Endogenous IGF-I and alphaVbeta3 integrin ligands regulate increased smooth muscle hyperplasia in stricturing Crohn's disease

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.

Vitronectin Destroyed Intestinal Epithelial Cell Differentiation through Activation of PDE4-Mediated Ferroptosis in Inflammatory Bowel Disease

Objective

Vitronectin (VTN) has been reported to trigger cell pyroptosis to aggravate inflammation in our previous study. However, the function of VTN in inflammatory bowel disease (IBD) remains to be addressed.

Methods

Real-time PCR and western blotting were performed to analyze VTN-regulated intestinal epithelial cell (IEC) differentiation through ferroptosis, and immunofluorescence (IF), luciferase, and chromatin immunoprecipitation were used to identify whether VTN-modulated ferroptosis is dependent on phosphodiesterase 4 (PDE4)/protein kinase A (PKA)/cyclic adenosine monophosphate-response element-binding protein (CREB) cascade pathway. In vivo experiment in mice and a pilot study in patients with IBD were used to confirm inhibition of PDE4-alleviated IECs ferroptosis, leading to cell differentiation during mucosal healing.

Results

Herein, we found that caudal-related homeobox transcription factor 2-mediated IECs differentiation was impaired in response to VTN, which was attributed to enhanced ferroptosis characterized by decreased glutathione peroxidase 4 (GPX4) and solute carrier family 7 member 11 expression. Inhibition of ferroptosis in IECs rescued the inhibitory effect of VTN on cell differentiation. Further analysis showed that VTN triggered phosphorylation of PDE4, leading to inhibit PKA/CREB activation and CREB nuclear translocation, which further reduced GPX4 transactivation. Endogenous PKA interacted with CREB, and this interaction was destroyed in response to VTN stimulation. What is more, overexpression of CREB in CaCO₂ cells overcame the promotion of VTN on ferroptosis. Most importantly, inhibition of PDE4 by roflumilast or dipyridamole could alleviate dextran sulfate sodium-induced colitis in mice and in a pilot clinical study confirmed by IF.

Conclusions

These findings demonstrated that highly expressed VTN disrupted IECs differentiation through PDE4-mediated ferroptosis in IBD, suggesting targeting PDE4 could be a promising therapeutic strategy for patients with IBD.

Trickle infection with Heligmosomoides polygyrus results in decreased worm burdens but increased intestinal inflammation and scarring

Introduction

Intestinal roundworms cause chronic debilitating disease in animals, including humans. Traditional experimental models of these types of infection use a large single-dose infection. However, in natural settings, hosts are exposed to parasites on a regular basis and when mice are exposed to frequent, smaller doses of Heligmosomoides polygyrus, the parasites are cleared more quickly. Whether this more effective host response has any negative consequences for the host is not known.

Results

Using a trickle model of infection, we found that worm clearance was associated with known resistance-related host responses: increased granuloma and tuft cell numbers, increased levels of granuloma IgG and decreased intestinal transit time, as well as higher serum IgE levels. However, we found that the improved worm clearance was also associated with an inflammatory phenotype in and around the granuloma, increased smooth muscle hypertrophy/hyperplasia, and elevated levels of Adamts gene expression.

Discussion

To our knowledge, we are the first to identify the involvement of this protein family of matrix metalloproteinases (MMPs) in host responses to helminth infections. Our results highlight the delicate balance between parasite clearance and host tissue damage, which both contribute to host pathology. When continually exposed to parasitic worms, improved clearance comes at a cost.

The Pathogenesis and Clinical Management of Stricturing Crohn Disease

Stricturing of the gastrointestinal tract is a common complication in Crohn disease and is a significant cause of morbidity and mortality among this population. The inflammatory process initiates fibrosis, leading to aberrant wound healing and excess deposition of extracellular matrix proteins. Our understanding of this process has grown and encompasses cellular mechanisms, epigenetic modifications, and inherent genetic predisposition toward fibrosis. Although medications can improve inflammation, there is still no drug to attenuate scar formation. As such, management of stricturing disease requires a multidisciplinary and individualized approach including medical management, therapeutic endoscopy, and surgery. This review details the current understanding regarding the pathogenesis, detection, and management of stricturing Crohn disease.

Mechanism of fibrosis and stricture formation in Crohn's disease

Crohn's disease (CD) is a chronic inflammatory disease of the gastrointestinal tract that leads to substantial suffering for millions of patients. In some patients, the chronic inflammation leads to remodelling of the extracellular matrix and fibrosis. Fibrosis, in combination with expansion of smooth muscle layers, leaves the bowel segment narrowed and stiff resulting in strictures, which often require urgent medical intervention. Although stricture development is associated with inflammation in the affected segment, anti‐inflammatory therapies fall far short of treating strictures. At best, current therapies might allow some patients to avoid surgery in a shorter perspective and no anti‐fibrotic therapy is yet available. This likely relates to our poor understanding of the mechanism underlying stricture development. Chronic inflammation is a prerequisite, but progression to strictures involves changes in fibroblasts, myofibroblasts and smooth muscle cells in a poorly understood interplay with immune cells and environmental cues. Much of the experimental evidence available is from animal models, cell lines or non‐strictured patient tissue. Accordingly, these limitations create the basis for many previously published reviews covering the topic. Although this information has contributed to the understanding of fibrotic mechanisms in general, in the end, data must be validated in strictured tissue from patients. As stricture formation is a serious complication of CD, we endeavoured to summarize findings exclusively performed using strictured tissue from patients. Here, we give an update of the mechanism driving this serious complication in patients, and how the strictured tissue differs from adjacent unaffected tissue and controls.

Toward Molecular Imaging of Intestinal Pathology

Inflammatory bowel disease (IBD) is defined by a chronic relapsing and remitting inflammation of the gastrointestinal tract, with intestinal fibrosis being a major complication. The etiology of IBD remains unknown, but it is thought to arise from a dysregulated and excessive immune response to gut luminal microbes triggered by genetic and environmental factors. To date, IBD has no cure, and treatments are currently directed at relieving symptoms and treating inflammation. The current diagnostic of IBD relies on endoscopy, which is invasive and does not provide information on the presence of extraluminal complications and molecular aspect of the disease. Cross-sectional imaging modalities such as computed tomography enterography (CTE), magnetic resonance enterography (MRE), positron emission tomography (PET), single photon emission computed tomography (SPECT), and hybrid modalities have demonstrated high accuracy for the diagnosis of IBD and can provide both functional and morphological information when combined with the use of molecular imaging probes. This review presents the state-of-the-art imaging techniques and molecular imaging approaches in the field of IBD and points out future directions that could help improve our understanding of IBD pathological processes, along with the development of efficient treatments.

