CaMKII Activation Promotes Cardiac Electrical Remodeling and Increases the Susceptibility to Arrhythmia Induction in High-fat Diet-Fed Mice With Hyperlipidemia Conditions

Abstract

Background: Obesity/hyperlipidemia is closely related to both atrial and ventricular arrhythmias. CaMKII, a multifunctional serine/threonine kinase, has been involved in cardiac arrhythmias of different etiologies. However, its role in obesity/hyperlipidemia-related cardiac arrhythmia is unexplored. The aim of this was to determine the involvement of CaMKII in the process.

Methods: Adult male APOE mice were fed a high-fat diet (HFD), administrated with KN93 (10 mg·kg·2d), a specific inhibitor of CaMKII. Serum lipid and glucose profile, cardiac function, and surface electrocardiogram were determined. Electrophysiological study and epicardial activation mapping were performed in Langendorff-perfused heart. Expression of cardiac ion channels, gap junction proteins, Ca handling proteins, and CaMKII were evaluated, coupled with histological analysis.

Results: 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 Ca handling proteins were also observed in HFD-induced heart. Interestingly, all these alterations were significantly inhibited by KN93 treatment.

Conclusion: Our results demonstrated an adverse effect of metabolic components on cardiac electrophysiology and implicated an important role of CaMKII underlying this process.

FIGURE 1.

The characteristics of surface ECG recording in the HFD-fed mice model. Representative ECG recordings (A) and the comparison of ECG parameters (B) under anesthesia at 16th weeks. n = 7–8.

FIGURE 2.

KN93 administration improved electrophysiological properties of the heart in HFD-fed mice. A–B, Representative action potential figures and statistical analysis of 90% APDs at different a PCL in Langendorff-perfused isolated heart (n = 7). C–D, Representative electric ALT figures and statistical analysis of the ALT thresholds (n = 6). E–F, Representative images of MAP recording and arrhythmia induction in ventricle and atria by burst-pacing stimulation. The summary data for VA episodes and AA episodes were showed below (n = 8). *P < 0.05.

FIGURE 3.

KN93 administration improved the ventricular CV, CX43 upregulation, and cardiac fibrosis in HFD-induced hearts. A, Left ventricle epicardium activation mapping and ventricular CV analyzed by MEA in Langendorff-perfused isolated hearts. Activation starts with red and propagates towards blue. The summary data for CV is shown. B, Western blot analysis of Cx43 protein level in the heart tissue. C–D, Representative images of masson trichrome staining and sirius red staining of ventricle and atria, the summary data for interstitial fibrosis area were shown. n = 5. *P < 0.05.

FIGURE 4.

KN93 administration attenuated the downregulation of Cav1.2 and Kv4.2/Kv4.3 in HFD-induced heart. Western blot analysis of protein level of Cav1.2, Kv4.2 and Kv4.3 in the heart tissues. n = 5. *P < 0.05.

FIGURE 5.

KN93 administration reversed CaMKII activation and the disturbed Ca²⁺ handling proteins in HFD-induced heart. A, Western blot analysis of phosphorylated CaMKII (p-CaMKII) at T287 site and the total protein CaMKII level in the heart tissue. B, Western blot analysis of phosphorylated RyR2 (p-RyR2) at S2807 and S2814 site, and the total protein level of RyR2 in the heart tissue. C, Western blot analysis of phosphorylated phospholamban (p-PLB) at T17 site and the total protein level of SERCA2 and PLB in the heart tissues. n = 5. *P < 0.05.