Abstract
Angiotensin II (Ang II) induced Atrial fibrillation (AF) often accompanied with reduced ATRAP which is a negative modulator of Ang II type 1 receptor (AT1R). Melatonin can protect against AF, but the underlying molecular mechanism remains poorly understood. In this study, Ang II was used to induce AF, and AF inducibility and duration were documented telemetrically. Ang II-infused mice had a higher AF incidence, which was associated with atrial fibrosis, inflammation, and oxidative stress. Melatonin partially inhibited these effects, and enforced expression of siRNA-ATRAP in atria counteracted the beneficial role of melatonin. Specifically, melatonin inhibited expression of Ang II-induced proteasome and immunoproteasome subunits β2, β2i, β5, and β5i as well as their corresponding trypsin-like and chymotrypsin-like activities and blocked ATRAP degradation. In turn, this inhibited AT1R-mediated NF-κB signaling, transforming growth factor (TGF)-β1/Smad signaling in the atria, and thereby affected atrial remodeling and AF. Melatonin receptor inhibition by the chemical inhibitor luzindole partially inhibited the inhibitory effects of melatonin on proteasome activity and also Ang II-induced pathological changes in the atria. Overall, our study demonstrates that melatonin protects against Ang II-induced AF by inhibiting proteasome activity and stabilizing ATRAP expression, and these effects are partially dependent on melatonin receptor activation.