Endoplasmic Reticulum Stress in Subepithelial Myofibroblasts Increases the TGF-β1 Activity That Regulates Fibrosis in Crohn's Disease

BACKGROUND

Endoplasmic reticulum (ER) stress is an essential response of epithelial and immune cells to inflammation in Crohn's disease. The presence and mechanisms that might regulate the ER stress response in subepithelial myofibroblasts (SEMFs) and its role in the development of fibrosis in patients with Crohn's disease have not been examined.

METHODS

Subepithelial myofibroblasts were isolated from the affected ileum and normal ileum of patients with each Montreal phenotype of Crohn's disease and from normal ileum in non-Crohn's subjects. Binding of GRP78 to latent TGF-β1 and its subcellular trafficking was examined using proximity ligation-hybridization assay (PLA). The effects of XBP1 and ATF6 on TGF-β1 expression were measured using DNA-ChIP and luciferase reporter assay. Endoplasmic reticulum stress components, TGF-β1, and collagen levels were analyzed in SEMF transfected with siRNA-mediated knockdown of DNMT1 and GRP78 or with DNMT1 inhibitor 5-Azacytidine or with overexpression of miR-199a-5p.

RESULTS

In SEMF of strictured ileum from patients with B2 Crohn's disease, expression of ER stress sensors increased significantly. Tunicamycin elicited time-dependent increase in GRP78 protein levels, direct interaction with latent TGF-β1, and activated TGF-β1 signaling. The TGFB1 DNA-binding activity of ATF-6α and XBP1 were significantly increased and elicited increased TGFB1 transcription in SEMF-isolated from affected ileum. The levels of ER stress components, TGF-β1, and collagen expression in SEMF were significantly decreased following knockdown of DNMT1 or GRP78 by 5-Azacytidine treatment or overexpression of miR-199a-5p.

CONCLUSIONS

Endoplasmic reticulum stress is present in SEMF of patients susceptible to fibrostenotic Crohn's disease and can contribute to development of fibrosis. Targeting ER stress may represent a novel therapeutic target to prevent fibrosis in patients with fibrostenotic Crohn's disease.

M2 Macrophages and Phenotypic Modulation of Intestinal Smooth Muscle Cells Characterize Inflammatory Stricture Formation in Rats

The progression of Crohn disease to intestinal stricture formation is poorly controlled, and the pathogenesis is unclear, although increased smooth muscle mass is present. A previously described rat model of trinitrobenzenesulfonic acid-induced colitis is re-examined here. Although inflammation of the mid-descending colon typically resolved, a subset showed characteristic stricturing by day 16, with an inflammatory infiltrate in the neuromuscular layers including eosinophils, CD3-positive T cells, and CD68-positive macrophages. Closer study identified CD163-positive, CD206-positive, and arginase-positive cells, indicating a M2 macrophage phenotype. Stricturing involved ongoing proliferation of intestinal smooth muscle cells (ISMC) with expression of platelet-derived growth factor receptor beta and progressive loss of phenotypic markers, and stable expression of hypoxia inducible factor 1 subunit alpha. In parallel, collagen I and III showed a selective and progressive increase over time. A culture model of the stricture phenotype of ISMC showed stable hypoxia inducible factor 1 subunit alpha expression that promoted growth and improved both survival and growth in models of experimental ischemia. This phenotype was hyperproliferative to serum and platelet-derived growth factor BB, and unresponsive to transforming growth factor beta, a prominent cytokine of M2 macrophages, compared with control ISMC. We identified a hyperplastic phenotype of ISMC, uniquely adapted to an ischemic environment to drive smooth muscle layer expansion, which may reveal new targets for treating intestinal fibrosis.

Correlation between the macroscopic severity of Crohn's disease in resected intestine and bowel wall thickness evaluated by water-immersion ultrasonography

Objectives: Transabdominal ultrasonography is a common and accurate tool for managing Crohn's disease (CD); however, the significance of the resulting data is poorly understood. This study was performed to determine the association between bowel wall thickness evaluated by water-immersion ultrasonography and macroscopic severity, namely, refractory inflammation and subsequent fibrosis in CD surgical specimens.Materials and methods: We retrospectively evaluated 100 segments of colon and small intestine from 27 patients with CD. The resected specimens were placed in saline postoperatively, and bowel wall thickness was measured by water-immersion ultrasonography and compared with macroscopic findings. Correlations between bowel wall thickness and macroscopic findings were assessed using analysis of variance and receiver operating characteristic curves.Results: According to the progression of macroscopic severity, the mean bowel wall thickness was increased as follows: macroscopically intact: 4.1 mm, longitudinal ulcer scars: 5.4 mm, longitudinal open ulcers: 6.0 mm, large ulcers: 6.4 mm, cobblestone-like lesions: 7.1 mm, and fibrotic strictures: 7.4 mm. For all lesions except longitudinal ulcer scars, the bowel wall thickness was significantly thicker than that of macroscopically-intact areas (p < .001). According to receiver operating characteristic curves, bowel wall thickness >4.5 mm was associated with CD lesions, and thickness >5.5 mm was associated with more severe lesions.Conclusions: The bowel wall thickness of CD lesions was evaluated by water-immersion ultrasonography correlated with macroscopic disease severity.

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.

Epigenetic modification of intestinal smooth muscle cell phenotype during proliferation

Inflammation causes proliferation of intestinal smooth muscle cells (ISMC), contributing to a thickened intestinal wall and to stricture formation in Crohn’s disease. Proliferation of ISMC in vitro and in vivo caused decreased expression of marker proteins, but the underlying cause is unclear. Since epigenetic change is important in other systems, we used immunocytochemistry, immunoblotting, and quantitative PCR to examine epigenetic modification in cell lines from rat colon at low passage or after extended growth to evaluate phenotype. Exposure to the histone deacetylase (HDAC) inhibitor trichostatin A or the DNA methyltransferase inhibitor 5-azacytidine reversed the characteristic loss of phenotypic markers among high-passage cell lines of ISMC. Expression of smooth muscle actin and smooth muscle protein 22, as well as functional expression of the neurotrophin glial cell line-derived neurotrophic factor, was markedly increased. Increased expression of muscarinic receptor 3 and myosin light chain kinase was correlated with an upregulated response to cholinergic stimulation. In human ISMC (hISMC) lines from the terminal ileum, phenotype was similarly affected by extended proliferation. However, in hISMC from resected Crohn’s strictures, we observed a significantly reduced contractile phenotype compared with patient-matched intrinsic controls that was associated with increased patient-specific expression of DNA methyltransferase 1, HDAC2, and HDAC5. Therefore, protracted growth causes epigenetic alterations that account for an altered phenotype of ISMC. A similar process may promote stricture formation in Crohn’s disease, where the potential for halting progression, or even reversal, of disease through control of phenotypic modulation may become a novel treatment option.

