Defective Desmosomal Adhesion Causes Arrhythmogenic Cardiomyopathy by involving an Integrin-αVβ6/TGF-β Signaling Cascade

Abstract

Background: Arrhythmogenic Cardiomyopathy (ACM) is characterized by progressive loss of cardiomyocytes with fibrofatty replacement, systolic dysfunction and life-threatening arrhythmias. A substantial proportion of ACM is caused by mutations in genes of the desmosomal cell-cell adhesion complex, but the underlying mechanisms are not well understood. So far, treatment options are only symptomatic. Here, we investigate the relevance of defective desmosomal adhesion for ACM development and progression. Methods: We mutated the binding site of desmoglein-2 (DSG2), a crucial desmosomal adhesion molecule in cardiomyocytes. This DSG2-W2A mutation abrogates the tryptophan swap, a central interaction mechanism of DSG2 based on structural data. Impaired adhesive function of DSG2-W2A was confirmed by cell-cell dissociation assays and force spectroscopy measurements by atomic force microscopy. We next generated a DSG2-W2A knock-in mouse model, which was analyzed by echocardiography and histological and bio-molecular techniques including RNA sequencing, transmission electron and super-resolution microscopy. The results were compared to ACM patient samples and their relevance was confirmed in cardiac slice cultures. Results: The DSG2-W2A mutation induced impaired binding and desmosomal adhesion dysfunction on cellular and molecular level. Mice bearing this mutation develop a severe cardiac phenotype recalling the characteristics of ACM, including cardiac fibrosis, impaired systolic function and arrhythmia. A comparison of the transcriptome of mutant mice with ACM patient data suggested deregulated integrin-αVβ6 and subsequent TGF-β signaling as driver of cardiac fibrosis. Accordingly, blocking antibodies targeting integrin-αVβ6 or inhibition of TGF-β receptor signaling both led to reduced expression of pro-fibrotic markers in cardiac slice cultures. Conclusions: Here, we show that disruption of desmosomal adhesion is sufficient to induce ACM, which confirms the dysfunctional adhesion hypothesis. Mechanistically, deregulation of integrin-αVβ6 signaling was identified as a central step towards fibrosis. This highlights the value of this model to discern mechanisms of cardiac fibrosis and to identify and test novel treatment options for ACM.