Circulating fibrocytes and Crohn's disease

Single cell sequencing data identify distinct B cell and fibroblast populations in stricturing Crohn's disease

Single cell RNA sequencing of human full thickness Crohn's disease (CD) small bowel resection specimens was used to identify potential therapeutic targets for stricturing (S) CD. Using an unbiased approach, 16 cell lineages were assigned within 14,539 sequenced cells from patient-matched SCD and non-stricturing (NSCD) preparations. SCD and NSCD contained identical cell types. Amongst immune cells, B cells and plasma cells were selectively increased in SCD samples. B cell subsets suggested formation of tertiary lymphoid tissue in SCD and compared with NSCD there was an increase in IgG, and a decrease in IgA plasma cells, consistent with their potential role in CD fibrosis. Two Lumican-positive fibroblast subtypes were identified and subclassified based on expression of selectively enriched genes as fibroblast clusters (C) 12 and C9. Cells within these clusters expressed the profibrotic genes Decorin (C12) and JUN (C9). C9 cells expressed ACTA2; ECM genes COL4A1, COL4A2, COL15A1, COL6A3, COL18A1 and ADAMDEC1; LAMB1 and GREM1. GO and KEGG Biological terms showed extracellular matrix and stricture organization associated with C12 and C9, and regulation of WNT pathway genes with C9. Trajectory and differential gene analysis of C12 and C9 identified four sub-clusters. Intra sub-cluster gene analysis detected 13 co-regulated gene modules that aligned along predicted pseudotime trajectories. CXCL14 and ADAMDEC1 were key markers in module 1. Our findings support further investigation of fibroblast heterogeneity and interactions with local and circulating immune cells at earlier time points in fibrosis progression. Breaking these interactions by targeting one or other population may improve therapeutic management for SCD.

Fibrosis in IBD: from pathogenesis to therapeutic targets

BACKGROUND

Intestinal fibrosis resulting in stricture formation and obstruction in Crohn's disease (CD) and increased wall stiffness leading to symptoms in ulcerative colitis (UC) is among the largest unmet needs in inflammatory bowel disease (IBD). Fibrosis is caused by a multifactorial and complex process involving immune and non-immune cells, their soluble mediators and exposure to luminal contents, such as microbiota and environmental factors. To date, no antifibrotic therapy is available. Some progress has been made in creating consensus definitions and measurements to quantify stricture morphology for clinical practice and trials, but approaches to determine the degree of fibrosis within a stricture are still lacking.

OBJECTIVE

We herein describe the current state of stricture pathogenesis, measuring tools and clinical trial endpoints development.

DESIGN

Data presented and discussed in this review derive from the past and recent literature and the authors' own research and experience.

RESULTS AND CONCLUSIONS

Significant progress has been made in better understanding the pathogenesis of fibrosis, but additional studies and preclinical developments are needed to define specific therapeutic targets.

Circulating fibrocyte percentage and neutrophil-lymphocyte ratio are accurate biomarkers of uncomplicated and complicated appendicitis: a prospective cohort study

BACKGROUND

There is increasing evidence that uncomplicated appendicitis (UA) may be treated nonoperatively in cases of UA. This study aimed to evaluate and compare the diagnostic accuracy of circulating fibrocyte percentage (CFP), white blood cell count, C-reactive protein, and neutrophil-lymphocyte ratio (NLR) in diagnosing uncomplicated and complicated appendicitis.

MATERIALS AND METHODS

Eighty consecutive adult patients presenting with suspected appendicitis were recruited in a cohort-based prospective study between June 2015 and February 2016 at University Hospital Limerick in Ireland. Peripheral venous samples were obtained at the presentation. Clinical, biochemical, radiological, and histopathological parameters were recorded. The CFP was determined by dual-staining for CD45 and collagen-I using flow cytometry analysis and correlated with histopathological diagnoses.

RESULTS

Of the 46 patients who underwent appendicectomy, 34 (73.9%) had histologically proven acute appendicitis. A comparison of the diagnostic accuracy of biomarkers demonstrated the CFP had the highest diagnostic accuracy for UA (area under the curve=0.83, sensitivity=72.7%, specificity=83.3%, P=0.002). The NLR had the highest diagnostic accuracy in relation to complicated appendicitis (area under the curve=0.84, sensitivity=75.5%, specificity=83.3%, P=0.005).

CONCLUSIONS

CFP and NLR are accurate biomarkers of UA and complicated appendicitis.

