Abstract
MicroRNAs (miRNA), small sequences of non-coding RNA which interact with complementary sequences on the 3’untranslated region of target messenger RNAs to modulate translation, have a pivotal role in the development of the heart and its response to injury. Myocardial infarction (MI) triggers a dynamic miRNA response with the potential of yielding therapeutic targets. Following miRNA array profiling in rat hearts 2, 7 and 14 days after MI induced by coronary ligation, we identified a progressive time-dependent up-regulation of miR-31 compared to sham rats. Increase of miR-31 in heart tissue in the acute and subacute phases after MI (up to 90-fold) was also detected by Real-Time PCR (P=0.02 at day 2; P<0.0001 at days 7 and 14, vs. sham). We found that miR-31 has a repressive effect on tissue mRNA expression of cardiac troponin-T (TNNT2), E2F transcription factor 6 (E2F6) and mineralocorticoid receptor (NR3C2). Reporter gene assays showed that miR-31 targets the 3′UTR of these genes, with a marked repressive effect on TNNT2. In vitro, exposure to hypoxia significantly induced the expression of miR-31 in neonatal rat cardiomyocytes (nRCM), rat cardiac fibroblasts (nRCF) and cardiomyoblasts (H9C2) and suppressed the expression of TNNT2, E2F6 and NR3C2 in nRCM and H9C2 cells, and of E2F6 and NR3C2 in nRCF. LNA-based oligonucleotide inhibition of miR-31(miR-31i) in vitro reversed its repressive effect on translation from target genes. Therapeutic modulation of miR-31 expression in vivo after MI via subcutaneous administration of miR-31i (25mg/Kg/q2w) in rats, led to cardiac repression of miR-31 and subsequent enhanced expression of target genes. Also, miR-31i led to preservation of cardiac function and structure by day 14 after treatment. An absolute 10% improvement in left ventricular (LV) ejection fraction (EF) was observed in miR-31i-treated rats from day 2 to 16 after MI, while control rats that received scrambled LNA inhibitor or placebo displayed 23% deterioration in EF (n=6-8/group, P<0.0001). We conclude that miR-31 induction after MI is deleterious to cardiac function and plays an important role in adverse remodeling, while its therapeutic inhibition in vivo ameliorates cardiac dysfunction and prevents the development of post-ischemic heart failure.
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