Mature and immature microRNA ratios in cultured rat cardiomyocytes during anoxia-reoxygenation.

Background: The critical role of microRNAs (miRNAs) in the global control of gene expression in the heart has recently been postulated; however, the mechanisms of miRNA regulation in cardiac pathology are not clear.

Objective: To evaluate the levels of miR-1, miR-208a and miR-29a expressed in neonatal rat cardiomyocytes during anoxia-reoxygenation (AR).

Methods: Reverse transcription coupled with real-time polymerase chain reaction was used to evaluate the level of mature and immature miRNAs in cardiomyocyte culture during AR.

Results: THE INITIAL LEVELS OF THE MATURE AND IMMATURE MIRNAS WERE DIFFERENT: mature - miR-1 7.46±4.440, miR-208a 0.02±0.015 and miR-29a 5.60±2.060; immature - miR-1 0.02±0.007, miR-208a 0.05±0.029 and miR-29a 0.01±0.008. The most prominent changes were observed for immature miRNAs during AR, with immature miR-1 and miR-29a expressed at significantly higher levels during remote reoxygenation (AR [0.5 h/24 h]) compared with control, while the level of expressed immature miR-208a was significantly decreased during acute reoxygenation (AR [0.5 h /1 h]) and returned to control levels during remote reoxygenation (AR [0.5h /24 h]). Also, the ratios of mature to immature miRNAs were significantly increased during acute reoxygenation for miR-1 and miR-208a, returning to control levels during remote reoxygenation, while for miR-29a, this ratio had the progressive tendency to decrease under AR.

Conclusion: The discordance between the estimated levels of mature and immature miRNA during AR supports the hypothesis that transcriptional and post-transcriptional regulatory mechanisms at the miRNA level play a role in the response of cardiomyocytes to AR, and could be a contributing factor in the differential resistance of cardiomyocytes to AR.