The Complex Relationship Between Microbiota, Immune Response and Creeping Fat in Crohn's Disease

In the last decade, there has been growing interest in the pathological involvement of hypertrophic mesenteric fat attached to the serosa of the inflamed intestinal segments involved in Crohn's disease [CD], known as creeping fat. In spite of its protective nature, creeping fat harbours an aberrant inflammatory activity which, in an already inflamed intestine, may explain why creeping fat is associated with a greater severity of CD. The transmural inflammation of CD facilitates the interaction of mesenteric fat with translocated intestinal microorganisms, contributing to activation of the immune response. This may be not the only way in which microorganisms alter the homeostasis of this fatty tissue: intestinal dysbiosis may also impair xenobiotic metabolism. All these CD-related alterations have a functional impact on nuclear receptors such as the farnesoid X receptor or the peroxisome proliferator-activated receptor γ, which are implicated in regulation of the immune response, adipogenesis and the maintenance of barrier function, as well as on creeping fat production of inflammatory-associated cells such as adipokines. The dysfunction of creeping fat worsens the inflammatory course of CD and may favour intestinal fibrosis and fistulizing complications. However, our current knowledge of the pathophysiology and pathogenic role of creeping fat is controversial and a better understanding might provide new therapeutic targets for CD. Here we aim to review and update the key cellular and molecular alterations involved in this inflammatory process that link the pathological components of CD with the development of creeping fat.

Role of Circulating Hematopoietic Fibrocytes in Chronic Hepatitis C Patients Induced Liver Fibrosis

Background: Bone marrow derived fibrocytes may play an important role in pathogenesis and resolution of liver fibrosis. These cells may offer new approaches for better understanding the pathogenesis of liver fibrosis. Aim of the work: To define the proportion of circulating fibrocytes with hematopoietic progenitor origin as defined by CD45 and CD34 positivity and to assess whether they are increased in patients with chronic C hepatitis in correlation to the degree of liver fibrosis. Subjects and Methods: Sixty HCV patients were classified according to METAVIR score into 4 stages of liver fibrosis, 15 age and sex-matched controls were included. Flowcytometric analysis for circulating levels of fibrocytes CD34+ve cells, CD45+ve cells, collagen type I+ve cells and CXCR4+ve cells was carried out using monoclonal antibodies (anti-CD34, CD45, collagen type I and CD184). GM-CSF, TGF-β and α-SMA were assessed using ELISA. Results and Conclusions: A significant increase in the circulating levels of GM-CSF, TGF- β and α-SMA, with a significant increase in the percentage of cells express CXCR4and in the co expression of CD34, CD45 and collagen type I positive cells in different groups of patients compared to control group, denoting the presence of an increased proportion of circulating fibrocytes in peripheral blood of these patients. The percentage of fibrocytes that positively expression CD34, CD45, collagen type I and CXCR4, were increased in step wise fashion in conjunction with worsening severity of liver disease. Liver fibrosis is associated with increased levels of circulating TGF-β1 and lipopolysaccharide, activation of myofibroblasts, and extensive deposition of extracellular matrix, mostly collagen Type I. TGF-β and LPS play a critical role in fibrogenesis and trigger fibrocyte recruitment to the injured liver promoting their differentiation into collagen type I producing myofibroblast, supporting that fibrocytes may become a novel target for anti fibrotic therapy.

Association of Circulating Fibrocytes With Fibrostenotic Small Bowel Crohn's Disease

BACKGROUND

Fibrocytes are hematopoietic cells with features of mesenchymal cells found in the circulation and inflammatory sites implicated in promoting fibrosis in many fibroinflammatory diseases. However, their role(s) in the development of intestinal fibrosis is poorly understood. Here, we investigated a potential role of fibrocytes in the development of fibrosis in Crohn's disease (CD) and sought factors that may impact their development and function.

METHODS

Plasma and mononuclear cells were collected from patients with and without fibrostenotic CD. Fibrocytes defined as CD11b+, CD34+, and Collagen 1+ were correlated with clinical assessments of fibrosis, including evaluation using intestinal ultrasound. We measured the levels of relevant circulating molecules via Luminex and studied the effect of patient plasma proteins on fibrocyte differentiation.

RESULTS

Fibrocyte numbers were increased in CD patients with stricturing Crohn's disease compared with patients with an inflammatory phenotype (P = .0013), with strong correlation between fibrocyte numbers and acoustic radiation force impulse (ARFI), a measure of bowel elasticity on intestinal ultrasound (R = .8383, P = .0127). Fibrostenotic plasma was a more potent inducer of fibrocyte differentiation in both primary human monocytes and cell line and contained increased levels of cytokines implicated in fibrocyte differentiation compared with plasma from inflammatory patients. Interestingly, increased fibrocyte numbers at time of ultrasound were associated with escalation of medical therapy and endoscopic/surgical management of small bowel strictures at 30 months follow-up.

CONCLUSIONS

Circulating fibrocytes strongly correlate with fibrostenotic disease in CD, and they may serve as predictors for escalation of medical +/- surgical therapy.

