Resumen de Therapeutic Potential of Intestinal Mesenchymal Stromal Cells in Inflammatory Bowel Disease and colorectal cancer
IntroductionInflammatory bowel disease (IBD) is a chronic disease with increasing incidence and prevalence, currently affecting millions of people worldwide, which can lead to an aggressive colitis-associated cancer (CAC) with a poor prognosis (1-3). Its etiology seems to rely on the complex combination of different factors, including environmental determinants, genetic predisposition, microbiota imbalance, and mucosa immune defects. This compromises the intestinal epithelial barrier, leading to an altered immune response characterized by excessive and sustained cytokine production and immune cell recruitment and activation. Thus, the state of intestinal mucosal tolerance, i.e. immunological unresponsiveness to innocuous food antigens and the commensal microbiota, becomes disrupted (4). Understanding these mechanisms has potential translational value for IBD therapy and management, as well as for preventing the development of CAC.Human intestinal mesenchymal cells (iMCs) represent a heterogeneous population of various cell types, such as fibroblasts, myofibroblasts, pericytes, smooth muscle cells and resident mesenchymal stromal cells (MSCs) (5), which reside in the subepithelial compartment where they provide much of the structural framework of the intestine. However, iMCs also play important roles regulating the homeostasis/maintenance of the epithelial barrier and promoting immunological tolerance against commensal bacteria and food antigens (6). Moreover, recent investigations have proposed that iMCs may play dual roles both inhibiting or supporting gut inflammation and injury in IBD, as well as reducing or promoting tumor growth and metastasis, depending on their response to inflammatory mediators and/or TLR agonists (7-9). The study of the stromal compartment of tissues was pioneered by Owen and Friendenstein, who discovered fibroblastic cells in the bone marrow with the capacity to give rise to bone, adipocytes and hematopoiesis-supporting stroma (10). Such MSCs are defined by a set of criteria postulated by the International Society for Cell Therapy (ISCT) (11), and can be isolated from a variety of adult and neonatal tissues. Importantly, cultured MSCs retain part of their in vivo characteristics and provide a suitable model to analyze various aspects of stromal cells in health and disease (12, 13). The design of new therapies against IBD and CAC should contemplate the importance of iMCs both in the homeostasis of the healthy intestine and the chronic inflammation (14) even though further studies are needed to fully understand their properties on tissue regeneration and immunomodulation.ObjectivesIn order to address this, we set the following objectives:1. Isolation and characterization of the immunomodulatory and tissue regenerative properties of intestinal MSCs (iMSCs) in vitro. 2. Analysis of the effect of iMSCs administration in dextran sulfate sodium (DSS)-induced acute colitis in mice: evaluation of disease severity, immune responses, tissue regeneration and microbiota composition.3. Analysis of the effect of iMSCs administration on cancer progression in a model of colitis-associated cancer: evaluation of tumor growth, immune responses, and microbiota composition. Results and discussionFirst, plastic-adherent iMCs were isolated from human intestinal resections and expanded in vitro. We then confirmed their identity as iMSCs according to the definition by ISCT (11), i.e: (i) expression of CD73, CD90, CD105, while lacking CD31, CD34 and CD45, and (ii) possessing the ability to differentiate into adipocytes, chondroblasts and osteoblasts in vitro. Second, we explored the immunomodulatory properties of iMSCs in vitro. Our data show that iMSCs significantly repressed CD4+ and CD8+ T cell proliferation, partly through a indoleamine-2,3-dioxygenase (IDO)-dependent mechanism. Furthermore, iMSCs reduced the LPS-mediated induction of TNF-α in THP-1 macrophages, suggesting a polarization into anti-inflammatory M2 macrophages. In addition, isolated iMSCs enhanced wound closure in a scratch wound healing assay, using human normal colon epithelial cells. Third, we analysed their properties in vivo in an experimental model of acute intestinal inflammation induced by DSS in C57/bl6 mice, which displays human IBD-like features(15, 16). One single intraperitoneal injection of iMSCs significantly reduced the disease activity index (DAI), the histological damage of the colon, and improved the integrity of the intestinal epithelium. The anti-inflammatory effect exerted by iMSCs was associated with a reduced expression of pro-inflammatory cytokines including Tnf-α, Il-6 and Il-12, as well as of the adhesion molecule Icam-1 and Inos, thus suggesting a M2-polarization of macrophages. Interestingly, when the microbiota was analysed, the treated mice presented a higher species richness (Chao1 index) and diversity (Shannon index), than the untreated colitic mice. Besides, iMSCs modified the abundance of key phyla affected by the DSS, such as Proteobacteria and Actinobacteria (17, 18).Finally, the iMSCs were evaluated in a murine model of CAC consisting of the injection of azoxymethane (AOM) followed by three cycles of DSS to C57/bl6 mice (19). Two intraperitoneal injections of iMSCs at the peaks of the two last DSS cycles significantly reduced colitis and the associated intestinal tumor development. The iMSCs reduced the colonic expression of several inflammatory mediators that drive CAC, including IL-6, TNF-α, IL-17/IL-23 and COX-2; the activation of the signaling pathways of PI3K/AKT and IL-6/STAT3 as well as the levels of tumor-promoting β-catenin (20). The iMSCs treatment also lowered the number of intestinal neutrophils and eosinophils in comparison to CAC mice. As shown in the DSS model, iMSCs also decreased the proportion of M1 macrophages, and partly restored the normal intestinal macrophage differentiation. Regarding their effect on microbiota composition, iMSCs reduced the CAC-induced dysbiosis, restoring the OTUs and Shannon parameters and diminishing the alterations in the relative abundance of Bacteroidetes and Verrucomicrobia.ConclusionIn summary, our data show that human iMSCs isolated from the noninflamed intestine possess potent tissue-regenerative and immunomodulatory capacities in vitro and in vivo, that could potentially be harnessed/restored to reduce IBD severity and protect against CAC.Bibliography1. Terzic J, Grivennikov S, Karin E, Karin M. Inflammation and colon cancer. Gastroenterology. 2010;138(6):2101-14 e5.2. Watanabe T, Konishi T, Kishimoto J, Kotake K, Muto T, Sugihara K, et al. Ulcerative colitis-associated colorectal cancer shows a poorer survival than sporadic colorectal cancer: a nationwide Japanese study. Inflamm Bowel Dis. 2011;17(3):802-8.3. Ou B, Zhao J, Guan S, Lu A. 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