Role of IGF-1R in ameliorating apoptosis of GNE deficient cells

Sialic acids (SAs) are nine carbon acidic amino sugars, found at the outermost termini of glycoconjugates performing various physiological and pathological functions. SA synthesis is regulated by UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE) that catalyzes rate limiting steps. Mutations in GNE result in rare genetic disorders, GNE myopathy and Sialuria. Recent studies indicate an alternate role of GNE in cell apoptosis and adhesion, besides SA biosynthesis. In the present study, using a HEK cell-based model for GNE myopathy, the role of Insulin-like Growth Factor Receptor (IGF-1R) as cell survival receptor protein was studied to counter the apoptotic effect of non-functional GNE. In the absence of functional GNE, IGF-1R was hyposialylated and transduced a downstream signal upon IGF-1 (IGF-1R ligand) treatment. IGF-1 induced activation of IGF-1R led to AKT (Protein Kinase B) phosphorylation that may phosphorylate BAD (BCL2 Associated Death Promoter) and its dissociation from BCL2 to prevent apoptosis. However, reduced ERK (Extracellular signal-regulated kinases) phosphorylation in GNE deficient cells after IGF-1 treatment suggests downregulation of the ERK pathway. A balance between the ERK and AKT pathways may determine the cell fate towards survival or apoptosis. Our study suggests that IGF-1R activation may rescue apoptotic cell death of GNE deficient cell lines and has potential as therapeutic target.

Intestinal fibrosis: ready to be reversed

PURPOSE OF REVIEW

Intestinal fibrosis is a common complication of several enteropathies, with inflammatory bowel disease (IBD) being the major cause. Intestinal fibrosis affects both ulcerative colitis and Crohn's disease, and no specific antifibrotic therapy exists. This review highlights recent developments in this area.

RECENT FINDINGS

The pathophysiology of intestinal stricture formation includes inflammation-dependent and inflammation-independent mechanisms. A better understanding of the mechanisms of intestinal fibrogenesis and the availability of compounds for other nonintestinal fibrotic diseases bring clincial trials in stricturing Crohn's disease within reach.

SUMMARY

Improved understanding of its mechanisms and ongoing development of clinical trial endpoints for intestinal fibrosis will allow the testing of novel antifibrotic compounds in IBD.

Smooth Muscle Hyperplasia/Hypertrophy is the Most Prominent Histological Change in Crohn's Fibrostenosing Bowel Strictures: A Semiquantitative Analysis by Using a Novel Histological Grading Scheme

BACKGROUND

The simplistically and ambiguously termed 'fibrostenosis' of bowel is a hallmark of severe Crohn's disease [CD] and a major contributor to medical treatment failure. Non-invasive imaging assessment and novel medical therapy targeting this condition are under investigation, which particularly requires a better understanding of the underlying histological basis.

METHODS

We analysed 48 patients with stricturing Crohn's ileitis or/and colitis that required surgical resection. The most representative sections of the fibrostenotic, non-stenotic and uninvolved regions were reviewed for histological analysis. For each layer of bowel wall (mucosa including muscularis mucosae [MU], submucosa [SM], muscularis propria [MP], subserosal adventitia [SS]), histological abnormalities were evaluated individually, including active and chronic inflammation, fibrosis, smooth muscle hyperplasia or hypertrophy, neuronal hypertrophy and adipocyte proliferation. A novel semiquantitative histological grading scheme was created.

RESULTS

The most significant histopathological features characterizing the stricturing intestines were smooth muscle hyperplasia of SM, hypertrophy of MP and chronic inflammation. The muscular alteration was predominant in all layers. The overall muscular hyperplasia/hypertrophy was positively correlated with chronic inflammation and negatively correlated with fibrosis, whereas SM muscular hyperplasia was also associated with MU active inflammation. Similar changes, to a lesser extent, occurred in the adjacent non-stenotic inflamed bowel as well.

CONCLUSIONS

In CD-associated 'fibrostenosis', it is the smooth muscle hyperplasia/hypertrophy that contributes most to the stricturing phenotype, whereas fibrosis is less significant. The 'inflammation-smooth muscle hyperplasia axis' may be the most important in the pathogenesis of Crohn's strictures.

Anti-TNFα alters the natural history of experimental Crohn's disease in rats when begun early, but not late, in disease

Anti-TNFα therapy decreases inflammation in Crohn's disease (CD). However, its ability to decrease fibrosis and alter the natural history of CD is not established. Anti-TNF-α prevents inflammation and fibrosis in the peptidoglycan-polysaccharide (PG-PS) model of CD. Here we studied anti-TNF-α in a treatment paradigm. PG-PS or human serum albumin (HSA; control) was injected into bowel wall of anesthetized Lewis rats at laparotomy. Mouse anti-mouse TNF-α or vehicle treatment was begun day (d)1, d7, or d14 postlaparotomy. Rats were euthanized d21-23. Gross abdominal and histologic findings were scored. Cecal levels of relevant mRNAs were measured by quantitative real-time PCR. There was a stepwise loss of responsiveness when anti-TNFα was begun on d7 and d14 compared with d1 that was seen in the percent decrease in the median gross abdominal score and histologic inflammation score in PG-PS-injected rats [as %decrease; gross abdominal score: d1 = 75% (P = 0.003), d7 = 57% (P = 0.18), d14 = no change (P = 0.99); histologic inflammation: d1 = 57% (P = 0.006), d7 = 50% (P = 0.019), d14 = no change (P = 0.99)]. This was also reflected in changes in IL-1β, IL-6, TNF-α, IGF-I, TGF-β1, procollagen I, and procollagen III mRNAs that were decreased or trended downward in PG-PS-injected animals given anti-TNF-α beginning d1 or d7 compared with vehicle-treated rats; there was no effect if anti-TNF-α was begun d14. This change in responsiveness to anti-TNFα therapy was coincident with a major shift in the cytokine milieu observed on d14 in the PG-PS injected rats (vehicle treated). Our data are consistent with the clinical observation that improved outcomes occur when anti-TNF-α therapy is initiated early in the course of CD.

