Abstract 1456: Microrna-499 Regulates (cardio)myocyte Differentiation in Human-Derived Cardiomyocyte Progenitor Cells

Abstract

To improve regeneration of the injured myocardium, it is necessary to enhance the intrinsic capacity of the heart to regenerate itself and/or replace the damaged tissue by cell transplantation. One of the potential sources for cell replacement therapy are heart-derived progenitor cells. Cardiomyocyte progenitor cells (CMPCs) are obtained from human fetal hearts and adult human biopsies, easily expanded in culture, and efficiently differentiated into beating cardiomyocytes. Recently, several studies have demonstrated that microRNAs (miRNAs) are important for transcriptional regulation during angiogenesis, heart development, and maintenance of stem cell populations by translational repression. We hypothesize that, since miRNAs regulate stem cell maintenance and differentiation, miRNAs are involved in differentiation of human cardiomyocyte progenitor cells in vitro . Methods and results: Human fetal CMPCs were isolated, cultured, and efficiently differentiated into beating cardiomyocytes. miRNA expression was profiled in proliferating and differentiated CMPCs. We observed that miRNA-499 was highly upregulated upon differentiation (>100 fold, microarray and qRT-PCR). Since tissue distribution of miRNA-499 was unknown, several mouse tissues were analyzed. qRT-PCR demonstrated that miRNA-499 is highly enriched in cardiac tissue. This was confirmed via in situ-hybridization, miRNA-499 was localized in cardiomyocytes in human fetal and adult hearts. Transient transfection of miRNA- 499 in undifferentiated CMPCs reduced their proliferation rate by 15% (MTT assay and FACS analysis). Moreover, upon miR-499 transfection spontaneous beating was observed earlier and expression levels of cardiac troponin T, alpha-cardiac actinin, and Mlc-2v was increased. This enhanced cardiomyocyte differentiation occurred via repression of Sox6. Conclusion: Our results demonstrate a strong regulatory role of miRNAs in human CMPC proliferation and differentiation into cardiomyocytes. By modulating miRNA-499 expression levels, the differentiation of CMPCs is affected, resulting in enhanced cardiomyogenesis.