation end products (RAGE) antagonist FPS-ZM1 and by neutralizing anti-RAGE antibody. Confocal immunofluorescence showed expression of RAGE in the basolateral membrane domain. Inhibition of HCO(3)(-) absorption by HMGB1 through RAGE was additive to inhibition by LPS through TLR4 and to inhibition by Gram-positive bacterial molecules through TLR2. Bath amiloride, which selectively prevents inhibition of MTAL HCO(3)(-) absorption mediated through Na⁺/H⁺ exchanger 1 (NHE1), eliminated inhibition by HMGB1. We conclude that HMGB1 inhibits MTAL HCO(3)(-) absorption through a RAGE-dependent pathway distinct from TLR4-mediated inhibition by LPS. These studies provide new evidence that HMGB1-RAGE signaling acts directly to impair the transport function of renal tubules. They reveal a novel paradigm for sepsis-induced renal tubule dysfunction, whereby exogenous pathogen-associated molecules and endogenous damage-associated molecules act directly and independently to inhibit MTAL HCO(3)(-) absorption through different receptor signaling pathways.
Collapse
Affiliation(s)
- David W Good
- Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas; and Department of Neuroscience and Cell Biology, The University of Texas Medical Branch, Galveston, Texas
| | - Thampi George
- Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas; and
| | - Bruns A Watts
- Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas; and
| |
Collapse
|
5
|
Watts BA, George T, Good DW. Lumen LPS inhibits HCO3(-) absorption in the medullary thick ascending limb through TLR4-PI3K-Akt-mTOR-dependent inhibition of basolateral Na+/H+ exchange. Am J Physiol Renal Physiol 2013; 305:F451-62. [PMID: 23698118 DOI: 10.1152/ajprenal.00102.2013] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Sepsis and endotoxemia induce defects in renal tubule function, but the mechanisms are poorly understood. Recently, we demonstrated that lipopolysaccharide (LPS) inhibits HCO3(-) absorption in the medullary thick ascending limb (MTAL) through activation of different Toll-like receptor 4 (TLR4) signaling pathways in the basolateral and apical membranes. Basolateral LPS inhibits HCO3(-) absorption through ERK-dependent inhibition of the apical Na(+)/H(+) exchanger NHE3. Here, we examined the mechanisms of inhibition by lumen LPS. Adding LPS to the lumen decreased HCO3(-) absorption by 29% in rat and mouse MTALs perfused in vitro. Inhibitors of phosphoinositide 3-kinase (PI3K) or its effectors Akt and mammalian target of rapamycin (mTOR) eliminated inhibition of HCO3(-) absorption by lumen LPS but had no effect on inhibition by bath LPS. Exposure to LPS for 15 min induced increases in phosphorylation of Akt and mTOR in microdissected MTALs that were blocked by wortmannin, consistent with activation of Akt and mTOR downstream of PI3K. The effects of lumen LPS to activate Akt and inhibit HCO3(-) absorption were eliminated in MTALs from TLR4(-/-) and MyD88(-/-) mice but preserved in tubules lacking Trif or CD14. Inhibition of HCO3(-) absorption by lumen LPS was eliminated under conditions that inhibit basolateral Na(+)/H(+) exchange and prevent inhibition of HCO3(-) absorption mediated through NHE1. Lumen LPS decreased basolateral Na(+)/H(+) exchange activity through PI3K. We conclude that lumen LPS inhibits HCO3(-) absorption in the MTAL through TLR4/MyD88-dependent activation of a PI3K-Akt-mTOR pathway coupled to inhibition of NHE1. Molecular components of the TLR4-PI3K-mTOR pathway represent potential therapeutic targets for sepsis-induced renal tubule dysfunction.
Collapse
Affiliation(s)
- Bruns A Watts
- Div. of Nephrology, 4.200 John Sealy Annex, The Univ. of Texas Medical Branch, 301 Univ. Blvd., Galveston, TX 77555-0562.
| | | | | |
Collapse
|
6
|
Watts BA, George T, Sherwood ER, Good DW. A two-hit mechanism for sepsis-induced impairment of renal tubule function. Am J Physiol Renal Physiol 2013; 304:F863-74. [PMID: 23324175 DOI: 10.1152/ajprenal.00608.2012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Renal insufficiency is a common and severe complication of sepsis, and the development of kidney dysfunction increases morbidity and mortality in septic patients. Sepsis is associated with a variety of defects in renal tubule function, but the underlying mechanisms are incompletely understood. We used a cecal ligation and puncture (CLP) model to examine mechanisms by which sepsis influences the transport function of the medullary thick ascending limb (MTAL). MTALs from sham and CLP mice were studied in vitro 18 h after surgery. The results show that sepsis impairs the ability of the MTAL to absorb HCO(3)(-) through two distinct mechanisms. First, sepsis induces an adaptive decrease in the intrinsic capacity of the tubules to absorb HCO(3)(-). This effect is associated with an increase in ERK phosphorylation in MTAL cells and is prevented by pretreatment of CLP mice with a MEK/ERK inhibitor. The CLP-induced reduction in intrinsic HCO(3)(-) absorption rate appears to involve loss of function of basolateral Na(+)/H(+) exchange. Second, sepsis enhances the ability of LPS to inhibit HCO(3)(-) absorption, mediated through upregulation of Toll-like receptor 4 (TLR4)-ERK signaling in the basolateral membrane. The two inhibitory mechanisms are additive and thus can function in a two-hit capacity to impair renal tubule function in sepsis. Both effects depend on ERK and are eliminated by interventions that prevent ERK activation. Thus the TLR4 and ERK signaling pathways represent potential therapeutic targets to treat or prevent sepsis-induced renal tubule dysfunction.
