When Insult Is Added to Injury: Cross Talk between ILCs and Intestinal Epithelium in IBD

Animal models of inflammatory bowel disease: category and evaluation indexes

Inflammatory bowel disease (IBD) research often relies on animal models to study the etiology, pathophysiology, and management of IBD. Among these models, rats and mice are frequently employed due to their practicality and genetic manipulability. However, for studies aiming to closely mimic human pathology, non-human primates such as monkeys and dogs offer valuable physiological parallels. Guinea pigs, while less commonly used, present unique advantages for investigating the intricate interplay between neurological and immunological factors in IBD. Additionally, New Zealand rabbits excel in endoscopic biopsy techniques, providing insights into mucosal inflammation and healing processes. Pigs, with their physiological similarities to humans, serve as ideal models for exploring the complex relationships between nutrition, metabolism, and immunity in IBD. Beyond mammals, non-mammalian organisms including zebrafish, Drosophila melanogaster, and nematodes offer specialized insights into specific aspects of IBD pathology, highlighting the diverse array of model systems available for advancing our understanding of this multifaceted disease. In this review, we conduct a thorough analysis of various animal models employed in IBD research, detailing their applications and essential experimental parameters. These include clinical observation, Disease Activity Index score, pathological assessment, intestinal barrier integrity, fibrosis, inflammatory markers, intestinal microbiome, and other critical parameters that are crucial for evaluating modeling success and drug efficacy in experimental mammalian studies. Overall, this review will serve as a valuable resource for researchers in the field of IBD, offering insights into the diverse array of animal models available and their respective applications in studying IBD.

Central administration of human opiorphin alleviates dextran sodium sulfate-induced colitis in mice through activation of the endogenous opioid system

The opioid system plays a crucial role in maintaining gastrointestinal homeostasis. Endogenous opioid peptide enkephalins have anti-inflammatory effect and participate in the treatment of inflammatory bowel diseases (IBDs). Here, we investigated the effect of natural enkephalinase inhibitor human opiorphin (HO) on dextran sodium sulfate (DSS)-induced colitis in mice. Our results showed that central administration of HO attenuated DSS-induced colitis, as indicated by the reduction of disease activity index (DAI) scores, macroscopic scores, histological scores, and the myeloperoxidase (MPO) activity. Moreover, HO alleviated DSS-induced inflammation by decreasing inflammatory cytokines TNF-α, IL-6, and IL-1β, and increasing anti-inflammatory cytokine IL-10 in both serum and colon tissues in DSS-treated mice. The potential anti-inflammatory effect of HO at a dose of 40 μg/kg was observed as evidenced by a decrease in nuclear factor κB (NF-κB) p65, toll-like receptor-4 (TLR-4), iNOS, and COX-2. HO also improved intestinal barrier function by enhancing the expression of tight junction proteins. Furthermore, HO treatment significantly inhibited activities of neutral endopeptidase (NEP) and aminopeptidase N (APN), elevated serum enkephalins concentrations, and increased expressions of mu and delta opioid receptors. In addition, pretreatment with opioid receptor antagonist naloxone hydrochloride (NH) compromised the protective effect of HO and aggravated colitis symptoms, as indicated by inhibited anti-inflammatory effects, disrupted intestinal barrier function, and decreased opioid receptor activity. In conclusion, these data indicate that HO protects against DSS-induced colitis by inhibiting TLR4/NF-κB pathway activation and improving intestinal barrier function through activation of the endogenous opioid system. Therefore, targeting the opioid system with peptidase inhibitors intervention would be a novel strategy in the therapy of IBD.

