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-β (CaMKK-β). Chelating intracellular Ca 2+ or abrogating CaMKK-β 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-ζ and promote Na,K-ATPase endocytosis. Inhibition or downregulation of AMPK via adenoviral delivery of dominant-negative AMPK-α 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 β-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 β-adrenergic agonists and cAMP.

High CO2 Levels Cause Skeletal Muscle Atrophy via AMP-activated Kinase (AMPK), FoxO3a Protein, and Muscle-specific Ring Finger Protein 1 (MuRF1)

“…We found that hypercapnia-driven muscle atrophy is mediated by AMPK␣2, which is the major catalytic subunit isoform in muscle (23). Previous evidence from lung alveolar epithelialcellssuggeststhatCO 2 -mediatedAMPK␣1phosphor-ylation occurs through Ca 2ϩ /calmodulin-dependent kinase kinase ␤ (CaMKK-␤) (27), making this pathway a possible activator of AMPK in the present model. Alternatively, given that CO 2 exposure was found to cause mitochondrial dysfunction, decreased O 2 consumption, and ATP production in fibroblasts and alveolar epithelial cells (52), AMPK activation could also occur via LKB1.…”

“…The chamber's atmosphere was continuously monitored and adjusted with ProOx/ProCO 2 controllers (BioSpherix Ltd) in order to maintain 10% CO 2 and 21% O 2 , with a temperature of 20 -26°C and a relative humidity between 40 and 50%. These settings resulted in an arterial partial pressure of carbon dioxide (paCO 2 ) of ϳ75 mm Hg and arterial partial pressure of oxygen (paO 2 ) of ϳ100 mm Hg, whereas in animals maintained in room air paCO 2 was ϳ40 mm Hg and paO 2 was ϳ100 mm Hg (7,27). None of the animals developed appreciable distress.…”

Mitochondrial Complex III-generated Oxidants Activate ASK1 and JNK to Induce Alveolar Epithelial Cell Death following Exposure to Particulate Matter Air Pollution

“…Kinase Assays to Measure the Activity of c-Jun-Kinase assays to measure the activity of c-Jun were performed using a commercially available assay according to the manufacturer's directions (Cell Signaling; catalog number 9810), except the incubation with ATP was extended to 1 h. Kinase assays were also performed using a modification of a procedure described previously (27). Briefly, cell lysates were obtained after exposure to PM 2.5 , and c-Jun was immunoprecipitated by incubating ϳ500 g of protein with 5 l of c-Jun antibody overnight (4°C) (Santa Cruz Biotechnology Inc.).…”

Elevated CO 2 levels affect development, motility, and fertility and extend life span in Caenorhabditis elegans

“…However, more recent studies have suggested that high pCO 2 can cause oxidative stress in the lung, and injury (3). More recently it has been reported that in rat lungs and human epithelial cells, high pCO 2 decreased alveolar fluid clearance independently of pH and ROS (4,5). In some reports it has been shown that CO 2 uptake involves the aquaporin and RH1 channels (6,7).…”