Abstract 441: Endogenous MicroRNAs Induced In vivo by Whole Body Heat Shock Limits Myocardial Infarct Size Following Ischemia/Reperfusion Injury in Mouse
Background: Non-coding microRNAs (miRNAs) have emerged as important gene regulators, rather than “evolutionary transcriptional debris”. They are a large class of endogenous short RNAs that repress gene expression. The role of miRNAs in myocardial protection has not been investigated. Whole body heat shock is a cardioprotective strategy that induces expression of therapeutic genes and development of ischemic tolerance. We hypothesized that miRNA induced in vivo by heat shock can protect heart against ischemia/reperfusion.
Methods & Results: ICR mice were heat-shocked (HS) at 42°C for 15 minutes. miRNAs were isolated from HS-mice using chemical and solid phase extraction techniques. The extracted miRNAs (40 μg) were injected (ip) into non-HS mice. Twenty-four hrs later, hearts were isolated and subjected to 30 min of global ischemia followed by 30 min of reperfusion in Langendorff mode. Infarct size (IS) was determined by computer morphometry of tetrazolium stained sections. Heat shock increased miRNA-1 (78%), miRNA-21 (103%) and miRNA-24 (61%) as compared to non-HS controls (p<0.05, n=3). Injection of the miRNAs into non-HS mice reduced infarct size as compared to non-miRNA treated group (Figure⇓). In addition, chemically synthesized miRNA-21 reduced infarct size, but the reduction was abolished by methylated antisense miRNA-21. miRNA treated mice showed 113% increase in BAG3, an anti-apoptotic Bcl-2 like gene, and 58% repression of Fas, a pro-apoptotic gene (p<0.05, n=3).
Conclusion: Heat shock preconditioning induces endogenous miRNAs that generate cardioprotective phenotype resistant to I/R injury, possibly through regulation of apoptotic genes Bag3 and Fas.