| Background The chief problems of wound treatment are promoting wound healing preventing scar formation, skin appendages regeneration and sweat glands reconstruction."Scarless wound healing" mechanism of fetal skin is the most important clues to solve these problems. Early-mid embryonic skin wound can heal without obvious inflammatory reactions and scarring, and skin appendages can be regenerated[1-2]. So far, a lot of research on embryonic skin development and wound healing mechanisms have been done, with certain achievements. However, limited by the lack of experimental methods, especially a human fetal skin in vitro experiments animal model, the research stalled. Therefore, we tried to transplant rat and human fetal skin to nude mice in order to construct an animal model for embryonic skin in vitro studies.Matrix metalloproteinases play an important role in wound healing, cell migration and embryonic skin and appendages development[3], granulation tissue formation and tissue remodeling[5]. It is known that MMP-2and MMP-7are closely related to the morphological development of the sweat glands and skin appendages in human fetal skin development process[4].Methods (1) Rat embryonic skin (rES) of different gestational age were implanted under dorsal flap of nude mouse. On3rd,7th,14th,21st day after rES survived, we obtained samples and observed the development of survived rES through HE staining.(2) Early pregnancy (E14w) human fetal skin (human fetal skin, hFS) were acquired through abortion and transplanted to nude mice under dorsal flap. We obtained hFS specimens on0,14th,42th,70th,98th day after hFS survived and observed the process of fetal skin and appendages development through HE staining. And we explored the expression pattern of K5, K.19, MMP-2and MMP-7through immunohistochemical staining.(3)2weeks after hFS survived, we constructed the early pregnancy hFS partial degree burn model. We obtained samples on2hours,1st,3rd,7lh,13th day after burned, and observed histological changes of fetal skin and appendages during early pregnancy hFS Ⅱ°burns wound healing process through HE staining. We adopted immunohistochemical staining methods to explore EGF, MMP-2and MMP-7expression pattern during early hFS Ⅱ°burn wound healing process.Results (1) Transplanted rES can successfully survived through implanted under nude mouse dorsal flap, especially the early rES, and generate a contact rat skin structure after development.(2) Transplanted hFS can also successfully survived through implanted under nude mouse dorsal flap, and generate a contact human skin structure after development. The hFS development process in nude mouse is similar to the process in uterus. K5and K19after transplantation of hFS also be able to express, K.5expressed transitionally in the hair follicle bulge from6weeks to10weeks after transplantation; K19expression mainly located in newborn skin appendage placode and hair follicle bulge. K.19expression was earlier and stronger compared with K5expression. During development process of survived hFS, MMP-2expression was positive, while MMP-7expression negative.(3) Observed through both naked eye and microscope, early pregnant hFS Ⅱ°burn wound healed with no scar formation, and new skin appendages placode regenerated. EGF expression was positive in the basal cells of the epidermis surround the wound, hair follicle epidermal cells and neoepidermis cells on the wound;7th day after burned, EGF expression level surround the wound reduced.24hours after burned, MMP-7expression appeared under wound eschar and form a belt area; expression reached a peak on3th day after burnd; on911day after burnd, expression decreased dramatically; on13th days after burned, MMP-7expression became very weak. MMP-2expression was negative under the wound eschar, but positive in apex of skin appendages.Conclusions (1) Rat embryonic skin nude mouse transplantation model can be successfully constructed through implantation under dorsal flap, especially the early rES. but the development period is too short for intervention and long-term observation.(2) Early hFS can also survived successfully through implantation under dorsal flap and maintain growth and development capacity and development process in vitro is stable. Therefore, early hFS-nude mouse transplantation model is an ideal animal model for the experiments on fetal skin development, wound healing and skin appendages regeneration.(3) MMP-2may play an important role in skin appendages development of early hFS after transplanted to nude mice, while MMP-7hold no significant correlation to it.(4) Early hFS partial degree burn wound can achieve scarless healing, in which, MMP-7might be indispensible, while MMP-2may not act in the process. |
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