Collapse
Affiliation(s)
- Bruns A Watts
- Department of Internal Medicine, University of Texas Medical Branch, Galveston, TX 77555, USA
| | | | | | | |
Collapse
|
7
|
Editorial Comment. Urology 2011; 78:e1; author reply e2. [DOI: 10.1016/j.urology.2011.04.059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2011] [Revised: 04/25/2011] [Accepted: 04/25/2011] [Indexed: 11/22/2022]
|
8
|
Watts BA, George T, Sherwood ER, Good DW. Basolateral LPS inhibits NHE3 and HCOFormula absorption through TLR4/MyD88-dependent ERK activation in medullary thick ascending limb. Am J Physiol Cell Physiol 2011; 301:C1296-306. [PMID: 21881005 DOI: 10.1152/ajpcell.00237.2011] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Sepsis is associated with defects in renal tubule function, but the underlying mechanisms are incompletely understood. Recently, we demonstrated that Gram-negative bacterial lipopolysaccharide (LPS) inhibits HCO(3)(-) absorption in the medullary thick ascending limb (MTAL) through activation of Toll-like receptor 4 (TLR4). Here, we examined the mechanisms responsible for inhibition of HCO(3)(-) absorption by basolateral LPS. Adding LPS to the bath decreased HCO(3)(-) absorption by 30% in rat and mouse MTALs perfused in vitro. The inhibition of HCO(3)(-) absorption was eliminated by the mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK)/ERK inhibitors U0126 and PD98059. LPS induced a rapid (<15 min) and sustained (up to 60 min) increase in ERK phosphorylation in microdissected MTALs that was blocked by PD98059. The effects of basolateral LPS to activate ERK and inhibit HCO(3)(-) absorption were eliminated in MTALs from TLR4(-/-) and myeloid differentiation factor 88 (MyD88)(-/-) mice but were preserved in MTALs from TIR (Toll/interleukin-1 receptor) domain-containing adapter-inducing interferon-β (Trif)(-/-) mice. Basolateral LPS decreased apical Na(+)/H(+) exchanger 3 NHE3 activity through a decrease in maximal velocity (V(max)). The inhibition of NHE3 by LPS was eliminated by MEK/ERK inhibitors. LPS inhibited HCO(3)(-) absorption despite the presence of physiological stimuli that activate ERK in the MTAL. We conclude that basolateral LPS inhibits HCO(3)(-) absorption in the MTAL through activation of a TLR4/MyD88/MEK/ERK pathway coupled to inhibition of NHE3. These studies identify NHE3 as a target of TLR4 signaling in the MTAL and show that bacterial molecules can impair the absorptive functions of renal tubules through inhibition of this exchanger. The ERK pathway links TLR4 to downstream modulation of ion transport proteins and represents a potential target for treatment of sepsis-induced renal tubule dysfunction.
Collapse
Affiliation(s)
- Bruns A Watts
- Division of Nephrology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0562, USA
| | | | | | | |
Collapse
|
9
|
Good DW, George T, Watts BA. High sodium intake increases HCO(3)- absorption in medullary thick ascending limb through adaptations in basolateral and apical Na+/H+ exchangers. Am J Physiol Renal Physiol 2011; 301:F334-43. [PMID: 21613418 DOI: 10.1152/ajprenal.00106.2011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A high sodium intake increases the capacity of the medullary thick ascending limb (MTAL) to absorb HCO(3)(-). Here, we examined the role of the apical NHE3 and basolateral NHE1 Na(+)/H(+) exchangers in this adaptation. MTALs from rats drinking H(2)O or 0.28 M NaCl for 5-7 days were perfused in vitro. High sodium intake increased HCO(3)(-) absorption rate by 60%. The increased HCO(3)(-) absorptive capacity was mediated by an increase in apical NHE3 activity. Inhibiting basolateral NHE1 with bath amiloride eliminated 60% of the adaptive increase in HCO(3)(-) absorption. Thus the majority of the increase in NHE3 activity was dependent on NHE1. A high sodium intake increased basolateral Na(+)/H(+) exchange activity by 89% in association with an increase in NHE1 expression. High sodium intake increased apical Na(+)/H(+) exchange activity by 30% under conditions in which basolateral Na(+)/H(+) exchange was inhibited but did not change NHE3 abundance. These results suggest that high sodium intake increases HCO(3)(-) absorptive capacity in the MTAL through 1) an adaptive increase in basolateral NHE1 activity that results secondarily in an increase in apical NHE3 activity; and 2) an adaptive increase in NHE3 activity, independent of NHE1 activity. These studies support a role for NHE1 in the long-term regulation of renal tubule function and suggest that the regulatory interaction whereby NHE1 enhances the activity of NHE3 in the MTAL plays a role in the chronic regulation of HCO(3)(-) absorption. The adaptive increases in Na(+)/H(+) exchange activity and HCO(3)(-) absorption in the MTAL may play a role in enabling the kidneys to regulate acid-base balance during changes in sodium and volume balance.
