Project description:Inducing cardiac myocytes to proliferate is considered a potential therapy to target heart disease, however, modulating cardiac myocyte proliferation has proven to be a technical challenge. The Hippo pathway is a kinase signaling cascade that regulates cell proliferation during the growth of the heart. Inhibition of the Hippo pathway increases the activation of the transcription factors YAP/TAZ, which translocate to the nucleus and upregulate transcription of pro-proliferative genes. The Hippo pathway regulates the proliferation of cancer cells, pluripotent stem cells, and epithelial cells through a cell-cell contact-dependent manner, however, it is unclear if cell density-dependent cell proliferation is a consistent feature in cardiac myocytes. Here, we used cultured human iPSC-derived cardiac myocytes (hiCMs) as a model system to investigate this concept. hiCMs have a comparable transcriptome to the immature cardiac myocytes that proliferate during heart development in vivo. Our data indicate that a dense syncytium of hiCMs can regain cell cycle activity and YAP expression and activity when plated sparsely or when density is reduced through wounding. We found that combining two small molecules, XMU-MP-1 and S1P, increased YAP activity and further enhanced proliferation of low-density hiCMs. Importantly, these compounds had no effect on hiCMs within a dense syncytium. These data add to a growing body of literature that link Hippo pathway regulation with cardiac myocyte proliferation and demonstrate that regulation is restricted to cells with reduced contact inhibition.
Project description:We report gene expression by RNAtag-seq after treatment with 75 different small molecule perturbations in culture of human iPSC-derived cardiac myocytes and genetically matched primary dermal fibroblasts. Perturbations were chosen from the SelleckChem Bioactive Library, among all molecules targeting any kinases or G-protein coupled receptors, and chosen to have as little overlap in annotated targets as possible. Based on these experiments (and others) we show that transcription factors important for cardiac development and cardiac myocyte identity maintenance were frequently up-regulated (i.e., "responsive") after small molecule perturbations of cultured iPSC-derived cardiac myocytes (i.e., responsive). We also show that the set of highly responsive transcription factors in fibroblasts are enriched for barriers to fibroblast reprogramming to iPSC.
