Mouse strain influences angiogenic response to dextran sodium sulfate–induced colitis

A murine colitis model developed using a combination of dextran sulfate sodium and Citrobacter rodentium

Adult mice were treated with dextran sulfate sodium (DSS) and infected with Citrobacter rodentium for developing a novel murine colitis model. C57BL/6N mice (7-week-old) were divided into four groups. Each group composed of control, dextran sodium sulfate-treated (DSS), C. rodentium-infected (CT), and DSS-treated and C. rodentium-infected (DSS-CT) mice. The DSS group was administered 1% DSS in drinking water for 7 days. The CT group was supplied with normal drinking water for 7 days and subsequently infected with C. rodentium via oral gavage. The DSS-CT group was supplied with 1% DSS in drinking water for 7 days and subsequently infected with C. rodentium via oral gavage. The mice were sacrificed 10 days after the induction of C. rodentium infection. The DSS-CT group displayed significantly shorter colon length, higher spleen to body weight ratio, and higher histopathological score compared to the other three groups. The mRNA expression levels of tumor necrosis factor (TNF)-α and interferon (INF)-γ were significantly upregulated; however, those of interleukin (IL)-6 and IL-10 were significantly downregulated in the DSS-CT group than in the control group. These results demonstrated that a combination of low DSS concentration (1%) and C. rodentium infection could effectively induce inflammatory bowel disease (IBD) in mice. This may potentially be used as a novel IBD model, in which colitis is induced in mice by the combination of a chemical and a pathogen.

Lack of Adrenomedullin Aggravates Acute TNBS-Induced Colitis Symptoms in Mice, Especially in Females

Adrenomedullin (AM) is a biologically active peptide which has been tested as a new therapy for inflammatory bowel disease (IBD) in animal models and in patients with severe ulcerative colitis. We used an inducible knockout (KO) mouse model for AM to evaluate the effects of endogenous levels of this peptide on the development and degree of pathogenesis of IBD. Acute colitis was induced in mice of both sexes by rectal instillation of 3 mg 2,4,6-trinitrobenzenesulfonic acid (TNBS) in 100 μL of 50% ethanol. Control mice received the same volume of saline in 50% ethanol. During the following 5 days, the weight and the disease severity index of all animals were recorded. After sacrifice, the inflammatory response was macroscopically assessed by analyzing the weight of the colon; by histomorphometrical analysis on histological sections; and by qRT-PCR determination of different inflammatory, adhesion, and regeneration molecules. TNBS administration caused a significantly more severe colitis in KO mice, and especially in females, when compared to wild type (WT) animals. Abrogation of the AM gene caused more severe diarrhea, accompanied by rectal bleeding, anorexia, and a significant increase of colon weight. Histological analysis of TNBS-treated KO mice showed large areas of lymphocyte infiltrates in the mucosa and submucosa, with loss of tissue architecture. No alterations were observed in the expression levels of inflammatory cytokines at the time of sacrifice; meanwhile lack of AM resulted in lower levels of some adhesion molecules and regeneration markers. Taken together, these results support the protective role of endogenous AM against the development of acute colitis, and that its effects are particularly beneficial on females.

Splenic dendritic cell involvement in FXR-mediated amelioration of DSS colitis

Inflammatory Bowel Disease (IBD) is a multifactorial disorder involving dysregulation of the immune response and bacterial translocation through the intestinal mucosal barrier. Previously, we have shown that activation of the bile acid sensor Farnesoid X Receptor (FXR), which belongs to the family of nuclear receptors, improves experimental intestinal inflammation, decreasing expression of pro-inflammatory cytokines and protecting the intestinal barrier. Here, we aimed to investigate the immunological mechanisms that ameliorate colitis when FXR is activated. We analyzed by FACS immune cell populations in mesenteric lymph nodes (MLN) and in the spleen to understand whether FXR activation alters the systemic immune response. We show that FXR activation by obeticholic acid (OCA) has systemic anti-inflammatory effects that include increased levels of plasma IL-10, inhibition of both DSS-colitis associated decrease in splenic dendritic cells (DCs) and increase in Tregs. Impact of OCA on DC relative abundance was seen in spleen but not MLN, possibly related to the increased FXR expression in splenic DCs compared to MLN DCs. Moreover, FXR activation modulates the chemotactic environment in the colonic site of inflammation, as Madcam1 expression is decreased, while Ccl25 is upregulated. Together, our data suggest that OCA treatment elicits an anti-inflammatory immune status including retention of DCs in the spleen, which is associated with decreased colonic inflammation. Pharmacological FXR activation is therefore an attractive new drug target for treatment of IBD.