Collapse
Affiliation(s)
- David W Good
- Departments of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas 77555-0562, USA.
| | | | | |
Collapse
|
10
|
Good DW, George T, Watts BA. Lipopolysaccharide directly alters renal tubule transport through distinct TLR4-dependent pathways in basolateral and apical membranes. Am J Physiol Renal Physiol 2009; 297:F866-74. [PMID: 19625374 DOI: 10.1152/ajprenal.00335.2009] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Bacterial infection of the kidney is associated with renal tubule dysfunction and dysregulation of systemic electrolyte balance. Whether bacterial molecules directly affect renal tubule transport is unknown. We examined the effects of LPS on HCO3(-) absorption in the isolated rat and mouse medullary thick ascending limb (MTAL). LPS decreased HCO3(-) absorption when added to bath or lumen. The MEK/ERK inhibitor U0126 eliminated inhibition by bath LPS but had no effect on inhibition by lumen LPS. Conversely, the mammalian target of rapamycin (mTOR) inhibitor rapamycin eliminated inhibition by lumen LPS but had no effect on inhibition by bath LPS. Inhibiting basolateral Na(+)/H(+) exchange with amiloride eliminated inhibition of HCO3(-) absorption by lumen but not bath LPS. Confocal immunofluorescence showed expression of TLR4 in basolateral and apical membrane domains. Inhibition of HCO3(-) absorption by bath and lumen LPS was eliminated in MTALs from TLR4(-/-) mice. Thus LPS inhibits HCO3(-) absorption through distinct TLR4-dependent pathways in basolateral and apical membranes. These results establish that bacterial molecules can directly impair the transport function of renal tubules, identifying a new mechanism contributing to tubule dysfunction during bacterial infection. The LPS-induced reduction in luminal acidification may contribute to Gram-negative pathogenicity by promoting bacterial adherence and growth and impairing correction of infection-induced systemic acid-base disorders.
Collapse
Affiliation(s)
- David W Good
- Div. of Nephrology, 4.200 John Sealy Annex, The Univ. of Texas Medical Branch, 301 Univ. Blvd., Galveston, TX 77555-0562, USA.
| | | | | |
Collapse
|
11
|
Good DW, George T, Watts BA. Nerve growth factor inhibits Na+/H+ exchange and formula absorption through parallel phosphatidylinositol 3-kinase-mTOR and ERK pathways in thick ascending limb. J Biol Chem 2008; 283:26602-11. [PMID: 18660503 DOI: 10.1074/jbc.m803019200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
In the medullary thick ascending limb, inhibiting the basolateral NHE1 Na(+)/H(+) exchanger with nerve growth factor (NGF) induces actin cytoskeleton remodeling that secondarily inhibits apical NHE3 and transepithelial HCO(3)(-) absorption. The inhibition by NGF is mediated 50% through activation of extracellular signal-regulated kinase (ERK). Here we examined the signaling pathway responsible for the remainder of the NGF-induced inhibition. Inhibition of HCO(3)(-) absorption was reduced 45% by the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 and 50% by rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR), a downstream effector of PI3K. The combination of a PI3K inhibitor plus rapamycin did not cause a further reduction in the inhibition by NGF. In contrast, the combination of a PI3K inhibitor plus the MEK/ERK inhibitor U0126 completely eliminated inhibition by NGF. Rapamycin decreased NGF-induced inhibition of basolateral NHE1 by 45%. NGF induced a 2-fold increase in phosphorylation of Akt, a PI3K target linked to mTOR activation, and a 2.2-fold increase in the activity of p70 S6 kinase, a downstream effector of mTOR. p70 S6 kinase activation was blocked by wortmannin and rapamycin, consistent with PI3K, mTOR, and p70 S6 kinase in a linear pathway. Rapamycin-sensitive inhibition of NHE1 by NGF was associated with an increased level of phosphorylated mTOR in the basolateral membrane domain. These findings indicate that NGF inhibits HCO(3)(-) absorption in the medullary thick ascending limb through the parallel activation of PI3K-mTOR and ERK signaling pathways, which converge to inhibit NHE1. The results identify a role for mTOR in the regulation of Na(+)/H(+) exchange activity and implicate NHE1 as a possible downstream effector contributing to mTOR's effects on cell growth, proliferation, survival, and tumorigenesis.