Innate Lymphoid Cells in Response to Intracellular Pathogens: Protection Versus Immunopathology

Innate lymphoid cells (ILCs) are a heterogeneous group of cytokine-producing lymphocytes which are predominantly located at mucosal barrier surfaces, such as skin, lungs, and gastrointestinal tract. ILCs contribute to tissue homeostasis, regulate microbiota-derived signals, and protect against mucosal pathogens. ILCs are classified into five major groups by their developmental origin and distinct cytokine production. A recently emerged intriguing feature of ILCs is their ability to alter their phenotype and function in response to changing local environmental cues such as pathogen invasion. Once the pathogen crosses host barriers, ILCs quickly activate cytokine production to limit the spread of the pathogen. However, the dysregulated ILC responses can lead to tissue inflammation and damage. Furthermore, the interplay between ILCs and other immune cell types shapes the outcome of the immune response. Recent studies highlighted the important role of ILCs for host defense against intracellular pathogens. Here, we review recent advances in understanding the mechanisms controlling protective and pathogenic ILC responses to intracellular pathogens. This knowledge can help develop new ILC-targeted strategies to control infectious diseases and immunopathology.

The Effect of a Novel Serine Protease Inhibitor on Inflammation and Intestinal Permeability in a Murine Colitis Transfer Model

Background: A protease/antiprotease disbalance is observed in inflammatory bowel diseases (IBD). We therefore studied the effect of the novel serine protease inhibitor UAMC-00050 on intestinal inflammation and permeability in a chronic colitis T cell transfer mouse model to get further insight into the regulation of T cell-mediated immunopathology. Methods: Colitis was induced in severe combined immunodeficient (SCID) mice, by the adoptive transfer of CD4⁺CD25^-CD62L⁺ T cells. Animals were treated intraperitoneally (i.p.) 2x/day with vehicle or UAMC-00050 (5 mg/kg) from week 2 onwards. Colonic inflammation was assessed by clinical parameters, colonoscopy, macroscopy, microscopy, myeloperoxidase activity and cytokine expression levels. At week 4, 4 kDa FITC-dextran intestinal permeability was evaluated and T helper transcription factors, protease-activated receptors and junctional proteins were quantified by RT-qPCR. Results: Adoptive transfer of CD4⁺CD25^-CD62L⁺ T cells resulted in colonic inflammation and an altered intestinal permeability. The serine protease inhibitor UAMC-00050 ameliorated both the inflammatory parameters and the intestinal barrier function. Furthermore, a decrease in colonic mRNA expression of Tbet and PAR4 was observed in colitis mice after UAMC-00050 treatment. Conclusion: The beneficial effect of UAMC-00050 on inflammation was apparent via a reduction of Tbet, IFN-γ, TNF-α, IL-1β and IL-6. Based on these results, we hypothesize a pivotal effect of serine protease inhibition on the Th1 inflammatory profile potentially mediated via PAR4.

Innate lymphoid cells in peripheral blood of patients with American Cutaneous Leishmaniasis

Innate lymphoid cells (ILCs) are classified by the expression of specific transcription factors: ILC1 depending on T-bet for IFN-γ production; ILC2 depending on GATA3 for IL-5 and IL-13; and ILC3 depending on ROR-γτ and AHR for IL-17 and IL-22. This study aimed to determine circulating ILCs in 23 patients with localized (LCL) = 7, mucocutaneous (MCL) = 10, intermediate (ICL) = 3 and diffuse (DCL) = 3 cutaneous leishmaniasis and 17 healthy controls from endemic area (EC) = 9 and non-endemic area (HC) = 8. Results evidenced a higher proportion of ILC1 in LCL than controls and MCL. ILC2 was higher in DCL compared with controls. ILC3 s were abundant in MCL and DCL concerning controls. A prevalence ratio was calculated to approach cell plasticity: in LCL, the ratio showed a prevalence of ILC1/ILC3 (plasticity 1), in contrast to DCL, and controls, where ILC2/ILC3 (plasticity 3) is prevalent. Also, MCL and ICL showed higher ILC1/ILC2 (plasticity 2). These results suggest that ILC1 and ILC3 in LCL are associated with disease control and regulation of inflammation, while MCL and ICL are related to immunopathology and uncontrolled inflammation. In DCL, ILC2 is associated with the tolerogenic state of these patients.

