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A novel tumor necrosis factor-mediated mechanism of direct epithelial sodium channel activation.

ABSTRACT: RATIONALE:Alveolar liquid clearance is regulated by Na(+) uptake through the apically expressed epithelial sodium channel (ENaC) and basolaterally localized Na(+)-K(+)-ATPase in type II alveolar epithelial cells. Dysfunction of these Na(+) transporters during pulmonary inflammation can contribute to pulmonary edema. OBJECTIVES:In this study, we sought to determine the precise mechanism by which the TIP peptide, mimicking the lectin-like domain of tumor necrosis factor (TNF), stimulates Na(+) uptake in a homologous cell system in the presence or absence of the bacterial toxin pneumolysin (PLY). METHODS:We used a combined biochemical, electrophysiological, and molecular biological in vitro approach and assessed the physiological relevance of the lectin-like domain of TNF in alveolar liquid clearance in vivo by generating triple-mutant TNF knock-in mice that express a mutant TNF with deficient Na(+) uptake stimulatory activity. MEASUREMENTS AND MAIN RESULTS:TIP peptide directly activates ENaC, but not the Na(+)-K(+)-ATPase, upon binding to the carboxy-terminal domain of the ? subunit of the channel. In the presence of PLY, a mediator of pneumococcal-induced pulmonary edema, this binding stabilizes the ENaC-PIP2-MARCKS complex, which is necessary for the open probability conformation of the channel and preserves ENaC-? protein expression, by means of blunting the protein kinase C-? pathway. Triple-mutant TNF knock-in mice are more prone than wild-type mice to develop edema with low-dose intratracheal PLY, correlating with reduced pulmonary ENaC-? subunit expression. CONCLUSIONS:These results demonstrate a novel TNF-mediated mechanism of direct ENaC activation and indicate a physiological role for the lectin-like domain of TNF in the resolution of alveolar edema during inflammation.

SUBMITTER: Czikora I

PROVIDER: S-EPMC4214088 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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A novel tumor necrosis factor-mediated mechanism of direct epithelial sodium channel activation.

Czikora István I Alli Abdel A Bao Hui-Fang HF Kaftan David D Sridhar Supriya S Apell Hans-Jürgen HJ Gorshkov Boris B White Richard R Zimmermann Astrid A Wendel Albrecht A Pauly-Evers Meike M Hamacher Jürg J Garcia-Gabay Irène I Fischer Bernhard B Verin Alexander A Bagi Zsolt Z Pittet Jean Francois JF Shabbir Waheed W Lemmens-Gruber Rosa R Chakraborty Trinad T Lazrak Ahmed A Matthay Michael A MA Eaton Douglas C DC Lucas Rudolf R

American journal of respiratory and critical care medicine 20140901 5

<h4>Rationale</h4>Alveolar liquid clearance is regulated by Na(+) uptake through the apically expressed epithelial sodium channel (ENaC) and basolaterally localized Na(+)-K(+)-ATPase in type II alveolar epithelial cells. Dysfunction of these Na(+) transporters during pulmonary inflammation can contribute to pulmonary edema.<h4>Objectives</h4>In this study, we sought to determine the precise mechanism by which the TIP peptide, mimicking the lectin-like domain of tumor necrosis factor (TNF), stimu ...[more]

PMID: 25029038

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Project description:Preeclampsia is a prevalent life-threatening hypertensive disorder of pregnancy for which the pathophysiology remains largely undefined. Recently, a circulating maternal autoantibody, the angiotensin II type I (AT(1)) receptor agonistic autoantibody (AA), has emerged as a contributor to disease features. Increased circulating maternal tumor necrosis factor alpha (TNF-alpha) is also associated with the disease; however, it is unknown whether this factor directly contributes to preeclamptic symptoms. Here we report that this autoantibody increases the proinflammatory cytokine TNF-alpha in the circulation of AT(1)-AA-injected pregnant mice but not in nonpregnant mice. Coinjection of AT(1)-AA with a TNF-alpha neutralizing antibody reduced cytokine availability in AT(1)-AA-injected pregnant mice. Moreover, TNF-alpha blockade in AT(1)-AA-injected pregnant mice significantly attenuated the key features of preeclampsia. Autoantibody-induced hypertension was reduced from 131+/-4 to 110+/-4 mm Hg, and proteinuria was reduced from 212+/-25 to 155+/-23 microg of albumin per milligram of creatinine (both P<0.05). Injection of AT(1)-AA increased the serum levels of circulating soluble fms-like tyrosine kinase 1 and soluble endoglin (34.1+/-5.1, 2.4+/-0.3 ng/mL, respectively) and coinjection with the TNF-alpha blocker significantly reduced their levels (21.7+/-3.4 and 1.2+/-0.4 ng/mL, respectively). Renal damage and placental abnormalities were also decreased by TNF-alpha blockade. Lastly, the elevated circulating TNF-alpha in preeclamptic patients is significantly correlated with the AT(1)-AA bioactivity in our patient cohort. Similarly, the autoantibody, through AT(1) receptor-mediated TNF-alpha induction, contributed to increased soluble fms-like tyrosine kinase 1, soluble endoglin secretion, and increased apoptosis in cultured human villous explants. Overall, AT(1)-AA is a novel candidate that induces TNF-alpha, a cytokine that may play an important pathogenic role in preeclampsia.

Project description:RationaleAnti-inflammatory and vascular protective actions of adiponectin are well recognized. However, many fundamental questions remain unanswered.ObjectiveThe current study attempted to identify the adiponectin receptor subtype responsible for adiponectin's vascular protective action and investigate the role of ceramidase activation in adiponectin anti-inflammatory signaling.Methods and resultsAdiponectin significantly reduced tumor necrosis factor (TNF)α-induced intercellular adhesion molecule-1 expression and attenuated TNFα-induced oxidative/nitrative stress in human umbilical vein endothelial cells. These anti-inflammatory actions were virtually abolished by adiponectin receptor 1 (AdipoR1-), but not AdipoR2-, knockdown (KD). Treatment with adiponectin significantly increased neutral ceramidase (nCDase) activity (3.7-fold; P<0.01). AdipoR1-KD markedly reduced globular adiponectin-induced nCDase activation, whereas AdipoR2-KD only slightly reduced. More importantly, small interfering RNA-mediated nCDase-KD markedly blocked the effect of adiponectin on TNFα-induced intercellular adhesion molecule-1 expression. AMP-activated protein kinase-KD failed to block adiponectin-induced nCDase activation and modestly inhibited adiponectin anti-inflammatory effect. In contrast, in caveolin-1 KD (Cav1-KD) cells, >87% of adiponectin-induced nCDase activation was lost. Whereas adiponectin treatment failed to inhibit TNFα-induced intercellular adhesion molecule-1 expression, treatment with sphingosine-1-phosphate or SEW (sphingosine-1-phosphate receptor agonist) remained effective in Cav1-KD cells. AdipoR1 and Cav1 colocalized and coprecipitated in human umbilical vein endothelial cells. Adiponectin treatment did not affect this interaction. There is weak basal Cav1/nCDase interaction, which significantly increased after adiponectin treatment. Knockout of AdipoR1 or Cav1 abolished the inhibitory effect of adiponectin on leukocyte rolling and adhesion in vivo.ConclusionsThese results demonstrate for the first time that adiponectin inhibits TNFα-induced inflammatory response via Cav1-mediated ceramidase recruitment and activation in an AdipoR1-dependent fashion.

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A novel tumor necrosis factor-mediated mechanism of direct epithelial sodium channel activation.

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A novel tumor necrosis factor-mediated mechanism of direct epithelial sodium channel activation.

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