Negative Regulators Of Inflammation Research Articles

Adaptor molecules mediate negative regulation of macrophage inflammatory pathways: a closer look.

Macrophages play a central role in initiating, maintaining, and terminating inflammation. For that, macrophages respond to various external stimuli in changing environments through signaling pathways that are tightly regulated and interconnected. This process involves, among others, autoregulatory loops that activate and deactivate macrophages through various cytokines, stimulants, and other chemical mediators. Adaptor proteins play an indispensable role in facilitating various inflammatory signals. These proteins are dynamic and flexible modulators of immune cell signaling and act as molecular bridges between cell surface receptors and intracellular effector molecules. They are involved in regulating physiological inflammation and also contribute significantly to the development of chronic inflammatory processes. This is at least partly due to their involvement in the activation and deactivation of macrophages, leading to changes in the macrophages' activation/phenotype. This review provides a comprehensive overview of the 20 adaptor molecules and proteins that act as negative regulators of inflammation in macrophages and effectively suppress inflammatory signaling pathways. We emphasize the functional role of adaptors in signal transduction in macrophages and their influence on the phenotypic transition of macrophages from pro-inflammatory M1-like states to anti-inflammatory M2-like phenotypes. This endeavor mainly aims at highlighting and orchestrating the intricate dynamics of adaptor molecules by elucidating the associated key roles along with respective domains and opening avenues for therapeutic and investigative purposes in clinical practice.

Regulatory T Cells in the Pathogenesis of Graves' Disease.

Maintaining a delicate balance between the prompt immune response to pathogens and tolerance towards self-antigens and commensals is crucial for health. T regulatory (Treg) cells are pivotal in preserving self-tolerance, serving as negative regulators of inflammation through the secretion of anti-inflammatory cytokines, interleukin-2 neutralization, and direct suppression of effector T cells. Graves' disease (GD) is a thyroid-specific autoimmune disorder primarily attributed to the breakdown of tolerance to the thyroid-stimulating hormone receptor. Given the limitations of currently available GD treatments, identifying potential pathogenetic factors for pharmacological targeting is of paramount importance. Both functional impairment and frequency reduction of Tregs seem likely in GD pathogenesis. Genome-wide association studies in GD have identified polymorphisms of genes involved in Tregs' functions, such as CD25 (interleukin 2 receptor), and Forkhead box protein P3 (FOXP3). Clinical studies have reported both functional impairment and a reduction in Treg frequency or suppressive actions in GD, although their precise involvement remains a subject of debate. This review begins with an overview of Treg phenotype and functions, subsequently delves into the pathophysiology of GD and into the existing literature concerning the role of Tregs and the balance between Tregs and T helper 17 cells in GD, and finally explores the ongoing studies on target therapies for GD.

NLR and Intestinal Dysbiosis-Associated Inflammatory Illness: Drivers or Dampers?

The intestinal microbiome maintains a close relationship with the host immunity. This connection fosters a health state by direct and indirect mechanisms. Direct influences occur mainly through the production of short-chain fatty acids (SCFAs), gastrointestinal hormones and precursors of bioactive molecules. Indirect mechanisms comprise the crosstalk between bacterial products and the host's innate immune system. Conversely, intestinal dysbiosis is a condition found in a large number of chronic intestinal inflammatory diseases, such as ulcerative colitis and Crohn's disease, as well as in diseases associated with low-grade inflammation, such as obesity, type 1 and 2 diabetes mellitus and cardiovascular diseases. NOD-Like receptors (NLRs) are cytoplasmic receptors expressed by adaptive and innate immune cells that form a multiprotein complex, termed the inflammasome, responsible for the release of mature interleukin (IL)-1β and IL-18. NLRs are also involved in the recognition of bacterial components and production of antimicrobial molecules that shape the gut microbiota and maintain the intestinal homeostasis. Recent novel findings show that NLRs may act as positive or negative regulators of inflammation by modulating NF-κB activation. This mini-review presents current and updated evidence on the interplay between NLRs and gut microbiota and their dual role, contributing to progression or conferring protection, in diabetes and other inflammatory diseases.

Distinct synovial tissue macrophage subsets regulate inflammation and remission in rheumatoid arthritis.

