AMP-activated protein kinase regulates CO2-induced alveolar epithelial dysfunction in rats and human cells by promoting Na,K-ATPase endocytosis
István Vadász, … , Werner Seeger, Jacob I. Sznajder
István Vadász, … , Werner Seeger, Jacob I. Sznajder
Published January 10, 2008
Citation Information: J Clin Invest. 2008;118(2):752-762. https://doi.org/10.1172/JCI29723.
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Research Article Pulmonology

AMP-activated protein kinase regulates CO2-induced alveolar epithelial dysfunction in rats and human cells by promoting Na,K-ATPase endocytosis

Abstract

Hypercapnia (elevated CO2 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 CO2-induced Na,K-ATPase endocytosis in alveolar epithelial cells (AECs) and alveolar epithelial dysfunction in rats. Elevated CO2 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 CO2-triggered increase in intracellular Ca2+ concentration and Ca2+/calmodulin-dependent kinase kinase-β (CaMKK-β). Chelating intracellular Ca2+ or abrogating CaMKK-β function by gene silencing or chemical inhibition prevented the CO2-induced AMPK activation in AECs. Activation of AMPK or overexpression of constitutively active AMPK was sufficient to activate PKC-ζ and promote Na,K-ATPase endocytosis. Inhibition or downregulation of AMPK via adenoviral delivery of dominant-negative AMPK-α1 prevented CO2-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 β-adrenergic agonist, isoproterenol, or a cAMP analog ameliorated the hypercapnia-induced impairment of AFR. Accordingly, we provide evidence that elevated CO2 levels are sensed by AECs and that AMPK mediates CO2-induced Na,K-ATPase endocytosis and alveolar epithelial dysfunction, which can be prevented with β-adrenergic agonists and cAMP.

Authors

István Vadász, Laura A. Dada, Arturo Briva, Humberto E. Trejo, Lynn C. Welch, Jiwang Chen, Péter T. Tóth, Emilia Lecuona, Lee A. Witters, Paul T. Schumacker, Navdeep S. Chandel, Werner Seeger, Jacob I. Sznajder

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Figure 1

High CO2 levels activate AMPK in a concentration- and time-dependent manner in ATII cells.

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High CO2 levels activate AMPK in a concentration- and time-dependent man...
(A) ATII cells were exposed to 40, 60, 80, and 120 mmHg CO2 with an extracellular pH (pHe) of 7.4 (white and black bars) or to 40 mmHg CO2 with a pHe of 7.2 (gray bar) for 5 min, and the phosphorylation of AMPK at Thr172 (pAMPK-α) and the total amount of AMPK-α was measured by Western blot analysis. Graph represents the pAMPK/AMPK ratio. Values are expressed as mean ± SEM. n = 4. Representative Western blots of pAMPK-α and total AMPK-α. (B) ATII cells were treated with 40 mmHg CO2 (white bar) for 5 min or with 120 mmHg CO2 for 15 s to 5 min (black bars) at a pHe of 7.4. Graph represents the pAMPK/AMPK ratio. Values are expressed as mean ± SEM. n = 4. Representative Western blots of pAMPK-α and total AMPK-α. *P < 0.05; **P < 0.01.