Expression of Fibrosis-Related Genes in Liver and Kidney Fibrosis in Comparison to Inflammatory Bowel Diseases

Fibrosis is an important feature of inflammatory bowel diseases (IBD), but its pathogenesis is incompletely understood. Our aim was to identify genes important for fibrosis in IBD by comparison with kidney and liver fibrosis. First, we performed bioinformatics analysis of Gene Expression Omnibus datasets of liver and kidney fibrosis and identified CXCL9, THBS2, MGP, PTPRC, CD52, GZMA, DPT and DCN as potentially important genes with altered expression in fibrosis. We then performed qPCR analysis of the selected genes’ expression on samples of fibrotic kidney, liver, Crohn’s disease (CD) with and without fibrosis and ulcerative colitis (UC), in comparison to corresponding normal tissue. We found significantly altered expression in fibrosis for all selected genes. A significant difference for some genes was observed in CD with fibrosis in comparison to CD without fibrosis and UC. We conclude that similar changes in the expression of selected genes in liver, kidney fibrosis and IBD provide further evidence that fibrosis in IBD might share common mechanisms with other organs, supporting the hypothesis that fibrosis is the common pathway in diseases of various organs. Some genes were already active in IBD with inflammation without fibrosis, suggesting the early activation of profibrotic pathways or overlapping function in fibrosis and inflammation.

Role of Extended Mesenteric Excision in Postoperative Recurrence of Crohn's Colitis: A Single-Center Study

INTRODUCTION

The mesentery is involved in Crohn's disease. The impact of the extent of mesenteric resection on postoperative disease progression in Crohn's disease remains unconfirmed. This study aimed to determine the association between resection of the mesentery and postoperative outcomes in patients with Crohn's colitis (CC) undergoing colorectal surgery.

METHODS

Patients with CC who underwent colorectal resection between January 2000 and December 2018 were reviewed, and the data were gathered from a prospectively maintained database. Patients were divided into 2 groups according to the extent of mesenteric resection, the extensive mesenteric excision (EME) group and the limited mesenteric excision (LME) group. Outcomes including early postoperative morbidities and surgical recurrence were compared between the 2 groups.

RESULTS

Of the 126 patients included, 60 were in the LME group and 66 in the EME group. There was no significant difference between the 2 groups in early postsurgical outcomes except the intraoperative blood loss was increased in the LME group (P = 0.002). Patients in the EME group had a longer postoperative surgical recurrence-free survival time when compared with those in the LME group (P = 0.01). LME was an independent predictor of postoperative surgical recurrence (hazard ratio 2.67, 95% confidence interval 1.04-6.85, P = 0.04). This was further confirmed in the subgroup analysis of patients undergoing colorectal resection and anastomosis (hazard ratio 2.83, 95% confidence interval 1.01-7.96, P = 0.048).

DISCUSSION

In patients undergoing surgery for CC, inclusion of the mesentery is associated with similar short-term outcomes and improved long-term outcomes compared with those seen when the mesentery is retained.

Nr4A1 modulates inflammation-associated intestinal fibrosis and dampens fibrogenic signaling in myofibroblasts

Intestinal fibrosis is a common complication of the inflammatory bowel diseases (IBDs), contributing to tissue stiffening and luminal narrowing. Human nuclear receptor 4A 1 (NR4A1) was previously reported to regulate mesenchymal cell function and dampen fibrogenic signaling. NR4A1 gene variants are associated with IBD risk, and it has been shown to regulate intestinal inflammation. Here, we tested the hypothesis that NR4A1 acts as a negative regulator of intestinal fibrosis through regulating myofibroblast function. Using the SAMP1/YitFc mouse, we tested whether two pharmacological agents known to enhance NR4A1 signaling, cytosporone B (Csn-B) or 6-mercaptopurine (6-MP), could reduce fibrosis. We also used the dextran sulfate sodium (DSS) model of colitis and assessed the magnitude of colonic fibrosis in mouse nuclear receptor 4A 1 (Nr4a1^-/-) and their wild-type littermates (Nr4a1^+/+). Lastly, intestinal myofibroblasts isolated from Nr4a1^-/- and Nr4a1^+/+ mice or primary human intestinal myofibroblasts were stimulated with transforming growth factor-β1 (TGF-β1), in the presence or absence of Csn-B or 6-MP, and proliferation and ECM gene expression assessed. Csn-B or 6-MP treatment significantly reduced ileal thickness, collagen, and overall ECM content in SAMP1/YitFc mice. This was associated with a reduction in proliferative markers within the mesenchymal compartment. Nr4a1^-/- mice exposed to DSS exhibited increased colonic thickening and ECM content. Nr4a1^-/- myofibroblasts displayed enhanced TGF-β1-induced proliferation. Furthermore, Csn-B or 6-MP treatment was antiproliferative in Nr4a1^+/+ but not Nr4a1^-/- cells. Lastly, activating NR4A1 in human myofibroblasts reduced TGF-β1-induced collagen deposition and fibrosis-related gene expression. Our data suggest that NR4A1 can attenuate fibrotic processes in intestinal myofibroblasts and could provide a valuable clinical target to treat inflammation-associated intestinal fibrosis.NEW & NOTEWORTHY Fibrosis and increased muscle thickening contribute to stricture formation and intestinal obstruction, a complication that occurs in 30%-50% of patients with CD within 10 yr of disease onset. More than 50% of those who undergo surgery to remove the obstructed bowel will experience stricture recurrence. To date, there are no drug-based approaches approved to treat intestinal strictures. In the current submission, we identify NR4A1 as a novel target to treat inflammation-associated intestinal fibrosis.

