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 (A20(AEC-KO)) mice, we show that A20 in club cells critically controls innate immune responses upon TNF or double stranded RNA stimulation. Surprisingly, A20(AEC-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 A20(AEC-KO) mice. These attenuated responses correlate with a dampened cytotoxic T cell (CTL) response at later stages during infection, indicating that A20(AEC-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 A20(AEC-KO) mice during later stages of infection. When A20(AEC-KO) mice were treated with recombinant CCL2 the protective effect was abrogated demonstrating the crucial contribution of this chemokine to the protection of A20(AEC-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

Enterocyte-specific A20 deficiency sensitizes to tumor necrosis factor–induced toxicity and experimental colitis

A20 is a nuclear factor κB (NF-κB) target gene that encodes a ubiquitin-editing enzyme that is essential for the termination of NF-κB activation after tumor necrosis factor (TNF) or microbial product stimulation and for the prevention of TNF-induced apoptosis. Mice lacking A20 succumb to inflammation in several organs, including the intestine, and A20 mutations have been associated with Crohn’s disease. However, ablation of NF-κB activity, specifically in intestinal epithelial cells (IECs), promotes intestinal inflammation. As A20 deficiency sensitizes cells to TNF-induced apoptosis yet also promotes NF-κB activity, it is not clear if A20 deficiency in IECs would exacerbate or ameliorate intestinal inflammation. We generated mice lacking A20 specifically in IECs. These mice did not show spontaneous intestinal inflammation but exhibited increased susceptibility to experimental colitis, and their IECs were hypersensitive to TNF-induced apoptosis. The resulting TNF-driven breakdown of the intestinal barrier permitted commensal bacterial infiltration and led to systemic inflammation. These studies define A20 as a major antiapoptotic protein in the intestinal epithelium and further indicate that defects in A20 might contribute to inflammatory bowel disease in humans

A20 critically controls microglia activation and inhibits inflammasome-dependent neuroinflammation

Microglia, the mononuclear phagocytes of the central nervous system (CNS), are important for the maintenance of CNS homeostasis, but also critically contribute to CNS pathology. Here we demonstrate that the nuclear factor kappa B (NF-kappa B) regulatory protein A20 is crucial in regulating microglia activation during CNS homeostasis and pathology. In mice, deletion of A20 in microglia increases microglial cell number and affects microglial regulation of neuronal synaptic function. Administration of a sublethal dose of lipopolysaccharide induces massive microglia activation, neuroinflammation, and lethality in mice with microgliaconfined A20 deficiency. Microglia A20 deficiency also exacerbates multiple sclerosis (MS) like disease, due to hyperactivation of the NIrp3 inflammasome leading to enhanced interleukin-113 secretion and CNS inflammation. Finally, we confirm a NIrp3 inflammasome signature and IL-1 beta expression in brain and cerebrospinal fluid from MS patients. Collectively, these data reveal a critical role for A20 in the control of microglia activation and neuroinflammation

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

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

The nuclear factor kappa B (NF-kappa B) 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-kappa B 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-kappa B 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

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-kappa B 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

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

Background: The paracaspase mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is crucial for lymphocyte activation through signaling to the transcription factor NF-kappa B. 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. Methods: The 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. Results: We 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. Conclusions: Altogether, 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