Postmortem mRNA expression patterns in left ventricular myocardial tissues and their implications for forensic diagnosis of sudden cardiac death

Abstract

Sudden cardiac death (SCD), which is primarily caused by lethal heart disorders resulting in structural and arrhythmogenic abnormalities, is one of the prevalent modes of death in most developed countries. Myocardial ischemia, mainly due to coronary artery disease, is the most common type of heart disease leading to SCD. However, postmortem diagnosis of SCD is frequently complicated by obscure histological evidence. Here, we show that certain mRNA species, namely those encoding hemoglobin A1/2 and B (Hba1/2 and Hbb, respectively) as well as pyruvate dehydrogenase kinase 4 (Pdk4), exhibit distinct postmortem expression patterns in the left ventricular free wall of SCD subjects when compared with their expression patterns in the corresponding tissues from control subjects with non-cardiac causes of death. Hba1/2 and Hbb mRNA expression levels were higher in ischemic SCD cases with acute myocardial infarction or ischemic heart disease without recent infarction, and even in cardiac death subjects without apparent pathological signs of heart injuries, than control subjects. By contrast, Pdk4 mRNA was expressed at lower levels in SCD subjects. In conclusion, we found that altered myocardial Hba1/2, Hbb, and Pdk4 mRNA expression patterns can be employed as molecular signatures of fatal cardiac dysfunction to forensically implicate SCD as the primary cause of death.

Fig. 1.

Cardiac and coronary features according to different causes of death. Heart weight (A) and the thickness of the left ventricular free-wall (B) were measured in subjects who died due to traumatic death (TD), ischemic heart disease (IH), acute myocardial infarction (MI), or non-ischemic sudden cardiac death (NI), and are expressed as means ± SEM. Extent of occlusion at the site where a major stenosis was found in the left anterior descending arteries (LCA; C) or the right coronary arteries (RCA; D) is expressed as the mean ± SEM (%). Data were statistically evaluated by one-way ANOVA followed by the Newman-Keuls test (*p < 0.05 and ** p < 0.01 vs. TD).

Fig. 2.

Hba1/2, Hbb, and Pdk4 mRNA expression in the left ventricular free wall in association with different causes of death. Hba1/2, Hbb, and Pdk4 mRNA expression profiles were quantitatively analyzed by real-time qRT-PCR in subjects who died due to traumatic death (TD), ischemic heart disease (IH), acute myocardial infarction (MI), or non-ischemic sudden cardiac death (NI). (A) Data were normalized to Gapdh mRNA levels and expressed as the mean ± SEM in arbitrary units (A.U.), where the mean values of the TD group were set to 1. Data were statistically evaluated by one-way ANOVA followed by the Newman-Keuls test (*p < 0.05 and **p < 0.01 vs. TD). (B) Relative mRNA levels were expressed by box-and-whisker diagrams with log scales. Median values are indicated by the lines in the middle of the boxes.

Fig. 3.

Hba1/2, Hbb, and Pdk4 mRNA expression in the occipital lobes of cerebral cortices. Hba1/2, Hbb, and Pdk4 mRNA expression profiles were analyzed quantitatively by real-time qRT-PCR in subjects who died due to traumatic death (TD) or sudden cardiac death (SCD) including both ischemic and non-ischemic heart injuries. (A) Data were normalized to Gapdh mRNA levels and expressed as the mean ± SEM in arbitrary units (A.U.), where the mean values of the TD group were set to 1. (B) Relative mRNA levels are shown in box-and-whisker diagrams with log scales. Median values are indicated by the lines in the middle of the boxes.

Fig. 4.

Pairwise analyses of relative mRNA abundances of Hba or Hbb in relation to Pdk4. (A) Pairwise analyses of Hba1/2 or Hbb mRNA levels in comparison with those of Pdk4. Normalized mRNA levels of Hba1/2 (upper) or Hbb (lower) relative to Gapdh were bi-directionally plotted in relation to those of Pdk4 on a logarithmic scale. Each symbol and error bar indicates the mean ± SEM. (B) Ratio of relative Hba1/2 (upper) or Hbb. (lower) mRNA level to that of Pdk4 in each case were calculated and expressed as means ± SEM. Data were statistically evaluated by one-way ANOVA followed by the Newman-Keuls test (*p < 0.05 and **p < 0.01 vs. TD). (C) The log ratios of Hba1/2 or Hbb to Pdk4 were expressed as box-and-whisker diagrams. Median values are indicated by the lines in the middle of the boxes.