Novel mechanisms and clinical trial endpoints in intestinal fibrosis

The incidence of inflammatory bowel diseases (IBD) worldwide has resulted in a global public health challenge. Intestinal fibrosis leading to stricture formation and bowel obstruction is a frequent complication in Crohn's disease (CD), and the lack of anti-fibrotic therapies makes elucidation of fibrosis mechanisms a priority. Progress has shown that mesenchymal cells, cytokines, microbial products, and mesenteric adipocytes are jointly implicated in the pathogenesis of intestinal fibrosis. This recent information puts prevention or reversal of intestinal strictures within reach through innovative therapies validated by reliable clinical trial endpoints. Here, we review the role of immune and non-immune components of the pathogenesis of intestinal fibrosis, including new cell clusters, cytokine networks, host-microbiome interactions, creeping fat, and their translation for endpoint development in anti-fibrotic clinical trials.

Role of circulating fibrocytes in the diagnosis of acute appendicitis

Background

Improved diagnostic biomarkers are required for acute appendicitis. The circulating fibrocyte percentage (CFP) is increased in inflammatory states, but has not been studied in acute appendicitis. This study aimed to determine CFP in acute appendicitis and compare diagnostic accuracy with standard serological biomarkers.

Methods

A prospective cohort study was carried out between June 2015 and February 2016 at University Hospital Limerick. The CFP was determined by dual‐staining peripheral venous samples for CD45 and collagen I using fluorescence‐activated cell sorting, and correlated with histopathological diagnoses. The accuracy of CFP in determining histological acute appendicitis was characterized and compared with the white cell count, C‐reactive protein concentration, neutrophil count, lymphocyte count and neutrophil : lymphocyte ratio.

Results

Of 95 adults recruited, 15 were healthy individuals and 80 had suspected appendicitis at presentation. Forty‐six of these 80 patients had an appendicectomy, of whom 34 had histologically confirmed appendicitis. The CFP was statistically higher in patients with pathologically proven acute appendicitis than in healthy controls (median 6·1 (i.q.r. 1·6–11·6) versus 2·3 (0·9–3·4) per cent respectively; P = 0·008). The diagnostic accuracy of CFP, as determined using the area under the receiver operating characteristic (ROC) curve, was similar to that of standard biomarkers. In multinomial regression analysis, only raised CFP was retained as an independent prognostic determinant of acute appendicitis (odds ratio 1·57, 95 per cent c.i. 1·05 to 2·33; P = 0·027).

Conclusion

The CFP is increased in histologically confirmed acute appendicitis and is as accurate as standard serological biomarkers in terms of diagnosis.

The fate of myofibroblasts during the development of fibrosis in Crohn's disease

Intestinal fibrosis is a devastating complication in patients with inflammatory bowel disease. Its characteristics include the loss of regular peristalsis and nutrition absorption, excessive deposition of extracellular matrix (ECM) components, thickness of intestinal lumen due to the formation of strictures and of scar tissue. As a major cell type involved in fibrogenesis, the myofibroblasts have already been shown to have a plastic and heterogeneous function in producing abundant collagen, fibronectin and connective tissue growth factor. The primary sources of ECM-producing and vimentin-positive myofibroblasts come from different precursor cells, including bone marrow-derived mesenchymal cells, fibrocytes, pericytes, epithelial to mesenchymal transition and endothelial to mesenchymal transition. Recent immunological research findings suggest that numerous cytokines and chemokines made from macrophages, in addition to T cells and other myeloid cell types, are also important drivers of myofibroblast differentiation and hence of the activation of myofibroblast-mediated transforming growth factor and collagen production. In this review we discuss the origins, roles and cell signaling of myofibroblasts during the development of fibrosis in different organs, particularly in Crohn's disease. Finally, we suggest that the epigenetic and immunological regulation of myofibroblast differentiation may provide a novel antifibrotic strategy in the near future.

