SP60. Insights Into Irradiation Effects on Vascular Tissues: Single-cell Transcriptional Analysis From Irradiated Internal Mammary Arteries and Aorta

PURPOSE: Despite advancements in oncology radiation, radiation-induced vascular damage remains a significant clinical challenge. Clinical studies indicate that patients previously treated with radiation therapy for various malignancies often experience significant alterations in their blood vessels, leading to radiation-induced fibrosis and vascular disease. These changes, for which there are few translational therapies, can have profound implications for cardiovascular health and reconstructive outcomes in affected individuals. METHODS: Internal mammary vessels were collected from six female patients undergoing post-oncologic breast reconstruction, with paired samples obtained from irradiated and non-irradiated sides. Additionally, aortas were harvested from 20 adult female C57BL/6J mice, divided into irradiated and non-irradiated groups. The irradiated group underwent dorsal irradiation to induce chronic fibrosis. Samples underwent histologic staining, immunochemistry, and transcriptional analysis. Single-cell RNA sequencing was conducted using the Chromium Sequencer (10X Genomics). Clustering analysis was performed using Seurat in R, with cell type identities assigned using the SingleR classifier. Differentially expressed genes were determined using non-parametric testing. RESULTS: Histological examination revealed significant changes in irradiated blood vessels compared to non-irradiated mice vessels, including increased intima/media ratio, myo-intimal proliferation, and increased collagen deposition in the media layer with disorganized collagen fibers deposition within the extracellular matrix. These findings were observed in both mice and human samples. Computational analysis of Masson Trichrome and Picrosirius Red stained sections, visualized on UMAP plot, demonstrated increased collagen density and distinct clustering of ECM features, respectively, of irradiated blood vessel compared to non-irradiated vessels. Single-cell analysis of irradiated blood vessels identified six distinct clusters of cells, including five different fibroblasts subclusters with and two endothelial cell clusters, representing the majority of sequenced cells. CONCLUSION: These findings provide valuable insights into the fibrotic processes occurring in irradiated blood vessels and identify potential targets for addressing vascular disease and optimizing post operative outcomes in affected patients.