On human development: lessons from stem cell systems

Species Choice and Model Use: Reviving Research on Human Development

While model organisms have had many historians, this article places studies of humans, and particularly our development, in the politics of species choice. Human embryos, investigated directly rather than via animal surrogates, have gone through cycles of attention and neglect. In the past 60 years they moved from the sidelines to center stage. Research was resuscitated in anatomy, launched in reproductive biomedicine, molecular genetics, and stem-cell science, and made attractive in developmental biology. I explain this surge of interest in terms of rivalry with models and reliance on them. The greater involvement of medicine in human reproduction, especially through in vitro fertilization, gave access to fresh sources of material that fed critiques of extrapolation from mice and met demands for clinical relevance or "translation." Yet much of the revival depended on models. Supply infrastructures and digital standards, including biobanks and virtual atlases, emulated community resources for model organisms. Novel culture, imaging, molecular, and postgenomic methods were perfected on less precious samples. Toing and froing from the mouse affirmed the necessity of the exemplary mammal and its insufficiency justified inquiries into humans. Another kind of model-organoids and embryo-like structures derived from stem cells-enabled experiments that encouraged the organization of a new field, human developmental biology. Research on humans has competed with and counted on models.

Pluripotent Stem Cell-Derived Hepatocyte-like Cells: Induction Methods and Applications

The development of regenerative medicine provides new options for the treatment of end-stage liver diseases. Stem cells, such as bone marrow mesenchymal stem cells, embryonic stem cells, and induced pluripotent stem cells (iPSCs), are effective tools for tissue repair in regenerative medicine. iPSCs are an appropriate source of hepatocytes for the treatment of liver disease due to their unlimited multiplication capacity, their coverage of the entire range of genetics required to simulate human disease, and their evasion of ethical implications. iPSCs have the ability to gradually produce hepatocyte-like cells (HLCs) with homologous phenotypes and physiological functions. However, how to induce iPSCs to differentiate into HLCs efficiently and accurately is still a hot topic. This review describes the existing approaches for inducing the differentiation of iPSCs into HLCs, as well as some challenges faced, and summarizes various parameters for determining the quality and functionality of HLCs. Furthermore, the application of iPSCs for in vitro hepatoprotective drug screening and modeling of liver disease is discussed. In conclusion, iPSCs will be a dependable source of cells for stem-cell therapy to treat end-stage liver disease and are anticipated to facilitate individualized treatment for liver disease in the future.

Sci-Seq of Human Fetal Salivary Tissue Introduces Human Transcriptional Paradigms and a Novel Cell Population

Multiple pathologies and non-pathological factors can disrupt the function of the non-regenerative human salivary gland including cancer and cancer therapeutics, autoimmune diseases, infections, pharmaceutical side effects, and traumatic injury. Despite the wide range of pathologies, no therapeutic or regenerative approaches exist to address salivary gland loss, likely due to significant gaps in our understanding of salivary gland development. Moreover, identifying the tissue of origin when diagnosing salivary carcinomas requires an understanding of human fetal development. Using computational tools, we identify developmental branchpoints, a novel stem cell-like population, and key signaling pathways in the human developing salivary glands by analyzing our human fetal single-cell sequencing data. Trajectory and transcriptional analysis suggest that the earliest progenitors yield excretory duct and myoepithelial cells and a transitional population that will yield later ductal cell types. Importantly, this single-cell analysis revealed a previously undescribed population of stem cell-like cells that are derived from SD and expresses high levels of genes associated with stem cell-like function. We have observed these rare cells, not in a single niche location but dispersed within the developing duct at later developmental stages. Our studies introduce new human-specific developmental paradigms for the salivary gland and lay the groundwork for the development of translational human therapeutics.

Naturally-Derived Biomaterials for Tissue Engineering Applications

Naturally-derived biomaterials have been used for decades in multiple regenerative medicine applications. From the simplest cell microcarriers made of collagen or alginate, to highly complex decellularized whole-organ scaffolds, these biomaterials represent a class of substances that is usually first in choice at the time of electing a functional and useful biomaterial. Hence, in this chapter we describe the several naturally-derived biomaterials used in tissue engineering applications and their classification, based on composition. We will also describe some of the present uses of the generated tissues like drug discovery, developmental biology, bioprinting and transplantation.

Generation of hepatobiliary organoids from human induced pluripotent stem cells

BACKGROUND & AIMS

Human induced pluripotent stem cell (hiPSC)-derived liver modeling systems have the potential to overcome the shortage of donors for clinical application and become a model for drug development. Although several strategies are available to generate hepatic micro-tissues, few have succeeded in generating a liver organoid with hepatobiliary structure from hiPSCs.