Genetic and epigenetic regulation of intestinal fibrosis

Crohn's disease affects those individuals with polygenic risk factors. The identified risk loci indicate that the genetic architecture of Crohn's disease involves both innate and adaptive immunity and the response to the intestinal environment including the microbiome. Genetic risk alone, however, predicts only 25% of disease, indicating that other factors, including the intestinal environment, can shape the epigenome and also confer heritable risk to patients. Patients with Crohn's disease can have purely inflammatory disease, penetrating disease or fibrostenosis. Analysis of the genetic risk combined with epigenetic marks of Crohn's disease and other disease associated with organ fibrosis reveals common events are affecting the genes and pathways key to development of fibrosis. This review will focus on what is known about the mechanisms by which genetic and epigenetic risk factors determine development of fibrosis in Crohn's disease and contrast that with other fibrotic conditions.

Cytokine and anti-cytokine therapies in prevention or treatment of fibrosis in IBD

The frequency of fibrosing Crohn's disease (CD) is significant, with approximately 40% of CD patients with ileal disease developing clinically apparent strictures throughout their lifetime. Although strictures may be subdivided into fibrotic, inflammatory, or mixed forms, despite immunosuppressive therapy in CD patients in the form of steroids or immunomodulators, the frequency of fibrostenosing complications has still remained significant. A vast number of genetic and epigenetic variables are thought to contribute to fibrostenosing disease, including those that affect cytokine biology, and therefore highlight the complexity of disease, but also shed light on targetable pathways. Exclusively targeting fibrosis may be difficult, however, because of the relatively slow evolution of fibrosis in CD, and the potential adverse effects of inhibiting pathways involved in tissue repair and mucosal healing. Acknowledging these caveats, cytokine-targeted therapy has become the mainstay of treatment for many inflammatory conditions and is being evaluated for fibrotic disorders. The question of whether anti-cytokine therapy will prove useful for intestinal fibrosis is, therefore, acutely relevant. This review will highlight some of the current therapeutics targeting cytokines involved in fibrosis.

Insulin-Like Growth Factor-1 Contributes to Mucosal Repair by β-Arrestin2-Mediated Extracellular Signal-Related Kinase Signaling in Experimental Colitis

Insulin-like growth factor-1 (IGF-1) possesses the ability to attenuate intestinal damage and promote mucosal repair of colitis. β-Arrestins, as the scaffolding proteins of G protein-coupled receptors or non-G protein-coupled receptors signaling, can be involved in IGF-1-mediated signaling pathways. However, the interaction of IGF-1 and β-arrestin2 in the mucosal repair of experimental colitis remains unexplored. Ulcerative colitis was induced in β-arrestin2 wild-type mice and β-arrestin2 knockout littermates by using 3% dextran sulfate sodium for 5 days, followed by regular water consumption for 1, 2, 3, and 4 weeks to analyze the mucosal repair from experimental colitis. Disease activity index and histologic score analyses were performed. Apoptosis and proliferation were assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and Ki-67 staining, respectively. The expressions of β-arrestin2, phospho (p)-IGF-1R, and p-extracellular signal-regulated kinase (ERK)1/2 were examined. Furthermore, β-arrestin2 was overexpressed or altered in HCT116 cells by transfection before IGF-1 treatment in vitro. IGF-1 and β-arrestin2 expression was up-regulated in the repairing phase of experimental colitis. Targeted deletion of β-arrestin2 delayed the repair of colitis by inhibiting cell proliferation without affecting the levels of IGF-1 and p-IGF-1R. The β-arrestin2/ERK signaling pathway was involved in IGF-1-mediated mucosal repair through promoting epithelial cell and goblet cell regeneration from experimental colitis. These results indicate that IGF-1 contributes to the mucosal repair by β-arrestin2-mediated ERK signaling in experimental colitis.

High glucose regulates LN expression in human liver sinusoidal endothelial cells through ROS/integrin αvβ3 pathway

Diabetes mellitus can cause a wide variety of vascular complications and is one of the major risk factors for Non Alcoholic Fatty Liver Disease (NAFLD). The present study was designed investigate the expression of laminin (LN) in human liver sinusoidal endothelial cells (HLSECs) induced by high glucose and the role of reactive oxygen species (ROS) and integrin αvβ3 in the regulation of LN expression. HLSECs were cultured and treated with media containing 25 mM glucose in the presence or absence of N-acetylcysteine (NAC) or clone LM609. The level of intracellular ROS of HLSECs was measured with 2',7' dichloro-fluorescein diacetate (DCFH-DA) probe. Expression of integrin αvβ3 was measured using RT-PCR and Western blot. Expression of LN was testified by immunofluorescence assay. Compared with that in control group, ROS level and the expression of integrin αvβ3 and LN increased in high glucose group. Compared with that in high glucose group, antioxidant NAC inhibited the expression of integrin αvβ3, NAC and the anti-body for blocking integrin αvβ3 (clone LM609) down-regulated the expression of LN. However, the above parameters did not differ between control and mannitol groups. High glucose up-regulates expression of LN in HLSECs through ROS/integrin αvβ3 pathway.

Cellular and Molecular Mechanisms of Phenotypic Switch in Gastrointestinal Smooth Muscle

As a general rule, smooth muscle cells (SMC) are able to switch from a contractile phenotype to a less mature synthetic phenotype. This switch is accompanied by a loss of differentiation with decreased expression of contractile markers, increased proliferation as well as the synthesis and the release of several signaling molecules such as pro-inflammatory cytokines, chemotaxis-associated molecules, and growth factors. This SMC phenotypic plasticity has extensively been investigated in vascular diseases, but interest is also emerging in the field of gastroenterology. It has in fact been postulated that altered microenvironmental conditions, including the composition of microbiota, could trigger the remodeling of the enteric SMC, with phenotype changes and consequent alterations of contraction and impairment of gut motility. Several molecular actors participate in this phenotype remodeling. These include extracellular molecules such as cytokines and extracellular matrix proteins, as well as intracellular proteins, for example, transcription factors. Epigenetic control mechanisms and miRNA have also been suggested to participate. In this review key roles and actors of smooth muscle phenotypic switch, mainly in GI tissue, are described and discussed in the light of literature data available so far. J. Cell. Physiol. 231: 295-302, 2016. © 2015 Wiley Periodicals, Inc.

