Abstract
Background: Although it is critically important to understand the underlying molecular and electrophysiological changes that predispose to the induction and maintenance of atrial fibrillation (Af), the underlying mechanism of Af is still poorly defined. Af is characterized as the electrophysiological and membrane integrity abnormality of the atrial cells, and claudin-5, a tight junction protein, may be involved in the pathophysiology of Af, however, the role of claudin-5 in Af is unknown. Methods and Results: Cardiac tissues from the left atrial appendage were obtained from AF patients with rheumatic valvular heart disease undergoing modified radiofrequency ablation maze procedure with approval from local human research ethic review and normal left atrial appendages were obtained from non-AF donors. Western blot, immunofluorescence and transmission electron microscope showed the expression of claudin-5 significantly decreased in cardiomyocytes from left atrium of AF patients compared to non-AF donors. Then proteomics analysis was performed to screen the specific protein expression and signal pathway changed in AF heart tissue vs. non-AF heart tissue, and showed that 83 proteins were downregulated and 102 proteins were upregulated in the left atrial appendage of AF patients. Among them, DAG, CACNA2D2, MYL2 were downregulated and MCU was upregulated. KEGG pathway analysis showed these changes would lead to hypertrophic and dilated cardiomyopathy. Finally, claudin-5 shRNA AAV was injected in mouse left ventricle to knockdown claudin-5 in cardiomyocytes to observe whether change of claudin-5 affects the protein expression in KEGG pathway analysis. We found claudin-5 deficiency caused severe ventricular dilation, ST elevation and arrythmia, and the protein level of DAG, CACNA2D2 and MYL2 were downregulated and MCU was upregulated. Co-immunoprecipitation also confirmed the specific protein-protein interaction between these targeted proteins and claudin-5. Conclusion: We demonstrated that the decrease of claudin-5 in the left atrium of AF patients with rheumatic valvular heart disease. The mechanism of AF might be associated with claudin-5 downregulation-induced decrease of DAG, CACNA2D2, MYL2 and increase of MCU in cardiomyocytes.
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