Translating Immunology into Therapeutic Concepts for Inflammatory Bowel Disease

CD74 Signaling Links Inflammation to Intestinal Epithelial Cell Regeneration and Promotes Mucosal Healing

BACKGROUND & AIMS

The inflammatory response to intestinal damage promotes healing through mechanisms that are incompletely understood. Gene expression of cluster of differentiation 74 (CD74), the receptor for cytokine macrophage migration inhibitory factor, is increased in patients with inflammatory bowel disease (IBD), however, the role of CD74 signaling in intestinal inflammation remains poorly understood. The aim of this study was to determine the functional role of CD74 signaling in intestinal inflammation.

METHODS

We studied the characteristics of CD74 protein expression in human IBD and experimental colitis. The functional role of CD74 signaling in the intestine was investigated using cellular models; wild-type, CD74^-/-, and bone marrow chimera mice; neutralizing anti-CD74 antibodies; flow cytometry; immunohistochemistry; immunofluorescence; immunoblotting; and clustered regularly interspaced short palindromic repeats and associated protein 9 technology.

RESULTS

In IBD patients and experimental colitis, CD74-receptor protein expression was increased in inflamed intestinal tissue, prominently in the crypt epithelial cells. By using distinct but complementary chemical and non-chemically induced mouse models of colitis with genetic and antibody neutralization approaches, we found that CD74 signaling was necessary for gut repair. Mechanistically, we found that the macrophage migration inhibitory factor cytokine, which also is increased in colitis, stimulated the CD74 receptor, enhancing intestinal epithelial cell proliferation through activation of the protein kinase B and the extracellular signal-regulated kinase pathways. Our data also suggest that CD74 signaling in immune cells was not essential for mucosal healing.

CONCLUSIONS

CD74 signaling is strongly activated during intestinal inflammation and protects the host by promoting epithelial cell regeneration, healing, and maintaining mucosal barrier integrity. Enhancing the CD74 pathway may represent a unique therapeutic strategy for promoting healing in IBD.

The ties that bind: skin, gut and spondyloarthritis

PURPOSE OF REVIEW

This article aims to review recent literature linking epithelial barrier inflammation and arthritis in spondyloarthritis (SpA), with a critical view on how they are bound by genetic, immunological and environmental ties.

RECENT FINDINGS

The epithelia-joint axis has become an intense area of both basic and clinical SpA research. The penultimate goal is to understand the immunopathologic links between epithelial inflammation and arthritis in SpA. Inflammatory bowel disease (IBD) and psoriasis (PsO) have strong links to SpA at several levels. Clinically, there is a strong association of IBD, PsO and SpA. Genetically, there are many shared risk factors; however, there are also distinct differences in the genetics of the respective diseases. Immunologically, type 3 immunity, especially interleukin (IL)-17 and IL-23 dysregulation, has been shown to play a central role in IBD, PsO and SpA. Environmentally, a microbial dysbiosis has been noted in each of these diseases, but whether the microbial signature is similar between diseases is not clear, nor is the effect of dysbiosis on the immune response known.

SUMMARY

It will be crucial to determine whether the relationship between epithelia inflammation and SpA is truly causal for both the understanding of pathogenesis and for future treatment strategies.

Role of intestinal microbiota and metabolites in inflammatory bowel disease

Objective:

The metabolites produced by the gut microbiota are of interest to scientists. The objective of this review was to provide an updated summary of progress regarding the microbiota and their metabolites and influences on the pathogenesis of inflammatory bowel disease (IBD).

Data sources:

The author retrieved information from the PubMed database up to January 2018, using various combinations of search terms, including IBD, microbiota, and metabolite.

Study selection:

Both clinical studies and animal studies of intestinal microbiota and metabolites in IBD were selected. The information explaining the possible pathogenesis of microbiota in IBD was organized.

