# Endogenous and Exogenous Small RNA Signatures as Novel Tools for Postmortem Interval Determination

## TL;DR

This study explores using small RNA changes in postmortem tissue to accurately estimate the time since death, offering a new forensic tool.

## Contribution

The study introduces a novel framework combining endogenous and bacterial-derived small RNAs for high-precision postmortem interval estimation.

## Key findings

- Cardiac RNA degradation strongly correlates with PMI, with a random forest model achieving high accuracy (R2 = 0.939).
- Seven novel sncRNA biomarkers were identified for PMI prediction (R2 = 0.760, MAE = 158.990 min).
- Bacterial-derived sRNAs, especially from Staphylococcus aureus, show complementary potential for PMI estimation.

## Abstract

Background: Accurate estimation of the postmortem interval (PMI), the time elapsed between death and body discovery, is a critical challenge in forensic science due to the complex interplay of factors affecting decomposition. Traditional methods based on macroscopic changes often lack precision, especially in later postmortem stages. Methods: This study aimed to develop a novel PMI estimation framework by integrating the dynamics of endogenous small non-coding RNAs (sncRNAs) and exogenous bacterial-derived small RNAs (sRNAs) using sRNA transcriptomics and machine learning. Results: Cardiac RNA degradation strongly correlated with PMI, with a random forest (RF) model achieving high accuracy (coefficient of determination (R2) = 0.939, mean absolute error (MAE) = 2.987 h). Employing PANDORA-seq, we profiled temporal changes in sncRNAs (miRNAs, tsRNAs and piRNAs) in postmortem cardiac tissue within 30 h in a mouse model, while simultaneously assessing RNA integrity (RIN) across eight organs. PANDORA-seq revealed stable sncRNA landscapes with specific dynamic shifts, leading to the identification of seven novel biomarkers (four tsRNAs, three piRNAs) for PMI prediction (R2 = 0.760, MAE = 158.990 min). Bacterial-derived sRNAs, predominantly from Staphylococcus aureus, were upregulated at 30 h postmortem, suggesting complementary biomarker potential. Bioinformatics analysis indicated that host miRNAs may target bacterial mRNAs, hinting at cross-kingdom interactions. Conclusion: These findings highlight the potential of integrated endogenous and exogenous sRNA analysis in PMI estimation, providing a high-precision, rapid diagnostic tool and revealing complex postmortem molecular processes.