Differentiation of Human Embryonic Stem Cells to Intestinal Fates
The roughly 25 feet of intestine in the adult human play numerous essential roles in daily life, such as nutrient absorption, secretion of hormones, and serving as a barrier to infection. Commensurate with these diverse roles, diseases of the intestine are a considerable source of human morbidity and mortality. Indeed, numerous pathologic conditions including inflammatory bowel diseases, mesenteric ischemia, congenital syndromes and trauma, with or without concomitant intestinal resection, all impair intestinal function to the extent that “short-gut” syndromes develop—resulting in effective intestinal failure. Current therapies rely on supportive measures such as total parenteral nutrition, in which patients receive all of their nutrition intravenously, or even intestinal transplantation.
The adult intestine is populated by specialized but highly active intestinal stem cells, which ideally could be harnessed for stem cell therapies of these disabling conditions. However, despite intensive research, no methods currently exist for identifying, isolating, and growing these intestinal stem cells for therapeutic purposes.
Our goal is to develop technologies enabling human embryonic stem (hES) cells to be reliably converted to intestinal cells in culture. Human ES cells can be readily grown in culture but represent a completely undifferentiated tabula rasa. Here, we propose studies to convert hES cells to intestinal stem cells and thence to mature intestinal cells. Towards this goal, we have developed the first methodology to induce intestinal cells to divide and expand as cultures, or “explants” outside of the body. This success has been reliant on the provision in our explants of a nutritive “niche”, a specialized area in which signals conductive to intestinal stem cell survival are highly concentrated. In this proposal, the hES cells will be placed in this niche of our explant culture, amidst signals that would promote their conversion from a naïve state into intestinal stem cells and their mature progeny. We will further refine these methods by coaxing hES cells along the first steps towards intestine prior to placing them in the explant niche, as well as by adding hormones to encourage growth of intestinal cells. The use of hES cells could greatly enhance the growth of our explant cultures, vastly expanding the yield of cultured intestine.
The therapeutic applications of this work are clear. The combination of ES cell technology along with our explant culture system holds considerable promise for the eventual generation of large quantities of intestinal stem cells, or even artificial intestine. Hopefully, these will yield effective therapies for the numerous conditions resulting in effective intestinal failure, for which currently available therapies are decidedly suboptimal.
The proposed research will develop new human embryonic stem cell-based technologies enabling the robust propagation of intestinal tissue and its associated stem cells outside of the human body, in laboratory culture. These studies have implications for the treatment of disabling conditions of the intestinal tract including inflammatory bowel disease, mesenteric ischemia and congentital intestinal disorders.
The human intestine participates in a tremendous array of processes that are essential for daily life, including absorption of nutrients, secretion of hormones, and function as an immune organ against bacteria, viruses and parasites. Because of this, diseases of the intestine such as inflammatory bowel diseases, mesenteric ischemia, congenital short gut syndromes and trauma can produce severe disability and even mortality. In extreme cases where the degree of intestinal compromise is extremely severe, patients may need receive all of their nutrition intravenously, or even undergo intestinal transplantation. The purpose of this research is to induce human embryonic stem cells to develop into intestinal derivatives, to provide a replacement tissue these disorders of severe intestinal dysfunction.
The first goal has been to place human embryonic stem cells into a nurturing enviroment, or niche, where they would be exposed to the same signals that intestinal cells receive in the human body. Accordingly, human embryonic stem cells have been injected into cultures of mouse intestine in which such signals are operative. Under these conditions, the embryonic stem cells incorporate adjacent to the mouse intestine as well as to supporting stromal cells, and undergo a dramatic change in morphology, although they do not acquire an intestinal identity. Injections of embryonic stem cells that have been induced to become endoderm, a precursor tissue to the intestine, appear more encouraging. The second goal has examined the ability of stimulation of the Wnt pathway to induce intestinal growth and differentiation of human embryonic stem cells. These studies have confirmed that Wnt pathway stimulation greatly promotes growth of intestinal cultures, suggesting that such a strategy could feasibly promote the differentiation of human embryonic stem cells to become intestine. Finally, the third goal is to develop niches for intestinal differentiation of human embryonic stem cells that are fully comprised of mouse tissue. Here, a variety of strategies of tissue preparation and culture are under evaluation.
- Proc Natl Acad Sci U S A (2011) The intestinal stem cell markers Bmi1 and Lgr5 identify two functionally distinct populations. (PubMed: 22190486)
- Nat Med (2009) Sustained in vitro intestinal epithelial culture within a Wnt-dependent stem cell niche. (PubMed: 19398967)