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 2

Cardiomyopathy can be prevented with early reintroduction of MYBPC3.

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Cardiomyopathy can be prevented with early reintroduction of MYBPC3. (A)...
(A) Schematic illustration of the transgenic line that allows conditional reactivation of MYBPC3 after administration of tamoxifen (Null R) (top). Western blot demonstrating successful reactivation of MYBPC3 protein expression at P10 in Null R mice injected with tamoxifen at P2 (Null R-P2) (bottom). (B) Phenotypic assessment of control (Ctl), MYBPC3-null (Null), and Null R-P2 hearts at P25 as determined by M-mode echocardiography (top), H&E–stained heart cross sections (middle, scale bar: 1 mm), and wheat-germ agglutinin (WGA) immunohistochemical staining (bottom, scale bar: 30 μm). (C and D) Fractional shortening (FS) (C) and interventricular septal thickness diastole at end diastole (IVSd) (D) of 25-day-old Ctl (n = 5), Null (n = 5), and Null R-P2 (n = 6) mice. (E and F) Heart weight (HW) (E) and HW to tibia length ratio (HW/TL) (F) of 25-day-old Ctl (n = 12), Null (n = 7), and Null R-P2 (n = 6) hearts. (G) Cardiomyocyte cross-sectional area of 25-day-old Ctl (n = 5), Null (n = 5), and Null R-P2 (n = 5) hearts as assessed by WGA staining of left ventricle cross sections. (H) Western blot of MYBPC3 protein levels from conditional reactivation mice administered different doses of tamoxifen (top). Percentage of MYBPC3 protein relative to 200 mg/kg tamoxifen dose (normalized to β-actin) (bottom) (n = 3/group). (I and J) P25 HW (I) and HW/TL (J) of Ctl (n = 12), Null (n = 7), and conditional reactivation mice administered different doses of tamoxifen: 200 mg/kg (n = 6), 25 mg/kg tamoxifen (n = 4), 12.5 mg/kg tamoxifen (n = 3) at P2. All results are shown as mean ± SEM. Statistical analysis performed using an unpaired, 2-tailed Student’s t test. N.S., not significant.