Collapse
Affiliation(s)
- David W Good
- Departments of Medicine, The University of Texas Medical Branch, Galveston, Texas 77555, USA.
| | | | | |
Collapse
|
12
|
Watts BA, George T, Good DW. Aldosterone inhibits apical NHE3 and HCO3- absorption via a nongenomic ERK-dependent pathway in medullary thick ascending limb. Am J Physiol Renal Physiol 2006; 291:F1005-13. [PMID: 16757729 DOI: 10.1152/ajprenal.00507.2005] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although aldosterone influences a variety of cellular processes through nongenomic mechanisms, the significance of nongenomic pathways for aldosterone-induced regulation of epithelial function is not understood. Recently, we demonstrated that aldosterone inhibits transepithelial HCO(3)(-) absorption in the medullary thick ascending limb (MTAL) through a nongenomic pathway. This inhibition is mediated through a direct cellular action of aldosterone to inhibit the apical membrane NHE3 Na(+)/H(+) exchanger. The present study was designed to identify the intracellular signaling pathway(s) responsible for this aldosterone-induced transport regulation. In rat MTALs perfused in vitro, addition of 1 nM aldosterone to the bath decreased HCO(3)(-) absorption by 30%. This inhibition was not mediated by cAMP/PKA and was not prevented by inhibitors of PKC or PI3-K, pertussis toxin, or rapamycin. The inhibition of HCO(3)(-) absorption by aldosterone was largely eliminated by the MEK/ERK inhibitors U-0126 and PD-98059. Aldosterone increased ERK activity 1.8-fold in microdissected MTALs. This ERK activation is rapid (</=5 min) and is blocked by U-0126 or PD-98059 but is unaffected by spironolactone or actinomycin D. Pretreatment with U-0126 to block ERK activation prevented the effect of aldosterone to inhibit apical NHE3. These data demonstrate that aldosterone inhibits NHE3 and HCO(3)(-) absorption in the MTAL through rapid activation of the ERK signaling pathway. The results identify NHE3 as a target for nongenomic regulation by aldosterone and establish a role for ERK in the acute regulation of NHE3 and its epithelial absorptive functions.
Collapse
Affiliation(s)
- Bruns A Watts
- 4.200 John Sealy Annex, Univ. of Texas Medical Branch, 301 Univ. Boulevard, Galveston, TX 77555-0562, USA
| | | | | |
Collapse
|
13
|
García-Suárez O, González-Martínez T, Germana A, Monjil DF, Torrecilla JR, Laurà R, Silos-Santiago I, Guate JL, Vega JA. Expression of TrkB in the murine kidney. Microsc Res Tech 2006; 69:1014-20. [PMID: 17013912 DOI: 10.1002/jemt.20367] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Neurotrophins acting through Trk signal-transducing receptors play essential roles in the nervous system, and probably in some nonneuronal tissues. In the present study we used Western-blot and immunohistochemistry to investigate the occurrence and cellular localization of TrkB in the mouse kidney. Furthermore, the structure and ultrastructure of the kidney in mice carrying a mutation in the trkB gene were analyzed. TrkB in the kidney was identical to the cerebral one (145 kDa). Since the antibody used recognize a sequence within the tyrosine-kinase domain of TrkB, the renal TrkB receptor identified here must be regarded as able to mediate biological effects of their ligands. TrkB immunoreactivity was restricted to the juxtaglomerular apparatus, including differentiated vascular cells and extaglomerular mesangial cells. In these cells, TrkB colocalized with renin. The structural analysis revealed no major changes in the kidney structure of TrkB-deficient mice, with the exception of a significant reduction of the glomerular area. Nevertheless, in these animals there was an apparent increase in the number of extraglomerular mesangial cells (which retain the ability to synthesize renin) and absence of the macula densa. Taken together, these results strongly suggest a role of TrkB and their ligands in the control of the normal development and maintenance of the juxtaglomerular apparatus.
Collapse
Affiliation(s)
- Olivia García-Suárez
- Departamento de Morfología y Biología Celular, Universidad de Oviedo, Oviedo, and Servicio de Urología, Hospital Clinico, Universidad de Valladolid, Spain
| | | | | | | | | | | | | | | | | |
Collapse
|
14
|
Good DW, George T, Watts BA. Nongenomic regulation by aldosterone of the epithelial NHE3 Na(+)/H(+) exchanger. Am J Physiol Cell Physiol 2005; 290:C757-63. [PMID: 16251474 DOI: 10.1152/ajpcell.00391.2005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The relevance of nongenomic pathways to regulation of epithelial function by aldosterone is poorly understood. Recently, we demonstrated that aldosterone inhibits transepithelial HCO(3)(-) absorption in the renal medullary thick ascending limb (MTAL) through a nongenomic pathway. Here, we examined the transport mechanism(s) responsible for this regulation, focusing on Na(+)/H(+) exchangers (NHE). In the MTAL, apical NHE3 mediates H(+) secretion necessary for HCO(3)(-) absorption; basolateral NHE1 influences HCO(3)(-) absorption by regulating apical NHE3 activity. In microperfused rat MTALs, the addition of 1 nM aldosterone rapidly decreased HCO(3)(-) absorption by 30%. This inhibition was unaffected by three maneuvers that inhibit basolateral Na(+)/H(+) exchange and was preserved in MTALs from NHE1 knockout mice, ruling out the involvement of NHE1. In contrast, exposure to aldosterone for 15 min caused a 30% decrease in apical Na(+)/H(+) exchange activity over the intracellular pH range from 6.5 to 7.7, due to a decrease in V(max). Inhibition of HCO(3)(-) absorption by aldosterone was not affected by 0.1 mM lumen Zn(2+) or 1 mM lumen DIDS, arguing against the involvement of an apical H(+) conductance or apical K(+)-HCO(3)(-) cotransport. These results demonstrate that aldosterone inhibits HCO(3)(-) absorption in the MTAL through inhibition of apical NHE3, and identify NHE3 as a target for nongenomic regulation by aldosterone. Aldosterone may influence a broad range of epithelial transport functions important for extracellular fluid volume and acid-base homeostasis through direct regulation of this exchanger.
