miR-1, miR-133a/b, and miR-208a in human fetal hearts correlate to the apoptotic and proliferation markers.

The heart is the first organ to function in the developing embryo. MicroRNAs (miRNAs) are small non-coding RNAs involved in the translational regulation of gene expression, which is beside transcriptional regulation crucial for the morphologic development of muscle tissue. The aim of our study was to test the hypothesis that the expression of miR-1, miR-133a/b, and miR-208a correlates with gestational age as well as with an apoptotic and proliferative index in the developing human heart. Our study included normal heart tissue samples obtained at autopsy from 46 fetuses, 12 children, and 15 adults. Proliferation and apoptosis were measured by the immunohistochemical detection of Ki67 and cleaved-CK18. Expression of miR-1, miR-133a, miR-133b, and miR-208a was measured using real-time PCR. We found a similar level of expression of miR-133a/b in fetal and children hearts that was different from the levels in healthy adults. We also found a correlation between a miR-208a expression to the gestational age of fetuses. We observed an inverse correlation between Ki67 expression and gestational age. Expression of Ki67 was positively correlated to the expression of miR-208a and miR-1, but inversely correlated to the expression of miR-133a/b. Expression of cleaved-CK18 was also inversely correlated to the expression of miR-133a/b. Our results showed a general decrease in the expression of miR-1 and an increase of miR-133a/b with increasing gestational age. We also found a general decrease in the expression of miR-208a, mimicking the expression of its host gene. Our results also suggest the involvement of miR-208a and miR-1 in the proliferation as well as anti-proliferative and anti-apoptotic roles of miR-133a/b.