Mesenteric excision surgery or conservative limited resection in Crohn's disease: study protocol for an international, multicenter, randomized controlled trial

Background

The structures of the mesentery including adipose tissue, nerves, and lymphatics play an important role in the pathogenesis and disease progression of Crohn’s disease (CD). Conventional surgical resection for CD usually does not involve resecting the mesentery en bloc with the specimen. This contrasts with complete mesocolic excision (CME) in colorectal cancer, which involves radical resection of the mesentery. Preliminary evidence from smaller studies suggests that applying the principle of mesocolic excision to CD surgery may reduce the risk of postoperative recurrence. This randomized controlled trial is designed to test whether applying the principles of mesocolic excision to CD results in reduced postoperative recurrence. It also aims to evaluate intra- and postoperative morbidity between the two approaches.

Methods

This international, multicenter, randomized controlled trial will randomize patients (n = 116) scheduled to undergo primary ileocolic resection to either receive extensive mesenteric excision (EME) or conventional ileocolic resection with limited mesenteric excision (LME). Five sites will recruit patients in three countries. In the EME group, the mesentery is resected following CME, while avoiding the root region, i.e., 1 cm from the root of the ileocolic artery and vein. In the LME group, the mesentery is retained, i.e., “close shave” or < 3 cm from the border of bowel. The primary end point will be surgical recurrence after surgery. The secondary end points will be the postoperative endoscopic and clinical recurrence, and intra- and postoperative morbidity. Demographics, risk factors, laboratory investigations, endoscopy, postoperative prophylaxis and imaging examination will be assessed. Analysis of the primary outcome will be on an intention-to-treat basis.

Discussion

If mesocolic excision in CD reduces postoperative disease recurrence and does not increase morbidity, this trial has the potential to change practice and reduce recurrence of CD after surgical resection.

Trial registration

Clinical Trials.gov, ID: NCT03769922. Registered on February 27, 2019.

Systemic Molecular Mediators of Inflammation Differentiate Between Crohn's Disease and Ulcerative Colitis, Implicating Threshold Levels of IL-10 and Relative Ratios of Pro-inflammatory Cytokines in Therapy

BACKGROUND AND AIMS

Faecal diversion is associated with improvements in Crohn's disease but not ulcerative colitis, indicating that differing mechanisms mediate the diseases. This study aimed to investigate levels of systemic mediators of inflammation, including fibrocytes and cytokines, [1] in patients with Crohn's disease and ulcerative colitis preoperatively compared with healthy controls and [2] in patients with Crohn's disease and ulcerative colitis prior to and following faecal diversion.

METHODS

Blood samples were obtained from healthy individuals and patients with Crohn's disease or ulcerative colitis. Levels of circulating fibrocytes were quantified using flow cytometric analysis and their potential relationship to risk factors of inflammatory bowel disease were determined. Levels of circulating cytokines involved in inflammation and fibrocyte recruitment and differentiation were investigated.

RESULTS

Circulating fibrocytes were elevated in Crohn's disease and ulcerative colitis patients when compared with healthy controls. Smoking, or a history of smoking, was associated with increases in circulating fibrocytes in Crohn's disease, but not ulcerative colitis. Cytokines involved in fibrocyte recruitment were increased in Crohn's disease patients, whereas patients with ulcerative colitis displayed increased levels of pro-inflammatory cytokines. Faecal diversion in Crohn's disease patients resulted in decreased circulating fibrocytes, pro-inflammatory cytokines, and TGF-β1, and increased IL-10, whereas the inverse was observed in ulcerative colitis patients.

CONCLUSIONS

The clinical effect of faecal diversion in Crohn's disease and ulcerative colitis may be explained by differing circulating fibrocyte and cytokine responses. Such differences aid in understanding the disease mechanisms and suggest a new therapeutic strategy for inflammatory bowel disease.

Thalidomide Prevented and Ameliorated Pathogenesis of Crohn's Disease in Mice via Regulation of Inflammatory Response and Fibrosis

Crohn's disease (CD) is a chronic, relapsing form of inflammatory bowel disease, seriously threatening human health. Thalidomide has been used for the treatment of CD. However, the effects and the possible mechanisms of thalidomide on CD are still unclear. Herein, our study demonstrated that thalidomide protected colon mucosa against trinitro-benzene-sulfonic acid (TNBS)-induced injury, diminished inflammatory infiltration and levels of IFN-γ, IGF-1, IL-6, IL-17, TNF-α, while increased the levels of IL-10 and TGF-γ. Moreover, it reversed the intestinal fibrosis and inhibited the accumulated infiltration, down-regulated the expression of col1a2, col3a2, MMP-3, MMP-9, MMP-1, TGF-γ, α-SMA, but up-regulated the expression of TIMP-1 and Vimentin. Although it could be observed that the effect of thalidomide administration in modeling was better than after modeling, there was no statistical difference between the two groups. The present study provided evidence that the therapeutic effect of thalidomide alleviated the inflammatory response and damage of colon tissue, mainly by restoring the imbalance of TH17/Treg cells and inhibiting intestinal fibrosis in TNBS-induced mice colitis.

