MicroRNAs (miRNAs) are very short (18–24 nucleotides) nucleic acids that are expressed in a number of biological tissues and have been shown to be more resistant to extreme temperatures and pH compared to longer RNA molecules, like mRNAs. As miRNAs contribute to diverse biological process and respond to various kinds of cellular stress, their utility as diagnostic biomarkers and/or therapeutic targets has recently been explored. Here, we have evaluated the usefulness of miRNA quantification during postmortem examination of cardiac tissue from acute myocardial infarction (AMI) patients. Cardiac tissue was collected within one week of the patient’s death and either frozen (19 samples) or fixed in formalin for up to three years (36 samples). RNA integrity was evaluated with an electropherogram, and it appears that longer RNAs are fragmented after death in the long-term fixed samples. Quantitative PCR was also performed for seven miRNAs and three other small RNAs in order to determine the appropriate controls for our postmortem analysis. Our data indicate that miR-191 and miR-26b are more suitable than the other types of small RNA molecules as they are stably detected after death and long-term fixation. Further, we also applied our quantitation method, using these endogenous controls, to evaluate the expression of three previously identified miRNA biomarkers, miR-1, miR-208b, and miR-499a, in formalin-fixed tissues from AMI patients. Although miR-1 and miR-208b decreased (1.4-fold) and increased (1.2-fold), respectively, in the AMI samples compared to the controls, the significance of these changes was limited by our sample size. In contrast, the relative level of miR-499a was significantly decreased in the AMI samples (2.1-fold). This study highlights the stability of miRNAs after death and long-term fixation, validating their use as reliable biomarkers for AMI during postmortem examination.

MicroRNAs (miRNAs) are small non-coding RNAs responsible for fine-tuning of gene expression at post-transcriptional level. The alterations in miRNA expression levels profoundly affect human health and often lead to the development of severe diseases. Currently, high throughput analyses, such as microarray and deep sequencing, are performed in order to identify miRNA biomarkers, using archival patient tissue samples. MiRNAs are more robust than longer RNAs, and resistant to extreme temperatures, pH, and formalin-fixed paraffin-embedding (FFPE) process. Here, we have compared the stability of miRNAs in FFPE cardiac tissues using next-generation sequencing. The mode read length in FFPE samples was 11 nucleotides (nt), while that in the matched frozen samples was 22 nt. Although the read counts were increased 1.7-fold in FFPE samples, compared with those in the frozen samples, the average miRNA mapping rate decreased from 32.0% to 9.4%. These results indicate that, in addition to the fragmentation of longer RNAs, miRNAs are to some extent degraded in FFPE tissues as well. The expression profiles of total miRNAs in two groups were highly correlated (0.88

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Respiratory syncytial virus (RSV) is the most common viral cause of bronchiolitis and pneumonia in young children worldwide. Premature birth, bronchopulmonary dysplasia, congenital heart disease, and Down syndrome are risk factors for high mortality and prolonged morbidity after RSV infection. Conversely, many previously healthy, full-term children are also admitted to the hospital because of RSV, and some of them experience severe sequelae or die due to the virus. Various complications of RSV infection have been reported, such as encephalopathy, encephalitis, and cardiomyopathy. However, the pathogenesis of serious cases in children without an underlying disease has not been elucidated. In this report, we present 2 RSV-related deaths of children who were born at full-term and developed normally up to the age of 19 months. Their cardiopulmonary arrests occurred within half a day after the onset of symptoms, such as cough and high fever. Many postmortem examinations were performed to investigate their unexpected deaths. Histopathological examinations revealed extensive bronchiolitis and mild pneumonia accompanying airway obstruction. Immunostaining revealed the presence of the virus mainly in bronchial epithelia, but not in alveoli. Complete brain edema was prominent, and encephalopathy was developing. Blood tests revealed that the IL-6 level was elevated more than >200-fold above normal, despite a normal C-reactive protein level. Because IL-6 may reflect the severity of bronchial epithelial damage and contribute to brain edema, an extreme elevation of IL-6 may predict the risk for sudden death in children with RSV infection.

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