THROMBOSIS AND HEMOSTASIS Hyperantithrombotic, noncytoprotective Glu149Ala-activated protein C mutant

Activated protein C (APC) reduces mortality in severe sepsis patients.APC exerts anticoagulant activities via inactivation of factors Va and VIIIa and cytoprotective activities via endothelial protein C receptor and proteaseactivated receptor-1. APC mutants with selectively altered and opposite activity profiles, that is, greatly reduced anticoagulant activity or greatly reduced cytoprotective activities, are compared here. Glu149AlaAPC exhibited enhanced in vitro anticoagulant and in vivo antithrombotic activity, but greatly diminished in vitro cytoprotective effects and in vivo reduction of endotoxininduced murine mortality. Thus, residue Glu149 and the C-terminal region of APC’s light chain are identified as functionally important for expression of multipleAPC activities. In contrast to Glu149Ala-APC, 5A-APC (Lys191-193Ala Arg229/230Ala) with protease domain mutations lacked in vivo antithrombotic activity, although it was potent in reducing endotoxin-induced mortality, as previously shown. These data imply that APC molecular species with potent antithrombotic activity, but without robust cytoprotective activity, are not sufficient to reduce mortality in endotoxemia, emphasizing the need for APC’s cytoprotective actions, but not anticoagulant actions, to reduce endotoxin-induced mortality. Protein engineering can provide APC mutants that permit definitive mechanism of action studies for APC’s multiple activities, and may also provide safer and more effective secondgenerationAPC mutants with reduced bleeding risk. (Blood. 2009;113:5970-5978)