Pathogenesis of fibrostenosing Crohn's disease

Crohn's disease (CD) is a chronic inflammatory disease, which could affect any part of the gastrointestinal tract. A severe complication of CD is fibrosis-associated strictures, which can cause bowel obstruction. Unfortunately, there is no specific antifibrotic therapy available. More than 80% of the patients with CD will have to undergo at least 1 surgery in their life and recurrence of strictures after surgery is common. Investigations on the mechanism of fibrostenosing CD have revealed that fibrosis is mainly driven by expansion of mesenchymal cells including fibroblasts, myofibroblasts, and smooth muscle cells. Being exposed to a pro-fibrotic milieu, these cells increase the secretion of extracellular matrix, as well as crosslinking enzymes, which drive tissue stiffness and remodeling. Fibrogenesis can become independent of inflammation in later stages of disease, which offers unique therapeutic potential. Exciting new evidence suggests smooth muscle cell hyperplasia as a strong contributor to luminal narrowing in fibrostenotic CD. Approval of new drugs in other fibrotic diseases, such as idiopathic pulmonary fibrosis, as well as new targets associated with fibrosis found in CD, such as cadherins or specific integrins, shed light on the development of novel antifibrotic approaches in CD.

The Mesenteric Fat and Intestinal Muscle Interface: Creeping Fat Influencing Stricture Formation in Crohn's Disease

Adipose tissue is present in close proximity to various organs in the human body. One prominent example is fat contained in the mesentery that is contiguous with all abdominal digestive organs including the intestine. Despite the fact that mesenteric fat-wrapping around the inflamed gut (so called "creeping fat") was described as a characteristic feature of Crohn's disease (CD) in the early 1930s, the functional implications of creeping fat have received only recent attention. As a potent producer of fatty acids, cytokines, growth factors, and adipokines, creeping fat plays an important role in regulation of immunity and inflammation. Increasing evidence points to a link between creeping fat and intestinal inflammation in CD, where histopathologic evaluation shows a significant association between creeping fat and connective tissue changes in the bowel wall, such as muscular hypertrophy, fibrosis, and stricture formation. In addition, emerging mechanistic data indicate a link between creeping fat, muscularis propria hyperplasia, and stricturing disease. Information on fat-mesenchymal interactions in other organs could provide clues to fill the fundamental knowledge gap on the role of distinct components of creeping fat in intestinal fibrosis and stricture formation. Future studies will provide important new information that in turn could lead to novel therapeutic agents aimed at prevention or treatment of CD-associated fibrosis and stricture formation.

Interaction Between CCR6+ Th17 Cells and CD34+ Fibrocytes Promotes Inflammation: Implications in Graves' Orbitopathy in Chinese Population

Purpose

Recent reports suggest that Th17 immunity and bone marrow-derived CD34+ fibrocytes contribute to the pathogenesis of Graves' orbitopathy (GO). This study investigated interactions between Th17 cells and fibrocytes in GO inflammation in Chinese subjects.

Methods

Th17 cells and fibrocytes were derived from blood samples from Chinese GO patients and healthy controls. Proportions and phenotypes of Th17 cells, regulatory T cells (Tregs), and fibrocytes were examined by flow cytometry. Exogenous IL-17A was used to study inflammatory activity of fibrocytes from GO patients and control subjects. Coculture, quantitative RT-PCR, Luminex, and transwell assays were performed to investigate the relationship between Th17 cells and fibrocytes.

Results

CC-chemokine receptor 6 (CCR6+) Th17 cells were increased in both active (P < 0.001) and inactive (P < 0.05) GO patients, compared with healthy controls. There was a positive correlation between number of CCR6+ Th17 cells and GO clinical activity score (P < 0.0001, r = 0.8176). Further, CD34+ fibrocytes were increased in GO patients, with increased expression of IL-17RA (P < 0.05), CD80 (P < 0.05), and CD86 (P < 0.05). A decreased population of effector Treg cells (P < 0.01) and increased CTLA-4 expression on naïve Treg cells (P < 0.05) were observed in GO patients. IL-17A stimulated cytokine production in fibrocytes; GO fibrocytes exhibited more robust production than normal fibrocytes. Autologous Th17 cells promoted inflammatory and antigen-presenting functions of GO fibrocytes; conversely, fibrocytes enhanced Th17 cell-function and recruited Th17 cells in a macrophage inflammatory protein 3 (MIP-3)/CCR6-dependent manner.

Conclusions

The crosstalk between CCR6+ Th17 cells and fibrocytes plays a role in the pathogenesis of GO. Suppressing these interactions may be a candidate molecular target for therapeutic approaches of GO.

