Bacterial lipopolysaccharide promotes profibrotic activation of intestinal fibroblasts

The Role of Gut Microbiota on Intestinal Fibrosis in Inflammatory Bowel Disease and Traditional Chinese Medicine Intervention

Inflammatory bowel disease (IBD) is a chronic, relapsing inflammatory disorder of the intestine, frequently complicated by intestinal fibrosis. As fibrosis progresses, it can result in luminal stricture and compromised intestinal function, significantly diminishing patients' quality of life. Emerging evidence suggests that gut microbiota and their metabolites contribute to the pathogenesis of IBD-associated intestinal fibrosis by influencing inflammation and modulating immune responses. This review systematically explores the mechanistic link between gut microbiota and intestinal fibrosis in IBD and evaluates the therapeutic potential of traditional Chinese medicine (TCM) interventions. Relevant studies were retrieved from PubMed, Web of Science, Embase, Scopus, CNKI, Wanfang, and VIP databases. Findings indicate that TCM, including Chinese herbal prescriptions and bioactive constituents, can modulate gut microbiota composition and microbial metabolites, ultimately alleviating intestinal fibrosis through anti-inflammatory, immunemodulatory, and anti-fibrotic mechanisms. These insights highlight the potential of TCM as a promising strategy for targeting gut microbiota in the management of IBD-associated fibrosis.

Fibroblast-Mediated Macrophage Recruitment Supports Acute Wound Healing

Epithelial and immune cells have long been appreciated for their contribution to the early immune response after injury; however, much less is known about the role of mesenchymal cells. Using single-nuclei RNA sequencing, we defined changes in gene expression associated with inflammation 1 day after wounding in mouse skin. Compared with those in keratinocytes and myeloid cells, we detected enriched expression of proinflammatory genes in fibroblasts associated with deeper layers of the skin. In particular, SCA1+ fibroblasts were enriched for numerous chemokines, including CCL2, CCL7, and IL-33, compared with SCA1- fibroblasts. Genetic deletion of Ccl2 in fibroblasts resulted in fewer wound-bed macrophages and monocytes during injury-induced inflammation, with reduced revascularization and re-epithelialization during the proliferation phase of healing. These findings highlight the important contribution of fibroblast-derived factors to injury-induced inflammation and the impact of immune cell dysregulation on subsequent tissue repair.

Phytochemical Compounds as Promising Therapeutics for Intestinal Fibrosis in Inflammatory Bowel Disease: A Critical Review

BACKGROUND/OBJECTIVE

Intestinal fibrosis, a prominent consequence of inflammatory bowel disease (IBD), presents considerable difficulty owing to the absence of licensed antifibrotic therapies. This review assesses the therapeutic potential of phytochemicals as alternate methods for controlling intestinal fibrosis. Phytochemicals, bioactive molecules originating from plants, exhibit potential antifibrotic, anti-inflammatory, and antioxidant activities, targeting pathways associated with inflammation and fibrosis. Compounds such as Asperuloside, Berberine, and olive phenols have demonstrated potential in preclinical models by regulating critical signaling pathways, including TGF-β/Smad and NFκB, which are integral to advancing fibrosis.

RESULTS

The main findings suggest that these phytochemicals significantly reduce fibrotic markers, collagen deposition, and inflammation in various experimental models of IBD. These phytochemicals may function as supplementary medicines to standard treatments, perhaps enhancing patient outcomes while mitigating the adverse effects of prolonged immunosuppressive usage. Nonetheless, additional clinical trials are necessary to validate their safety, effectiveness, and bioavailability in human subjects.

CONCLUSIONS

Therefore, investigating phytochemicals may lead to crucial advances in the formulation of innovative treatment approaches for fibrosis associated with IBD, offering a promising avenue for future therapeutic development.

Deep skin fibroblast-mediated macrophage recruitment supports acute wound healing

Epithelial and immune cells have long been appreciated for their contribution to the early immune response after injury; however, much less is known about the role of mesenchymal cells. Using single nuclei RNA-sequencing, we defined changes in gene expression associated with inflammation at 1-day post-wounding (dpw) in mouse skin. Compared to keratinocytes and myeloid cells, we detected enriched expression of pro-inflammatory genes in fibroblasts associated with deeper layers of the skin. In particular, SCA1+ fibroblasts were enriched for numerous chemokines, including CCL2, CCL7, and IL33 compared to SCA1- fibroblasts. Genetic deletion of Ccl2 in fibroblasts resulted in fewer wound bed macrophages and monocytes during injury-induced inflammation with reduced revascularization and re-epithelialization during the proliferation phase of healing. These findings highlight the important contribution of deep skin fibroblast-derived factors to injury-induced inflammation and the impact of immune cell dysregulation on subsequent tissue repair.

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.

Gut Microbiota Metabolites: Unveiling Their Role in Inflammatory Bowel Diseases and Fibrosis

In recent years, there has been a growing focus on the intricate interplay between the gut microbiota and host health, specifically in the context of inflammatory bowel diseases (IBDs). The gut microbiota produces a diverse array of metabolites, influencing the host's immune response and tissue homeostasis. Noteworthy metabolites, such as short-chain fatty acids, bile acids, and indoles, exert significant effects on intestinal inflammation and fibrosis. This review integrates current research findings to clarify the mechanisms through which gut microbiota metabolites contribute to the progression of IBD and fibrosis, offering insights into potential therapeutic targets and strategies for managing these intricate gastrointestinal conditions. The unraveling of the complex relationship between gut microbiota metabolites and inflammatory processes holds promise for the development of targeted interventions that could lead to more effective and personalized treatment approaches for individuals affected by IBD and subsequent intestinal fibrosis.

