Full-thickness wounding of the mouse tail as a model for delayed wound healing: accelerated wound closure in Smad3 knock-out mice.

Experimentally induced wounds in animal models are useful in gaining a better understanding of the cellular and molecular processes of wound healing, and in the initial evaluation of the safety and effectiveness of potential therapeutic agents. However, studying delayed healing has proved difficult in animals, whose wounds heal within a few days. In this report, we describe a novel method for establishing mouse wounds that require up to 3 weeks or more for complete closure, and we show the validity of this model in Smad3 null mice, which are known to display accelerated healing. Full-thickness wounds, measuring 0.3 by 1.0 cm, were made down to fascia on the dorsal aspect of the mouse tail in Smad3 knock-out mice and control littermates, approximately 1 cm distal to the body of the animal. The wounds were left to heal by secondary intention and were assessed histologically by computerized planimetry for wound closure at various times after wounding. The wounds in wild-type mice displayed delayed healing, with full closure occurring between 14 and 25 days after wounding. Complete closure of similar wounds in Smad3 null mice healed 30 percent faster (p < 0.01). By immunostaining for ki67, a marker for proliferation, Smad3 null animals also showed increased proliferation of dermal wound cells by day 4 after wounding. Cultured dermal fibroblasts from Smad3 null mice had increased baseline DNA synthesis and, interestingly, an enhanced response to transforming growth factor-beta1. By Western blot analysis, Smad3 null mice fibroblasts showed a compensatory increase in mitogen-activated protein kinase phosphorylation in response to transforming growth factor-beta1, suggesting that mitogen-activated protein kinase overcompensation together with loss of Smad3 may be involved in the modulation of faster healing. We conclude that this novel tail-wounding model may be useful for studying delayed wound closure.