Loss of αT-catenin alters the hybrid adhering junctions in the heart and leads to dilated cardiomyopathy and ventricular arrhythmia following acute ischemia

It is generally accepted that the intercalated disc (ICD) required for mechano-electrical coupling in the heart consists of three distinct junctional complexes: adherens junctions, desmosomes and gap junctions. However, recent morphological and molecular data indicate a mixing of adherens junctional and desmosomal components, resulting in a 'hybrid adhering junction' or 'area composita'. The alpha-catenin family member alpha T-catenin, part of the N-cadherin-catenin adhesion complex in the heart, is the only alpha-catenin that interacts with the desmosomal protein plakophilin-2 (PKP2). Thus, it has been postulated that alpha T-catenin might serve as a molecular integrator of the two adhesion complexes in the area composita. To investigate the role of alpha T-catenin in the heart, gene targeting technology was used to delete the Ctnna3 gene, encoding alpha T-catenin, in the mouse. The alpha T-catenin-null mice are viable and fertile; however, the animals exhibit progressive cardiomyopathy. Adherens junctional and desmosomal proteins were unaffected by loss of alpha T-catenin, with the exception of the desmosomal protein PKP2. Immunogold labeling at the ICD demonstrated in the alpha T-catenin-null heart a preferential reduction of PKP2 at the area composita compared with the desmosome. Furthermore, gap junction protein Cx43 was reduced at the ICD, including its colocalization with N-cadherin. Gap junction remodeling in alpha T-catenin-knockout hearts was associated with an increased incidence of ventricular arrhythmias after acute ischemia. This novel animal model demonstrates for the first time how perturbation in alpha T-catenin can affect both PKP2 and Cx43 and thereby highlights the importance of understanding the crosstalk between the junctional proteins of the ICD and its implications for arrhythmogenic cardiomyopathy.