Adipose tissue depot specific expression and regulation of fibrosis-related genes and proteins in experimental obesity

Transforming growth factor beta (Tgfb) is a well-studied pro-fibrotic cytokine, which upregulates cellular communication network factor 2 (Ccn2), collagen, and actin alpha 2, smooth muscle (Acta2) expression. Obesity induces adipose tissue fibrosis, which contributes to metabolic diseases. This work aimed to analyze the expression of Tgfb, Ccn2, collagen1a1 (Col1a1), Acta2 and BMP and activin membrane-bound inhibitor (Bambi), which is a negative regulator of Tgfb signaling, in different adipose tissue depots of mice fed a standard chow, mice fed a high fat diet (HFD) and ob/ob mice. Principally, these genes were low expressed in brown adipose tissues and this difference was less evident for the ob/ob mice. Ccn2 and Bambi protein as well as mRNA expression, and collagen1a1 mRNA were not induced in the adipose tissues upon HFD feeding whereas Tgfb and Acta2 mRNA increased in the white fat depots. Immunoblot analysis showed that Acta2 protein was higher in subcutaneous and perirenal fat of these mice. In the ob/ob mice, Ccn2 mRNA and Ccn2 protein were upregulated in the fat depots. Here, Tgfb, Acta2 and Col1a1 mRNA levels and serum Tgfb protein were increased. Acta2 protein was, however, not higher in subcutaneous and perirenal fat of these mice. Col6a1 mRNA was shown before to be higher in obese fat tissues. Current analysis proved the Col6a1 protein was induced in subcutaneous fat of HFD fed mice. Notably, Col6a1 was reduced in perirenal fat of ob/ob mice in comparison to the respective controls. 3T3-L1 cells express Ccn2 and Bambi protein, whose levels were not changed by fatty acids, leptin, lipopolysaccharide, tumor necrosis factor and interleukin-6. All of these factors led to higher Tgfb in 3T3-L1 adipocyte media but did not increase its mRNA levels. Free fatty acids induced necrosis whereas apoptosis did not occur in any of the in vitro incubations excluding cell death as a main reason for higher Tgfb in cell media. In summary, Tgfb mRNA is consistently induced in white fat tissues in obesity but this is not paralleled by a clear increase of its target genes. Moreover, discrepancies between mRNA and protein expression of Acta2 were observed. Adipocytes seemingly do not contribute to higher Tgfb mRNA levels in obesity. These cells release more Tgfb protein when challenged with obesity-related metabolites connecting metabolic dysfunction and fibrosis.

Stromal Cell Regulation of Intestinal Inflammatory Fibrosis

Intestinal inflammatory fibrosis is a severe consequence of inflammatory bowel diseases (IBDs). There is currently no cure for the treatment of intestinal fibrosis in IBD. Although inflammation is necessary for triggering fibrosis, the anti-inflammatory agents used to treat IBD are ineffective in preventing the progression of intestinal fibrosis and stricture formation once initiated, suggesting that inflammatory signals are not the sole drivers of fibrosis progression once it is established. Among multiple mechanisms involved in the initiation and progression of intestinal fibrosis in IBD, stromal cells play critical roles in mediating the process. In this review, we summarize recent progress on how stromal cells regulate intestinal fibrosis in IBD and how they are regulated by focusing on immune regulation and gut microbiota. We also outline the challenges moving forward in the field.

The Pregnane X Receptor and Indole-3-Propionic Acid Shape the Intestinal Mesenchyme to Restrain Inflammation and Fibrosis

BACKGROUND & AIMS

Fibrosis is a common complication of inflammatory bowel diseases (IBDs). The pregnane X receptor (PXR) (encoded by NR1I2) suppresses intestinal inflammation and has been shown to influence liver fibrosis. In the intestine, PXR signaling is influenced by microbiota-derived indole-3-propionic acid (IPA). Here, we sought to assess the role of the PXR in regulating intestinal inflammation and fibrosis.

METHODS

Intestinal inflammation was induced using dextran sulfate sodium (DSS). Fibrosis was assessed in wild-type (WT), Nr1i2^-/-, epithelial-specific Nr1i2^-/-, and fibroblast-specific Nr1i2^-/- mice. Immune cell influx was quantified by flow cytometry and cytokines by Luminex. Myofibroblasts isolated from WT and Nr1i2^-/- mice were stimulated with cytomix or lipopolysaccharide, and mediator production was assessed by quantitative polymerase chain reaction and Luminex.

RESULTS

After recovery from DSS-induced colitis, WT mice exhibited fibrosis, a response that was exacerbated in Nr1i2^-/- mice. This was correlated with greater neutrophil infiltration and innate cytokine production. Deletion of the PXR in fibroblasts, but not the epithelium, recapitulated this phenotype. Inflammation and fibrosis were reduced by IPA administration, whereas depletion of the microbiota exaggerated intestinal fibrosis. Nr1i2-deficient myofibroblasts were hyperresponsive to stimulation, producing increased levels of inflammatory mediators compared with WT cells. In biopsies from patients with active Crohn's disease (CD) and ulcerative colitis (UC), expression of NR1I2 was reduced, correlating with increased expression of fibrotic and innate immune genes. Finally, both CD and UC patients exhibited reduced levels of fecal IPA.

