Conor Mc Guire

A20 (TNFAIP3) deficiency in myeloid cells triggers erosive polyarthritis resembling rheumatoid arthritis

A20 (TNFAIP3) is a protein that is involved in the negative feedback regulation of NF-κB signaling in response to specific proinflammatory stimuli in different cell types and has been suggested as a susceptibility gene for rheumatoid arthritis. To define the contribution of A20 to rheumatoid arthritis pathology, we generated myeloid-specific A20-deficient mice and show that specific ablation of Tnfaip3 in myeloid cells results in spontaneous development of a severe destructive polyarthritis with many features of rheumatoid arthritis. Myeloid-A20–deficient mice have high levels of inflammatory cytokines in their serum, consistent with a sustained NF-κB activation and higher TNF production by macrophages. Destructive polyarthritis in myeloid A20 knockout mice was TLR4-MyD88 and IL-6 dependent but was TNF independent. Myeloid A20 deficiency also promoted osteoclastogenesis in mice. Together, these observations indicate a critical and cell-specific function for A20 in the etiology of rheumatoid arthritis, supporting the idea of developing A20 modulatory drugs as cell-targeted therapies.

Matrix Metalloprotease 8-Dependent Extracellular Matrix Cleavage at the Blood–CSF Barrier Contributes to Lethality during Systemic Inflammatory Diseases

Systemic inflammatory response syndrome (SIRS) is a highly mortal inflammatory disease, associated with systemic inflammation and organ dysfunction. SIRS can have a sterile cause or can be initiated by an infection, called sepsis. The prevalence is high, and available treatments are ineffective and mainly supportive. Consequently, there is an urgent need for new treatments. The brain is one of the first organs affected during SIRS, and sepsis and the consequent neurological complications, such as encephalopathy, are correlated with decreased survival. The choroid plexus (CP) that forms the blood–CSF barrier (BCSFB) is thought to act as a brain “immune sensor” involved in the communication between the peripheral immune system and the CNS. Nevertheless, the involvement of BCSFB integrity in systemic inflammatory diseases is seldom investigated. We report that matrix metalloprotease-8 (MMP8) depletion or inhibition protects mice from death and hypothermia in sepsis and renal ischemia/reperfusion. This effect could be attributed to MMP8-dependent leakage of the BCSFB, caused by collagen cleavage in the extracellular matrix of CP cells, which leads to a dramatic change in cellular morphology. Disruption of the BCSFB results in increased CSF cytokine levels, brain inflammation, and downregulation of the brain glucocorticoid receptor. This receptor is necessary for dampening the inflammatory response. Consequently, MMP8+/+ mice, in contrast to MMP8−/− mice, show no anti-inflammatory response and this results in high mortality. In conclusion, we identify MMP8 as an essential mediator in SIRS and, hence, a potential drug target. We also propose that the mechanism of action of MMP8 involves disruption of the BCSFB integrity.

Nuclear factor kappa B (NF-κB) in multiple sclerosis pathology

The nuclear factor kappa B (NF-κB) signaling cascade plays a critical role in the regulation of immune and inflammatory responses and has been implicated in the pathogenesis of autoimmune demyelinating diseases such as multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), the main animal model of MS. NF-κB is essential for peripheral immune cell activation and the induction of pathology, but also plays crucial roles in resident cells of the central nervous system (CNS) during disease development. Here we review recent evidence clarifying the role of NF-κB in the different cell compartments contributing to MS pathology and its implications for the development of therapeutic strategies for the treatment of MS and other demyelinating pathologies of the CNS.

