The Impact of Adiponectin, IGFBP1, and Osteopontin on Neonatal Cardiomyocyte Cell Cycle Regulation

Background: Cardiomyocytes (CM) in mammals lose their ability to proliferate shortly after birth. This might have clinical relevance, as preterm birth and congenital heart disease potentially result in myocardial hypoplasia in newborns and a reduced number of CMs cannot be replenished postnatally. In rodents, CM cell cycle arrest occurs within 2 weeks after birth, yet the underlying molecular mechanisms are incompletely understood. A previous proteomics screen identified alterations of growth factors and cytokines in the perinatal mouse heart. Among others, adiponectin, insulin-like growth factor binding protein 1 (IGFBP1), and osteopontin show increased levels in neonatal compared with fetal hearts. Therefore, the aim of this study was to investigate their potential to alter cell cycle activity in neonatal CMs.

Methods: Hearts and serum from fetal and neonatal mice were used to quantify cytokines using ELISA. H9c2 cells, a cardiomyoblast cell line from the embryonic rat heart, and primary neonatal mouse CM were treated in vitro with adiponectin, IGFBP1, or osteopontin under various conditions. Immunofluorescence microscopy was applied to quantify cell cycle activity via BrdU incorporation (indicating S-phase completion) and to determine CM size.

Results: Adiponectin, IGFBP1, and osteopontin show increased protein levels in the heart and serum of neonatal compared with fetal mice immediately after birth. BrdU incorporation revealed that none of the three factors stimulates cell cycle activity in H9c2 cells and neonatal mouse CM after 24 or 48 hours. In contrast, the percentage of BrdU-positive nuclei decreases in H9c2 cells after 24 hours of adiponectin and osteopontin treatment whereas IGFBP1 had no effect. Importantly, cell cycle activity decreases in neonatal mouse CM treated with adiponectin (4.6 ± 0.53% BrdU-positive CM nuclei, p < 0.05), osteopontin (4.8 ± 0.37%, p < 0.05), and IGFBP1 (4.5 ± 0.29%, p < 0.01) compared with 6.8 ± 0.63% in the control group after 24 hours. Additionally, cardiomyocyte size was decreased by adiponectin but not IGFBP1 treatment after 48 hours.

Conclusion: Our study shows that adiponectin, IGFBP1, and osteopontin inhibit cell cycle activity in neonatal mouse CMs in vitro while adiponectin furthermore decreases cell size. This supports the idea that the differential availability of growth factors and cytokines in the heart after birth might play a role in perinatal CM cell cycle arrest and the transition from hyperplastic to hypertrophic growth.

Publication History

Article published online:
11 February 2025