Scientific Resources

Cholangiocytes are the target of a heterogeneous group of liver diseases known as the cholangiopathies. An evolving understanding of the mechanisms driving biliary development provides the theoretical underpinnings for rational development of induced pluripotent stem cell (iPSC)-derived cholangiocytes (iDCs). Therefore,the aims of this study were to develop an approach to generate iDCs and to fully characterize the cells in vitro and in vivo. Human iPSC lines were generated by forced expression of the Yamanaka pluripotency factors. We then pursued a stepwise differentiation strategy toward iDCs,using precise temporal exposure to key biliary morphogens,and we characterized the cells,using a variety of morphologic,molecular,cell biologic,functional,and in vivo approaches. Morphology shows a stepwise phenotypic change toward an epithelial monolayer. Molecular analysis during differentiation shows appropriate enrichment in markers of iPSC,definitive endoderm,hepatic specification,hepatic progenitors,and ultimately cholangiocytes. Immunostaining,western blotting,and flow cytometry demonstrate enrichment of multiple functionally relevant biliary proteins. RNA sequencing reveals that the transcriptome moves progressively toward that of human cholangiocytes. iDCs generate intracellular calcium signaling in response to ATP,form intact primary cilia,and self-assemble into duct-like structures in three-dimensional culture. In vivo,the cells engraft within mouse liver,following retrograde intrabiliary infusion. In summary,we have developed a novel approach to generate mature cholangiocytes from iPSCs. In addition to providing a model of biliary differentiation,iDCs represent a platform for in vitro disease modeling,pharmacologic testing,and individualized,cell-based,regenerative therapies for the cholangiopathies. View Publication

Gene- and cell-based therapies are promising strategies for the treatment of degenerative retinal diseases such as age-related macular degeneration,Stargardt disease,and retinitis pigmentosa. Cellular engineering before transplantation may allow the delivery of cellular factors that can promote functional improvements,such as increased engraftment or survival of transplanted cells. A current challenge in traditional DNA-based vector transfection is to find a delivery system that is both safe and efficient,but using mRNA as an alternative to DNA can circumvent these major roadblocks. In this study,we show that both unmodified and modified mRNA can be delivered to retinal pigmented epithelial (RPE) cells with a high efficiency compared with conventional plasmid delivery systems. On the other hand,administration of unmodified mRNA induced a strong innate immune response that was almost absent when using modified mRNA. Importantly,transfection of mRNA encoding a key regulator of RPE gene expression,microphthalmia-associated transcription factor (MITF),confirmed the functionality of the delivered mRNA. Immunostaining showed that transfection with either type of mRNA led to the expression of roughly equal levels of MITF,primarily localized in the nucleus. Despite these findings,quantitative RT-PCR analyses showed that the activation of the expression of MITF target genes was higher following transfection with modified mRNA compared with unmodified mRNA. Our findings,therefore,show that modified mRNA transfection can be applied to human embryonic stem cell-derived RPE cells and that the method is safe,efficient,and functional. View Publication