Abstract Body (Do not enter title and authors here): Background information: Despite decades of research, diagnosis and management of arrhythmogenic cardiomyopathies (ACM) remain challenging owing mostly to poor understanding of disease mechanisms. Heretofore, inflammation was regarded as a consequence of myocyte death. However, recent studies suggest that inflammation in fact drives the myocardial injury and arrhythmia phenotypes characterising ACM through activation of the NFκB pathway. We previously demonstrated that pathological processes occurring in the hearts of ACM patients are mirrored by equivalent abnormalities in the buccal epithelium, with NFκB activation occurring both in cardiac and buccal cells during periods of unstable disease activity.

Aim: We sought to characterize NFκB signalling in buccal mucosa cells from paediatric ACM-patients and silent gene carriers. We correlated disease status and NFκB activation with shifts in junctional proteins previously linked to ACM onset and progression.

Methods: 48 paediatric ACM patients and 44 silent gene carriers (desmosomal n=44; Titin n=7) were recruited from a single paediatric referral centre. Buccal swabs were collected every 3-6 months over a 7-year period and subjected to immunocytochemistry. Immunoreactive signal for RelA/p65 in buccal cell nuclei served as a marker for aberrant NFκB activation. Distribution of the desmosomal proteins desmoplakin (DSP), plakophilin 1 (PKP1), plakoglobin (JUP), and the gap junction protein connexin43 (Cx43) were also examined.

Results: In 13 individuals (15%), junctional protein distribution changes in buccal epithelium correlated with NFκB activation. Two affected individuals showed multiple instances of protein changes alongside nuclear RelA signal. In 3 patients, positive RelA signal correlated with both protein signal depression and clinical deterioration (worsening LVEF, LV/RV dysfunction, syncope, NSVT). DSP variant carriers (n=12) exhibited more nuclear RelA episodes than PKP2 carriers (n=6), both in single (DSP n=7, PKP2 n=4) and multiple (DSP n=5, PKP2 n=2) instances, aligning well with clinical observations of a more pronounced inflammatory response in DSP carriers.

Conclusion: Analysis of serial check smears revealed that NFκB activation precedes and likely promotes cascade redistribution of junctional proteins in both children with ACM and silent gene carriers. These findings add further evidence to the belief that inflammation is a primary driver of ACM pathogenesis.