Studies on mRNA expression of tissue-type plasminogen activator in bruises for wound age estimation

We investigated mRNA expression of tissue-type plasminogen activator (tPA) and inflammatory cell dynamics for wound age estimation of bruises in mice. Neutrophils were detected from 1 h post-injury. Up to 8 h, they accumulated in subcutaneous tissue and the lower part of the dermis, and thereafter they extended to all the layers. Macrophages became detectable 3 h post-injury, and moderate infiltration of lymphocytes was seen from 144 h. In addition, epidermal thickening was also seen from 72 h. tPA mRNA expression peaked at 1 h, and increased slightly at 72 h post-injury. tPA mRNA was detected in epidermal cells, fibroblasts, and endothelial cells before and after injury, from 3 h in neutrophils and from 72 h in macrophages, respectively. This study presents the time-dependent expression of tPA mRNA in bruises in relation to temporal histologic characteristics during wound healing, which was considered to be useful for wound age estimation. Furthermore, it is suggested that tPA plays an important role in the first step of tissue remodeling.