An autoantibody profile detects Brugada syndrome and identifies abnormally expressed myocardial proteins

Abstract

Aims Brugada syndrome (BrS) is characterized by a unique electrocardiogram (ECG) pattern and life-threatening arrhythmias. However, the Type 1 Brugada ECG pattern is often transient, and a genetic cause is only identified in <25% of patients. We sought to identify an additional biomarker for this rare condition. As myocardial inflammation may be present in BrS, we evaluated whether myocardial autoantibodies can be detected in these patients. Methods and results For antibody (Ab) discovery, normal human ventricular myocardial proteins were solubilized and separated by isoelectric focusing (IEF) and molecular weight on two-dimensional (2D) gels and used to discover Abs by plating with sera from patients with BrS and control subjects. Target proteins were identified by mass spectrometry (MS). Brugada syndrome subjects were defined based on a consensus clinical scoring system. We assessed discovery and validation cohorts by 2D gels, western blots, and ELISA. We performed immunohistochemistry on myocardium from BrS subjects (vs. control). All (3/3) 2D gels exposed to sera from BrS patients demonstrated specific Abs to four proteins, confirmed by MS to be α-cardiac actin, α-skeletal actin, keratin, and connexin-43, vs. 0/8 control subjects. All (18/18) BrS subjects from our validation cohorts demonstrated the same Abs, confirmed by western blots, vs. 0/24 additional controls. ELISA optical densities for all Abs were elevated in all BrS subjects compared to controls. In myocardium obtained from BrS subjects, each protein, as well as SCN5A, demonstrated abnormal protein expression in aggregates. Conclusion A biomarker profile of autoantibodies against four cardiac proteins, namely α-cardiac actin, α-skeletal actin, keratin, and connexin-43, can be identified from sera of BrS patients and is highly sensitive and specific, irrespective of genetic cause for BrS. The four involved proteins, along with the SCN5A-encoded Nav1.5 alpha subunit are expressed abnormally in the myocardium of patients with BrS.

Serum Anti-Heart and Anti-Intercalated Disk Autoantibodies: Novel Autoimmune Markers in Cardiac Sarcoidosis

“…This is not surprising, taking into consideration that myosin is the most abundant protein in the myocardium and that myosin has also been identified as a key autoantigenic target also in postinfectious immune-mediated diseases, such as rheumatic heart disease and Chagas cardiomyopathy [ 23 , 30 , 31 , 32 ]. Similarly, AIDAs and/or other autoantibody specificities to the intercalated disk proteins [ 33 ] are found in lymphocytic, giant-cell and sarcoidotic myocarditis, as well as in arrhythmogenic right ventricular cardiomyopathy [ 33 ] and in Brugada syndrome [ 34 ]. Thus, our findings suggest that in lymphocytic, giant-cell and sarcoidotic myocarditis, as well as in arrhythmogenic right ventricular cardiomyopathy and Brugada syndrome, all highly arrhythmogenic diseases, with similar and often overlapping clinical features, autoimmunity to myosin and intercalated disk proteins may be a common immunopathogenic link.…”

The Role of Autoantibodies in Arrhythmogenesis

“…Brugada syndrome constitutes a further primary arrhythmia syndrome next to LQTS and SQTS. It is widely accepted that a genetic mutation in a cardiac ion channel is the main cause of the condition, although structural changes and inflammatory processes have been attributed a pathogenic role [34]. Autoantibodies targeting α-cardiac actin, α-skeletal muscle actin, keratin-24, and connexin-43 have now been revealed as biomarkers of Brugada syndrome [34].…”

“…It is widely accepted that a genetic mutation in a cardiac ion channel is the main cause of the condition, although structural changes and inflammatory processes have been attributed a pathogenic role [34]. Autoantibodies targeting α-cardiac actin, α-skeletal muscle actin, keratin-24, and connexin-43 have now been revealed as biomarkers of Brugada syndrome [34]. The functional role of these autoantibodies is not clear, and further studies will be needed to clarify the pathomechanisms underlying the autoimmune response [34].…”

“…Autoantibodies targeting α-cardiac actin, α-skeletal muscle actin, keratin-24, and connexin-43 have now been revealed as biomarkers of Brugada syndrome [34]. The functional role of these autoantibodies is not clear, and further studies will be needed to clarify the pathomechanisms underlying the autoimmune response [34].…”

The year in cardiovascular medicine 2020: arrhythmias

“…In total, 18/18 BrS subjects demonstrated this autoantibody profile vs. 0/8 normal controls and 0/20 cardiomyopathy cases, which included arrhythmogenic right ventricular cardiomyopathy (ARVC), hypertrophic cardiomyopathy (HCM), and dilated cardiomyopathy (DCM) patients. 50 In a subgroup of BrS patients, each of these proteins and the sodium channel protein type 5 alpha subunit (NaV1.5) aggregated in the sarcoplasm of myocardial cells. The mechanism as to why antibodies to these proteins identified BrS cases is unclear but could relate to sarcolemmal membrane damage either due to a myocarditic process in the disease course or abnormal cell adhesion resulting in an immune response.…”