Cardiac sympathetic neurons are additional cells affected in genetically determined arrhythmogenic cardiomyopathy.

Key points Arrhythmogenic cardiomyopathy (AC) is a familial cardiac disease, mainly caused by mutations in desmosomal genes, which accounts for most cases of stress‐related arrhythmic sudden death, in young and athletes. AC hearts display fibro‐fatty lesions that generate the arrhythmic substrate and cause contractile dysfunction. A correlation between physical/emotional stresses and arrhythmias supports the involvement of sympathetic neurons (SNs) in the disease, but this has not been confirmed previously. Here, we combined molecular, <italic>in vitro</italic> and <italic>ex vivo</italic> analyses to determine the role of AC‐linked DSG2 downregulation on SN biology and assess cardiac sympathetic innervation in desmoglein‐2 mutant (<italic>Dsg2mut/mut</italic>) mice. Molecular assays showed that SNs express DSG2, implying that DSG2‐mutation carriers would harbour the mutant protein in SNs. Confocal immunofluorescence of heart sections and 3‐D reconstruction of SN network in clarified heart blocks revealed significant changes in the physiologialc SN topology, with massive hyperinnervation of the intact subepicardial layers and heterogeneous distribution of neurons in fibrotic areas. Cardiac SNs isolated from <italic>Dsg2mut/mut</italic> neonatal mice, prior to the establishment of cardiac innervation, show alterations in axonal sprouting, process development and distribution of varicosities. Consistently, virus‐assisted DSG2 downregulation replicated, in PC12‐derived SNs, the phenotypic alterations displayed by <italic>Dsg2mut/mut</italic> primary neurons, corroborating that AC‐linked <italic>Dsg2</italic> variants may affect SNs. Our results reveal that altered sympathetic innervation is an unrecognized feature of AC hearts, which may result from the combination of cell‐autonomous and context‐dependent factors implicated in myocardial remodelling. Our results favour the concept that AC is a disease of multiple cell types also hitting cardiac SNs. Arrhythmogenic cardiomyopathy is a genetically determined cardiac disease, which accounts for most cases of stress‐related arrhythmic sudden death. Arrhythmogenic cardiomyopathy linked to mutations in desmoglein‐2 (DSG2) is frequent and leads to a left‐dominant form of the disease. Arrhythmogenic cardiomyopathy has been approached thus far as a disease of cardiomyocytes, but we here unveil that DSG2 is expressed, in addition to cardiomyocytes, by cardiac and extracardiac sympathetic neurons, although not organized into desmosomes. AC‐linked DSG2 downregulation primarily affect sympathetic neurons, resulting in the significant increase in cardiac innervation density, accompanied by alterations in sympathetic neuron distribution. Our data supports the notion that AC develops with the contribution of several ‘desmosomal protein‐carrying’ cell types and systems. [ABSTRACT FROM AUTHOR]