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Abstract The epithelial signaling pathways involved in damage and regeneration, and neoplastic transformation are known to be similar. We noted upregulation of argininosuccinate synthetase (ASS1) in hyperproliferative intestinal epithelium. Since ASS1 leads to de novo synthesis of arginine, an important amino acid for the growth of intestinal epithelial cells, its upregulation can contribute to epithelial proliferation necessary to be sustained during oncogenic transformation and regeneration. Here we investigated the function of ASS1 in the gut epithelium during tissue regeneration and tumorigenesis, using intestinal epithelial conditional Ass1 knockout mice and organoids, and tissue specimens from colorectal cancer patients. We demonstrate that ASS1 is strongly expressed in the regenerating and Apc-mutated intestinal epithelium. Furthermore, we observe an arrest in amino acid flux of the urea cycle, which leads to an accumulation of intracellular arginine. However, loss of epithelial Ass1 does not lead to a reduction in proliferation or increase in apoptosis in vivo, also in mice fed an arginine-free diet. Epithelial loss of Ass1 seems to be compensated by altered arginine metabolism in other cell types and the liver.

Abstract Enforcing differentiation of cancer stem cells is considered as a potential strategy to sensitize colorectal cancer cells to irradiation and chemotherapy. Activation of the unfolded protein response, due to endoplasmic reticulum (ER) stress, causes rapid stem cell differentiation in normal intestinal and colon cancer cells. We previously found that stem cell differentiation was mediated by a Protein kinase R-like ER kinase (PERK) dependent arrest of mRNA translation, resulting in rapid protein depletion of WNT-dependent transcription factor c-MYC. We hypothesize that ER stress dependent stem cell differentiation may rely on the depletion of additional transcriptional regulators with a short protein half-life that are rapidly depleted due to a PERK-dependent translational pause. Using a novel screening method, we identify novel transcription factors that regulate the intestinal stem cell fate upon ER stress. ER stress was induced in LS174T cells with thapsigargin or subtilase cytotoxin (SubAB) and immediate alterations in nuclear transcription factor activity were assessed by the CatTFRE assay in which transcription factors present in nuclear lysate are bound to plasmid DNA, co-extracted and quantified using mass-spectrometry. The role of altered activity of transcription factor CtBP2 was further examined by modification of its expression levels using CAG-rtTA3-CtBP2 overexpression in small intestinal organoids, shCtBP2 knockdown in LS174T cells, and familial adenomatous polyposis patient-derived organoids. CtBP2 overexpression organoids were challenged by ER stress and ionizing irradiation. We identified a unique set of transcription factors with altered activation upon ER stress. Gene ontology analysis showed that transcription factors with diminished binding were involved in cellular differentiation processes. ER stress decreased CtBP2 protein expression in mouse small intestine. ER stress induced loss of CtBP2 expression which was rescued by inhibition of PERK signaling. CtBP2 was overexpressed in mouse and human colorectal adenomas. Inducible CtBP2 overexpression in organoids conferred higher clonogenic potential, resilience to irradiation-induced damage and a partial rescue of ER stress-induced loss of stemness. Using an unbiased proteomics approach, we identified a unique set of transcription factors for which DNA-binding activity is lost directly upon ER stress. We continued investigating the function of co-regulator CtBP2, and show that CtBP2 mediates ER stress-induced loss of stemness which supports the intestinal stem cell state in homeostatic stem cells and colorectal cancer cells.

Background & Aims: Activation factor-1 transcription factor family members activating transcription factors 2 and 7 (ATF2 and ATF7) have highly redundant functions owing to highly homologous DNA binding sites. Their role in intestinal epithelial homeostasis and repair is unknown. Here, we assessed the role of these proteins in these conditions in an intestine-specific mouse model. Methods: We performed in vivo and ex vivo experiments using Villin-CreERT2Atf2fl/flAtf7ko/ko mice. We investigated the effects of intestinal epithelium-specific deletion of the Atf2 DNA binding region in Atf7-/- mice on cellular proliferation, differentiation, apoptosis, and epithelial barrier function under homeostatic conditions. Subsequently, we exposed mice to 2% dextran sulfate sodium (DSS) for 7 days and 12 Gy whole-body irradiation and assessed the response to epithelial damage. Results: Activating phosphorylation of ATF2 and ATF7 was detected mainly in the crypts of the small intestine and the lower crypt region of the colonic epithelium. Under homeostatic conditions, no major phenotypic changes were detectable in the intestine of ATF mutant mice. However, on DSS exposure or whole-body irradiation, the intestinal epithelium showed a clearly impaired regenerative response. Mutant mice developed severe ulceration and inflammation associated with increased epithelial apoptosis on DSS exposure and were less able to regenerate colonic crypts on irradiation. In vitro, organoids derived from double-mutant epithelium had a growth disadvantage compared with wild-type organoids, impaired wound healing capacity in scratch assay, and increased sensitivity to tumor necrosis factor-α–induced damage. Conclusions: ATF2 and ATF7 are dispensable for epithelial homeostasis, but are required to maintain epithelial regenerative capacity and protect against cell death during intestinal epithelial damage and repair.

