Alterations in sarcomere function modify the hyperplastic to hypertrophic transition phase of mammalian cardiomyocyte development
Benjamin R. Nixon, Alexandra F. Williams, Michael S. Glennon, Alejandro E. de Feria, Sara C. Sebag, H. Scott Baldwin, Jason R. Becker
Benjamin R. Nixon, Alexandra F. Williams, Michael S. Glennon, Alejandro E. de Feria, Sara C. Sebag, H. Scott Baldwin, Jason R. Becker
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Research Article Cardiology Development

Alterations in sarcomere function modify the hyperplastic to hypertrophic transition phase of mammalian cardiomyocyte development

Abstract

It remains unclear how perturbations in cardiomyocyte sarcomere function alter postnatal heart development. We utilized murine models that allowed manipulation of cardiac myosin-binding protein C (MYBPC3) expression at critical stages of cardiac ontogeny to study the response of the postnatal heart to disrupted sarcomere function. We discovered that the hyperplastic to hypertrophic transition phase of mammalian heart development was altered in mice lacking MYBPC3 and this was the critical period for subsequent development of cardiomyopathy. Specifically, MYBPC3-null hearts developed evidence of increased cardiomyocyte endoreplication, which was accompanied by enhanced expression of cell cycle stimulatory cyclins and increased phosphorylation of retinoblastoma protein. Interestingly, this response was self-limited at later developmental time points by an upregulation of the cyclin-dependent kinase inhibitor p21. These results provide valuable insights into how alterations in sarcomere protein function modify postnatal heart development and highlight the potential for targeting cell cycle regulatory pathways to counteract cardiomyopathic stimuli.

Authors

Benjamin R. Nixon, Alexandra F. Williams, Michael S. Glennon, Alejandro E. de Feria, Sara C. Sebag, H. Scott Baldwin, Jason R. Becker

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Figure 4

MYBPC3 cardiomyopathy alters the hyperplastic to hypertrophic transition phase of heart development.

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MYBPC3 cardiomyopathy alters the hyperplastic to hypertrophic transition...
(A) Immunofluorescence staining of Ki67 (red) in control (Ctl) and MYBPC3-null (Null) myocardial tissue at P2, P7, and P25. Cardiomyocytes were identified with sarcomeric α-actinin (green), with nuclei labeled with DAPI (blue). Scale bars: 100 μm. (B) Quantification of Ki67-positive cardiomyocytes (CMs) in Ctl (n = 3 per age) and Null (n = 3 per age) hearts (minimum 4,000 cells per sample). (C) Quantification of phospho-histone H3–positive (pH H3–positive) CMs in Ctl (n = 3 per age) and Null (n = 3 per age) hearts (minimum 4,000 cells per sample). (D) Immunofluorescence staining of aurora B (red) in myocardial tissue demonstrating aurora B staining in CM cleavage furrow (left), CM non–cleavage furrow (middle), and non-CM aurora B cleavage furrow (right). CMs were identified with sarcomeric α-actinin (green), with nuclei labeled with DAPI (blue). Scale bars: 100 μm. (E) Quantification of aurora B cleavage furrow–positive CMs per mm2 in Ctl (n = 3 per age) and Null (n = 3 per age) hearts. (F–H) Quantification of Ki67 (F), pH H3 (G), and aurora B cleavage furrow CMs (H) from Ctl (n = 3), Null (n = 3), and MYBPC3 conditional reactivation administered tamoxifen at P2 (Null R-P2) (n = 3). (I) Quantification of total CMs per left ventricular (LV) wall section in Ctl (n = 5), Null (n = 5), and Null R-P2 (n = 5) hearts. All results are shown as mean ± SEM. Statistical analysis performed using an unpaired, 2-tailed Student’s t test. N.S., not significant.