CONCLUSIONS

These data highlight a role for IPA and its interactions with the PXR in regulating the mesenchyme and the development of inflammation and fibrosis, suggesting microbiota metabolites may be a vital determinant in the progression of fibrotic complications in IBD.

Functional responses of dermal fibroblasts to low nutrition and pro-inflammatory stimuli mimicking a wound environment in vitro

Dermal fibroblasts (DF) constitute one of key cells involved in wound healing. However, the functions they perform in wound conditions remain poorly understood. This study involved exposing DF to low nutrition and to low nutrition + LPS for 5 d as conditions representing the wound. Although DF exhibited increasing metabolic activity in time under all conditions including control, the proliferation did not change in both low nutrition and low nutrition + LPS. Only the low nutrition + LPS was found to potentiate the migration and pro-inflammatory phenotype (IL6 release) of DF. The potential of DF to contract collagen hydrogel declined only under low nutrition as a consequence of low cell number. The expression of α-SMA was reduced under both conditions independently of the cell number. The remodeling capability of DF was affected under both conditions as documented by the enhanced MMP2 activity. Finally, the production of collagen type I was not affected by either condition. The study shows that low nutrition as the single factor is able to delay the healing process. Moreover, the addition of the mild pro-inflammatory stimulus represented by LPS may amplify the cell response in case of decreased α-SMA expression or excite DF to produce IL6 impairing the healing process.

Contribution of the Gut Microbiota to Intestinal Fibrosis in Crohn's Disease

In Crohn's disease (CD), intestinal fibrosis is a critical determinant of a patient's prognosis. Although inflammation may be a prerequisite for the initiation of intestinal fibrosis, research shows that the progression or continuation of intestinal fibrosis can occur independently of inflammation. Thus, once initiated, intestinal fibrosis may persist even if medical treatment controls inflammation. Clearly, an understanding of the pathophysiological mechanisms of intestinal fibrosis is required to diminish its occurrence. Accumulating evidence suggests that the gut microbiota contributes to the pathogenesis of intestinal fibrosis. For example, the presence of antibodies against gut microbes can predict which CD patients will have intestinal complications. In addition, microbial ligands can activate intestinal fibroblasts, thereby inducing the production of extracellular matrix. Moreover, in various animal models, bacterial infection can lead to the development of intestinal fibrosis. In this review, we summarize the current knowledge of the link between intestinal fibrosis in CD and the gut microbiota. We highlight basic science and clinical evidence that the gut microbiota can be causative for intestinal fibrosis in CD and provide valuable information about the animal models used to investigate intestinal fibrosis.

Gut microbiota: sculptors of the intestinal stem cell niche in health and inflammatory bowel disease

Intestinal epithelium represents a dynamic and diverse cellular system that continuously interacts with gut commensals and external cues. Intestinal stem cells, which lie at the heart of epithelial renewal and turnover, proliferate to maintain a steady stem cell population and differentiate to form functional epithelial cell types. This rather sophisticated assembly-line is maintained by an elaborate micro-environment, sculpted by a myriad of host and gut microbiota-derived signals, forming an intestinal stem cell niche. This complex, yet crucial signaling niche undergoes dynamic changes during homeostasis and chronic intestinal inflammation. Inflammatory bowel disease refers to a chronic inflammatory response toward pathogenic or commensal microbiota, in a genetically susceptible host. Compositional and functional alterations in gut microbiota are pathognomonic of IBD.The present review highlights the modulatory role of gut microbiota on the intestinal stem cell niche during homeostasis and inflammatory bowel disease. We discuss the mechanisms of direct action of gut commensals (through microbiota-derived or microbiota-influenced metabolites) on ISCs, followed by their effects via other epithelial and immune cell types.

Gut Microbiome and Organ Fibrosis

Fibrosis is a pathological process associated with most chronic inflammatory diseases. It is defined by an excessive deposition of extracellular matrix proteins and can affect nearly every tissue and organ system in the body. Fibroproliferative diseases, such as intestinal fibrosis, liver cirrhosis, progressive kidney disease and cardiovascular disease, often lead to severe organ damage and are a leading cause of morbidity and mortality worldwide, for which there are currently no effective therapies available. In the past decade, a growing body of evidence has highlighted the gut microbiome as a major player in the regulation of the innate and adaptive immune system, with severe implications in the pathogenesis of multiple immune-mediated disorders. Gut microbiota dysbiosis has been associated with the development and progression of fibrotic processes in various organs and is predicted to be a potential therapeutic target for fibrosis management. In this review we summarize the state of the art concerning the crosstalk between intestinal microbiota and organ fibrosis, address the relevance of diet in different fibrotic diseases and discuss gut microbiome-targeted therapeutic approaches that are current being explored.

