Lipopolysaccharide-induced pulmonary endothelial barrier disruption and lung edema: critical role for bicarbonate stimulation of AC10

Abstract

Bacteria-induced sepsis is a common cause of pulmonary endothelial barrier dysfunction and can progress toward acute respiratory distress syndrome. Elevations in intracellular cAMP tightly regulate pulmonary endothelial barrier integrity; however, cAMP signals are highly compartmentalized: whether cAMP is barrier-protective or -disruptive depends on the compartment (plasma membrane or cytosol, respectively) in which the signal is generated. The mammalian soluble adenylyl cyclase isoform 10 (AC10) is uniquely stimulated by bicarbonate and is expressed in pulmonary microvascular endothelial cells (PMVECs). Elevated extracellular bicarbonate increases cAMP in PMVECs to disrupt the endothelial barrier and increase the filtration coefficient (Kf) in the isolated lung. We tested the hypothesis that sepsis-induced endothelial barrier disruption and increased permeability are dependent on extracellular bicarbonate and activation of AC10. Our findings reveal that LPS-induced endothelial barrier disruption is dependent on extracellular bicarbonate: LPS-induced barrier failure and increased permeability are exacerbated in elevated bicarbonate compared with low extracellular bicarbonate. The AC10 inhibitor KH7 attenuated the bicarbonate-dependent LPS-induced barrier disruption. In the isolated lung, LPS failed to increase Kf in the presence of minimal perfusate bicarbonate. An increase in perfusate bicarbonate to the physiological range (24 mM) revealed the LPS-induced increase in Kf, which was attenuated by KH7. Furthermore, in PMVECs treated with LPS for 6 h, there was a dose-dependent increase in AC10 expression. Thus these findings reveal that LPS-induced pulmonary endothelial barrier failure requires bicarbonate activation of AC10.

International Union of Basic and Clinical Pharmacology. CI. Structures and Small Molecule Modulators of Mammalian Adenylyl Cyclases

“…(6)-2-(1H-Benzimidazol-2-ylthio)propanoic acid 2-[(5-bromo-2-hydroxyphenyl)methylene]hydrazide (KH7) is the most widely used sAC inhibitor in intact-cell studies (Kumar et al, 2009;Schmid et al, 2010;Kolodecik et al, 2012;Bitterman et al, 2013;Dey et al, 2014;Hasan et al, 2014;Nickols et al, 2015;De Rasmo et al, 2015;Sosa et al, 2016). Caution must be exerted when Pharmacological Modulation of Mammalian Adenylyl Cyclases interpreting intact-cell studies with KH7 because of toxic effects of this compound in mitochondria (Di Benedetto et al, 2013) and b cells (Tian et al, 2011).…”

Extracellular vesicles: another compartment for the second messenger, cyclic adenosine monophosphate

“…Lungs from male Sprague-Dawley rats (Charles River Laboratories International,) were isolated as described previously (34,36,45). All experimental procedures were performed in accordance with current provisions of the US Animal Welfare Act and were approved by the Institutional Animal Care and Use Committee of the University of South Alabama.…”

Vildagliptin ameliorates pulmonary fibrosis in lipopolysaccharide-induced lung injury by inhibiting endothelial-to-mesenchymal transition

“…The etiology of fibrotic diseases can vary widely. Given that one of the main initial targets of endotoxins is vascular endothelial cells especially in case of ARDS from extra-pulmonary origin [ 6 , 10 ], EndMT could thus be closely involved in the pathogenesis of pulmonary fibrosis after systemic endotoxemic injury.…”