Results:

In IBD patients, the biodiversity of feces/mucosa-associated microbiota is decreased, and the probiotic microbiota is also decreased, whereas the pathogenic microbiota are increased. The gut microbiota may be a target for diagnosis and treatment of IBD. Substantial amounts of data support the view that the microbiota and their metabolites play pivotal roles in IBD by affecting intestinal permeability and the immune response.

Conclusions:

This review highlights the advances in recent gut microbiota research and clarifies the importance of the gut microbiota in IBD pathogenesis. Future research is needed to study the function of altered bacterial community compositions and the roles of metabolites.

Effects of a β-type glycosidic polysaccharide from Flammulina velutipes on anti-inflammation and gut microbiota modulation in colitis mice

Using the Flammulina velutipes polysaccharide (FVP) extracted from our previous study, herein, we investigated the improvement of this β-type glycosidic polysaccharide in alleviating dextran sodium sulfate-induced ulcerative colitis (UC) in mice.

Remission of Inflammatory Bowel Disease in Glucose-6-Phosphatase 3 Deficiency by Allogeneic Haematopoietic Stem Cell Transplantation

Mendelian disorders in glucose-6-phosphate metabolism can present with inflammatory bowel disease [IBD]. Using whole genome sequencing we identified a homozygous variant in the glucose-6-phosphatase G6PC3 gene [c.911dupC; p.Q305fs*82] in an adult patient with congenital neutropenia, lymphopenia and childhood-onset, therapy-refractory Crohn's disease. Because G6PC3 is expressed in several haematopoietic and non-haematopoietic cells it was unclear whether allogeneic stem cell transplantation [HSCT] would benefit this patient with intestinal inflammation. We show that HSCT resolves G6PC3-associated immunodeficiency and the Crohn's disease phenotype. It illustrates how even in adulthood, next-generation sequencing can have a significant impact on clinical practice and healthcare utilization in patients with immunodeficiency and monogenic IBD.

Pancreas–Microbiota Cross Talk in Health and Disease

The pancreas controls metabolism through endocrine and exocrine functions. Pancreatic diseases comprise a spectrum of mild to life-threatening conditions, including acute and chronic pancreatitis, diabetes, and pancreatic cancer, which affect endocrine and exocrine pancreatic function and impose a substantial disease burden on individuals. Increasing experimental evidence demonstrates that the intestinal microbiota has an important impact on pancreatic function and diseases. This influence may be conferred by bacterial metabolites, such as short-chain fatty acids, or the modulation of immune responses. In turn, pancreatic factors, such as the excretion of antimicrobials, might have a substantial impact on the composition and functional properties of the gut microbiota. Here, we summarize experimental and clinical approaches used to untie the intricate pancreas–microbiota cross talk. Future advances will allow clinicians to manipulate the intestinal microbiota and guide patient management in pancreatic diseases.

Very early-onset inflammatory bowel disease: an integrated approach

PURPOSE OF REVIEW

Immune dysregulation disorders are among the most rapidly growing set of inborn errors of immunity. One particular subset is the category where early-onset inflammatory bowel disease (IBD) is the most common manifestation. These disorders are being increasingly appreciated although there has been minimal effort to articulate a unified approach to their diagnosis and management. This review will cover current thinking and strategies related to diagnosis and management of very early-onset IBD.

RECENT FINDINGS

There is an expanding set of monogenic causes of early-onset IBD. In many cases, the precise genetic cause dictates management. Lessons learned from the management of these monogenic conditions can sometimes be extrapolated to other refractory cases of IBD.

SUMMARY

An integrated approach to diagnosis, risk analysis, and management can include diagnostic approaches not often utilized for traditional IBD such as whole exome sequencing. Management can also include nontraditional approaches such as targeted biologics or hematopoietic cell transplantation.