Structure, Function, and Therapeutic Potential of the Trefoil Factor Family in the Gastrointestinal Tract

Trefoil factor family peptides (TFF1, TFF2, and TFF3) are key players in protecting, maintaining, and repairing the gastrointestinal tract. Accordingly, they have the therapeutic potential to treat and prevent a variety of gastrointestinal disorders associated with mucosal damage. TFF peptides share a conserved motif, including three disulfide bonds that stabilize a well-defined three-loop-structure reminiscent of a trefoil. Although multiple functions have been described for TFF peptides, their mechanisms at the molecular level remain poorly understood. This review presents the status quo of TFF research relating to gastrointestinal disorders. Putative TFF receptors and protein partners are described and critically evaluated. The therapeutic potential of these peptides in gastrointestinal disorders where altered mucosal biology plays a crucial role in the underlying etiology is discussed. Finally, areas of investigation that require further research are addressed. Thus, this review provides a comprehensive update on TFF literature as well as guidance toward future research to better understand this peptide family and its therapeutic potential for the treatment of gastrointestinal disorders.

Crohn's disease

Crohn's disease is an inflammatory bowel disease that is characterized by chronic inflammation of any part of the gastrointestinal tract, has a progressive and destructive course and is increasing in incidence worldwide. Several factors have been implicated in the cause of Crohn's disease, including a dysregulated immune system, an altered microbiota, genetic susceptibility and environmental factors, but the cause of the disease remains unknown. The onset of the disease at a young age in most cases necessitates prompt but long-term treatment to prevent disease flares and disease progression with intestinal complications. Thus, earlier, more aggressive treatment with biologic therapies or novel small molecules could profoundly change the natural history of the disease and decrease complications and the need for hospitalization and surgery. Although less invasive biomarkers are in development, diagnosis still relies on endoscopy and histological assessment of biopsy specimens. Crohn's disease is a complex disease, and treatment should be personalized to address the underlying pathogenetic mechanism. In the future, disease management might rely on severity scores that incorporate prognostic factors, bowel damage assessment and non-invasive close monitoring of disease activity to reduce the severity of complications.

Mesenchymal Stem Cells Decrease Oxidative Stress in the Bowels of Interleukin-10 Knockout Mice

Background/Aims: Inflammatory bowel disease (IBD) is an autoimmune disease characterized by chronic inflammation mainly in the large intestine. The interleukin-10 knockout (IL-10 KO) mouse is a well-known animal model of IBD that develops spontaneous intestinal inflammation resembling Crohn's disease. Oxidative stress is considered to be the leading cause of cell and tissue damage. Reactive oxygen species (ROS) can cause direct cell injury and/or indirect cell injury by inducing the secretion of cytokines from damaged cells. This study evaluated the effects of mesenchymal stem cell (MSC) on the progression of IBD. Methods: In this study, human bone marrow-derived MSCs were injected into IL-10 KO mice (MSC). Oxidative stress and inflammation levels were evaluated in the large intestine and compared with those in control IL-10 KO mice (CON) and normal wild-type control mice (Wild). Results: The levels of ROS (superoxide and hydrogen peroxidase) and a secondary end-product of lipid peroxidation (malondialdehyde) were considerably higher in the CON, while superoxide dismutase and catalase levels were lower in the MSC. Inflammation-related marker (interferon-γ, tumor necrosis factor-α, IL-4, and CD8) expression and inflammatory histological changes were much less pronounced in MSC than in CON. Conclusions: MSCs affect the redox balance, leading to the suppression of IBD.

Innate Lymphoid Cells: A Link between the Nervous System and Microbiota in Intestinal Networks

Innate lymphoid cells (ILCs) are a novel family of innate immune cells that act as key coordinators of intestinal mucosal surface immune defense and are essential for maintaining intestinal homeostasis and barrier integrity by responding to locally produced effector cytokines or direct recognition of exogenous or endogenous danger patterns. ILCs are also involved in the pathogenesis of inflammatory bowel disease (IBD). Many studies have demonstrated the occurrence of crosstalk between ILCs and intestinal microbiota, and ILCs have recently been shown to be connected to the enteric nervous system (ENS). Thus, ILCs may act as a key link between the nervous system and microbiota in intestinal networks. In this review, we briefly summarize the role of the ILCs in the intestinal tract (particularly in the context of IBD) and discuss the relationship between ILCs and the microbiota/ENS.