Immune-regulatory mechanisms of drug-free remission in rheumatoid arthritis (RA) are unknown. We hypothesized that synovial tissue macrophages (STM), which persist in remission, contribute to joint homeostasis. We used single-cell transcriptomics to profile 32,000 STMs and identified phenotypic changes in patients with early/active RA, treatment-refractory/active RA and RA in sustained remission. Each clinical state was characterized by different frequencies of nine discrete phenotypic clusters within four distinct STM subpopulations with diverse homeostatic, regulatory and inflammatory functions. This cellular atlas, combined with deep-phenotypic, spatial and functional analyses of synovial biopsy fluorescent activated cell sorted STMs, revealed two STM subpopulations (MerTKposTREM2high and MerTKposLYVE1pos) with unique remission transcriptomic signatures enriched in negative regulators of inflammation. These STMs were potent producers of inflammation-resolving lipid mediators and induced the repair response of synovial fibroblasts in vitro. A low proportion of MerTKpos STMs in remission was associated with increased risk of disease flare after treatment cessation. Therapeutic modulation of MerTKpos STM subpopulations could therefore be a potential treatment strategy for RA.

Endothelial cell-glucocorticoid receptor interactions and regulation of Wnt signaling.

Vascular inflammation is present in many cardiovascular diseases, and exogenous glucocorticoids have traditionally been used as a therapy to suppress inflammation. However, recent data have shown that endogenous glucocorticoids, acting through the endothelial glucocorticoid receptor, act as negative regulators of inflammation. Here, we performed ChIP for the glucocorticoid receptor, followed by next-generation sequencing in mouse endothelial cells to investigate how the endothelial glucocorticoid receptor regulates vascular inflammation. We identified a role of the Wnt signaling pathway in this setting and show that loss of the endothelial glucocorticoid receptor results in upregulation of Wnt signaling both in vitro and in vivo using our validated mouse model. Furthermore, we demonstrate glucocorticoid receptor regulation of a key gene in the Wnt pathway, Frzb, via a glucocorticoid response element gleaned from our genomic data. These results suggest a role for endothelial Wnt signaling modulation in states of vascular inflammation.

Liver X Receptor Nuclear Receptors Are Transcriptional Regulators of Dendritic Cell Chemotaxis.

The liver X receptors (LXRs) are ligand-activated nuclear receptors with established roles in the maintenance of lipid homeostasis in multiple tissues. LXRs exert additional biological functions as negative regulators of inflammation, particularly in macrophages. However, the transcriptional responses controlled by LXRs in other myeloid cells, such as dendritic cells (DCs), are still poorly understood. Here we used gain- and loss-of-function models to characterize the impact of LXR deficiency on DC activation programs. Our results identified an LXR-dependent pathway that is important for DC chemotaxis. LXR-deficient mature DCs are defective in stimulus-induced migration in vitro and in vivo Mechanistically, we show that LXRs facilitate DC chemotactic signaling by regulating the expression of CD38, an ectoenzyme important for leukocyte trafficking. Pharmacological or genetic inactivation of CD38 activity abolished the LXR-dependent induction of DC chemotaxis. Using the low-density lipoprotein receptor-deficient (LDLR-/-) LDLR-/- mouse model of atherosclerosis, we also demonstrated that hematopoietic CD38 expression is important for the accumulation of lipid-laden myeloid cells in lesions, suggesting that CD38 is a key factor in leukocyte migration during atherogenesis. Collectively, our results demonstrate that LXRs are required for the efficient emigration of DCs in response to chemotactic signals during inflammation.

Day 1 Post‐Myocardial Infarction Cardiac Macrophage Transcriptomic Signatures that Link to LV Infarct Wall Thinning

