Lost in translation: miRNAs and mRNAs in ischemic preconditioning and ischemia/reperfusion injury.

Ischemic stress involves nutrient deprivation, hypoxia, acidosis, and altered levels of various ions and metabolites. Reperfusion, which abruptly alters these parameters, is a second stress to already stressed cells. Ischemic preconditioning, in which brief ischemia alternates with reperfusion to elicit a protective response to ischemia/reperfusion (I/R) injury, revealed the existence of a highly conserved, cell-autonomous, and nearly ubiquitous program. While we often assume that evolutionary selection is irrelevant with respect to myocardial infarctions-which generally occur long after reproduction-the program of ischemia tolerance may date back much further, to hibernating squirrels, turtles, and estivating frogs and snails (extremophiles), which must survive by entering a hypometabolic state. This relationship is further strengthened by the presence of similar signaling pathways and regulatory mechanisms such as mRNA localization and miRNA regulation. These parallels may offer new insights into the myocardial response to I/R injury. This review will explore some of the recent advances in our understanding of autophagy and mitochondrial turnover in the setting of I/R injury, and related findings drawn from research on hibernating extremophiles.