METHODS

At differentiation stages I and II (day 1-15), 25% of mTeSR™ culture medium was added to hepatic differentiation medium to induce endodermal and mesodermal commitment and thereafter hepatic and biliary co-differentiation. At stage III (day 15-45), 10% cholesterol+ MIX was added to the maturation medium to promote the formation and maturation of the hepatobiliary organoids. Phenotypes and functions of organoids were determined by specific markers and multiple functional assays both in vitro and in vivo.

RESULTS

In this system, hiPSCs were induced to form 3D hepatobiliary organoids and to some extent recapitulated key aspects of early hepatogenesis in a parallel fashion. The organoids displayed a series of functional attributes. Specifically, the induced hepatocyte-like cells could take up indocyanine green, accumulate lipid and glycogen, and displayed appropriate secretion ability (albumin and urea) and drug metabolic ability (CYP3A4 activity and inducibility); the biliary structures in the system showed gamma glutamyltransferase activity and the ability to efflux rhodamine and store bile acids. Furthermore, after transplantation into the immune-deficient mice, the organoids survived for more than 8 weeks.

CONCLUSION

This is the first time that functional hepatobiliary organoids have been generated from hiPSCs. The organoid model will be useful for in vitro studies of the molecular mechanisms of liver development and has important potential in the therapy of liver diseases.

LAY SUMMARY

Herein, we established a system to generate human induced pluripotent stem cell-derived functional hepatobiliary organoids in vitro, without any exogenous cells or genetic manipulation. To some extent this model was able to recapitulate several key aspects of hepatobiliary organogenesis in a parallel fashion, holding great promise for drug development and liver transplantation.

Self-assembled liver organoids recapitulate hepatobiliary organogenesis in vitro

Several three-dimensional cell culture systems are currently available to create liver organoids. In gneral, these systems display better physiologic and metabolic aspects of intact liver tissue compared with two-dimensional culture systems. However, none reliably mimic human liver development, including parallel formation of hepatocyte and cholangiocyte anatomical structures. Here, we show that human fetal liver progenitor cells self-assembled inside acellular liver extracellular matrix scaffolds to form three-dimensional liver organoids that recapitulated several aspects of hepatobiliary organogenesis and resulted in concomitant formation of progressively more differentiated hepatocytes and bile duct structures. The duct morphogenesis process was interrupted by inhibiting Notch signaling, in an attempt to create a liver developmental disease model with a similar phenotype to Alagille syndrome. Conclusion: In the current study, we created an in vitro model of human liver development and disease, physiology, and metabolism, supported by liver extracellular matrix substrata; we envision that it will be used in the future to study mechanisms of hepatic and biliary development and for disease modeling and drug screening. (Hepatology 2018;67:750-761).

An Innovative, Comprehensive Mapping and Multiscale Analysis of Registered Trials for Stem Cell-Based Regenerative Medicine

We aim to provide an innovative, comprehensive way of mapping the profusion of stem cell-based clinical trials registered at ClinicalTrials.gov to explore the diversity of the fields of application and the temporal complexity of the domain. We used a chord diagram and phylogenetic-like tree visualizations to assist in data mining and knowledge discovery. The search strategy used the following terms: "stromal OR stem OR mesenchymal OR progenitor." The Medical Subject Headings (MeSH) thesaurus was used to more finely classify diseases treated by stem cells, from large fields of application to specific diseases. Of the 5,788 trials screened, 939 were included, 51.1% of which were related to mesenchymal stem cells (MSCs). No real specificity emerged as to the therapeutic uses of the different types of stem cells. More than half the MSC studies concerned allogeneic MSCs and received more support from industry than autologous MSC studies (p < .001). Over time, the uses of cultured cells have increased greatly, particularly since 2009. Cells derived from adipose tissue are also increasingly used in trials compared with bone marrow cells. The use of adipose-derived stromal cells was predominantly autologous (p < .001), restricted to European countries (p < .01), and supported by industry (p = .02) compared with other MSCs. Details about MeSH keywords are available at http://multireview.perso.sfr.fr/. In conclusion, mapping may reveal a lack of global strategy despite the regulations and the related costs associated with good manufacturing practices. A systematic approach to preclinical data, intended to objectively and robustly reveal the most appropriate fields with the most efficient cells, is needed. Repeated exchanges between the bench and the bedside are necessary.

SIGNIFICANCE

Except for a few trials concerning specific tissue stem cells used in their corresponding tissues, this global analysis revealed no real specificity of stem cell uses (including mesenchymal stromal cells). This raised the question of the physiopathological rationale for these uses and the lack of a global strategy despite the regulations and the related costs associated with good manufacturing practices. This original method, leading to the development of new concepts from already available data, would help policymakers to optimize resources and investments in terms of public health priorities. Such an approach should draw parallels between in vitro, in vivo, and human data. Exchanges in both directions between preclinical and clinical research could optimize the parameters of clinical trials step by step.