title: Hypercapnia Inhibits Autophagy and Bacterial Killing in Human Macrophages by Increasing Expression of Bcl-2 and Bcl-xL.
abstract: Hypercapnia, the elevation of CO2 in blood and tissue, commonly develops in patients with advanced lung disease and severe pulmonary infections, and it is associated with high mortality. We previously reported that hypercapnia alters expression of host defense genes, inhibits phagocytosis, and increases the mortality of Pseudomonas pneumonia in mice. However, the effect of hypercapnia on autophagy, a conserved process by which cells sequester and degrade proteins and damaged organelles that also plays a key role in antimicrobial host defense and pathogen clearance, has not previously been examined. In the present study we show that hypercapnia inhibits autophagy induced by starvation, rapamycin, LPS, heat-killed bacteria, and live bacteria in the human macrophage. Inhibition of autophagy by elevated CO2 was not attributable to acidosis. Hypercapnia also reduced macrophage killing of Pseudomonas aeruginosa. Moreover, elevated CO2 induced the expression of Bcl-2 and Bcl-xL, antiapoptotic factors that negatively regulate autophagy by blocking Beclin 1, an essential component of the autophagy initiation complex. Furthermore, small interfering RNA targeting Bcl-2 and Bcl-xL and the small molecule Z36, which blocks Bcl-2 and Bcl-xL binding to Beclin 1, prevented hypercapnic inhibition of autophagy and bacterial killing. These results suggest that targeting the Bcl-2/Bcl-xL-Beclin 1 interaction may hold promise for ameliorating hypercapnia-induced immunosuppression and improving resistance to infection in patients with advanced lung disease and hypercapnia.
authors.affiliation: Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611; marinamatsuda@northwestern.edu.
authors.forename: S Marina
authors.identifier: http://orcid.org/0000-0002-7566-4560
authors.initials: SM
authors.lastname: Casalino-Matsuda
authors.affiliation: Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611;
authors.forename: Aisha
authors.initials: A
authors.lastname: Nair
authors.affiliation: Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208; and.
authors.forename: Greg J
authors.initials: GJ
authors.lastname: Beitel
authors.affiliation: Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611;
authors.forename: Khalilah L
authors.initials: KL
authors.lastname: Gates
authors.affiliation: Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611; Jesse Brown Veterans Affairs Medical Center, Chicago, IL 60612.
authors.forename: Peter H S
authors.initials: PH
authors.lastname: Sporn
mesh_terms: D000138:Acidosis; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000037:antagonists & inhibitors; D001343:Autophagy / Q000187:drug effects / Q000276:immunology*; D000071186:Beclin-1; D002245:Carbon Dioxide / Q000097:blood / Q000494:pharmacology; D002460:Cell Line; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000276:immunology*; D007211:Indoles / Q000494:pharmacology; D008070:Lipopolysaccharides; D008171:Lung Diseases / Q000473:pathology; D016676:Macrophages, Alveolar / Q000276:immunology* / Q000382:microbiology; D008565:Membrane Proteins / Q000037:antagonists & inhibitors; D051379:Mice; D010587:Phagocytosis / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics*; D011550:Pseudomonas aeruginosa / Q000276:immunology; D034622:RNA Interference; D034741:RNA, Small Interfering; D020123:Sirolimus / Q000494:pharmacology; D051020:bcl-X Protein / Q000096:biosynthesis / Q000235:genetics*
chemical_list: C543336:5-fluoro-1-(3'-dimethylamino)propyl-indolin-2-one; D051017:Apoptosis Regulatory Proteins; C494811:BCL2L1 protein, human; C491997:BECN1 protein, human; D000071186:Beclin-1; D007211:Indoles; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D051020:bcl-X Protein; D002245:Carbon Dioxide; D020123:Sirolimus