Human Bone Marrow-Derived Stem Cells Acquire Epithelial Characteristics through Fusion with Gastrointestinal Epithelial Cells

Bone marrow-derived mesenchymal stem cells (MSC) have the ability to differentiate into a variety of cell types and are a potential source for epithelial tissue repair. Several studies have demonstrated their ability to repopulate the gastrointestinal tract (GIT) in bone marrow transplanted patients or in animal models of gastrointestinal carcinogenesis where they were the source of epithelial cancers. However, mechanism of MSC epithelial differentiation still remains unclear and controversial with trans-differentiation or fusion events being evoked. This study aimed to investigate the ability of MSC to acquire epithelial characteristics in the particular context of the gastrointestinal epithelium and to evaluate the role of cell fusion in this process. In vitro coculture experiments were performed with three gastrointestinal epithelial cell lines and MSC originating from two patients. After an 8 day coculture, MSC expressed epithelial markers. Use of a semi-permeable insert did not reproduce this effect, suggesting importance of cell contacts. Tagged cells coculture or FISH on gender-mismatched cells revealed clearly that epithelial differentiation resulted from cellular fusion events, while expression of mesenchymal markers on fused cells decreased over time. In vivo cell xenograft in immunodeficient mice confirmed fusion of MSC with gastrointestinal epithelial cells and self-renewal abilities of these fused cells. In conclusion, our results indicate that fusion could be the predominant mechanism by which human MSC may acquire epithelial characteristics when in close contact with epithelial cells from gastrointestinal origin . These results could contribute to a better understanding of the cellular and molecular mechanisms allowing MSC engraftment into the GIT epithelium

Dystrophin-dependent muscle degeneration requires a fully functional contractile machinery to occur in C. elegans.

In mammals, the lack of dystrophin leads to a degeneration of skeletal muscles. It has been known for many years that this pathology can be blocked by denervation or immobilization of muscles. It is not yet clear, however, whether this suppressing effect is due to the absence of fiber contraction per se, or to other mechanisms which may be induced by such treatments. We took advantage of the genetic tools available in the animal model Caenorhabditis elegans to address this question. Using RNA interference and existing mutants, we genetically impaired the excitation-contraction cascade at specific points in a dystrophin-deficient C. elegans strain which normally undergoes extensive muscle degeneration. Our data show that reducing sarcomere contraction by slightly impairing the contraction machinery is sufficient to dramatically suppress muscle degeneration. Thus, it is the physical tension exerted on the muscle fibers which is the key deleterious event in the absence of dystrophin

Regulatory T cells may participate in Helicobacter pylori persistence in gastric MALT lymphoma: lessons from an animal model.

International audienceIt has been postulated that the emergence of autoimmune gastritis in neonatal thymectomised (d3Tx) BALB/c mice may be a consequence of post-surgery deficit in Tregs. In this study, previously obtained samples from d3Tx mice were used in order to determine whether thymectomy creates a deficit in this T cell subset thereby allowing the emergence of autoimmune phenomena as a prerequisite for GML. The splenic Treg reserve and the local recruitment of these cells in the gastric mucosa were investigated using complementary molecular and immunohistochemistry approaches. Higher Foxp3/CD3 ratios were found in the spleen of non-infected d3Tx mice compared to non-thymectomised (NTx) controls. These results indicate a relative enrichment of Tregs following thymectomy in adult mice. The absence of Treg depletion in d3Tx mice is in line with the absence of auto-immune gastritis in non-infected d3Tx mice. Higher levels of T cell and Treg infiltration were also found in the stomach of GML-developing d3Tx mice versus NTx mice. Surprisingly, inflammatory scores inversely correlated with the bacterial inoculum. The presence of a small Treg containing compartment among gastric biopsies of GML developing d3Tx mice may play a role in perseverance of a minimal bacterial numbers thereby maintaining an antigen-dependent stimulation and proliferation

Blocking of striated muscle degeneration by serotonin in C. elegans.

Prevention of muscle fiber degeneration is a key issue in the treatment of muscular dystrophies such as Duchenne Muscular Dystrophy (DMD). It is widely postulated that existing pharmaceutical compounds might potentially be beneficial to DMD patients, but tools to identify them are lacking. Here, by using a Caenorhabditis elegans model of dystrophin-dependent muscular dystrophy, we show that the neurohormone serotonin and some of its agonists are potent suppressors of muscle degeneration. Inhibitors of serotonin reuptake transporters, which prolong the action of endogenous serotonin, have a similar effect. Moreover, reduction of serotonin levels leads to degeneration of non-dystrophic muscles. Our results demonstrate that serotonin is critical to C. elegans striated muscles. These findings reveal a new function of serotonin in striated muscles

<i>Helicobacter pylori</i> Initiates a Mesenchymal Transition through ZEB1 in Gastric Epithelial Cells

