In forensic practice, it is important to diagnose wound age accurately. We analyzed the proteome of injured murine skin to identify a novel protein marker of wound age after recent injury. We used samples from 3 days after injury, with 0 days as the control. The proteins were separated with two-dimensional electrophoresis. Using mass spectrometry, we identified a protein, chitinase-like 3 (Chil3). Chil3 messenger RNA (mRNA) expression showed temporal changes, which included a peak increase at 2 days after injury. Next, we produced an anti-Chil3 antibody and confirmed its specificity with western blotting. Similar to the mRNA results, an analysis of temporal changes in Chil3 protein expression revealed a peak at 2 days after injury. We also investigated the time course of changes in Chil3 tissue localization using immunohistochemistry. Chil3 signals remained in the wounded area for up to 9 days. However, Chil3-positive cells were observed in the scab, the edge of the dermal layer, and neogenetic granulation tissue between 1 and 3 days. Thus, wound age can be histologically determined using the localization of Chil3 but not its general existence. Additionally, double-labeled fluorescent immunohistochemistry revealed that the Chil3-expressing cells were mainly neutrophils. These data show that Chil3 is expressed in neutrophils during the early stage of wound healing in mice; thus, Chil3 is a potential histological marker of 1-3-day-old wounds.
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