The Multifaceted Role of the Inflammasome in Inflammatory Bowel Diseases

Inflammasomes are intracellular multiprotein complexes that coordinate the maturation of interleukin (IL)-1β and IL-18 in response to pathogens and metabolic danger. Both cytokines have been linked to intestinal inflammation. However, recently evolving concepts ascribe a major role to the inflammasome in maintaining intestinal homeostasis. This review recapitulates its position in the development of inflammatory bowel disease, thereby outlining a model in which hypo- as well as hyperfunctionality can lead to an imbalance of the system, depending on the specific cell population affected. In the epithelium, the inflammasome is essential for regulation of permeability and epithelial regeneration through sensing of commensal microbes, while excessive inflammasome activation within the lamina propria contributes to severe intestinal inflammation

The multifaceted role of the inflammasome in inflammatory bowel diseases

Inflammasomes are intracellular multiprotein complexes that coordinate the maturation of interleukin (IL)-1β and IL-18 in response to pathogens and metabolic danger. Both cytokines have been linked to intestinal inflammation. However, recently evolving concepts ascribe a major role to the inflammasome in maintaining intestinal homeostasis. This review recapitulates its position in the development of inflammatory bowel disease, thereby outlining a model in which hypo-as well as hyperfunctionality can lead to an imbalance of the system, depending on the specific cell population affected. In the epithelium, the inflammasome is essential for regulation of permeability and epithelial regeneration through sensing of commensal microbes, while excessive inflammasome activation within the lamina propria contributes to severe intestinal inflammation. KEYWORDS: cytokines, inflammatory bowel diseases, inflammasome Interleukin (IL)-1β and IL-18, both belonging to the IL-1 family, represent two crucial cytokines involved in the pathogenesis of both acute and chronic inflammatory disorders The first description of what is now referred to as IL-1 dates back a long time This review recapitulates recently evolving concepts of inflammasome activation and its relevance in vivo, concentrating on its complex and controversially discussed role within intestinal inflammation and mucosal injury. Based on the literature, a model will be outlined in which the inflammasome, as an Lissner and Siegmund: Inflammasomes in Inflammatory Bowel Diseases TheScientificWorldJOURNAL (2011) 11, 1536-1547 1537 important member of the innate immune system, plays a decisive role in maintaining intestinal homeostasis, where hypo-as well as hyperfunctionality can result in an imbalance of the system, depending on the specific cell population affected. THE INFLAMMASOME Inflammasomes are high-molecular-weight platforms in the cytosol of diverse cell types. Because they represent a component of the innate immune system, most studies identifying inflammasome-expressing cells have focused on derivatives of the myeloid lineage, such as macrophages and dendritic cells As explained above, two signals are required for the secretion of active IL-1β and IL-18 (see For NLRP3 activation, several mechanisms have been proposed (see Since one fundamental function of the inflammasome is the coordinated response to pathogen infections, its dominant activators are whole microorganisms and PAMPs. Potential identifiable pathogens include fungi (Candida albicans, Saccharomyces cerevisiae) INFLAMMASOME-ASSOCIATED HUMAN DISEASES There is evidence for a number of inflammatory diseases to be associated with inflammasome dysfunction. For some of them, hyperfunctional genetic mutations within the NLRP3 gene are proven and lead to their name, cryopyrin-associated periodic syndromes (CAPS) In addition to these rare autoinflammatory diseases, there is increasing evidence for the involvement of the inflammasome pathway on other, more common, medical conditions for which hereditary as well as acquired components seem likely. One such disease is rheumatoid arthritis (RA), for which the combination of NLRP3 and CARD8 polymorphisms represents a risk factor GENETIC MUTATIONS WITHIN THE INFLAMMASOME PATHWAY ASSOCIATED WITH INFLAMMATORY BOWEL DISEASES In genome-wide association studies, single nucleotide polymorphisms (SNPs) in the NLRP3 gene have recently been linked to the susceptibility to develop Crohn's disease (CD) INFLAMMASOME AND INFLAMMATORY BOWEL DISEASES IBD represent a chronic inflammatory condition of the gut, for which the innate as well as the adaptive immune system play a crucial role. Although the exact mechanisms are not fully understood, the concept of an inadequate immune response against commensal microbiota in the gut lumen is widely accepted In vivo Studies: Neutralization Strategies The first evidence for effective IL-1β inhibition was reported in vivo by applying a soluble IL-1 receptor antagonist (IL-1Ra) to suppress immune-complex colitis in rabbit

Celiac Disease Monocytes Induce a Barrier Defect in Intestinal Epithelial Cells

Intestinal epithelial barrier function in celiac disease (CeD) patients is altered. However, the mechanism underlying this effect is not fully understood. The aim of the current study was to evaluate the role of monocytes in eliciting the epithelial barrier defect in CeD. For this purpose, human monocytes were isolated from peripheral blood mononuclear cells (PBMCs) from active and inactive CeD patients and healthy controls. PBMCs were sorted for expression of CD14 and co-cultured with intestinal epithelial cells (IECs, Caco2BBe). Barrier function, as well as tight junctional alterations, were determined. Monocytes were characterized by profiling of cytokines and surface marker expression. Transepithelial resistance was found to be decreased only in IECs that had been exposed to celiac monocytes. In line with this, tight junctional alterations were found by confocal laser scanning microscopy and Western blotting of ZO-1, occludin, and claudin-5. Analysis of cytokine concentrations in monocyte supernatants revealed higher expression of interleukin-6 and MCP-1 in celiac monocytes. However, surface marker expression, as analyzed by FACS analysis after immunostaining, did not reveal significant alterations in celiac monocytes. In conclusion, CeD peripheral monocytes reveal an intrinsically elevated pro-inflammatory cytokine pattern that is associated with the potential of peripheral monocytes to affect barrier function by altering TJ composition

