Adenosine A3 Receptor induced Delayed Preconditioning: Essential Role of Nuclear Factor κB, Nitric Oxide Synthase and Mitochondrial KATP channels

Abstract

We investigated the signaling mechanism of adenosine A3 receptor (A3AR) induced delayed cardioprotection. Mice pretreated with selective A3AR agonist, N6-(3-iodobenzyl) adenosine-5′-N-methyluronamide (IB-MECA) demonstrated significant reduction in necrosis and improvement in post-ischemic myocardial performance 24hrs later as compared to vehicle-treated controls. Pretreatment with A3AR antagonist, MRS1191 abolished delayed cardioprotection while selective adenosine A1 receptor antagonist, 8-8-cyclopentyl-1,3-dipropyl xanthine (DPCPX) had no effect. Electrophoretic mobility shift assay demonstrated increased nuclear factor-κB (NF-κB) binding in nuclear extracts following A3AR stimulation, which was diminished by MRS1191 and NF-κB inhibitor, pyrro-lidinediethyldithiocarbamate (PDTC). Also, the cardioprotection was abrogated by PDTC as well as targeted ablation of p50 subunit of NF-κB in mice. The inhibition of inducible nitric oxide synthase (iNOS) with S-methylisothiourea and targeted disruption of iNOS gene abolished the protective effect of A3AR stimulation. Expression of iNOS mRNA and NO production were enhanced after 6 and 24hrs of IB-MECA treatment respectively. MRS1191 and PDTC but not DPCPX blocked NO generation after A3AR stimulation. MitoKATP channel blocker, 5-hydroxydecanoate abolished the protective effect of A3AR. These studies suggest that signaling cascade involving NF-κB activation, synthesis of NO from iNOS and subsequent opening of mitoKATP channel play an essential role in A3AR-induced delayed phase of ischemic protection in the heart. We propose that selective activation of A3AR with its pharmacological drugs can potentially be used to enhance the endogenous defense mechanisms that may provide long lasting ischemic protection of the ischemic heart.