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Repression of Ect2 induces cytokinesis failure and decreases heart muscle cell proliferation in congenital heart disease

ABSTRACT: Proliferation of heart muscle cells (cardiomyocytes) is the basis for heart development and regeneration. In mammals, cardiomyocytes become binucleated, which is thought to limit their proliferative capacity, but mechanisms are unknown. Here, we show the detailed mechanisms of formation of binucleated cardiomyocytes and how these mechanisms are dysregulated in congenital heart disease (CHD). Cardiomyocytes become binucleated by failing the last stage of cytokinesis, abscission. We identified the underlying molecular mechanism with single-cell transcriptional profiling, which showed repression of the cytokinesis gene Ect2, a Rho-guanine-nucleotide exchange factor. Inactivating Ect2 tripled the proportion of binucleated cardiomyocytes and reduced the number of cardiomyocytes by 34% in newborn mice, which was lethal. Cardiomyocyte-specific overexpression of Ect2 in transgenic mice decreased cytokinesis failure. We demonstrate that the Ect2 gene is regulated by the Hippo tumor suppressor pathway, and upstream of that, by β-adrenergic receptor signaling. In neonatal mice, stimulating β-adrenergic signaling pathway output with forskolin decreased the number of cardiomyocytes, and administration of β-blockers increased the number of cardiomyocytes. Finally, we show that patients with tetralogy of Fallot with pulmonary stenosis (ToF/PS), a common type of CHD, develop a 2.2-fold increase in bi- and multi-nucleated cardiomyocytes. Using in vivo labeling of one ToF/PS patient with 15N-thymidine, followed by imaging mass spectrometry, we demonstrate that this increase happens after birth. Organotypic cultures of myocardium from infants with ToF/PS showed that cardiomyocyte binucleation could be reduced with β-blockers. These results demonstrate how cardiomyocyte proliferation stops and provide the basis for new therapeutic strategies to increase cardiomyocyte proliferation in patients with CHD.

ORGANISM(S): Mus musculus

PROVIDER: GSE108359 | GEO | 2019/09/30

REPOSITORIES: GEO

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Project description:Cardiomyocytes exhibit differential growth patterns throughout development. In fetal life the increase in cardiac mass is associated with hyperplastic growth and cardiomyocyte proliferation. The majority of fetal cardiomyocytes are also mononucleated. During the early neonatal period in mice there is a switch from hyperplastic to hypertrophic growth of cardiomyocytes. This period is characterized by bi-nucleation and polyploidization of cardiomyocyte nuclei and a decreased capacity for cardiomyocytes to proliferate and complete cytokinesis. Increases in myocardial mass occur predominantly via hypertrophic growth. Adult mammalian cardiomyocytes are generally accepted to have little or no proliferative capacity and to be terminally withdrawn from the cell cycle. The vast majority of adult murine cardiomyocytes are bi-nucleated. The present study sought to accurately establish the growth pattern of cardiomyocytes throughout development in mice and identify genes associated with the switch from hyperplastic to hypertrophic growth. These cell cycle associated genes are crucial to the understanding of the mechanisms of bi-nucleation, polyploidization and hypertrophy in the neonatal period. Cardiomyocytes were FACS sorted from the hearts of ED11-12 embryos, neonatal day 3-4 and adult (10 week) eGFP ?-MHC mice whereby GFP expression is driven constitutively by the ?-MHC promoter. Gene analyses identified genes whose expression was predicted to be particular to day 3 -4 neonatal cardiomyocytes, compared to embryonic or adult cells. Cell cycle associated genes are crucial to the understanding of the mechanisms of bi-nucleation and hypertrophy in the neonatal period, and offer attractive candidates for manipulation. Total RNA obtained from isolated cardiomyocytes from ED11-12; Neonatal day 3-4 and adult timepoints compared with each other. Several hearts per sample, RNA was pooled within samples. FACS samples were prepared in the following manner: embryonic, neonatal and adult hearts were dissected and dissociated to single cell solution with Liberase Blendzyme 3 (0.1 mg/ml) (Roche Diagnostics), washed and spun down and resuspended in cardiomyocyte isolation buffer (130 mM NaCl; 5 mM KCl; 1.2 mM KH2PO4; 6 mM HEPES; 5 mM NaHCO3; 1 mM MgCl2; 5 mM Glucose).

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Repression of Ect2 induces cytokinesis failure and decreases heart muscle cell proliferation in congenital heart disease

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