7 WORLD GASTROENTEROLOGY NEWS OCTOBER 2014 Editorial | Expert Point of View | Gastro 2015: AGW/WGO | WDHD News | WGO & WGOF News | WGO Global Guidelines | Calendar of Events of the intestinal epithelial barrier in either the aetiology or pathology of IBD (3). However, mainly due to the lack of suitable tools, progress of the study of epithelial specific functions has been limited. Considerable advances in determining the role of intestinal bacteria in IBD have been achieved by using germfree and genetically modified animal models (e.g. IL-10- /- mice, (4)) but these only partially mirror the complex human physiol-ogy. Furthermore, identification of epithelial specific functions in these models is complicated by the influ-ence of local and systemic immune signals. Alternatively immortalized cell lines do not recapitulate the com-plexity of the intestinal epithelium, which consists of multiple cell types, including enterocytes, goblet cells, enteroendocrine cells and, in the small intestine, Paneth cells. In an attempt to resolve this, multiple attempts have been made to develop primary cultures of the intestinal epithelium, but few have gained wide acceptance mainly due to a low yield of viable cells, short-term survival, limited variety of cell types present and other technical difficulties (5). This changed in 2009, when Sato et al. published the first example of ex vivo long-term growth and mainte-nance of the intestinal epithelium (6). This epithelium was grown from stem cells located in the base of the small intestinal epithelial crypts of mice. The growth and survival of the epithe-lium was dependent on suspension of the cells in laminin-rich Matrigel and inclusion of a range of growth factors, such as Wnt, R-spondin 1, Noggin, in the media. This resulted in the growth of organoids, three-dimensional structures in which a single layer of epithelial cells surrounds a lumen (6). Within the epithelium all major cell types of the small intestinal epitheli-um were present and they were main-tained over multiple passages similar to commercially available cell lines, e.g. CaCo2 cells, without losing their tissue identity or genomic integrity. As often when new techniques are devel-oped, the multitude of recent publica-tions resulted in a significant variation of names and descriptions of these structures. The NIH Intestinal Stem Cell Consortium, therefore, proposed a systematic nomenclature to enable comparison between publications (7). We and others are now able to grow organoids from most intestinal epithe-lial tissues from mouse and humans (8, 9). These organoids (gastroids, colonoids, etc.) allow us to study not only the developmental stages of the intestinal epithelium in the presence/ absence of microbiological stimuli, but also the role of physical and bio-chemical components of the epithelial barrier and the involvement of the epithelium in the generation of an appropriate immune response to the commensal and pathogenic bacteria in the absence of confounding variables introduced by immune cells. Using this approach Wilson et al. recently showed that, irrespective of NOD2 status, α-defensins contribute to the restriction of growth of multi-ple strains of non-invasive Salmonella enterica serovar Typhimurium follow-ing microinjection into the lumen of mouse small intestinal organoids (10). This is interesting as NOD2 muta-tions in Crohn’s disease have been linked to reduced α-defensin expres-sion and function (11), a view that is lately disputed (12). Strain-specific virulence factors and host responses are thought to be responsible for the development of gastric cancers in some patients infected with Helico-bacter pylori. Luminal microinjection into mouse gastroids was used to investigate the role of the oncogene CagA expressed by H. pylori in cancer development (13). The authors were able to clarify a number of suspected mechanisms in cancer development. CagA positive H. pylori infections leads to enhanced cell proliferation due to β-catenin activation, but also of note was that infected gastroids showed a reduced expression of caludin-7, which has previously been implicated in carcinogenesis (14). It is now also possible to grow cancer de-rived organoids to study fundamental cancer biology and also apply these, for instance, to drug screenings (15). A glimpse into how these organ-oids could be used for treatment of patients with intestinal disorders was provided by Li and Clevers with the successful transplantation of expanded colonic organoids into the colon of DSS-treated mice. The organoids were tracked using RFP (red fluorescent protein) technology and seemed to have been integrated into the existing mucosa to heal mucosal lesions (16). The development of stem cell derived organoids has provided us with a new tool to study the intestinal epithelium. Initial studies focused on developmental questions in relation to the epithelial barrier formation in the absence of confounding variables coming from the intestinal microbi-ome and the immune system. This led to significant advances in stem-cell research. However, researchers already are starting to reassemble the gut with the introduction of individual microorganisms into the lumen of these mini-guts to study host-microbe interactions. An advantage is the possibility to link the findings to the specific genetic background of the host. This is of considerable impor-tance in IBD where genes associated with at least 163 specific loci contrib-ute to susceptibility, with the function of most only partially understood. In the future it will be possible to study, not only all three components, the immune system, the epithelial barrier and the microbiome simultaneously to generate a deeper understanding
ewgn-vol19-issue3-FINAL
To see the actual publication please follow the link above