Adipocyte regeneration after free fat transplantation: promotion by stromal vascular fraction cells.

Our objective was to explore the mechanism of cell-assisted adipose transplantation by using freshly isolated human stromal vascular fraction (SVF) cells and to observe the dynamic changes of the graft after transplantation. The SVF was isolated from human liposuction aspirates, and 0.5 ml adipose tissue was mixed with 1 × 10(6) SVF cells or culture medium then injected to nude mice subcutaneously. At 1, 4, 7, 14, 30, 60, and 90 days after transplantation, samples were harvested for 1) general observation and retention rate; 2) whole-mount stain; 3) H&E stain; 4) immunohistochemical staining for S100, CD68, and CD34; 5) ELISA for VEGF and bFGF; 6) peroxisome proliferator-activated receptor-γ (PPARγ) fluorescence in situ hybridization. The retention rate in the experiment group was markedly higher than that in the control group. Whole-mount stain shows most of the cells in the center of the graft could not survive the ischemia until day 14. Histology showed new vessels on the surface of the graft at 3 days. However, in the control group, fewer newly formed vessels were detected until day 7. In the late stage of transplantation, gradual fibrosis was found in the graft, and the tissue was divided into a grid-like structure. A large number of round neonatal adipocytes with big nuclei in the center were found surrounding the new vessels, which were S100 and CD34 positive and CD68 negative. In the late stage of transplantation, most of the neonatal adipocytes were human PPARγ positive. Moreover, the SVF group showed a higher level of VEGF and bFGF. SVF assisting adipose transplantation could increase the retention rate of the graft through promoting adipose tissue regeneration via secretion of growth factors, promotion of angiogenesis, and increasing the density of mesenchymal stem cells.