Collapse
Affiliation(s)
- David W Good
- 4.200 John Sealy Annex, The University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0562, USA.
| | | | | |
Collapse
|
15
|
Arcamone N, Lucini C, Borzacchiello G, Castaldo L, Gargiulo G, De Girolamo P. Distribution of NGF and NT-3-like protein immunoreactivity in the teleost kidney. Microsc Res Tech 2005; 66:17-24. [PMID: 15816034 DOI: 10.1002/jemt.20138] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
By means of immunochemistry and immunohistochemistry, we investigated in the kidney of freshwater and marine teleostean species for the presence and localization of three neurotrophins: nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin (NT)-3. In both species studied, NGF-like and NT-3-like immunoreactivity were present in the kidney with different distribution patterns, while BDNF-like immunoreactivity was never detected. In goldfish, NGF-like and NT-3-like immunoreactivity were identified extensively in cells along part of the arterial branches adjacent to the afferent arterioles. In scorpion fish, NGF-like and NT-3-like immunoreactive cells were observed both on afferent arterioles and on adjacent secondary branches derived from renal arteries. No immunoreactivity was detected in other renal structures. A staining pattern of immunoreactivity similar to that obtained for NGF and NT-3 was detected utilizing S100 antibody as a juxtaglomerular (JG) cell marker. Double immunolabellings NGF/S100 and NT-3/S100 evidenced the coexistence of neurotrophin-like proteins and S100-like protein in the same immunoreactive cells, thus identifying them as juxtaglomerular cells. Western blot analysis revealed the presence of molecules immunoreactive to NGF and NT-3, whose molecular weights were very similar to those of the corresponding mammalian neurotrophins. These findings extend the presence and distribution of NGF-like and NT-3-like IR in the kidney to teleost species, suggesting a probable participation of these proteins in the renal functions of freshwater and marine teleosts.
Collapse
Affiliation(s)
- Nadia Arcamone
- Dipartimento di Strutture, Funzioni e Tecnologie Biologiche, Università di Napoli Federico II, Via F. Delpino 1, 1 I-80137 Naples, Italy
| | | | | | | | | | | |
Collapse
|
16
|
Oliver R, Friday E, Turturro F, Lacy A, Welbourne T. Troglitazone's rapid and sustained activation of ERK1/2 induces cellular acidosis in LLC-PK1-F+cells: physiological responses. Am J Physiol Renal Physiol 2005; 288:F1257-66. [PMID: 15687249 DOI: 10.1152/ajprenal.00205.2004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We studied the signal pathway through which troglitazone (TRO) acts in inducing cellular acidosis in LLC-PK1-F+cells in relation to ammoniagenesis and DNA synthesis. Cells were grown to confluent monolayers in 30-mm chambers and monitored for intracellular pH (pHi) by the BCECF assay and activated ERK by phospo-ERK1/2 antibodies. TRO induces a severe cellular acidosis (pHi6.68 ± 0.10 vs. 7.28 ± 0.07 time control at 4 min, P < 0.01), whereas phospho-ERK1/2 to total ERK1/2 ratio increases 3.4-fold ( P < 0.01). To determine whether ERK1/2 was activated by cellular acidosis or TRO was acting via MEK1/2 to activate ERK1/2, cells were pretreated with specific inhibitors of MEK1/2 activity, PD-098059 and U-0126, followed by the addition of TRO or vehicle. With MEK1/2 activity inhibited, TRO treatment failed to activate ERK1/2. Preventing ERK1/2 activation abrogated the TRO-induced cellular acidosis and maintained the pHiwithin the low normal range (7.06 ± 0.11). To determine whether blocking ERK activation prevents TRO's inhibitory effect on NHE activity, cells were acid-loaded and the recovery response was monitored as ΔpHi/ t over a 4-min recovery period. TRO inhibited NHE activity by 85% ( P < 0.01), whereas blocking ERK activation restored the response. We measured activated ERK levels and pHiafter 3- and 18-h exposure to TRO or extracellular acidosis (pHe = 6.95) to determine whether ERK activation was sustained. Whereas both TRO and extracellular acidosis increased activated ERK and decreased pHiafter 3 h, only TRO sustained this response at 18 h. Furthermore, both enhanced ammoniagenesis and decreased DNA synthesis reflected the effect of TRO to induce and sustain a cellular acidosis.
