Differential cutaneous wound healing in thermally injured MRL/MPJ mice

Adult wound repair occurs with an initial inflammatory response, reepithelialization, and the formation of a permanent scar. MRL/MpJ mice following ear-hole punch biopsies display accelerated healing and tissue regeneration. In this study, we characterized the healing responses in both MRL/MpJ and BALB/c mice following a 15% total body surface area full-thickness cutaneous burn injury. Macroscopic and histological observations show that delayed wound closure in MRL/MpJ mice is accompanied by an increase in edema, reduced neutrophil infiltration, and more prominent eschar. In vivo bromodeoxyuridine labeling showed no defect in keratinocyte proliferation and migration (reepithelialization). In comparison with BALB/c mice, MRL/MpJ wounds had greater collagen deposition, less granulation tissue formation, and contained fewer α-smooth muscle actin-positive myofibroblasts. An observed reduction in dermal neutrophil infiltration and myofibroblast development correlated with enhanced angiogenesis. Overall, BALB/c wounds contracted sooner and to a larger degree, resulting in a significant decrease in scar formation. Interestingly, MRL/MpJ mice showed overt abnormalities in hair follicle proliferation, morphogenesis, and subsequent hair regrowth postburn injury. No substantial evidence of tissue regeneration was observed in either BALB/c or MRL/MpJ wounds. Our results convincingly demonstrate that MRL/MpJ skin burn wounds heal with scar formation with delays in two critical wound healing events: wound closure, and myofibroblast development.