We evaluated the relationships between the macrophage transcriptome at day 1 following myocardial infarction (MI) and infarct wall thinning. C57BL/6J male mice (3–6 months old) were subjected to permanent coronary artery ligation to induce MI, and macrophages were isolated from the infarct region at day 1 post‐MI. Day 0 no MI cardiac macrophages served as the negative control. Whole transcriptome analysis was performed using next‐generation RNA sequencing (Illumina NextSeq 500 platform) on n=4 pooled sets for each time, representing a total of 59 mice. Infarct wall thinning (Day 0 – Day 1) was assessed by echocardiography. A total of 16,696 genes were quantified and passed quality control (FPKM > 0 for at least 3 replicates per group). Of these, 3,062 were differentially expressed (fold change ≥ 2.0, p<0.05), of which 1,019 were upregulated and 2,043 were downregulated. Gene ontology pathways enriched for the upregulated genes included inflammatory response and response to hypoxia, while pathways enriched for the downregulated genes included extracellular matrix organization. To determine potential contributions of individual genes to the wall thinning phenotype, large scale correlation analysis was performed. Of the 3,062 differentially expressed genes, 119 positively correlated with the decrease in wall thickness, while 93 negatively correlated. Of interest, positive correlations between several pro‐inflammatory genes and wall thinning were observed, includingTlr1 (r=0.99, p=0.01), Tnfrsf1b (r=0.95; p=0.047), Hrh4 (r=0.96; p=0.036), and Stat5a (r=0.95; p=0.048), all of which play pro‐inflammatory roles in response to inflammatory stimuli. Genes that negatively correlated with wall thinning included Vegfa (r=−0.96, p=0.04) and Nfkbie (r=−0.99, p=0.009), which are negative regulators of inflammation. Of the positively correlated genes, NF‐kappaB was a major enriched pathway (p=0.009), suggesting excessive NF‐kappaB signaling in macrophages exacerbates post‐MI wall thinning. For negatively correlated genes, Kit signaling, which has been linked to immune suppression and the anti‐inflammatory M2 phenotype, was a major enriched pathway (p=0.00001). Combined, these results indicate that promoting pro‐inflammatory and limiting anti‐inflammatory gene expression in post‐MI day 1 cardiac macrophages is directly linked to LV wall thinning.Support or Funding InformationFunding: NIH GM103328, GM103476, GM104357, GM114833, GM115428, HL051971, HL075360, HL105324, HL129823, AHA 15SDG22930009, and VA 5I01BX000505 and IK2BX003922This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Negative regulators that mediate ocular immune privilege.

The ocular microenvironment has adapted several negative regulators of inflammation to maintain immune privilege and health of the visual axis. Several constitutively produced negative regulators within the eye TGF-β2, α-melanocyte stimulating hormone (α-MSH), Fas ligand (FasL), and PD-L1 standout because of their capacity to influence multiple pathways of inflammation, and that they are part of promoting immune tolerance. These regulators demonstrate the capacity of immune privilege to prevent the activation of inflammation, and to suppress activation of effector immune cells even under conditions of ocular inflammation induced by endotoxin and autoimmune disease. In addition, these negative regulators promote and expand immune cells that mediate regulatory and tolerogenic immunity. This in turn makes the immune cells themselves negative regulators of inflammation. This provides for a greater understanding of immune privilege in that it includes both molecular and cellular negative regulators of inflammation. This would mean that potentially new approaches to the treatment of autoimmune disease can be developed through the use of molecules and cells as negative regulators of inflammation.

Biliary tract instillation of a SMAC mimetic induces TRAIL-dependent acute sclerosing cholangitis-like injury in mice

Primary sclerosing cholangitis (PSC) is a cholestatic liver disease of unknown etiopathogenesis characterized by fibrous cholangiopathy of large and small bile ducts. Systemic administration of a murine TNF-related apoptosis-inducing ligand (TRAIL) receptor agonist induces a sclerosing cholangitis injury in C57BL/6 mice, suggesting endogenous TRAIL may contribute to sclerosing cholangitis syndromes. Cellular inhibitor of apoptosis proteins (cIAP-1 and cIAP-2) are negative regulators of inflammation and TRAIL receptor signaling. We hypothesized that if endogenous TRAIL promotes sclerosing cholangitis, then cIAP depletion should also induce this biliary tract injury. Herein, we show that cIAP protein levels are reduced in the interlobular bile ducts of human PSC livers. Downregulation of cIAPs in normal human cholangiocytes in vitro by use of a SMAC mimetic (SM) induces moderate, ripoptosome-mediated apoptosis and RIP1-independent upregulation of proinflammatory cytokines and chemokines. Cytokine and chemokine expression was mediated by the non-canonical activation of NF-κB. To investigate whether downregulation of cIAPs is linked to generation of a PSC-like phenotype, an SM was directly instilled into the mouse biliary tree. Twelve hours after biliary instillation, TUNEL-positive cholangiocytes were identified; 5 days later, PSC-like changes were observed in the SM-treated mice, including a fibrous cholangiopathy of the interlobular bile ducts, portal inflammation, significant elevation of serum markers of cholestasis and cholangiographic evidence of intrahepatic biliary tract injury. In contrast, TRAIL and TRAIL-receptor deficient mice showed no sign of cholangiopathy following SM intrabiliary injection. We conclude that in vivo antagonism of cIAPs in mouse biliary epithelial cells is sufficient to trigger cholangiocytes apoptosis and a proinflammatory response resulting in a fibrous cholangiopathy resembling human sclerosing cholangitis. Therefore, downregulation of cIAPs in PSC cholangiocytes may contribute to the development of the disease. Our results also indicate that inhibition of TRAIL signaling pathways may be beneficial in the treatment of PSC.

