Transcriptome-wide profiling of thyroid hormone and adrenergic interactions in the mouse heart

During the first weeks after birth, cardiomyocytes within the mouse heart progressively exit the cell cycle, binucleate, and lose regenerative capacity. We have determined that combined pharmacological inhibition of thyroid hormone and adrenergic signaling during postnatal development robustly enhances cardiomyocyte proliferation, retention of diploid cardiomyocytes, and functional cardiac regeneration at postnatal day 14. In this study, we perform transcriptome-wide analyses to understand the genetic pathways regulated by thyroid hormone, alpha-adreneric, and beta-adrenergic signaling - individually and in combination - that promote cardiomyocyte cell-cycle arrest and loss of cardiac regenerative potential. Thyroid hormone was inhibited by treating pregnant female mice with chow containing propylthiouracil (thyroid hormone inhibitor; 0.15% in iodine deficient diet) starting at E13.5 and then maintained thereafter. Newborn pups were injected subcutaneously with phenoxybenzamine (alpha-adrenergic inhibitor; 10 ug/g/day) and/or propranolol (beta-adrenergic inhibitor; 20 ug/g/day) daily from P1 to P14. Using these drug administration protocols, thyroid hormone, alpha-adreneric receptor, and beta-adrenergic receptor signaling were inhibited individually or in combination and hearts were harvested at P14. Heart tissues were harvested at P14 from three animals treated with each experimental condition, total RNA was extracted, and RNA-seq was performed to identify differentially expressed genes.