Molecular pathways driving disease-specific alterations of intestinal epithelial cells

Taurine Alleviates Experimental Colitis by Enhancing Intestinal Barrier Function and Inhibiting Inflammatory Response through TLR4/NF-κB Signaling

Taurine (Tau) is a semiessential amino acid in mammals with preventive and therapeutic effects on several intestinal disorders. However, the exact function of taurine in ulcerative colitis (UC) is still largely unclear. In this study, we used two taurine-deficient mouse models (CSAD-/- and TauT-/- mice) to explore the influence of taurine on the progression of UC in both dextran sulfate sodium (DSS)-induced colitis and LPS-stimulated Caco-2 cells. We found that cysteine sulfinic acid decarboxylase (CSAD) and taurine transporter (TauT) expressions and taurine levels were markedly reduced in colonic tissues of mice treated with DSS. The CSAD and TauT knockouts exacerbated DSS-induced clinical symptoms and pathological damage and aggravated the intestinal barrier dysfunction and the colonic mucosal inflammatory response. Conversely, taurine pretreatment enhanced the intestinal barrier functions by increasing goblet cells and upregulating tight junction protein expression. Importantly, taurine bound with TLR4 and inhibited the TLR4/NF-κB pathway, ultimately reducing proinflammatory factors (TNF-α and IL-6) and oxidative stress. Our findings highlight the essential role of taurine in maintaining the intestinal barrier integrity and inhibiting intestinal inflammation, indicating that taurine is a promising supplement for colitis treatment.

Colitis-associated carcinogenesis: crosstalk between tumors, immune cells and gut microbiota

Colorectal cancer (CRC) is the third most common cancer worldwide. One of the main causes of colorectal cancer is inflammatory bowel disease (IBD), which includes ulcerative colitis (UC) and Crohn's disease (CD). Intestinal epithelial cells (IECs), intestinal mesenchymal cells (IMCs), immune cells, and gut microbiota construct the main body of the colon and maintain colon homeostasis. In the development of colitis and colitis-associated carcinogenesis, the damage, disorder or excessive recruitment of different cells such as IECs, IMCs, immune cells and intestinal microbiota play different roles during these processes. This review aims to discuss the various roles of different cells and the crosstalk of these cells in transforming intestinal inflammation to cancer, which provides new therapeutic methods for chemotherapy, targeted therapy, immunotherapy and microbial therapy.

Multifaceted Impacts of Periodontal Pathogens in Disorders of the Intestinal Barrier

Periodontal disease, a common inflammatory disease, is considered a hazardous factor that contributes to the development of diseases of the digestive system as well as other systems. The bridge between periodontitis and systemic diseases is believed to be periodontal pathogens. The intestine, as part of the lower gastrointestinal tract, has a close connection with the oral cavity. Within the intestine, the intestinal barrier acts as a multifunctional system including microbial, mucous, physical and immune barrier. The intestinal barrier forms the body's first line of defense against external pathogens; its breakdown can lead to pathological changes in the gut and other organs or systems. Reports in the literature have described how oral periodontal pathogens and pathobiont-reactive immune cells can transmigrate to the intestinal mucosa, causing the destruction of intestinal barrier homeostasis. Such findings might lead to novel ideas for investigating the relationship between periodontal disease and other systemic diseases. This review summarizes studies on the effects of periodontal pathogens on the intestinal barrier, which might contribute to understanding the link between periodontitis and gastrointestinal diseases.

Hyperglycemia minimally alters primary self-renewing human colonic epithelial cells while TNFα-promotes severe intestinal epithelial dysfunction

Hyperglycemia is thought to increase production of inflammatory cytokines and permeability of the large intestine. Resulting intestinal inflammation is then often characterized by excess secretion of tumor necrosis factor alpha (TNFα). Thus, hyperglycemia in hospitalized patients suffering from severe trauma or disease is frequently accompanied by TNFα secretion, and the combined impact of these insults on the intestinal epithelium is poorly understood. This study utilized a simple yet elegant model of the intestinal epithelium, comprised of primary human intestinal stem cells and their differentiated progeny, to investigate the impact of hyperglycemia and inflammatory factors on the colonic epithelium. When compared to epithelium cultured under conditions of physiologic glucose, cells under hyperglycemic conditions displayed decreased mucin-2 (MUC2), as well as diminished alkaline phosphatase (ALP) activity. Conditions of 60 mM glucose potentiated secretion of the cytokine IL-8 suggesting that cytokine secretion during hyperglycemia may be a source of tissue inflammation. TNFα measurably increased secretion of IL-8 and IL-1β, which was enhanced at 60 mM glucose. Surprisingly, intestinal permeability and paracellular transport were not altered by even extreme levels of hyperglycemia. The presence of TNFα increased MUC2 presence, decreased ALP activity, and negatively impacted monolayer barrier function. When TNFα hyperglycemia and ≤30 mM glucose and were combined, MUC2 and ALP activity remained similar to that of TNFα alone, although synergistic effects were seen at 60 mM glucose. An automated image analysis pipeline was developed to assay changes in properties of the zonula occludens-1 (ZO-1)-demarcated cell boundaries. While hyperglycemia alone had little impact on cell shape and size, cell morphologic properties were extraordinarily sensitive to soluble TNFα. These results suggest that TNFα acted as the dominant modulator of the epithelium relative to glucose, and that control of inflammation rather than glucose may be key to maintaining intestinal homeostasis.

