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In the gut, tumorigenesis arises from intestinal or colonic crypt stem cells. Currently, no definitive markers exist that reliably identify gut stem cells. Here, we used the putative stem cell marker doublecortin and CaM kinase-like-1 (DCAMKL-1) to examine radiation-induced stem cell apoptosis and adenomatous polyposis coli (APC)/multiple intestinal neoplasia (min) mice to determine the effects of APC mutation on DCAMKL-1 expression. Immunoreactive DCAMKL-1 staining was demonstrated in the intestinal stem cell zone. Furthermore, we observed apoptosis of the cells negative for DCAMKL-1 at 6 hours. We found DNA damage in all the cells in the crypt region, including the DCAMKL-1-positive cells. We also observed stem cell apoptosis and mitotic DCAMKL-1-expressing cells 24 hours after irradiation. Moreover, in APC/min mice, DCAMKL-1-expressing cells were negative for proliferating cell nuclear antigen and nuclear ␤-catenin in normal-appearing intestine. However, ␤-catenin was nuclear in DCAMKL-1-positive cells in adenomas. Thus, nuclear translocation of ␤-catenin distinguishes normal and adenoma stem cells. Targeting DCAMKL-1 may represent a strategy for developing novel chemotherapeutic agents. STEM CELLS 2008;26:630 -637 Disclosure of potential conflicts of interest is found at the end of this article.

We identified cellular and molecular mechanisms within the stem cell niche that control the activity of colonic epithelial progenitors (ColEPs) during injury. Here, we show that while WT mice maintained ColEP proliferation in the rectum following injury with dextran sodium sulfate, similarly treated Myd88 -/-(TLR signaling-deficient) and prostaglandin-endoperoxide synthase 2 -/-(Ptgs2 -/-) mice exhibited a profound inhibition of epithelial proliferation and cellular organization within rectal crypts. Exogenous addition of 16,16-dimethyl PGE 2 (dmPGE 2 ) rescued the effects of this injury in both knockout mouse strains, indicating that Myd88 signaling is upstream of Ptgs2 and PGE 2 . In WT and Myd88 -/-mice, Ptgs2 was expressed in scattered mesenchymal cells. Surprisingly, Ptgs2 expression was not regulated by injury. Rather, in WT mice, the combination of injury and Myd88 signaling led to the repositioning of a subset of the Ptgs2-expressing stromal cells from the mesenchyme surrounding the middle and upper crypts to an area surrounding the crypt base adjacent to ColEPs. These findings demonstrate that Myd88 and prostaglandin signaling pathways interact to preserve epithelial proliferation during injury using what we believe to be a previously undescribed mechanism requiring proper cellular mobilization within the crypt niche.

BackgroundThe small intestinal epithelium is highly sensitive to radiation and is a major site of injury during radiation therapy and environmental overexposure.ObjectiveTo examine probiotic bacteria as potential radioprotective agents in the intestine.Methods8-week-old C57BL/6 wild-type or knockout mice were administered probiotic by gavage for 3 days before 12 Gy whole body radiation. The intestine was evaluated for cell-positional apoptosis (6 h) and crypt survival (84 h).ResultsGavage of 5×107 Lactobacillus rhamnosus GG (LGG) improved crypt survival about twofold (p<0.01); the effect was observed when administered before, but not after, radiation. Conditioned medium (CM) from LGG improved crypt survival (1.95-fold, p<0.01), and both LGG and LGG-CM reduced epithelial apoptosis particularly at the crypt base (33% to 18%, p<0.01). LGG was detected in the distal ileal contents after the gavage cycle, but did not lead to a detectable shift in bacterial family composition. The reduction in epithelial apoptosis and improved crypt survival offered by LGG was lost in MyD88−/−, TLR-2−/− and cyclo-oxygenase-2−/− (COX-2) mice but not TLR-4−/− mice. LGG administration did not lead to increased jejunal COX-2 mRNA or prostaglandin E2 levels or a change in number of COX-2-expressing cells. However, a location shift was observed in constitutively COX-2-expressing cells of the lamina propria from the villi to a position near the crypt base (villi to crypt ratio 80:20 for control and 62:38 for LGG; p<0.001). Co-staining revealed these COX-2-expressing small intestinal lamina propria cells to be mesenchymal stem cells.ConclusionsLGG or its CM reduce radiation-induced epithelial injury and improve crypt survival. A TLR-2/MyD88 signalling mechanism leading to repositioning of constitutive COX-2-expressing mesenchymal stem cells to the crypt base is invoked.