Myocardin regulates BMP10 expression and is required for heart development
Jianhe Huang, … , Xiaohong Zhu, Michael S. Parmacek
Jianhe Huang, … , Xiaohong Zhu, Michael S. Parmacek
Published September 17, 2012
Citation Information: J Clin Invest. 2012;122(10):3678-3691. https://doi.org/10.1172/JCI63635.
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Myocardin regulates BMP10 expression and is required for heart development

Abstract

Myocardin is a muscle lineage–restricted transcriptional coactivator that has been shown to transduce extracellular signals to the nucleus required for SMC differentiation. We now report the discovery of a myocardin/BMP10 (where BMP10 indicates bone morphogenetic protein 10) signaling pathway required for cardiac growth, chamber maturation, and embryonic survival. Myocardin-null (Myocd) embryos and embryos harboring a cardiomyocyte-restricted mutation in the Myocd gene exhibited myocardial hypoplasia, defective atrial and ventricular chamber maturation, heart failure, and embryonic lethality. Cardiac hypoplasia was caused by decreased cardiomyocyte proliferation accompanied by a dramatic increase in programmed cell death. Defective chamber maturation and the block in cardiomyocyte proliferation were caused in part by a block in BMP10 signaling. Myocardin transactivated the Bmp10 gene via binding of a serum response factor–myocardin protein complex to a nonconsensus CArG element in the Bmp10 promoter. Expression of p57kip2, a BMP10-regulated cyclin-dependent kinase inhibitor, was induced in Myocd–/– hearts, while BMP10-activated cardiogenic transcription factors, including NKX2.5 and MEF2c, were repressed. Remarkably, when embryonic Myocd–/– hearts were cultured ex vivo in BMP10-conditioned medium, the defects in cardiomyocyte proliferation and p57kip2 expression were rescued. Taken together, these data identify a heretofore undescribed myocardin/BMP10 signaling pathway that regulates cardiomyocyte proliferation and apoptosis in the embryonic heart.

Authors

Jianhe Huang, John Elicker, Nina Bowens, Xi Liu, Lan Cheng, Thomas P. Cappola, Xiaohong Zhu, Michael S. Parmacek

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Figure 8

Bmp10 rescues the defect in cardiomyocyte proliferation and p57kip2 expression observed in Myocd–/– hearts.

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Bmp10 rescues the defect in cardiomyocyte proliferation and p57kip2 expr...
E9.5 WT and Myocd–/– mutant hearts were grown for 48 hours in conditioned medium harvested from NIH3T3 cells that were stably transduced with lentivirus encoding EGFP (control) or mouse Bmp10 (+ Bmp10) (n = 5 hearts per group). (A–C) Whole mount of WT heart (A), Myocd–/– heart grown in control medium (B), and Myocd–/– heart grown in Bmp10-conditioned medium (C). Myocd–/– hearts were smaller than WT hearts and beat more slowly and less vigorously. See also Supplemental Videos 7–10. (D–F) DAPI staining (blue nuclear stain) of WT, Myocd–/–, and Myocd–/– + Bmp10 explanted hearts. Scale bars in microns are shown. (G–I) BrdU incorporation in WT, Myocd–/–, and Myocd–/– explanted hearts grown in Bmp10-conditioned medium. Sections of explanted hearts were immunostained with BrdU antibody (orange stain). BrdU-positive cardiomyocytes per high power field were quantified by a blinded observer, and data are expressed as mean percentage of BrdU-positive cardiomyocytes ± SEM. (J–L) pHH3 expression (orange stain) in WT, Myocd–/–, and Myocd–/– explanted hearts grown in Bmp10 conditioned medium. Cardiomyocytes undergoing mitosis in prophase/metaphase exhibited centronuclear staining, while cardiomyocytes in anaphase (arrowheads) exhibit speckled nuclear staining. pHH3-positive cardiomyocytes per high power field were quantified by a blinded observer and data expressed as mean percentage of pHH3-positive cardiomyocytes ± SEM. (M–O) Sections immunostained for p57kip2 (brown stain) demonstrating marked increased in p57kip2 in Myocd–/– heart, which decreases significantly when grown in Bmp10-conditioned medium.