Pathogenic aspects and therapeutic avenues of intestinal fibrosis in Crohn's disease

In Crohn's disease, one of the two major forms of inflammatory bowel diseases in human beings, persistent and chronic inflammation promotes fibrotic processes thereby facilitating formation of strictures, the most common indication for surgical intervention in this disorder. The pathogenesis of Crohn's disease-associated fibrosis is not fully understood, but variants of genes involved in the recognition of microbial components/products [e.g. CARD15 (caspase-activating recruitment domain 15) and ATG16L1 (autophagy-related 16-like 1)] are associated with this phenotype, and experimental evidence suggests that intestinal fibrosis results from an altered balance between deposition of ECM (extracellular matrix) and degradation of ECM by proteases. Studies have also contributed to identify the main phenotypic and functional alterations of cells involved in the fibrogenic process, as well as molecules that stimulate such cells to produce elevated amounts of collagen and other ECM-related proteins. In the present review, we assess the current knowledge about cellular and molecular mediators of intestinal fibrosis and describe results of recent studies aimed at testing the preventive/therapeutic effect of compounds in experimental models of intestinal fibrosis.

Increased IGF-IEc expression and mechano-growth factor production in intestinal muscle of fibrostenotic Crohn's disease and smooth muscle hypertrophy

The igf1 gene is alternatively spliced as IGF-IEa and IGF-IEc variants in humans. In fibrostenotic Crohn's disease, the fibrogenic cytokine TGF-β1 induces IGF-IEa expression and IGF-I production in intestinal smooth muscle and results in muscle hyperplasia and collagen I production that contribute to stricture formation. Mechano-growth factor (MGF) derived from IGF-IEc induces skeletal and cardiac muscle hypertrophy following stress. We hypothesized that increased IGF-IEc expression and MGF production mediated smooth muscle hypertrophy also characteristic of fibrostenotic Crohn's disease. IGF-IEc transcripts and MGF protein were increased in muscle cells isolated from fibrostenotic intestine under regulation by endogenous TGF-β1. Erk5 and MEF2C were phosphorylated in vivo in fibrostenotic muscle; both were phosphorylated and colocalized to nucleus in response to synthetic MGF in vitro. Smooth muscle-specific protein expression of α-smooth muscle actin, γ-smooth muscle actin, and smoothelin was increased in affected intestine. Erk5 inhibition or MEF2C siRNA blocked smooth muscle-specific gene expression and hypertrophy induced by synthetic MGF. Conditioned media of cultured fibrostenotic muscle induced muscle hypertrophy that was inhibited by immunoneutralization of endogenous MGF or pro-IGF-IEc. The results indicate that TGF-β1-dependent IGF-IEc expression and MGF production in patients with fibrostenotic Crohn's disease regulates smooth muscle cell hypertrophy a critical factor that contributes to intestinal stricture formation.

Noncanonical STAT3 activation regulates excess TGF-β1 and collagen I expression in muscle of stricturing Crohn's disease

Increased TGF-β1 and TGF-β1-dependent Collagen I production in intestinal mesenchymal cells result in fibrosis in patients with Montreal B2 fibrostenotic Crohn's disease. Numerous cytokines, including IL-6, are produced by activated mesenchymal cells themselves and activate STAT3. The aim of the current study was to determine the mechanisms by which STAT-3 activation might result in intestinal fibrosis. Cytokine levels were measured by ELISA. STAT3 and suppressor of cytokine signaling 3 protein levels were measured by immunoblot, STAT3-TGFB1 DNA-binding activity by chromatin immunoprecipitation, and TGFB1 transcriptional activity by luciferase reporter assay. TGF-β1 (TGFB1), Collagen1α1, and connective tissue growth factor (CTGF) gene expression was measured by quantitative RT-PCR. The role of STAT3 activation was determined using STAT3 inhibitor, Stattic, and by transfection of STAT3 mutants. Autocrine production of cytokines was increased in muscle cells of B2 phenotype patients from strictures and normal intestine in the same patient and compared with other Crohn's phenotypes, ulcerative colitis, and non-Crohn's patients. A unique pattern of STAT3 phosphorylation emerged: high STAT3(S727) and low STAT3(Y705) in strictures and the opposite in unaffected intestine. TGFB1 transcriptional activity was regulated by phospho-STAT3(S727) and was decreased by Stattic or dominant-negative STAT3(S727A). TGF-β1, COL1A1, and CTGF expression was inhibited by Stattic or dominant-negative STAT3(S727A). Treatment of normal muscle cells with IL-6 or expression of constitutively active STAT3(S727E) phenocopied muscle cells from strictured intestine. Neutralization of autocrine IL-6 reversed STAT3 phosphorylation and normalized expression of TGF-β1 in strictured intestinal muscle. The ability of Stattic to improve development of fibrosis was confirmed in mice with 2,4,6-trinitrobenzenesulfonic acid-induced colitis. We observed a unique phospho-STAT3(S727) response in patients with Montreal B2 Crohn's disease, particularly in response to IL-6 leading to increased TGF-β1, collagen, and CTGF production in ileal strictures.

Intestinal smooth muscle phenotype determines enteric neuronal survival via GDNF expression

Intestinal inflammation causes initial axonal degeneration and neuronal death, as well as the proliferation of intestinal smooth muscle cells (ISMC), but subsequent axonal outgrowth leads to re-innervation. We recently showed that expression of glial cell-derived neurotrophic factor (GDNF), the critical neurotrophin for the post-natal enteric nervous system (ENS) is upregulated in ISMC by inflammatory cytokines, leading us to explore the relationship between ISMC growth and GDNF expression. In co-cultures of myenteric neurons and ISMC, GDNF or fetal calf serum (FCS) was equally effective in supporting neuronal survival, with neurons forming extensive axonal networks among the ISMC. However, only GDNF was effective in low-density cultures where neurons lacked contact with ISMC. In early-passage cultures of colonic circular smooth muscle cells (CSMC), polymerase chain reaction (PCR) and western blotting showed that proliferation was associated with expression of GDNF, and the successful survival of neonatal neurons co-cultured on CSMC was blocked by vandetanib or siGDNF. In tri-nitrobenzene sulfonic acid (TNBS)-induced colitis, immunocytochemistry showed the selective expression of GDNF in proliferating CSMC, suggesting that smooth muscle proliferation supports the ENS in vivo as well as in vitro. However, high-passage CSMC expressed significantly less GDNF and failed to support neuronal survival, while expressing reduced amounts of smooth muscle marker proteins. We conclude that in the inflamed intestine, smooth muscle proliferation supports the ENS, and thus its own re-innervation, by expression of GDNF. In chronic inflammation, a compromised smooth muscle phenotype may lead to progressive neural damage. Intestinal stricture formation in human disease, such as inflammatory bowel disease (IBD), may be an endpoint of failure of this homeostatic mechanism.

