title: The efficacy of activated protein C in murine endotoxemia is dependent on integrin CD11b.
abstract: Activated protein C (APC), the only FDA-approved biotherapeutic drug for sepsis, possesses anticoagulant, antiinflammatory, and barrier-protective activities. However, the mechanisms underlying its anti-inflammatory functions are not well defined. Here, we report that the antiinflammatory activity of APC on macrophages is dependent on integrin CD11b/CD18, but not on endothelial protein C receptor (EPCR). We showed that CD11b/CD18 bound APC within specialized membrane microdomains/lipid rafts and facilitated APC cleavage and activation of protease-activated receptor-1 (PAR1), leading to enhanced production of sphingosine-1-phosphate (S1P) and suppression of the proinflammatory response of activated macrophages. Deletion of the gamma-carboxyglutamic acid domain of APC, a region critical for its anticoagulant activity and EPCR-dependent barrier protection, had no effect on its antiinflammatory function. Genetic inactivation of CD11b, PAR1, or sphingosine kinase-1, but not EPCR, abolished the ability of APC to suppress the macrophage inflammatory response in vitro. Using an LPS-induced mouse model of lethal endotoxemia, we showed that APC administration reduced the mortality of wild-type mice, but not CD11b-deficient mice. These data establish what we believe to be a novel mechanism underlying the antiinflammatory activity of APC in the setting of endotoxemia and provide clear evidence that the antiinflammatory function of APC is distinct from its barrier-protective function and anticoagulant activities.
authors.affiliation: Center for Vascular and Inflammatory Diseases, Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
authors.forename: Chunzhang
authors.initials: C
authors.lastname: Cao
authors.forename: Yamei
authors.initials: Y
authors.lastname: Gao
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.forename: Toni M
authors.initials: TM
authors.lastname: Antalis
authors.forename: Francis J
authors.initials: FJ
authors.lastname: Castellino
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
mesh_terms: D015055:1-Carboxyglutamic Acid / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D019446:Endotoxemia / Q000378:metabolism*; D016023:Integrins / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism / Q000494:pharmacology; D008246:Lysophospholipids; D021962:Membrane Microdomains / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017853:Phosphotransferases (Alcohol Group Acceptor); D011486:Protein C / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D018805:Sepsis / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives; D000099157:Sphingosine Kinase
chemical_list: D015055:1-Carboxyglutamic Acid; D016023:Integrins; D008070:Lipopolysaccharides; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D011486:Protein C; D013110:Sphingosine; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate
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