Inflammasome activation has an important role in the development of spontaneous colitis

IL-10 engages macrophages to shift Th17 cytokine dependency and pathogenicity during T-cell-mediated colitis

Polymorphisms attenuating IL-10 signalling confer genetic risk for inflammatory bowel disease. Yet, how IL-10 prevents mucosal autoinflammation is incompletely understood. We demonstrate using lineage-specific deletions of IL-10Rα that IL-10 acts primarily through macrophages to limit colitis. Colitis depends on IL-6 to support pathologic Th17 cell generation in wild-type mice. However, specific ablation of macrophage IL-10Rα provokes excessive IL-1β production that overrides Th17 IL-6 dependency, amplifying the colonic Th17 response and disease severity. IL-10 not only inhibits pro-IL-1β production transcriptionally in macrophages, but suppresses caspase-1 activation and caspase-1-dependent maturation of pro-IL-1β to IL-1β. Therefore, lineage-specific effects of IL-10 skew the cytokine dependency of Th17 cell development required for colitis pathogenesis. Coordinated interventions may be needed to fully suppress Th17-mediated immunopathology.

Role of inflammasomes in intestinal inflammation and Crohn's disease

: Inflammasomes are multiprotein complexes that process procytokines into mature forms of interleukin 1β and interleukin 18 and induce pyroptotic cell death. Evidence linking NLRP3, NLRC4, and NLRP6 inflammasomes to intestinal inflammation is reviewed to provide a basis to understand how the innate immune system discriminates pathogenic bacteria from commensal bacteria and shapes microbial ecology. Inflammasomes have a direct and important role limiting colitis by directing effective immune responses against pathogenic bacterial infections in the intestine. Chronic granulomatous disease is presented to reveal a contrasting proinflammatory effect of inflammasomes. This pathogenic effect is unmasked in a state of immunodeficiency where bacterial growth is poorly controlled increasing inflammasome activity. The role of inflammasomes in inflammation associated with Crohn's disease and ulcerative colitis is discussed. Finally, mechanistic studies linking genetic polymorphisms in ATG16L and NOD2 to inflammasome activation provide a basis for new hypotheses to explain how genetic polymorphism associated with Crohn's disease modulate intestinal inflammation. A deeper understanding of the role of inflammasomes in intestinal inflammation is expected to identify new ways of treating inflammatory bowel disease.

Defective expression of SIRT1 contributes to sustain inflammatory pathways in the gut

In inflammatory bowel disease (IBD), tissue damage is driven by an excessive immune response, poorly controlled by counter-regulatory mechanisms. SIRT1, a class III NAD+-dependent deacetylase, regulates negatively the expression of various proteins involved in the control of immune-inflammatory pathways, such as Stat3, Smad7, and NF-κB. Here we examined the expression, regulation, and function of SIRT1 in IBD. SIRT1 RNA and protein expression was less pronounced in whole biopsies and lamina propria mononuclear cells (LPMCs) of IBD patients in comparison with normal controls. SIRT1 expression was downregulated in control LPMC by tumor necrosis factor (TNF)-α and interleukin (IL)-21, and upregulated in IBD LPMC by neutralizing TNF-α and IL-21antibodies. Consistently, SIRT1 expression was increased in mucosal samples taken from IBD patients successfully treated with Infliximab. Treatment of IBD LPMC with Cay10591, a specific SIRT1 activator, reduced NF-κB activation and inhibited inflammatory cytokine synthesis, whereas Ex527, an inhibitor of SIRT1, increased interferon (IFN)-γ in control LPMC. SIRT1 was also reduced in mice with colitis induced by 2,4,6-trinitrobenzenesulphonic acid or oxazolone. Cay10591 prevented and cured experimental colitis whereas Ex527 exacerbated disease by modulating T cell-derived cytokine response. Data indicate that SIRT1 is downregulated in IBD patients and colitic mice and suggest that SIRT1 activation can help attenuate inflammatory signals in the gut.

Inflammasomes and the microbiota--partners in the preservation of mucosal homeostasis

Inflammasomes are multiprotein complexes that serve as signaling platforms initiating innate immune responses. These structures are assembled upon a large array of stimuli, sensing both microbial products and endogenous signals indicating loss of cellular homeostasis. As such, inflammasomes are regarded as sensors of cellular integrity and tissue health, which, upon disruption of homeostasis, provoke an inflammatory response by the release of potent cytokines. Recent evidence suggests that in addition to sensing cellular integrity, inflammasomes are involved in the homeostatic mutualism between the host and its indigenous microbiota. Here, we summarize the involvement of various inflammasomes in host-microbiota interactions and focus on the role of commensal as well as pathogenic bacteria in inflammasome signaling.