NLRX1 attenuates damage following traumatic brain injury through negatively regulating NF-κB signaling

Abstract Mechanical trauma to the CNS results in the disruption of the cellular microenvironment leading to massive necrotic and apoptotic loss of neuronal and glia populations. The progressive cascade of secondary events, including ischemia, inflammation, excitotoxicity and free radial release contribute to neural tissue damage. Members of the NLR family of pattern recognition receptors are essential mediators of the host immune response. Recently, our lab and others identified a novel sub-group of NLRs that function as negative regulators of inflammation. One of the members of this sub-group, NLRX1, is a potent regulator of interferon, NF-κB, ROS production and autophagy. Thus, we hypothesized that NLRX1 attenuates Traumatic Brain Injury (TBI) through the negative regulation of overzealous innate immune system signaling. To evaluate this hypothesis, we utilized Nlrx1−/− mice in a controlled cortical impact (CCI) injury model. The Nlrx1−/− mice exhibited significantly larger brain lesions and increased motor deficits following CCI injury. We also observed significant proliferation of microglia within the Nlrx1−/− lesions compared to wild type animals. Mechanistically, our data indicates that NLRX1 attenuates TBI progression through the microglia compartment via negative regulation of NF-κB signaling and IL-6 production. Together, our data extends the function of NLRX1 beyond its currently characterized role in host-pathogen defense and identifies this highly novel NLR as a significant modulator of TBI progression.

Behçet's: A Disease or a Syndrome? Answer from an Expression Profiling Study.

Behçet’s disease (BD) is a chronic, relapsing, multisystemic inflammatory disorder with unanswered questions regarding its etiology/pathogenesis and classification. Distinct manifestation based subsets, pronounced geographical variations in expression, and discrepant immunological abnormalities raised the question whether Behçet’s is “a disease or a syndrome”. To answer the preceding question we aimed to display and compare the molecular mechanisms underlying distinct subsets of BD. For this purpose, the expression data of the gene expression profiling and association study on BD by Xavier et al (2013) was retrieved from GEO database and reanalysed by gene expression data analysis/visualization and bioinformatics enrichment tools. There were 15 BD patients (B) and 14 controls (C). Three subsets of BD patients were generated: MB (isolated mucocutaneous manifestations, n = 7), OB (ocular involvement, n = 4), and VB (large vein thrombosis, n = 4). Class comparison analyses yielded the following numbers of differentially expressed genes (DEGs); B vs C: 4, MB vs C: 5, OB vs C: 151, VB vs C: 274, MB vs OB: 215, MB vs VB: 760, OB vs VB: 984. Venn diagram analysis showed that there were no common DEGs in the intersection “MB vs C” ∩ “OB vs C” ∩ “VB vs C”. Cluster analyses successfully clustered distinct expressions of BD. During gene ontology term enrichment analyses, categories with relevance to IL-8 production (MB vs C) and immune response to microorganisms (OB vs C) were differentially enriched. Distinct subsets of BD display distinct expression profiles and different disease associated pathways. Based on these clear discrepancies, the designation as “Behçet’s syndrome” (BS) should be encouraged and future research should take into consideration the immunogenetic heterogeneity of BS subsets. Four gene groups, namely, negative regulators of inflammation (CD69, CLEC12A, CLEC12B, TNFAIP3), neutrophil granule proteins (LTF, OLFM4, AZU1, MMP8, DEFA4, CAMP), antigen processing and presentation proteins (CTSS, ERAP1), and regulators of immune response (LGALS2, BCL10, ITCH, CEACAM8, CD36, IL8, CCL4, EREG, NFKBIZ, CCR2, CD180, KLRC4, NFAT5) appear to be instrumental in BS immunopathogenesis.

