The role of adipose tissue-associated macrophages and T lymphocytes in the pathogenesis of inflammatory bowel disease

Modulating Cellular Responses to Mechanical Forces to Promote Wound Regeneration

Significance: Skin scarring poses a major biomedical burden for hundreds of millions of patients annually. However, this burden could be mitigated by therapies that promote wound regeneration, with full recovery of skin's normal adnexa, matrix ultrastructure, and mechanical strength. Recent Advances: The observation of wound regeneration in several mouse models suggests a retained capacity for postnatal mammalian skin to regenerate under the right conditions. Mechanical forces are a major contributor to skin fibrosis and a prime target for devices and therapeutics that could promote skin regeneration. Critical Issues: Wound-induced hair neogenesis, Acomys "spiny" mice, Murphy Roths Large mice, and mice treated with mechanotransduction inhibitors all show various degrees of wound regeneration. Comparison of regenerating wounds in these models against scarring wounds reveals differences in extracellular matrix interactions and in mechanosensitive activation of key signaling pathways, including Wnt, Sonic hedgehog, focal adhesion kinase, and Yes-associated protein. The advent of single-cell "omics" technologies has deepened this understanding and revealed that regeneration may recapitulate development in certain contexts, although it is unknown whether these mechanisms are relevant to healing in tight-skinned animals such as humans. Future Directions: While early findings in mice are promising, comparison across model systems is needed to resolve conflicting mechanisms and to identify conserved master regulators of skin regeneration. There also remains a dire need for studies on mechanomodulation of wounds in large, tight-skinned animals, such as red Duroc pigs, which better approximate human wound healing.

The impact of visceral obesity on chronic constipation, inflammation, immune function and cognitive function in patients with inflammatory bowel disease

Objective: Obesity has gained attention among patients with inflammatory bowel disease (IBD). The impact of visceral obesity on chronic constipation, inflammation, immune function and cognition after diagnosis of IBD is still unknown.

Methods: This is a cross-sectional study of 150 IBD patients. Patients’ visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) were measured and were grouped according to visceral obesity. The potential impact of visceral obesity on cognitive function were evaluated using Mini-Mental State Examination. We evaluated patients’ incidence of chronic constipation, levels of interleukin-6 (IL-6), T cells and body mass index in two groups.

Results: The prevalence of visceral obesity was 51% (37 out of 72) for Crohn’s disease (CD) patients and 26% for UC patients (20 out of 78 patients). CD patients with visceral obesity has higher incidence of chronic constipation (81% vs. 57%, P = 0.028), higher IL-6 levels (15.28 pg/ml vs. 9.429 pg/ml, P = 0.007) and lower CD4⁺ T cells (32.7% vs. 44.0%, P < 0.001). VAT/SAT ratio is associated with BMI (P < 0.001).

Conclusions: IBD patients had high risks of visceral obesity. CD Patients with visceral obesity had higher prevalence of chronic constipation, higher inflammation levels, decreased immune function.

Intestinal Alkaline Phosphatase Combined with Voluntary Physical Activity Alleviates Experimental Colitis in Obese Mice. Involvement of Oxidative Stress, Myokines, Adipokines and Proinflammatory Biomarkers

Intestinal alkaline phosphatase (IAP) is an essential mucosal defense factor involved in the process of maintenance of gut homeostasis. We determined the effect of moderate exercise (voluntary wheel running) with or without treatment with IAP on the course of experimental murine 2,4,6-trinitrobenzenesulfonic acid (TNBS) colitis by assessing disease activity index (DAI), colonic blood flow (CBF), plasma myokine irisin levels and the colonic and adipose tissue expression of proinflammatory cytokines, markers of oxidative stress (SOD2, GPx) and adipokines in mice fed a standard diet (SD) or high-fat diet (HFD). Macroscopic and microscopic colitis in sedentary SD mice was accompanied by a significant decrease in CBF, and a significant increase in the colonic expression of tumor necrosis factor-alpha (TNF-α), IL-6, IL-1β and leptin mRNAs and decrease in the mRNA expression of adiponectin. These effects were aggravated in sedentary HFD mice but reduced in exercising animals, potentiated by concomitant treatment with IAP, especially in obese mice. Exercising HFD mice demonstrated a substantial increase in the mRNA for adiponectin and a decrease in mRNA leptin expression in intestinal mucosa and mesenteric fat as compared to sedentary animals. The expression of SOD2 and GPx mRNAs was significantly decreased in adipose tissue in HFD mice, but these effects were reversed in exercising mice with IAP administration. Our study shows for the first time that the combination of voluntary exercise and oral IAP treatment synergistically favored healing of intestinal inflammation, strengthened the antioxidant defense and ameliorated the course of experimental colitis; thus, IAP may represent a novel adjuvant therapy to alleviate inflammatory bowel disease (IBD) in humans.

