SUMMARY The mitochondrion is the primary source of reactive oxygen species (ROS) in eukaryotic cells. With the aid of a novel mitochondrial matrix-targeted superoxide indicator, here we show that individual mitochondria undergo spontaneous bursts of superoxide generation, termed “superoxide flashes”. Superoxide flashes occur randomly in space and time, exhibit all-or-none properties, and reflect elementary events of superoxide production within single mitochondria across a wide diversity of cells. Individual flashes are triggered by transient openings of the mitochondrial permeability transition pore (mPTP) and are fueled by electron transfer complexes-dependent superoxide production. While decreased during cardiac hypoxia/anoxia, a flurry of superoxide flash activity contributes to the destructive rebound ROS burst observed during early reoxygenation after anoxia. The discovery of superoxide flashes reveals a novel mechanism for quantal ROS production by individual mitochondria and substantiates the central role of mPTP in oxidative stress related pathology in addition to its well-known role in apoptosis.

Directional movement is a property common to all cell types during development and is critical to tissue remodelling and regeneration after damage1–3. In migrating cells, calcium plays a multifunctional role in directional sensing, cytoskeleton redistribution, traction force generation, and relocation of focal adhesions1, 4–7. Here we visualise, for the first time, high-calcium microdomains (“calcium flickers”), and their patterned activation in migrating fibroblasts. Calcium flicker activity is dually coupled to membrane tension (via TRPM7, a stretch-activated Ca2+-permeant channel of the transient receptor potential superfamily8) and chemoattractant signal transduction (via type 2 inositol 1,4,5-trisphosphate receptors). Interestingly, calcium flickers are most active at the leading lamella of migrating cells, displaying a 4:1 front-to-rear polarisation opposite to the global calcium gradient6. When exposed to a PDGF gradient perpendicular to cell movement, asymmetric calcium flicker activity develops across the lamella and promotes the turning of migrating fibroblasts. These findings illustrate how the exquisite spatiotemporal organisation of calcium microdomains can orchestrate complex cellular processes such as cell migration.

Recombinant human MG53 protein can increase membrane repair after injury in cells and can reduce pathology in animal models of muscle injury and muscular dystrophy.

Background-Ischemic heart disease is the greatest cause of death in Western countries. The deleterious effects of cardiac ischemia are ameliorated by ischemic preconditioning (IPC), in which transient ischemia protects against subsequent severe ischemia/reperfusion injury. IPC activates multiple signaling pathways, including the reperfusion injury salvage kinase pathway (mainly PI3K-Akt-glycogen synthase kinase-3␤ [GSK3␤] and ERK1/2) and the survivor activating factor enhancement pathway involving activation of the JAK-STAT3 axis. Nevertheless, the fundamental mechanism underlying IPC is poorly understood. Methods and Results-In the present study, we define MG53, a muscle-specific TRIM-family protein, as a crucial component of cardiac IPC machinery. Ischemia/reperfusion or hypoxia/oxidative stress applied to perfused mouse hearts or neonatal rat cardiomyocytes, respectively, causes downregulation of MG53, and IPC can prevent ischemia/ reperfusion-induced decrease in MG53 expression. MG53 deficiency increases myocardial vulnerability to ischemia/ reperfusion injury and abolishes IPC protection. Overexpression of MG53 attenuates whereas knockdown of MG53 enhances hypoxia-and H 2 O 2 -induced cardiomyocyte death. The cardiac protective effects of MG53 are attributable to MG53-dependent interaction of caveolin-3 with phosphatidylinositol 3 kinase and subsequent activation of the reperfusion injury salvage kinase pathway without altering the survivor activating factor enhancement pathway. Conclusions-These results establish MG53 as a primary component of the cardiac IPC response, thus identifying a potentially important novel therapeutic target for the treatment of ischemic heart disease. (Circulation. 2010;121:2565-2574.)Key Words: hypoxia Ⅲ ischemia Ⅲ myocardial infarction Ⅲ myocytes Ⅲ stress I schemic heart disease remains the greatest cause of mortality in Western countries and the predicted leading source of mortality worldwide by 2020. 1 Blockage of heart blood flow leads to myocardial ischemia. Persistent ischemia causes myocardial infarctions, resulting in profound myocyte death, irreversible myocardial damage, and a permanent loss of contractile mass. Timely reperfusion of ischemic heart is the only way to preserve cardiac cell viability. However, reperfusion can trigger further damage to the myocardium (ie, ischemia/reperfusion [IR] injury) via reactive oxygen species-induced oxidative stress, calcium overload, or calpain activation. [2][3][4] Both ischemic injury and subsequent IR injury after restoration of blood flow represent important therapeutic targets. Editorial on p 2547 Clinical Perspective on p 2574Interventional approaches against IR injury have centered on the study of ischemic preconditioning (IPC), in which nonlethal ischemic stress to the heart (IPC) protects against subsequent lethal IR injury in the heart. 5-7 IPC is the most powerful intrinsic cellular mechanism to protect the heart as well as other organs, such as brain, liver, and kidney, from IR injury. 8 -11 A variety of signaling mo...