The stomach is a complex and physiologically necessary organ and plays an important role in food storage and digestion. Large differences in physiology between mouse and human stomachs have impeded the translation of physiological discoveries and drug screens performed using murine gastric tissues. Gastric organoids emerged as medicine and science improved.
A gastric organoid is an organoid model derived from gastric stem cells or pluripotent stem cells. Its essence is to culture gastric stem cells or pluripotent stem cells and various types of gastric epithelial cells derived from them in a simulated gastric epithelial microenvironment in vitro. The differentiated gastric organoids include all types of terminally differentiated gastric epithelial cells, including main cells, parietal cells, surface mucous cells, cervical mucous cells, and endocrine cells [1-3]. Gastric organoids are highly similar to gastric epithelial tissue in terms of cellular components, tissue architecture, and specific functions, enabling the replication of gastric epithelial tissue in vitro. A gastric organoid is a good basic experimental model, which is superior to animal experimental models and conventional cell culture models in many aspects. Especially, The human-derived gastric organoids open a new "window" for understanding the real condition of the human stomach in vitro.
At present, gastric organoids have been used in the fields of stomach formation and physiology, Helicobacter pylori infection-related diseases, disease-causing gene research, drug screening and development, and regenerative medicine. The gastric tumor-derived organoid model, as a new generation of preclinical tumor models, has played a prominent role in the study of the biological characteristics and mechanisms of gastric cancer and the screening of anti-tumor drugs.
Figure 1. Establishment process of gastric organoids
In 2010, Barker et al. first reported a method to construct gastric organoids from mouse LGR5+ gastric stem cells [4]. The protocol was developed on the basis of the previous series of studies on the culture system of small intestinal organoids and the regulatory signals of digestive tract stem cells.
McCracken et al. first described the iPSC-based gastric organoid construction method in 2014 [5]. Its essence is to simulate the development process of the embryonic intestine in vitro and induce iPSC to directedly differentiate into gastric tissues by giving a series of signal stimulation.
The first murine adult stem cell-derived stomach organoid culture was established from antrum glands containing Lgr5+ stem cells [6].
Using the gastric organoids, McCracken et al. found that blocking the Wnt/β-catenin signaling pathway can lead to the transformation of gastric fundus epithelial cell type to gastric antrum epithelial cell type, while the activation of β-catenin can make the constructed gastric organ closer to gastric fundus epithelial cell type, indicating that gastric organoids are ideal models for studying the regulation mechanism of gastric epithelial cell differentiation [7]. Studies of gastric organoids containing mesenchymal cells provided insight into the epithelial-mesenchymal interaction and further gained an understanding of stomach formation [8] [9].
The research results of Sebrell et al. showed that gastric organoids were not stationary, but kept rolling in place, even though they did not move much physical distance. In addition, they observed that the organoids grew pseudopodia-like structures, which may be the underlying cause of the organoids' rotation [10].
Morey et al. found that Helicobacter pylori (Hp) infection reduced the cholesterol level of gastric mucosal epithelial cells by mediating the phosphorylation of CagA, and then blocked the IFNG signaling pathway, ultimately promoting immune escape of Hp and the occurrence of gastric cancer [11]. These results indicate that gastric organs are good models of Hp infection, and are expected to further reveal the role of Hp in the occurrence and development of infection-related gastric diseases.
Seidlitz et al. introduced p53 gene mutation into normal gastric epithelial organs of mice and successfully established a mouse gastric cancer model. The results showed that the mutated gastric organs showed the characteristics of tumor cells [12]. Nadauld et al. found that TGFBR2 mutated organoid tissue can grow into diffuse tumor tissue after transplantation into mice, suggesting that the mutation of the TGFBR2 gene is related to genetic susceptibility to gastric cancer and is also a key event in the process of gastric cancer metastasis [13].
References:
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[2] Munera JO, Wells JM. Generation of gastrointestinal organoids from human pluripotent stem cells [J]. Methods Mol Biol, 2017,1597: 167-177.
[3] Merker SR, Weitz J. Stange DE. Gastrointestinal organoids: How they gut it out [J]. Dev Biol, 2016,420 (2) : 239-250.
[4] Barker N, Huch M, et al. Lgr5+ve Stem Cells Drive Self-Renewal in the Stomach and Build Long-Lived Gastric Units In Vitro. Cell Stem Cell. 2010;6:25–36.
[5] McCracken KW, Catd EM, Crawford CM, et al. Modelling human development and disease in pluripotent stem-cell-derived gastric organoids [J]. Nature, 2014,516(7531) : 400-404.
[6] Bartfeld S, Clevers H. Organoids as model for infectious diseases: culture of human and murine stomach organoids and microinjection of helicobacter pylori [J]. J Vis Exp (105): 53359, 2015.
[7] McCracken KW, Aihara E, Martin B, et al. Wnt/β-catenin promotes gastric fundus specification in mice and humans [J].Nature, 2017,541 (7636) : 182-187.
[8] Kim TH, Shivdasani RA. Stomach development, stem cells and disease [J]. Development, 2016, 143(4) :554-565.
[9] Dedhia PH, Bertaux-Skeirik N, Zavros Y, et al. Organoid model of human gastrointestinal development and disease [J]. Gastroenterology, 2016. 150 (5): 1098-1112.
[10] Sebrell TA, Sidar B, Bruns R, et al. Live imaging analysis of human gastric epithelial spheroids reveals spontaneous rupture, rotation and fusion events [J]. Cell Tissue Res, 2018,371 (2):293-307.
[11] Morey P, Pfannkuch L, Pang E, et al. Helicobacter pylori Depletes Cholesterol in Gastric Glands to Prevent InterferonGamma Signaling and Escape the Inflammatory Response [J]. Gastroenterology, 2018, 154 (5): 1391-1404.e9.
[12] Seidlitz T, Merker SR, Rothe A, et al. Human gastrie cancer modeling using organoids [J]. Gut, 2018, In press.
[13] Nadauld LD, Garcia S, Natsoulis G, et al. Metastatic tumor evolution and organoid modeling implicate TGFBR2 as a cancer driver in diffuse gastric cancer [J]. Genome Biol, 2014, 15(8):428.
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