Emerging significance of NLRs in inflammatory bowel disease.

Pattern recognition receptors are essential mediators of host defense and inflammation in the gastrointestinal system. Recent data have revealed that toll-like receptors and nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs) function to maintain homeostasis between the host microbiome and mucosal immunity. The NLR proteins are a diverse class of cytoplasmic pattern recognition receptors. In humans, only about half of the identified NLRs have been adequately characterized. The majority of well-characterized NLRs participate in the formation of a multiprotein complex, termed the inflammasome, which is responsible for the maturation of interleukin-1β and interleukin-18. However, recent observations have also uncovered the presence of a novel subgroup of NLRs that function as positive or negative regulators of inflammation through modulating critical signaling pathways, including NF-κB. Dysregulation of specific NLRs from both proinflammatory and inhibitory subgroups have been associated with the development of inflammatory bowel disease (IBD) in genetically susceptible human populations. Our own preliminary retrospective data mining efforts have identified a diverse range of NLRs that are significantly altered at the messenger RNA level in colons from patients with IBD. Likewise, studies using genetically modified mouse strains have revealed that multiple NLR family members have the potential to dramatically modulate the immune response during IBD. Targeting NLR signaling represents a promising and novel therapeutic strategy. However, significant effort is necessary to translate the current understanding of NLR biology into effective therapies.

Mechanoresponsive networks controlling vascular inflammation.

Atherosclerosis is a chronic inflammatory disease of arteries that develops preferentially at branches and bends that are exposed to disturbed blood flow. Vascular function is modified by flow, in part, via the generation of mechanical forces that alter multiple physiological processes in endothelial cells. Shear stress has profound effects on vascular inflammation; high uniform shear stress prevents leukocyte recruitment to the vascular wall by reducing endothelial expression of adhesion molecules and other inflammatory proteins, whereas low oscillatory shear stress has the opposite effects. Here, we review the molecular mechanisms that underpin the effects of shear stress on endothelial inflammatory responses. They include shear stress regulation of inflammatory mitogen-activated protein kinase and nuclear factor-κB signaling. High shear suppresses these pathways through the induction of several negative regulators of inflammation, whereas low shear promotes inflammatory signaling. Furthermore, we summarize recent studies indicating that inflammatory signaling is highly sensitive to pulse wave frequencies, magnitude, and direction of flow. Finally, the importance of systems biology approaches (including omics studies and functional screening) to identify novel mechanosensitive pathways is discussed.

Deletion of CD24 impairs development of heat shock protein gp96-driven autoimmune disease through expansion of myeloid-derived suppressor cells.

CD24 binds to and suppresses inflammation triggered by danger-associated molecular patterns such as heat shock proteins (HSPs) and high-mobility group box 1. Paradoxically, CD24 has been shown to enhance autoimmune disease. In this study, we attempt to reconcile this paradox by deletion of CD24 (24KO) in a lupus-like disease model driven by forced expression of HSP gp96 at the cell surface (transgenic mice [tm]). As expected, tm24KO mice showed increased CD11c(+) dendritic cell activation coupled to a significant increase in dendritic cell-specific IL-12 production compared with tm mice. However, tm24KO mice showed less CD4 T cell activation and peripheral inflammatory cytokine production in comparison with tm mice. We characterized an enhanced immune suppressive milieu in tm24KO mice distinguished by increased TGF-β and greater regulatory T cell-suppressive capacity. We found greater absolute numbers of myeloid-derived suppressor cells (MDSCs) in tm24KO mice and showed that the Ly6C(+) MDSC subset had greater suppressive capacity from tm24KO mice. Deletion of CD24 in tm mice led to diminished lupus-like pathology as evidenced by anti-nuclear Ab deposition and glomerulonephritis. Finally, we show that expanded MDSC populations were mediated by increased free high-mobility group box 1 in tm24KO mice. Thus, the deletion of CD24 in an HSP-driven model of autoimmunity led to the unexpected development of regulatory T cell and MDSC populations that augmented immune tolerance. Further study of these populations as possible negative regulators of inflammation in the context of autoimmunity is warranted.

