Publications

Since first being described in the fruit fly Drosophila melanogaster, Toll-like receptors (TLRs) have proven to be of great interest to immunologists and investigators interested in the molecular basis to inflammation. They recognize pathogen-derived factors and also products of inflamed tissue, and trigger signaling pathways that lead to activation of transcription factors such as nuclear factor-kappaB and the interferon regulatory factors. These in turn lead to induction of immune and inflammatory genes, including such important cytokines as tumor necrosis factor-alpha and type I interferon. Much evidence points to a role for TLRs in immune and inflammatory diseases and increasingly in cancer. Examples include clear roles for TLR4 in sepsis, rheumatoid arthritis, ischemia/reperfusion injury, and allergy. TLR2 has been implicated in similar pathologic conditions and also in systemic lupus erythematosus (SLE) and tumor metastasis. TLR7 has also been shown to be important in SLE. TLR5 has been shown to be radioprotective. Recent advances in our understanding of signaling pathways activated by TLRs, structural insights into TLRs bound to their ligands and antagonists, and approaches to inhibit TLRs (including antibodies, peptides, and small molecules) are providing possiblemeans by which to interfere with TLRs clinically. Here we review these recent advances and speculate about whether manipulating TLRs is likely to be successful in fighting off different diseases.

We have gathered sufficient evidence to claim that inhibition of glycolysis impairs proinflammatory responses while favoring antiinflammatory outcomes. Specifically, modulation of glycolytic reprogramming can predominantly affect inflammatory immune or cancer cells, offering low on-target toxicity. Not surprisingly, this has been exploited by researchers focused on the development of novel therapeutic interventions. Here, we describe emerging metabolic targets and profile clinically approved and clinical-stage drugs that target metabolism as a critical mechanism of action. Therapies targeting glycolysis include both pharmacologic inhibitors of key enzymes and receptors antagonists, while approaches focused on the citric acid—or tricarboxylic acid cycle (TCA)—cycle additionally explore analogs of metabolites that possess cytokine-like properties. There are numerous preclinical programs and patents generated at university start-ups in addition to many biotech and big pharma-led projects aimed at targeting glycolysis and citric acid pathways clinically. Contrary to expectations, programs based on modulation of glycolysis and the citric acid cycle seem to hold the most promise in cancers, genetic, and autoimmune diseases, rather than the classical definition of physiological metabolic diseases.

Malonylation is a recently uncovered protein post-translational modification. It involves the attachment of a malonyl group to lysines, resulting in an extra 86 Da mass, as well as a change in charge comparable to that of phosphorylation. The enzyme responsible for malonylation has not yet been uncovered, but it seems like malonylation levels are dependent on malonyl-CoA concentration. The discovery of this new modification took place during a time in which immunometabolism became an emerging field and many studies into the metabolism of immune cells have recently highlighted the tight link existing between the metabolic status and the function of these cells. This led us to investigate whether protein malonylation might be a new mechanism by which the cell's metabolism can control the inflammatory response. We have been able to show that protein malonylation can be induced in macrophages following activation with various toll-like receptor ligands. In addition, the TLR4 ligand, LPS, can specifically increase malonylation of the glycolytic enzyme GAPDH in macrophages. Through mass-spec analysis we identified a single malonylated lysine present in GAPDH in resting macrophages, while two were identified following activation with LPS. Interestingly, GAPDH enzymatic activity increases under the same conditions. Furthermore, as part of the GAIT complex, GAPDH is capable of binding to the 3'-UTR region of the death-associated protein kinase (DAPK) mRNA and inhibit its translation. Our data would suggest that following activation, GAPDH releases DAPK mRNA. Overall, our results suggest that protein malonylation is an important signal for LPS signaling in macrophages, that may be responsible for controlling the functions of the glycolytic enzyme GAPDH following macrophage activation. This research is supported by Science Foundation Ireland.

Emerging evidence suggests that alterations in immunometabolism contribute to pathogenesis of inflammatory diseases, providing potential therapeutic targets. Anti-inflammatory drugs such as glucocorticoids, metformin, and dimethyl fumarate (DMF) modulate key immunometabolic pathways. Glucocorticoids boost itaconate production, which exerts anti-inflammatory effects via multiple targets, including by modification of cysteines on inflammatory proteins. Metformin, known for inhibiting gluconeogenesis in type 2 diabetes, also blocks mitochondrial Complex I and increases GDF-15, a regulator of food intake with anti-inflammatory properties, which may explain effects of metformin on inflammation. DMF, like itaconate, modifies cysteines on target proteins, notably KEAP1, leading to Nrf2 activation, which induces antioxidant enzymes and suppresses inflammatory gene expression. These immunometabolic actions suggest that targeting immune cell metabolism could provide new strategies for treating autoimmune diseases. This review explores recent advances in itaconate, GDF-15, and Nrf2 signaling and how harnessing these pathways may lead to novel anti-inflammatory therapies for patients with inflammatory diseases.

