Role of hsp-27 in cardiac transplant rejection

Abstract

Prevention of allograft rejection following cardiac transplantation is the major obstacle to long-term graft survival. Previous studies have suggested that overexpression of hsp-27 protects against non-transplant atherosclerosis and cardiac allograft vasculopathy in humans and ex vivo induced I/R injury in mice. The purpose of this study was to investigate whether overexpression of hsp-27 protects the heart from acute and chronic rejection using mice overexpressing HA-tagged human hsp-27 as donors. Overexpression of HA-tagged hsp-27 was confirmed by western blot and immunocytochemistry. ELISA showed presence of hsp-27 in the serum of transgenic animals. In the acute rejection model, B10.A hearts from transgenic or littermate controls were transplanted into C57BL/6 wild-type recipients. Survival of transgenic allografts was significantly prolonged compared to littermate control allografts. Furthermore, RT-PCR and immunohistochemistry results demonstrated decreased cellular infiltration of CD3+ and CD8+ T-cells and decreased inflammatory cytokines in transgenic allografts compared to controls. A chronic rejection model was established by grafting B10.A donor hearts into CD4+ T-cell depleted CBA recipients. Cardiac allografts harvested at 4, 6 and 8 weeks post-transplant showed reduced intimal thickening and less vessels affected in transgenic allografts compared to littermate controls. This was associated with significant diminution of infiltrating T-cells but augmentation of IL-4 production in transgenic grafts. Flow cytometry analyses showed that hsp-27 may not influence alloantibody production. Ex vivo studies suggest that overexpression of hsp-27 significantly decreased the activity of caspase-3, -9 and -1 following ischaemia. In addition, the increase in caspase-3 activity was significantly reduced in transgenic hearts following I/R injury in vivo. However, this study failed to demonstrate the immunomodulatory effect of hsp-27 in vitro. Our data suggest that hsp-27 protects against acute and chronic rejection. Protective mechanisms include a delay in inflammatory responses and protection against apoptosis of cardiomyocytes.