Stem Cells. 2018 Oct 30. doi: 10.1002/stem.2943. [Epub ahead of print]

SMAD4 is essential for human cardiac mesodermal precursor cell formation.

Xu J¹, Gruber PJ², Chien KR^1,3.

Abstract

Understanding stage-specific molecular mechanisms of human cardiomyocyte progenitor formation and subsequent differentiation are critical to identify pathways that might lead to congenital cardiovascular defects and malformations. In particular, gene mutations in the TGF-β superfamily signaling pathways can cause human congenital heart defects, and murine loss of function studies of a central component in this pathway, Smad4, leads to early embryonic lethality. To define the role of SMAD4 at the earliest stages of human cardiogenesis, we generated SMAD4 mutant human embryonic stem cells (hESC). Herein, we show that the loss of SMAD4 has no effect on hESC self-renewal, or neuroectoderm formation, but is essential for the formation of cardiac mesoderm, with a subsequent complete loss of cardiomyocyte formation during human ES cell cardiogenesis. Via transcriptional profiling, we show that SMAD4 mutant cell lines fail to generate cardiac mesodermal precursors, clarifying a role of NODAL/SMAD4 signaling in cardiac mesodermal precursor formation via enhancing the expression of primitive streak genes. Since SMAD4 relative pathways have been linked to congenital malformations, it will become of interest to determine whether these may due, in part, to defective cell fate decision during cardiac mesodermal precursor formation.