Longitudinal study of circulating protein biomarkers in inflammatory bowel disease

Inflammatory bowel diseases (IBDs) are chronic and progressive inflammatory disorders of the gastrointestinal tract. In IBD, protein serological biomarkers could be relevant tools for assessing disease activity, performing early-stage diagnosis and managing the treatment. Using the interleukin-10 knockout (IL-10(-/-)) mouse, a model that develops a time-dependent IBD-like disorder that predominates in the colon; we performed longitudinal studies of circulating protein biomarkers in IBD. Circulating protein profiles in serum samples collected from 30-, 93-, to 135-day-old IL-10(-/-) mice were investigated using two-dimensional differential gel electrophoresis and MALDI-TOF/TOF tandem mass spectrometry. A total of 15 different proteins were identified and confirmed by ELISA and Western blot to be differentially accumulated in serum samples from mid- to late-stage IL-10(-/-) mice compared to early non-inflamed IL-10(-/-) mice. The use of another model of colitis and an extra-intestinal inflammation model validated this biomarker panel and demonstrated that comprised some global inflammatory markers, some intestinal inflammation-specific markers and some chronic intestinal inflammation markers. Statistical analyses using misclassification error rate charts validated the use of these identified proteins as powerful biomarkers of colitis. Unlike standard biomarker screening studies, our analyses identified a panel of proteins that allowed the definition of protein signatures that reflect colitis status.

BIOLOGICAL SIGNIFICANCE

Crohn's disease (CD) and ulcerative colitis (UC) are the most common inflammatory bowel diseases (IBDs) occurring in humans. The major current diagnosis tool is colonoscopy, which is invasive and could lead to false diagnosis. The emergence of serological biomarkers enables the use of new diagnosis tools such as protein signatures for IBD diagnosis/management. Using 2D-DIGE coupled to mass spectrometry, our longitudinal study in a mouse model of colitis identified a signature of protein biomarkers for specific stages of disease.

Endoplasmic reticulum stress in hepatic steatosis and inflammatory bowel diseases

As an adaptive response to the overloading with misfolded proteins in the endoplasmic reticulum (ER), ER stress plays critical roles in maintaining protein homeostasis in the secretory pathway to avoid damage to the host. Such a conserved mechanism is accomplished through three well-orchestrated pathways known collectively as unfolded protein response (UPR). Persistent and pathological ER stress has been implicated in a variety of diseases in metabolic, inflammatory, and malignant conditions. Furthermore, ER stress is directly linked with inflammation through UPR pathways, which modulate transcriptional programs to induce the expression of inflammatory genes. Importantly, the inflammation induced by ER stress is directly responsible for the pathogenesis of metabolic and inflammatory diseases. In this review, we will discuss the potential signaling pathways connecting ER stress with inflammation. We will also depict the interplay between ER stress and inflammation in the pathogenesis of hepatic steatosis, inflammatory bowel diseases and colitis-associated colon cancer.

Inflammasomes and intestinal homeostasis: regulating and connecting infection, inflammation and the microbiota

Inflammasomes are large cytosolic protein complexes that detect infection and stress-associated signals and promote immediate inflammatory responses. In the intestine, activation of the inflammasome leads to an inflammatory response that is important for controlling enteric infections but can also result in pathological tissue damage. Recent studies have suggested that the inflammasome also regulates intestinal homeostasis through its effects on the intestinal microbiota. Notably, many conflicting studies have been published regarding the effect of inflammasome deficiencies on intestinal homeostasis. Here, we attempt to reconcile these contrasting data by highlighting the many ways that the inflammasome contributes to intestinal homeostasis and pathology and exploring the potential role of alterations in the microbiota in these conflicting studies.

The complex role of inflammasomes in the pathogenesis of Inflammatory Bowel Diseases - lessons learned from experimental models

Inflammasomes are a large family of multiprotein complexes recognizing pathogen-associated molecular pattern molecules (PAMPs) and damage-associated molecular patterns (DAMPs). This leads to caspase-1 activation, promoting the secretion of mature IL-1β, IL-18 and under certain conditions even induce pyroptosis. Inflammatory Bowel Diseases (IBD) is associated with alterations in microbiota composition, inappropriate immune responses and genetic predisposition associated to bacterial sensing and autophagy. Besides their acknowledged role in mounting microbial induced host responses, a crucial role in maintenance of intestinal homeostasis was revealed in inflammasome deficient mice. Further, abnormal activation of these functions appears to contribute to the pathology of intestinal inflammation including IBD and colitis-associated cancer. Herein, the current literature implicating the inflammasomes, microbiota and IBD is comprehensively reviewed.