Celiac Disease: Role of the Epithelial Barrier

In celiac disease (CD) a T-cell–mediated response to gluten is mounted in genetically predisposed individuals, resulting in a malabsorptive enteropathy histologically highlighted by villous atrophy and crypt hyperplasia. Recent data point to the epithelial layer as an under-rated hot spot in celiac pathophysiology to date. This overview summarizes current functional and genetic evidence on the role of the epithelial barrier in CD, consisting of the cell membranes and the apical junctional complex comprising sealing as well as ion and water channel-forming tight junction proteins and the adherens junction. Moreover, the underlying mechanisms are discussed, including apoptosis of intestinal epithelial cells, biology of intestinal stem cells, alterations in the apical junctional complex, transcytotic uptake of gluten peptides, and possible implications of a defective epithelial polarity. Current research is directed toward new treatment options for CD that are alternatives or complementary therapeutics to a gluten-free diet. Thus, strategies to target an altered epithelial barrier therapeutically also are discussed

COVID-19—from mucosal immunology to IBD patients

Viral infections with SARS-CoV-2 can cause a multi-facetted disease, which is not only characterized by pneumonia and overwhelming systemic inflammatory immune responses, but which can also directly affect the digestive system and infect intestinal epithelial cells. Here, we review the current understanding of intestinal tropism of SARS-CoV-2 infection, its impact on mucosal function and immunology and summarize the effect of immune-suppression in patients with inflammatory bowel disease (IBD) on disease outcome of COVID-19 and discuss IBD-relevant implications for the clinical management of SARS-CoV-2 infected individuals

Combined Pulse Electroporation – A Novel Strategy for Highly Efficient Transfection of Human and Mouse Cells

The type of a nucleic acid and the type of the cell to be transfected generally affect the efficiency of electroporation, the versatile method of choice for gene regulation studies or for recombinant protein expression. We here present a combined square pulse electroporation strategy to reproducibly and efficiently transfect eukaryotic cells. Cells suspended in a universal buffer system received an initial high voltage pulse that was continuously combined with a subsequent low voltage pulse with independently defined electric parameters of the effective field and the duration of each pulse. At comparable viable cell recoveries and transfection efficiencies of up to 95% of all cells, a wide variety of cells especially profited from this combined pulse strategy by high protein expression levels of individual cells after transfection. Long-term silencing of gene expression by transfected small interfering RNA was most likely due to the uptake of large nucleic acid amounts as shown by direct detection of fluorochromated small interfering RNA. The highly efficient combined pulse electroporation strategy enables for external regulation of the number of naked nucleic acid molecules taken up and can be easily adapted for cells considered difficult to transfect

A case series in patients with enteropathy and granulomatous diseases

Background Although sarcoidosis and celiac disease are both chronic immunologic disorders involving multiple organ systems, reports about association of diseases in individual patients are sparse. While sarcoidosis is a chronic granulomatous disease presumably reflecting an exaggerated response to an unknown antigen, celiac disease is a T cell-driven disease triggered by ingestion of gluten, a protein composite found in wheat and related grains. Case presentation We present three cases with a longstanding history of sarcoidosis that have been additionally diagnosed with celiac-like enteropathy. In two cases, celiac disease was established applying celiac- specific serology and duodenal histology, while one case was revealed as an AIE-75-positive autoimmune enteropathy. The HLA-DR3/DQ2 haplotype was confirmed in both celiac patients, hence confirming previous data of linkage disequilibrium as a cause for disease association. Remarkably, one celiac patient presented with granulomatous nodulae in the ileum, thus reflecting an intestinal sarcoid manifestation. In contrast the patient with an autoimmune enteropathy, was HLA-DQ9/DQ6-positive, also arguing against CD. Conclusions Associations of sarcoidosis and celiac disease are rare but do occur. Determining the HLA status in patients with complex autoimmune associations might help classifying involved disease entities

dPGS Regulates the Phenotype of Macrophages via Metabolic Switching

The synthetic compound dendritic polyglycerol sulfate (dPGS) is a pleiotropic acting molecule but shows a high binding affinity to immunological active molecules as L-/P-selectin or complement proteins leading to well described anti-inflammatory properties in various mouse models. In order to make a comprehensive evaluation of the direct effect on the innate immune system, macrophage polarization is analyzed in the presence of dPGS on a phenotypic but also metabolic level. dPGS administered macrophages show a significant increase of MCP1 production paralleled by a reduction of IL-10 secretion. Metabolic analysis reveals that dPGS could potently enhance the glycolysis and mitochondrial respiration in M0 macrophages as well as decrease the mitochondrial respiration of M2 macrophages. In summary the data indicate that dPGS polarizes macrophages into a pro-inflammatory phenotype in a metabolic pathway-dependent manner