The Role Of Fatty Triglyceride Lipase In Angiotensin Ⅱ-induced Atrial Fibrillation In Mice And The Underlying Molecular Mechanism

Background Atrial fibrillation(AF)is the most common persistent arrhythmia in clinical practice,which is related to the morbidity and mortality of various cardiovascular diseases.Atrial structural and electrophysiological remodeling are the main pathophysiological mechanisms of AF.Studies have demonstrated that abnormal lipid metabolism plays an important role in the occurrence and development of AF.Adipose triglyceride lipase(ATGL)is a key enzyme involved in intracellular degradation of triacylglycerols and plays an important role in lipid and energy metabolism.ATGL deficiency can reduce the protein level of peroxisome proliferator activated receptor(PPARα)and inhibit the oxidation of fatty acids and activate inflammatory response in myocardium.However,the role of ATGL in the regulation of angiotensin Ⅱ(Ang Ⅱ)-induced AF remains unclear.AimsTo determine the role of ATGL in Ang Ⅱ-induced AF in mice and the underlying mechanism,and will provide new evidence for elucidating the molecular mechanism and identifying new intervention targets for AF development.Methods:1.Animal model establishmentMale 8-10 weeks old ATGL knockout mice(ATGL-KO)and their wild(WT)littermates were infused with Ang Ⅱ(2000 ng/kg/min)using an osmotic mini-pump for 1-3 weeks to establish AF model.Intracardiac pacing was conducted by inserting a Millar catheter via right jugular vein into the right atrium and ventricle.Electrical stimulation was given to induce the occurrence of AF.The PPARα agonist clofibric acid(CA,50 mg/kg,once every other days,intraperitoneal injection)was administered to ATGL-KO mice during Ang Ⅱ infusion.2.Measurement of left atrial volumeEchocardiography was performed to evaluate left atrial dimension by using a Vevo 1100High-Resolution Imaging System3.Histopathological examinationsHematoxylin & Eosin(H&E)staining was performed to evaluate the degree of inflammatory cell infiltration in the atria;Masson(Masson’s trichrome)staining was used to detect the extent of atrial fibrosis;Dihydroethidium(DHE)staining was conducted to measure superoxide production.4.Real-time quantitative PCR and western blot analysisReal-time quantitative PCR was performed to analyze the expression levels of ATGL,IL-1β,IL-6 and TNF-αin the atria.Western blot was used to detect protein levels of ATGL,PPARα,p-P65,p65,p-AKT,AKT,TGF-β,p-Smad2/3,Kir2.1,KCNA5,and Cx43 in the atria.5.Statistical analysis methodsAll data are presented as mean ± standard deviation(Mean ± SEM),and analyzed using SPSS 19.0 statistical package.P value < 0.05 were considered statistically significant.Results1.After 3 weeks of Ang Ⅱ infusion,ATGL expression at both m RNA and protein levels was time-dependently downregulated in atrial tissues compared with saline control.2.After 3 weeks of Ang Ⅱ infusion,ATGL-KO mice had a significant increase in higher incidence and duration of AF in mice,left atrial dilation,atrial fibrosis,inflammatory cell infiltration and superoxide production as well as the protein levels of p-p65,p-AKT,TGF-β1,p-Smad2/3 and abnormalities of Kir2.1 KCNA5 and Cx43 compared with WT controls.However,there was no significant difference between the WT and ATGL-KO groups after saline treatment.3.After 3 weeks of Ang Ⅱ infusion,the downregulation of ATGL in Ang Ⅱ-infused WT mice was further reduced in the atrial tissues of ATGL-KO mice.Conversely,treatment of ATGL-KO mice with the PPARα agonist Clofibric Acid(CA)significantly attenuated Ang Ⅱ-induced increase in the incidence and duration of AF,left atria dilation as well as activation of P65、p-AKT、AKT、TGF-β、Smad2/3and abnormalities of Kir2.1、KCNA5and Cx43 compared with vehicle control.ConclusionsOur results identify ATGL-KO enhances AF inducibility through inhibiting PPARαand activation of the downstream signaling pathways(TGF-β-Smad2/3 and NF-κB),and suggest that activating ATGL may be a new therapeutic target for treating hypertensive AF.