Contribution of intestinal smooth muscle to Crohn's disease fibrogenesis

Mesenchymal cells transdifferentiation and extracellular matrix deposition are involved in the fibrotic process of Crohn's disease (CD). Mesenchymal smooth muscle cells (SMCs) de-differentiation, driven by Platelet-derived growth factor (PDGF) that counteracts Transforming growth factor (TGF-β) has been studied in vascular muscle. The role of SMCs in intestinal fibrogenesis is still not clearly elucidated. Aim of the study was to evaluate the possible myogenic contribution to CD fibrotic process through the comparative analysis of histological, morphometric and molecular alterations occurring in human smooth muscle. Full thickness specimens were obtained from CD (non-involved and stenotic tracts) and healthy (control) ileum. Tissues were processed for histological and immunohistochemical (IHC) analyses and SMCs were isolated from the muscularis propria for morphofunctional and molecular (qPCR) analyses. CD stenotic ileum showed a significant increased thickness of all layers compared to CD non-involved and control ileum. IHC revealed an overexpression of α-smooth muscle actin and collagens I-III throughout all intestinal layers only in stenotic tracts. The two growth factors, PDGF and TGF-β, showed a progressive increase in expression in the muscle layer from CD non-involved to stenotic tracts. Freshly isolated SMCs presented alterations in CD non-involved tracts that progressively increased in the stenotic tracts consisting in a statistical increase in mRNA encoding for PDGF-β and collagen III, paralleled to a decrease in TGF-β and Tribbles-like protein-3 mRNA, and altered morphofunctional parameters consisting in progressive decreases in cell length and contraction to acetylcholine. These findings indicate that intrinsic myogenic alterations occur in CD ileum, that they likely precede stricture formation, and might represent suitable new targets for anti-fibrotic interventions.

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.

Inflammatory cytokines promote growth of intestinal smooth muscle cells by induced expression of PDGF-Rβ

Thickening of the inflamed intestinal wall involves growth of smooth muscle cells (SMC), which contributes to stricture formation. Earlier, the growth factor platelet-derived growth factor (PDGF)-BB was identified as a key mitogen for SMC from the rat colon (CSMC), and CSMC growth in colitis was associated with both appearance of its receptor, PDGF-Rβ and modulation of phenotype. Here, we examined the role of inflammatory cytokines in inducing and modulating the growth response to PDGF-BB. CSMC were enzymatically isolated from Sprague–Dawley rats, and the effect of tumour necrosis factor (TNF)-α, interleukin (IL)-1β, transforming growth factor (TGF), IL-17A and IL-2 on CSMC growth and responsiveness to PDGF-BB were assessed using proliferation assays, PCR and western blotting. Conditioned medium (CM) was obtained at 48 hrs of trinitrobenzene sulphonic acid-induced colitis. Neither CM alone nor cytokines caused proliferation of early-passage CSMC. However, CM from inflamed, but not control colon significantly promoted the effect of PDGF-BB. IL-1β, TNF-α and IL-17A, but not other cytokines, increased the effect of PDGF-BB because of up-regulation of mRNA and protein for PDGF-Rβ without change in receptor phosphorylation. PDGF-BB was identified in adult rat serum (RS) and RS-induced CSMC proliferation was inhibited by imatinib, suggesting that blood-derived PDGF-BB is a local mitogen in vivo. In freshly isolated CSMC, CM from the inflamed colon as well as IL-1β and TNF-α induced the early expression of PDGF-Rβ, while imatinib blocked subsequent RS-induced cell proliferation. Thus, pro-inflammatory cytokines both initiate and maintain a growth response in CSMC via PDGF-Rβ and serum-derived PDGF-BB, and control of PDGF-Rβ expression may be beneficial in chronic intestinal inflammation.

Serum concentrations of insulin-like growth factor-binding protein 5 in Crohn’s disease

AIM: To investigate serum insulin-like growth factor-binding protein 5 (IGFBP-5) levels and intestinal IGFBP-5 expression in patients with Crohn’s disease (CD).

METHODS: We analyzed the serum concentrations and intestinal expression of IGFBP-5 in 42 patients with CD, of whom 26 had endoscopically or radiologically proven stricture formation. Nine of the 42 patients had active disease, with a Crohn’s disease activity index > 150. Serum IGFBP-5 levels were analyzed in 20 healthy controls matched by sex and age to the CD patients. Serum IGFBP-5 was measured using an enzyme-linked immunosorbent assay. Intestinal tissue was obtained from patients through endoscopic biopsies. IGFBP-5 expression was detected using immunohistochemistry and was scored semiquantitatively.

RESULTS: The median serum IGFBP-5 concentrations of CD patients were significantly lower compared with healthy controls [median 7.2 (IQR: 5.5-11.3) ng/mL vs 11.3 (8.0-44.6) ng/mL, P < 0.001]. There was no significant difference between median serum IGFBP-5 levels in CD patients with or without stricture formation [6.9 (5.5-11.3) ng/mL vs 7.8 (5.3-10.1) ng/mL, P = 0.815]. The serum IGFBP-5 levels were not significantly different between patients with active disease and inactive disease [7.2 (6.5-7.6) ng/mL vs 7.2 (5.5-11.3) ng/mL, P = 0.890]. However, a significant correlation was observed between serum IGFBP-5 levels and platelet count (PLT) (r = 0.319, P = 0.0395). No significant correlation was found between tissue IGFBP-5 immunohistochemical staining intensity scores and serum IGFBP-5 levels. No significant difference was found when comparing the serum IGFBP-5 levels among the patients with different tissue IGFBP-5 staining scores (absent/very weak, weak, moderate or strong). There was a significant correlation between tissue IGFBP-5 staining scores and white blood cell count (r = 0.391, P = 0.01) and PLT (r = 0.356, P = 0.021).

CONCLUSION: Our results indicate that serum IGFBP-5 concentrations were lower in CD patients compared to healthy controls regardless of disease activity or the presence of stricture formation.