Dual immune functions of IL-33 in inflammatory bowel disease

Interleukin-33 (IL-33) has emerged as a critical regulator in a variety of diseases, including inflammatory bowel disease (IBD). IL-33 can be produced by various tissues and cells, and typically induces Th2-type immune responses via binding to the receptor ST2. In addition, accumulated data have shown that IL-33 also plays a modulatory role in the function of regulatory T cells (Tregs), B cells, and innate immune cells such as macrophages and innate lymphoid cells (ILCs). IBD, including Crohn's disease and ulcerative colitis, are characterized by aberrant immunological responses leading to intestinal tissue injury and destruction. Although IL-33 expression is increased in IBD patients and correlates with the patients' disease activity index, mechanistic studies to date have demonstrated both pathogenic and protective roles in animal models of experimental colitis. In this review, we will summarize the roles and mechanisms of IL-33 in IBD, which is essential to understand the pathogenesis of IBD and determine potential therapies.

Combining Mathematical Models With Experimentation to Drive Novel Mechanistic Insights Into Macrophage Function

This perspective outlines an approach to improve mechanistic understanding of macrophages in inflammation and tissue homeostasis, with a focus on human inflammatory bowel disease (IBD). The approach integrates wet-lab and in-silico experimentation, driven by mechanistic mathematical models of relevant biological processes. Although wet-lab experimentation with genetically modified mouse models and primary human cells and tissues have provided important insights, the role of macrophages in human IBD remains poorly understood. Key open questions include: (1) To what degree hyperinflammatory processes (e.g., gain of cytokine production) and immunodeficiency (e.g., loss of bacterial killing) intersect to drive IBD pathophysiology? and (2) What are the roles of macrophage heterogeneity in IBD onset and progression? Mathematical modeling offers a synergistic approach that can be used to address such questions. Mechanistic models are useful for informing wet-lab experimental designs and provide a knowledge constrained framework for quantitative analysis and interpretation of resulting experimental data. The majority of published mathematical models of macrophage function are based either on animal models, or immortalized human cell lines. These experimental models do not recapitulate important features of human gastrointestinal pathophysiology, and, therefore are limited in the extent to which they can fully inform understanding of human IBD. Thus, we envision a future where mechanistic mathematical models are based on features relevant to human disease and parametrized by richer human datasets, including biopsy tissues taken from IBD patients, human organ-on-a-chip systems and other high-throughput clinical data derived from experimental medicine studies and/or clinical trials on IBD patients.

Gut microbiota modulation and anti-inflammatory properties of anthocyanins from the fruits of Lycium ruthenicum Murray in dextran sodium sulfate-induced colitis in mice

In the present study, the therapeutic effects of crude anthocyanins (ACN) from the fruits of Lycium ruthenicum Murray and the main monomer of ACN, petunidin 3-O-[rhamnopyranosyl-(trans-p-coumaroyl)]-5-O-[β-d-glucopyranoside] (P3G), on the dextran sodium sulfate (DSS)-induced colitis in mice were investigated. Both ACN and P3G showed intestinal anti-inflammatory effects, evidenced by restoration of various physical signs (body weight, feed quantity, solid fecal weight and colon length were increased, and DAI score was decreased), reduction of the expression of proinflammatory cytokines and related mRNA (such as TNF-α, IL-6, IL-1β and IFN-γ), and promotion of the intestinal barrier function by histological and immunofluorescence analysis (proteins such as ZO-1, occludin and claudin-1 were increased). Furthermore, the effects on gut microbiota community of DSS-induced colitis in mice have been investigated. It was found that Porphyromonadaceae, Helicobacter, Parasutterella, Parabacteroides, Oscillibacter and Lachnospiraceae were the key bacteria associated with inflammatory bowel disease. Taken together, P3G and ACN ameliorated DSS-induced colitis in mice through three aspects including blocking proinflammatory cytokines, increasing tight junction protein and modulating gut microbiota. What's more, P3G showed better anti-inflammatory effects than ACN.

