Cross‐linking by tissue transglutaminase‐2 alters fibrinogen‐directed macrophage proinflammatory activity

Abstract

BackgroundThe blood coagulation factor fibrin(ogen) can modulate inflammation by altering leukocyte activity. Analyses of fibrin(ogen)‐mediated proinflammatory activity have largely focused on leukocyte integrin binding activity revealed by conversion of fibrinogen to a stabilized fibrin polymer by blood coagulation enzymes. In addition to coagulation enzymes, fibrinogen is a substrate for tissue transglutaminase‐2 (TG2), a widely expressed enzyme that produces unique fibrinogen Aα‐γ chain cross‐linked products. ObjectivesWe tested the hypothesis that TG2 dependent cross‐linking alters the proinflammatory activity of surface‐adhered fibrinogen. MethodsMouse bone marrow‐derived macrophages (BMDMs) were cultured on tissue culture plates coated with fibrinogen or TG2‐cross‐linked fibrinogen (10 µg/ml) and then stimulated with lipopolysaccharide (LPS, 1 ng/ml) or vehicle for various times. ResultsIn the absence of LPS stimulation, TG2‐cross‐linked fibrin(ogen) enhanced inflammatory gene induction (e.g., Tnfα) compared with unmodified fibrinogen. LPS stimulation induced mitogen‐activated protein kinase phosphorylation, IκBα degradation, and expression of proinflammatory cytokines (e.g., tumor necrosis factor α) within 60 min. This initial cellular activation was unaffected by unmodified or TG2‐cross‐linked fibrinogen. In contrast, LPS induction of interleukin‐10 mRNA and protein and STAT3 phosphorylation was selectively attenuated by TG2‐cross‐linked fibrinogen, which was associated with enhanced proinflammatory cytokine secretion by LPS‐stimulated BMDMs at later time points (6 and 24 h). ConclusionsThe results indicate that atypical cross‐linking by TG2 imparts unique proinflammatory activity to surface‐adhered fibrinogen. The results suggest a novel coagulation‐independent mechanism controlling fibrinogen‐directed macrophage activation.