Increased activation of latent TGF-β1 by αVβ3 in human Crohn's disease and fibrosis in TNBS colitis can be prevented by cilengitide

BACKGROUND

Strictures develop in >30% of patients affected with Crohn's disease. No available medication prevents stricture development in susceptible patients. In Crohn's strictures, but not adjacent normal intestine, TGF-β1 increases in muscularis smooth muscle, increasing collagen I production and strictures. Muscle cells express αVβ3 integrin containing an Arg-Gly-Asp (RGD) binding domain. The aim was to determine whether increased TGF-β1 levels in strictures were the result of latent TGF-β1, which contains an RGD sequence, binding to and activation by αVβ3; and whether cilengitide, which is an RGD-containing αVβ3 integrin inhibitor, decreases TGF-β1 activation and development of fibrosis in chronic 2,4,6 trinitrobenzene sulfonic acid (TNBS)-induced colitis.

DESIGN

Muscle cells isolated from Crohn's disease strictures and normal resection margin and from the colon of rats after 42 days of chronic TNBS-induced colitis were used to prepare RNA and protein lysates and to initiate primary cultures. The mechanisms leading to increased TGF-β1 activation, collagen I production, and fibrosis were examined in human muscle and in rats. Human cultured cells in vitro and rats in vivo were treated with cilengitide to determines it efficacy to decrease TGF-β1-activation, collagen production, and decrease the development of fibrosis.

RESULTS

Latent TGF-β1 is activated by the αVβ3 RGD domain in human and rat intestinal smooth muscles. Increased activation of TGF-β1 in Crohn's disease and in TNBS-induced colitis causes increased collagen production, and fibrosis that could be inhibited by cilengitide.

CONCLUSIONS

Cilengitide, an αVβ3 integrin RGD inhibitor, could be a novel treatment to diminish excess TGF-β1 activation, collagen I production, and development of fibrosis in Crohn's disease.

Human conditions of insulin-like growth factor-I (IGF-I) deficiency

Insulin-like growth factor I (IGF-I) is a polypeptide hormone produced mainly by the liver in response to the endocrine GH stimulus, but it is also secreted by multiple tissues for autocrine/paracrine purposes. IGF-I is partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions). IGF-I is a closely regulated hormone. Consequently, its logical therapeutical applications seems to be limited to restore physiological circulating levels in order to recover the clinical consequences of IGF-I deficiency, conditions where, despite continuous discrepancies, IGF-I treatment has never been related to oncogenesis. Currently the best characterized conditions of IGF-I deficiency are Laron Syndrome, in children; liver cirrhosis, in adults; aging including age-related-cardiovascular and neurological diseases; and more recently, intrauterine growth restriction. The aim of this review is to summarize the increasing list of roles of IGF-I, both in physiological and pathological conditions, underlying that its potential therapeutical options seem to be limited to those proven states of local or systemic IGF-I deficiency as a replacement treatment, rather than increasing its level upper the normal range.

Mechanisms of smooth muscle responses to inflammation

BACKGROUND

Inflammation-induced changes in smooth muscle may be the consequence of changes in the properties of smooth muscle itself, in the control by nerves and hormones, in the microenvironment, or in the balance of constitutive or induced mediators. A general concept is that the specific characteristics and effects of inflammation can be linked to the nature of the infiltrate and the associated mediators, which are dictated predominantly by the immune environment. Inflammatory mediators may regulate smooth muscle function by directly acting on smooth muscle cells or, indirectly, through stimulation of the release of mediators from other cells. In addition, smooth muscle is not a passive bystander during inflammation and our knowledge of molecular signaling pathways that control smooth muscle function, and the contribution of the immune mechanisms to smooth muscle homeostasis, has expanded greatly in the last decade. Recent studies also demonstrated the relevance of extracellular proteases, of endogenous or exogenous origin, redox imbalance, or epigenetic mechanisms, to gastrointestinal dismotility and inflammation in the context of functional and organic disorders.

PURPOSE

In this review we discuss the various types of inflammation and the established and emerging mechansims of inflammation-induced changes in smooth muscle morphology and function.

Insulin-like growth factors in the gastrointestinal tract and liver

The liver is a major source of insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) that are present in the circulation and have important endocrine activities relating to energy metabolism, body size, carcinogenesis, and various organ-specific functions. Although IGFs have only minor effects on the normal liver itself, production of IGFs and IGFBPs in a tissue-specific manner in the gastrointestinal tract exert important regulatory effects on cellular proliferation, survival, and apoptosis. IGFs and IGFBPs play important regulatory roles in the response of both the liver and the gastrointestinal tract to inflammation and in the development of neoplasia.

High glucose down-regulates the expression of endogenous insulin-like growth factor-1 in rat colonic smooth muscle cells

AIM: To investigate the effect of high glucose on the expression of endogenous insulin-like growth factor-1 (IGF-1) in rat colonic smooth muscle cells (SMCs).

METHODS: Rat colonic SMCs were separated, cultured, identified by immunofluorescence staining of α-actin, and divided into three groups: normal glucose group (5.5 mmol/L glucose), mannitol control group (5.5 mmol/L glucose plus 19.5 mmol/L mannitol) and high glucose group (25 mmol/L glucose). After treatment, cell proliferation was determined using Cell Counting Kit-8, and cell cycle analysis was performed by flow cytometry. ELISA was designed to measure the content of IGF-I in SMCs culture supernatants. Real-time quantitative-PCR and Western blotting were performed to analyze the mRNA and protein expression of IGF-1 in SMCs.

RESULTS: Compared to the normal glucose group, treatment with high glucose significantly inhibited the proliferation of rat colonic SMCs (0.494 ± 0.0030 vs 0.597 ± 0.044, P < 0.05), resulted in cell accumulation in the G₁ phase (90.850% ± 0.706% vs 55.202% ± 3.807%, P < 0.05) and a significant decrease in the percentage of cells in the S phase (3.622% ± 0.156% vs 30.780% ± 3.808%, P < 0.05), and decreased the content of IGF-I in SMCs culture supernatants (208.000 ng/L ± 31.443 ng/L vs 265.750 ng/L ± 26.538 ng/L, P < 0.05) and the expression of IGF-I mRNA and protein (2.037 ± 0.196 vs 2.257 ± 0.273; 0.247 ± 0.045 vs 0.906 ± 0.103, both P < 0.05). However, there were no significant differences in the above parameters between the normal glucose group and mannitol control group.

CONCLUSION: High glucose inhibits the proliferation of rat colonic SMCs and decreases the expression of endogenous IGF-1 in SMCs.

Clinical significance of peripheral blood levels of insulin-like growth factor in patients with Crohn's disease

AIM: To analyze the clinical significance of peripheral blood levels of insulin-like growth factor (IGF) in patients with Crohn's disease (CD).