NLRX1 attenuates tumorigenesis through the negative regulation of AKT and NF-κB signaling (TUM7P.924)

Abstract Members of the NLR family of pattern recognition receptors are essential mediators of the host immune response. Recently, our lab and others identified a novel sub-group of NLRs that function as negative regulators of inflammation. One of the members of this sub-group, NLRX1, is a potent regulator of interferon, NF-κB and autophagy signaling. Each of these signaling pathways has been linked to diverse types of cancer. Thus, we hypothesized that NLRX1 attenuates tumorigenesis through the negative regulation of overzealous innate immune system signaling. To evaluate this hypothesis, we utilized a urethane based model of tumorigenesis and explored disease progression in Nlrx1-/- mice. Mice lacking NLRX1 exhibited dramatically increased morbidity and mortality and were found to develop a rare neoplasia, diagnosed as histiocytic sarcoma. Of the already rare histiocytic disorders in humans, histiocytic sarcoma is exceedingly uncommon and the rarity of this disease has resulted in a paucity of data pertaining to diagnostic and therapeutic options. Mechanistically, our data indicates that NLRX1 attenuates tumorigenesis through the negative regulation of AKT and NF-κB signaling. These pathways were found to be associated with macrophage hyperproliferation in the absence of NLRX1. Our data extends the function of NLRX1 beyond its currently characterized role in host-pathogen defense and reveals a significant contribution for this NLR in cancer pathobiology.

Protective Effects of N-Acetylcysteine on Experimentally Undescended Testis

We evaluated the efficacy of N-acetylcysteine for testicular damage induced by undescended testes in rats. Flutamide was injected in the abdomen of pregnant rats daily from days 14 to 20 of gestation. Male offspring with cryptorchidism were randomly divided into 2 groups. Healthy male rats without undescended testes comprised the control group (group 1). Group 2 (undescended testes without N-acetylcysteine) received no treatment. Group 3 (undescended testes plus N-acetylcysteine) received intraperitoneal N-acetylcysteine daily. At 70 days after experiment initiation the testes were removed for histopathological and biochemical analysis. Mean malonyl dialdehyde values were lowest in group 1 and highest in group 2. In group 3 malonyl dialdehyde levels were significantly lower than in group 2 (p <0.001). Conversely, mean glutathione peroxidase was highest in group 1 and lowest in group 2. Glutathione peroxidase levels in group 3 were significantly higher than in group 2 (p <0.001). Histopathological differences between groups 1 and 3 in the modified Johnsen score were not significant (p = 0.041). However, the differences between these groups and group 2 were significant (p <0.001). The median apoptotic cell count did not differ between groups 1 and 3 but it was significantly higher in group 2 than in the other groups (p = 0.03 and <0.001, respectively). N-acetylcysteine may alleviate undescended testis induced damage to testes through its antioxidant effects. The underlying mechanism of these effects merits further investigation. Long-term studies are also needed as well as comparative animal and human studies.

Fibulin-7, a member of the extracellular matrix fibulin family, regulates immune cell migration and function (P5124)

Abstract Interactions of immune cells with matrix proteins and their bioactive fragments via integrins could influence their activation and differentiation. Fibulins are a family of secreted glycoproteins that are associated with extracellular matrices. Fibulins form intermolecular bridges within the extracellular matrix and serve as mediators for cellular processes and tissue remodeling. We previously identified the latest member of the extracellular protein fibulin family, TM14/fibulin-7, and found that fibulin-7 (Fbln7) is a cell adhesion molecule that binds to dental mesenchymes and odontoblasts. Fbln7 is also expressed in cartilage, placenta, and eyes. Because of Fbln7 expression in immunotolerant tissues, we hypothesized that Fbln7 or its fragment may function as an immunomodulator. In this report, we examined the effect of the full-length Fbln7-d2 and its C-terminal fragment Fbln7-d3 on immune cell functions using human monocytes. We showed that monocytes interacted with both Fbln7-d2 and -d3 in part through integrins α5β1 and α2β1. We found that Fbln7-d3 inhibited cell spreading and stress fiber formation and blocked the production of inflammatory cytokine IL-6 and MMP-1/9, while Fbln7-d2 reduced production of IL-6 and also promoted the production of IL-10. Fbln7-d3 reduced phosphorylation of Erk1/2 in TNFα-activated monocytes in vitro. Our results suggest that both full length Fbln7-d2 and Fbln7-d3 fragment are negative regulators of inflammation with distinct effects.