Antiinflammatory Properties of a Plant-Derived Nonsteroidal, Dissociated Glucocorticoid Receptor Modulator in Experimental Autoimmune Encephalomyelitis

Compound A (CpdA), a plant-derived phenyl aziridine precursor, was recently characterized as a fully dissociated nonsteroidal antiinflammatory agent, acting via activation of the glucocorticoid receptor, thereby down-modulating nuclear factor-kappaB-mediated transactivation, but not supporting glucocorticoid response element-driven gene expression. The present study demonstrates the effectiveness of CpdA in inhibiting the disease progress in experimental autoimmune encephalomyelitis (EAE), a well-characterized animal model of multiple sclerosis. CpdA treatment of mice, both early and at the peak of the disease, markedly suppressed the clinical symptoms of EAE induced by myelin oligodendrocyte glycoprotein peptide immunization. Attenuation of the clinical symptoms of EAE by CpdA was accompanied by reduced leukocyte infiltration in the spinal cord, reduced expression of inflammatory cytokines and chemokines, and reduced neuronal damage and demyelination. In vivo CpdA therapy suppressed the encephalogenicity of myelin oligodendrocyte glycoprotein peptide-specific T cells. Moreover, CpdA was able to inhibit TNF- and lipopolysaccharide-induced nuclear factor-kappaB activation in primary microglial cells in vitro, in a differential mechanistic manner as compared with dexamethasone. Finally, in EAE mice the therapeutic effect of CpdA, in contrast to that of dexamethasone, occurred in the absence of hyperinsulinemia and in the absence of a suppressive effect on the hypothalamic-pituitary-adrenal axis. Based on these results, we propose CpdA as a compound with promising antiinflammatory characteristics useful for therapeutic intervention in multiple sclerosis and other neuroinflammatory diseases.

Death receptor signalling in central nervous system inflammation and demyelination

Death receptors (DRs) are members of the tumor necrosis factor receptor (TNF-R) superfamily that are characterised by the presence of a conserved intracellular death domain and are able to trigger a signalling pathway leading to apoptosis. Strong evidence suggests that DRs contribute to the pathology of tissue destructive diseases, including multiple sclerosis (MS), the most common inflammatory demyelinating disease of the central nervous system (CNS). Here, we review the evidence supporting a role for DRs in MS pathology and its implications for the development of therapeutic strategies for MS and other demyelinating pathologies of the CNS.

Paracaspase MALT1 Deficiency Protects Mice from Autoimmune-Mediated Demyelination

The paracaspase MALT 1 is a major player in lymphocyte activation and proliferation. MALT1 mediates Ag-induced signaling to the transcription factor NF-κB by functioning both as a scaffold protein and cysteine protease. We studied the role of MALT1 in the development of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. MALT1-knockout mice did not develop any clinical symptoms of EAE. In addition, lymphocyte and macrophage infiltration into the spinal cord was absent in MALT1-knockout mice, as were demyelination and proinflammatory gene expression. Adoptive transfer experiments showed that MALT1 deficiency in splenocytes is sufficient for EAE resistance. Moreover, autoreactive T cell activation was severely impaired in MALT1-deficient T cells, suggesting the inability of MALT1-deficient effector T cells to induce demyelinating inflammation in the CNS. Finally, the MALT1 substrates A20 and CYLD were completely processed in wild-type T cells during EAE, which was partially impaired in MALT1-deficient T cells, suggesting a contribution of MALT1 proteolytic activity in T cell activation and EAE development. Together, our data indicate that MALT1 may be an interesting therapeutic target in the treatment of multiple sclerosis.

A20 controls intestinal homeostasis through cell-specific activities

The transcription factor NF-κB is indispensable for intestinal immune homeostasis, but contributes to chronic inflammation and inflammatory bowel disease (IBD). A20, an inhibitor of both NF-κB and apoptotic signalling, was identified as a susceptibility gene for multiple inflammatory diseases, including IBD. Despite absence of spontaneous intestinal inflammation in intestinal epithelial cell (IEC) specific A20 knockout mice, we found additional myeloid-specific A20 deletion to synergistically drive intestinal pathology through cell-specific mechanisms. A20 ensures intestinal barrier stability by preventing cytokine-induced IEC apoptosis, while A20 prevents excessive cytokine production in myeloid cells. Combining IEC and myeloid A20 deletion induces ileitis and severe colitis, characterized by IEC apoptosis, Paneth and goblet cell loss, epithelial hyperproliferation and intestinal microbiota dysbiosis. Continuous epithelial cell death and regeneration in an inflammatory environment sensitizes cells for neoplastic transformation and the development of colorectal tumours in aged mice.

