No abstract

Acute myocardial infarction (MI) is a major cause of death and disability worldwide. In patients with MI, the treatment of choice for reducing acute myocardial ischemic injury and limiting MI size is timely and effective myocardial reperfusion using either thombolytic therapy or primary percutaneous coronary intervention (PPCI). However, the process of reperfusion can itself induce cardiomyocyte death, known as myocardial reperfusion injury, for which there is still no effective therapy. A number of new therapeutic strategies currently under investigation for preventing myocardial reperfusion injury have the potential to improve clinical outcomes in patients with acute MI treated with PPCI.

Background-Whether alterations in mitochondrial morphology affect the susceptibility of the heart to ischemia/ reperfusion injury is unknown. We hypothesized that modulating mitochondrial morphology protects the heart against ischemia/reperfusion injury. Methods and Results-In response to ischemia, mitochondria in HL-1 cells (a cardiac-derived cell line) undergo fragmentation, a process that is dependent on the mitochondrial fission protein dynamin-related protein 1 (Drp1). Transfection of HL-1 cells with the mitochondrial fusion proteins mitofusin 1 or 2 or with Drp1 K38A , a dominantnegative mutant form of Drp1, increased the percentage of cells containing elongated mitochondria (65Ϯ4%, 69Ϯ5%, and 63Ϯ6%, respectively, versus 46Ϯ6% in control: nϭ80 cells per group; PϽ0.05), decreased mitochondrial permeability transition pore sensitivity (by 2.4Ϯ0.5-, 2.3Ϯ0.7-, and 2.4Ϯ0.3-fold, respectively; nϭ80 cells per group; PϽ0.05), and reduced cell death after simulated ischemia/reperfusion injury (11.6Ϯ3.9%, 16.2Ϯ3.9%, and 12.1Ϯ2.9%, respectively, versus 41.8Ϯ4.1% in control: nϭ320 cells per group; PϽ0.05). Treatment of HL-1 cells with mitochondrial division inhibitor-1, a pharmacological inhibitor of Drp1, replicated these beneficial effects. Interestingly, elongated interfibrillar mitochondria were identified in the adult rodent heart with confocal and electron microscopy, and in vivo treatment with mitochondrial division inhibitor-1 increased the percentage of elongated mitochondria from 3.6Ϯ0.5% to 14.5Ϯ2.8% (Pϭ0.023). Finally, treatment of adult murine cardiomyocytes with mitochondrial division inhibitor-1 reduced cell death and inhibited mitochondrial permeability transition pore opening after simulated ischemia/reperfusion injury, and in vivo treatment with mitochondrial division inhibitor-1 reduced myocardial infarct size in mice subject to coronary artery occlusion and reperfusion (21.0Ϯ2.2% with mitochondrial division inhibitor-1 versus 48.0Ϯ4.5% in control; nϭ6 animals per group; PϽ0.05). Conclusion-Inhibiting mitochondrial fission protects the heart against ischemia/reperfusion injury, suggesting a novel pharmacological strategy for cardioprotection. Key Words: cardiomyocytes Ⅲ hypoxia Ⅲ ischemia Ⅲ myocardial infarction Ⅲ reperfusion I nnovative treatment strategies for protecting the heart from ischemia/reperfusion injury (IRI) are needed to improve clinical outcomes in patients with coronary heart disease. Previous studies suggest that mitochondria are highly dynamic and that changes in mitochondrial shape can affect a variety of biological processes such as apoptosis, respiration, mitosis, and development. 1,2 Mitochondria change their morphology by undergoing either fusion or fission, resulting in either elongated, tubular, interconnected mitochondrial networks or fragmented, discontinuous mitochondria, respectively. 1,2 These 2 opposing processes are regulated by the mitochondrial fusion proteins mitofusin (Mfn) 1, Mfn2, and optic atrophy protein 1 and the mitochondrial fission proteins dynamin-related...