Early Macrophage Infiltration Improves the Fat Graft Survival by Inducing Angiogenesis and Hematopoietic Stem Cell Recruitment.

Background: Fat grafting is a popular soft tissue filler method; however, its results are variable and technique-dependent. Macrophages are present in fat grafts and closely associated with tissue regeneration. We hypothesized that activation/depletion of early macrophages in transferred fat improves/impairs fat graft survival. Methods: Mouse inguinal fat (~150 mg) was transferred autologously. Fat grafting was first performed without other manipulations to obtain baseline information. Then, liposome-encapsulated clodronate and macrophage-colony stimulating factor were used in a mouse fat grafting model for local macrophage depletion or activation. We examined the graft stromal vascular fraction (SVF) by fluorescence-activated cell sorting (FACS) at 1, 2, 4, and 12 weeks post-transplantation in manipulation/control groups. Graft weight, vascularization, and secreted factors were also compared. Results: FACS of graft SVF cells demonstrated that at 1 week post-transplantation 24+/-3% of cells were macrophages with high TNF-[alpha] expression. At 4 weeks post-transplantation, massive angiogenesis (p=0.014, vs. Week 1) was observed in the grafts, and 33+/-6% of SVF cells were macrophages with high TGF-[beta] expression. Early depletion of macrophages resulted in incompetent angiogenesis, feeble Sca-1+/CD45+ stem cell recruitment, and eventually a poor retention rate (34+/-6 mg vs. control 84+/-15 mg, p=0.006), whereas up-regulated macrophages allowed better angiogenesis and survival (117+/-12 mg vs. control 84+/-15 mg, p=0.043). Conclusions: In fat grafting, macrophages and their polarization initiated changes in the levels of dominant secreted factors and influenced blood-derived stem cell infiltration, indicating that macrophages were crucial for tissue revascularization. The macrophage manipulation models described here show that graft macrophage number can profoundly influence graft survival. (C)2017American Society of Plastic Surgeons