The fates of different types of adipose tissue after transplantation in mice

Fat grafting is one of the most commonly applied procedure for soft-tissue repair. However, it remains unclear whether the type of adipose tissue would have any effects on fat graft survival. The present study aimed to determine fates of fat grafting of three different types of fat tissue. In this study, mice were randomly divided into three groups, white adipose tissue (WAT) group, beige adipose tissue (beige AT) group and brown adipose tissue (BAT) group. Before transplantation, donor mice were injected with rosiglitazone or phosphate-buffered saline (PBS). The WAT and BAT were obtained from PBS-treated mice while beige AT was obtained from the rosiglitazone-treated mice. Three types of fat tissue (150 mg each) were transplanted in three groups, respectively, and harvested at 2, 4 or 12 weeks. The BAT and beige AT contained smaller adipocytes and expressed higher level of uncoupling protein-1 gene. The retention rate of the transplanted fat was significantly higher for beige than for white fat, but was significantly lower for brown than for white fat. Transplanted brown fat was characterized by upregulated inflammation and high endoplasmic reticulum stress. By contrast, fat grafts in beige AT group showed the best adipogenic capacity, moderate inflammation level and superior angiongenesis. In vitro, under hypoxic condition, fewer apoptotic cells were found in beige adipocyte group than that in brown and white adipocyte group. Conditioned medium from brown adipocytes induced M1 polarization of RAW 264.7 macrophages while that from beige adipocytes effectively promoted M2 polarization. Therefore, we suggest that beige AT provides a new potential choice for fat grafting because of low inflammation and superior survival but BAT might not be ideal for fat grafting due to its poor survival.