Expression of microRNAs and their target mRNAs in human stem cell-derived cardiomyocyte clusters and in heart tissue.

Recent studies have shown that microRNAs (miRNAs) act as posttranscriptional regulators and that they play important roles during heart development and in cardiac function. Thus, they may provide new means of altering stem cell fate and differentiation processes. However, information about the correlation between global miRNA and mRNA expression in cardiomyocyte clusters (CMCs) derived from human embryonic stem cells (hESC) and in fetal and adult heart tissue is lacking. In the present study the global miRNA and mRNA expression in hESC-derived CMCs and in fetal and adult heart tissue was investigated in parallel using microarrays. Target genes for the differentially expressed miRNAs were predicted using computational methods, and the concordance in miRNA expression and mRNA levels of potential target genes was determined across the experimental samples. The biology of the predicted target genes was further explored regarding their molecular functions and involvement in known regulatory pathways. A clear correlation between the global miRNA expression and corresponding target mRNA expression was observed. Using three different sources of cardiac tissue-like samples, we defined the similarities between in vitro hESC-derived CMCs and their in vivo counterparts. The results are in line with previously reported observations that miRNAs repress mRNA expression and additionally identify a number of novel miRNAs with potential important roles in human cardiac tissue. The concordant miRNA expression pattern observed among all the cardiac tissue-like samples analyzed here provide a starting point for future ambitious studies aiming towards assessment of the functional roles of specific miRNAs during cardiomyocyte differentiation.