Abstract 411: Endogenous miRNA Induced By Ischemic Preconditioning Reduces Myocardial Infarct Size following Ischemia/Reperfusion In Mice
BACKGROUND: Due to its short length (~24 nt) and non-coding nature, microRNA (miRNA) used to be regarded as “evolutionary transcriptional debris”. Recent evidence suggests that miRNA is a novel regulator for transcription and translation. It is known that brief episodes of ischemia during ischemic preconditioning (IPC) trigger complex genetic pro-survival program that results in modulation of several key proteins involved in protection against I/R injury. We hypothesized that miRNA synthesized during IPC is the potential mediator of such protection.
METHODS / RESULTS: Hearts were isolated from 3 groups (n = 6/group) of adult ICR mice and subjected to the following treatments in Langendorff mode: 120 min of perfusion with Krebs-Henseleit buffer (control); 30 min global ischemia followed by 1 hr reperfusion (I/R); 2 cycles of 30 sec ischemia and 90 sec reperfusion followed by 30 min ischemia and 1 hr reperfusion (IPC). Infarct size (IS) was measured by triphenyl tetrazolium staining. IPC in the Langendorff model reduced IS from 29.7 ± 2.1% in the I/R hearts to 9.1 ± 1.8 % in the IPC group. This protection was associated with a significant induction of miRNA-1 (162 ± 13%), miRNA-21 (118 ± 6%), and miRNA-24 (46 ± 12%). To test its protective role, miRNA was extracted from 6 hearts following the IPC protocol; and then injected in vivo into the left ventricle wall in another group of 6 mice. Forty-eight hrs later, these mice were subjected to I/R injury in vivo by left coronary artery ligation for 30 min followed by reperfusion for 24 hr. In addition, a subset of mice was treated with miRNA inhibitors (methylated antisense miRNA) in conjunction with miRNA from IPC hearts. The results show that miRNA extracted from the IPC hearts reproduced a protective phenotype with significantly lower infarction (18.8 ± 2.5 %) in vivo as compared to saline-treated control (37.5 ± 2.2%). This protective effect was totally abolished by specific inhibitors of miRNA-1 and miRNA-21 (IS: 43.7 ± 2.1%).
CONCLUSION: miRNA extracted from preconditioned hearts shows a protective role against I/R injury. The detection of miRNA in preconditioned hearts offers a novel strategy in cardioprotection. Further studies are needed to identify the gene targets by which miRNA generate protective phenotype.