1: Fat Grafting Improves Dorsal Skin Fibrosis after Radiation in an Engrailed-1 Mouse Model

• Main Authors: Darren B. Abbas, M.D., Evan J. Fahy, MB BCh BAO, MCh, Christopher Lavin, B.S., Michelle Griffin, MBChB, Ph.D., Sandeep Adem, M.S., Nestor M. Diaz Deleon, Shamik Mascharak, B.S., Megan King, B.S., Daniel Lee, M.D., Michael T. Longaker, M.D., M.B.A, Derrick C. Wan, M.D.
• Format: Article
• Language: English
• Published: Wolters Kluwer 2021-07-01
• Series: Plastic and Reconstructive Surgery, Global Open
• Online Access: http://journals.lww.com/prsgo/fulltext/10.1097/01.GOX.0000769928.40352.e5

Purpose: Fat grafting is known to rejuvenate and improve fibrosis in irradiated skin, but the underlying mechanisms behind these effects are poorly understood. We have previously identified the Engrailed-1 fibroblast sub-population as having a role in post-natal dorsal skin fibrosis in mice. Using a radiation model to the scalp of Engrailed-1 mice, we sought to better understand the regenerative effects of fat grafting in irradiated tissue. Methods: Adult (60-day old) En1Cre;R26mTmG transgenic mice (n=5) underwent total body irradiation with 9 Gy for immunodepletion. Mice were then immediately reconstituted with 2 million nucleated bone marrow cells from donor NSG(NOD.CB17-Prkdcsscid/J) mice via retro-orbital injections. Reconstitution was confirmed with fluorescence-activated cell sorting (FACS) 2 weeks after whole body irradiation. Mice scalps were then irradiated with 5 Gy every other day for 12 days (30 Gy total) and allowed to recover for 4 weeks to facilitate fibrotic conversion. Irradiated scalps were grafted with 200μL of fresh human lipoaspirate. Graph retention was measured in-vivo for 8 weeks using Micro-Computed Tomography Scanner (Bruker SkyScan 1726™) and scalp skin was harvest for histology. Results: Two weeks post bone-marrow transplant, >90% of circulating hematopoietic cells (CD45+) cells in En1Cre;R26mTmG reporter mice were non-fluorescent, signifying successful reconstitution. Volumetric analysis of fat grafting in-vivo was performed using 3-dimensional reconstruction. At 8 weeks post-grafting, 4 of the 5 grafts demonstrated >50% graft retention, confirming successful grafting. Histological sections of scalp skin 8 weeks post-grafting demonstrated significantly less En1+GFP cells compared to non-grafted scalp skin, signifying less presence of En1+ fibroblasts. Furthermore, histology demonstrated significantly less dermal thickening, epidermal thinning, and collagen deposition and disorganization in fat grafted irradiated scalp skin compared to non-grafted scalp skin. Conclusion: Fat grafting mitigates radiation-induced fibrosis in scalp skin by decreasing collagen deposition, remodeling collagen formation, decreasing epidermal thinning, and reducing presence of pro-fibrotic fibroblast sub-populations.