Activation of AP-1 Contributes to the β-Adrenoceptor-Mediated Myocardial Induction of Interleukin-6

The induction of proinflammatory cytokines in stressed myocardium is considered an innate immune response, but the role of β-adrenergic signaling in this proinflammatory response and the mechanisms of cardioprotection by β-blockers are not fully understood. In the present study, we analyzed interleukin-6 (IL-6) formation and promoter activation in β-adrenoceptor-stimulated neonatal rat cardiomyocytes, in transgenic mice with cardiac overexpression of β1-adrenoceptors, and in failing human myocardium. IL-6 formation and release in cultured cardiomyocytes under β-adrenoceptor stimulation requires the activation of activating protein-1 (AP-1) binding sites and of cAMP response elements (CRE) in the IL-6 promoter, but this release (140 ± 6 pg/mL medium under 10−6 M isoproterenol vs. 81 ±3 pg/mL unstimulated, P< 0.05) is moderate compared with that under inflammatory stimulation (855 ± 44 pg/mL, endotoxin 0.1µg/mL). Similarly, IL-6 is induced together with CRE- and AP-1 activation in the left ventricle (LV) of β1-transgenic mice before the onset of failure. However, we observed IL-6 induction with activation of NF-κB in addition to CRE and AP-1 in β1-transgenic mice at the age of 22 weeks and in explanted human LV after full development of failure. Treatment with β-blockers lowered myocardial IL-6 as well as AP-1, NF-κB, and CRE activation. Therefore, the activation of AP-1 and CRE is part of β-adrenergic signal transduction for IL-6 induction in nonfailing and failing cardiomyocytes, whereas NF-κB activation contributes only in overloaded failing myocardium.