Myosin-1c promotes E-cadherin tension and force-dependent recruitment of α-actinin to the epithelial cell junction

Actomyosin II contractility in epithelial cell plays an essential role in tension-dependent adhesion strengthening. One key unsettling question is how cellular contraction transmits force to the nascent cell-cell adhesion when there is no stable attachment between the nascent adhesion complex and actin filament. Here, we show that myosin-1c is localized to the lateral membrane of polarized epithelial cells and facilitates the coupling between actin and cell-cell adhesion. Knockdown of myosin-1c compromised the integrity of the lateral membrane, reduced the generation of tension at E-cadherin, decreased the strength of cell-cell cohesion in an epithelial cell monolayer and prevented force-dependent recruitment of junctional α-actinin. Application of exogenous force to cell-cell adhesions in a myosin-1c-knockdown cell monolayer fully rescued the localization defect of α-actinin, indicating that junction mechanoregulation remains intact in myosin-1c-depleted cells. Our study identifies a role of myosin-1c in force transmission at the lateral cell-cell interface and underscores a non-junctional contribution to tension-dependent junction regulation.

Chromogranin-A Regulates Macrophage Function and the Apoptotic Pathway in Murine DSS colitis

Chromogranin-A (CHGA) is elevated in inflammatory bowel disease (IBD), but little is known about its role in colonic inflammation. IBD is associated with impaired functions of macrophages and increased apoptosis of intestinal epithelial cells. We investigated CHGA expression in human subjects with active ulcerative colitis (UC) and the underlying mechanisms in Chga ^-/- mice. In UC, CHGA, classically activated macrophage (M1) markers, caspase-3, p53, and its associated genes were increased, while alternatively activated macrophage (M2) markers were decreased without changes in the extrinsic apoptotic pathway. CHGA correlated positively with M1 and the apoptotic pathway and negatively with M2. In the murine dextran sulfate sodium (DSS)-induced colitis, Chga deletion reduced the disease severity and onset, pro-inflammatory mediators, M1, and p53/caspase-3 activation, while it upregulated anti-inflammatory cytokines and M2 markers with no changes in the extrinsic apoptotic markers. Compared to Chga ^+/+ , M1 and p53/caspase-3 activation in Chga ^-/- macrophages were decreased in vitro, while M2 markers were increased. CHGA plays a critical role during colitis through the modulation of macrophage functions via the caspase-3/p53 pathway. Strategies targeting CHGA to regulate macrophage activation and apoptosis might be developed to treat UC patients.

KEY MESSAGES

• Chromogranin-A (CHGA) is pro-hormone and is secreted in the gut. CHGA is elevated in colitis and is associated with the disease severity. The lack of GHGA has beneficial immunomodulatory properties during the development of intestinal inflammation. The lack of CHGA regulates the plasticity of macrophages and p53/caspase activation in colitis. Functional analysis of CHGA may lead to a novel therapy for IBD.

The ubiquitin ligase ITCH coordinates small intestinal epithelial homeostasis by modulating cell proliferation, differentiation, and migration

