Benjamin Bertin

Obesity, visceral fat and Crohn's disease.

Purpose of reviewIncreasing evidence indicates that adipose tissue is an active endocrine organ involved in metabolic syndrome and regulation of inflammation. Visceral fat accumulation is a hallmark of both obesity and Crohns disease. Here, we present recent data describing the immune properties of intra-abdominal adipose tissue that could link the innate immune response to obesity-related disorders and gut inflammation. Recent findingsInnate immune properties of adipocytes have become well characterized since recent studies described the Toll-like receptor (TLR) expression repertoire and specific TLR ligand responses of adipocytes. Adipokine secretion profiles have also been elucidated both in obese patients, when they may be involved in obesity-associated metabolic disease, and in Crohns disease. Whereas mesenteric fat hypertrophy and fat wrapping of the bowel are characteristic of Crohns disease, there exists a paucity of information concerning this important pathophysiological aspect. Our current classical animal models are of limited interest when investigating the role of mesenteric fat in gut inflammation. Recent new alternative disease paradigms could help to design more specific models for elucidating chronic transmural inflammation of the gut. SummaryObesity and Crohns disease share common features with the development of mesenteric fat that may be involved in gut inflammation. Further studies are required to clearly assess the origin and influence of intestinal fat deposits upon gut inflammation, notably during Crohns disease development.

Visceral fat and gut inflammation.

The etiology of inflammatory bowel disease and, in particular, Crohns disease involves a deregulated mucosal immune system under the influence of intestinal flora and environmental factors in genetically susceptible individuals. A new hypothesis has focused on mesenteric fat hypertrophy and the presence of ectopic fat surrounding inflamed bowel, the so-called creeping fat, which are hallmarks of Crohns disease. Mesenteric adipose tissue is currently recognized as an active actor in immunity with a capacity for mediator secretion. These mediators include classic pro- and anti-inflammatory cytokines or chemokines and hormone-like adipokines with multiple effects. Mesenteric fat participates in the course of Crohns disease and may play an active role in the regulation of intestinal inflammation. However, little is known about the origin and role of mesenteric fat in Crohns disease, essentially because of a lack of experimental models that develop creeping fat. The purpose of this review is to present the recent data describing the immune properties of mesenteric fat and the recent advances in animal models, which have suggested a new hypothesis about the role of creeping fat in Crohns disease.

PPAR-gamma in ulcerative colitis: a novel target for intervention.

Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor, originally described in adipose tissue, that controls the expression of a large number of regulatory genes in lipid metabolism and insulin sensitization. Well known by endocrinologists, thiazolidinediones (TZDs) are classical PPARγ synthetic agonists which were currently used as insulin-sensitizing agents in the treatment of type 2 diabetes. While the clinical benefits of TZDs in treating metabolic disorders have been clearly demonstrated, new studies performed in animal models of colitis and in patients with ulcerative colitis have also revealed the key roles of PPARγ activation in the regulation of inflammation and immune response, notably in the colon through epithelial cells. During inflammation, PPAR acts directly to negatively regulate gene expression of proinflammatory genes in a ligand-dependent manner by antagonizing the activities of other transcription factors such as members of the NF-κB and AP-1 families. A major mechanism that underlies the ability of PPARs to interfere with the activities of these transcription factors has been termed transrepression. PPARγ acts by inhibiting signaldependent transcription factors that mediate inflammatory programs of gene activation. However, due to safety issues concerning particularly the greater risk of myocardial infarction, use of TZDs has been severely limited for the treatment of type 2 diabetes and/or inflammatory diseases, justifying the development of a new family of PPARγ agonists with major transrepressive effects and without toxicity. By the demonstration that the anti-inflammatory effects of 5- aminosalicylic acid (5-ASA) in patients with ulcerative colitis were mediated by PPARγ activation, several molecules having 5-ASA similarities have been developed and screened leading to the selection of a aminophenyl-alpha-methoxypropionic acids named GED-0507-34-Levo (GED). This compound activating PPARγ has 100-to 150-fold higher anti-inflammatory activity than 5-ASA. This new PPAR modulator is giving promising results both in vitro and in vivo, without toxicity and is currently evaluated in a phase 2 clinical trial. The aim of this review is to present and discuss the evidence suggesting that PPARγ targeting is of therapeutic interest in the treatment of UC.

