Postmortem muscle protein degradation in humans as a tool for PMI delimitation

Abstract

Forensic estimation of time since death relies on diverse approaches, including measurement and comparison of environmental and body core temperature and analysis of insect colonization on a dead body. However, most of the applied methods have practical limitations or provide insufficient results 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). Following a previous work on skeletal muscle degradation in the porcine model, we analyzed human postmortem skeletal muscle samples of 40 forensic cases by Western blotting and casein zymography. Our results demonstrate predictable protein degradation processes in human muscle that are distinctly associated with temperature and the PMI. We provide information on promising degradation markers for certain periods of time postmortem, which can be useful tools for time since death delimitation. In addition, we discuss external influencing factors such as age, body mass index, sex, and cause of death that need to be considered in future routine application of the method in humans.

Keywords: Degradation; Human; Postmortem interval (PMI); Protein; Skeletal muscle.

Fig. 1

Degradation behavior of tropomyosin, cTnT, desmin, and calpain of four individual cases with varying ADD. Western blot (a–c) and zymography (d) analyses of muscle protein degradation. Tropomyosin bands (a) remain stable independent of ADD and no degradation products are found. By contrast, degradation products (dp) of cTnT (b), desmin (c), and calpain 1 (d) appear in samples that exceed a certain ADD. The protein profiles shown originate from four individual muscle samples but are exemplary for all cases investigated

Fig. 2

Logistic regression curves of significantly ADD-correlated degradation products cTnT dp2 (a), calpain 1 dp (b), desmin dp1 (c), and desmin dp2 (d) represent presence probability development. Regression curves are plotted within the ADD range from 2.6 to 36.0. Solid lines stand for the regression of the total group (40 samples), whereas broken lines represent age-corrected (dashes) and BMI-corrected (dots) groups. With increasing ADD, the presence probability of all degradation products rises. Especially, the age-corrected regressions are steep in all cases and exceed the P = 0.95 confidence limit (dotted horizontal line) at lower ADD compared to the total group