Pharmacological inhibition of MALT1 protease activity protects mice in a mouse model of multiple sclerosis.

BackgroundThe paracaspase mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is crucial for lymphocyte activation through signaling to the transcription factor NF-κB. Besides functioning as a scaffold signaling protein, MALT1 also acts as a cysteine protease that specifically cleaves a number of substrates and contributes to specific T cell receptor-induced gene expression. Recently, small molecule inhibitors of MALT1 proteolytic activity were identified and shown to have promising anticancer properties in subtypes of B cell lymphoma. However, information on the therapeutic potential of small compound inhibitors that target MALT1 protease activity in autoimmunity is still lacking.MethodsThe present study aimed to elucidate whether MALT1 protease inhibitors are also useful in the treatment of lymphocyte-mediated autoimmune pathologies such as multiple sclerosis (MS). For this, we studied the therapeutic potential of a recently identified inhibitor of MALT1 protease activity, the phenothiazine derivative mepazine, in the context of experimental autoimmune encephalomyelitis (EAE), the main animal model for MS.ResultsWe demonstrate that administration of mepazine prophylactically or after disease onset, can attenuate EAE. Importantly, while complete absence of MALT1 affects the differentiation of regulatory T (Treg) cells in vivo, the MALT1 protease inhibitor mepazine did not affect Treg development.ConclusionsAltogether, these data indicate that small molecule inhibitors of MALT1 not only hold great promise for the treatment of B cell lymphomas but also for autoimmune disorders such as MS.

Optineurin deficiency in mice is associated with increased sensitivity to Salmonella but does not affect proinflammatory NF-κB signaling.

Optineurin (OPTN) is an evolutionary conserved and ubiquitously expressed ubiquitin‐binding protein that has been implicated in glaucoma, Paget bone disease, amyotrophic lateral sclerosis, and other neurodegenerative diseases. From in vitro studies, OPTN was shown to suppress TNF‐induced NF‐κB signaling and virus‐induced IRF signaling, and was identified as an autophagy receptor required for the clearance of cytosolic Salmonella upon infection. To assess the in vivo functions of OPTN in inflammation and infection, we generated OPTN‐deficient mice. OPTN knockout mice are born with normal Mendelian distribution and develop normally without any signs of spontaneous organ abnormality or inflammation. However, no differences in NF‐κB activation could be observed in OPTN knockout mice or fibroblasts derived from these mice upon TNF or LPS treatment. Primary bone marrow‐derived macrophages from OPTN‐deficient mice had slightly impaired IRF signaling and reduced IFN type I production in response to LPS or poly(I,C). Finally, OPTN‐deficient mice were more susceptible to infection with Salmonella, confirming in vivo the importance of OPTN in bacterial clearance.

A20 Deficiency in Lung Epithelial Cells Protects against Influenza A Virus Infection

A20 negatively regulates multiple inflammatory signalling pathways. We here addressed the role of A20 in club cells (also known as Clara cells) of the bronchial epithelium in their response to influenza A virus infection. Club cells provide a niche for influenza virus replication, but little is known about the functions of these cells in antiviral immunity. Using airway epithelial cell-specific A20 knockout (A20AEC-KO) mice, we show that A20 in club cells critically controls innate immune responses upon TNF or double stranded RNA stimulation. Surprisingly, A20AEC-KO mice are better protected against influenza A virus challenge than their wild type littermates. This phenotype is not due to decreased viral replication. Instead host innate and adaptive immune responses and lung damage are reduced in A20AEC-KO mice. These attenuated responses correlate with a dampened cytotoxic T cell (CTL) response at later stages during infection, indicating that A20AEC-KO mice are better equipped to tolerate Influenza A virus infection. Expression of the chemokine CCL2 (also named MCP-1) is particularly suppressed in the lungs of A20AEC-KO mice during later stages of infection. When A20AEC-KO mice were treated with recombinant CCL2 the protective effect was abrogated demonstrating the crucial contribution of this chemokine to the protection of A20AEC-KO mice to Influenza A virus infection. Taken together, we propose a mechanism of action by which A20 expression in club cells controls inflammation and antiviral CTL responses in response to influenza virus infection.