Switching invariant natural killer T (iNKT) cell response from anticancerous to anti-inflammatory effect: molecular bases.

Since the discovery in 1995 of α-galactosylceramide 1 (α-GalCer), also known as KRN7000,1 hundreds of compounds have been synthesized in order to activate invariant natural killer T (iNKT) cells. Such keen interest for this lymphocyte cell type is due to its ability to produce different cytokines that bias the immune response toward a Th1 or Th2 profile. Thus, an understanding of the immune polarization mechanism via iNKT activation may pave the way toward new therapeutics in various domains including cancer and infectious and autoimmune diseases. In this review, we propose an up-to-date analysis of iNKT activators associated with a structure-activity relationship (SAR) study aimed at complementing available reviews by highlighting molecular bases for a selective immune response.

Novel PPARγ Modulator GED-0507-34 Levo Ameliorates Inflammation-driven Intestinal Fibrosis.

Background:Intestinal fibrosis is mainly associated with Crohns disease and is defined as a progressive and excessive deposition of extracellular matrix components. No specific antifibrotic therapies are available. In this study, we evaluate the antifibrotic effect of a novel 5-ASA analog able to activate the peroxisome proliferator-activated receptor &ggr;, named GED-0507-34 Levo. Methods:Colonic fibrosis was induced in 110 C57BL/6 mice by 3 cycles of 2.5% (wt/vol) dextran sulfate sodium administration for 6 weeks. The preventive effects of oral daily GED (30 mg·kg−1·d−1) administration were evaluated using a macroscopic and histological score and also through biological endpoints. Expression of main markers of myofibroblasts activation was determined in transforming growth factor (TGF-&bgr;)–stimulated intestinal fibroblasts and epithelial cells. Results:GED improved macroscopic and microscopic intestinal lesions in dextran sulfate sodium-treated animals and reduced the profibrotic gene expression of Acta2, COL1a1, and Fn1 by 1.48-folds (P < 0.05), 1.93-folds (P < 0.005), and 1.03-fold (P < 0.05), respectively. It reduced protein levels of main markers of fibrosis (&agr;-SMA and Collagen I-II) and the main TGF-&bgr;/Smad pathway components. GED also decreased the interleukin-13 and connective tissue growth factor expression by 1.89-folds (P < 0.05) and 2.2-folds (P < 0.005), respectively. GED inhibited TGF-&bgr;–induced activation of both fibroblast and intestinal epithelial cell lines, by regulating mRNA expression of &agr;-SMA and fibronectin, and restoring the TGF-&bgr;–induced loss of intestinal epithelial cell markers. GED treatment also reduced the TGF-&bgr; and ACTA1 expression in primary human intestinal fibroblasts from ulcerative colitis patients. Conclusions:GED ameliorates intestinal fibrosis in dextran sulfate sodium-induced chronic colitis in mice and regulates major profibrotic cellular and molecular mechanisms.

Colonic Inflammation in Mice Is Improved by Cigarette Smoke through iNKT Cells Recruitment

