[Effect of circulating estrogen level on the outcome of free fat grafting in nude mice].

OBJECTIVE: To investigate the effect of circulating estrogen level on the outcome of free fat grafting in nude mice.
METHODS: Eighteen female nude mice aged 6-8 weeks (weighing, 20-25 g) were randomly divided into 3 groups ( n=6). The nude mice in the ovariectomized group were treated with ovariectomy. The nude mice in the high estrogen group and the normal estrogen group only made the same incision to enter the peritoneum without ovariectomy. The nude mice in the high estrogen group were given the estradiol (0.2 mg/g) every 3 days for 30 days. The other two groups were given the same amount of PBS every 3 days. At 30 days after operation, the tail vein blood of nude mice in 3 groups were detected by estradiol ELISA kit, and the free fat (0.3 mL) donated by the females was injected into the sub-scalp of nude mice. After 8 weeks of fat grafting, the samples were taken for gross observation and weighing, and the prepared slices were stained with HE staining, CD31-perilipin fluorescence staining, immunohistochemical staining of uncoupling protein 1 (UCP1), and immunofluorescence staining of estrogen receptor α. The diameter of adipocytes and vascular density of adipose tissue were measured. The mRNA expressions of UCP1 and estrogen receptor α were detected by realtime fluorescence quantitative PCR (qRT-PCR).
RESULTS: All nude mice survived during experiment. ELISA test showed that the concentration of estradiol significantly decreased in the ovariectomized group and increased in the high estrogen group compared with the normal estrogen group ( P<0.05). At 8 weeks after fat grafting, the graft volume from large to small was ovariectomized group, normal estrogen group, and high estrogen group. There was significant difference in wet weight between the ovariectomized group and high estrogen group ( P<0.05). Section staining showed that compared with the normal estrogen group, the adipocytes in the ovariectomized group were larger, the expression of peri-lipoprotein was weaker, the vascular density decreased, and the expressions of UCP1 was negative, and the estrogen receptor α positive cells reduced. The above observation results in the high estrogen group were contrary to those in the ovariectomized group. There were significant differences in the diameter of adipocytes, the vascular density of adipose tissue, the number of the estrogen receptor α positive cells between groups ( P<0.05). The results of qRT-PCR showed that the mRNA expressions of UCP1 and estrogen receptor α significantly increased in the high estrogen group and decreased in the ovariectomized group compared with the normal estrogen group, and the differences were significant ( P<0.05).
CONCLUSION: The level of circulating estrogen has a significant effect on the outcome of free fat grafting in nude mice. Low estrogen level leads to hypertrophy of graft adipocytes, while high estrogen level leads to the production of a large amount of beige fat and high vascular density in fat grafts, which may be related to the activation of estrogen receptor α on adipocytes.