Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an autosomal dominant cardiomyopathy characterised by progressive fibrofatty replacement of right ventricular myocytes, ventricular arrhythmias and sudden cardiac death. Genetic studies have demonstrated the central role of desmosomal proteins in this disease, as heterozygous mutations in PKP2 (Plakophilin-2), DSG2 (Desmoglein-2), DSC2 (Desmocollin-2), DSP (Desmoplakin) and JUP (Plakoglobin) are found in 50% of ARVC cases. However, physiopathological pathways remain to be elucidated. Numerous nonsense or frame-shift mutations suggestive of a haploinsufficiency mechanism have been reported. Moreover, electron-micrographs of ARVC cardiac tissue reproducibly show a drastic decrease in desmosomal length and adhesive strength. We thus hypothesized that a decrease in desmosomal protein expression at intercalated disks could be a general feature triggering ARVC.Methods
We compared DSG2, DSC2, JUP and PKP2 protein levels from seven independent ARVC hearts samples, using seven dilated cardiomyopathy (DCM) heart samples as controls. Ventricular sections were examined by immunofluorescence, and proteins extracts were used for immunoblot analysis.Results
Desmosomal proteins were localised at the intercalated disks in all patient samples as expected by immunochemistry, however a slight decrease in labelling intensity was observed in three of the patient samples. Immunoblotting demonstrated a marked decrease of DSG2 (-74% ± 14.3) and DSC2 (-43% ± 18.9) standardised to the cardiac specific protein actinin-2, in all ARVC patients. This observation was independent of the mutation status of the ARVC cases (only three patients were carriers of a cadherin mutation). No such modification was observed in DCM controls. By quantitative RT-PCR on ventricular mRNA, we verified that DSC2 and DSG2 transcript levels were similar in ARVC and DCM controls, suggesting that the decreased protein level results from a loss of cadherin stability rather than transcriptional regulation.Conclusion
Despite correct localization of cardiac desmosomal cadherin at intercalated disks, we observed a strong decrease in DSC2 and DSG2 in all human ARVC ventricular samples in our study. Cadherin decrease thus appears as a specific molecular signature for the disease, and likely results from a loss of stability. These results suggest a central role for cadherin in the mechanism triggering ARVC, not only through its mechanical effect on cardiomyocyte adhesion, but also possibly through signaling pathways implicated in physiological pathways.