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...

Human adult mesenchymal stem cells (MSCs) support the engineering of functional tissue constructs by secreting angiogenic and cytoprotective factors, which act in a paracrine fashion to influence cell survival and vascularization. MSCs have been isolated from many different tissue sources, but little is known about how paracrine factor secretion varies between different MSC populations. We evaluated paracrine factor expression patterns in MSCs isolated from adipose tissue (ASCs), bone marrow (BMSCs), and dermal tissues [dermal sheath cells (DSCs) and dermal papilla cells (DPCs)]. Specifically, mRNA expression analysis identified insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor-D (VEGF-D), and interleukin-8 (IL-8) to be expressed at higher levels in ASCs compared with other MSC populations whereas VEGF-A, angiogenin, basic fibroblast growth factor (bFGF), and nerve growth factor (NGF) were expressed at comparable levels among the MSC populations examined. Analysis of conditioned media (CM) protein confirmed the comparable level of angiogenin and VEGF-A secretion in all MSC populations and showed that DSCs and DPCs produced significantly higher concentrations of leptin. Functional assays examining in vitro angiogenic paracrine activity showed that incubation of endothelial cells in ASC(CM) resulted in increased tubulogenic efficiency compared with that observed in DPC(CM). Using neutralizing antibodies we concluded that VEGF-A and VEGF-D were 2 of the major growth factors secreted by ASCs that supported endothelial tubulogenesis. The variation in paracrine factors of different MSC populations contributes to different levels of angiogenic activity and ASCs maybe preferred over other MSC populations for augmenting therapeutic approaches dependent upon angiogenesis.

This is the first study to demonstrate that necrostatins inhibit myocardial cell death and reduce infarct size, possibly via a mechanism independent of the MPTP.