<div><p>Chronic <i>Helicobacter pylori</i> infection provokes an inflammation of the gastric mucosa, at high risk for ulcer and cancer development. The most virulent strains harbor the <i>cag</i> pathogenicity island (<i>cag</i>PAI) encoding a type 4 secretion system, which allows delivery of bacterial effectors into gastric epithelial cells, inducing pro-inflammatory responses and phenotypic alterations reminiscent of an epithelial-to-mesenchymal transition (EMT). This study characterizes EMT features in <i>H. pylori</i>-infected gastric epithelial cells, and investigates their relationship with NF-κB activation. Cultured human gastric epithelial cell lines were challenged with a <i>cag</i>PAI<i>+ H. pylori</i> strain or <i>cag</i> isogenic mutants. Morphological changes, epithelial and mesenchymal gene expression and EMT-related microRNAs were studied. <i>H. pylori</i> up-regulates mesenchymal markers, including ZEB1. This transcription factor is prominently involved in the mesenchymal transition of infected cells and its up-regulation depends on <i>cag</i>PAI and NF-κB activation. ZEB1 expression and NF-κB activation were confirmed by immunohistochemistry in gastric mucosa from <i>cag</i>PAI<i>+ H. pylori</i>-infected patients. Gastric epithelial cell lines express high miR-200 levels, which are linked to ZEB1 in a reciprocal negative feedback loop and maintain their epithelial phenotype in non-infected conditions. However, miR-200b/c were increased upon infection, despite ZEB1 up-regulation and mesenchymal morphology. In the miR-200b-200a-429 cluster promoter, we identified a functional NF-κB binding site, recruiting NF-κB upon infection and trans-activating the microRNA cluster transcription. In conclusion, in gastric epithelial cells, <i>cag</i>PAI+ <i>H. pylori</i> activates NF-κB, which transactivates ZEB1, subsequently promoting mesenchymal transition. The unexpected N-FκB-dependent increase of miR-200 levels likely thwarts the irreversible loss of epithelial identity in that critical situation.</p> </div

An Eighteen-Month Helicobacter Infection Does Not Induce Amyloid Plaques or Neuroinflammation in Brains of Wild Type C57BL/6J Mice

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Changes in mesenchymal and epithelial gene expression and miR-200 levels. 10 days post-infection with cagPAI+ H. pylori (Hp WT) or the isogenic CagA-deficient strain.

<p>48 hrs post-infection at a MOI 100, infected and non-infected cells were trypsinized and subcultured for 10 days in a 6-well plate starting at an initial cell density of 2,000 cells/well. The culture medium was changed every other day. Data represent mean ± SD of RTqPCR results of the individual genes or miRNAs relative to HPRT1 or snoR25, respectively, and compared to non infected cells; n = 4; *: p-value <0.05, **: p-value <0.01, ***: p-value <0.001.</p

Kinetics of changes in IL-8 induction (A), ZEB1 and pri-miR-200b (B) and E-cadherin and vimentin (C) expressions upon infection.

<p>Cells were infected with either wt <i>H. pylori</i> (WT) or its <i>cagA</i>-deletion isogenic mutant (ΔCagA) at MOI 100 bacteria/cells for the indicated period of times. Bars indicate the fold changes of the individual genes upon infection (mean of duplicates ± SD of RNA expression normalized to HPRT1 and compared to NI).</p

NF-κB-dependent mesenchymal phenotype of infected AGS cells.

<p>In all experiments, AGS cells were infected or not (NI) with <i>cagPAI+ H. pylori</i> (WT) at MOI 100 bacteria/cells for 24 h. (A) Activities of SV40 promoter (pGL3-p), or <i>miR-200b-200a-429</i> promoter wild type (pGL3-prom200b) or mutated on the NF-κB site (pGL3-prom200b mut); bars represent mean ± SD of relative luciferase activities of each promoter reporter normalized to that of NI pGL3-p transfected cells (n = 3; ** p<0.01). (B) NF-κB activation upon infection (WT) in cells transfected either with pEGFP or with pEGFP-IκB. Bars represent mean ± SD of relative NF-κB reporter luciferase activity compared to NI pEGFP-transfected cells (n = 3; *p<0.05). (C) Cell morphology observed by phase contrast microscopy, in the same conditions. Bar, 20 µm. (D) RT-qPCR data of ZEB1 and pri-miR-200b-200a-429 in pEGFP- or pEGFP-IκB-transfected cells. Bars indicate mean ± SD of RNA expression normalized to HPRT1 and compared to NI (n = 3, * p<0.05, *** p<0.001). (E) <i>MiR-200b-200a-429</i> promoter activities measured as in (A) in cells transfected either with pEGFP or with pEGFP-IκB. (F) Chromatin immunoprecipitation assays using anti-NF-κB antibody on the promoters of miR-200b (prom200b), IL-8 (promIL-8) or ZEB1 (promZEB1). Bars represent NF-κB enrichment on a given promoter in either uninfected or infected cells, calculated as the following ratio: 2^{−ΔCt IPNF-κB}/2^{−ΔCt controlIP}, with ΔCt = Ct IP (with NF-κB antibody or without (control)) – Ct input (input corresponds to chromatin before immunoprecipitation).</p

<i>H. pylori</i>, ZEB1, p65 NF-κB, E-cadherin immunostaining and miR-200b <i>in situ</i> hybridization in non infected human gastric mucosa (left pannels) or mucosa infected with <i>cag</i>PAI+ <i>H. pylori</i> (right pannels).

<p>Images are representatives of the detection by immunohistochemistry coupled to peroxydase activity (in brown) of <i>H. pylori</i> in the lumen of gastric glands at the apical surface of gastric epithelial cells, which display an intense ZEB1 and p65 expression mainly in the nucleus, despite a similar E-cadherin expression and localization at cell/cell junction in the <i>H. pylori</i> infected specimen and the non-infected one. MiR-200b detected by ISH coupled to phosphatase alkaline activity (in dark blue) is highly expressed in gastric glands of <i>H. pylori</i>–infected case. Typical images of the same case out of three infected patients and the same case out of three uninfected cases are shown. Bar, 50 µm.</p