8. Post-mastectomy Radiation Promotes Pro-fibrotic Mechanosensitive Fibroblast Populations Within Human Breast Implant Capsules

PURPOSE: Post-mastectomy radiation (PMRT) has become an integral part of the multimodal therapeutic approach for breast cancer. It has been demonstrated that PMRT adversely affects outcomes of implant-based and autologous breast reconstruction. In patients for whom PMRT seems likely, delayed autologous reconstruction with tissue expander (TE) placement at the time of mastectomy is often performed. On a cellular level, the impact of radiation on cellular subpopulations and signaling pathways within expander/implant capsules remain poorly understood, and it is still unclear whether specific cell populations persist within breast implant capsules that sustain the long-term effects of radiation-induced periprosthetic fibrosis. METHODS: Breast implant capsule specimens were harvested from irradiated and non-irradiated breasts in patients undergoing delayed immediate breast reconstruction with microvascular free flaps 6 - 12 months after TE placement (n = 16 samples). Tissue was processed for single-cell RNA sequencing using the 10X Genomics chromium platform and histologic analysis. Bioinformatics analysis was performed using the Seurat package in R. RESULTS: A total of 149,191 cells were captured, and distinct populations of fibroblasts, myeloid cells, lymphoid cells, and endothelial cells were identified. Fibroblasts had the highest number of differentially expressed genes between irradiated and control samples (> 1000). Fibroblasts from irradiated samples demonstrated an increased expression of fibrosis-associated and mechanotransduction markers including FOS, CD9, YAP/TAZ, and the focal adhesion kinase pathway compared to non-irradiated controls. In addition, we found that regenerative markers such as APOE, EGR1, and WNT3 were depleted in irradiated breast implant capsules compared to controls. CONCLUSION: Our findings indicate that radiation exposure promotes pro-fibrotic mechanosensitive fibroblast populations and demonstrate their long-term persistence within human breast implant capsules. Moreover, our data point to a therapeutic rationale for mechanotransduction inhibitors to reduce radiation-induced periprosthetic fibrosis in breast reconstruction.