Mechano-Immunomodulation: Mechanoresponsive Changes in Macrophage Activity and Polarization

In recent years, biomaterial- and scaffold-based immunomodulation strategies were implemented in tissue regeneration efforts for manipulating macrophage polarization (a.k.a. phenotype or lineage commitment, or differentiation). Yet, most of our understanding of macrophage phenotype commitment and phagocytic capacity is limited to how physical cues (extracellular matrix stiffness, roughness, and topography) and soluble chemical cues (cytokines and chemokines released from the scaffold) influence macrophage polarization. In the context of immune response-tissue interaction, the mechanical cues experienced by the residing cells within the tissue also play a critical role in macrophage polarization and inflammatory response. However, there is no compiled study discussing the effect of the dynamic mechanical environment around the tissues on macrophage polarization and the innate immune response. The aim of this comprehensive review paper is 2-fold; (a) to highlight the importance of mechanical cues on macrophage lineage commitment and function and (b) to summarize the important studies dedicated to understand how macrophage polarization changes with different mechanical loading modalities. For the first time, this review paper compiles and compartmentalizes the studies investigating the role of dynamic mechanical loading with various modalities, amplitude, and frequency on macrophage differentiation. A deeper understanding of macrophage phenotype in mechanically dominant tissues (i.e. musculoskeletal tissues, lung tissues, and cardiovascular tissues) provides mechanistic insights into the design of mechano-immunomodulatory tissue scaffold for tissue regeneration.

Stromal and immune cells in gut fibrosis: the myofibroblast and the scarface

Post-inflammatory scarring is the end-result of excessive extracellular matrix (ECM) accumulation and tissue architectural destruction. It represents a failure to effectively remodel ECM and achieve proper reinstitution and healing during chronic relapsing inflammatory processes. Scarring may affect the functionality of any organ, and in the case of inflammatory bowel disease (IBD)-associated fibrosis leads to stricture formation and often surgery to remove the affected bowel. The activated myofibroblast is the final effector cell that overproduces ECM under the influence of various mediators generated by an intense interplay of classic and non-classic immune cells. This review focuses on how proinflammatory mediators from various sources produced in different stages of intestinal inflammation can form profibrotic pathways that eventually lead to tissue scarring through sustained activation of myofibroblasts.

Effects of Gliadin consumption on the Intestinal Microbiota and Metabolic Homeostasis in Mice Fed a High-fat Diet

Dietary gluten causes severe disorders like celiac disease in gluten-intolerant humans. However, currently understanding of its impact in tolerant individuals is limited. Our objective was to test whether gliadin, one of the detrimental parts of gluten, would impact the metabolic effects of an obesogenic diet. Mice were fed either a defined high-fat diet (HFD) containing 4% gliadin (n = 20), or a gliadin-free, isocaloric HFD (n = 20) for 23 weeks. Combined analysis of several parameters including insulin resistance, histology of liver and adipose tissue, intestinal microbiota in three gut compartments, gut barrier function, gene expression, urinary metabolites and immune profiles in intestinal, lymphoid, liver and adipose tissues was performed. Mice fed the gliadin-containing HFD displayed higher glycated hemoglobin and higher insulin resistance as evaluated by the homeostasis model assessment, more hepatic lipid accumulation and smaller adipocytes than mice fed the gliadin-free HFD. This was accompanied by alterations in the composition and activity of the gut microbiota, gut barrier function, urine metabolome, and immune phenotypes within liver and adipose tissue. Our results reveal that gliadin disturbs the intestinal environment and affects metabolic homeostasis in obese mice, suggesting a detrimental effect of gluten intake in gluten-tolerant subjects consuming a high-fat diet.

Exercise and Self-Reported Limitations in Patients with Inflammatory Bowel Disease

BACKGROUND

Limited evidence suggests that exercise may have beneficial, anti-inflammatory effects in patients with inflammatory bowel disease (IBD).

AIMS

The purpose of this study was to evaluate the prevalence of exercise in patients with IBD and the limitations they experience secondary to their disease.

METHODS

Two hundred and fifty IBD patients were prospectively enrolled in this study at an academic medical center at the time of their outpatient visits between March and October 2013. Subjects were asked to complete a one-time survey that asks questions about medical and surgical history, exercise frequency and intensity, and the limitations and barriers they experience.

