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:Applications of human induced pluripotent stem cell derived-cardiac myocytes (hiPSC-CMs) would be strengthened by the ability to generate specific cardiac myocyte (CM) lineages. However, purification of lineage-specific hiPSC-CMs is limited by the lack of cell marking techniques. Here, we have developed an iPSC-CM marking system using recombinant adenoviral reporter constructs with atrial- or ventricular-specific myosin light chain-2 (MLC-2) promoters. MLC-2a and MLC-2v selected hiPSC-CMs were purified by fluorescence-activated cell sorting and their biochemical and electrophysiological phenotypes analyzed. We demonstrate that the phenotype of both populations remained stable in culture and they expressed the expected sarcomeric proteins, gap junction proteins and chamber-specific transcription factors. Compared to MLC-2a cells, MLC-2v selected CMs had larger action potential amplitudes and durations. In addition, by immunofluorescence, we showed that MLC-2 isoform expression can be used to enrich hiPSC-CM consistent with early atrial and ventricular myocyte lineages. However, only the ventricular myosin light chain-2 promoter was able to purify a highly homogeneous population of iPSC-CMs. Using this approach, it is now possible to develop ventricular-specific disease models using iPSC-CMs while atrial-specific iPSC-CM cultures may require additional chamber-specific markers.
Project description:RationaleDuring each beat, cardiac myocytes (CMs) generate the mechanical output necessary for heart function through contractile mechanisms that involve shortening of sarcomeres along myofibrils. Human-induced pluripotent stem cells (hiPSCs) can be differentiated into CMs (hiPSC-CMs) that model cardiac contractile mechanical output more robustly when micropatterned into physiological shapes. Quantifying the mechanical output of these cells enables us to assay cardiac activity in a dish.ObjectiveWe sought to develop a computational platform that integrates analytic approaches to quantify the mechanical output of single micropatterned hiPSC-CMs from microscopy videos.Methods and resultsWe micropatterned single hiPSC-CMs on deformable polyacrylamide substrates containing fluorescent microbeads. We acquired videos of single beating cells, of microbead displacement during contractions, and of fluorescently labeled myofibrils. These videos were independently analyzed to obtain parameters that capture the mechanical output of the imaged single cells. We also developed novel methods to quantify sarcomere length from videos of moving myofibrils and to analyze loss of synchronicity of beating in cells with contractile defects. We tested this computational platform by detecting variations in mechanical output induced by drugs and in cells expressing low levels of myosin-binding protein C.ConclusionsOur method can measure the cardiac function of single micropatterned hiPSC-CMs and determine contractile parameters that can be used to elucidate mechanisms that underlie variations in CM function. This platform will be amenable to future studies of the effects of mutations and drugs on cardiac function.
Project description:Human induced pluripotent stem cells (iPSCs) represent a powerful human model to study cardiac disease in vitro, notably channelopathies and sarcomeric cardiomyopathies. Different protocols for cardiac differentiation of iPSCs have been proposed either based on embroid body formation (3D) or, more recently, on monolayer culture (2D). We performed a direct comparison of the characteristics of the derived cardiomyocytes (iPSC-CMs) on day 27 ± 2 of differentiation between 3D and 2D differentiation protocols with two different Wnt-inhibitors were compared: IWR1 (inhibitor of Wnt response) or IWP2 (inhibitor of Wnt production). We firstly found that the level of Troponin T (TNNT2) expression measured by FACS was significantly higher for both 2D protocols as compared to the 3D protocol. In the three methods, iPSC-CM show sarcomeric structures. However, iPSC-CM generated in 2D protocols constantly displayed larger sarcomere lengths as compared to the 3D protocol. In addition, mRNA and protein analyses reveal higher cTNi to ssTNi ratios in the 2D protocol using IWP2 as compared to both other protocols, indicating a higher sarcomeric maturation. Differentiation of cardiac myocytes with 2D monolayer-based protocols and the use of IWP2 allows the production of higher yield of cardiac myocytes that have more suitable characteristics to study sarcomeric cardiomyopathies.
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.