Purpose: Fat grafting has been used clinically to alleviate the sequalae of unintended radiation to the skin, however the mechanism of this effect is unknown. We hypothesize that it is related to the delivery of adipose derived stem cells and subsequent neovascularization.

Methods: The dorsum of adult wild-type FVB mice was shaved and depilitated. The dorsal skin was then distracted away from the body and radiated (45 Gy) using a Varian 2300 Linear Accelerator. Tissue oximetry and gross photometric analysis were carried out biweekly for the duration of the experiment. 4 weeks following radiation, fat/sham grafts were placed in the dorsal subcutaneous space. Fat grafts consisted of 1.5 cc's of high density lipoaspirate harvested from human donors and processed using the Coleman technique. Sham grafts consisted of 1.5 cc's of sterile saline. Animals were sacrificed at 4 and 8 weeks following fat/sham grafting and their dorsal skin was processed for histologic analysis. Neovascularization was measured by CD31 staining. Fibrosis was assessed using Smad-3 staining, Picrosirius Red staining (Scar-Index), and epidermal thickness measurements.

Results: Chronic ulceration and fibrotic skin thickening stabilized 4 weeks post-irradiation. Alopecia, skin color/texture, and ulceration were improved in fat-grafted mice compared to sham-treated controls when analyzed photometrically. Tissue oximetry demonstrated significantly increased blood oxygenation in treated animals beginning two weeks following grafting (8 weeks post graft 77.1±1.4% vs 68.5±2.2%, p<0.03). Vascular density of irradiated skin was increased in fat grafted mice compared to radiated controls at 4 weeks (7.3±0.04% vs 5.2±0.09%, p<0.01). Relative intensity of Smad-3 staining was significantly decreased in treated animals at both 4 and 8 weeks (2.77±0.3% vs 4.98±.9%, p<0.01; 3.05±.2% vs 5.81±.3%, p<0.03). Picrosirius Red staining demonstrated a diminished scar-index in treated animals at both 4 and 8 weeks (.54±0.05 vs .74±.07, p<0.03; .55±.06 vs .93±.07, p<0.01). Finally, epidermal thickness measurements demonstrated a decreased thickness in treated animals at both 4 and 8 weeks as well (20.6±1.5µm vs 55.2±5.6 µm, p<0.01; 17.6±1.1µm vs 36.3±6.1 µm, p<0.04).

Conclusion: Human fat grafting has a marked phenotypic and experimental impact on radiation skin damage in a murine model. These affects are related to neovascularization and the downregulation of the TGF-β/Smad3 pathway, which results in restoration of normal skin architecture with decreased fibrosis and epidermal thickness.