Finding Waldo in a puzzle book filled with look-alike cartoon figures is no easy task at first glance. But if you keep your eyes peeled for his unique outfit, you’ll be able to find him reliably on every page. In the same way, researchers looking for a specific subpopulation of cells first need to know what makes them distinct from all the other cells in the body.
Epithelial stem cells are specialist tissue populations that usually ensure the daily renewal of the linings of many organs. However, they also serve as key sources of many cancers following mutation. The resulting tumors themselves contain similar populations called cancer stem cells, which are responsible for cancer growth, dissemination and resistance to clinical therapies. Lgr5 is used to identify many epithelial stem cells, including those in the mouse distal stomach, but the equivalent population in the human stomach remains undiscovered.
“Furthermore, because of its expression on multiple stem cell populations throughout the gastrointestinal tract like the small intestine and colon, as well as the lack of available anti-LGR5 antibodies facilitating the isolation of both mouse and human stomach stem cells, we sought to identify a more highly expressed surface marker that is specific for stomach stem cells,” said Nick Barker, a Research Director at A*STAR’s Institute of Medical Biology (IMB).
By comparing the genes in LGR5-expressing stem cells present in the small and large intestines as well as different parts of the stomach, the team first shortlisted six genes found primarily in the pylorus. Of these, AQP5 emerged as a promising candidate due to its robust, yet highly selective expression on the surface of pyloric stem cells, as well as the commercial availability of good anti-AQP5 antibodies.
Using these antibodies, the team isolated AQP5-positive cells from a healthy human stomach for the first time, and showed these to be stem-cell-like by virtue of their ability to grow organoids—3D cellular structures resembling cells lining the stomach wall—in vitro.
Delving deeper into the molecular mechanisms driving oncogenesis in humans, the team employed quantum computing to identify key signaling pathways—including the Wnt pathway—that are commonly dysregulated in human gastric cancer. Using this knowledge, they targeted these pathway mutations in mouse gastric stem cells in vivo, resulting in the rapid generation of invasive cancers in the distal stomach.
“This is the first demonstration of stomach stem cells being important sources of Wnt-driven gastric cancer following mutation,” said Barker.
The resulting mouse gastric cancers contained an AQP5-expressing subpopulation, which behaved as cancer stem cells in organoid assays. Similarly, most human gastric cancers were found to harbor similar subsets of AQP5-expressing cells, suggesting the clinical relevance of the team’s findings.
“If human AQP5-expressing gastric cancer cells are indeed cancer stem cells, it will be an important therapeutic target for the future development of more effective treatments in the clinic,” said Barker.
Moving forward, the team plans to further evaluate human AQP5-expressing cells as potential gastric cancer stem cells through in vivo transplantation experiments and explore whether AQP5 itself influences tumor migration, invasion and survival. They hope to eventually establish AQP5 as a novel therapeutic target to improve gastric cancer diagnosis and treatment in the clinic.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Medical Biology (IMB), Genome Institute of Singapore (GIS), the Singapore Immunology Network (SIgN) and the Skin Research Institute of Singapore (SRIS).