Pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) hold tremendous promise in tissue engineering and regenerative medicine applications because of their unique combination of two properties, pluripotency and an extremely high proliferative capacity. Theoretically, almost unlimited supplies of cells and tissues could be generated from a single clonal source if we can regulate PSC growth and differentiation. Hurdles facing utilization of PSCs in regenerative medicine include a lack of reliable and efficient methods to differentiate PSCs to desired developmental lineages.
Several critical factors regulate whether a PSC chooses to self-renew or differentiate. Soluble signals bind receptors and stimulate chemical pathways that lead to global changes in gene transcription and cell differentiation state. Likewise, immobilized extracellular matrix cues synergize with soluble signals to control cell signaling and differentiation. Cell-cell communication is also an important consideration in PSC culture; at low cell densities cell growth rates diminish while at high cell densities spontaneous differentiation occurs. Finally, mechanical signals have recently been shown to affect self-renewal and differentiation. I will discuss examples that illustrate how each of these microenvironmental stimuli can be incorporated in culture systems to expand or differentiate PSCs along desired lineages. We have developed culture systems and engineered cell lines to control developmental pathways that regulate hPSC differentiation toward cardiomyocytes. We have identified canonical Wnt signaling as a key regulator of cardiomyocyte differentiation and designed a protocol that produces high purity cardiomyocytes in a defined, xeno-free, growth factor-free system via appropriate temporal presentation of small molecule modulators of Wnt signaling. Furthermore, we have determined that a different canonical Wnt signaling profile can direct hPSCs to vascular endothelial progenitors. I will discuss the development of a defined, growth factor-free process to generate endothelial cells from hPSCs using small molecule agonists of Wnt signaling. Finally, I will present data illustrating differentiation of pluripotent stem cells to blood-brain barrier microvascular endothelial cells (BMECs) by co-culture of endothelial progenitors with developing neural cell types. These BMECs are currently being used to construct in vitro models of the blood-brain barrier to predict drug passage to the brain.
Sean Palecek is the Milton J. and A. Maude Shoemaker Professor of Chemical & Biological Engineering at the University of Wisconsin – Madison. Sean received a bachelor’s degree in chemical engineering at the University of Delaware. He performed his graduate research with Doug Lauffenburger and Rick Horwitz, earning an M.S. in chemical engineering from the University of Illinois at Urbana-Champaign and a Ph.D. in chemical engineering from MIT. Sean performed postdoctoral research in molecular genetics and cell biology at the University of Chicago under the supervision of Steve Kron. Sean’s lab studies mechanisms of developmental fate choices in human pluripotent stem cells, designs strategies to direct human pluripotent stem cells to desired cell types, and generates 3D tissues from human pluripotent stem cells. Sean’s recent awards include the Cozzarelli Prize of the National Academy of Sciences and the Biotechnology Progress Excellence in Research Publication Award.