Systems biology in inflammatory bowel diseases: on the way to precision medicine

Inflammatory bowel diseases (IBD) are chronic and recurrent inflammatory disorders of the gastrointestinal tract. The elucidation of their etiopathology requires complex and multiple approaches. Systems biology has come to fulfill this need in approaching the pathogenetic mechanisms of IBD and its etiopathology, in a comprehensive way, by combining data from different scientific sources. In combination with bioinformatics and network medicine, it uses principles from computer science, mathematics, physics, chemistry, biology, medicine and computational tools to achieve its purposes. Systems biology utilizes scientific sources that provide data from omics studies (e.g., genomics, transcriptomics, etc.) and clinical observations, whose combined analysis leads to network formation and ultimately to a more integrative image of disease etiopathogenesis. In this review, we analyze the current literature on the methods and the tools utilized by systems biology in order to cover an innovative and exciting field: IBD-omics.

Curcumin and Intestinal Inflammatory Diseases: Molecular Mechanisms of Protection

Intestinal inflammatory diseases, such as Crohn’s disease, ulcerative colitis, and necrotizing enterocolitis, are becoming increasingly prevalent. While knowledge of the pathogenesis of these related diseases is currently incomplete, each of these conditions is thought to involve a dysfunctional, or overstated, host immunological response to both bacteria and dietary antigens, resulting in unchecked intestinal inflammation and, often, alterations in the intestinal microbiome. This inflammation can result in an impaired intestinal barrier allowing for bacterial translocation, potentially resulting in systemic inflammation and, in severe cases, sepsis. Chronic inflammation of this nature, in the case of inflammatory bowel disease, can even spur cancer growth in the longer-term. Recent research has indicated certain natural products with anti-inflammatory properties, such as curcumin, can help tame the inflammation involved in intestinal inflammatory diseases, thus improving intestinal barrier function, and potentially, clinical outcomes. In this review, we explore the potential therapeutic properties of curcumin on intestinal inflammatory diseases, including its antimicrobial and immunomodulatory properties, as well as its potential to alter the intestinal microbiome. Curcumin may play a significant role in intestinal inflammatory disease treatment in the future, particularly as an adjuvant therapy.

Oxysterols in intestinal immunity and inflammation

Cholesterol is an essential molecule for life. It is a component of the cell membrane, and it is a precursor molecule for bile acids, vitamin D and steroid hormones. Cholesterol is actively metabolized, but the impact of endogenous cholesterol metabolites on immune function, especially in the intestine, is poorly understood. In this review, I focus on oxysterols, hydroxylated forms of cholesterol, and their specialized functions in intestinal immunity. Oxysterols act through various intracellular and extracellular receptors and serve as key metabolic signals, coordinating immune activity and inflammation. Our recent work has identified an unexpected link between cholesterol metabolism, innate lymphoid cell function and intestinal homeostasis. We discovered that oxysterol sensing through the G protein-coupled receptor 183 (GPR183) directs the migration of innate lymphoid cells, which is essential for the formation of lymphoid tissue in the colon. Moreover, we found that the interaction of GPR183 with oxysterols regulates intestinal inflammation. I will discuss the therapeutic potential of oxysterols and future possibilities of treating inflammatory bowel disease through the modulation of cholesterol metabolism.

MiR-155 controls follicular Treg cell-mediated humoral autoimmune intestinal injury by inhibiting CTLA-4 expression

High expression levels of miR-155 are involved in the pathogenesis of inflammatory bowel disease (IBD). We observed an increase in miR-155 in peripheral regulatory T (Treg) cells from IBD patients. Mice that specifically overexpress miR-155 in Foxp3+ Treg cells exhibit spontaneous autoimmunity and more severe dextran sulfate sodium (DSS)-induced intestinal injury. MiR-155 overexpression can lead to a lack of follicular Treg (Tfr) cells and central Treg (cTreg), whereas DSS treatment further depletes the Tfr cells. Furthermore, miR-155 can target the expression of CTLA-4 in cTreg and Tfr, directly inhibiting Tfr cell production and promoting enhanced germinal center (GC) B cell activation and autoantibody overproduction. This outcome may be the cause of severe intestinal injury in patients with autoimmune IBD.

