Abstract 141: Histone Methyltransferase Setdb2 is important for miRNA mediated cardiac reprogramming

Abstract

Rationale: Regeneration of damaged cardiac tissue after injury presents a daunting challenge in cardiovascular medicine. Recent developments in reprogramming of somatic cells directly to cells of other lineages have raised the possibility of using this approach for cardiac regenerative therapy. Our group recently demonstrated successful miRNA mediated cardiac reprogramming in vitro and in vivo using a combination of miRNAs 1, 133, 206 and 499. Although, the molecular mechanisms underlying miRNA mediated fibroblast reprogramming to cardiomyocytes are yet unknown, accumulating evidence suggest that reprogramming acts through distinct phases and that histone modifications play an important role in these processes. Objective: Identify key genes involved in initiating miRNA mediated reprogramming via histone modifications. Methods and Results: For this, we analyzed the expression levels of 81 different genes involved in chromatin modification 4 days after miRNA transfection using PCR arrays. This analysis revealed that 6 of the 81 tested genes showed differential gene expression (≤-1.5-fold and p <0.02). JAK inhibitor-1 treatment, known for increasing reprogramming efficiency, further enhanced gene expression changes in 5 of these 6 genes. Setdb2, an H3K9 methyltransferase, was one of the most down-regulated targets 4 days after miRNA transfection (-1.4 fold, p<0.001). This effect was enhanced further when miRNAs were combined with the JAK inhibitor-1 (-2.6 fold, p<0.001). Silencing of Setdb2 using siRNAs further accentuated miRNA cardiac reprogramming as measured by cardiac transcription factor expression at 3 days and 6 days post treatment. Similar trends were observed by FACS analysis detecting increased percentage of αMHC-positive cells in siRNA treated fibroblasts compared to control treated only with the miRNA combination. Interestingly, our data showed that Setdb2 silencing alone was sufficient to initiate cardiac reprogramming, suggesting that Setdb2 might play a crucial role in defining cardiac cell fate. Conclusion: In conclusion our results indicate that Setdb2 down-regulation plays an important role in the direct reprogramming of fibroblasts to cardiomyocyte-like cells.