Postdoctoral Fellow Mount Sinai Hospital, Toronto Toronto, Ontario, Canada
Abstract: The outermost layer of the small intestine, termed the intestinal epithelium, is critical for regulating digestion, nutrient absorption, and microbiota in the gut. As such, this epithelial layer shows remarkable regenerative capacity, completely restoring its cellular architecture within a few days following damage. For a long time, the cellular mechanisms driving this regeneration were unclear as the stereotypical intestinal stem cells, called crypt base cells (CBCs), are lost following irradiation and chemical injury. Our lab previously identified a novel ‘revival stem cell’ (revSC) population in the mouse intestinal epithelium, marked by the expression of the Clu gene. RevSCs, while normally rare in the homeostatic intestine, are strongly induced by irradiation damage and give rise to new CBCs. However, the cellular signaling mechanisms driving revSC induction were still unclear. We find that the TGF-b signaling pathway is strongly activated in the mouse intestinal epithelium following irradiation. Consistent with this, treatment of mouse intestinal organoids with the TGF-b1 ligand results in strong Clu upregulation. These TGFb1-induced organoids also upregulate other revSC marker genes, F3 and Anxa1, that we previously indentified. Additionally, when isolated and replated, TGF-b1 induced Clu-expressing cells give rise to new organoids confirming their regenerative capacity. Next, using a combination of small molecule modulators of the Notch and Wnt signaling pathways, we generated specialized organoids enriched for Enterocytes, Paneth, or Goblet cells, the three most abundant cell populations in the intestinal epithelium. By treating these enriched organoids with TGF-b1, we found that each of these populations could give rise to Clu+ stem cells, demonstrating that revSCs appear from pre-exisiting differentiated epithelial cells. Together, these data help uncover the complex cellular and molecular mechanisms driving the emergence of revSCs, a critical injury-induced stem cell population in the intestinal epithelium. Further, we identify the TGF-b signaling pathway as a potential therapeutic target to drive revSC-mediated regeneration in the intestine.
