Transplantation of human embryonic stem cells (hESC) into immune-deficient mice leads to the formation of differentiated tumors comprising all three germ layers, resembling spontaneous human teratomas. Teratoma assays are considered the gold standard for demonstrating differentiation potential of pluripotent hESC and hold promise as a standard for assessing safety among hESC-derived cell populations intended for therapeutic applications. We tested the potency of teratoma formation in seven anatomical transplantation locations (kidney capsule, muscle, subcutaneous space, peritoneal cavity, testis, liver, epididymal fat pad) in SCID mice with and without addition of Matrigel, and found that intramuscular teratoma formation was the most experimentally convenient, reproducible, and quantifiable. In the same experimental setting, we compared undifferentiated hESC and differentiated populations enriched for either beating cardiomyocytes or definitive endoderm derivatives (insulin-secreting beta cells), and showed that all cell preparations rapidly formed teratomas with varying percentages of mesoderm, ectoderm, and endoderm. In limiting dilution experiments, we found that as little as two hESC colonies spiked into feeder fibroblasts produced a teratoma, while a more rigorous single-cell titration achieved a detection limit of 1/4000. In summary, we established core parameters essential for facilitating safety profiling of hESC-derived products for future therapeutic applications.

Human embryonic stem (hES) cells represent a potentially unlimited source of transplantable beta-cells for the treatment of diabetes. Here we describe a differentiation strategy that reproducibly directs HES3, an National Institutes of Health (NIH)-registered hES cell line, into cells of the pancreatic endocrine lineage. HES3 cells are removed from their feeder layer and cultured as embryoid bodies in a three-dimensional matrix in the presence of Activin A and Bmp4 to induce definitive endoderm. Next, growth factors known to promote the proliferation and differentiation of pancreatic ductal epithelial cells to glucose-sensing, insulin-secreting beta-cells are added. Pdx1 expression, which identifies pancreatic progenitors, is detected as early as day 12 of differentiation. By day 34, Pdx1+ cells comprise between 5% and 20% of the total cell population and Insulin gene expression is up-regulated, with release of C-peptide into the culture medium. Unlike another recent report of the induction of insulin+ cells in differentiated hES cell populations, we are unable to detect the expression of other pancreatic hormones in insulin+ cells. When transplanted into severe combined immunodeficiency (SCID) mice, differentiated cell populations retain their endocrine identity and synthesize insulin.

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The sarcomeric troponin-tropomyosin complex is a critical mediator of excitation-contraction coupling, sarcomeric stability and force generation. We previously reported that induced pluripotent stem cellderived cardiomyocytes (iPSC-CMs) from patients with a dilated cardiomyopathy (DCM) mutation, troponin T (TnT)-R173W, display sarcomere protein misalignment and impaired contractility. Yet it is not known how TnT mutation causes dysfunction of sarcomere microdomains and how these events contribute to misalignment of sarcomeric proteins in presence of DCM TnT-R173W. Using a human iPSC-CM model combined with CRISPR/Cas9-engineered isogenic controls, we uncovered that TnT-R173W destabilizes molecular interactions of troponin with tropomyosin, and limits binding of PKA to local sarcomere microdomains. This attenuates troponin phosphorylation and dysregulates local sarcomeric microdomains in DCM iPSC-CMs. Disrupted microdomain signaling impairs MYH7mediated, AMPK-dependent sarcomere-cytoskeleton filament interactions and plasma membrane attachment. Small molecule-based activation of AMPK can restore TnT microdomain interactions, and partially recovers sarcomere protein misalignment as well as impaired contractility in DCM TnT-R173W iPSC-CMs. Our findings suggest a novel therapeutic direction targeting sarcomere-cytoskeleton interactions to induce sarcomere re-organization and contractile recovery in DCM.Sarcomeres are the basic contractile unit of cardiac cells, whose particularly specialized function depends on a highly organized structure. The troponin-tropomyosin (Tn-Tm) complex at sarcomeric thin filaments is a critical component for excitation-contraction coupling. Stability and anchoring of the Tn-Tm complex on sarcomeres is provided by binding of the troponin T (TnT) subunit to Tm and the troponin I subunit (TnI) on actin myofilaments. Tropomyosin (TPM) together with TnI regulates actin/myosin binding and ATPase function in presence of micromolar, cytocolic Ca 2+ , which is bound by the troponin C subunit (TnC). This highly sensitive mechanisms is fine-tuned by post-translational modifications, such as PKA-mediated phosphorylation of TnI. Mutations in the Tn-Tm complex lead to severe disease, such as dilated cardiomyopathy (DCM). DCM is featured by left ventricular dilatation, contractile dysfunction, and arrhythmias 1 and represents a frequent cause of heart failure. More than 25% of DCM cases are caused by inherited mutations, particularly in sarcomeric proteins 2 . Recently, human iPSC-derived cardiomyocytes (iPSC-CMs) have been utilized for human genetic disease modeling 3-6 and drug testing 7 . Here, we analyze a sarcomeric mutation in cardiac troponin T (TnT), TnT-R173W. This mutation is located within one of the two tropomyosin binding regions of TnT, the T1 domain 8 and was the first DCM mutation reported in a human patient-specific iPSC-derived cardiomyocyte model 9 . This report www.nature.com/scientificreports www.nature.com/scientificreports/ demonstrated DCM patient-specific iPSC-CMs to display mole...