Defect in Sensing Human Thrombin by Porcine Endothelial Protease-Activated Receptor-1: Molecular Incompatibility Between Porcine PAR-1 and Human Thrombin.

Xenotransplantation, the transplantation of organs from pigs to humans, presents significant challenges due to immune rejection, which is driven by molecular incompatibilities between species. This study investigates the compatibility between human thrombin and porcine protease-activated receptor-1 (PAR-1), a key regulator of both coagulation and inflammatory responses. Human thrombin activates PAR-1 in human vascular endothelial cells, but our results demonstrate that human thrombin does not effectively activate PAR-1 in porcine vascular endothelial cells due to differences in amino acid sequences, particularly at the thrombin cleavage site and the Hir domain. Protein-protein docking analysis further reveals that porcine PAR-1 forms less stable interactions with human thrombin compared to human PAR-1, resulting in reduced activation. This molecular incompatibility likely contributes to impaired nitric oxide (NO) production, endothelial dysfunction, and increased inflammation, which are critical for the survival of transplanted organs. Additionally, experiments using the PAR-1 inhibitor vorapaxar (Vor) show that inhibiting PAR-1 signaling can suppress inflammatory cytokine and chemokine expression in co-cultures of human macrophages and porcine endothelial cells. These findings suggest that selective PAR-1 inhibitors or targeted therapies regulating thrombin-PAR-1 signaling may improve the success rate of xenotransplantation. However, further in vivo studies are needed to validate these findings and explore therapeutic interventions targeting thrombin-PAR-1 interactions to enhance xenograft survival.