Characterization of NLRP12 during the In Vivo Host Immune Response to Klebsiella pneumoniae and Mycobacterium tuberculosis

The majority of nucleotide binding domain leucine rich repeats-containing (NLR) family members has yet to be functionally characterized. Of the described NLRs, most are considered to be proinflammatory and facilitate IL-1β production. However, a newly defined sub-group of NLRs that function as negative regulators of inflammation have been identified based on their abilities to attenuate NF-κB signaling. NLRP12 (Monarch-1) is a prototypical member of this sub-group that negatively regulates both canonical and noncanonical NF-κB signaling in biochemical assays and in colitis and colon cancer models. The role of NLRP12 in infectious diseases has not been extensively studied. Here, we characterized the innate immune response of Nlrp12−/− mice following airway exposure to LPS, Klebsiella pneumoniae and Mycobacterium tuberculosis. In response to E. coli LPS, Nlrp12−/− mice showed a slight decrease in IL-1β and increase in IL-6 production, but these levels were not statistically significant. During K. pneumoniae infection, we observed subtle differences in cytokine levels and significantly reduced numbers of monocytes and lymphocytes in Nlrp12−/− mice. However, the physiological relevance of these findings is unclear as no overt differences in the development of lung disease were observed in the Nlrp12−/− mice. Likewise, Nlrp12−/− mice demonstrated pathologies similar to those observed in the wild type mice following M. tuberculosis infection. Together, these data suggest that NLRP12 does not significantly contribute to the in vivo host innate immune response to LPS stimulation, Klebsiella pneumonia infection or Mycobacterium tuberculosis.

Fibroblasts as negative regulators of inflammation: implications for the pathogenesis of rheumatoid arthritis?

Backgroundand objectivesFibroblasts possess immune regulatory capacities. They are able to suppress the proliferation of T lymphocytes and to modulate the differentiation of dendritic cells (DC). Being ubiquitously present at the...

TLR2 Expression Is Regulated by MicroRNA miR-19 in Rheumatoid Fibroblast-like Synoviocytes

Resident cells, such as fibroblast-like synoviocytes (FLS), play a crucial role in rheumatoid arthritis (RA). They are implicated in the inflammatory response and play a key role in osteoarticular destruction. Moreover, RA FLS spread RA to unaffected joints. Pathogen-associated molecular patterns and damage-associated molecular patterns have been found to activate RA FLS by interacting with pattern recognition receptors, such as TLR. RA FLS express a large number of TLR, and TLR2 was demonstrated to be involved in RA inflammation. Because microRNA have emerged as important controllers of TLR expression and signaling, the aim of this study was to evaluate their potential involvement in the control of TLR2 expression by RA FLS. We first showed that Tlr2 expression is strongly upregulated in RA FLS in response to TLR2 ligands. Using a microRNA microarray analysis, we identified one miRNA in activated RA FLS, miR-19b, which was downregulated and predicted to target Tlr2 mRNA. Downregulation of miR-19b and miR-19a, which belongs to the same cluster, was confirmed by real-time quantitative PCR. Transfection of RA FLS with miR-19a/b mimics decreased TLR2 protein expression. In parallel, we found that both IL-6 and matrix metalloproteinase 3 secretion was significantly downregulated in activated FLS transfected with either mimic. Moreover, using a luciferase assay, we showed that miR-19a/b directly target Tlr2 mRNA. Taken together, our data point toward an important role for miR-19a/b in the regulation of IL-6 and matrix metalloproteinase 3 release by controlling TLR2 expression, as well as provide evidence that miR-19a/b can act as negative regulators of inflammation in humans.