Intestinal Fibrosis and Gut Microbiota: Clues From Other Organs

Fibrosis is a complex and difficult to elucidate pathological process with no available therapies. Growing evidence implicates intestinal microbiota in the occurrence and development of fibrosis, and the potential mechanisms involved in different organs have been explored in several studies. In this review, we summarize the causative and preventive effects of gut microbiota on intestinal fibrosis, as well as the relationships between gut microbiota and fibrosis in other organs. Interestingly, several colonized microbes are associated with fibrosis via their structural components and metabolic products. They may also play essential roles in regulating inflammation and fibroblast activation or differentiation, which modulates extracellular matrix formation. While the relationships between intestinal fibrosis and gut microbiota remain unclear, lessons can be drawn from the effects of gut microbiota on hepatic, cardiac, nephritic, and pulmonary fibrosis. Various intestinal microbes alterations have been detected in different fibrotic organs; however, the results were heterogeneous. Mechanisms by which the intestinal microbiota regulate fibrotic processes in other organs, such as novel metabolic products or specific microbes, are also discussed. The specific microbiota associated with fibrosis in other organs could instruct future studies aiming to discover prospective mechanisms regulating intestinal fibrosis.

Intestinal stricture in Crohn's disease: A 2020 update

Crohn's disease (CD) is a chronic and relapsing-remitting inflammatory disorder of the gastrointestinal tract. Approximately 70% of patients inevitably develop fibrosis-associated intestinal stricture after 10 years of CD diagnosis, which seriously affects their quality of life. Current therapies play limited role in preventing or reversing the process of fibrosis and no specific anti-fibrotic therapy is yet available. Nearly half of patients thus have no alternative but to receive surgery. The potential mechanisms of intestinal fibrosis remain poorly understood; extracellular matrix remodeling, aberrant immune response, intestinal microbiome imbalance and creeping fat might exert fundamental influences on the multiple physiological and pathophysiological processes. Recently, the emerging new diagnostic techniques have markedly promoted an accurate assessment of intestinal stricture by distinguishing fibrosis from inflammation, which is crucial for guiding treatment and predicting prognosis. In this review, we concisely summarized the key studies published in the year 2020 covering pathogenesis, diagnostic modalities, and therapeutic strategy of intestinal stricture. A comprehensive and timely review of the updated researches in intestinal stricture could provide insight to further elucidate its pathogenesis and identify novel drug targets with anti-fibrotic potentiality.

COVID-19 and Toll-Like Receptor 4 (TLR4): SARS-CoV-2 May Bind and Activate TLR4 to Increase ACE2 Expression, Facilitating Entry and Causing Hyperinflammation

Causes of mortality from COVID-19 include respiratory failure, heart failure, and sepsis/multiorgan failure. TLR4 is an innate immune receptor on the cell surface that recognizes pathogen-associated molecular patterns (PAMPs) including viral proteins and triggers the production of type I interferons and proinflammatory cytokines to combat infection. It is expressed on both immune cells and tissue-resident cells. ACE2, the reported entry receptor for SARS-CoV-2, is only present on ~1-2% of the cells in the lungs or has a low pulmonary expression, and recently, the spike protein has been proposed to have the strongest protein-protein interaction with TLR4. Here, we review and connect evidence for SARS-CoV-1 and SARS-CoV-2 having direct and indirect binding to TLR4, together with other viral precedents, which when combined shed light on the COVID-19 pathophysiological puzzle. We propose a model in which the SARS-CoV-2 spike glycoprotein binds TLR4 and activates TLR4 signalling to increase cell surface expression of ACE2 facilitating entry. SARS-CoV-2 also destroys the type II alveolar cells that secrete pulmonary surfactants, which normally decrease the air/tissue surface tension and block TLR4 in the lungs thus promoting ARDS and inflammation. Furthermore, SARS-CoV-2-induced myocarditis and multiple-organ injury may be due to TLR4 activation, aberrant TLR4 signalling, and hyperinflammation in COVID-19 patients. Therefore, TLR4 contributes significantly to the pathogenesis of SARS-CoV-2, and its overactivation causes a prolonged or excessive innate immune response. TLR4 appears to be a promising therapeutic target in COVID-19, and since TLR4 antagonists have been previously trialled in sepsis and in other antiviral contexts, we propose the clinical trial testing of TLR4 antagonists in the treatment of severe COVID-19. Also, ongoing clinical trials of pulmonary surfactants in COVID-19 hold promise since they also block TLR4.

Selective deletion of MyD88 signaling in α-SMA positive cells ameliorates experimental intestinal fibrosis via post-transcriptional regulation

Intestinal fibrosis leading to strictures remains a significant clinical problem in inflammatory bowel diseases (IBD). The role of bacterial components in activating intestinal mesenchymal cells and driving fibrogenesis is largely unexplored. Tamoxifen-inducible α-SMA promoter Cre mice crossed with floxed MyD88 mice were subjected to chronic dextran sodium sulfate colitis. MyD88 was deleted prior to or after induction of colitis. Human intestinal myofibroblasts (HIMF) were exposed to various bacterial components and assessed for fibronectin (FN) and collagen I (Col1) production. RNA sequencing was performed. Post-transcriptional regulation was assessed by polysome profiling assay. Selective deletion of MyD88 in α-SMA-positive cells prior to, but not after induction of, experimental colitis decreased the degree of intestinal fibrosis. HIMF selectively responded to flagellin with enhanced FN or Col1 protein production in a MyD88-dependent manner. RNA sequencing suggested minimal transcriptional changes induced by flagellin in HIMF. Polysome profiling revealed higher proportions of FN and Col1 mRNA in the actively translated fractions of flagellin exposed HIMF, which was mediated by eIF2 alpha and 4EBP1. In conclusion, selectivity of flagellin-induced ECM secretion in HIMF is post-transcriptionally regulated. The results may represent a novel and targetable link between the gut microbiota and intestinal fibrogenesis.