The post-receptor events which follow the binding of interleukin 1 (IL1) to cells are unclear. The present studies provide evidence for the activation of a guanine nucleotide binding protein (G protein) by IL1 in the membranes of an IL1 receptor-rich strain (NOB-1) of the EL4 murine thymoma line. IL1 alpha and beta increased the binding of the GTP analogue [35S]guanosine 5'-[gamma-thiol]trisphosphate (GTP gamma S) to membranes prepared from these cells. By 1 min after addition of IL1 there was a 2-fold enhancement in binding which was dose dependent in the range 0.1-100 ng/ml. A qualitatively similar result was obtained with IL1 beta although it was 10 times less potent. Specific neutralizing antisera to IL1 alpha and IL1 beta abolished the response. Experiments in which the concentration of [35S]GTP gamma S was varied revealed that IL1 increased the affinity of the binding sites for [35S]GTP gamma S and not their number. IL1 alpha was shown to stimulate GTPase activity in the membranes, the time and concentration dependence of this was similar to that observed for increased [35S]GTP gamma S binding. Half-maximal enhancement of [35S]GTP gamma S binding by IL1 alpha, measured after 4 min, occurred at 5% IL1 receptor occupancy. Maximal stimulation was achieved when 30% of receptors were occupied. Experiments with pertussis and cholera toxins revealed that pretreating membranes with pertussis toxin (100 ng/ml) inhibited by 50% the IL1-induced [35S]GTP gamma S binding and [gamma-32P]GTP hydrolysis. Cholera toxin (100 ng/ml) was without effect. However, both pertussis and cholera toxins at concentrations of 100 ng/ml inhibited IL1-induced IL2 secretion in EL4 NOB-1 cells. These results show that the IL1 receptor of a responsive thymoma line activates, and may be coupled to, a G protein(s). This is a possible mechanism of IL1 signal transduction.

Luke O'Neill is professor of biochemistry in the School of Biochemistry and Immunology at Trinity College Dublin, and his main research focus is innate immunity and its key output, inflammation. His work has explored the key sensors and mediators of infection, including the Toll-like receptors, inflammasomes and cytokines in the interleukin-1 (IL-1) family. Luke received the Royal Irish Academy Gold Medal for Life Sciences in 2012 and the European Federation of Immunology Societies Medal in 2014. He was elected a member of the European Molecular Biology Organisation (EMBO) in 2005 and a Fellow of the Royal Society in 2016. In this interview, Luke talks about the necessary collaboration between immunologists and cancer scientists, inflammaging, and his rock-star alter-ego as frontman of The Metabollix.

The innate immune sensor RIG-I responds to infection by binding to viral double-stranded RNA (dsRNA). In this issue of Cell, Kowalinski et al. (2011) and Luo et al. (2011) reveal the structure of RIG-I, and in combination with functional analyses, they show how RIG-I recognizes viral RNA to initiate signaling and a type I interferon response.

No abstract is provided for this article.

MicroRNAs (miRNAs) are recently discovered regulators of gene expression, and early studies have indicated that they have a role in the regulation of haematopoiesis, the immune response and inflammation. They bind the 3'UTR of target mRNAs and mainly prevent translation of the protein product. Dysregulation of these molecules has been shown to be a hallmark of cancer and now investigators are examining their role in the pathogenesis of inflammatory diseases. miR-146 and miR-155 have been a particular focus for investigators, and these two miRNAs have been shown to be induced by proinflammatory stimuli such as interleukin 1, tumour necrosis factor α (TNFα) and Toll-like receptors (TLRs). They have also been detected in synovial fibroblasts and rheumatoid synovial tissue. Both have multiple targets, with miR-146 inhibiting TLR signalling and miR-155 regulating Th1 cells and also, interestingly, positively regulating mRNA for TNFα. The potential of miRNAs for improving our understanding of the pathogenesis of diseases such as rheumatoid arthritis, and for developing potentially new treatments for these diseases, is substantial.

No abstract is provided for this article.