Researchers from MIT and Brigham and Women’s Hospital in Boston, MA have discovered a protocol that allows them to grow unlimited quantities of intestinal stem cells. These intestinal stem cells can then be induced to differentiate into pure populations of various types of mature intestinal cells. Scientists can used these cultured intestinal cells to develop new drugs and treat gastrointestinal diseases, such as Crohn’s disease or ulcerative colitis.,
The small intestine has a small repository of adult stem cells that differentiate into mature adult cells that have specialized functions. Until recently, there was no good way to grow large numbers of these intestinal stem cells in culture. Intestinal stem cells, you see, only retain their immature characteristics when they are in contact with supportive cells known as Paneth cells.
In order to grow intestinal stem cells in culture, researchers from the laboratories of Robert Langer at the MIT Koch Institute for Integrative Cancer Research and Jeffrey Karp from the Harvard Medical School and Brigham and Women’s Hospital, determined the specific molecules that Paneth cells make that keep the intestinal stem cells in their immature state. Then they designed small molecules that mimic the Paneth cell-specific molecules. When Langer and Karp’s groups grew the intestinal stem cells in culture with those small molecules, the cells remained immature and grew robustly in culture.
Langer said, “This opens the door to doing all kinds of thing, ranging from someday engineering a new gut for patients with intestinal diseases to doing drug screening for safety and efficacy. It’s really the first time this has been done.”
The inner mucosal layer of the intestine has several vital functions: the absorption of nutrients, the secretion of mucus of create a barrier between our own cells and the bacteria and viruses and habitually inhabit our bowels, and alerting the immune system to the presence of potential disease-causing agents in the bowel.
The intestinal mucosa is organized into a collection of folds with small indentations called “intestinal crypts.” At the bottom of each crypt is a small pool of intestinal stem cells that divide to routinely replace the specialized cells of the intestinal epithelium. Because the cells of the intestinal epithelium show a high rate of turnover (they only last for about five days), these stem cells must constantly divide to replenish the intestine.
Once these intestinal stem cells divide, they can differentiate into any type of mature intestinal cell type. Therefore, these intestinal stem cells provide a marvelous example of a “multipotent stem cell.”
Obtaining large quantities of intestinal stem cells could certainly help gastroenterologists treat gastrointestinal diseases that damage the epithelial layer of the gut. Fortunately, recent studies in laboratory animals have demonstrated that the delivery of intestinal stem cells can promote the healing of ulcers and regeneration of new tissue, which offers a new way to treat inflammatory bowel diseases like ulcerative colitis.
This, however, is only one of the many uses for cultured intestinal stem cells. Researchers are literally salivating over the potential of studying things like goblet cells, which control the immune response to proteins in foods to which many people are allergic. Alternatively, scientists would like to investigate the properties of enteroendocrine cells, which secrete hunger hormones and play a role in obesity. I think you can see, that large numbers of intestinal stem cells could be a boon to gastrointestinal research.
Karp said, “If we had ways of performing high-throughput screens of large numbers of these very specific cell types, we could potentially identify new targets and develop completely new drugs for diseases ranging from inflammatory bowel disease to diabetes.”
The laboratory of Hans Clevers in 2007 identified a molecule that is specifically made by intestinal stem cells called Lgr5. Clevers is a professor at the Hubrecht Institute in the Netherlands and he and his co-workers have just identified particular molecules that enable intestinal stem cells to grow in synthetic culture. In culture, these small clusters of intestinal stem cells differentiate and form small sphere-like structures called “organoids,” because they consist of a ball of intestinal cells that have many of the same organizational properties of our own intestines, but are made in culture.
Clevers and his colleagues tried to properly define the molecules that bind Paneth cells and intestinal stem cell together. The purpose of this was to mimic the Paneth cells in culture so that the intestinal stem cells would grow robustly in culture. Clevers’ team discovered that Paneth cells use two signal transduction pathways (biochemical pathways that cells use to talk to each other) to coordinate their “conversations” with the adjacent stem cells. These two signal transduction pathways are the Notch and Wnt pathways.
Fortunately, two molecules could be used to induce intestinal stem cell proliferation and prevent their differentiation: valproic acid and CHIR-99021. When Clevers and others grew mouse intestinal stem cells in the presence of these two compounds, they found that large clusters of cells grew that consisted of 70-90 percent pure stem cells. When they used inhibitors of the Notch and Wnt pathway, they could drive the cells to form particular types of mature intestinal cells.
“We used different combinations of inhibitors and activators to drive stem cells to differentiate into specific populations of mature cells,” said Xiaolei Yin, first author of this paper. Yin and others were able to get this strategy to work with mouse stomach and colon cells, and that these small molecules also drove the proliferation of human intestinal stem cells.
Presently, Clevers’ laboratory is trying to engineering intestinal tissues for potential transplantation in human patients and for rapidly testing the effects of drugs on intestinal cells.
Ramesh Shivdasani from Harvard Medical School and Dana-Farber Cancer Institute would like to use these cells to investigate what gives stem cells their ability to self-renew and differentiate into other cell types. “There are a lot of things we don’t know about stem cells,” said Shivdasani. “Without access to large quantities of these cells, it’s very difficult to do any experiments. This opens the door to a systematic, incisive, reliable way of interrogating intestinal stem cell biology.”
X. Yi, et al. “Niche-independent high-purity cultures of Lgr5 intestinal stem cells and their progeny.” Nature Methods 2013; DOI:10.1038/nmeth.2737.