By closely studying how the intestine renews its epithelial cells, scientists have learned how to emulate intestinal renewal processes in vitro, raising hopes that gut tissues could be produced in the laboratory, then introduced to patients suffering gastrointestinal disorders such as ulcers or Crohn’s disease. If these hopes are realized, inflamed or diseased gut tissue could be swapped out almost as readily as faulty plumbing.
Until recently, efforts to recapitulate intestinal self-renewal via the manipulation of stem cells had limited success. Stem cells could be expanded for multiple passages in the form of organoids, but culture conditions provided hardly any control over their self-renewal and differentiation. Typical cultures consisted of heterogeneous cell populations including stem cells and differentiated cells.
Nonetheless, scientists remained focused on a key observation: The renewal of intestinal epithelium is driven by Lgr5+ stem cells that reside at the bottom of intestinal structures called crypts. The scientists were also aware that Lgr5+ stem cells remain immature so long as they remain in contact with specialized cells called Paneth cells.
On the basis of this knowledge, scientists at Brigham and Women's Hospital (BWH) and MIT tried removing Paneth cells. In addition, the scientists introduced two small molecules involved in cell signaling. Under the experimental conditions created by the scientists, these molecules—CHIR99021 and valproic acid—could direct the Lgr5+ stem cells to develop into pure populations of proliferating stem cells. Then the scientists introduced other molecules into the mix. These molecules—the Wnt pathway inhibitor IWP-2 and Notch inhibitor DAPT—induced the pure cells to further develop into specialized mature intestinal stem cells.
The scientists reported their results December 1 in Nature Methods, in an article entitled “Niche-independent high-purity cultures of Lgr5+intestinal stem cells and their progeny.” In this paper, the authors wrote that they made use of their homogenous cultures “to identify conditions employing simultaneous modulation of Wnt and Notch signaling to direct lineage differentiation into mature enterocytes, goblet cells, and Paneth cells.”
Commenting on the importance of being able to expand intestinal stem cell numbers, Jeffrey Karp, Ph.D., a co-senior study author and co-director of the Center for Regenerative Therapeutics at the BWH, pointed to potential stem cell therapies in which “cells could be delivered to patients to treat diseases such as Crohn’s disease and ulcerative colitis.” Dr. Karp added that the stem cells could also be useful to pharmaceutical companies, which could “screen and identify new drugs that could regulate diseases from inflammatory bowel disease, to diabetes, to obesity.”
Dr. Karp and his colleagues also noted that their findings could be potentially applied for in vivo use of small molecule drugs to help regenerate cells to replace tissues ravaged by gastrointestinal diseases.
“This opens the door to doing all kinds of things, ranging from someday engineering a new gut for patients with intestinal diseases to doing drug screening for safety and efficacy,” said Robert Langer, Sc.D., MIT, another co-senior study author.