Toll-like receptors (TLRs)-2 and -4 are important proteins in innate immunity, recognizing microbial products and eliciting host defense responses. Both use the adapter proteins MyD88 and MyD88 adapter-like (Mal) to activate signaling pathways. Here we report that Mal but not MyD88 interacts with caspase-1, the enzyme that processes the precursors of the proinflammatory cytokines IL-1beta and IL-18. The interaction was found in a yeast two-hybrid screen and was confirmed by reciprocal GST pull-downs and coimmunoprecipitation of endogenous proteins. We were unable to implicate Mal in regulating caspase-1 activation. However, we found that Mal was cleaved by caspase-1 and that inhibition of caspase-1 activity blocked TLR2- and TLR4-mediated NF-kappaB and p38 MAP kinase activation but not IL-1 or TLR7 signaling, which are Mal independent. These responses, and the induction of TNF, were also attenuated in caspase-1-deficient cells. Finally, unlike wild-type Mal, a mutant Mal, which was not cleaved by caspase-1, was unable to signal and acted as a dominant negative inhibitor of TLR2 and TLR4 signaling. Our study therefore reveals a role for caspase-1 in the regulation of TLR2 and TLR4 signaling pathways via an effect on Mal. This functional interaction reveals an important aspect of the coordination between TLRs and caspase-1 during the innate response to pathogens.
Background— Reperfusion therapy for myocardial infarction is hampered by detrimental inflammatory responses partly via Toll-like receptor (TLR) activation. Targeting TLR signaling may optimize reperfusion therapy and enhance cell survival and heart function after myocardial infarction. Here, we evaluated the role of TLR2 as a therapeutic target using a novel monoclonal anti-TLR2 antibody. Method and Results— Mice underwent 30 minutes of ischemia followed by reperfusion. Compounds were administered 5 minutes before reperfusion. Cardiac function and dimensions were assessed at baseline and 28 days after infarction with 9.4-T mouse magnetic resonance imaging. Saline and IgG isotype treatment resulted in 34.5±3.3% and 31.4±2.7% infarction, respectively. Bone marrow transplantation experiments between wild-type and TLR2-null mice revealed that final infarct size is determined by circulating TLR2 expression. A single intravenous bolus injection of anti-TLR2 antibody reduced infarct size to 18.9±2.2% ( P =0.001). Compared with saline-treated mice, anti-TLR2–treated mice exhibited less expansive remodeling (end-diastolic volume 68.2±2.5 versus 76.8±3.5 μL; P =0.046) and preserved systolic performance (ejection fraction 51.0±2.1% versus 39.9±2.2%, P =0.009; systolic wall thickening 3.3±6.0% versus 22.0±4.4%, P =0.038). Anti-TLR2 treatment significantly reduced neutrophil, macrophage, and T-lymphocyte infiltration. Furthermore, tumor necrosis factor-α, interleukin-1α, granulocyte macrophage colony-stimulating factor, and interleukin-10 were significantly reduced, as were phosphorylated c-jun N-terminal kinase, phosphorylated p38 mitogen-activated protein kinase, and caspase 3/7 activity levels. Conclusions— Circulating TLR2 expression mediates myocardial ischemia/reperfusion injury. Antagonizing TLR2 just 5 minutes before reperfusion reduces infarct size and preserves cardiac function and geometry. Anti-TLR2 therapy exerts its action by reducing leukocyte influx, cytokine production, and proapoptotic signaling. Hence, monoclonal anti-TLR2 antibody is a potential candidate as an adjunctive for reperfusion therapy in patients with myocardial infarction.
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Abstract Lipids play crucial roles in immunity and inflammation via controlling immune cell metabolism and function. In particular, phospholipids (PLs), as essential structural elements of biological membranes, critically orchestrate innate and inflammatory responses through coordinating membrane plasticity and cellular signaling. Researches over the past decade have revealed the versatile roles of PL metabolism in innate immunity and inflammation as well as their differential physiological and pathological consequences, highlighting PL metabolites or enzymes as promising potential biomarkers and therapeutic targets. Further unveiling the spatiotemporal characteristics and mechanistic links between phospholipid metabolism, innate immunity, and the development of inflammatory diseases will add new insights into immunometabolism underlying health and diseases, and may suggest new strategies for manipulating PL metabolism toward novel immunotherapy against harmful inflammation and cancer. In this review, we discussed the roles of distinct lipids in innate immunity and inflammation, with particular focus on how phospholipid metabolism and membrane homeostasis are actively reprogrammed during the innate immune response, and how the crosstalk between phospholipids and innate immunity finally orchestrates the outcome of host defense and tissue homeostasis. We also discussed how dysregulation of PL metabolism contributes to pathological processes in inflammatory diseases, such as autoimmune diseases, cardiovascular diseases and cancers, and the potential strategies of restoring PL homeostasis for disease treatment.
