Human pluripotent stem cells (hPSCs) offer the potential to generate large numbers of functional cardiomyocytes from clonal and patient-specific cell sources. Here we show that temporal modulation of Wnt signaling is both essential and sufficient for efficient cardiac induction in hPSCs under defined, growth factor-free conditions. shRNA knockdown of β-catenin during the initial stage of hPSC differentiation fully blocked cardiomyocyte specification, whereas glycogen synthase kinase 3 inhibition at this point enhanced cardiomyocyte generation. Furthermore, sequential treatment of hPSCs with glycogen synthase kinase 3 inhibitors followed by inducible expression of β-catenin shRNA or chemical inhibitors of Wnt signaling produced a high yield of virtually (up to 98%) pure functional human cardiomyocytes from multiple hPSC lines. The robust ability to generate functional cardiomyocytes under defined, growth factor-free conditions solely by genetic or chemically mediated manipulation of a single developmental pathway should facilitate scalable production of cardiac cells suitable for research and regenerative applications.

The protocols described here efficiently direct human pluripotent stem cells (hPSCs) to functional cardiomyocytes in a completely defined, serum-free system by temporal modulation of regulators of canonical Wnt signaling. Appropriate temporal application of Gsk3 inhibitor followed by expression of β-catenin shRNA or a chemical Wnt inhibitor is sufficient to produce a high yield (0.8–1.3 million cardiomyocytes/cm2) of virtually pure (80%–98%) functional cardiomyocytes from multiple hPSC lines without cell sorting or selection. Characterization of differentiated cells is performed in qualitative (immunostaining) and quantitative (flow cytometry) manners to assess expression of cardiac transcription factors and myofilament proteins. Flow cytometry of BrdU incorporation or Ki67 expression in conjuction with cardiac sarcomere myosin protein expression can be used to determine the proliferative capacity of hPSC-derived cardiomyocytes. Functional human cardiomyocytes differentiated via these protocols may constitute a potential cell source for heart disease modeling, drug screening, and cell-based therapeutic applications.

The blood-brain barrier (BBB) plays an important role in brain health and is often compromised in disease. Moreover, as a result of its significant barrier properties, this endothelial interface restricts neurotherapeutic uptake. Thus, a renewable source of human BBB endothelium could prove enabling for brain research and pharmaceutical development. Herein, we demonstrate that endothelial cells generated from human pluripotent stem cells (hPSCs) can be specified to possess many BBB attributes, including well-organized tight junctions, expression of nutrient transporters, and polarized efflux transporter activity. Importantly, hPSC-derived BBB endothelial cells respond to astrocytic cues yielding impressive barrier properties as measured by transendothelial electrical resistance (1450±140 Ωxcm2) and molecular permeability that correlates well with in vivo brain uptake. In addition, specification of hPSC-derived BBB endothelial cells occurs in concert with neural cell co-differentiation via Wnt/β-catenin signaling, consistent with previous transgenic studies. This study represents the first example of organ-specific endothelial differentiation from hPSCs.

Blood-brain barrier (BBB) models are often used to investigate BBB function and screen brain-penetrating therapeutics, but it has been difficult to construct a human model that possesses an optimal BBB phenotype and is readily scalable. To address this challenge, we developed a human in vitro BBB model comprising brain microvascular endothelial cells (BMECs), pericytes, astrocytes and neurons derived from renewable cell sources. First, retinoic acid (RA) was used to substantially enhance BBB phenotypes in human pluripotent stem cell (hPSC)-derived BMECs, particularly through adherens junction, tight junction, and multidrug resistance protein regulation. RA-treated hPSC-derived BMECs were subsequently co-cultured with primary human brain pericytes and human astrocytes and neurons derived from human neural progenitor cells (NPCs) to yield a fully human BBB model that possessed significant tightness as measured by transendothelial electrical resistance (~5,000 Ωxcm2). Overall, this scalable human BBB model may enable a wide range of neuroscience studies.

The differentiation of human embryonic stem cells (hESCs) into cardiomyocytes (CMs) using embryoid bodies (EBs) is relatively inefficient and highly variable. Formation of EBs using standard enzymatic disaggregation techniques results in a wide range of sizes and geometries of EBs. Use of a 3-D cuboidal microwell system to culture hESCs in colonies of defined dimensions, 100 to 500 μm in lateral dimensions and 120 μm in depth, enabled formation of more uniform sized EBs. The 300 μm microwells produced highest percentage of contracting EBs, but flow cytometry for myosin light chain 2A (MLC2a) expressing cells revealed a similar percentage (~3%) of cardiomyocytes formed in EBs from 100 μm and 300 μm microwells. These data, and immunolabeling with anti- Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access