Cigarette smoke (CS) protects against intestinal inflammation during ulcerative colitis. Immunoregulatory mechanisms sustaining this effect remain unknown. The aim of this study was to assess the effects of CS on experimental colitis and to characterize the intestinal inflammatory response at the cellular and molecular levels. Using the InExpose® System, a smoking device accurately reproducing human smoking habit, we pre-exposed C57BL/6 mice for 2 weeks to CS, and then we induced colitis by administration of dextran sodium sulfate (DSS). This system allowed us to demonstrate that CS exposure improved colonic inflammation (significant decrease in clinical score, body weight loss and weight/length colonic ratio). This improvement was associated with a significant decrease in colonic proinflammatory Th1/Th17 cytokine expression, as compared to unexposed mice (TNF (pu200a=u200a0.0169), IFNγ (p<0.0001), and IL-17 (pu200a=u200a0.0008)). Smoke exposure also induced an increased expression of IL-10 mRNA (pu200a=u200a0.0035) and a marked recruitment of iNKT (invariant Natural Killer T; CD45+ TCRβ+ CD1d tetramer+) cells in the colon of DSS-untreated mice. Demonstration of the role of iNKT cells in CS-dependent colitis improvement was performed using two different strains of NKT cells deficient mice. Indeed, in Jα18KO and CD1dKO animals, CS exposure failed to induce significant regulation of DSS-induced colitis both at the clinical and molecular levels. Thus, our study demonstrates that iNKT cells are pivotal actors in the CS-dependent protection of the colon. These results highlight the role of intestinal iNKT lymphocytes and their responsiveness to environmental stimuli. Targeting iNKT cells would represent a new therapeutic way for inflammatory bowel diseases.

Intestinal steroidogenesis controls PPARγ expression in the colon and is impaired during ulcerative colitis

Background and aims Immune tolerance breakdown during UC involves the peroxisome proliferator-activated receptor-γ (PPARγ), a key factor in mucosal homoeostasis and the therapeutic target of 5-aminosalycilates, which expression is impaired during UC. Here we assess the impact of glucocorticoids (GCs) on PPARγ expression, focusing especially on extra-adrenal cortisol production by colonic epithelial cells (CECs). Methods Activation of PPARγ in the colon was evaluated using transgenic mice for the luciferase gene under PPAR control (peroxisome proliferator response element-luciferase mice). Protein and mRNA expression of PPARγ were evaluated with colon fragments and purified CEC from mice. Cortisol production and steroidogenic factor expression were quantified in human CEC of patients with UC and those of controls. Gene expression knockdown by short hairpin RNA in Caco-2 cells was used for functional studies. Results GCs were able to raise luciferase activity in peroxisome proliferator response element-luciferase mice. In the mice colons and Caco-2 cells, PPARγ expression was increased either with GCs or with an inducer of steroidogenesis and then decreased after treatment with a steroidogenesis inhibitor. Cortisol production and steroidogenic factor expression, such as liver receptor homologue-1 (LRH-1), were decreased in CEC isolated from patients with UC, directly correlating with PPARγ impairment. Experiments on Caco-2 cells lacking LRH-1 expression confirmed that LRH-1 controls PPARγ expression by regulating GC synthesis in CEC. Conclusions These results demonstrate cortisol control of PPARγ expression in CEC, highlighting cortisol production deficiency in colonocytes as a key molecular event in the pathophysiology of UC.

The 5-aminosalicylic acid antineoplastic effect in the intestine is mediated by PPARγ.

Epidemiological evidences suggested that 5-aminosalicylic acid (5-ASA) therapy may prevent the development of colorectal cancer in inflammatory bowel disease patients. Our aim is to investigate whether peroxisome proliferator-activated receptor-γ (PPARγ) mediates the antineoplastic effects of 5-ASA. HT-29 and Caco-2 cells were treated by 5-ASA, rosiglitazone (PPARγ ligand) or etoposide (anticarcinogenic drug). Epithelial cell growth, proliferation and apoptosis were assessed by cell count, Ki-67 staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay, respectively. The antineoplastic effect of 5-ASA was evaluated in a xenograft tumor model in SCID mice and in azoxymethane (AOM)-induced colon carcinogenesis in A/JOlaHsd mice. The role of PPARγ was examined by administration of PPARγ antagonist, GW9662 and in PPAR knockdown cells. Compared with untreated cells, treatment of HT-29 cells by 5-ASA inhibited significantly cell growth and cell proliferation (respectively, 60% and 63%) and induced apoptosis in 75% of cells. These effects were abolished by co-treatment with GW9662 and blunted in PPAR knockdown cells. Contrarily to etoposide, similar inhibitory effects of GW9662 were obtained in HT-29 cells treated with rosiglitazone. In the xenograft model, GW9662 abolished the therapeutic effect of 5-ASA, which decreased tumor weight and volume by 80% in SCID mice compared with untreated mice. In A/JOlaHsd mice, 5-ASA suppressed colon carcinogenesis by decreasing the number of aberrant crypt foci (75%) and aberrant crypts (22%) induced by AOM treatment with an absence of 5-ASA response after GW9662 administration. In conclusion, 5-ASA exerts potent antineoplastic effects that are mediated through PPARγ. These data provide new rational for designing more effective and safe antineoplastic PPARγ ligands with topical effects.

