Molecular analysis of different classes of RNA molecules from formalin-fixed paraffin-embedded autoptic tissues: a pilot study

For a long time, it has been thought that fresh and frozen tissues are the only possible source of biological material useful to extract nucleic acids suitable for downstream molecular analysis. Recently, for forensic purpose such as personal identification, also fixed tissues have been used to recover DNA molecules, whereas RNA extracted from such material is still considered too degraded for gene expression studies. In the present pilot study, we evaluated the possibility to use forensic formalin-fixed paraffin-embedded (FFPE) samples, collected at autopsy at different postmortem intervals (PMI) from four individuals, to perform advanced molecular analyses. In particular, we performed qualitative and quantitative analyses of total RNAs extracted from different FFPE tissues and put expression profiles in relation with the organ type and the duration of PMI. Different classes of RNA molecular targets were studied by real-time quantitative RT-PCR. We report molecular evidence that small RNAs are the only RNA molecules still detectable in all the FFPE autoptic tissues. In particular, microRNAs (miRNAs) represent a consistent, stable, and well-preserved molecular target detectable even from tissue sources displaying signs of ongoing putrefaction at autopsy. In this pilot study, we show that miRNAs could represent a highly sensitive and potentially useful forensic marker. Amplification of specific miRNAs using paraffin-embedded blocks could facilitate retrospective molecular analysis using specific forensic-archived tissues chosen as most suitable according to PMI, and this approach would address molecular evidence in forensic cases in which fresh or frozen material is no longer available.