Mitochondrially Mediated Cell Death in Ischemia/Reperfusion Injury after Fatty Liver Transplantation
Final Report Abstract
Damage to liver caused by ischemia/reperfusion can be a limiting factor in clinical settings of liver surgery and transplantation. The main aim of this project was to evaluate whether mitochondrial dysfunction is a key event in animal models of liver reperfusion injury. First, we tested the hypothesis that minocycline, a tetracycline previously shown to have cytoprotective properties, decreases storage/reperfusion injury after rat liver transplantation by inhibition of the mitochondrial permeability transition (MPT). Additionally, we investigated the effects of NIM811, a nonimmunosuppressive CsA derivative that blocks the MPT. Our findings showed that minocycline and NIM811 decreased necrosis and apoptosis in liver grafts after rat liver transplantation and improved graft survival to a similar extent. Although NIM811 is a well established inhibitor of the MPT, the mechanism of minocycline inhibition has been unclear. Our findings indicated that minocycline cytoprotection like that of NIM811 was mediated by suppression of the MPT. The MPT causes mitochondrial depolarization with consequent uncoupling of oxidative phosphorylation, mitochondrial swelling and cell death by necrosis and apoptosis. Intravital confocal imaging showed directly mitochondria depolarization after liver transplantation after a time of cold ischemic storage leading to graft injury and failure. This depolarization signifying the MPT preceded onset of necrotic cell death. Minocycline like NIM811 substantially prevented mitochondrial depolarization, and in isolated liver mitochondria minocycline blocked onset of CsA sensitive mitochondrial swelling induced by Ca2+. Tetracycline, which did not decrease graft failure and ALT release after transplantation, did not block MPT onset in isolated mitochondria and did not prevent mitochondrial depolarization assessed by intravital confocal microscopy after liver transplantation. Hence, protection by both minocycline and NIM811 appeared to be due to blockade of the MPT and prevention of mitochondrial depolarization, a consequence ofthe MPT. Furthermore, we have demonstrated that specifically the c-Jun kinase JNK2 represents a crucial player in mitochondrial dysfunction, as shown in our mouse model of warm liver ischemia as well as in our mouse model of liver transplantation. Here we utilized specific knockout mice and established the microsurgical challenging model of orthotopic mouse liver transplantation. Our findings showed that JNK2 deficient liver grafts had decreased necrosis and apoptosis after transplantation and warm liver ischemia. In addition, in comparison to wildtype liver grafts, failure of JNK2 deficient grafts was delayed. Protection in JNK2 deficient grafts was associated with prevention of mitochondrial depolarization, as assessed by intravital multiphoton microscopy and decreased oxidative stress. Our results could provide a unique therapeutic target in the treatment and prevention of warm ischemia/reperfusion injury as well as after cold storage/reperfusion injury following liver transplantation. At present, JNK inhibitors have only modest specificity for different JNK isoforms, but development of specific JNK2 inhibitors could lead to effective therapies to treat and prevent cold storage/reperfusion injury. Marginal donor livers have increased susceptibility to storage/reperfusion injury. Thus, treatment of marginal livers with a specific JNK2 inhibitor has the potential for allowing more frequent and successful use of marginal livers in clinical transplantation.
Publications
- Endothelial Nitric Oxide Synthase Protects Transplanted Mouse Livers Against Storage/Reperfusion Injury: Role of Vasodilatory and Innate Immunity Pathways. Transplant Proc 2006 Dec;38(10):3351-7
Theruvath TP, Zhong Z, Currin RT, Ramshesh VK, Lemasters JJ
- c-Jun N-Terminal Kinase-2 promotes liver injury via the mitochondrial permeability transition after mouse liver transplantation. Am J Transplant 2008 Sept;8:1819-1828
Theruvath TP, Czerny C, Ramshesh VK, Zhong Z, Chavin KD, Lemasters JJ
- Minocycline and N-Methyl-4-lsoleucine Cyclosporine (NIM811) Mitigate Storage/Reperfusion Injury After Rat Liver Transplantation Through Suppression of the Mitochondrial Permeability Transition. Hepatology 2008 Jan;47(1):236-46
Theruvath TP, Zhong Z, Pediaditakis P, Ramshesh VK, Currin RT, Tikunov A, Holmuhamedov E, Lemasters JJ
- Mitochondrial permeability transition in liver ischemia and reperfusion: role of c-Jun N-Terminal Kinase 2. Transplantation 2008 May;85(10):1500-4
Theruvath TP, Snoddy M, Zhong Z, Lemasters JJ