Background & Aims: Recent evidence has suggested that the intact intestinal epithelial barrier protects our body from a range of immune-mediated diseases. The epithelial layer has an impressive ability to reconstitute and repair upon damage and this process of repair increasingly is seen as a therapeutic target. In vitro models to study this process in primary intestinal cells are lacking. Methods: We established and characterized an in vitro model of intestinal damage and repair by applying γ-radiation on small-intestinal organoids. We then used this model to identify novel regulators of intestinal regeneration. Results: We identified hepatocyte nuclear factor 4α (HNF4α) as a pivotal upstream regulator of the intestinal regenerative response. Organoids lacking Hnf4a were not able to propagate in vitro. Importantly, intestinal Hnf4a knock-out mice showed impaired regeneration after whole-body irradiation, confirming intestinal organoids as a valuable alternative to in vivo studies. Conclusions: In conclusion, we established and validated an in vitro damage–repair model and identified HNF4α as a crucial regulator of intestinal regeneration. Transcript profiling: GSE141515 and GSE141518.

Dendritic cells (DC) are important for maintaining immune homeostasis in the gut, but how they promote intestinal inflammation upon bacterial infection is still unclear. Here the authors show that IgA immune complexes induce proinflammatory cytokine production by metabolic reprogramming of otherwise tolerogenic human CD103+ DCs.

Summary: Intestinal epithelial cells have a defined hierarchy with stem cells located at the bottom of the crypt and differentiated cells more at the top. Epithelial cell renewal and differentiation are strictly controlled by various regulatory signals provided by epithelial as well as surrounding cells. Although there is evidence that stromal cells contribute to the intestinal stem cell niche, their markers and the soluble signals they produce have been incompletely defined. Using a number of established stromal cell markers, we phenotypically and functionally examined fibroblast populations in the colon. CD90+ fibroblasts located in close proximity to stem cells in vivo support organoid growth in vitro and express crucial stem cell growth factors, such as Grem1, Wnt2b, and R-spondin3. Moreover, we found that CD90+ fibroblasts express a family of proteins—class 3 semaphorins (Sema3)—that are required for the supportive effect of CD90+ fibroblasts on organoid growth. : Stem cell proliferation is dependent on regulatory signals from surrounding cells, including stromal cells. Karpus et al. identify a membrane marker, CD90, that specifically marks stem cell niche fibroblasts in the colon. CD90+ fibroblasts produce class 3 semaphorins that promote stem cell proliferation via the Nrp2 receptor. Keywords: colon, intestine, stem cell, niche, fibroblast, stroma, Gli1, CD90, semaphorin, Nrp2

The Hedgehog signalling pathway can drive tumorigenesis. Here, the authors show that in a colitis-associated colon cancer model downstream Hedgehog signalling is restricted to the stroma and its over-activation can inhibit tumorigenesis, associated with activation of BMP signaling.

Upon intestinal epithelial damage a complex wound healing response is initiated to restore epithelial integrity and defend against pathogenic invasion. Epithelium-derived Indian Hedgehog (Ihh) functions as a critical sensor in this process. Signaling occurs in a paracrine manner because the receptor for Ihh is expressed only in the mesenchyme, but the exact Hedgehog target cell has remained elusive. The aim of this study was to elucidate further the nature of this target cell in the context of intestinal inflammation. Methods: Hedgehog activity was modulated genetically in both cell type–specific and body-wide models and the resulting animals were analyzed for gene expression profiles and sensitivity for dextran sodium sulfate (DSS) colitis. To characterize the Hedgehog target cell, Gli1-CreERT2-Rosa26-ZsGreen animals were generated, which express ZsGreen in all Hedgehog-responsive cells. These cells were characterized using flow cytometry and immunofluorescence. Results: Loss of Indian Hedgehog from the intestinal epithelium resulted in a rapid increase in expression of inflammation-related genes, accompanied by increased influx of immune cells. Animals with epithelium-specific deletion of Ihh or lacking the Hedgehog receptor Smoothened from Hedgehog target cells were more sensitive to DSS colitis. In contrast, specific deletion of Smoothened in the myeloid compartment did not alter the response to DSS. This suggests that Hedgehog signaling does not repress intestinal immunity through an effect on myeloid cells. Indeed, we found that Hedgehog-responsive cells expressed gp38, smooth muscle actin, and desmin, indicating a fibroblastic nature. Ihh signaling inhibited expression of C-X-C motif chemokine ligand 12 (CXCL12) in fibroblasts in vitro and in vivo, thereby impairing the recruitment of immune cells. Conclusions: We show that epithelium-derived Indian Hedgehog signals exclusively to fibroblasts in the intestine. Loss of Ihh leads to a rapid immune response with up-regulation of fibroblast-derived CXCL12, and migration of immune cells into the lamina propria.

