M. R. Borrelli1, D. Irizarry1, R. E. Brewer1, R. Patel1, C. Blackshear1, J. Sokol1, A. Momeni1, M. T. Longaker1, D. C. Wan1 1Stanford University,Plastic Surgery,Palo Alto, CA, USA
Introduction Radiotherapy (RT) is extremely effective at shrinking tumor size and reducing local cancer recurrence but causes significant damage to the healthy soft tissue in the radiation field. This collateral soft tissue fibrosis can cause, in addition to cosmetic disturbances, significant functional alterations such as contracture of extremities. Fat grafting is increasingly recognized as a technique able to prevent or reverse the radiation-induced fibrosis in the skin, and clinical reports have demonstrated functional improvements for patients following RT for both breast and head and neck cancer. Animal models to study this effect, however, are limited.
Methods We irradiated the right hind limbs of Prrx1Cre/mTmG mice, a transgenic mouse where the fibrogenic subpopulation of fibroblasts in ventral skin (Prrx1+) are labelled by embryonic expression Cre. Mice received 30 Gy fractionated in 5 Gy doses every two days for a total of 12 days. After a one-month recovery period followed to allow contracture to develop, the mice were sacrificed, and hind limbs were processed for histology. To explore the therapeutic effects of fat graft grafting, CD-1 nude mice were irradiated using the same dosing regimen. At one-month post recovery, the irradiated hind limbs were injected with 200ul of human lipoaspirate fat grafts or lipoaspirate with enriched SVFs (stromal vascular fraction cells, 10,000 cells/ml) into the subcutaneous space. Lipoaspirate was obtained from healthy female donors (n=3). Control mice were injected with saline or received sham surgery with no injection. Limb extensibility was measured every two weeks for a total of 12-weeks. Mice were then sacrificed, and hind limbs were processed for histology. Finally, hind limb skin underwent mechanical strength testing (MST).
Results: Hind limb irradiation significantly reduced limb extensibility (Fig1A). These functional differences were associated with a significant increase in the fibrogenic fibroblast subpopulation (Fig1B). Fat grafting progressively improved limb extension (Fig1C) and reduced skin stiffness; the greatest benefit was observed in the mice who received fat supplemented with SVFs, with little or no benefit seen in mice who received saline or sham treatment.
Conclusion: We have created a mouse model of radiation-induced hind limb contracture which allows for detailed dissection of the interaction between the transfer of autologous transferred fat and radiation-induced soft tissue contracture. Using this model, we have demonstrated radiation-induced functional hindlimb contractures to be associated with increased fibrogenic subpopulations within the dermis. Transfer of fat also resulted in improved limb extension and reduction in stiffness.
