Visualizing Hormonal Effects on Cardiomyocyte Hypertrophic Growth Dynamics Using Digital Holographic Microscopy: Does Size Matter?

Heart disease continues to be the leading cause of death in the United States. Humans are unable to regenerate their heart tissue following an injury. However, neonatal mice are able to regenerate their heart tissue when cardiomyocytes (CMs) proliferate. This regenerative ability is lost approximately one week after birth when proliferating mononucleated CMs become binucleated and can no longer complete the cell-cycle. Recent studies have shown the combined inhibition of thyroid hormone (T3) and norepinephrine (NE) increases CM proliferation, promotes heart regeneration, and reduces cell size in vivo . Using digital holographic microscopy, the aim of this study was to (1) validate the novel Halomonitor approach and (2) visualize and quantify the effects of T3 and NE on cardiomyocyte size. CMs were isolated from neonatal rats 1 to 2 days after birth which were then treated with NE and/or T3 in serum-free culture. Live cell imaging was visualized utilizing digital holographic microscopy and changes in CM dynamics and morphology were quantitatively tracked and analyzed using HoloMonitor software. The results from this study validate the HoloMonitor technology by demonstrating that NE induced hypertrophy in CMs after 12 hours. Our results also demonstrate the ability of HaloMonitor technology to differentiate between CMs and non-CMs in living, serum-free culture, while also studying and quantifying their dynamics in vitro . Lastly, our data shows that T3 has little effect on CM growth and that NE decreased CM motility.