Organoid Derivation and Orthotopic Xenotransplantation for Studying Human Intestinal Stem Cell Dynamics

Visualization of Differentiated Cells in 3D and 2D Intestinal Organoid Cultures

The intestinal epithelium maintains self-renewal and differentiation capacities via coordination of key signaling pathways, including the Wnt, bone morphogenetic protein (BMP), epidermal growth factor (EGF), and Notch signaling pathways. Based on this understanding, a combination of stem cell niche factors, EGF, Noggin, and the Wnt agonist R-spondin was shown to enable the growth of mouse intestinal stem cells and the formation of organoids with indefinite self-renewal and full differentiation capacity. Two small-molecule inhibitors, including a p38 inhibitor and a TGF-beta inhibitor, were added to propagate cultured human intestinal epithelium but at the cost of differentiation capacity. There have been improvements in culture conditions to overcome these issues. Substitution of the EGF and a p38 inhibitor with insulin-like growth factor-1 (IGF-1) and fibroblast growth factor-2 (FGF-2) enabled multilineage differentiation. Monolayer culture with mechanical flow to the apical epithelium promoted the formation of villus-like structures with mature enterocyte gene expression. Here, we summarize our recent technological improvements in human intestinal organoid culture that will deepen the understanding of intestinal homeostasis and diseases.

In Vivo Intestinal Research Using Organoid Transplantation

Our understanding of the biology of the intestinal epithelium has advanced since the establishment of an organoid culture system. Although organoids have enabled investigation of the mechanism of self-renewal of human intestinal stem cells in vitro, it remains difficult to clarify the behavior of human normal and diseased intestinal epithelium in vivo. Recently, we developed a xenotransplantation system in which human intestinal organoids are engrafted onto epithelium-depleted mouse colons. This xenograft recapitulated the original tissue structures. Upon xenotransplantation, normal colon organoids developed normal colon crypt structures without tumorigenesis, whereas tumor-derived organoids formed colonic tumors resembling the original tumors. The non-tumorigenicity of human intestinal organoids highlights the safety of organoid-based regenerative medicine. As an example of regenerative medicine for short bowel syndrome, we devised a unique organ-repurposing approach to convert colons into small intestines by organoid transplantation. In this approach, the transplanted rat small intestinal organoids not only engrafted onto the rat colons but also remodeled the colon subepithelial structures into a small intestine-like conformation. Luminal flow accelerated the maturation of villi in the small intestine, which promoted the formation of a lymphovascular network mimicking lacteals. In this review, we provide an overview of recent advances in gastrointestinal organoid transplantation and share our understanding of human disease biology and regenerative medicine derived from these studies.

From Patient Material to New Discoveries: a Methodological Review and Guide for Intestinal Stem Cell Researchers

Intestinal stem cells (ISC) are characterized by their ability to continuously self-renew and differentiate into various functionally distinct intestinal epithelial cell types. Impaired stem cell proliferation and differentiation can cause severe dysfunction of the gastrointestinal tract and lead to the development of several clinical disorders. Animal mouse models provide a valuable platform to study ISC function, disease mechanisms, and the intestinal epithelium's regenerative capacity upon tissue damage. However, advanced in vitro systems that are more relevant to human physiology are needed to understand better the diverse disease-triggering factors and the heterogeneity in clinical manifestations. Intestinal biopsies from patients might serve as potent starting material for such "gut-in-a-dish" approaches. While many promising tools for intestinal tissue processing, in vitro expansion, and downstream analysis have been developed in recent years, a comprehensive guide with recommendations to successfully launch or improve intestinal stem cell culture is missing. In this review, we present a selection of currently established methods, highlight recent publications and discuss the potential and limitations of those methodological approaches to facilitate and support the future design of novel and more personalized therapeutic options.

Biomaterials for intestinal organoid technology and personalized disease modeling

Recent advances in intestinal organoid technologies have paved the way for in vitro recapitulation of the homeostatic renewal of adult tissues, tissue or organ morphogenesis during development, and pathogenesis of many disorders. In vitro modelling of individual patient diseases using organoid systems have been considered key in establishing rational design of personalized treatment strategies and in improving therapeutic outcomes. In addition, the transplantation of organoids into diseased tissues represents a novel approach to treat currently incurable diseases. Emerging evidence from intensive studies suggests that organoid systems' development and functional maturation depends on the presence of an extracellular matrix with suitable biophysical properties, where advanced synthetic hydrogels open new avenues for theoretical control of organoid phenotypes and potential applications of organoids in therapeutic purposes. In this review, we discuss the status, applications, challenges and perspectives of intestinal organoid systems emphasising on hydrogels and their properties suitable for intestinal organoid culture. We provide an overview of hydrogels used for intestinal organoid culture and key factors regulating their biological activity. The comparison of different hydrogels would be a theoretical basis for establishing design principles of synthetic niches directing intestinal cell fates and functions. STATEMENT OF SIGNIFICANCE: Intestinal organoid is an in vitro recapitulation of the gut, which self-organizes from intestinal stem cells and maintains many features of the native tissue. Since the development of this technology, intestinal organoid systems have made significant contribution to rapid progress in intestinal biology. Prevailing methodology for organoid culture, however, depends on animal-derived matrices and suffers from variability and potential risk for contamination of pathogens, limiting their therapeutic application. Synthetic scaffold matrices, hydrogels, might provide solutions to these issues and deepen our understanding on how intestinal cells sense and respond to key biophysical properties of the surrounding matrices. This review provides an overview of developing intestinal models and biomaterials, thereby leading to better understanding of current intestinal organoid systems for both biologists and materials scientists.

An organoid-based organ-repurposing approach to treat short bowel syndrome

The small intestine is the main organ for nutrient absorption, and its extensive resection leads to malabsorption and wasting conditions referred to as short bowel syndrome (SBS). Organoid technology enables an efficient expansion of intestinal epithelium tissue in vitro¹, but reconstruction of the whole small intestine, including the complex lymphovascular system, has remained challenging². Here we generate a functional small intestinalized colon (SIC) by replacing the native colonic epithelium with ileum-derived organoids. We first find that xenotransplanted human ileum organoids maintain their regional identity and form nascent villus structures in the mouse colon. In vitro culture of an organoid monolayer further reveals an essential role for luminal mechanistic flow in the formation of villi. We then develop a rat SIC model by repositioning the SIC at the ileocaecal junction, where the epithelium is exposed to a constant luminal stream of intestinal juice. This anatomical relocation provides the SIC with organ structures of the small intestine, including intact vasculature and innervation, villous structures, and the lacteal (a fat-absorbing lymphatic structure specific to the small intestine). The SIC has absorptive functions and markedly ameliorates intestinal failure in a rat model of SBS, whereas transplantation of colon organoids instead of ileum organoids invariably leads to mortality. These data provide a proof of principle for the use of intestinal organoids for regenerative purposes, and offer a feasible strategy for SBS treatment.