Sanne Rosekrans

ER Stress Causes Rapid Loss of Intestinal Epithelial Stemness through Activation of the Unfolded Protein Response

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.

Hedgehog signaling and maintenance of homeostasis in the intestinal epithelium.

Homeostasis of the rapidly renewing intestinal epithelium depends on a balance between cell proliferation and loss. Indian hedgehog (Ihh) acts as a negative feedback signal in this dynamic equilibrium. We discuss recent evidence that Ihh may be one of the key epithelial signals that indicates epithelial integrity to the underlying mesenchyme.

Oestrogens promote tumorigenesis in a mouse model for colitis-associated cancer

Background Hormone replacement therapy increases the risk of developing ulcerative colitis in postmenopausal women. Chronic intestinal inflammation predisposes to colon cancer development, but effects of female hormones on colitis-associated cancer development have not been examined. Aim To investigate the role of female hormones in the dextran sodium sulfate (DSS)-azoxymethane (AOM) mouse model for colitis-associated cancer. Design We performed ovariectomies, or sham operations, on mice, and supplemented these animals with indicated hormones. Additionally, we used oestrogen receptor α or β (Erα or Erβ) mutant mice. To study colitis or colitis-associated cancer, we used DSS only, or DSS and AOM, respectively. Results Ovariectomy protects female mice against colitis-associated tumour development. Hormone replacement in ovariectomised mice with either oestradiol (E2), medroxyprogesterone acetate or a combination of both suggests that oestrogens are the ovary-derived factor that promotes tumour development in the context of inflammatory damage. E2-treated animals showed increased clinical symptoms and Il-6 production upon DSS-induced colitis and enhanced epithelial proliferation. Treatment with E2 markedly increased the numbers of polyps in ovariectomised mice and also strongly promoted tumour progression with all E2-treated animals developing at least one invasive adenocarcinoma, whereas, placebo-treated animals developed adenomas only. Using Er mutant mice, we find that the protumorigenic effect of oestrogen depends on both Erα and Erβ. Conclusions Our results suggest that oestrogens promote inflammation-associated cancer development by impairing the mucosal response to inflammatory damage.

Stromal Indian Hedgehog Signaling Is Required for Intestinal Adenoma Formation in Mice

BACKGROUND & AIMS Indian hedgehog (IHH) is an epithelial-derived signal in the intestinal stroma, inducing factors that restrict epithelial proliferation and suppress activation of the immune system. In addition to these rapid effects of IHH signaling, IHH is required to maintain a stromal phenotype in which myofibroblasts and smooth muscle cells predominate. We investigated the role of IHH signaling during development of intestinal neoplasia in mice. METHODS Glioma-associated oncogene (Gli1)-CreERT2 and Patched (Ptch)-lacZ reporter mice were crossed with Apc(Min) mice to generate Gli1CreERT2-Rosa26-ZSGreen-Apc(Min) and Ptch-lacZ-Apc(Min) mice, which were used to identify hedgehog-responsive cells. Cyp1a1Cre-Apc (Apc(HET)) mice, which develop adenomas after administration of β-naphthoflavone, were crossed with mice with conditional disruption of Ihh in the small intestine epithelium. Apc(Min) mice were crossed with mice in which sonic hedgehog (SHH) was overexpressed specifically in the intestinal epithelium. Intestinal tissues were collected and analyzed histologically and by immunohistochemistry and quantitative reverse-transcription polymerase chain reaction. We also analyzed levels of IHH messenger RNA and expression of IHH gene targets in intestinal tissues from patients with familial adenomatous polyposis (n = 18) or sessile serrated adenomas (n = 15) and normal colonic tissue from control patients (n = 12). RESULTS Expression of IHH messenger RNA and its targets were increased in intestinal adenomas from patients and mice compared with control colon tissues. In mice, IHH signaling was exclusively paracrine, from the epithelium to the stroma. Loss of IHH from Apc(HET) mice almost completely blocked adenoma development, and overexpression of SHH increased the number and size of adenomas that developed. Loss of IHH from Apc(HET) mice changed the composition of the adenoma stroma; cells that expressed α-smooth muscle actin or desmin were lost, along with expression of cyclooxygenase-2, and the number of vimentin-positive cells increased. CONCLUSIONS Apc mutant epithelial cells secrete IHH to maintain an intestinal stromal phenotype that is required for adenoma development in mice.