Colon cancer stem cells (colon-CSCs) are more resistant to conventional chemotherapy than differentiated cancer cells. This subset of therapy refractory cells is therefore believed to play an important role in post-therapeutic tumor relapse. In order to improve the rate of sustained response to conventional chemotherapy, development of approaches is warranted that specifically sensitize colon-CSCs to treatment. Here, we report that ER-stress-induced activation of the unfolded protein response (UPR) forces colon-CSCs to differentiate, resulting in their enhanced sensitivity to chemotherapy in vitro and in vivo. Our data suggest that agents that induce activation of the UPR may be used to specifically increase sensitivity of colon-CSCs to the effects of conventional chemotherapy.

Stem cells generate rapidly dividing transit-amplifying cells that have lost the capacity for self-renewal but cycle for a number of times until they exit the cell cycle and undergo terminal differentiation. We know very little of the type of signals that trigger the earliest steps of stem cell differentiation and mediate a stem cell to transit-amplifying cell transition. We show that in normal intestinal epithelium, endoplasmic reticulum (ER) stress and activity of the unfolded protein response (UPR) are induced at the transition from stem cell to transit-amplifying cell. Induction of ER stress causes loss of stemness in a Perk-eIF2α-dependent manner. Inhibition of Perk-eIF2α signaling results in stem cell accumulation in organoid culture of primary intestinal epithelium. Our findings show that the UPR plays an important role in the regulation of intestinal epithelial stem cell differentiation.

Nature Communications 7:12321 doi: (2016); Published 5 Aug 2016; Updated 13 Sep 2016 In Fig. 6f of this Article, the labelling of the two immunohistochemistry images was inadvertently changed from ‘Haematoxylin, ki67’ to ‘Haematoxylin, Casp-3’ during the production process. The correct version of Fig.

Overt fibrostenotic disease is a relative contraindication for anti-TNF therapy in Crohn's disease. We hypothesized that subclinical fibrosis may also contribute to an incomplete response to anti-TNF therapy before the onset of symptomatic stenosis.In a previous trial, patients with ileocecal Crohn's disease were randomized to either immediate ileocecal resection or medical treatment with Infliximab. In case of insufficient response to Infliximab, the latter underwent secondary ileocecal resection. We compared specimens from those patients undergoing immediate resection (Infliximab naïve, n = 20) to those who failed Infliximab therapy (n = 20).Infliximab naïve and Infliximab failure patients had similar severity of inflammation when assessed by CRP levels (median 14 vs 9 mg/L) and histology (Geboes-D'Haens-score, median 10 vs 11 points). On immunohistochemistry, collagen-III and fibronectin depositions were increased in patients previously exposed to Infliximab compared to patients naïve to Infliximab. On mRNA level, procollagen peptidase showed significantly more mucosal mRNA expression in Crohn's disease patients who failed Infliximab. Infliximab responders showed no increase of this marker after 4 weeks of successful Infliximab treatment.Failure to Infliximab therapy is associated with subclinical fibrosis in Crohn's disease.

[This corrects the article DOI: 10.1371/journal.pone.0022620.].

Clinical data suggest that progestins have chemopreventive properties in the development of colorectal cancer. We set out to examine a potential protective effect of progestins and progesterone signaling on colon cancer development. In normal and neoplastic intestinal tissue, we found that the progesterone receptor (PR) is not expressed. Expression was confined to sporadic mesenchymal cells. To analyze the influence of systemic progesterone receptor signaling, we crossed mice that lacked the progesterone receptor (PRKO) to the Apc(Min/+) mouse, a model for spontaneous intestinal polyposis. PRKO-Apc(Min/+) mice exhibited no change in polyp number, size or localization compared to Apc(Min/+). To examine effects of progestins on the intestinal epithelium that are independent of the PR, we treated mice with MPA. We found no effects of either progesterone or MPA on gross intestinal morphology or epithelial proliferation. Also, in rats treated with MPA, injection with the carcinogen azoxymethane did not result in a difference in the number or size of aberrant crypt foci, a surrogate end-point for adenoma development. We conclude that expression of the progesterone receptor is limited to cells in the intestinal mesenchyme. We did not observe any effect of progesterone receptor signaling or of progestin treatment in rodent models of intestinal tumorigenesis.