Collapse
Affiliation(s)
- Robert Oliver
- Dept. of Molecular and Cellular Physiology, LSUHSC, Shreveport, LA 71130, USA
| | | | | | | | | |
Collapse
|
17
|
Watts BA, George T, Good DW. The basolateral NHE1 Na+/H+ exchanger regulates transepithelial HCO3- absorption through actin cytoskeleton remodeling in renal thick ascending limb. J Biol Chem 2005; 280:11439-47. [PMID: 15644322 DOI: 10.1074/jbc.m410719200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the renal medullary thick ascending limb (MTAL), inhibiting the basolateral NHE1 Na(+)/H(+) exchanger with amiloride or nerve growth factor (NGF) results secondarily in inhibition of the apical NHE3 Na(+)/H(+) exchanger, thereby decreasing transepithelial HCO3- absorption. MTALs from rats were studied by in vitro microperfusion to identify the mechanism underlying cross-talk between the two exchangers. The basolateral addition of 10 microM amiloride or 0.7 nM NGF decreased HCO3- absorption by 27-32%. Jasplakinolide, which stabilizes F-actin, or latrunculin B, which disrupts F-actin, decreased basal HCO3- absorption by 30% and prevented the inhibition by amiloride or NGF. Jasplakinolide had no effect on HCO3- absorption in tubules bathed with amiloride or a Na(+)-free bath to inhibit NHE1. Jasplakinolide and latrunculin B did not prevent inhibition of HCO3- absorption by vasopressin or stimulation by hyposmolality, factors that regulate HCO3- absorption through primary effects on apical Na(+)/H(+) exchange. Treatment of MTALs with amiloride or NGF for 15 min decreased polymerized actin with no change in total cell actin, as assessed both by fluorescence microscopy and by actin Triton X-100 solubility. Jasplakinolide prevented amiloride-induced actin remodeling. Vasopressin, which inhibits HCO3- absorption by an amount similar to that observed with amiloride and NGF but does not act via NHE1, did not affect cellular F-actin content. These results indicate that basolateral NHE1 regulates apical NHE3 and HCO3- absorption in the MTAL by controlling the organization of the actin cytoskeleton.
Collapse
Affiliation(s)
- Bruns A Watts
- Department of Medicine, University of Texas Medical Branch, Galveston, Texas 77555-0562, USA
| | | | | |
Collapse
|
18
|
Good DW, Watts BA, George T, Meyer JW, Shull GE. Transepithelial HCO3- absorption is defective in renal thick ascending limbs from Na+/H+ exchanger NHE1 null mutant mice. Am J Physiol Renal Physiol 2004; 287:F1244-9. [PMID: 15292047 DOI: 10.1152/ajprenal.00176.2004] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In the medullary thick ascending limb (MTAL) of rat kidney, inhibiting basolateral Na(+)/H(+) exchange with either amiloride or nerve growth factor (NGF) results secondarily in inhibition of apical Na(+)/H(+) exchange, thereby decreasing transepithelial HCO(3)(-) absorption. To assess the possible role of the Na(+)/H(+) exchanger NHE1 in this regulatory process, MTALs from wild-type and NHE1 knockout (NHE1(-/-)) mice were studied using in vitro microperfusion. The rate of HCO(3)(-) absorption was decreased 60% in NHE1(-/-) MTALs (15.4 +/- 0.5 pmol.min(-1).mm(-1) wild-type vs. 6.0 +/- 0.5 pmol.min(-1).mm(-1) NHE1(-/-)). Transepithelial voltage, an index of the NaCl absorption rate, did not differ in wild-type and NHE1(-/-) MTALs. Basolateral addition of 10 microM amiloride or 0.7 nM NGF decreased HCO(3)(-) absorption by 45-49% in wild-type MTALs but had no effect on HCO(3)(-) absorption in NHE1(-/-) MTALs. Inhibition of HCO(3)(-) absorption by vasopressin and stimulation by hyposmolality, both of which regulate MTAL HCO(3)(-) absorption through primary effects on apical Na(+)/H(+) exchange, were similar in wild-type and NHE1(-/-) MTALs. Thus the regulatory defect in NHE1(-/-) MTALs is specific for factors (bath amiloride and NGF) shown previously to inhibit HCO(3)(-) absorption through primary effects on basolateral Na(+)/H(+) exchange. These findings demonstrate a novel role for NHE1 in transepithelial HCO(3)(-) absorption in the MTAL, in which basolateral NHE1 controls the activity of apical NHE3. Paradoxically, a reduction in NHE1-mediated H(+) extrusion across the basolateral membrane leads to a decrease in apical Na(+)/H(+) exchange activity that reduces HCO(3)(-) absorption.
Collapse
Affiliation(s)
- David W Good
- Department of Medicine, University of Texas Medical Branch, 301 Univ. Boulevard, Galveston, TX 77555, USA.