ER stress induces epithelial differentiation in the mouse oesophagus

Objective Stress in the endoplasmic reticulum (ER) leads to activation of the unfolded protein response (UPR). Xbp1, a key component of the UPR has recently been linked to the risk of developing oesophageal squamous cell carcinoma, suggesting an important role for the UPR in the oesophageal epithelium. Here we examined the role of ER stress and the UPR in oesophageal epithelial homoeostasis. Design We examined the expression of components of the UPR in the oesophageal epithelium. We used a pharmacological approach and a genetic approach to examine the effects of ER stress in vivo in the mouse oesophagus. The oesophagus of these mice was examined using immunohistochemistry and real-time reverse transcription (RT)-PCR. Results Components of the UPR were heterogeneously expressed in the basal layer of the epithelium. Induction of ER stress by 24-h treatment with thapsigargin resulted in depletion of proliferating cells in the basal layer of the oesophagus and induced differentiation. We next activated the UPR by inducible deletion of the major ER chaperone Grp78 in Ah1Cre-Rosa26-LacZ-Grp78−/− mice in which mutant cells could be traced by expression of LacZ. In these mice LacZ-positive mutant cells in the basal layer lost their proliferative capacity, migrated towards the oesophageal lumen and were replaced by LacZ-negative non-mutant cells. We observed no apoptosis in mutant cells. Conclusions These results show that ER stress induces epithelial differentiation in precursor cells in the oesophageal epithelium. This UPR induced differentiation may serve as a quality control mechanism that protects against oesophageal cancer development.

Esophageal development and epithelial homeostasis

The esophagus is a relatively simple organ that evolved to transport food and liquids through the thoracic cavity. It is the only part of the gastrointestinal tract that lacks any metabolic, digestive, or absorptive function. The mucosa of the adult esophagus is covered by a multilayered squamous epithelium with a remarkable similarity to the epithelium of the skin despite the fact that these tissues originate from two different germ layers. Here we review the developmental pathways involved in the establishment of the esophagus and the way these pathways regulate gut-airway separation. We summarize current knowledge of the mechanisms that maintain homeostasis in esophageal epithelial renewal in the adult and the molecular mechanism of the development of Barretts metaplasia, the precursor lesion to esophageal adenocarcinoma. Finally, we examine the ongoing debate on the hierarchy of esophageal epithelial precursor cells and on the presence or absence of a specific esophageal stem cell population. Together the recent insights into esophageal development and homeostasis suggest that the pathways that establish the esophagus during development also play a role in the maintenance of the adult epithelium. We are beginning to understand how reflux of gastric content and the resulting chronic inflammation can transform the squamous esophageal epithelium to columnar intestinal type metaplasia in Barretts esophagus.

HDAC1 and HDAC2 collectively regulate intestinal stem cell homeostasis

Histone deacetylases (HDACs) are post‐translational modifiers that deacetylate proteins. Despite their crucial role in numerous biological processes, the use of broad‐range HDAC inhibitors (HDACi), has shown clinical efficacy. However, undesired side effects highlight the necessity to better understand the biology of different HDACs and target the relevant HDACs. Using a novel mouse model, in which HDAC1 and HDAC2 can be simultaneously deleted in the intestine of adult mice, we show that the simultaneous deletion of HDAC1 and HDAC2 leads to a rapid loss of intestinal homeostasis. Importantly, this deletion cannot be sustained, and 8 days after initial ablation, stem cells that have escaped HDAC1 or HDAC2 deletion swiftly repopulate the intestinal lining. In vitro ablation of HDAC1 and HDAC2 using intestinal organoid cultures resulted in a down‐regulation of multiple intestinal stem cell markers and functional loss of clonogenic capacity. Importantly, treatment of wild‐type organoids with class I‐specific HDACi MS‐275 also induced a similar loss of stemness, providing a possible rationale for the gastrointestinal side effects often observed in HDACi‐treated patients. In conclusion, these data show that HDAC1 and HDAC2 have a redundant function and are essential to maintain intestinal homeostasis.—Zimberlin, C. D., Lancini, C., Sno, R., Rosekrans, S. L., McLean, C. M., Vlaming, H., van den Brink, G. R., Bots, M., Medema, J. P., Dannenberg, J.‐H. HDAC1 and HDAC2 collectively regulate intestinal stem cell homeostasis. FASEB J. 29, 2070‐2080 (2015). www.fasebj.org

Hedgehog signalling stimulates precursor cell accumulation and impairs epithelial maturation in the murine oesophagus

