Lumen LPS inhibits HCO3 - absorption in the medullary thick ascending limb through TLR4-PI3K-Akt-mTOR-dependent inhibition of basolateral Na+/H+ exchange

Bruns Watts, Thampi George, David Good

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17 Citations (Scopus)

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.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Renal Physiology
Volume305
Issue number4
DOIs
StatePublished - May 8 2013

Fingerprint

Toll-Like Receptor 4
1-Phosphatidylinositol 4-Kinase
Sirolimus
Lipopolysaccharides
Extremities
Sepsis
Kidney
Sodium-Hydrogen Antiporter
Endotoxemia
Baths
Phosphorylation

Keywords

  • Acid-base balance
  • Kidney
  • Na/H exchange
  • Sepsis
  • TLR4 signaling

ASJC Scopus subject areas

  • Physiology
  • Urology

Cite this

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title = "Lumen LPS inhibits HCO3 - absorption in the medullary thick ascending limb through TLR4-PI3K-Akt-mTOR-dependent inhibition of basolateral Na+/H+ exchange",
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.",
keywords = "Acid-base balance, Kidney, Na/H exchange, Sepsis, TLR4 signaling",
author = "Bruns Watts and Thampi George and David Good",
year = "2013",
month = "5",
day = "8",
doi = "10.1152/ajprenal.00102.2013",
language = "English (US)",
volume = "305",
journal = "American Journal of Physiology - Endocrinology and Metabolism",
issn = "0193-1849",
publisher = "American Physiological Society",
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TY - JOUR

T1 - Lumen LPS inhibits HCO3 - absorption in the medullary thick ascending limb through TLR4-PI3K-Akt-mTOR-dependent inhibition of basolateral Na+/H+ exchange

AU - Watts, Bruns

AU - George, Thampi

AU - Good, David

PY - 2013/5/8

Y1 - 2013/5/8

N2 - 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.

AB - 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.

KW - Acid-base balance

KW - Kidney

KW - Na/H exchange

KW - Sepsis

KW - TLR4 signaling

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U2 - 10.1152/ajprenal.00102.2013

DO - 10.1152/ajprenal.00102.2013

M3 - Article

VL - 305

JO - American Journal of Physiology - Endocrinology and Metabolism

JF - American Journal of Physiology - Endocrinology and Metabolism

SN - 0193-1849

IS - 4

ER -