Does altered protein metabolism interfere with postmortem degradation analysis for PMI estimation?

Abstract

An accurate estimation of the postmortem interval (PMI) is a central aspect in forensic routine. Recently, a novel approach based on the analysis of postmortem muscle protein degradation has been proposed. However, a number of questions remain to be answered until sensible application of this method to a broad variety of forensic cases is possible. To evaluate whether altered in vivo protein metabolism interferes with postmortem degradation patterns, we conducted a comparative study. We developed a standardized animal degradation model in rats, and collected additional muscle samples from animals recovering from muscle injury and from rats with developed disuse muscle atrophy after induced spinal cord injury. All samples were analyzed by SDS-PAGE and Western blot, labeling well-characterized muscle proteins. Tropomyosin was found to be stable throughout the investigated PMI and no alterations were detected in regenerating and atrophic muscles. In contrast, significant predictable postmortem changes occurred in desmin and vinculin protein band patterns. While no significant deviations from native patterns were detected in at-death samples of disuse muscle atrophy, interestingly, samples of rats recovering from muscle injury revealed additional desmin and vinculin degradation bands that did not occur in this form in any of the examined postmortem samples regardless of PMI. It remains to be investigated whether in vivo-altered metabolism influences postmortem degradation kinetics or if such muscle samples undergo postmortem degradation in a regular fashion.

Postmortem proteomics to discover biomarkers for forensic PMI estimation

“…However, if certain timeframes can be excluded in future application, such transiently appearing protein bands can be of potential interest. The transient character of the 41 kDa desmin degradation product in this experimental series was in accordance with earlier studies [ 16 , 34 ]. Together with the loss of the native band and the appearance of the 34 kDa band (both significant correlations with the PMI), it could clearly be confirmed that desmin is a reliable marker for early phase time since death estimation.…”

“…In the case of the 84 kDa vinculin band within the rat model, which was negative (−, no measureable band) in all 0-hpm samples and positive (+, measurable band) in all samples with larger PMI, lower correlation values resulted from a less balanced overall ± ratio. Still, in accordance with previous studies [ 16 ], all results of the animal model were found to significantly correlate with the PMI.…”

“…Postmortem changes, such as the loss of the native protein band or the occurrence of specific degradation products, were additionally shown to significantly correlate with the PMI. Among these proteins are calcineurin A, protein phosphatase 2A [ 13 ], titin, nebulin [ 14 ], desmin, troponin [ 15 ], vinculin [ 16 ], AMP-activated protein kinase, caspase 3, and glycogen synthase [ 17 ]. Furthermore, PMI-dependent desmin and cardiac troponin T degradation has been confirmed in humans [ 15 ] and was already successfully applied to obtain evidence about the succession of events in a criminal case [ 18 ].…”

A field study to evaluate PMI estimation methods for advanced decomposition stages

“…To reduce a possible destructive impact on the experimental design (e.g., by removing the brushwood for extensive sampling) and the associated examinations (e.g., estimating the TBS), larval samples were mainly collected from the carrion surface and/or the region between body and ground. For the same reasons, and to avoid to disturb the colonizing fauna, 4 days were chosen as "days of discovery" (days 3,7,11,14), where the sampling of larvae at a crime scene was simulated. Inexperienced assessors received a short practical training in sample collection and treatment, which reflects the situation in practical routine very well.…”

“…In later stages, the life cycle of necrophagous insects developing on the body [7], the analysis of tissue degradation [8][9][10], or morphological changes [11] of a dead body can contribute to exclude specific timeframes or provide minimum postmortem intervals (PMI min ). However, these methods can only be applied under specific circumstances (mere presence of insects, or remaining tissue, no exclusion criteria such as myiasis [12,13], or altered in vivo tissue metabolism [14], etc.) and only little is known about how the investigated phenomena influence each other.…”