Maintenance of the intestinal mucosa is driven by local signals that coordinate epithelial proliferation, differentiation, and turnover in order to separate antigenic luminal contents from the host's immune system. Breaches in this barrier promote gastrointestinal pathologies ranging from inflammatory bowel disease to cancer. The ubiquitin ligase ITCH is known to regulate immune responses, and loss of function of ITCH has been associated with gastrointestinal inflammatory disorders, particularly in the colon. However, the small intestine appears to be spared from this pathology. Here we explored the physiological mechanism that underlies the preservation of mucosal homeostasis in the small intestine in mice lacking ITCH (Itch^a18H/a18H). Histological analysis of the small intestines from young adult mice revealed architectural changes in animals deficient for ITCH, including villus blunting with cell crowding, crypt expansion, and thickening of the muscularis propria relative to age-matched mice sufficient for ITCH. These differences were more prominent in the distal part of the small intestine and were not dependent upon lymphoid cells. Underlying the observed changes in the epithelium were expansion of the Ki67⁺ proliferating transit amplifying progenitor population and increased numbers of terminally differentiated mucus-secreting goblet and anti-microbial producing Paneth cells, which are both important in controlling local inflammation in the small intestine and are known to be dysregulated in inflammatory bowel disease. Homeostasis in the small intestine of Itch^a18H/a18H animals was maintained by increased cell turnover, including accelerated migration of epithelial cells along the crypt-villus axis and increased apoptosis of epithelial cells at the crypt-villus junction. Consistent with this enhanced turnover, Itch^a18H/a18H mice carrying the Min mutation (Itch^a18H/a18H; Apc^Min/+) displayed a 76% reduction in tumor burden as compared to Apc^Min/+ littermates with normal levels of ITCH. These findings highlight the role of ITCH as an important modulator of intestinal epithelial homeostasis.

VSL#3 probiotic differently influences IEC-6 intestinal epithelial cell status and function

The data here reported introduce the wound-healing assay as a tool for testing probiotics aimed at protecting gastrointestinal mucosal surfaces and to verify the consistency of their manufacturing. At the scope, we compared the in vitro effects of two multi-strain high concentration formulations both commercialized under the same brand VSL#3 but sourced from different production sites (USA and Italy) on a non-transformed small-intestinal epithelial cell line, IEC-6. The effects on cellular morphology, viability, migration, and H₂ O₂ -induced damage, were assessed before and after the treatment with both VSL#3 formulations. While the USA-sourced product ("USA-made") VSL#3 did not affect monolayer morphology and cellular density, the addition of bacteria from the Italy-derived product ("Italy-made") VSL#3 caused clear morphological cell damage and strongly reduced cellularity. The treatment with "USA-made" lysate led to a higher rate of wounded monolayer healing, while the addition of "Italy-made" bacterial lysate did not influence the closure rate as compared to untreated cells. While lysates from "USA-made" VSL#3 clearly enhanced the formation of elongated and aligned stress fibers, "Italy-made" lysates had not similar effect. "USA-made" lysate was able to cause a total inhibition of H₂ O₂ -induced cytotoxic effect whereas "Italy-made" VSL#3 lysate was unable to protect IEC-6 cells from H₂ O₂ -induced damage. ROS generation was also differently influenced, thus supporting the hypotesis of a protective action of "USA-made" VSL#3 lysates, as well as the idea that "Italy-made" formulation was unable to prevent significantly the H₂ O₂ -induced oxidative stress.

Potential roles of enteric glia in bridging neuroimmune communication in the gut

The enteric nervous system (ENS) is a network of neurons and glia that controls ongoing gastrointestinal (GI) functions. Damage or injury to the ENS can lead to functional GI disorders. Current data support the conclusion that many functional GI disorders are caused by an imbalance between gut microbes and the immune system, but how the ENS is involved in these interactions is less understood. Because of the proximity of the ENS to bacteria and other foreign antigens in the GI tract, it is important to prevent the passage of these antigens through the GI epithelium. If any foreign compounds manage to pass through the GI epithelium, an immune response is triggered to prevent injury to the ENS and underlying structures. However, careful modulation of the inflammatory response is required to allow for adequate elimination of foreign antigens while avoiding inappropriate overactivation of the immune system as in autoimmune disorders. Enteric neurons and glial cells are capable of performing these immunomodulatory functions to provide adequate protection to the ENS. We review recent studies examining the interactions between the ENS and the immune system, with specific focus on enteric glial cells and their ability to modulate inflammation in the ENS.