No Differences in Cell Cycle Activity between Right and Left Ventricular Myocytes in Neonatal Mice

Background: After birth, cardiomyocytes (CM) leave the cell cycle, lose their ability to proliferate and remain predominantly in a postmitotic state throughout life. It is not known which stimuli lead to the cell cycle arrest. One reason could be the change in postnatal afterload. Postpartum, left-ventricular afterload increases while right-ventricular afterload decreases. Thus, the comparison of both ventricles allows investigation of the influence of afterload on cell proliferation rate.

Method: CM proliferation was studied in (neonatal) mice at postnatal days (PN) 0, 1, 3, 7, 10, and 21. To determine CM proliferation rate immunofluorescence staining for phosphohistone 3 (PH3; detecting mitotic cells) and α-actinin-2 as a CM marker was performed. Three-dimensional z-stack images were acquired with confocal microscopy. Additionally mRNA expression of a panel of mitosis-related genes (anilin, aurora-A kinase, polo-like kinase 1, survivin, cyclin B1, and K_i-67) was measured by qPCR in three mice at each time point.

Results: mRNA expression did not differ between the right and left ventricle. There was a small increase in expression for Ki-67, survivin and anilin (peak at PN3). In all genes analyzed, the highest expression level ever reached was before PN10. From PN10 on, all genes showed a steady decrease and reached their minimum at PN21. Similar to the ventricular gene expression levels, the number of PH3 positive CM nuclei showed a gradual and steady decrease from PN3 to PN21. Hardly any mitotic CM was observed after PN14. The expression pattern was similar between the right and left ventricles.

Conclusion: Our data showed the typical decrease of cell cycle activity in postnatal cardiomyocytes within the first 21 days after birth in mice. No differences in the degree of cardiomyocyte proliferation rate were observed between the left and right ventricles. Thus the change in postnatal afterload does not seem to have an effect on neonatal cell cycle activity.

Publication History

Article published online:
12 February 2022