• Apoptosis;
  • mitochondria;
  • mPTP;
  • transplantation

Acute cardiac graft rejection (ACGR) is associated with cardiomyocyte apoptosis. We investigated the respective role of the Fas/FasL and mitochondrial permeability transition pore (mPTP) pathways in cardiomyocyte apoptosis accompanying ACGR. Heterotopic cardiac transplantations were performed in 7–9-week old C57BL6 or C3H mice. Wild type or Fas-deficient (lpr) mice underwent syngeneic (GS) or allogeneic (GA) transplantation, and received either saline or NIM811, a specific inhibitor of the mPTP. At day 5, we assessed ACGR by histology, cardiomyocyte apoptosis by caspase-3 activity and cytochrome c release, Ca2+-induced mPTP opening by a potentiometric approach, and expression of Fas, FasL, TNFα, perforin, granzyme using RT-PCR. Myocardial infiltration of CD8+ T lymphocytes was performed by immunohistochemistry. Allogenic transplantation increased infiltration of inflammatory cells, upregulated FasL, perforin, granzyme, and TNFα, favored Ca2+-induced mPTP opening and increased caspase-3 activity and cytochrome c release in WT grafts. NIM811, but not Fas-deficiency, significantly reduced all these effects. NIM811 also limited infiltration of CD8+ into WT and lpr transplants. These data suggest that the mPTP pathway plays a major role in cardiomyocyte apoptosis associated with ACGR. Inhibition of mPTP opening may attenuate cardiomyocyte apoptosis either directly or indirectly via a limitation of CD8+ T-cell activation.