Trauma is the leading cause of mortality all over the world (Eming et al. 2014). Different histological and molecular changes occur in the incisional wound (Paladini et al. 1996). Forensic scientists could use these changes to evaluate the effect of the time passed since death in the incisional wounds (Gunn et al. 2014; Lv et al. 2014).
Few researchers had described the forensic aspect of histologic changes of the skin injuries (Siddiqui et al. 2016; Obac et al. 2011; Vinay et al. 2017; Vidinský et al. 2006). Most of these studies were conducted on blunt injuries. No such study was conducted to detect molecular and histological changes in incisional injuries occurred just before death. Therefore, there is a need for such study.
Skin-wound healing starts immediately after mechanical damage. It consists of three phases: inflammation, proliferation, and maturation. Following trauma, there is an overlap in the early inflammation phase and can be recognized as healing signs of wound vitality (Obac et al. 2011).
Vidinský et al. (Vidinský et al. 2006) studied the rats’ skin morphology for a period of 7 days after incisional wound. During 24 h after incision, they noted intense acute inflammatory reaction in the wound area in the form of cellular infiltration, the thickened epidermis at wound margins, and fibrin network filling the incisional space. Starting from day 2 to 7, they noted healing process in the form of a scab formation, thickened epidermis, keratinocyte migration, starting re-epithelization, and randomly distributed fibroblasts with no collagen formation.
Similarly, in the our specimens, acute inflammatory cells appeared at wound margin immediately after incision, and with increasing time passed since injury infliction, incisional wounds showed collagen, fibrous, and hemosiderin depositions.
Obac et al. (Obac et al. 2011) evaluated fibrin deposition; a marker of vital reaction, in rats’ skin after incisional injuries. The fibrin accumulated at the margins of the ante-mortem incisions (1 h after incision). They concluded that fibrin is feasible to distinguish between ante-mortem and postmortem lesions.
The incisional injury in our study showed significantly higher miRNA-205 and miRNA-21 expressions in group II (24 h after death) than other groups. Although there is a rapid decrease in miRNA-205 and miRNA-21 expressions in wounded samples, this decrease did not show any statistical significant correlation with postmortem interval. Of note, short duration passed after death did not show a significant increase in mRNA degradation.
A previous study had concluded that miR-205 expression significantly increased in the wound area at 12 h after wound infliction. Overexpressed miR-205 accelerated the cellular regrowth rate, cellular migration, and cellular proliferation during wound-healing process (Lin et al. 2013).
Long et al. (Long et al. 2018) studied the effect of miR-21 on wound healing process in aged mice. They found that miR-21 expression retained a high level in the wound area and allowed better skin repairing capacity. Its level was upregulated at day 7 more than twofold compared to those of day 3. Its dysregulation may contribute to impaired wound repair.
Ludwig et al. (Ludwig et al. 2016) reported that the miR-205 was highly expressed in human skin and can resist environmental variations and PM degradation. This trend could be related to its short length 21–25 bp. Moreover, McClure et al. (McClure et al. 2014) stated that genetic susceptibility and health condition could affect miR-21expression.
Molecular degradation in dead bodies increases, as the postmortem duration increases. Therefore, gene expressions decrease constantly with increasing time after death (Bauer et al. 2003; Sampaio-Silva et al. 2013).
The studied miRNA had been continuously expressed up to 48 h after death, but at lower level. MicroRNAs can resist ribonuclease degradation due to their being tightly bound to the active RNA-induced silencing complex and play special functions in keeping alive cells after death. Hence, miRNAs can be continuously expressed (Wang et al. 2016).
In this study, we had not demonstrate a significant negative correlation between miRNA expressions and time passed since death. Our results were inconsistent with other studies (Lv et al. 2014; Bauer et al. 2003; Sampaio-Silva et al. 2013; Wang et al. 2013). Possible reasons for these conflicting results could be related to studied molecular molecule, examined tissue, and chosen postmortem duration (Ali et al. 2017).
Our findings were augmented by the Nagy et al.’s findings (Nagy et al. 2015), who also demonstrated that miRNA expressions in postmortem brain tissue were stable and continuously expressed for up to 4 days.
When the results of the present study were compared with published literature, the histologic pattern and bio-molecular findings are more or less similar, but the progression of histologic and bio-molecular changes were different. The reason for this difference is related mainly to the methodological variations; especially the assessment time. The skin samples in our study were examined after death as postmortem samples of perimortal wound. Moreover, the condition of storage environment can greatly affect the speed of bio-molecular and histological changes (Ibrahim 2018).