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LDL receptor‐related protein 1 contributes to the clearance of the activated factor VII –antithrombin complex
Author(s) -
Fazavana J. G.,
Muczynski V.,
Proulle V.,
Wohner N.,
Christophe O. D.,
Lenting P. J.,
Denis C. V.
Publication year - 2016
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/jth.13502
Subject(s) - antithrombin , receptor , chemistry , medicine , heparin
SummaryEssentials Factor VIIa is cleared principally as a complex with antithrombin. Enzyme/serpin complexes are preferred ligands for the scavenger‐receptor LRP1. Factor VIIa/antithrombin but not factor VIIa alone is a ligand for LRP1. Macrophage‐expressed LRP1 contributes to the clearance of factor VIIa/antithrombin.Summary Background Recent findings point to activated factor VII ( FVII a) being cleared predominantly (± 65% of the injected protein) as part of a complex with the serpin antithrombin. FVII a–antithrombin complexes are targeted to hepatocytes and liver macrophages. Both cells lines abundantly express LDL receptor‐related protein 1 ( LRP 1), a scavenger receptor mediating the clearance of protease–serpin complexes. Objectives To investigate whether FVII a–antithrombin is a ligand for LRP 1. Methods Binding of FVII a and pre‐formed FVII a–antithrombin to purified LRP 1 Fc‐tagged cluster IV ( rLRP 1‐ cIV /Fc) and to human and murine macrophages was analyzed. FVII a clearance was determined in macrophage LRP 1 (mac LRP 1)‐deficient mice. Results Solid‐phase binding assays showed that FVII a–antithrombin bound in a specific, dose‐dependent and saturable manner to rLRP 1‐ cIV /Fc. Competition experiments with human THP 1 macrophages indicated that binding of FVII a but not of FVII a–antithrombin was reduced in the presence of annexin‐V or anti‐tissue factor antibodies, whereas binding of FVII a–antithrombin but not FVII a was inhibited by the LRP 1‐antagonist GST ‐ RAP . Additional experiments revealed binding of both FVII a and FVII a–antithrombin to murine control macrophages. In contrast, no binding of FVII a–antithrombin to macrophages derived from mac LRP 1‐deficient mice could be detected. Clearance of FVII a–antithrombin but not of active site‐blocked FVII a was delayed 1.5‐fold (mean residence time of 3.3 ± 0.1 h versus 2.4 ± 0.2 h) in mac LRP 1‐deficient mice. The circulatory presence of FVII a was prolonged to a similar extent in mac LRP 1‐deficient mice and in control mice. Conclusions Our data show that FVII a–antithrombin but not FVII a is a ligand for LRP 1, and that LRP 1 contributes to the clearance of FVII a–antithrombin in vivo .