| Objective:To construct a systematical humanized nude mouse model including adult skin and fetal skins at each stage of pregnancy,and further establish the injury repair model for the deep second degree after skin survival,and systematically observe the growth and development of fetal skin in vitro and changes of wound repair process after burn.Using exogenous mature immune cells and exogenous neurotoxin,neuroactive peptides to interfere with the fetal skins suffered from deep second degree burn,to analyze the role and the mechanism of immune and neurological factors to the healing process of fetal skin wounds.Methods:Fetal skins at each stage of pregnancy and adult skin were transplanted into the back of nude mice with T cell immunodeficiency,The postoperative flap incubation method was used to promote the skins survival.The humanized nude mice model was systematically observed after the survival.Through gross observation and histopathological staining,the growth and development of fetal skins at each stage of pregnancy and adult skins after transplantation were recorded.On the basis of this model,a deep second degree burn wound was made on the survival fetal skins of the nude mice by thermostatically controlled perm apparatus to establish the injury repair model.The model was used to observe the histopathological changes of the wound repair process after scald,and the expression of MMP-2,MMP-7,MMP-9 andTIMP-1 in the repair process of wounds was detected.Exogenous peripheral blood mononuclear cells were injected into the fetal skin of the midterm stage of pregnancy to perform immunological intervention,The wound healing rate of immunological intervention group was compared with the control group.And the changes in expression of MMP-9 and TIMP-1 was detected after immune cell intervention.Exogenous neurotoxin(botulinum toxin type A)and exogenous neuroactive peptide(substance P)were locally injected into the fetal skin of the midterm stage of pregnancy,The wound healing rate of neurological intervention group was compared with the control group.Results:Fetal skins at each stage of pregnancy and adult skin were successfully transplanted into the back of the nude mice after different time of flap incubation.The humanized nude mouse model was successfully constructed.The injury repair model of deep second degree burn was made successfully.The growth and development of fetal skins was nomal after transplantation into the back of nude mice.The wound can be healed quickly after burn,without obvious scar formation.MMP-2 was not expressed during wound healing,and the expression of MMP-7 was closely related to wound repair process.MMP-9 changes with the migration and proliferation of repaired cells.The expression of TIMP-1 is later than that of MMP-9,and the change pattern is similar to that of MMP-9.The injection of exogenous mature immune cells(hPBMC)prolonged the healing time of deep second degree burn wounds and caused scar formation,and also changed the expression pattern of MMP-9 and TIMP-1 during the wound repair process.Exogenous neurotoxin(botulinum toxin type A)delayed wound healing after injection,but maintained the characteristics of scarless healing.Exogenous neuroactive peptide(substance P)accelerated the healing of the wound.Conclusions:1,Human embryonic skins in the early,midterm and late stages of pregnancy transplanted into the back of the nude mice can be survived by appropriate methods such as embedding under the skin flaps and incubating after the flaps with different time,thus a stable humanized nude mouse model was successfully established.2,The growth and development of the fetal skin in the early and midrerm stages of pregnancy after transplantation in the humanized nude mouse model is no different from the developmental process in the uterine cavity.3,The wound repair humanized nude mouse model is relatively stable and is suitable for the study of the mechanism of human early embryonic skin with scarless healing and the wound healing process with deep second degree burn.4,MMP-7 may be one of the major matrix metalloproteinases involved in the removal of inactivated tissue,induction of epidermal cell migration and angiogenesis,and remodeling of connective tissue during burn wound healing.MMP-2 is mainly associated with hair follicle development in skin attachments,and is not closely related to the wound healing process.MMP-9 and TIMP-1 are the main enzymes regulating ECM degradation and synthesis.The imbalance of MMP-9/TIMP-1 ratio is one of the important mechanisms for the occurrence and development of various diseases.5,The embryonic skins in early or midterm stage of pregnancy can achieve scarless regenerative healing.Epidermal stem cells with mighty proliferating and differentiation ability,the lack of local inflammatory immune response of wounds,timely regulation of extracellular matrix degradation and deposition,rapid migration,colonization and differentiation of the repair cells is closely related to this result.6,Under the intervention of exogenous immune cells,in the deep inflammatory burn wound of the fetal skin,the local inflammatory reaction is aggravated,the migration of the proliferating epithelial cells is reduced,the wound repair process becomes slow and complicated,and finally the repair time is extension and scarring formation.7,Under the intervention of exogenous neuropeptide SP,Fb and endothelial cells proliferate and migrate to the wound surface,which can effectively promote wound healing;while exogenous neurotoxin(botulinum toxin type A)interferes with local wounds,it has a dual role,on the one hand,it inhibit the proliferative activity of Fb in granulation tissue,reduce the expression of related regulatory cytokines,which leading to delayed recovery of wound repair.on the other hand,it can regulate the composition and the deposition of extracellular matrix,mainly collagen,thereby reducing the chance of scar hyperplasia and contracture. |
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