Expression of Connexin 43 in the Myocardium in Sudden Unexplained Nocturnal Death Syndrome

Abstract

Background: Sudden unexplained nocturnal death syndrome (SUNDS) occurs predominantly in Southeast Asian people including Koreans. SUNDS is problematic for forensic pathologists because the diagnosis depends on the “exclusion of diagnosis.” Moreover, the pathogenesis of SUNDS is still unclear although some cases are known to be intimately related to the Brugada syndrome. Connexin43 (Cx43) is a principal protein of gap junction in adult cardiac myocytes, being distributed to the intercalated discs and phosphorylated in normal condition. Ischemia and hypoxia alter the expression of total Cx43 (tCx43) resulting in redistribution of non-phosphorylated Cx43 (npCx43) to the sarcoplasm or lateral cell borders of cardiac myocytes by continuing dephosphorylation. This study aimed to compare the immunoexpression pattern of Cx43 in the cardiac myocytes of SUNDS and ischemic heart disease (IHD). Methods: The study group included SUNDS victims (SUNDS group, N=26; all males; aged 22-43 years; median age, 30.4 years), had a characteristic premortem history and negative autopsy findings. The control group was individuals who died suddenly due to IHD with severe coronary atherosclerosis, showing no myocardial ischemic change (IHD group, N=24; 22 males and 2 females; aged 35-76 years; median age, 53.5 years). Immunostaining was performed using the ABC method. The primary antibodies were rabbit polyclonal anti-Cx43 antibody (1:2,000, Sigma-Aldrich, St. Louis, MO, USA), which react to both phosphorylated forms of Cx3 and npCx43, and mouse monoclonal anti-npCx43 antibody (1:100, Life Technologies, Frederick, MD, USA), which detect only npCx43. Expression patterns were grouped as no staining (NO), intercalated disc pattern (ID pattern, confined mostly to the intercalated discs), and redistribution pattern (R pattern, extended to the lateral borders of sarcoplasmic membrane). The chi-square test was used to analyze the relationship of tCx43 and npCx43 immunoexpression pattern with SUNDS group and IHD group. A p-value less than 0.05 was considered statistically significant. Results: 1. Expression of tCx43 in the SUNDS and IHD group. The results of tCx43 expression in the cardiac myocytes of the SUNDS and IHD group are summarized: In the SUNDS group, 7/26 cases (26.9%) displayed the NO pattern; 19/26 cases (73.1%), the ID pattern. The R pattern was not observed in the SUNDS group. In the IHD group, 14/24 cases (58.3%) displayed the ID pattern; 10/24 cases (41.7%), the R pattern. The NO pattern was not observed in the IHD group. There was a significant difference in the tCx43 expression between the SUNDS and IHD group (p<0.001). 2. Expression of npCx43 in the SUNDS and IHD group. The results of npCx43 expression in the cardiac myocytes of the SUNDS and IHD group are summarized: In the SUNDS group, 1/26 cases (3.8%) displayed the NO pattern; 23/26 cases (88.5%), the ID pattern; and 2/26 (7.7%), the R pattern. In the IHD group, 7/24 cases (29.2%) displayed the ID pattern; 17/24 cases (70.8%), the R pattern. There was a significant difference in the npCx43 expression between the SUNDS and IHD group (p<0.001). Conclusion: There was a significantly different expression of both tCx43 and npCX43 between the SUNDS and IHD group. A greater reduction in both tCx43 and npCx43 a more delayed redistribution pattern was seen in the myocardium of SUNDS when compared with IHD. In conclusion, these results suggest that the reduced Cx43 expression in SUNDS may be inherent and indicate a risk of arrhythmia.