The Mesentery, Systemic Inflammation, and Crohn's Disease

Initially thought to be a structure that only provided support to the abdominal contents, the mesentery has now gained special attention in the scientific community. The new approach of studying the mesentery as an individual organ has highlighted its importance in the development of local and systemic inflammatory diseases and its potential role in Crohn's disease. Its topographical relationship with the intestine in the setting of active inflammation and "creeping fat" is possibly one of the most important arguments for including the mesentery as an important factor in the pathogenesis of Crohn's disease. In this review, we discuss the importance of the mesentery from the anatomical and embryological standpoints. We also will summarize data on mesenteric inflammation in patients with Crohn's disease. The significance of the mesentery in systemic inflammatory syndromes will be discussed, and we provide an overview of primary inflammatory disorders of the mesentery. Finally, we discuss surgical approaches for patients requiring resection for Crohn's disease that incorporate mesenteric factors, pointing out recent data suggesting that these have the potential for improving outcomes and reducing disease recurrence. 10.1093/ibd/izy201_video1izy201.video15794169491001.

Significant contribution of TRPC6 channel-mediated Ca2+ influx to the pathogenesis of Crohn's disease fibrotic stenosis

Intestinal fibrosis is an intractable complication of Crohn's disease (CD), and, when occurring excessively, causes severe intestinal obstruction that often necessitates surgical resection. The fibrosis is characterized by an imbalance in the turnover of extracellular matrix (ECM) components, where intestinal fibroblasts/myofibroblasts play active roles in ECM production, fibrogenesis and tissue remodeling, which eventually leads to the formation of stenotic lesions. There is however a great paucity of knowledge about how intestinal fibrosis initiates and progresses, which hampers the development of effective pharmacotherapies against CD. Recently, we explored the potential implications of transient receptor potential (TRP) channels in the pathogenesis of intestinal fibrosis, since they are known to act as cellular stress sensors/transducers affecting intracellular Ca²⁺ homeostasis/dynamics, and are involved in a broad spectrum of cell pathophysiology including inflammation and tissue remodeling. In this review, we will place a particular emphasis on the intestinal fibroblast/myofibroblast TRPC6 channel to discuss its modulatory effects on fibrotic responses and therapeutic potential for anti-fibrotic treatment against CD-related stenosis.

The mesentery: structure, function, and role in disease

Systematic study of the mesentery is now possible because of clarification of its structure. Although this area of science is in an early phase, important advances have already been made and opportunities uncovered. For example, distinctive anatomical and functional features have been revealed that justify designation of the mesentery as an organ. Accordingly, the mesentery should be subjected to the same investigatory focus that is applied to other organs and systems. In this Review, we summarise the findings of scientific investigations of the mesentery so far and explore its role in human disease. We aim to provide a platform from which to direct future scientific investigation of the human mesentery in health and disease.

The mesentery in Crohn's disease: friend or foe?

PURPOSE OF REVIEW

This article assesses the role of the mesentery in Crohn's disease.

RECENT FINDINGS

The mesentery is centrally positioned both anatomically and physiologically. Overlapping mesenteric and submucosal mesenchymal contributions are important in the pathobiology of Crohn's disease. Mesenteric contributions explain the topographic distribution of Crohn's disease in general and mucosal disease in particular. Operative strategies that are mesenteric based (i.e. mesocolic excision) may reduce rates of postoperative recurrence.

SUMMARY

The net effect of mesenteric events in Crohn's disease is pathologic. This can be targeted by operative means.

VIDEO ABSTRACT

http://links.lww.com/COG/A18.

Contribution of bone marrow-derived fibrocytes to liver fibrosis

Since the discovery of fibrocytes in 1994 by Dr. Bucala and colleagues, these bone marrow (BM)-derived collagen Type I producing CD45(+) cells remain the most fascinating cells of the hematopoietic system. Despite recent reports on the emerging contribution of fibrocytes to fibrosis of parenchymal and non-parenchymal organs and tissues, fibrocytes remain the most understudied pro-fibrogenic cellular population. In the past years fibrocytes were implicated in the pathogenesis of liver, skin, lung, and kidney fibrosis by giving rise to collagen type I producing cells/myofibroblasts. Hence, the role of fibrocytes in fibrosis is not well defined since different studies often contain controversial results on the number of fibrocytes recruited to the site of injury versus the number of fibrocyte-derived myofibroblasts in the same fibrotic organ. Furthermore, many studies were based on the in vitro characterization of fibrocytes formed after outgrowth of BM and/or peripheral blood cultures. Therefore, the fibrocyte function(s) still remain(s) lack of understanding, mostly due to (I) the lack of mouse models that can provide complimentary in vivo real-time and cell fate mapping studies of the dynamic differentiation of fibrocytes and their progeny into collagen type I producing cells (and/or possibly, other cell types of the hematopoietic system); (II) the complexity of hematopoietic cell differentiation pathways in response to various stimuli; (III) the high plasticity of hematopoietic cells. Here we summarize the current understanding of the role of CD45(+) collagen type I(+) BM-derived cells in the pathogenesis of liver injury. Based on data obtained from various organs undergoing fibrogenesis or other type of chronic injury, here we also discuss the most recent evidence supporting the critical role of fibrocytes in the mediation of pro-fibrogenic and/or pro-inflammatory responses.

