Glaesserella parasuis induces tissue transglutaminase-mediated fibrinogen crosslinking through NF-κB activation

Glaesserella parasuis (GPS) is the causative agent of Glässer's disease, leading to significant economic losses in the global swine industry. During post-mortem inspection, the main observation in pigs affected by Glässer's disease is the presence of serofibrinous or fibrinopurulent exudate on the mucosal surface. Nevertheless, the mechanism by which fibrinogen is converted into a fibrin clot during Glässer's disease is not fully understood. In this study, we discovered in the liver, lung, and kidney, that GPS infection upregulates the expression of tissue transglutaminase (tTG) and promotes the co-localization of tTG with fibrin. In porcine aortic endothelial cells, knockdown of tTG significantly reduced fibrinogen cross-linking and pro-inflammatory factor production after GPS infection. In addition, in investigating the mechanism of tTG upregulation by GPS infection, inhibitor assays revealed the involvement of the NF-κB signaling pathway in the upregulation of tTG expression during GPS infection. Further data from dual-luciferase assays and chromatin immunoprecipitation confirmed that phosphorylated p65 binding to the tTG promoter sequences increased tTG expression and the specific binding site was discovered at GACCTTCCCT (-1082 to -1072 bp), AGGGAAATTG (-807 to -797 bp), and TAAGTTCCCC (+22 to +32 bp). The above results indicate that GPS infection may promote the cross-linking of fibrinogen by tTG, thereby mediating exudative fibrinous inflammation, providing new insights into the pathogenesis of GPS infection, and suggesting potential molecular targets for therapeutic intervention.