The role of cytokine and immune responses in intestinal fibrosis

The rapidly increasing incidence of inflammatory bowel disease (IBD) in South America, eastern Europe, Asia, and Africa has resulted in a global public health challenge. Intestinal fibrosis is a common complication in patients with long-term IBD, which may develop into stenosis and subsequent obstruction. Hitherto, the origin of IBD is unclear and several factors may be involved, including genetic, immune, environmental and microbial influences. Little is known about how the recurrent inflammation in patients with IBD develops into intestinal fibrosis and currently, there is no suitable treatment to reverse intestinal fibrosis in these patients. Here, we review the role of immune components in the pathogenesis of IBD and intestinal fibrosis, including cytokine networks, host-microbiome interactions, and immune cell trafficking.

Wuda granule, a traditional Chinese herbal medicine, ameliorates postoperative ileus by anti-inflammatory action

BACKGROUND

Postoperative ileus (POI) is a temporary disturbance in gastrointestinal motility following surgery, and intestinal inflammatory response plays a critical role in the pathogenesis of POI. Wuda granule (WDG), a gastrointestinal prokinetic Chinese herbal medicine, is prescribed to promote recovery of gastrointestinal function after abdominal surgery. However, it has remained unclear whether WDG shows anti-inflammatory effects in POI. In the present study, we investigated the effects of WDG in a rat POI model and attempted to clarify the detailed mechanisms of action.

METHOD

Experimental POI was induced in adult male SD rats by intestinal manipulation (IM). WDG were orally administered after surgery at the same points (6 h, 12 h, 18 h, 24 h). Histological changes of mesenterium, levels of cytokines, and CD68 and iNOS expression were determined in rats treated or not with WDG. We also investigated the transcriptome profile of rats treated with WDG in a POI model.

RESULTS

Experimental POI in rats was characterized by a marked intestinal and systemic inflammatory response. WDG significantly inhibited the infiltration of neutrophils and macrophages, reduced the levels of IL-6, and CRP, and inhibited protein expressions of CD68 and iNOS in mesentery. Comparison analysis showed that there are 1432 differentially expressed genes (DEGs) between the POI and CON sample, whereas 331 DEGs between the WDG -treated sample and the POI group. And 16 DEGs were shared by the POI vs CON and WDG vs POI groups, among which 6 hub genes associated with immune system processes were identified and verified.

CONCLUSIONS

WDG treatment ameliorates the impaired gastrointestinal motility in the rat model of POI through inhibiting the inflammatory response of mesentery.

Amphiregulin modulates murine lung recovery and fibroblast function following exposure to agriculture organic dust

Exposure to agricultural bioaerosols can lead to chronic inflammatory lung diseases. Amphiregulin (AREG) can promote the lung repair process but can also lead to fibrotic remodeling. The objective of this study was to determine the role of AREG in altering recovery from environmental dust exposure in a murine in vivo model and in vitro using cultured human and murine lung fibroblasts. C57BL/6 mice were intranasally exposed to swine confinement facility dust extract (DE) or saline daily for 1 wk or allowed to recover for 3-7 days while being treated with an AREG-neutralizing antibody or recombinant AREG. Treatment with the anti-AREG antibody prevented resolution of DE exposure-induced airway influx of total cells, neutrophils, and macrophages and increased levels of TNF-α, IL-6, and CXCL1. Neutrophils and activated macrophages (CD11c+CD11bhi) persisted after recovery in lung tissues of anti-AREG-treated mice. In murine and human lung fibroblasts, DE induced the release of AREG and inflammatory cytokines. Fibroblast recellularization of primary human lung mesenchymal matrix scaffolds and wound closure was inhibited by DE and enhanced with recombinant AREG alone. AREG treatment rescued the DE-induced inhibitory fibroblast effects. AREG intranasal treatment for 3 days during recovery phase reduced repetitive DE-induced airway inflammatory cell influx and cytokine release. Collectively, these studies demonstrate that inhibition of AREG reduced, whereas AREG supplementation promoted, the airway inflammatory recovery response following environmental bioaerosol exposure, and AREG enhanced fibroblast function, suggesting that AREG could be targeted in agricultural workers repetitively exposed to organic dust environments to potentially prevent and/or reduce disease.

Toll-like receptor 4 activation attenuates profibrotic response in control lung fibroblasts but not in fibroblasts from patients with IPF