METHODS: Fifty-four patients with CD were collected and divided into mild, moderate, and severe groups according to the severity of the disease. Enzyme-labeled chemiluminescent immunometric assay was used to detect peripheral blood levels of IGF-I and insulin-like growth factor-binding protein 3 (IGFBP3) in patients before and after standard treatment to assess their association with the severity of CD and therapeutic efficacy. Fifty healthy people were enrolled as controls.

RESULTS: The levels of IGF-I and IGFBP3 were significantly lower in the moderate and severe groups than in the control group (all P < 0.05) and decreased with the increase in clinical severity (P < 0.05). No significant difference was noted in the levels of IGF-I and IGFBP3 between the mild group and control group. However, the levels of IGF-I and IGFBP3 were significantly higher in patients with moderate or severe CD after treatment than before treatment (all P < 0.05). No significant difference was noted in the levels of IGF-I and IGFBP3 in patients with mild CD between before and after treatment.

CONCLUSION: Peripheral blood levels of IGF-I and IGFBP3 are useful to evaluate disease severity and therapeutic efficacy in patients with CD.

Generalized neuromuscular hypoplasia, reduced smooth muscle myosin and altered gut motility in the klotho model of premature aging

BACKGROUND

  Gastrointestinal symptoms, particularly constipation, increase with aging, but their underlying mechanisms are poorly understood due to lack of experimental models. Previously we established the progeric klotho mouse as a model of aging-associated anorexia and gastric dysmotility. We also detected reduced fecal output in these animals; therefore, the aim of this study was to investigate in vivo function and cellular make-up of the small intestinal and colonic neuromuscular apparatus.

METHODS

Klotho expression was studied by RT-PCR and immunohistochemistry. Motility was assessed by dye transit and bead expulsion. Smooth muscle and neuron-specific gene expression was studied by Western immunoblotting. Interstitial cells of Cajal (ICC) and precursors were analyzed by flow cytometry, confocal microscopy, and three-dimensional reconstruction. HuC/D(+) myenteric neurons were enumerated by fluorescent microscopy.

KEY RESULTS

Klotho protein was detected in neurons, smooth muscle cells, and some ICC classes. Small intestinal transit was slower but whole-gut transit of klotho mice was accelerated due to faster colonic transit and shorter intestinal lengths, apparent only after weaning. Fecal water content remained normal despite reduced output. Smooth muscle myosin expression was reduced. ICC, ICC precursors, as well as nitrergic and cholinergic neurons maintained their normal proportions in the shorter intestines.

CONCLUSIONS & INFERENCES

Progeric klotho mice express less contractile proteins and develop generalized intestinal neuromuscular hypoplasia mainly arising from stunted postweaning growth. As reduced fecal output in these mice occurs in the presence of accelerated colonic and whole-gut transit, it likely reflects reduced food intake rather than intestinal dysmotility.

Amelioration of excess collagen IαI, fibrosis, and smooth muscle growth in TNBS-induced colitis in IGF-I(+/-) mice

BACKGROUND

Strictures occur in ≈ 30% of patients with Crohn's disease (CD) and are characterized by intestinal smooth muscle hyperplasia, hypertrophy, and fibrosis due to excess extracellular matrix production including collagen. Insulin-like growth factor-I (IGF-I) expression is increased in smooth muscle cells of the muscularis propria in CD and in animal models of CD, including trinitrobenzene sulfonic acid (TNBS)-induced colitis. While upregulated IGF-I is conjectured to cause smooth muscle cell growth and collagen production in the inflamed intestine, its role in the development of fibrosis has not been directly demonstrated.

METHODS

Colitis was induced in IGF-I(+/-) or wildtype C57BL/6J mice by rectal administration of TNBS or ethanol vehicle. After 7 days, colonic smooth muscle cells were isolated and used to prepare RNA or protein lysates. Transcript levels of IGF-IEa, IGF binding protein (IGFBP)-3, IGFBP-5, TGF-β1, and collagen IαI were measured by quantitative reverse-transcription polymerase chain reaction (RT-PCR). Corresponding protein levels were measured by Western blot or enzyme-linked immunosorbent assay (ELISA). Fibrosis was measured using digital image analysis of Masson's trichrome-stained histologic sections.

RESULTS

In IGF-I(+/-) mice, which express significantly lower levels of IGF-I than wildtype, the response to TNBS-induced colitis: upregulation of IGF-I, IGFBP-3, IGFBP-5 muscle growth, and collagen IαI expression, the resulting collagen deposition, and fibrosis are all significantly diminished compared to C57BL/6J wildtype controls. TGF-β1 expression and its increase following TNBS administration are not altered in IGF-I(+/-) mice compared to wildtype.

CONCLUSIONS

The findings indicate that IGF-I is a key regulator in intestinal smooth muscle hyperplasia and excess collagen production that leads to fibrosis and long term to stricture formation.

Endogenous IGFBP-3 regulates excess collagen expression in intestinal smooth muscle cells of Crohn's disease strictures

BACKGROUND

Stricture formation occurs in ≈30% of patients with Crohn's disease (CD) and is a significant cause of morbidity. Strictures are characterized by intestinal smooth muscle cell hyperplasia, smooth muscle cell hypertrophy, and fibrosis due to excess net extracellular matrix production, including collagen. Transforming growth factor-β1 (TGF-β1) has profibrotic effects in many tissues due to its ability to regulate collagen expression and extracellular matrix dynamics. We previously showed that both insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) and TGF-β1 are expressed by normal human intestinal smooth muscle cells, bind to, and activate TGF-βRII/I receptors in these cells.

METHODS

Smooth muscle cells isolated from the muscularis propria of patients were used to prepare RNA, protein lysates, or placed into primary culture. IGFBP-3, TGF-β1, and collagen IαI expression was measured with quantitative reverse-transcription polymerase chain reaction (RT-PCR) and protein levels by enzyme-linked immunosorbent assay (ELISA) or immunoblot.

RESULTS

Expression and production of IGFBP-3, TGF-β1, and collagen IαI were significantly increased specifically in smooth muscle cells isolated from regions of strictured intestine in CD compared to nonstrictured histologically normal resection margin. IGFBP-3 and TGF-β1 regulated collagen IαI expression and production via a TGF-βRII/I-dependent and Smad2/3-dependent mechanism. Upregulated (excess) collagen IαI expression and production in smooth muscle cells of strictures and basal collagen IαI in smooth muscle cells of normal margin were inhibited by immunoneutralization of IGFBP-3 or TGF-β1.

CONCLUSIONS

The findings indicate that upregulated endogenous IGFBP-3 and TGF-β1 expression regulates excess collagen IαI production and contributes to fibrosis and stricture formation in CD.