| | | | | | | | | |
Collapse
|
19
|
Watts BA, Good DW. An apical K+-dependent HCO3− transport pathway opposes transepithelial HCO3− absorption in rat medullary thick ascending limb. Am J Physiol Renal Physiol 2004; 287:F57-63. [PMID: 15026301 DOI: 10.1152/ajprenal.00395.2003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Absorption of HCO3− in the medullary thick ascending limb (MTAL) is mediated by apical membrane Na+/H+ exchange. The identity and function of other apical acid-base transporters in this segment have not been defined. The present study was designed to examine apical membrane HCO3−/OH−/H+ transport pathways in the rat MTAL and to determine their role in transepithelial HCO3− absorption. MTALs were perfused in vitro in Na+- and Cl−-free solutions containing 25 mM HCO3−, 5% CO2. Lumen addition of either 120 mM Cl− or 50 mM Na+ (50 μM EIPA present) had no effect on intracellular pH (pHi). Lumen Cl− addition also had no effect on pHi in the presence of 145 mM Na+ or in the nominal absence of HCO3−/CO2. Thus there was no evidence for apical Cl−/HCO3− (OH−) exchange, Na+-dependent Cl−/HCO3− exchange, or Na+-HCO3− cotransport. In contrast, in tubules studied in Na+- and Cl−-free solutions containing 25 mM HCO3−, 5% CO2 and 120 mM K+, removal of luminal K+ induced a rapid and pronounced decrease in pHi (ΔpHi = 0.56 ± 0.06 pH U). pHi recovered following lumen K+ readdition. The initial rate of net base efflux induced by lumen K+ removal was decreased 85% at the same pHi in the nominal absence of HCO3−/CO2, indicating a dependence on HCO3−/CO2 and arguing against apical K+/H+ exchange. A combination of the apical K+ channel blockers quinidine (0.1 mM) and glybenclamide (0.25 mM) had no effect on the lumen K+-induced pHi changes, arguing against electrically coupled K+ and HCO3− conductances. The effect of lumen K+ on pHi was inhibited by 1 mM H2DIDS. In addition, lumen addition of DIDS increased transepithelial HCO3− absorption from 10.7 ± 0.7 to 14.9 ± 0.7 pmol·min−1·mm−1 ( P < 0.001) and increased pHi slightly in MTAL studied in physiological solutions (25 mM HCO3− and 4 mM K+). Lumen DIDS stimulated HCO3− absorption in the absence and presence of furosemide. These results are consistent with an apical membrane K+-dependent HCO3− transport pathway that mediates coupled transfer of K+ and HCO3− from cell to lumen in the MTAL. This mechanism, possibly an apical K+-HCO3− cotransporter, functions in parallel with apical Na+/H+ exchange and opposes transepithelial HCO3− absorption.
Collapse
Affiliation(s)
- Bruns A Watts
- Department of Medicine, University of Texas Medical Branch, Galveston, TX 77555, USA
| | | |
Collapse
|
20
|
Good DW, George T, Watts BA. Aldosterone inhibits HCO absorption via a nongenomic pathway in medullary thick ascending limb. Am J Physiol Renal Physiol 2002; 283:F699-706. [PMID: 12217861 DOI: 10.1152/ajprenal.00133.2002] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Rapid actions of aldosterone that are independent of transcription and translation have been described in a variety of cells; however, whether nongenomic pathways mediate aldosterone-induced regulation of renal tubule transport has not been determined. We report here that aldosterone induces rapid (<3.5 min) inhibition of HCO absorption in the medullary thick ascending limb (MTAL) of the rat. This inhibition is observed over the physiological range of hormone concentrations (IC(50) approximately 0.6 nM) and is not affected by pretreatment with actinomycin D (12.5 microg/ml), cycloheximide (40 microg/ml), or spironolactone (10 microM). The glucocorticoids dexamethasone, cortisol, and corticosterone (1 or 500 nM) did not affect HCO absorption in the absence or presence of carbenoxolone. Thus the specificity of rapid aldosterone action is not dependent on 11beta-hydroxysteroid dehydrogenase activity. The inhibition by aldosterone is additive to inhibition by angiotensin II and vasopressin, indicating that these factors regulate MTAL transport through distinct pathways. These results demonstrate that aldosterone inhibits HCO absorption in the MTAL via a pathway that is rapid, highly selective, independent of transcription and protein synthesis, and not mediated through the classic mineralocorticoid receptor. The results establish a role for nongenomic pathways in mediating aldosterone-induced regulation of transepithelial transport in the mammalian kidney. The novel action of aldosterone to inhibit luminal acidification in the MTAL may play a role in enabling the kidney to regulate acid-base balance independently of Na(+) balance and extracellular fluid volume.
Collapse
Affiliation(s)
- David W Good
- Department of Medicine, University of Texas Medical Branch, Galveston 77555, USA.
| | | | | |
Collapse
|
21
|
Watts BA, Good DW. ERK mediates inhibition of Na(+)/H(+) exchange and HCO(3)(-) absorption by nerve growth factor in MTAL. Am J Physiol Renal Physiol 2002; 282:F1056-63. [PMID: 11997322 DOI: 10.1152/ajprenal.00133.2001] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mitogen-activated protein (MAP) kinases mediate a variety of critical cellular events, but their role in the regulation of epithelial transport is largely undefined. Recently, we demonstrated that nerve growth factor (NGF) inhibits HCO(3)(-) absorption in the rat medullary thick ascending limb (MTAL) through an unusual mechanism: 1) NGF inhibits basolateral membrane Na(+)/H(+) exchange activity, an effect opposite to the stimulation of Na(+)/H(+) exchange by growth factors in other cells; and 2) inhibition of basolateral Na(+)/H(+) exchange results secondarily in inhibition of apical Na(+)/H(+) exchange, thereby inhibiting HCO(3)(-) absorption. In this study, we examined the role of MAP kinases in mediating inhibition by NGF. In tissue strips from the inner stripe of the outer medulla and in microdissected MTALs, NGF increased extracellular signal-regulated kinase (ERK) activity twofold but had no effect on c-Jun NH(2)-terminal kinase (JNK) or p38 MAP kinase activity. The selective MAP kinase kinase (MEK1/2) inhibitors U0126 and PD-98059 abolished the NGF-induced ERK activation and largely eliminated (> or = 60%) the effects of NGF to inhibit basolateral Na(+)/H(+) exchange activity and transepithelial HCO absorption in perfused MTALs. The MEK1/2 inhibitors did not affect inhibition of HCO(3)(-) absorption by bath ethylisopropyl amiloride, indicating that ERK activation is not involved in mediating interaction between the basolateral and apical Na(+)/H(+) exchangers. These results demonstrate that NGF inhibits basolateral Na(+)/H(+) exchange activity and HCO(3)(-) absorption in the MTAL through activation of the ERK signaling pathway. These findings identify a novel action of ERK to inhibit Na(+)/H(+) exchange activity and establish a role for MAP kinase pathways in the acute regulation of Na(+)/H(+) exchange activity and transepithelial acid secretion in renal tubules.