Idiopathic pulmonary fibrosis (IPF) is a devastating lung disease with a median survival of 3 yr. IPF deteriorates upon viral or bacterial lung infection although pulmonary infection (pneumonia) in healthy lungs rarely induces fibrosis. Bacterial lipopolysaccharide (LPS) activates Toll-like receptor 4 (TLR4), initiating proinflammatory pathways. As TLR4 has already been linked to hepatic fibrosis and scleroderma, we now investigated the role of TLR4 in IPF fibroblasts. Lung tissue sections from patients with IPF were analyzed for TLR4 expression. Isolated normal human lung fibroblasts (NL-FB) and IPF fibroblasts (IPF-FB) were exposed to LPS and transforming growth factor-β (TGF-β) before expression analysis of receptors, profibrotic mediators, and cytokines. TLR4 is expressed in fibroblast foci of IPF lungs as well as in primary NL-FB and IPF-FB. As a model for a gram-negative pneumonia in the nonfibrotic lung, NL-FB and IPF-FB were coexposed to LPS and TGF-β. Whereas NL-FB produced significantly less connective tissue growth factor upon costimulation compared with TGF-β stimulation alone, IPF-FB showed significantly increased profibrotic markers compared with control fibroblasts after costimulation. Although levels of antifibrotic prostaglandin E2 were elevated after costimulation, they were not responsible for this effect. However, significant downregulation of TGF-β receptor type 1 in control fibroblasts seems to contribute to the reduced profibrotic response in our in vitro model. Normal and IPF fibroblasts thus differ in their profibrotic response upon LPS-induced TLR4 stimulation.

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.

LPS/TLR4-mediated stromal cells acquire an invasive phenotype and are implicated in the pathogenesis of adenomyosis

The present study tested whether the LPS/TLR4 signal pathway in endometrial stromal cells is essential for the pathogenesis of adenomyosis. We tested the expression of TLR4, MD2 in the endometrium without adenomyosis (CE), the eutopic endometrium with adenomyosis (EuE) and the ectopic endometrium with adenomyosis (EE). We isolated the stromal cells from CE, EuE and EE (CESC, EuESC, EESC), treated with lipopolysaccharide (LPS) and TLR4 antagonist and detected the cell viability. And we also measured the key protein of the TLR4 signal pathway and inflammatory proliferation and invasive growth of experimental cells. We found that the viability of experimental cells treated with LPS was significantly greater than that of the non-treated cells, blocked by the TLR4 antagonist VIPER. TLR4 signal pathway and inflammatory proliferation and invasive growth of experimental cells stimulated by LPS, and it was inhibited by VIPER. This study suggested that stromal cells were activated by the TLR4 signalling pathway, which processed the cellular inflammatory proliferation and invasive growth involved in the pathogenesis of adenomyosis.

Sirtuin 1 suppresses nuclear factor κB induced transactivation and pro-inflammatory cytokine expression in cat fibroblast cells

Nuclear factor κB (NF-κB) is a key factor in the development of chronic inflammation and is deeply involved in age-related and metabolic diseases development. These diseases have become a serious problem in cats. Sirtuin 1 (SIRT1) is associated with aging and metabolism through maintaining inflammation via NF-κB. In addition, fibroblasts are considered an important factor in the development of chronic inflammation. Therefore, we aimed to examine the effect of cat SIRT1 (cSIRT1) on NF-κB in cat fibroblast cells. The up-regulation of NF-κB transcriptional activity and pro-inflammatory cytokine mRNA expression by p65 subunit of NF-κB and lipopolysaccharide was suppressed by cSIRT1 in cat fibroblast cells. Our findings show that cSIRT1 is involved in the suppression of inflammation in cat fibroblast cells.

Fibrosis in ulcerative colitis: mechanisms, features, and consequences of a neglected problem

Chronic intestinal inflammation and impaired tissue repair leading to intestinal fibrosis are a commonly observed complication in inflammatory bowel disease. This is particularly true for small bowel Crohn's disease. However, the development of fibrosis in ulcerative colitis has remained largely unexplored. This is surprising, given knowledge about its prevalence for decades, well described histopathologic features of fibrotic and stricturing ulcerative colitis, the relevance of the extracellular matrix for intestinal inflammation and fibrosis, and the clinical impact of fibrosis on stricture formation, motility, and the necessary discrimination from colonic malignancy. This systematic review summarizes the current knowledge of ulcerative colitis-related fibrosis, including epidemiology, basic mechanisms, histopathology, and clinical implications.

TLR4 activation enhances the PD-L1-mediated tolerogenic capacity of colonic CD90+ stromal cells

Signaling via programmed death ligand-1 (PD-L1) and PD-L2 is crucial for maintaining peripheral tolerance. CD90(+) myofibroblasts/fibroblasts (CMFs) are major programmed cell death-1 (PD-1) ligand-expressing cells in normal human colonic mucosa. CMFs suppress activated CD4(+) T cell proliferation via PD-1 ligands. It is not known whether signaling through TLRs contribute to the regulation PD-1 ligands on CMFs upon colonic mucosal tolerance. In this study, we demonstrated that stimulation of TLR4 on human CMFs upregulates PD-L1, but not PD-L2, and reinforces CMF-mediated suppression of CD4(+) T cell proliferation and IFN-γ production. TLR4-mediated upregulation of PD-L1 on CMFs involved NF-κB pathways and was JAK2 and MyD88 dependent. MyD88-dependent stimulation of TLR1/2 and TLR5 also upregulated PD-L1 expression on CMFs in culture. PD-L1 expression was drastically decreased in vivo in the colonic mucosa of mice devoid of MyD88. Induction of MyD88 deficiency in CMFs in fibroblast-specific MyD88 conditional knockout mice resulted in a strong increase in a mucosal IFN-γ expression concomitantly with the abrogation of PD-L1 expression in CMFs under homeostasis and epithelial injury induced by dextran sodium sulfate. Together, these data suggest that MyD88-dependent TLR stimulation of CMFs in the normal colonic mucosa may reinforce these cells' anti-inflammatory capacity and thus contribute to the maintenance of mucosal tolerance.

