[Show abstract][Hide abstract] ABSTRACT: We have previously shown that MRL/MpJ mice have a capacity for regeneration instead of scar formation following an ear punch wound. Understanding the differences that occur between scar-free regeneration or repair with scarring will have great impact upon advances in skin tissue engineering. A key question that remains unanswered in the MRL/MpJ mouse model is whether regeneration was restricted to the ear or whether it extended to the skin. A histological analysis was conducted up to 4 months post-wounding, not only with 2-mm punch wounds to the ear but also to the skin on the backs of the same animals. MRL/MpJ mouse ear wounds regenerate faster than control strains, with enhanced blastema formation, a markedly thickened tip epithelium and reduced scarring. Interestingly, in the excisional back wounds, none of these regenerative features was observed and both the C57BL/6 control and MRL/MpJ mice healed with scarring. This review gives an insight into how this regenerative capacity may be due to evolutionary processes as well as ear anatomy. The ear is thin and surrounded on both sides by epithelia, and the dorsal skin is devoid of cartilage and under greater tensile strain. Analysis of apoptosis during ear regeneration is also discussed, assessing the role and expression of various members of the Bcl-2 family of proteins. Ongoing studies are focusing on de novo cartilage development in the regenerating ear, as well as understanding the role of downstream signalling cascades in the process. Identification of such signals could lead to their manipulation and use in a novel tissue-engineered skin substitute with scar-free integration.
Journal of Anatomy 11/2006; 209(4):439-46. DOI:10.1111/j.1469-7580.2006.00632.x · 2.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The adult MRL/MpJ mouse regenerates all differentiated structures after through-and-through ear punch wounding in a scar-free process. We investigated whether this regenerative capacity was also shown by skin wounds. Dorsal skin wounds were created, harvested and archived from the same animals (MRL/MpJ and C57BL/6 mice) that received through-and-through ear punch wounds. Re-epithelialization was complete in dorsal wounds in both strains by day 5 and extensive granulation tissue was present by day 14 post-wounding. By day 21, wounds from both strains contained dense amounts of collagen that healed with a scar. The average wound area, as well as alpha-smooth muscle actin expression and macrophage influx were investigated during dorsal skin wound healing and did not significantly differ between strains. Thus, MRL/MpJ mice regenerate ear wounds in a scar-free manner, but heal dorsal skin wounds by simple repair with scar formation. A significant conclusion can be drawn from these data; mechanisms of regeneration and repair can occur within the same animal, potentially utilizing similar molecules and signalling pathways that subtly diverge dependent upon the microenvironment of the injury.
Journal of Anatomy 11/2006; 209(4):547-59. DOI:10.1111/j.1469-7580.2006.00641.x · 2.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Collagen undergoes dramatic reorganization during wound repair. Matrix metalloproteinases degrade and remodel collagen in a tightly controlled process. The collagenase-resistant mouse, Col1a1tm1Jae, produces type I collagen, which is resistant to degradation by human matrix metalloproteinase 1. These mice grow normally but develop thickened skin with age. We have previously reported that the early wound repair response in homozygous mutant (Col1a1r/r) mice is delayed compared to wild type (Col1a1+/+). However, the late-stage scar of Col1a1r/r wounds was not significantly altered compared to Col1a1+/+. Here we have investigated the response of heterozygous mice (Col1a1+/r) to wounding, not previously reported. Wound reepithelialization was delayed to a similar degree to wounds in the Col1a1r/r mice. However, the recovery of impaired wound contraction was faster in Col1a1+/r than in Col1a1r/r mice, but still slower than in wild-type animals. Analysis of wound protein extracts showed expression of some matrix metalloproteinases was prolonged in both the Col1a1r/r and Col1a1+/r wounds compared to wild type. We suggest the partial resistance of collagen to collagenase-mediated degradation in the heterozygous animals causes equivalent impairment of keratinocyte migration compared to homozygous collagenase-resistant mice, but that wound contraction during late-stage healing is only partially retarded.
[Show abstract][Hide abstract] ABSTRACT: Collagen in the skin undergoes dramatic reorganization during wound repair. Matrix metalloproteinases degrade and remodel the collagen in a tightly controlled process. The collagenase-resistant mouse, Col1a1(tm1Jae), has been developed to produce collagen type I, which is resistant to degradation by human matrix metalloproteinase 1. These mice grow normally but develop thickened skin with age. We investigated the effect of this mutant collagen on wound repair. Incisional wounds were made on Col1a1(tm1Jae) homozygous mutant (Col1a1(r/r)) and wild-type (Col1a1+/+) mice and these wounds were harvested at 1 and 6 h, 1, 2, 3, 7, 10, 14, and 70 d post wounding. Wound healing was severely delayed in Col1a1(r/r) wounds, with wounds remaining significantly wider than wild-type for the first 2 wk after injury. Reepithelialization of the Col1a1(r/r) wounds took 7 d longer than in the wild-type. The Col1a1(r/r) wounds had a prolonged early inflammatory response. Immunostaining for matrix metalloproteinases revealed significant upregulation of matrix metalloproteinase 13 in Col1a1(r/r) wounds, but minimal changes in other matrix metalloproteinases. There was no significant difference in scarring between Col1a1(r/r) and Col1a1+/+ wounds after 70 d.
[Show abstract][Hide abstract] ABSTRACT: regeneration of tissue mass may in part be brought about by apoptosis of primitive cells in MRL/MpJ regeneration following punch injury to the ear, the role of the Bcl-2 family of proteins and the caspases was investigated. Cartilage regeneration in the ear was also studied as was wounding in the backs of these animals. METHODS: A histological analysis was conducted up to 4 months post-wounding, not only on 2mm punch wounds to the ear but also 4mm wounds to the skin on the backs of the same animals. To investigate the changes in tissue architecture leading to ear wound closure, we investigated whether the type of trauma (clinical biopsy v. crude punch) applied to the ears of different strains of mice including MRL/MpJ influenced the rate of wound healing. Wound healing in the backs of the same animals was also investigated. Tissue samples were wax embedded and H&E and Masson's Trichrome stains were performed. Glycosaminglycan deposition in the regenerating ear was assessed using Alcian blue. RESULTS: MRL/MpJ mouse ear wounds heal faster than control strains with enhanced blastema formation and markedly thickened tip epithelium. The reduced inflammatory infiltrate seen with the biopsy as opposed to the crude punch, correlated with a faster, more regenerative repair process with reduced scarring. Interestingly, in the excisional back wounds, none of these regenerative features were observed and both the C57BL/6 control and MRL/MpJ healed with scarring. Analysis of apoptosis was undertaken assessing the expression of various members of the Bcl-2 family of proteins. By day 5 post-wounding Bcl-2, Bcl-x, Bax, Bak, Bim and Bid are all expressed but there was little difference of expression between the control and MRL/MpJ strains. By day 14 post- wounding however, in the MRL/MpJ strain, in