Collapse
Affiliation(s)
- Bruns A Watts
- Department of Medicine, University of Texas Medical Branch, Galveston, Texas 77555, USA
| | | |
Collapse
|
22
|
Good DW, George T. Neurotrophin-3 inhibits HCO absorption via a cAMP-dependent pathway in renal thick ascending limb. Am J Physiol Cell Physiol 2001; 281:C1804-11. [PMID: 11698238 DOI: 10.1152/ajpcell.2001.281.6.c1804] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Neurotrophins are expressed in the adult kidney, but their significance is unclear. We showed previously that nerve growth factor (NGF) inhibits HCO absorption in the rat medullary thick ascending limb (MTAL) via an extracellular signal-regulated kinase (ERK)-dependent pathway. Here we examined whether other neurotrophic factors affect MTAL HCO absorption. Brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor had no effect. In contrast, neurotrophin-3 (NT-3, 0.7 nM) inhibited HCO absorption by 40% (half-maximal inhibition at approximately 0.4 nM). Inhibition by NT-3 was additive to inhibition by NGF. Inhibitors of ERK activation that block inhibition by NGF had no effect on inhibition by NT-3. In contrast, 8-bromo-cAMP or forskolin pretreatment blocked inhibition by NT-3 but not NGF. Inhibition by NT-3 was also blocked by the specific protein kinase A (PKA) inhibitor myristoylated PKI(14-22) amide and by vasopressin, which inhibits HCO absorption via cAMP. Inhibitors of phosphatidylinositol 3-kinase or protein kinase C did not affect NT-3-induced inhibition, but inhibition by NT-3 was eliminated by genistein, consistent with involvement of a receptor tyrosine kinase. These results demonstrate that NT-3 inhibits HCO absorption via a cAMP- and PKA-dependent pathway. NT-3 and NGF regulate MTAL ion transport through different signal transduction mechanisms. These studies establish a direct role for NT-3 in regulation of renal tubule transport and identify the MTAL as an important target for neurotrophins, which may be involved in the control of renal acid excretion.
Collapse
Affiliation(s)
- D W Good
- Department of Medicine, University of Texas Medical Branch, Galveston, Texas 77555, USA.
| | | |
Collapse
|
23
|
Chapter 12 Molecular physiology of mammalian epithelial Na+/H+ exchangers NHE2 and NHE3. CURRENT TOPICS IN MEMBRANES 2000. [DOI: 10.1016/s1063-5823(00)50014-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
|
24
|
Watts BA, Good DW. Hyposmolality stimulates apical membrane Na(+)/H(+) exchange and HCO(3)(-) absorption in renal thick ascending limb. J Clin Invest 1999; 104:1593-602. [PMID: 10587523 PMCID: PMC409859 DOI: 10.1172/jci7332] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The regulation of epithelial Na(+)/H(+) exchangers (NHEs) by hyposmolality is poorly understood. In the renal medullary thick ascending limb (MTAL), transepithelial bicarbonate (HCO(3)(-)) absorption is mediated by apical membrane Na(+)/H(+) exchange, attributable to NHE3. In the present study we examined the effects of hyposmolality on apical Na(+)/H(+) exchange activity and HCO(3)(-) absorption in the MTAL of the rat. In MTAL perfused in vitro with 25 mM HCO(3)(-) solutions, decreasing osmolality in the lumen and bath by removal of either mannitol or sodium chloride significantly increased HCO(3)(-) absorption. The responses to lumen addition of the inhibitors ethylisopropyl amiloride, amiloride, or HOE 694 are consistent with hyposmotic stimulation of apical NHE3 activity and provide no evidence for a role for apical NHE2 in HCO(3)(-) absorption. Hyposmolality increased apical Na(+)/H(+) exchange activity over the pH(i) range 6.5-7.5 due to an increase in V(max). Pretreatment with either tyrosine kinase inhibitors or with the tyrosine phosphatase inhibitor molybdate completely blocked stimulation of HCO(3)(-) absorption by hyposmolality. These results demonstrate that hyposmolality increases HCO(3)(-) absorption in the MTAL through a novel stimulation of apical membrane Na(+)/H(+) exchange and provide the first evidence that NHE3 is regulated by hyposmotic stress. Stimulation of apical Na(+)/H(+) exchange activity in renal cells by a decrease in osmolality may contribute to such pathophysiological processes as urine acidification by diuretics, diuretic resistance, and renal sodium retention in edematous states.
Collapse
Affiliation(s)
- B A Watts
- Department of Medicine, University of Texas Medical Branch, Galveston, Texas 77555, USA
| | | |
Collapse
|