RESULTS

Two hundred and twenty-seven patients (148 female patients) completed the survey. Crohn's disease was present in 140 patients (61.5 %), while 87 had ulcerative colitis. Forty-one patients (16.4 %) never exercised, 82 patients (32.8 %) exercised 1-2 times per week, 59 (23.6 %) exercised 3-4 times per week, and 45 (18.0 %) exercised more than four times per week. Of the 186 who regularly exercise, 95 (51 %) reported moderate exercise intensity, 61 (33 %) reported light intensity, and 30 (16 %) reported vigorous intensity. Ninety-nine patients (44 %) reported that their IBD limited their exercise for reasons including fatigue (n = 81), joint pain (n = 37), embarrassment (n = 23), weakness (n = 21), and others.

CONCLUSIONS

Although they may benefit from exercise, IBD patients experience considerable barriers to regular exercise secondary to the relapsing and remitting nature of IBD. Larger studies are needed to determine the effects of exercise on disease symptomatology and activity.

Involvement of Visceral Adipose Tissue in Immunological Modulation of Inflammatory Cascade in Preeclampsia

Objectives. The pathophysiology of preeclampsia is characterized by abnormal placentation, an exaggerated inflammatory response, and generalized dysfunction of the maternal endothelium. We investigated the effects of preeclampsia serum on the expression of inflammation-related genes by adipose tissue. Materials and Methods. Visceral adipose tissue was obtained from the omentum of patients with early ovarian cancer without metastasis. Adipose tissue was incubated with sera obtained from either five women affected with severe preeclampsia or five women from control pregnant women at 37°C in a humidified incubator at 5% CO₂ for 24 hours. 370 genes in total mRNA were analyzed with quantitative RT-PCR (Inflammatory Response & Autoimmunity gene set). Results. Gene expression analysis revealed changes in the expression levels of 30 genes in adipose tissue treated with preeclampsia sera. Some genes are related to immune response, oxidative stress, insulin resistance, and adipogenesis, which plays a central role in excessive systemic inflammatory response of preeclampsia. In contrast, other genes have shown beneficial effects in the regulation of Th2 predominance, antioxidative stress, and insulin sensitivity. Conclusion. In conclusion, visceral adipose tissue offers protection against inflammation, oxidative insults, and other forms of cellular stress that are central to the pathogenesis of preeclampsia.

Understanding the Mysterious M2 Macrophage through Activation Markers and Effector Mechanisms

The alternatively activated or M2 macrophages are immune cells with high phenotypic heterogeneity and are governing functions at the interface of immunity, tissue homeostasis, metabolism, and endocrine signaling. Today the M2 macrophages are identified based on the expression pattern of a set of M2 markers. These markers are transmembrane glycoproteins, scavenger receptors, enzymes, growth factors, hormones, cytokines, and cytokine receptors with diverse and often yet unexplored functions. This review discusses whether these M2 markers can be reliably used to identify M2 macrophages and define their functional subdivisions. Also, it provides an update on the novel signals of the tissue environment and the neuroendocrine system which shape the M2 activation. The possible evolutionary roots of the M2 macrophage functions are also discussed.

Metabolic inflammation in inflammatory bowel disease: crosstalk between adipose tissue and bowel

Epidemiological studies show that both the incidence of inflammatory bowel disease (IBD) and the proportion of people with obesity and/or obesity-associated metabolic syndrome increased markedly in developed countries during the past half century. Obesity is also associated with the development of more active IBD and requirement for hospitalization and with a decrease in the time span between diagnosis and surgery. Patients with IBD, especially Crohn's disease, present fat-wrapping or "creeping fat," which corresponds to ectopic adipose tissue extending from the mesenteric attachment and covering the majority of the small and large intestinal surface. Mesenteric adipose tissue in patients with IBD presents several morphological and functional alterations, e.g., it is more infiltrated with immune cells such as macrophages and T cells. All these lines of evidence clearly show an association between obesity, adipose tissue, and functional bowel disorders. In this review, we will show that the mesenteric adipose tissue and creeping fat are not innocent by standers but actively contribute to the intestinal and systemic inflammatory responses in patients with IBD. More specifically, we will review evidence showing that adipose tissue in IBD is associated with major alterations in the secretion of cytokines and adipokines involved in inflammatory process, in adipose tissue mesenchymal stem cells and adipogenesis, and in the interaction between adipose tissue and other intestinal components (immune, lymphatic, neuroendocrine, and intestinal epithelial systems). Collectively, these studies underline the importance of adipose tissue for the identification of novel therapeutic approaches for IBD.

Role of fat and adipokines in intestinal inflammation

PURPOSE OF REVIEW

This review summarizes current knowledge on the contribution of mesenteric adipose tissue in intestinal inflammation. We will describe the cellular and humoral characteristics of creeping fat, their potential impact for Crohn's disease and propose a working model for the critical interplay between the creeping fat and the inflamed intestine.

