Role of TLR-8 in the activation of nuclear factor κB by oxidative stress in cardiac myocytes

Growing evidence from patients with heart failure and from experimental animal models implicates effecters of innate immunity in the pathogenesis of this syndrome. The expression of the innate immunity signaling protein, Toll-like receptor 4 (TLR4), is increased in cardiac myocytes in situ and in failing myocardium, but the mechanism by which TLRs may be activated in the failing heart remains unclear. We report that TLR2, which is expressed in cardiac myocytes, participates in the response of these cells to oxidative stress, a major contributor to the pathogenesis of cardiac dysfunction. Hydrogen peroxide increased nuclear factor kappaB (NF-kappaB) activation in Chinese hamster ovary fibroblasts that overexpress TLR2 but not in normal or TLR4-overexpressing Chinese hamster ovary cells, an effect that was abrogated by an alpha -TLR2 antibody. In neonatal rat ventricular myocytes, the alpha -TLR2 antibody inhibited hydrogen peroxide-induced nuclear translocation of NF-kappaB and activator protein-1 (AP-1), Inhibition of TLR2 had no effect on tumor necrosis factor alpha -induced NF-kappaB or AP-1 activation, on the DNA binding of the basal transcription factor Oct-1, or on hydrogen peroxide-induced phosphorylation of p38 MAP kinase. Importantly, oxidative stress-induced cytotoxicity was enhanced by blocking TLR2. Given the importance of cytotoxicity and apoptosis to the pathology of the ischemic heart, an anti-apoptotic effect of TLR2 in cardiac myocytes exposed to elevated levels of ROS may limit further cardiac dysfunction.