Regulatory T cell adaptation in the intestine and skin

The intestine and skin are distinct microenvironments with unique physiological functions and are continually exposed to diverse environmental challenges. Host adaptation at these sites is an active process that involves interaction between immune cells and tissue cells. Regulatory T cells (T_reg cells) play a pivotal role in enforcing homeostasis at barrier surfaces, illustrated by the development of intestinal and skin inflammation in diseases caused by primary deficiency in T_reg cells. T_reg cells at barrier sites are phenotypically distinct from their lymphoid-organ counterparts, and these 'tissue' signatures often reflect their tissue-adapted function. We discuss current understanding of T_reg cell adaptation in the intestine and skin, including unique phenotypes, functions and metabolic demands, and how increased knowledge of T_reg cells at barrier sites might guide precision medicine therapies.

IL-22 Preserves Gut Epithelial Integrity and Promotes Disease Remission during Chronic Salmonella Infection

The cytokine IL-22 is rapidly induced at barrier surfaces where it regulates host-protective antimicrobial immunity and tissue repair but can also enhance disease severity in some chronic inflammatory settings. Using the chronic Salmonella gastroenteritis model, Ab-mediated neutralization of IL-22 impaired intestinal epithelial barrier integrity and, consequently, exaggerated expression of proinflammatory cytokines. As disease normally resolved, neutralization of IL-22 caused luminal narrowing of the cecum-a feature reminiscent of fibrotic strictures seen in Crohn disease patients. Corresponding to the exaggerated immunopathology caused by IL-22 suppression, Salmonella burdens in the gut were reduced. This enhanced inflammation and pathogen clearance was associated with alterations in gut microbiome composition, including the overgrowth of Bacteroides acidifaciens Our findings thus indicate that IL-22 plays a protective role by limiting infection-induced gut immunopathology but can also lead to persistent pathogen colonization.

The Short Chain Fatty Acid Butyrate Imprints an Antimicrobial Program in Macrophages

Host microbial cross-talk is essential to maintain intestinal homeostasis. However, maladaptation of this response through microbial dysbiosis or defective host defense toward invasive intestinal bacteria can result in chronic inflammation. We have shown that macrophages differentiated in the presence of the bacterial metabolite butyrate display enhanced antimicrobial activity. Butyrate-induced antimicrobial activity was associated with a shift in macrophage metabolism, a reduction in mTOR kinase activity, increased LC3-associated host defense and anti-microbial peptide production in the absence of an increased inflammatory cytokine response. Butyrate drove this monocyte to macrophage differentiation program through histone deacetylase 3 (HDAC3) inhibition. Administration of butyrate induced antimicrobial activity in intestinal macrophages in vivo and increased resistance to enteropathogens. Our data suggest that (1) increased intestinal butyrate might represent a strategy to bolster host defense without tissue damaging inflammation and (2) that pharmacological HDAC3 inhibition might drive selective macrophage functions toward antimicrobial host defense.

Early-onset inflammatory bowel disease as a model disease to identify key regulators of immune homeostasis mechanisms

Rare, monogenetic diseases present unique models to dissect gene functions and biological pathways, concomitantly enhancing our understanding of the etiology of complex (and often more common) traits. Although inflammatory bowel disease (IBD) is a generally prototypic complex disease, it can also manifest in an early-onset, monogenic fashion, often following Mendelian modes of inheritance. Recent advances in genomic technologies have spurred the identification of genetic defects underlying rare, very early-onset IBD (VEO-IBD) as a disease subgroup driven by strong genetic influence, pinpointing key players in the delicate homeostasis of the immune system in the gut and illustrating the intimate relationships between bowel inflammation, systemic immune dysregulation, and primary immunodeficiency with increased susceptibility to infections. As for other human diseases, it is likely that adult-onset diseases may represent complex diseases integrating the effects of host genetic susceptibility and environmental triggers. Comparison of adult-onset IBD and VEO-IBD thus provides beautiful models to investigate the relationship between monogenic and multifactorial/polygenic diseases. This review discusses the present and novel findings regarding monogenic IBD as well as key questions and future directions of IBD research.