Molecular pathology of brain edema after severe burns in forensic autopsy cases with special regard to the importance of reference gene selection

Brain edema is believed to be linked to high mortality incidence after severe burns. The present study investigated the molecular pathology of brain damage and responses involving brain edema in forensic autopsy cases of fire fatality (n = 55) compared with sudden cardiac death (n = 11), mechanical asphyxia (n = 13), and non-brain injury cases (n = 22). Postmortem mRNA and immunohistochemical expressions of aquaporins (AQPs), claudin5 (CLDN5), and matrix metalloproteinases (MMPs) were examined. Prolonged deaths due to severe burns showed an increase in brain water content, but relative mRNA quantification, using different normalization methods, showed inconsistent results: in prolonged deaths due to severe burns, higher expression levels were detected for all markers when three previously validated reference genes, PES1, POLR2A, and IPO8, were used for normalization, higher for AQP1 and MMP9 when GAPDH alone was used for normalization and higher for MMP9, but lower for MMP2 when B2M alone was used for normalization. Additionally, when B2M alone was used for normalization, higher expression of AQP4 was detected in acute fire deaths. Furthermore, the expression stability values of these five reference genes calculated by geNorm demonstrated that B2M was the least stable one, followed by GAPDH. In immunostaining, only AQP1 and MMP9 showed differences among the causes of death: they were evident in most prolonged deaths due to severe burns. These findings suggest that systematic analysis of gene expressions using real-time PCR might be a useful procedure in forensic death investigation, and validation of reference genes is crucial.