title: Calcium-dependent phospholipase A2 modulates infection-induced diaphragm dysfunction.
abstract: Calpain activation contributes to the development of infection-induced diaphragm weakness, but the mechanisms by which infections activate calpain are poorly understood. We postulated that skeletal muscle calcium-dependent phospholipase A2 (cPLA2) is activated by cytokines and has downstream effects that induce calpain activation and muscle weakness. We determined whether cPLA2 activation mediates cytokine-induced calpain activation in isolated skeletal muscle (C2C12) cells and infection-induced diaphragm weakness in mice. C2C12 cells were treated with the following: 1) vehicle; 2) cytomix (TNF-α 20 ng/ml, IL-1β 50 U/ml, IFN-γ 100 U/ml, LPS 10 μg/ml); 3) cytomix + AACOCF3, a cPLA2 inhibitor (10 μM); or 4) AACOCF3 alone. At 24 h, we assessed cell cPLA2 activity, mitochondrial superoxide generation, calpain activity, and calpastatin activity. We also determined if SS31 (10 μg/ml), a mitochondrial superoxide scavenger, reduced cytomix-mediated calpain activation. Finally, we determined if CDIBA (10 μM), a cPLA2 inhibitor, reduced diaphragm dysfunction due to cecal ligation puncture in mice. Cytomix increased C2C12 cell cPLA2 activity (P < 0.001) and superoxide generation; AACOCF3 and SS31 blocked increases in superoxide generation (P < 0.001). Cytomix also activated calpain (P < 0.001) and inactivated calpastatin (P < 0.01); both AACOCF3 and SS31 prevented these changes. Cecal ligation puncture reduced diaphragm force in mice, and CDIBA prevented this reduction (P < 0.001). cPLA2 modulates cytokine-induced calpain activation in cells and infection-induced diaphragm weakness in animals. We speculate that therapies that inhibit cPLA2 may prevent diaphragm weakness in infected, critically ill patients.
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Kentucky, Lexington, Kentucky; and Center for Muscle Biology, University of Kentucky, Lexington, Kentucky.
authors.forename: Gerald S
authors.initials: GS
authors.lastname: Supinski
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Kentucky, Lexington, Kentucky; and Center for Muscle Biology, University of Kentucky, Lexington, Kentucky.
authors.forename: Alexander P
authors.initials: AP
authors.lastname: Alimov
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Kentucky, Lexington, Kentucky; and Center for Muscle Biology, University of Kentucky, Lexington, Kentucky.
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Kentucky, Lexington, Kentucky; and Center for Muscle Biology, University of Kentucky, Lexington, Kentucky.
authors.forename: Xiao-Hong
authors.initials: XH
authors.lastname: Song
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Kentucky, Lexington, Kentucky; and Center for Muscle Biology, University of Kentucky, Lexington, Kentucky lacall2@email.uky.edu.
authors.forename: Leigh A
authors.initials: LA
authors.lastname: Callahan
mesh_terms: D000818:Animals; D002460:Cell Line; D003964:Diaphragm / Q000201:enzymology / Q000382:microbiology / Q000503:physiopathology*; D054513:Group IV Phospholipases A2 / Q000502:physiology*; D051379:Mice; D018908:Muscle Weakness; D018805:Sepsis / Q000201:enzymology* / Q000503:physiopathology*; D013481:Superoxides / Q000378:metabolism
chemical_list: D013481:Superoxides; D054513:Group IV Phospholipases A2
keywords: cPLA2; calpain; cytokines; diaphragm weakness; sepsis