MBL‐associated serine protease 1 (MASP‐1) is necessary for thrombin substrate cleavage in vitro

Abstract

Bleeding disorders and thrombotic complications constitute a major cause of death and disability worldwide. Previous research established a connection between the complement and coagulation systems; however no studies have specifically investigated the molecular mechanisms underlying this interaction. Thus, the purpose of this study was to elucidate the role of complement, specifically the lectin pathway, in thrombin‐like activity in vitro. MBL‐complexes were captured on mannan‐coated plates using serum collected from wild‐type (WT) and a variety of complement deficient mice. The captured MBL‐complexes were incubated with a chromogenic thrombin substrate, S2238, for 1.5hrs at 37°C, and cleavage was measured using a fluorometer. MBL‐complexes captured from WT, C2/fB−/−, MBL‐A−/− or MBL‐C−/− sera showed no significant difference in S2238 cleavage between groups. In contrast, complexes captured from MBL null and MASP‐1/3−/− mouse sera demonstrated significantly decreased S2238 cleavage compared to WT (P<0.01). Recombinant human (rh)MBL alone also failed to cleave S2238, yet cleavage could be restored when rMASP‐1 was added back to either MASP1/3−/− sera or rhMBL. Taken together, these findings indicate that the MBL‐complex with MASP‐1 has thrombin‐like activity, and may suggest a key role for lectin complexes in thrombus formation and coagulopathy in vivo. Supported by HL56086, HL92469 and HL99130.