Background: The beta 3-adrenoceptor (β3-AR) is closely associated with energy metabolism. This study aimed to explore the role of β3-AR in energy remodeling in a rabbit model of pacing-induced atrial fibrillation (AF). Methods: Rabbits with a sham-operation or pacing-induced AF were used for this study, and the latter group was further divided into three subgroups: 1) the pacing group, 2) the β3-AR agonist (BRL37344)-treated group, and 3) the β3-AR antagonist (SR59230A)-treated group. Atrial electrogram morphology and surface ECG were used to monitor the induction of AF and atrial effective refractory period (AERP). RT-PCR and western blot (WB) were used to show alterations in β3-AR and metabolic-related protein. Results: RT-PCR and WB results showed that β3-AR was significantly upregulated in the pacing group, and that it corresponded with high AF inducibility and significantly decreased AERP₂₀₀ and ATP production in this group. Inhibition of β3-AR decreased the AF induction rate, reversed AERP₂₀₀ reduction, and restored ATP levels in the AF rabbits. Further activation of β3-AR using agonist BRL37344 exacerbated AF-induced metabolic disruption. Periodic acid Schiff (PAS) and Oil Red O staining showed β3-AR-dependent glycogen and lipid droplet accumulation in cardiac myocytes with AF. Glucose transporter-4 (GLUT-4) and CD36, key transporters of glucose and fatty acids, were downregulated in the pacing group. Expression of carnitine-palmitoyltransferase I (CPT-1), a key regulator in fatty acid metabolism, was also significantly downregulated in the pacing group. Reduced glucose transportation and fatty acid oxidation could be restored by inhibition of β3-AR. Furthermore, key regulators of metabolism, peroxisome proliferator-activated receptor-α (PPARα) and PPAR co-activator (PGC-1α) can be regulated by pharmacological intervention of the β3-AR. Conclusions: β3-AR is involved in metabolic protein remodeling in AF. PPARα/PGC-1α signaling pathway might be the relevant down-stream molecular machinery in response to AF-induced activation of β3-AR. β3-AR might be a novel target in AF treatment.

Background/Aims: Angiotensin II receptor blockers (ARBs) have been proved to be effective in preventing atrial structural and electrical remodelinq in atrial fibrillation (AF). Previous studies have shown that parasympathetic remodeling plays an important role in AF. However, the effects of ARBs on atrial parasympathetic remodeling in AF and the underlying mechanisms are still unknown. Methods: Canines were divided into sham-operated, pacing and valsartan + pacing groups. Rats and HL-1 cardiomyocytes were divided into control, angiotensin II (Ang II) and Ang II + valsartan groups, respectively. Atrial parasympathetic remodeling was quantified by immunocytochemical staining with anti-choline acetyltransferase (ChAT) antibody. Western blot was used to analysis the protein expression of neurturin. Results: Both inducibility and duration were increased in chronic atrial rapid-pacing canine model, which was significantly inhibited by the treatment with valsartan. The density of ChAT-positive nerves and the protein level of neurturin in the atria of pacing canines were both increased than those in sham-operated canines. Ang II treatment not only induced atrial parasympathetic remodeling in rats, but also up-regulated the protein expression of neurturin. Valsartan significantly prevented atrial parasympathetic remodeling, and suppressed the protein expression of neurturin. Meanwhile, valsartan inhibited Ang II -induced up-regulation of neurturin and MAPKs in cultured cardiac myocytes. Inhibition of MAPKs dramatically attenuated neurturin up-regulation induced by Ang II. Conclusion: Parasympathetic remodeling was present in animals subjected to rapid pacing or Ang II infusion, which was mediated by MAPKs/neurturin pathway. Valsartan is able to prevent atrial parasympathetic remodeling and the occurrence of AF via inhibiting MAPKs/neurturin pathway.