MicroRNA Regulation of Hsp70.3 Protein Expression in Late Ischemic Preconditioning

Introduction We showed that the Hsp70.3 isoform is induced by NF‐κB after late ischemic preconditioning (IPC) and contributes to cardioprotection. However, the nearly identical Hsp70.1 isoform does not contribute to IPC induced cardioprotection. We propose that the functional differences between the twoHSP70s are due to post‐transcriptional regulation involving the 3' UTRs, which are divergent. Results Though NF‐κB inhibition completely reduces protein expression, it only partially reduces Hsp70.3 mRNA levels, showing that Hsp70.3 is regulated by both pre‐ and post‐transcriptional mechanisms after IPC. We hypothesized that an IPC stimulus reduces expression of Hsp70.3‐suppressing miRNA(s) allowing for post‐transcriptional stabilization of Hsp70.3 mRNA and increased Hsp70.3 protein levels. We assessed in vivo levels of 356 miRNAs in a mouse model of IPC, to identify miRNAs that are; 1) downregulated after IPC, and 2) predicted to target Hsp70.3. We identified miR‐378* as the only miRNA of those surveyed to meet these criteria and demonstrated functional inhibition of Hsp70.3 by miR‐378*. Discussion This work demonstrates post‐transcriptional (via miRNA) regulation of Hsp70.3. It appears that coordinated transcriptional upregulation (promoter) as well as suppression of targeting miRNAs are involved in increasing Hsp70.3 protein expression after IPC. This work was supported by the American Society of Pharmacology and Experimental Therapeutics (ASPET) with funds generously provided by ASPET and the University of Cincinnati.