Objective:The study aimed to investigate the effect of exosomes derived from bone marrow mesenchymal stem cells (BMSC-Exo) in promoting angiogenesis of fat grafts by regulating Notch signaling pathway.Methods:Fat from the abdomen of a 30-year-old healthy female who received liposuction in the Department of Plastic Surgery of the First Affiliated Hospital of Air Force Military Medical University in August 2020 was collected. Fat transplantation models were established using 12 BALB/c nude mice, with 0.5 ml of processed fat particles injected into the left and right sides of the backs. 100 μl BMSC-Exo (50 μg) was injected into the left side of the back of nude mice once per week for 4 weeks after fat grafting, which was the exosome group. The right side of the back was injected with 100 μl of phosphate-buffered saline at the same time points for 4 weeks after fat grafting, which was the control group. The following items were observed: (1) Fat grafts were collected and weighed at 4 weeks and 8 weeks after transplantation, the retention rate was calculated. (2) HE staining and immunofluorescence staining of Perilipin A was used to visualize the structure and integrity of adipocytes at 8 weeks after transplantation. (3) At 8 weeks after transplantation, immunohistochemical staining was used to detect CD31 positive cells, calculate micro vessel density, detect Notch1 and Notch4 positive cells and calculate the proportion of positive area.(4) At 8 weeks after transplantation, the relative expressions levels of Notch1, Notch4 and VEGF mRNA in fat grafts were detected by real-time fluorescence quantitative PCR. The data were analyzed by Graphpad Prism 8.0. T-test was used for comparison between groups. P<0.05 indicated the difference was statistically significant. Results:(1) At 4 and 8 weeks after transplantation, the retention rates of adipose tissue wet weight in the control group were (41.15±9.68)% and (34.30±6.45)% respectively. The results in the exosome group were (61.77±10.98)% and (55.93±5.89)%, which were higher than those in the control group ( P<0.05). (2) At 8 weeks after transplantation, the structural integrity of adipocytes in the exosome group was better than the control group, with more neovascularization. There were more intact Perilipin A positive adipocytes in the exosome group and less in the control group. (3) At 8 weeks after transplantation, the density of micro vessels in the control group was 4.67±0.57, which was significantly lower than that in the exosome group (13.00±2.00, P<0.05). The proportion of Notch1 and Notch4 positive area per visual field in the control group was lower than that in the exosome group [(0.53±0.28)% vs. (1.67±0.11)%, (0.11±0.06)% vs. (1.20±0.24)%, P<0.05]. (4) The mRNA expression levels of Notch1, Notch4 and VEGF were 1.53±0.20, 1.50±0.26 and 2.56±0.55 in the exosome group, which were significantly higher than those in the control group (1.00+ 0.00) ( P<0.05). Conclusions:BMSC-Exo may promote angiogenesis and improve retention rate of transplanted fat grafts through the elevation of VEGF expression and the activation of Notch signaling pathway.

Objective:The study aimed to investigate the effect of exosomes derived from bone marrow mesenchymal stem cells (BMSC-Exo) in promoting angiogenesis of fat grafts by regulating Notch signaling pathway.Methods:Fat from the abdomen of a 30-year-old healthy female who received liposuction in the Department of Plastic Surgery of the First Affiliated Hospital of Air Force Military Medical University in August 2020 was collected. Fat transplantation models were established using 12 BALB/c nude mice, with 0.5 ml of processed fat particles injected into the left and right sides of the backs. 100 μl BMSC-Exo (50 μg) was injected into the left side of the back of nude mice once per week for 4 weeks after fat grafting, which was the exosome group. The right side of the back was injected with 100 μl of phosphate-buffered saline at the same time points for 4 weeks after fat grafting, which was the control group. The following items were observed: (1) Fat grafts were collected and weighed at 4 weeks and 8 weeks after transplantation, the retention rate was calculated. (2) HE staining and immunofluorescence staining of Perilipin A was used to visualize the structure and integrity of adipocytes at 8 weeks after transplantation. (3) At 8 weeks after transplantation, immunohistochemical staining was used to detect CD31 positive cells, calculate micro vessel density, detect Notch1 and Notch4 positive cells and calculate the proportion of positive area.(4) At 8 weeks after transplantation, the relative expressions levels of Notch1, Notch4 and VEGF mRNA in fat grafts were detected by real-time fluorescence quantitative PCR. The data were analyzed by Graphpad Prism 8.0. T-test was used for comparison between groups. P<0.05 indicated the difference was statistically significant. Results:(1) At 4 and 8 weeks after transplantation, the retention rates of adipose tissue wet weight in the control group were (41.15±9.68)% and (34.30±6.45)% respectively. The results in the exosome group were (61.77±10.98)% and (55.93±5.89)%, which were higher than those in the control group ( P<0.05). (2) At 8 weeks after transplantation, the structural integrity of adipocytes in the exosome group was better than the control group, with more neovascularization. There were more intact Perilipin A positive adipocytes in the exosome group and less in the control group. (3) At 8 weeks after transplantation, the density of micro vessels in the control group was 4.67±0.57, which was significantly lower than that in the exosome group (13.00±2.00, P<0.05). The proportion of Notch1 and Notch4 positive area per visual field in the control group was lower than that in the exosome group [(0.53±0.28)% vs. (1.67±0.11)%, (0.11±0.06)% vs. (1.20±0.24)%, P<0.05]. (4) The mRNA expression levels of Notch1, Notch4 and VEGF were 1.53±0.20, 1.50±0.26 and 2.56±0.55 in the exosome group, which were significantly higher than those in the control group (1.00+ 0.00) ( P<0.05). Conclusions:BMSC-Exo may promote angiogenesis and improve retention rate of transplanted fat grafts through the elevation of VEGF expression and the activation of Notch signaling pathway.

Objective:To investigate the immobilizing effect of full-thickness skin subcutaneous grafting on allogeneic full-thickness skin graft in rats.Methods:The experimental research method was used. The inbred male Brown-Norway rats ( n=10) and Lewis rats ( n=10) were used as donors and recipients respectively. After subcutaneously full-thickness separation of a 2.2 cm×2.2 cm area on the nape of the recipient rat, a full-thickness skin of 2.0 cm×2.0 cm taken from the abdomen of the donor rat was subcutaneously grafted, and the donor site was pulled together and sutured. The autologous skin over the allograft in the recipient rat was excised 5-6 d after grafting, and the stitches were removed 7 d after excision. Within 2 months after grafting, the feeding, activity, and survival of the donor and recipient rats, behavior of tearing and scratching the wounds of the recipient rats, the wound condition after autologous skin excision in recipient rats, and the survival and hair growth of the grafted allogeneic skin were observed. Results:Within 2 months after grafting, the donor and recipient rats all ate normally and could move freely with no abnormal death. No tearing or scratching of the wounds occurred in recipient rats. There was a small amount of exudation and partial epidermal desquamation after autologous skin excision in recipient rats. All transplanted allografts survived, which were free of infection and necrosis, with new hairs growing out smoothly.Conclusions:The immobilizing method of full-thickness skin subcutaneous grafting of allogeneic full-thickness skin graft in rats is simple and time-saving without postoperative dressing change, with reliable pressure fixation and high survival rate of skin grafts, which can be promoted for animal skin grafting models.