Inflammation in arrhythmogenic cardiomyopathy: the driver or the passenger?

Background information Despite decades of research, the diagnosis and management of arrhythmogenic cardiomyopathies (ACM) remain challenging, mostly owing to poor understanding of disease mechanisms. Heretofore, inflammation was regarded as a consequence of myocyte death. However, recent studies suggest that inflammation is in fact driving both the myocardial injury and arrhythmias that characterise ACM through activation of the NFκB pathway. We have previously shown that pathological processes occurring in the hearts of ACM patients are mirrored by equivalent abnormalities in the buccal epithelium. As such, NFκB is activated in both cardiac and buccal cells during periods of unstable disease activity. Purpose/Aim We sought to characterize NFκB signalling in buccal mucosa cells from paediatric ACM-patients and silent gene carriers. We aimed to correlate disease status and activation of NFκB signalling with any shifts in key junctional proteins that have been previously shown to occur alongside ACM onset and progression. Methods 48 paediatric ACM patients, alongside silent gene carriers for a desmosomal (n=44) or Titin (TTN) variant (n=7), were recruited from a single paediatric referral centre. Buccal swabs were collected every 3-6 months and subjected to immunocytochemistry. Presence of immunoreactive signal for RelA/p65 in nuclei of buccal cells was used as a reliable indicator of aberrantly active NFκB signalling. Distribution of the desmosomal proteins desmoplakin (DSP), plakophilin 1 (PKP1) and plakoglobin (JUP), as well as the gap junction protein connexin43 (Cx43), was also examined. Results In 13 individuals (40%), changes in the distribution of junctional proteins in the buccal epithelium coincided with aberrant activation of NFκB. Multiple instances of protein changes alongside positive RelA signal was observed in 2 affected individuals. In 3 patients, RelA signal corresponded with both protein signal depression and clinical deterioration (inc. worsening LVEF, progressive LV/RV dysfunction, syncope, NSVT). Furthermore, DSP variant carriers showed more episodes of positive RelA than PKP2 carriers (DSP n=12, PKP2 n=6), both in single (DSP n=7, PKP2 n=4) and multiple (DSP n=5, PKP2 n=2) instances of immune signalling, agreeing well with the clinical observations that DSP-variant carriers exhibit a more pronounced inflammatory response. Conclusion Analysis of serial cheek smears showed that aberrant activation of the NFκB pathway precedes and likely promotes cascade redistribution of junctional proteins both in children diagnosed with ACM as well as silent carriers of ACM-causing variants. Our results add further evidence to the theory that inflammation is not a consequence, but actually a primary driving force, of ACM pathogenesis.