Muscle protein degradation for time since death estimation

Estimation of the time since death is a crucial aspect in forensic science. This is necessary to gain crucial information about the circumstances of death and is, in criminal cases, essential for the confirmation or invalidation of alibis and ultimately for the solution of a crime. Several methods are used to delimitate the post mortem interval (PMI) in every day forensic work, such as the temperature method which is based on the decrease of the body core temperature from 37C. However, this method is only useful in the early postmortem phase (until up to two days postmortem). Forensic entomology which analyses the presence of cadaver feeding insects and their developmental stages requires accessibility of the body to such insects and was shown to deliver valuable information only for minimal PMI values. Thus, additional methods to delimitate the time since death are required that produce reliable information in a minimum of time and can easily be implemented in any forensic laboratory. Our previous results demonstrate that muscle proteins degrade in a predictable fashion after death. Analyses of the presence and absence of these proteins and their split products using molecular biological methods (Western blotting, zymography) allows to draw relatively precise conclusions about the time of death. The proposed project is aimed to identify a large number of muscle proteins in humans and pigs which can be used for delimitation of the time since death. In addition, the influence of internal and external factors (such as temperature, age, gender, body mass index, etc.) on post mortem degradation behaviour of these proteins will be evaluated. The exact time course of human muscle protein degradation will be investigated in collaboration with the Forensic Anthropology Center at the University of Tennessee at Knoxville, USA. The results of this project are aimed to build the foundation for establishment of this method in forensic laboratories. The collected data will be used to establish a database which can be used by forensic examiners from all over the world to delimitate the time since death.

The delimitation of the time since death is a very difficult, but crucial aspect in forensic sciences. However, most of the applied methods have practical limitations or provide sufficient results only under certain circumstances. Thus, new methods that can easily be implemented into forensic routine work are required to deliver more and discrete information about the postmortem interval (PMI). With this project we show that skeletal muscle protein degradation is of significant value for PMI estimation in forensic routine because muscle proteins degrade in a predictable fashion after death. We investigated various important aspects to improve our understanding of postmortem protein decomposition. Specifically, we were able to expand the numbers of useful marker proteins for PMI determination and established a standard protocol for the use of protein degradation in skeletal muscle in daily forensic routine. In a next step, the effect of temperature on protein degradation dynamics was examined. Additional important factors that influence muscle degradation were identified, such as age, body weight and access and activity of necrophagous insects. Using bodies of donors (collaborations with human taphonomy facilities in Amsterdam, The Netherlands and Marquette, MI, USA), we characterized muscle protein degradation in longitudinal studies and described the time course of muscle protein degradation events in humans. The results of this project are of major significance to establish protein degradation analysis as a standard method for PMI estimation in forensic laboratories all over the world, but are also of high relevance to other scientific areas (cell biology, sports science).