Innate Lymphoid Cells as Regulators of Epithelial Integrity: Therapeutic Implications for Inflammatory Bowel Diseases

The occurrence of epithelial defects in the gut relevantly contributes to the pathogenesis of inflammatory bowel diseases (IBD), whereby the impairment of intestinal epithelial barrier integrity seems to represent a primary trigger as well as a disease amplifying consequence of the chronic inflammatory process. Besides epithelial cell intrinsic factors, accumulated and overwhelmingly activated immune cells and their secretome have been identified as critical modulators of the pathologically altered intestinal epithelial cell (IEC) function in IBD. In this context, over the last 10 years increasing levels of attention have been paid to the group of innate lymphoid cells (ILCs). This is in particular due to a preferential location of these rather newly described innate immune cells in close proximity to mucosal barriers, their profound capacity to secrete effector cytokines and their numerical and functional alteration under chronic inflammatory conditions. Aiming on a comprehensive and updated summary of our current understanding of the bidirectional mucosal crosstalk between ILCs and IECs, this review article will in particular focus on the potential capacity of gut infiltrating type-1, type-2, and type-3 helper ILCs (ILC1s, ILC2s, and ILC3s, respectively) to impact on the survival, differentiation, and barrier function of IECs. Based on data acquired in IBD patients or in experimental models of colitis, we will discuss whether the different ILC subgroups could serve as potential therapeutic targets for maintenance of epithelial integrity and/or mucosal healing in IBD.

Novel Functions of the Septin Cytoskeleton: Shaping Up Tissue Inflammation and Fibrosis

Chronic inflammatory diseases cause profound alterations in tissue homeostasis, including unchecked activation of immune and nonimmune cells leading to disease complications such as aberrant tissue repair and fibrosis. Current anti-inflammatory therapies are often insufficient in preventing or reversing these complications. Remodeling of the intracellular cytoskeleton is critical for cell activation in inflamed and fibrotic tissues; however, the cytoskeleton has not been adequately explored as a therapeutic target in inflammation. Septins are GTP-binding proteins that self-assemble into higher order cytoskeletal structures. The septin cytoskeleton exhibits a number of critical cellular functions, including regulation of cell shape and polarity, cytokinesis, cell migration, vesicle trafficking, and receptor signaling. Surprisingly, little is known about the role of the septin cytoskeleton in inflammation. This article reviews emerging evidence implicating different septins in the regulation of host-pathogen interactions, immune cell functions, and tissue fibrosis. Targeting of the septin cytoskeleton as a potential future therapeutic intervention in human inflammatory and fibrotic diseases is also discussed.

Apoptosis Exerts a Vital Role in the Treatment of Colitis-Associated Cancer by Herbal Medicine

Colitis-associated cancer (CAC) is known as inflammatory bowel disease (IBD)-developed colorectal cancer, the pathogenesis of which involves the occurrence of apoptosis. Western drugs clinically applied to CAC are often single-targeted and exert many adverse reactions after long-term administration, so it is urgent to develop new drugs for the treatment of CAC. Herbal medicines commonly have multiple components with multiple targets, and most of them are low-toxicity. Some herbal medicines have been reported to ameliorate CAC through inducing apoptosis, but there is still a lack of systematic review. In this work, we reviewed articles published in Sci Finder, Web of Science, PubMed, Google Scholar, CNKI, and other databases in recent years by setting the keywords as apoptosis in combination with colitis-associated cancer. We summarized the herbal medicine extracts or their compounds that can prevent CAC by modulating apoptosis and analyzed the mechanism of action. The results show the following. (1) Herbal medicines regulate both the mitochondrial apoptosis pathway and death receptor apoptosis pathway. (2) Herbal medicines modulate the above two apoptotic pathways by affecting signal transductions of IL-6/STAT3, MAPK/NF-κ B, Oxidative stress, Non-canonical TGF-β1, WNT/β-catenin, and Cell cycle, thereby ameliorating CAC. We conclude that following. (1) Studies on the role of herbal medicine in regulating apoptosis through the Ras/Raf/ERK, WNT/β-catenin, and Cell cycle pathways have not yet been carried out in sufficient depth. (2) The active constituents of reported anti-CAC herbal medicine mainly include polyphenols, terpenoids, and saccharide. Also, we identified other herbal medicines with the constituents mentioned above as their main components, aiming to provide a reference for the clinical use of herbal medicine in the treatment of CAC. (3) New dosage forms can be utilized to elevate the targeting and reduce the toxicity of herbal medicine.