Significance: Reactive oxygen species (ROS) are often considered to be undesirable toxic molecules that are generated under conditions of cellular stress, which can cause damage to critical macromolecules such as DNA. However, ROS can also contribute to the pathogenesis of cancer and many other chronic inflammatory disease conditions, including atherosclerosis, metabolic disease, chronic obstructive pulmonary disease, neurodegenerative disease, and autoimmune disease. Recent Advances: The field of ROS biology is expanding, with an emerging paradigm that these reactive species are not generated haphazardly, but instead produced in localized regions or in specific subcellular compartments, and this has important consequences for immune system function. Currently, there is evidence for ROS generation in extracellular spaces, in endosomal compartments, and within mitochondria. Intriguingly, the specific location of ROS production appears to be influenced by the type of invading pathogen (i.e., bacteria, virus, or fungus), the size of the invading pathogen, as well as the expression/subcellular action of pattern recognition receptors and their downstream signaling networks, which sense the presence of these invading pathogens. Critical Issues: ROS are deliberately generated by the immune system, using specific NADPH oxidases that are critically important for pathogen clearance. Professional phagocytic cells can sense a foreign bacterium, initiate phagocytosis, and then within the confines of the phagosome, deliver bursts of ROS to these pathogens. The importance of confining ROS to this specific location is the impetus for this perspective. Future Directions: There are specific knowledge gaps on the fate of the ROS generated by NADPH oxidases/mitochondria, how these ROS are confined to specific locations, as well as the identity of ROS-sensitive targets and how they regulate cellular signaling.
The human IKK [IκB (inhibitor of NF-κB) kinase] family has four members; they are the central kinases of innate immunity. Two members, IKKα and IKKβ, the so-called canonical members, phosphoryate IκBα, leading to activation of the transcription factor NF-κB (nuclear factor κB), which controls the expression of many immune and inflammatory genes. The IKK-related proteins TBK-1 (TANK-binding kinase 1) and IKKϵ have a different substrate – IRF3 (interferon regulatory factor 3) – which regulates a different set of genes, the products of which include Type I interferons. Toll-like receptors (TLRs) such as the lipopolysaccharide receptor TLR4 or the poly(I:C) receptor TLR3 activate each of the IKKs, but the pro-inflammatory cytokine IL-1 (interleukin 1), which signals in a broadly similar way to the TLRs, has so far been shown to activate only the canonical IKKs. In this issue of the Biochemical Journal, Clark et al. bring new insights into the regulation of IKKs. They demonstrate that IL-1 is in fact able to activate IKKϵ/TBK-1, which occurs via IKKα/IKKβ. The consequence of this is not IRF3 activation, but a negative feedback effect on IKKα/IKKβ. This provides us with yet another regulatory feedback loop in a system already replete with control mechanisms. It attests yet again to the importance of keeping these innate immune pathways in check, since if they proceed uncontrolled, inflammatory diseases can occur. Importantly, this study utilized new and specific inhibitors of these kinases, suggesting that the interpretation of any effects the compound might have in vivo may be complex, since for example the inhibition of IKKϵ/TBK-1 might actually have a pro-inflammatory effect.
Conference Article| February 01 1996 Activation of NFkB and potentiation of TNF-induced NFkB activation by ceramide analogues in leukemic cell lines despite the absence of an observed sphingomyelinase signalling event Marion P. Boland; Marion P. Boland 1Biochemistry Department, Trinity College Dublin, Ireland Search for other works by this author on: This Site PubMed Google Scholar Steven J. Foster; Steven J. Foster ∗VIM Research, Zeneca Pharmaceuticals, Cheshire SK10 4TG, UK. Search for other works by this author on: This Site PubMed Google Scholar Luke A. J. O'neill Luke A. J. O'neill Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1996) 24 (1): 1S. https://doi.org/10.1042/bst024001s Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn Email Cite Icon Cite Get Permissions Citation Marion P. Boland, Steven J. Foster, Luke A. J. O'neill; Activation of NFkB and potentiation of TNF-induced NFkB activation by ceramide analogues in leukemic cell lines despite the absence of an observed sphingomyelinase signalling event. Biochem Soc Trans 1 February 1996; 24 (1): 1S. doi: https://doi.org/10.1042/bst024001s Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1996 Biochemical Society1996 Article PDF first page preview Close Modal You do not currently have access to this content.
Toll‐like receptors (TLRs) play a critical role in the induction of the immune response to invading pathogens. The detection of pathogens by TLRs initiates a signalling cascade that results in the activation of transcription factors such as nuclear factor (NF)‐ κ B and interferon regulatory factors leading to the production of pro‐inflammatory cytokines and type 1 interferons. Five cytoplasmic adaptors, MyD88, Mal, Trif, TRAM and SARM, are utilized by the TLRs to activate these signalling pathways. Through the years the main focus of research has been on the activation and function of TLRs in monocytic cells. This review discusses several additional roles of TLRs. TLR activation plays a role in influencing the differentiation of haematopoietic stem cells. Their activation also prevents apoptosis in neutrophils following pathogen invasion. B cells and T cells proliferation and differentiation is influenced by TLR activation and the possible therapeutic benefits of using TLR ligands for the treatment of chronic lymphocytic leukaemia will also be discussed.
