Abstract: ATAC-seq Reveals Heterogeneity of Fibroblasts During Transition from Scarless Fetal to Scar-Forming Adult Wound Repair

Abstract

INTRODUCTION: Cutaneous wounds in early gestation heal without a scar in a process resembling regeneration.1 Although myriad studies have been performed to understand this phenomenon, the exact mechanism for fetal scarless repair is unknown. We previously characterized a fibroblast lineage in the dorsal skin of adult mice defined by embryonic expression of Engrailed-1 (En1) thought to be responsible for scar formation.2 Here, we investigate the role of this lineage during fetal wound healing. MATERIALS AND METHODS:En1-derived fibroblasts were traced by crossing En1Cre and ROSA26mTmG mice. A murine model of fetal scarless wound healing allowed for investigation of En1-derived fibroblast behavior before and after the scarless to scarring transition. En1-derived fibroblasts were characterized using flow cytometry. ATAC-seq (Assay for Transposase-Accessible Chromatin with high throughput sequencing) was also performed in isolated pre- and post-gestational fibroblasts at a series of time points. RESULTS: Dorsal wounds created at embryonic day (E)16.5 healed scarlessly with minimal connective tissue deposition. However, wounds created at E18.5 healed with substantial scar deposited primarily by En1-lineage-derived fibroblasts. The abundance of En1-lineage-derived fibroblasts and the expression of CD26, a previously identified marker of the En1 lineage, steadily increased from E12.5 through postnatal day 1. Differential transcriptional activity shown by ATAC-seq further demonstrates the heterogeneic nature of fibroblasts within the dorsal dermis. CONCLUSION: The En1 lineage of fibroblasts plays a critical role in the transition from scarless wound healing during fetal development. These results hold promise for the development of therapeutic approaches to fibrotic disease and adult wound healing. DISCLOSURE/FINANCIAL SUPPORT:Supported by CIRM Clinical Fellow training grant TG2-01159 (to Dr. Michael S. Hu), Stanford University School of Medicine Transplant and Tissue Engineering Fellowship Award (to Drs. Michael S. Hu, H. Peter Lorenz, and Michael T. Longaker), ASMS/MSF Research Grant Award (to Drs. Michael S. Hu, H. Peter Lorenz, and Michael T. Longaker), PSF Research Fellowship Grant 114288 (to Dr. Zeshaan N. Maan), NIH grant R01 GM087609 (to Dr. H. Peter Lorenz), a gift from Ingrid Lai and Bill Shu in honor of Anthony Shu (to Dr. H. Peter Lorenz), Hagey Laboratory for Pediatric Regenerative Medicine and The Oak Foundation (to Drs. Geoffrey C. Gurtner, H. Peter Lorenz, and Michael T. Longaker), Gunn/Olivier fund (to Drs. Irving L. Weissman and Michael T. Longaker), and NIH grant U01 HL099776 (to Dr. Michael T. Longaker). None of the authors has a financial interest in any of the products, devices, or drugs mentioned in this manuscript. REFERENCES: 1. Gurtner GC, Werner S, Barrandon Y, Longaker MT. Wound repair and regeneration. Nature. 2008;453(7193):314–321. 2. Rinkevich Y, Walmsley GG, Hu MS, et al. Skin fibrosis. Identification and isolation of a dermal lineage with intrinsic fibrogenic potential. Science. 2015;348(6232):aaa2151.