The cathepsin-S/protease-activated receptor-(PAR)-2 axis drives chronic allograft vasculopathy and is a molecular target for therapeutic intervention.

Background: Cathepsin S ( CatS) and proteinase - activated receptor ( PAR)- 2 are involved in the remodelling of vascular walls and neointima formation as well as in alloantigen presentation and T-cell priming. Therefore, we hypothesized that CatS/PAR-2 inhibition/deficiency would attenuate chronic allograft vasculopathy. Methods: Heterotopic aortic murine transplantation was performed from 657BL/ 63 donors to £ 57BL/ 6J re- cipients (syngeneic control group), Balb/c to 657BL/6J without treatment (allogenic control group), Balb/c to 657BL/ 63 with twice daily oral CatS inhibitor (allogenic treatment group ) and Balb/ c to Parl-/- C57BL/6J (allogenic knockout group). The recipients were sacrificed on day 28 and the grafts were harvested for histological analysis and RT-qPCR. Results: After 28 days, mice of the allogenic control group exhibited significant neointima formation and massive CD8 T-cell infiltration into the neointima while the syngeneic control group showed negligible allograft vasculopathy. The mRNA expression level of CatS in allografts was 5-fold of those in syngeneic grafts. Neointima formation and therefore intima/media-ratio were significantly decreased in the treatment and knockout group in comparison to the allogenic control group. Mice in treatment group also displayed significantly fewer CD8 T cells in the neointima compared with allogeneic controls. Additionally, treatment with the CatS inhibitor and PAR2- deficiency decreased mRNA-levels of interleukins and cytokines. Conclusion: In conclusion. our data indicate that inhibiting CatS and PAR-2 deficiency led to a marked reduction of neointima formation and associated inflammation in a murine heterotopic model for allograft vasculopathy. [ABSTRACT FROM AUTHOR]