Objective In the intestine Hedgehog (Hh) signalling is directed from epithelium to mesenchyme and negatively regulates epithelial precursor cell fate. The role of Hh signalling in the oesophagus has not been studied in vivo. Here the authors examined the role of Hh signalling in epithelial homeostasis of oesophagus. Design The authors used transgenic mice in which the Hh receptor Patched1 (Ptch1) could be conditionally inactivated in a body-wide manner and mice in which Gli1 could be induced specifically in the epithelium of the skin and oesophagus. Effects on epithelial homeostasis of the oesophagus were examined using immunohistochemistry, in situ hybridisation, transmission electron microscopy and real-time PCR. Hh signalling was examined in patients with oesophageal squamous cell carcinoma (SCC) by quantitative real-time PCR. Results Sonic Hh is signalled in an autocrine manner in the basal layer of the oesophagus. Activation of Hh signalling resulted in an expansion of the epithelial precursor cell compartment and failure of epithelial maturation and migration. Levels of Hh targets GLI1, HHIP and PTCH1 were increased in SCC compared with normal tissue from the same patients. Conclusion Here the authors find that Hh signalling positively regulates the precursor cell compartment in the oesophageal epithelium in an autocrine manner. Since Hh signalling targets precursor cells in the oesophageal epithelium and signalling is increased in SCCs, Hh signalling may be involved in oesophageal SCC formation.

Azathioprine does not reduce adenoma formation in a mouse model of sporadic intestinal tumorigenesis.

AIM To investigate if azathioprine could reduce adenoma formation in Apc(Min/+) , a mouse model of sporadic intestinal tumorigenesis. METHODS Azathioprine was administered via drinking water (estimated 6-20 mg/kg body weight per day) to Apc(Min/+) and wildtype mice. Control animals received vehicle only (DMSO) dissolved in drinking water. At 15 wk of age all mice were sacrificed and intestines of Apc(Min/+) were harvested for evaluation of polyp number. Azathioprine induced toxicity was investigated by immunohistochemical analysis on spleens. RESULTS All azathioprine treated mice showed signs of drug-associated toxicity such as weight loss and development of splenic T-cell lymphomas. Although this suggests that the thiopurine concentration was clearly in the therapeutic range, it did not reduce tumor formation (48 ± 3.1 adenomas vs 59 ± 5.7 adenomas, P = 0.148). CONCLUSION We conclude that in the absence of inflammation, azathioprine does not affect intestinal tumorigenesis.

Tu1651 Indian Hedgehog Is Required for Intestinal Adenoma Formation

Introduction: Activating mutations in the Hedgehog pathway are found in basal cell carcinomas and medulloblastomas. The role of Hedgehog signaling in intestinal tumorigenesis has not yet been clarified. Hedgehog is expressed by differentiated enterocytes and signals in a paracrine manner from the epithelium to the mesenchyme. Hedgehog controls mesenchymal factors such as Bone Morphogenetic Proteins and Activins which negatively regulate the proliferation of precursor cells. Since Indian Hedgehog (Ihh) is the major Hedgehog expressed in the intestinal epithelium we decided to study the potential role of Ihh signaling in intestinal adenoma formation.Methods: In order to study the effect of loss of Ihh signaling in sporadic tumorigenesis we conditionally deleted Ihh in adult mice in the intestinal epithelium using the Cyp1a1Cre promoter. These compound mice were crossed with conditional mutant Apc mice to generate Cyp1a1Cre-Ihh-Apc mice. At 4-7 weeks of age mice were intraperitoneally injected with 80 mg/kg β-naphthoflavone for 5 days. Cyp1a1Cre-IhhApc littermates served as controls. Four months after recombination, we sacrificed and analyzed the mice (n=15). Results: Ihh expression was upregulated in polyps of Cyp1a1CreIhh-Apc mice as assessed by in situ hybridization. Deletion of Ihh resulted in a marked reduction of 90.3% in the number of polyps (17.2 ± 13.65 polyps per mouse vs. 1.7 ± 1.5, P < 0.01). The average polyp size did not differ between groups. Neither did the number of proliferating or apoptotic cells in the polyps, as assessed by immunostaining for BrdU and cleaved caspase 3. Hh responsive cells in the adenomawere restricted to themesenchyme. In those adenomas that did develop in Ihh mutant mice, we observed a remarkable loss of α-sma/desmin double positive smooth muscle cells. COX2 is expressed early in adenoma to carcinoma transition and believed to play an important role in adenoma formation. Stromal cells are known to be a source of COX2. In accordance with this, examination of Cox2 expression by Q-PCR and immunostaining showed up regulation in polyps ofCyp1a1Cre-Ihh -Apc mice in compared to normal intestinal epithelium (P < 0.01, resp. P < 0.05). In contrast, Cox2 expression in the polyps of Cyp1a1Cre-Ihh-Apc mice was not significantly up regulated. Conclusion: Surprisingly, in contrast to its role as an anti-proliferative signal in the normal epithelium, Ihh acts as a tumor promoter. Our data show that Ihh signaling is increased during intestinal adenoma formation and as in the normal intestine Ihh signaling is exclusively from the epithelium to the mesenchyme. Loss of Ihh signaling is associated with major changes in the composition of the adenoma mesenchyme and decreased Cox2 expression, which significantly impairs adenoma formation.