ATF2 and ATF7 Are Critical Mediators of Intestinal Epithelial Repair

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.

Neutrophil-induced genomic instability impedes resolution of inflammation and wound healing

Neutrophil (PMN) infiltration of the intestinal mucosa is a hallmark of tissue injury associated with inflammatory bowel diseases (IBDs). The pathological effects of PMNs are largely attributed to the release of soluble mediators and reactive oxygen species (ROS). We identified what we believe is a new, ROS-independent mechanism whereby activated tissue-infiltrating PMNs release microparticles armed with proinflammatory microRNAs (miR-23a and miR-155). Using IBD clinical samples, and in vitro and in vivo injury models, we show that PMN-derived miR-23a and miR-155 promote accumulation of double-strand breaks (DSBs) by inducing lamin B1-dependent replication fork collapse and inhibition of homologous recombination (HR) by targeting HR-regulator RAD51. DSB accumulation in injured epithelium led to impaired colonic healing and genomic instability. Targeted inhibition of miR-23a and miR-155 in cultured intestinal epithelial cells and in acutely injured mucosa decreased the detrimental effects of PMNs and enhanced tissue healing responses, suggesting that this approach can be used in therapies aimed at resolution of inflammation, in wound healing, and potentially to prevent neoplasia.

Ceramide synthase 2 deficiency aggravates AOM-DSS-induced colitis in mice: role of colon barrier integrity

Loss of intestinal barrier functions is a hallmark of inflammatory bowel disease like ulcerative colitis. The molecular mechanisms are not well understood, but likely involve dysregulation of membrane composition, fluidity, and permeability, which are all essentially regulated by sphingolipids, including ceramides of different chain length and saturation. Here, we used a loss-of-function model (CerS2+/+ and CerS2-/- mice) to investigate the impact of ceramide synthase 2, a key enzyme in the generation of very long-chain ceramides, in the dextran sodium salt (DSS) evoked model of UC. CerS2-/- mice developed more severe disease than CerS2+/+ mice in acute DSS and chronic AOM/DSS colitis. Deletion of CerS2 strongly reduced very long-chain ceramides (Cer24:0, 24:1) but concomitantly increased long-chain ceramides and sphinganine in plasma and colon tissue. In naive CerS2-/- mice, the expression of tight junction proteins including ZO-1 was almost completely lost in the colon epithelium, leading to increased membrane permeability. This could also be observed in vitro in CerS2 depleted Caco-2 cells. The increase in membrane permeability in CerS2-/- mice did not manifest with apparent clinical symptoms in naive mice, but with slight inflammatory signs such as an increase in monocytes and IL-10. AOM/DSS and DSS treatment alone led to a further deterioration of membrane integrity and to severe clinical symptoms of the disease. This was associated with stronger upregulation of cytokines in CerS2-/- mice and increased infiltration of the colon wall by immune cells, particularly monocytes, CD4+ and Th17+ T-cells, and an increase in tumor burden. In conclusion, CerS2 is crucial for the maintenance of colon barrier function and epithelial integrity. CerS2 knockdown, and associated changes in several sphingolipids such as a drop in very long-chain ceramides/(dh)-ceramides, an increase in long-chain ceramides/(dh)-ceramides, and sphinganine in the colon, may weaken endogenous defense against the endogenous microbiome.

Intestinal microbiota contributes to colonic epithelial changes in simulated microgravity mouse model

Exposure to microgravity leads to alterations in multiple systems, but microgravity-related changes in the gastrointestinal tract and its clinical significance have not been well studied. We used the hindlimb unloading (HU) mouse model to simulate a microgravity condition and investigated the changes in intestinal microbiota and colonic epithelial cells. Compared with ground-based controls (Ctrls), HU affected fecal microbiota composition with a profile that was characterized by the expansion of Firmicutes and decrease of Bacteroidetes. The colon epithelium of HU mice showed decreased goblet cell numbers, reduced epithelial cell turnover, and decreased expression of genes that are involved in defense and inflammatory responses. As a result, increased susceptibility to dextran sulfate sodium-induced epithelial injury was observed in HU mice. Cohousing of Ctrl mice with HU mice resulted in HU-like epithelial changes in Ctrl mice. Transplantation of feces from Ctrl to HU mice alleviated these epithelial changes in HU mice. Results indicate that HU changes intestinal microbiota, which leads to altered colonic epithelial cell homeostasis, impaired barrier function, and increased susceptibility to colitis. We further demonstrate that alteration in gastrointestinal motility may contribute to HU-associated dysbiosis. These animal results emphasize the necessity of evaluating astronauts' intestinal homeostasis during distant space travel.-Shi, J., Wang, Y., He, J., Li, P., Jin, R., Wang, K., Xu, X., Hao, J., Zhang, Y., Liu, H., Chen, X., Wu, H., Ge, Q. Intestinal microbiota contributes to colonic epithelial changes in simulated microgravity mouse model.