Cardiomyocyte ploidy is dynamic during postnatal development and varies across genetic backgrounds

Area of Science:

• Cardiovascular Biology
• Cell Biology
• Developmental Biology

Background:

• Somatic polyploidization, increasing DNA content for growth, occurs in cardiomyocytes but often reduces proliferation.
• Genetics influence cardiomyocyte ploidy, yet developmental pathways are poorly understood.
• Hypertrophy is considered the primary postnatal heart growth mechanism.

Purpose of the Study:

• To investigate cardiomyocyte ploidy dynamics during development in divergent mouse strains.
• To identify genetic factors influencing cardiomyocyte cell cycle activity and ploidy.
• To challenge the sole reliance on hypertrophy for postnatal cardiac growth.

Main Methods:

• Comparative analysis of cardiomyocyte number, cell cycle activity, and ploidy in C57BL/6J and A/J mice.
• Assessment of ploidy dynamics across developmental stages.
• Investigation of Tnni3k and Runx1 roles in cardiomyocyte ploidy and cell division.

Main Results:

• Significant differences in cardiomyocyte ploidy composition and developmental progression were observed between the two mouse strains.
• Tnni3k was confirmed as a mediator of cardiomyocyte ploidy.
• Runx1 was identified as a novel factor in cardiomyocyte ploidy dynamics and cell division during development and after injury.

Conclusions:

• Cardiomyocyte polyploidization follows distinct developmental paths influenced by genetic background.
• Runx1 plays a critical role in cardiomyocyte cell division and ploidy regulation.
• Cardiac growth may involve mechanisms beyond hypertrophy, including developmental polyploidization pathways.