Interferon Gamma Counteracts the Angiogenic Switch and Induces Vascular Permeability in Dextran Sulfate Sodium Colitis in Mice

BACKGROUND

Interferon (IFN)-γ is a central pathogenesis factor in inflammatory bowel disease (IBD) with pleiotropic effects on many different cell types. However, as yet, the immune modulatory functions of IFN-γ in IBD have been predominantly investigated. Based on previous studies showing that IFN-γ acts antiangiogenic in colorectal carcinoma, we investigated the effects of IFN-γ on the vascular system in IBD.

METHODS

Colon tissues of patients with IBD and dextran sulfate sodium-induced colitis in mice were subjected to immunohistochemistry, quantitative real-time polymerase chain reactions, and in situ hybridization to quantify cell activation, angiogenesis, and immune responses. Vascular structure and permeability in mice were analyzed by ultramicroscopy and in vivo confocal laser endomicroscopy.

RESULTS

We showed a significantly increased blood vessel density in IBD and dextran sulfate sodium colitis. In mice, this was associated with a disorganized blood vessel structure and profound vascular leakage. As compared with genes associated with angiogenesis, genes associated with inflammatory cell activation including IFN-γ were more strongly upregulated in colitis tissues. IFN-γ exerted direct effects on endothelial cells in IBD tissues in vivo, as indicated by the expression of IFN-γ-induced guanylate binding protein 1 (GBP-1). Neutralization of IFN-γ in the acute dextran sulfate sodium colitis model demonstrated that this cytokine exerts endogenous angiostatic activity in IBD and contributes to increased vascular permeability.

CONCLUSIONS

The dissection of the pleiotropic activities of IFN-γ in IBD provides new insights to the pathological functions of this cytokine and may be of high relevance for the optimization of combination therapy approaches.

Chloride intracellular channel 4 is required for maturation of the cerebral collateral circulation

The number and diameter of native collaterals in tissues of healthy mice vary widely, resulting in large differences in tissue injury in occlusive diseases. Recent studies suggest similar variation may exist in humans. Collateral variation in mice is determined by genetic background-dependent differences in embryonic collateral formation, by variation in maturation of the nascent collaterals, and by environmental factors such as aging that cause collateral rarefaction in the adult. Recently, formation of the collateral circulation in the brain was found to involve a unique VEGF-A-dependent "arteriolar" angiogenic sprouting-like mechanism. Elsewhere, chloride intracellular protein 4 (CLIC4) was implicated but not investigated directly, prompting the present study. Deletion of Clic4 had no effect on embryonic collaterogenesis. However, during collateral maturation from embryonic day 18.5 to postnatal day 7, reduced mural cell investment was observed and excessive pruning of collaterals occurred. Growth in collateral diameter was reduced. This resulted in 50% fewer collaterals of smaller diameter in the adult and thus larger infarct volume after middle cerebral artery occlusion. During collateral maturation, CLIC4 deficiency resulted in reduced expression of Vegfr2, Vegfr1, Vegfc, and mural cell markers, but not notch-pathway genes. Overexpression of VEGF-A in Clic4(-/-) mice had no effect on collaterogenesis, but rescued the above defects in collateral maturation by preventing mural cell loss and collateral pruning, thus restoring collateral number and diameter and reducing stroke severity in the adult. CLIC4 is not required for collaterogenesis but is essential for perinatal maturation of nascent collaterals through a mechanism that supports VEGF signaling.