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Signal transduction in inflammation: from gene to organism

Research project P6/18 (Research action P6)

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Inflammation is a physiological process that normally leads to recovery from injury by healing. However, if targeted destruction and assisted repair are not properly phased, inflammation can lead to persistent tissue damage by activated leukocytes, including reorganization of the extracellular matrix. Cytokines produced by the activated leukocytes trigger signal transduction cascades and positive feedback loops which will further lead to chronic/persistent effects. This chain of events is observed in several pathologies that are considered as acute or chronic 'inflammatory' diseases where one or several signal(s) or checkpoints in the control of the inflammatory process are deregulated. Importantly, an emerging link between chronic inflammation and cancer is being established and some cancers can also be considered as chronic inflammatory diseases. Mediators released by different cell types (neutrophils, macrophages, mast cells,...) control the proper phasing of the inflammation process by steering gene transcription in target cells. The transcription factor NF-B has a central role in controlling these events.

The first scientific objective of our research proposal will be the understanding of the signal transduction intermediates involved in the control of NF-B activation. Two main signalling pathways controlling NF-B activation are known: (i) the classical pathway which is activated upon recognition of microbes and pro-inflammatory cytokines, including the Tumour Necrosis Factor (TNF) and (ii) the alternative pathway which is triggered by some ligands from the TNF family such as BAFF, LT, CD40L,….. The first part of the project will be focused on a better understanding of the intermediates involved in these signalling pathways and on their regulation coming from interactions between activating and inhibiting signalling molecules and receptors. We will also characterize NF-B-dependent cellular promoters (IL-6) activated by pro-inflammatory cytokines and the role of chromatin structure (nucleosome remodelling, histone post-translational modifications) in their transcriptional regulation. Among the NF-B target genes, we will mainly pay attention to intracellular targets (e.g. cytoskeletal proteins, protein kinases and phosphatases) and extracellular marker molecules (e.g. matrix metalloproteinases). The activation of the NALP1 and NALP2/3 inflammasomes and the subsequent caspase 1-mediated processing and secretion of the pro-inflammatory cytokines IL-1 and IL-18 will also be investigated in various inflammatory cells, especially in neutrophils and macrophages. More recently, it has been demonstrated that the stressosome complex, containing PIDD, RAIDD, caspase-2, caspase-8, TRAF2, NEMO and Hsp90 also mediates NF-B activation after exposure to several forms of stress such as DNA damage. The role of caspases in this complex will be examined.

Inflammatory mediators lead not only to gene regulation but in some cases also to cell death. The second objective will focus on signal transduction leading to cell death. The molecular features underlying apoptosis and necrosis induced by TNF and Reactive Oxygen Species (ROS) will be studied. ROS generation will be triggered by physiologically and therapeutically relevant stimuli in order to fully understand how they can either signal to cell death, both dependent or independent on caspase signalling, or trigger the release/expression of pro-inflammatory, chemotactic, and angiogenic mediators (eicosanoids, VEGF, MMPs,…). Particular emphasis will be placed on unravelling the functional role of caspase- (caspase-1, -2, -7) and protein kinase-driven (RIP1 kinase,..) pathways in the control of cell death (apoptosis, necrosis, autophagic cell death).

Starting from the complex and multi-factorial setting of inflammatory diseases in the living organism, the molecular processes involved in the onset of inflammation and/or its further pathological progression will be studied in animal models. Hereto, a dual approach will be followed. An in-depth analysis of regulatory checkpoints in specific experimental models will go hand in hand with their transposition to the molecular level in order to identify the underlying signalling pathways, and inversely a selected group of genes and molecules will be validated in the organism for their causal/regulatory function. Experimental models representing different types of inflammatory disorders and of relevance for human disease will be applied, primarily extrinsic allergic alveolitis (Th1-driven immune disorder) and experimental asthma (Th2-driven immune disorder), Pseudomonas-induced pneumonia (local infectious disorder), and sepsis- and endotoxemia-induced acute shock (systemic infectious and endotoxin-driven disorder, respectively). The information thus obtained will be instrumental for a better understanding of the function of these processes and molecules at the level of the organism.

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