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Myocardial ischaemia-reperfusion (MIR) triggers a sterile inflammatory response important for myocardial healing, but which may also contribute to adverse ventricular remodelling. Such inflammation is initiated by molecular danger signals released by damaged myocardium, which induce innate immune responses by activating toll-like receptors (TLRs). Detrimental roles have been recently reported for TLR2, TLR3 and TLR4. The role of other TLRs is unknown. We therefore evaluated the role of TLR5, expressed at high level in the heart, in the development of myocardial damage and inflammation acutely triggered by MIR. TLR5(-/-) and wild-type (WT) mice were exposed to MIR (30 min ischaemia, 2 h reperfusion). We measured infarct size, markers of cardiac oxidative stress, myocardial phosphorylation state of mitogen-activated protein (MAP) kinases and AKT, expression levels of chemokines and cytokines in the heart and plasma, as well as cardiac function by echography and conductance volumetry. TLR5-deficient mice had normal cardiac morphology and function under physiological conditions. After MIR, the absence of TLR5 promoted an increase in infarct size and myocardial oxidative stress. Lack of TLR5 fostered p38 phosphorylation, reduced AKT phosphorylation and markedly increased the expression of inflammatory cytokines, whereas it precipitated acute LV (left ventricle) dysfunction. Therefore, contrary to the detrimental roles of TLR2, TLR3 and TLR4 in the infarcted heart, TLR5 is important to limit myocardial damage, inflammation and functional compromise after MIR.

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 high-mobility group box-1, the TLRs, the NLRP-3 receptor, and the inflammasome, as well as the transcription factor nuclear factor-κB.

Background: Inflammation comes out to be a critical biological process in the pathophysiology of myocardial infarction (MI). We hypothesize that this inflammation is triggered by necrotic cardiomyocytes (Cmc) that release a set of endogenous molecules (DAMPs: danger-associated molecular patterns) activating inflammatory responses in cardiac fibroblasts.Aim: Analyze in vitro the immune activation of cardiac fibroblasts exposed to necrotic Cmc conditioned media.Methods: Primary neonatal murine cardiac fibroblasts and Cmc were obtained by digestion of neonatal hearts and differential plating technique allowing a selection for cardiomyocytes and cardiac fibroblasts. Cmc were killed by necrotic stimuli including oxidants (hydrogen peroxide) and mechanic stresses (freeze-thaw). Necrosis was assessed using Hoechst/PI stainings. Fibroblasts were exposed to necrotic Cmc conditioned media and mRNA expression of inflammatory genes was measured by real-time PCR and ELISA. Activation of signaling pathways was analyzed by western blot. We used cardiac cells from Myd88-/-, Trif-/- and Nlrp3-/- animals to evaluate the contribution of TLRs/IL1-R and NLRP3 inflammasome in the sensing of necrotic DAMPs.Results: mRNA expression of chemokines such as MCP-1, MIP-2 and IP-10 were induced in fibroblasts exposed to necrotic Cmc conditioned media. Alternatively, fibroblasts exposed to necrotic fibroblasts conditioned media showed a lower increase in mRNA expression of these chemokines. In addition, in fibroblasts from Myd88-/- mice, response to Cmc conditioned media was fully abrogated whereas no difference was observed in Trif-/- and Nlrp3-/- fibroblasts.Conclusion: Cardiac fibroblasts are able to produce a rapid and specific inflammatory response to necrotic Cmc conditioned media involving the expression of neutrophil and monocyte chemoattractants. The dependence on MyD88 adaptor protein strongly suggests that this response relies on TLR/IL-1R signaling. These results engage cardiac fibroblasts as key players in post-MI inflammatory responses as they are able to sense DAMPs from necrotic Cmc and possibly recruit inflammatory cells.Research supported by the Swiss National Science Foundation, Grant n° 310030_135394/1 [ABSTRACT FROM AUTHOR]