Endotoxin-induced endothelial fibrosis is dependent on expression of transforming growth factors β1 and β2

During endotoxemia-induced inflammatory disease, bacterial endotoxins circulate in the bloodstream and interact with endothelial cells (ECs), inducing dysfunction of the ECs. We previously reported that endotoxins induce the conversion of ECs into activated fibroblasts. Through endotoxin-induced endothelial fibrosis, ECs change their morphology and their protein expression pattern, thereby suppressing endothelial markers and upregulating fibrotic proteins. The most commonly used fibrotic inducers are transforming growth factor β1 (TGF-β1) and TGF-β2. However, whether TGF-β1 and TGF-β2 participate in endotoxin-induced endothelial fibrosis remains unknown. We have shown that the endotoxin-induced endothelial fibrosis process is dependent on the TGF-β receptor, ALK5, and the activation of Smad3, a protein that is activated by ALK5 activation, thus suggesting that endotoxin elicits TGF-β production to mediate endotoxin-induced endothelial fibrosis. Therefore, we investigated the dependence of endotoxin-induced endothelial fibrosis on the expression of TGF-β1 and TGF-β2. Endotoxin-treated ECs induced the expression and secretion of TGF-β1 and TGF-β2. TGF-β1 and TGF-β2 downregulation inhibited the endotoxin-induced changes in the endothelial marker VE-cadherin and in the fibrotic proteins α-SMA and fibronectin. Thus, endotoxin induces the production of TGF-β1 and TGF-β2 as a mechanism to promote endotoxin-induced endothelial fibrosis. To the best of our knowledge, this is the first report showing that endotoxin induces endothelial fibrosis via TGF-β secretion, which represents an emerging source of vascular dysfunction. These findings contribute to understanding the molecular mechanism of endotoxin-induced endothelial fibrosis, which could be useful in the treatment of inflammatory diseases.

The gut microbiome in intestinal fibrosis: environmental protector or provocateur?

In individuals with inflammatory bowel diseases, intestinal fibrosis is a serious clinical complication with no specific therapies. Patients develop bowel fistulae and strictures that usually require surgery and often reoccur. The main driver of gut fibrogenesis is believed to be chronic inflammation, which leads to mesenchymal cell recruitment and activation. Recent findings suggest that the environment--in particular, the microbiome--plays a critical role in this process.

Toll-like receptor regulation of intestinal development and inflammation in the pathogenesis of necrotizing enterocolitis

Toll-like receptors (TLRs) are a structurally related family of molecules that respond to a wide variety of endogenous and exogenous ligands, and which serve as important components of the innate immune system. While TLRs have established roles in host defense, these molecules have also been shown to play important roles in the development of various disease states. A particularly important example of the role of TLRs in disease induction includes necrotizing enterocolitis (NEC), which is the most common gastrointestinal disease in preterm infants, and which is associated with extremely high morbidity and mortality rates. The development of NEC is thought to reflect an abnormal interaction between microorganisms and the immature intestinal epithelium, and emerging evidence has clearly placed the spotlight on an important and exciting role for TLRs, particularly TLR4, in NEC pathogenesis. In premature infants, TLR4 signaling within the small intestinal epithelium regulates apoptosis, proliferation and migration of enterocytes, affects the differentiation of goblet cells, and reduces microcirculatory perfusion, which in combination result in the development of NEC. This review will explore the signaling properties of TLRs on hematopoietic and non-hematopoietic cells, and will examine the role of TLR4 signaling in the development of NEC. In addition, the effects of dampening TLR4 signaling using synthetic and endogenous TLR4 inhibitors and active components from amniotic fluid and human milk on NEC severity will be reviewed. In so doing, we hope to present a balanced approach to the understanding of the role of TLRs in both immunity and disease pathogenesis, and to dissect the precise roles for TLR4 in both the cause and therapeutic intervention of necrotizing enterocolitis.

Mechanisms of tissue remodeling in inflammatory bowel disease

The clinical course of inflammatory bowel disease (IBD) is highly heterogeneous and often unpredictable, with multiple and serious complications that range from stricture formation to bowel obstruction or perforation, fistula formation and the need for surgery. All these problems are manifestations of tissue remodeling, a secondary but universal response to the insults of chronic inflammation. The factors involved in tissue remodeling are several, including the site and duration of inflammation, soluble molecules, the gut microbiota, and the type of mesenchymal cell response. The prototypical and most common type of tissue remodeling in IBD, and Crohn's disease (CD) in particular, is a fibrotic response, and this review will focus on the factors and mechanisms involved in fibrogenesis, and speculate on what is needed for the development of a rational treatment of intestinal fibrosis.

Intestinal stromal cells in mucosal immunity and homeostasis

A growing body of evidence suggests that non-hematopoietic stromal cells of the intestine have multiple roles in immune responses and inflammation at this mucosal site. Despite this, many still consider gut stromal cells as passive structural entities, with past research focused heavily on their roles in fibrosis, tumor progression, and wound healing, rather than their contributions to immune function. In this review, we discuss our current knowledge of stromal cells in intestinal immunity, highlighting the many immunological axes in which stromal cells have a functional role. We also consider emerging data that broaden the potential scope of their contribution to immunity in the gut and argue that these so-called "non-immune" cells are reclassified in light of their diverse contributions to intestinal innate immunity and the maintenance of mucosal homeostasis.

