title: AMP-activated protein kinase regulates CO2-induced alveolar epithelial dysfunction in rats and human cells by promoting Na,K-ATPase endocytosis.
abstract: Hypercapnia (elevated CO(2) levels) occurs as a consequence of poor alveolar ventilation and impairs alveolar fluid reabsorption (AFR) by promoting Na,K-ATPase endocytosis. We studied the mechanisms regulating CO(2)-induced Na,K-ATPase endocytosis in alveolar epithelial cells (AECs) and alveolar epithelial dysfunction in rats. Elevated CO(2) levels caused a rapid activation of AMP-activated protein kinase (AMPK) in AECs, a key regulator of metabolic homeostasis. Activation of AMPK was mediated by a CO(2)-triggered increase in intracellular Ca(2+) concentration and Ca(2+)/calmodulin-dependent kinase kinase-beta (CaMKK-beta). Chelating intracellular Ca(2+) or abrogating CaMKK-beta function by gene silencing or chemical inhibition prevented the CO(2)-induced AMPK activation in AECs. Activation of AMPK or overexpression of constitutively active AMPK was sufficient to activate PKC-zeta and promote Na,K-ATPase endocytosis. Inhibition or downregulation of AMPK via adenoviral delivery of dominant-negative AMPK-alpha(1) prevented CO(2)-induced Na,K-ATPase endocytosis. The hypercapnia effects were independent of intracellular ROS. Exposure of rats to hypercapnia for up to 7 days caused a sustained decrease in AFR. Pretreatment with a beta-adrenergic agonist, isoproterenol, or a cAMP analog ameliorated the hypercapnia-induced impairment of AFR. Accordingly, we provide evidence that elevated CO(2) levels are sensed by AECs and that AMPK mediates CO(2)-induced Na,K-ATPase endocytosis and alveolar epithelial dysfunction, which can be prevented with beta-adrenergic agonists and cAMP.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
authors.forename: István
authors.initials: I
authors.lastname: Vadász
authors.forename: Laura A
authors.initials: LA
authors.lastname: Dada
authors.forename: Arturo
authors.initials: A
authors.lastname: Briva
authors.forename: Humberto E
authors.initials: HE
authors.lastname: Trejo
authors.forename: Lynn C
authors.initials: LC
authors.lastname: Welch
authors.forename: Jiwang
authors.initials: J
authors.lastname: Chen
authors.forename: Péter T
authors.initials: PT
authors.lastname: Tóth
authors.forename: Emilia
authors.initials: E
authors.lastname: Lecuona
authors.forename: Lee A
authors.initials: LA
authors.lastname: Witters
authors.forename: Paul T
authors.initials: PT
authors.lastname: Schumacker
authors.forename: Navdeep S
authors.initials: NS
authors.lastname: Chandel
authors.forename: Werner
authors.initials: W
authors.lastname: Seeger
authors.forename: Jacob I
authors.initials: JI
authors.lastname: Sznajder
mesh_terms: D055372:AMP-Activated Protein Kinases; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects / Q000235:genetics; D045604:Extracellular Fluid / Q000378:metabolism; D006801:Humans; D006935:Hypercapnia / Q000201:enzymology*; D007545:Isoproterenol / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000201:enzymology; D051381:Rats; D017207:Rats, Sprague-Dawley; D020545:Respiratory Mucosa / Q000201:enzymology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D000099221:Protein Kinase C zeta
chemical_list: D055372:AMP-Activated Protein Kinases; D000318:Adrenergic beta-Agonists; D002118:Calcium; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D002245:Carbon Dioxide; D002614:Chelating Agents; D000242:Cyclic AMP; D007545:Isoproterenol; D009097:Multienzyme Complexes; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D000254:Sodium-Potassium-Exchanging ATPase; D000099221:Protein Kinase C zeta; C526180:PRKAA1 protein, human