RECENT FINDINGS

Creeping fat can be distinguished from healthy adipose tissue by its distinctively small adipocytes, by a specific microenvironment defined by high levels of adipokines and by a dominant immune cell infiltration. In Crohn's disease transmural inflammation facilitates increased bacterial translocation into the creeping fat. Translocalizing antigens can directly activate (pre)adipocytes via innate receptors. Adipocyte-derived mediators modulate phenotype and function of innate and adaptive immune cells. Activated (pre)adipocytes and adipokine-modulated immune cells might support a degree of inflammatory activation within the creeping fat that allows competent immune defense against exogenous factors while preventing systemic inflammation.

SUMMARY

Fat tissue as an active organ in health and disease has been ignored for too long. The last few years of research provided evidence for the complex metabolic and immunological functions of adipose tissue. On the basis of the available data, creeping fat in Crohn's disease exerts a protective function by a localized anti-inflammatory effect, thus preventing a systemic inflammatory response.

Results of the 4th scientific workshop of the ECCO (I): pathophysiology of intestinal fibrosis in IBD

The fourth scientific workshop of the European Crohn's and Colitis Organization (ECCO) focused on the relevance of intestinal fibrosis in the disease course of inflammatory bowel disease (IBD). The objective was to better understand the pathophysiological mechanisms of intestinal fibrosis, to identify useful markers and imaging modalities of fibrosis in order to assess its presence and progression, and, finally, to point out possible approaches for the prevention and the treatment of fibrosis. The results of this workshop are presented in three separate manuscripts. This first section describes the most important mechanisms that contribute to the initiation and progression of intestinal fibrosis in IBD including the cellular and molecular mediators, the extracellular matrix molecules and matrix metalloproteinases/tissue inhibitors of metalloproteinases-system, the microbiota products, the role of fat, genetic and epigenetic factors, as well as the currently available experimental models. Furthermore, it identifies unanswered questions in the field of intestinal fibrosis and provides a framework for future research.

Defective apoptosis in intestinal and mesenteric adipose tissue of Crohn's disease patients

BACKGROUND

Crohn's disease (CD) is associated with complex pathogenic pathways involving defects in apoptosis mechanisms. Recently, mesenteric adipose tissue (MAT) has been associated with CD ethiopathology, since adipose thickening is detected close to the affected intestinal area. However, the potential role of altered apoptosis in MAT of CD has not been addressed.

AIMS

To evaluate apoptosis in the intestinal mucosa and MAT of patients with CD.

METHODS

Samples of intestinal mucosa and MAT from patients with ileocecal CD and from non-inflammatory bowel diseases patients (controls) were studied. Apoptosis was assessed by TUNEL assay and correlated with the adipocytes histological morphometric analysis. The transcriptional and protein analysis of selected genes and proteins related to apoptosis were determined.

RESULTS

TUNEL assay showed fewer apoptotic cells in CD, when compared to the control groups, both in the intestinal mucosa and in MAT. In addition, the number of apoptotic cells (TUNEL) correlated significantly with the area and perimeter of the adipose cells in MAT. Transcriptomic and proteomic analysis reveal a significantly lower transcript and protein levels of Bax in the intestinal mucosa of CD, compared to the controls; low protein levels of Bax were found localized in the lamina propria and not in the epithelium of this tissue. Furthermore, higher level of Bcl-2 and low level of Caspase 3 were seen in the MAT of CD patients.

CONCLUSION

The defective apoptosis in MAT may explain the singular morphological characteristics of this tissue in CD, which may be implicated in the pathophysiology of the disease.

The role of physical exercise in inflammatory bowel disease

We reviewed and analyzed the relationship between physical exercise and inflammatory bowel disease (IBD) which covers a group of chronic, relapsing, and remitting intestinal disorders including Crohn's disease (CD) and ulcerative colitis. The etiology of IBD likely involves a combination of genetic predisposition and environmental risk factors. Physical training has been suggested to be protective against the onset of IBD, but there are inconsistencies in the findings of the published literature. Hypertrophy of the mesenteric white adipose tissue (mWAT) is recognized as a characteristic feature of CD, but its importance for the perpetuation of onset of this intestinal disease is unknown. Adipocytes synthesize proinflammatory and anti-inflammatory cytokines. Hypertrophy of mWAT could play a role as a barrier to the inflammatory process, but recent data suggest that deregulation of adipokine secretion is involved in the pathogenesis of CD. Adipocytokines and macrophage mediators perpetuate the intestinal inflammatory process, leading to mucosal ulcerations along the mesenteric border, a typical feature of CD. Contracting skeletal muscles release biologically active myokines, known to exert the direct anti-inflammatory effects, and inhibit the release of proinflammatory mediators from visceral fat. Further research is required to confirm these observations and establish exercise regimes for IBD patients.