Abstract 3223: miR-21 Promotes Cardiomyocyte Regeneration in Ischemic Mouse Heart by Triggering Stem Cell Activation and Cardiomyocyte-Committed Differentiation
BACKGROUND: Micro-RNAs are non-coding RNAs of 18 –24 nucleotides that are involved in post-transcriptional regulation of protein expression. microRNA-21 (miR-21) is induced following ischemic preconditioning and reduces infarct size after myocardial ischemia/reperfusion injury. However, the role of miR-21 in cardiac regeneration is currently unknown. We hypothesized that miR-21 promotes cardiomyocyte regeneration in the ischemic heart by triggering stem cell activation and cardiomyocyte-committed differentiation.
METHODS/RESULTS: Mice were subjected to ischemia/reperfusion injury by left coronary artery ligation for 30 min followed by reperfusion. Seven days later, one group was treated with chemically synthesized miR-21 (5 μg per heart) and the other with volume-matched PBS (30 μl) through direct cardiac injection. To label regenerated cells, both groups were treated with bromode-oxyuridin (BrdU) (50 mg/kg, i.p. daily, plus 1mg/ml in drinking water). Hearts were sampled after 7- and 21-day treatment for evaluation of cardiomyocyte regeneration. The miR-21-injected group had a smaller scar area than the PBS group (2.8±0.5% vs. 13.3±3.5% of tissue section area at 21 days). BrdU labeling detected more newly formed cells in the miR-21 group than in the PBS group (22±4 vs. 2±2 per 200x field), confirming augmented regeneration with miR-21. Moreover, immunohistochemistry results identified cells with positive stem cell markers which were present in the border zone of the miR-21-treated hearts (8±3 and 7±2 per 200x field for c-kit and Mdr-1 positive cells, respectively), that were nearly absent in the PBS group (1±1 for both markers). Additionally, RT-PCR and immunoblotting detected increases in both mRNA (+1.53 fold) and protein (+1.77 fold) of GATA-4 with miR-21 group compared to PBS. Immunohistochemistry data demonstrated that the increased GATA-4 positive cells were present in the border zone in the miR-21 group, indicating more cardiomyocyte-committed differentiation, which may account for the reduced scar area observed in the miR-21 group.
CONCLUSION: miR-21 plays a key role in cardiac regeneration following ischemia in mice, possibly through triggering stem cell activation and subsequent cardiomyocyte-committed differentiation.