Challenges to, and prospects for, reverse engineering the gastrointestinal tract using organoids

Abstract

Organoids are self-organizing 3D cell culture systems that constitute a unique tool for studying development and disease.Over the past decade, efficient protocols to grow organoids that resemble the different parts of the GIT have been established.Bioengineering approaches have been used to improve organoid cultures.Organoid fusion and on-chip methods are explored to increase complexity of organoids to better recapitulate in vivo tissues. For over a decade, organoids mimicking the development, physiology, and disease of the digestive system have been a topic of broad interest and intense study. Establishing organoid models that recapitulate all distinct regions of the gastrointestinal tract (GIT) has proven challenging since each tissue surrogate requires tailor-made modifications of the original protocol to generate intestinal organoids. In this review, we discuss the challenges and current advances of the GIT organoid models. Moreover, we envision the next-generation GIT organoids as integrated organoid models, able to recapitulate structural and functional characteristics of multiple regions of the digestive tube in a single in vitro model. We discuss these new trends and provide an outlook for the future of GIT in vitro models. For over a decade, organoids mimicking the development, physiology, and disease of the digestive system have been a topic of broad interest and intense study. Establishing organoid models that recapitulate all distinct regions of the gastrointestinal tract (GIT) has proven challenging since each tissue surrogate requires tailor-made modifications of the original protocol to generate intestinal organoids. In this review, we discuss the challenges and current advances of the GIT organoid models. Moreover, we envision the next-generation GIT organoids as integrated organoid models, able to recapitulate structural and functional characteristics of multiple regions of the digestive tube in a single in vitro model. We discuss these new trends and provide an outlook for the future of GIT in vitro models. The emergence of, and rapid progress in, organoid models have contributed significantly to the field of stem cell research. Organoids can be derived from two main stem cell types: pluripotent stem cells (PSCs; see Glossary) or organ-specific adult stem cells (ASCs). For PSC-derived models, both embryonic (ESCs) and induced pluripotent (iPSCs) stem cells can be used. The resulting organoids contain either both epithelial and mesenchymal cell types or only epithelial cells [1.Broutier L. et al.Culture and establishment of self-renewing human and mouse adult liver and pancreas 3D organoids and their genetic manipulation.Nat. 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These self-organizing, 3D models are promising tools to bridge the gap between in vitro monolayer cultures and in vivo studies, because they recapitulate tissue function and structure more accurately than do conventional 2D cell cultures. Although they are characterized by an increased structural and functional complexity, they are amenable to most standard experimental techniques [5.Fatehullah A. et al.Organoids as an in vitro model of human development and disease.Nat. Cell Biol. 2016; 18: 246-254Crossref PubMed Scopus (820) Google Scholar, 6.Min S. et al.Gastrointestinal tract modeling using organoids engineered with cellular and microbiota niches.Exp. Mol. Med. 2020; 52: 227-237Crossref PubMed Scopus (65) Google Scholar, 7.Dedhia P.H. et al.Organoid models of human gastrointestinal development and disease.Gastroenterology. 2016; 150: 1098-1112Abstract Full Text Full Text PDF PubMed Scopus (170) Google Scholar, 8.Merker S.R. et al.Gastrointestinal organoids: how they gut it out.Dev. Biol. 2016; 420: 239-250Crossref PubMed Scopus (49) Google Scholar]. In this review, we focus on organoid models of the GIT and discuss the potential future directions to further approximate these models to the intricate complexity of a multiregional digestive tract by using recently developed technologies and bioengineering approaches (Figure 1, Key figure). Insights into the development and homeostasis of the alimentary canal laid the foundation for the generation and culture of organoids (Box 1). Intestinal organoids constitute the first organoid model described for a specific region of the GIT. In 2009, two pioneering models for growing intestinal organoids from adult mouse tissues were described. The first was developed by Clever’s team, who used previously identified Lgr5+ stem cells [9.Barker N. et al.Identification of stem cells in small intestine and colon by marker gene Lgr5.Nature. 2007; 449: 1003-1007Crossref PubMed Scopus (3894) Google Scholar] to generate 3D epithelial organoids that resembled the crypt-villus architecture and expressed all the differentiated cell types present in the intestine in vivo [10.Sato T. et al.Single Lgr5 stem cells build crypt-villus in vitro a mesenchymal PubMed Scopus Google Scholar]. The model was described by team, who small intestinal in and in a 3D system A. et in vitro intestinal epithelial culture a stem cell Med. PubMed Scopus Google Scholar]. of the first PSC-derived intestinal organoid model was described. 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Full Text Full Text PDF PubMed Scopus Google Scholar]. progress in this organoids are from a system and with and as the of of complexity and of and In an to improve this approaches have been described either on or on a of and to increase complexity and further and methods have been used. and techniques have been to and to better organoid In this review, we provide an of methods that have been to of these the of the organoid field an the generation of 3D in vitro models, are of modeling multiregional and by multiple distinct regions of tissues or in We discuss the of technologies in this on the of systems and the recently organoid fusion organoids have been used as an in vitro model to study development, physiology, and in their in and the of or These are derived from mouse their and are to and they et of pluripotent stem intestinal Cell 2019; Full Text Full Text PDF PubMed Scopus Google Scholar]. have to with a a and an structural was able to the of mouse intestinal organoids et for in vitro 3D culture of adult intestinal PubMed Google Scholar]. were to the and of mouse intestinal stem cells into organoids N. et for intestinal stem cell and organoid 2016; PubMed Scopus Google Scholar]. 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These recapitulate the in vivo the of and that and intestinal characteristics to be present in this system since these tissues from the and of and in the should be more in future approaches be to parts of the GIT. For the a fusion of and can be derived using the different of organoid characteristics of the and the resulting in a more and multiregional intestinal organoid model. The of and organoids in a organoid the in vivo more be the by of the to the and the of different organoid the of the fusion and the development of specific tissues. the different for the and of each tissue and be to the and provide distinct culture fusion of and organoid models, that all regions of the digestive system from gut to a more techniques for and and techniques to be further to the of a fusion of organoids on In a used 3D to generate intestinal structural and functional in characteristics et tissue organoid 2020; PubMed Scopus Google Scholar]. 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A. PubMed Scopus Google Scholar] (Figure the and organoids A. et in an integrated PubMed Scopus Google Scholar] (Figure In both each organoid in a of a and all the are with to a these are with and that in of the organoids. systems have been used to study the of the organoids to a as the of the tract and of Intestinal each a different of the digestive These are in and research. a be to organoids the different regions of the alimentary canal and provide the to have a GIT on a to the are between the culture and of the GIT organoids. For the of culture and the it should be to these different organoids in the for they a the architecture the of the different types of organoid are the and all a (Figure we envision that an with integrated the new standard in of the development, and of the digestive multiple types of organoid both and research. 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