Plasmodium falciparum Inhibitor-3 Homolog Increases Protein Phosphatase Type 1 Activity and Is Essential for Parasitic Survival

Background: Little is known about the regulators of phosphatase 1 enzyme activity in Plasmodium falciparum. Results: An activator, its binding motifs, and its nuclear location are presented. Reverse genetics show its essentiality for parasite survival. Conclusion: There is a potential link between this activator and the nuclear activity of this enzyme. Significance: This regulator is essential and can be considered as a potential drug target. Growing evidence indicates that the protein regulators governing protein phosphatase 1 (PP1) activity have crucial functions because their deletion drastically affects cell growth and division. PP1 has been found to be essential in Plasmodium falciparum, but little is known about its regulators. In this study, we have identified a homolog of Inhibitor-3 of PP1, named PfI3. NMR analysis shows that PfI3 belongs to the disordered protein family. High affinity interaction of PfI3 and PfPP1 is demonstrated in vitro using several methods, with an apparent dissociation constant KD of 100 nm. We further show that the conserved 41KVVRW45 motif is crucial for this interaction as the replacement of the Trp45 by an Ala45 severely decreases the binding to PfPP1. Surprisingly, PfI3 was unable to rescue a yeast strain deficient in I3 (Ypi1). This lack of functional orthology was supported as functional assays in vitro have revealed that PfI3, unlike yeast I3 and human I3, increases PfPP1 activity. Reverse genetic approaches suggest an essential role of PfI3 in the growth and/or survival of blood stage parasites because attempts to obtain knock-out parasites were unsuccessful, although the locus of PfI3 is accessible. The main localization of a GFP-tagged PfI3 in the nucleus of all blood stage parasites is compatible with a regulatory role of PfI3 on the activity of nuclear PfPP1.

In vivo imaging reveals selective PPAR activity in the skin of peroxisome proliferator‐activated receptor responsive element‐luciferase reporter mice

Peroxisome proliferator‐activated receptors (PPARs) have been revealed as key regulators of several skin disorders. This has led to a growing interest in the development of drugs targeting PPARs as therapeutics for skin diseases. To evaluate skin PPAR activity, we developed peroxisome proliferator responsive element‐luciferase (PPRE‐Luc) mice, a mouse model in which the luciferase gene expression is under the control of a PPAR‐inducible promoter in all organs. Our aim was to define and validate experimental conditions to establish PPRE‐Luc mice as a valuable tool for in vivo non‐invasive evaluation of PPARs activation in the skin. We demonstrated by optical imaging that topical application of 40 mm of Luciferin for 10 min was enough to reveal the optimal luciferase activity in mice skin. The treatment of mice skin with the PPARγ and PPARα agonists, pioglitazone and WY14643, was associated with significant increase in photons emission reaching maximal signalling at 6 h. We have performed dose response studies by testing a large range of pioglitazone and WY14643 concentrations on mouse skin. The specificity of bioluminescence signal induced by pioglitazone and WY14643 was assessed using PPARγ and PPARα antagonists, GW9662 and GW6471, respectively. This approach revealed that the isoform specificity of PPARs agonists decreased when high ligand concentrations were applied on mouse skin. These results were further confirmed by in vitro measurement of luciferase activity in skin extracts. Overall, our results demonstrated that PPRE‐Luc mice represent a valuable reporter mouse model for the in vivo pharmacological profiling of drugs targeting PPARs in the skin.