Intestinal stem cells? As many as you want!
The method developed at MIT allows you to grow
unlimited number of intestinal stem cells
LifeSciencesToday based on MIT materials: Researchers unlock a new means of growing intestinal stem cellsScientists from the Massachusetts Institute of Technology (MIT) and Brigham and Women's Hospital (BWH) have learned how to grow unlimited amounts of intestinal stem cells, and then direct their development into various mature types, obtaining almost pure populations of specialized cells.
The cells grown by the new method will help pharmaceutical companies in the development and testing of new drugs for the treatment of diseases such as ulcerative colitis.
Intestinal stem cells grown in new conditions,
expressing green fluorescent protein. (Photo: MIT)
In the small intestine, as in most other tissues of the body, there is a small supply of immature adult stem cells that can differentiate into cells of more mature specialized types. However, obtaining a large number of intestinal stem cells is a difficult task, since they remain immature only when in contact with the so–called Paneta cells.
In an article published in the online edition of the journal Nature Methods (Yin et al., Niche-independent high-purity cultures of Lgr5 intestinal stem cells and their progeny), scientists report that they managed to replace the effect of the presence of Paneta cells with the action of two low-molecular compounds that support the undifferentiated state of stem cells and stimulate them proliferation. Stem cells grown in an environment containing these molecules can remain immature indefinitely, and by adding other molecules, including inhibitors and activators, scientists can control what types of cells they will eventually become.
"This opens the way to achieving many goals, starting with the future cultivation of new intestines for patients with intestinal diseases and ending with screening for the safety and effectiveness of medicines. This is really done for the first time," says Robert Langer, an associate at The David H. Koch Institute for Integrative Cancer Research at MIT, one of the senior authors of the article.
The inner layer of the intestine performs several important functions. Some of its cells specialize in absorbing nutrients from digested food; others form a mucus-secreting barrier that prevents viruses and bacteria from entering the blood; others warn the immune system about the presence of pathogens.
This layer, known as the intestinal epithelium, is covered with many crypts. At the base of each crypt is a small pool of epithelial stem cells, which constantly form specialized intestinal epithelial cells that live for about five days. These stem cells can become any type of intestinal epithelial cells, but they do not have the pluripotency of embryonic stem cells capable of differentiating into any cell of the body.
If scientists learn how to obtain large amounts of intestinal epithelial stem cells, they can be used to treat gastrointestinal diseases that damage the epithelium. Recent animal studies have shown that stem cells delivered to the intestine can anchor in ulcers and help repair tissue – a potential way to treat ulcerative colitis.
The use of intestinal stem cells to produce large populations of specialized cells would be of great benefit in the development and testing of drugs, the researchers believe. With large numbers of goblet cells controlling the immune response to food proteins, scientists could study food allergies; enteroendocrine cells secreting hunger hormones could help in testing new treatments for obesity.
Goblet-shaped cells (red) differentiated from pure stem cells. (Photo: MIT)
"If we had ways to perform high–throughput screening of a large number of these very specific cell types, we could identify new targets and develop completely new drugs for the treatment of a wide range of diseases – from inflammatory bowel diseases to diabetes," says Jeffrey, associate professor of medicine at Harvard Medical School and BWH Karp (Jeffrey Karp), senior author of the article.
In 2007, Hans Clevers, a professor at the Hubrecht Institute, the Netherlands, identified a marker of intestinal epithelial stem cells – a protein, Lgr5. In addition, Dr. Klevers, one of the authors of an article in Nature Methods, identified growth factors that allow these stem cells to multiply and spontaneously differentiate into mature cells in vitro, forming small structures called organoids that mimic the natural architecture of the intestinal lining.
In the new study, the scientists' goal was to learn how to obtain the cleanest possible populations of intestinal stem cells, in other words, to figure out how to maintain the proliferation of stem cells while preventing their differentiation. This is not an easy task, because intestinal stem cells begin to differentiate as soon as they lose contact with Paneta cells.
Paneta cells control two signaling pathways known as Notch and Wnt that coordinate cell proliferation, especially during embryonic development. Researchers have identified two low molecular weight compounds – valproic acid and CHIR-99021 – which together induce stem cell proliferation and prevent their differentiation.
By growing mouse intestinal stem cells in an environment containing these two small molecules, the researchers obtained large clusters consisting of 70-90 percent stem cells. Having obtained almost pure stem cell populations, they showed that they can be "forced" to develop into certain types of intestinal cells by adding other factors affecting the Wnt and Notch pathways.
"To induce the differentiation of stem cells into specific populations of mature cells, we used various combinations of inhibitors and activators," explains lead author Xiaolei Yin, a postdoctoral fellow at the Koch Institute and BWH.
Paneta cells (red) differentiated from pure stem cells. (Photo: MIT)
As the researchers found, this approach also works on the cells of the stomach and colon of mice. In addition, small molecules stimulate the proliferation of human intestinal stem cells. Currently, scientists are working on creating intestinal tissues for transplantation to patients and developing new methods for quickly checking the effect of drugs on its cells.
Another area of use of these cells is to study the biology underlying the unique ability of stem cells to self–renew and differentiate into other cell types, says Ramesh Shivdasani, associate professor of medicine at Harvard Medical School and the Dana-Farber Cancer Institute.
"There is a lot we don't know about stem cells," continues Shivdasani, who was not involved in this study. "Without having large quantities of these cells at your disposal, it is very difficult to conduct any experiments. They open the way to a systematic, accurate, reliable way to study the biology of intestinal stem cells."
Portal "Eternal youth" http://vechnayamolodost.ru11.12.2013