Mechanisms of maladaptive repair after AKI leading to accelerated kidney ageing and CKD

Acute kidney injury is an increasingly common complication of hospital admission and is associated with high levels of morbidity and mortality. A hypotensive, septic, or toxic insult can initiate a cascade of events, resulting in impaired microcirculation, activation of inflammatory pathways and tubular cell injury or death. These processes ultimately result in acutely impaired kidney function and initiation of a repair response. This Review explores the various mechanisms responsible for the initiation and propagation of acute kidney injury, the prototypic mechanisms by which a substantially damaged kidney can regenerate its normal architecture, and how the adaptive processes of repair can become maladaptive. These mechanisms, which include G2/M cell-cycle arrest, cell senescence, profibrogenic cytokine production, and activation of pericytes and interstitial myofibroblasts, contribute to the development of progressive fibrotic kidney disease. The end result is a state that mimics accelerated kidney ageing. These mechanisms present important opportunities for the design of targeted therapeutic strategies to promote adaptive renal recovery and minimize progressive fibrosis and chronic kidney disease after acute insults.

The types of hepatic myofibroblasts contributing to liver fibrosis of different etiologies

Liver fibrosis results from dysregulation of normal wound healing, inflammation, activation of myofibroblasts, and deposition of extracellular matrix (ECM). Chronic liver injury causes death of hepatocytes and formation of apoptotic bodies, which in turn, release factors that recruit inflammatory cells (neutrophils, monocytes, macrophages, and lymphocytes) to the injured liver. Hepatic macrophages (Kupffer cells) produce TGFβ1 and other inflammatory cytokines that activate Collagen Type I producing myofibroblasts, which are not present in the normal liver. Secretion of TGFβ1 and activation of myofibroblasts play a critical role in the pathogenesis of liver fibrosis of different etiologies. Although the composition of fibrogenic myofibroblasts varies dependent on etiology of liver injury, liver resident hepatic stellate cells and portal fibroblasts are the major source of myofibroblasts in fibrotic liver in both experimental models of liver fibrosis and in patients with liver disease. Several studies have demonstrated that hepatic fibrosis can reverse upon cessation of liver injury. Regression of liver fibrosis is accompanied by the disappearance of fibrogenic myofibroblasts followed by resorption of the fibrous scar. Myofibroblasts either apoptose or inactivate into a quiescent-like state (e.g., stop collagen production and partially restore expression of lipogenic genes). Resolution of liver fibrosis is associated with recruitment of macrophages that secrete matrix-degrading enzymes (matrix metalloproteinase, collagenases) and are responsible for fibrosis resolution. However, prolonged/repeated liver injury may cause irreversible crosslinking of ECM and formation of uncleavable collagen fibers. Advanced fibrosis progresses to cirrhosis and hepatocellular carcinoma. The current review will summarize the role and contribution of different cell types to populations of fibrogenic myofibroblasts in fibrotic liver.

Mechanisms that mediate the development of fibrosis in patients with Crohn's disease

Crohn's disease is complicated by the development of fibrosis and stricture in approximately 30% to 50% of patients over time. The pathogenesis of fibrostenotic disease is multifactorial involving the activation of mesenchymal cells by cytokines, growth factors, and other mediators released by immune cells, epithelial cells, and mesenchymal cells. Transforming growth factor β, a key activator of mesenchymal cells, is central to the process of fibrosis and regulates numerous genes involved in the disordered wound healing including collagens, and other extracellular matrix proteins, connective tissue growth factor, and insulin-like growth factors. The activated mesenchymal compartment is expanded by recruitment of new mesenchymal cells through epithelial to mesenchymal transition, endothelial to mesenchymal transition, and invasion of circulating fibrocytes. Cellular hyperplasia and increased extracellular matrix production, particularly collagens, from fibroblasts, myofibroblasts, and smooth muscle cells add to the disturbed architecture and scarring on the intestine. Extracellular matrix homeostasis is further disrupted by alterations in the expression of matrix metalloproteinases and tissue inhibitors of metalloproteinase in the gut. Among the 163 susceptibility genes identified that contribute to susceptibility in inflammatory bowel disease mutations in NOD2/CARD15, innate immune system components and autophagy jointly contribute to the activation of mesenchymal cells and pathogenesis of fibrosis in this polygenic disorder. Numerous growth factors cytokines and other mediators also contribute to development of fibrosis in the susceptible patient. This review focuses on the molecular mechanisms that regulate mesenchymal cell function, particularly smooth muscle cells, the largest compartment of mesenchyme in the intestine, that lead to fibrosis in Crohn's disease.