In Vitro Stomach?
Researchers have developed an advanced, long-term, 3-dimensional organoid culture system for primary, untransformed human gastric epithelium. The system, described in the January issue of Gastroenterology, provides evidence for the presence of stem cells in adult human gastric tissue and can be used to study changes that occur in the gastric epithelium during carcinogenesis or Helicobacter pylori infection.
The gastrointestinal epithelium protects against infections and maintains tolerance to commensal microbes, but an in vitro system is needed to study these interactions. Cell lines and rodent models do not provide accurate models of the human gastric epithelium. There has been no method for expanding human primary gastric cells, which would would more closely represent the gastric epithelium.
To generate a culture system for human gastric epithelium, Sina Bartfeld et al isolated gastric glands from human gastric corpus tissue, collected during surgeries of patients with gastric or esophageal cancer, and observed growth of organoids under different culture conditions.
They identified a combination of growth factors and inhibitors that formed organoids with appropriate phenotypes and longevity. The organoids could be grown for 1 year without losing any of their features. After 3 months of culture, the authors detected no chromosomal aberrations.
Bartfeld et al showed that the organoids could generate all 4 lineages of the stomach: pit mucous cells, gland mucous cells, chief cells, and enteroendocrine cells, but did not express intestinal markers. The authors could direct the gastric organoids to develop into gland- or pit-type organoids, based on WNT gradient (see figure).
These findings provide evidence for the importance of the WNT pathway in development of the human gastric epithelium. WNT signaling is activated during development of intestinal cancers, and up to 30% of gastric tumors contain activated WNT pathway. Two stem cell markers in the mouse stomach, Troy and Lgr5, are WNT target genes.
Bartfeld et al used the organoids to study the effects of H pylori on the gastric epithelium. They injected the organoids with H pylori and measured epithelial responses using microarray and quantitative PCR analyses.
The most highly up-regulated gene was human CGB, which has been associated with gastric cancer. Other upregulated genes were regulated by the nuclear factor-κB (NFκB, which is activated in H pylori infection), such as IL8. The strength of this response depended on the differentiated cell types in the organoids.
The authors conclude that these organoids provide a new model of self-renewing gastric epithelium, grown from stem cells, that can be directed into the different lineages of the stomach—a large improvement of currently used cell lines.
This method might be used to compare samples from normal and cancerous gastric cells of the same patient, as well in drug screens, gastric stem cell research, and studies of host–pathogen interactions.