Abstract:The production of various reactive oxidant species in excess of endogenous antioxidant defense mechanisms promotes the development of a state of oxidative stress, with significant biological consequences. In recent years, evidence has emerged that oxidative stress plays a crucial role in the development and perpetuation of inflammation, and thus contributes to the pathophysiology of a number of debilitating illnesses, such as cardiovascular diseases, diabetes, cancer, or neurodegenerative processes. Oxidants affect all stages of the inflammatory response, including the release by damaged tissues of molecules acting as endogenous danger signals, their sensing by innate immune receptors from the Toll-like (TLRs) and the NOD-like (NLRs) families, and the activation of signaling pathways initiating the adaptive cellular response to such signals. In this article, after summarizing the basic aspects of redox biology and inflammation, we review in detail the current knowledge on the fundamental connections between oxidative stress and inflammatory processes, with a special emphasis on the danger molecule highmobility group box-1, the TLRs, the NLRP-3 receptor, and the inflammasome, as well as the transcription factor nuclear factor-κB.

Regulated by histone acetyltransferases and deacetylases (HDACs), histone acetylation is a key epigenetic mechanism controlling chromatin structure, DNA accessibility, and gene expression.

Recognition of pathogens and altered self must be efficient and highly specific to orchestrate appropriate responses while limiting excessive inflammation and autoimmune reaction to normal self. AIM2 is a member of innate immune sensors that detects the presence of DNA, arguably the most conserved molecules in living organisms. However, AIM2 achieves specificity by detecting altered or mislocalized DNA molecules. It can detect damaged DNA, and the aberrant presence of DNA within the cytosolic compartment such as genomic DNA released into the cytosol upon loss of nuclear envelope integrity. AIM2 is also a key sensor of pathogens that detects the presence of foreign DNA accumulating in the cytosol during the life cycle of intracellular pathogens including viruses, bacteria, and parasites. AIM2 activation initiates the assembly of the inflammasome, an innate immune complex that leads to the activation of inflammatory caspases. This triggers the maturation and secretion of the cytokines IL-1β and IL-18. It can also initiate pyroptosis, a proinflammatory form of cell death. The AIM2 inflammasome contributes to physiological responses and diseases. It is a key player in host defenses, but its deregulation can contribute immune-linked diseases, such as autoinflammatory and autoimmune pathologies. Moreover, AIM2 may play a role in cancer development. Recent studies have shown that the detection of self-DNA species by AIM2 is an important factor that contributes to diseases associated with perturbation of cellular homeostasis. Thus, in addition of being a sensor of pathogen associated molecular patterns (PAMPs), the AIM2 inflammasome is emerging as a key guardian of cellular integrity.

Myocardial infarction (MI) induces a sterile inflammatory response which contributes to adverse cardiac remodeling. The initiating mechanisms of this response remain incompletely defined. We found that necrotic cardiomyocytes released a heat-labile pro-inflammatory signal activating MAP kinases and NF-κB in cardiac fibroblasts, with secondary production of cytokines. This response was abolished in Myd88−/− fibroblasts, but was unaffected in nlrp3-deficient fibroblasts. Despite MyD88-dependency, the response was TLR-independent, as explored in TLR reporter cells, pointing to the implication of the IL-1 pathway. Indeed, necrotic cardiomyocytes released IL-1α, but not IL-1β, and the immune activation of cardiac fibroblasts was abrogated by an IL-1 receptor antagonist and an IL-1α blocking antibody. Moreover, immune responses triggered by necrotic Il1a−/− cardiomyocytes were markedly reduced. In vivo, mice exposed to MI released IL-1α in the plasma, and post-ischemic inflammation was attenuated in Il1a−/− mice. Thus, our findings identify IL-1α as a crucial early danger signal triggering post-MI inflammation.