The Role Of CaMKII In Obesity-induced Cardiac Remodelling And Arrythmogenesis And Its Mechanism

Background:The cellular mechanisms of obesity/hyperlipidemia-induced cardiac remodeling and arrhythmiogenesis not completely elucidated.Ca2+/calmodulin-dependent protein kinase II(CaMKII),a multifunctional serine/threonine kinase,has been reported to be involved in a variety of cardiovascular structural diseases and cardiac arrhythmias of different etiologies.However,its role in obesity/hyperlipidemia-induced cardiac remodeling and cardiac arrhythmia is still unknown.Objective:The objective of this study was to demonstrate the role of CaMKII in the pathogenesis of obesity/hyperlipidemia-induced cardiac remodeling and cardiac arrhythmogenesis.Methods:(1)To determine the role of CaMKII in obesity-induced cardiac remodeling,we build the cell model of saturated free fatty acids(palmitate)stimulated H9C2 cells in vitro,and high fat diet(HFD)-fed APOE-/-mice model in vivo,we then test the effects of pharmacological inhibition of CaMKII by KN93 or Myr-AIP on cardiac pathological injury(including cardiac apoptosis,hypertrophy and fibrosis as well as various pathological signaling events(including inflammation,oxidative stress,ER stress,autophagy and mitochondrial dysfunction)in the cell and mice model.(2)To determine the role of CaMKII in obesity-induced cardiac arrhythmias,we build the high fat diet(HFD)-fed APOE-/-mice model in vivo,and administrated the mice with CaMKII inhibitor,KN93(10mg/kg/2day).Electrophysiological study and epicardial activation mapping were performed in Langendorff-perfused heart.Expression of cardiac ion channels,gap junction proteins,Ca2+ handling proteins,and CaMKII were evaluated,coupled with histological analysis.Results:(1)In cardiac-derived H9C2 cells,palmitate treatment induced cell apoptosis coupled with activation of the mitochondrial apoptotic pathway,and cell hypertrophic and fibrotic responses.All of these alterations were inhibited by pharmacological inhibition of CaMKII with either of two specific inhibitors,Myr-AIP and KN93.In addition,an increased inflammatory response coupled with activation of the MAPKs and NF-κB signaling pathway,exaggerated oxidative stress,ER stress and autophagy were also observed in palmitate-treated H9C2 cells,while pretreatment with CaMKII inhibitors decreased these pathological signals.Furthermore,we also demonstrated that TLR4 is upstream signal of CaMKII in palmitate-treated H9C2 cells.In APOE-/-mice fed a high-fat diet(HFD)for 16 weeks,serum lipid profiles(FFAs,TG,TC)and blood glucose levels were significantly increased compared with mice fed a normal diet.In addition,apparent cardiac hypertrophy,fibrosis and apoptosis associated with increased inflammation,ER stress,and autophagy were also observed in the hearts of HFD-fed mice.However,all these changes were reversed by 8-weeks of KN93 peritoneal injections.KN93 also increased antioxidant defense as evidenced by increased expression of the Nrf2 system in the hearts of HFD-fed mice.(2)A hyperlipidemia condition was induced by HFD in the APOE-/-mice,which was associated with increased expression and activity of CaMKII in the hearts.In Langendorff-perfused hearts,HFD-induced heart showed increased arrhythmia inducibility,prolonged action potential duration,and decreased action potential duration alternans thresholds,coupled with slow ventricular conduction,connexin-43 upregulation,and interstitial fibrosis.Downregulation of ion channels including Cav1.2 and Kv4.2/Kv4.3 and disturbed Ca2+handling proteins were also observed in HFD-induced heart.Interestingly,all these alterations were significantly inhibited by KN93 treatment.Conclusions:(1)Our results demonstrate a critical role of CaMKII in the pathogenesis of obesity/hyperlipidemia-induced cardiac remodeling.Also,TLR4 may be an upstream signal of cardiac CaMKII under hyperlipidemia conditions.These results suggest that CaMKII has the potential to be a therapeutic target in the prevention of obesity/hyperlipidemia-induced cardiac remodeling.(2)Our results also demonstrated an adverse effect of metabolic components on cardiac electrophysiology and implicated an important role of CaMKII underlying this process.