Red wine polyphenolics reduce the expression of inflammation markers in human colon-derived CCD-18Co myofibroblast cells: potential role of microRNA-126

Chronic intestinal inflammation is an established risk factor for colon cancer. Polyphenolic compounds from fruit and vegetables have been shown to have anti-inflammatory properties in several cell lines and tissues. However, their anti-inflammatory mechanisms, involving microRNAs in the regulation of inflammation, have not been extensively investigated. The goal of this research was to assess the chemopreventive potential of polyphenolics extracted from red wine made with Lenoir grapes (Vitis aestivalis hybrid) in human colon-derived CCD-18Co myofibroblasts cells, and to assess the potential involvement of microRNA-126 (miR-126) in the underlying mechanisms. The results show that the polyphenolic red wine extract (WE) decreased mRNA expression of lipopolysaccharide (LPS)-induced inflammatory mediators NF-kB, ICAM-1, VCAM-1, and PECAM-1 by 1.95-, 1.98-, 1.52-, and 1.84-fold respectively, in a dose dependent manner (0-100 μg of gallic acid equivalent (GAE) mL(-1)) down to 0.80-, 0.79-, 0.66-, and 0.68-fold in DMSO-treated control cells not challenged with LPS, respectively. Correspondingly, miR-126, which has a target region within the 3'-UTR of VCAM-1 mRNA, was increased 2.79-fold by the WE at 100 μg GAE mL(-1). The potential role of miR-126 was confirmed by transfecting cells with a specific miR-126-antagomir, as-miR-126. Transfection with as-miR-126 down-regulated miR-126 to 0.71-fold in the control cells and up-regulated mRNA levels of NF-kB, ICAM-1, VCAM-1, and PECAM-1 to 1.80-, 1.49-, 2.30-, and 1.95-fold of controls, respectively. WE at 100 μg GAE mL(-1) partially reversed the effects of the as-miR-126 to 1.02-, 1.01-, 1.04-, and 1.05-fold, for mRNA levels of NF-kB, ICAM-1, VCAM-1, and PECAM-1 respectively. This indicates the potential role of miR-126 in the anti-inflammatory properties of polyphenolics from red wine in CCD-18Co myofibroblasts cells.

Activation of COL1A2 promoter in human fibroblasts by Escherichia coli

The relationship between bacterial infection and collagen production was investigated using human fibroblasts transfected with the promoter of COL1A2 , which encodes the α1 chain of human type I collagen, linked to a luciferase reporter. The cells were used to assess the gene promoter activity of COL1A2 following bacterial stimulation. The COL1A2 promoter was activated by stimulation with fixed Escherichia coli in a dose-dependent manner, but not by fixed Staphylococcus aureus. Enhancement of collagen production was observed in the E. coli-stimulated fibroblasts compared to those without stimulation. Both anti-human Toll-like receptor (TLR) 4 antibody and polymyxin B clearly blocked the COL1A2 promoter activity stimulated by E. coli, while antibodies against human TLR2 and human transforming growth factor-β (TGF-β) receptor type II did not. These results indicate that E. coli can directly interact with TLR4 expressed on the surface of fibroblasts and can further induce human type I collagen gene expression and collagen production in these cells. These data also suggest that infection by gram-negative bacteria may cause fibrosis.

Lipopolysaccharide enhances transforming growth factor β1-induced platelet-derived growth factor-B expression in bile duct epithelial cells

BACKGROUND AND AIM

Platelet-derived growth factor (PDGF)-B is a potent profibrogenic mediator expressed by bile duct epithelial cells (BDECs) that contributes to liver fibrosis after bile duct ligation. However, the mechanism of PDGF-B induction in BDECs during cholestasis is not known. Transforming growth factor β (TGFβ) and lipopolysaccharide (LPS) also contribute to the profibrogenic response after bile duct ligation. We tested the hypothesis that LPS and TGFβ1 synergistically induce PDGF-B expression in BDECs.

METHODS

Transformed human BDECs (MMNK-1 cells) and primary rat BDECs were stimulated with LPS and/or TGFβ1, and signaling pathways through which LPS potentiates TGFβ1-induced PDGF-B mRNA expression were investigated.

RESULTS

Stimulation of MMNK-1 cells with LPS alone did not significantly induce PDGF-B mRNA expression. However, LPS co-treatment enhanced TGFβ1 induction of PDGF-B mRNA in MMNK-1 cells and also in primary rat BDECs. Importantly, co-treatment of MMNK-1 cells with LPS and TGFβ1 also significantly increased PDGF-BB protein expression. Interestingly, LPS did not affect TGFβ1 activation of a SMAD-dependent reporter construct. Rather, stimulation of MMNK-1 cells with LPS, but not TGFβ1, increased JNK1/2 phosphorylation. Expression of dominant negative JNK2, but not dominant negative JNK1, inhibited the LPS potentiation of TGFβ1-induced PDGF-B mRNA expression in MMNK-1 cells. In addition, LPS treatment caused IκBα degradation and activation of a nuclear factor κB (NFκB)-dependent reporter construct. Expression of an IκBα super repressor inhibited activation of NFκB and attenuated LPS potentiation of TGFβ1-induced PDGF-B mRNA.

CONCLUSIONS

The results indicate that LPS activation of NFκB and JNK2 enhances TGFβ1-induced PDGF-B expression in BDECs.