Evidence of Sialylation pathways alteration in peripheral blood of Brugada Syndrome patients

Abstract

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): RICERCA CORRENTE, Italian Ministry of Health Background Brugada syndrome (BrS) is a cardiac arrhythmia associated with an increased risk of sudden cardiac death (SCD). BrS is considered a genetic disorder, and the most commonly mutated gene is SCN5A, which encodes the alpha subunit of the voltage-gated cardiac sodium channel (NaV1.5). Mutations of SCN5A generally cause impairment of NaV1.5 function, resulting in alteration of the action potential. However, mutations of SCN5A are responsible for only 30% of BrS cases. Therefore, it is conceivable that other mechanisms such as post-translational modifications (PTMs) could affect NaV1.5 activity. Among others, sialylation may alter ion channel activity by carrying a sugar with a negative charge. Alterations in sialylation have previously been described in several cardiovascular diseases, including myocardial infarction, Chagas disease, and congenital disorders of glycosylation, a family of diseases affecting the heart. For these reasons, the aim was to study alterations in sialylation in BrS patients to get new information about the pathogenesis of BrS. Materials and Methods Peripheral blood mononuclear cells (PBMCs) were collected from BrS patients and healthy controls. To characterize the protein sialylation status of PBMCs, SNA lectin, which is sialic acid-binding proteins, was used by Western blot and flow cytometry. Gene expression of enzymes involved in the biosynthesis, activation, transfer, degradation, and recycling of sialic acid was examined in PBMCs by real-time PCR. Results The extracellular and intracellular sialylation levels of PBMCs differed between BrS patients and controls. In particular, CD3+/CD4+ T cells exhibited a lower significant amount of sialic acid. Moreover, gene expression of enzymes involved in the biosynthesis and activation of sialic acid was downregulated in patients compared to controls. In contrast, the sialyltransferases St3Gal1, St3Gal4, and St6Gal2, enzymes responsible for binding sialic acid to the protein surface, showed significant enzyme-specific differences between BrS patients and controls. Moreover, the levels of sialyltransferases and sialylated proteins are inversely correlated with the epicardial area of the cardiac pathological substrate and with potential duration, two clinical indicators of BrS severity. Discussion These preliminary results demonstrate the involvement of sialylation in BrS syndrome and suggest that impairment of the sialylation process may be associated with the onset and/or manifestation of BrS. In addition, biochemical alteration of cells of the BrS immune system was reported for the first time, supporting the hypothesis that BrS is a systemic disease whose final manifestation is an increased risk of SCD.