title: FXIa and platelet polyphosphate as therapeutic targets during human blood clotting on collagen/tissue factor surfaces under flow.
abstract: Factor XIIa (FXIIa) and factor XIa (FXIa) contribute to thrombosis in animal models, whereas platelet-derived polyphosphate (polyP) may potentiate contact or thrombin-feedback pathways. The significance of these mediators in human blood under thrombotic flow conditions on tissue factor (TF) -bearing surfaces remains inadequately resolved. Human blood (corn trypsin inhibitor treated [4 μg/mL]) was tested by microfluidic assay for clotting on collagen/TF at TF surface concentration ([TF]wall) from ∼0.1 to 2 molecules per μm(2). Anti-FXI antibodies (14E11 and O1A6) or polyP-binding protein (PPXbd) were used to block FXIIa-dependent FXI activation, FXIa-dependent factor IX (FIX) activation, or platelet-derived polyP, respectively. Fibrin formation was sensitive to 14E11 at 0 to 0.1 molecules per µm(2) and sensitive to O1A6 at 0 to 0.2 molecules per µm(2). However, neither antibody reduced fibrin generation at ∼2 molecules per µm(2) when the extrinsic pathway became dominant. Interestingly, PPXbd reduced fibrin generation at low [TF]wall (0.1 molecules per µm(2)) but not at zero or high [TF]wall, suggesting a role for polyP distinct from FXIIa activation and requiring low extrinsic pathway participation. Regardless of [TF]wall, PPXbd enhanced fibrin sensitivity to tissue plasminogen activator and promoted clot retraction during fibrinolysis concomitant with an observed PPXbd-mediated reduction of fibrin fiber diameter. This is the first detection of endogenous polyP function in human blood under thrombotic flow conditions. When triggered by low [TF]wall, thrombosis may be druggable by contact pathway inhibition, although thrombolytic susceptibility may benefit from polyP antagonism regardless of [TF]wall.
authors.affiliation: Department of Chemical and Biomolecular Engineering, and Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, PA; and.
authors.forename: Shu
authors.identifier: http://orcid.org/0000-0003-3070-3068
authors.initials: S
authors.lastname: Zhu
authors.affiliation: Department of Biochemistry, University of Illinois, Urbana, IL.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Travers
authors.affiliation: Department of Biochemistry, University of Illinois, Urbana, IL.
authors.forename: James H
authors.identifier: http://orcid.org/0000-0002-1570-1569
authors.initials: JH
authors.lastname: Morrissey
authors.affiliation: Department of Chemical and Biomolecular Engineering, and Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, PA; and.
authors.forename: Scott L
authors.identifier: http://orcid.org/0000-0002-9791-2238
authors.initials: SL
authors.lastname: Diamond
mesh_terms: D000906:Antibodies / Q000494:pharmacology; D001777:Blood Coagulation; D001780:Blood Coagulation Tests; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D003094:Collagen / Q000378:metabolism; D015945:Factor XIa / Q000378:metabolism*; D006801:Humans; D058990:Molecular Targeted Therapy; D011122:Polyphosphates / Q000378:metabolism*; D015398:Signal Transduction; D013917:Thrombin / Q000378:metabolism; D013925:Thromboplastin / Q000378:metabolism*; D013927:Thrombosis / Q000188:drug therapy / Q000378:metabolism
chemical_list: D000906:Antibodies; D011122:Polyphosphates; D003094:Collagen; D013925:Thromboplastin; D015945:Factor XIa; D013917:Thrombin