Single Cell and Spatial Transcriptomics Implicate Vascular Cell Orchestration of Inflammatory Changes After Ultraviolet Light Exposure [Spatial Transcriptomics]

To elucidate the complex effects of acute UV radiation (UVR) on the skin, we exposed shaved mouse skin to UVB and performed transcriptomic profiling of the epidermis, deep dermis and adipose tissue. Spatial transcriptomic analysis revealed the most pronounced gene expression changes in the epidermis, peaking at 24 hours post-irradiation. While CD45? immune cells showed differential expression of chemokines, cytokines, and acute-phase proteins, cytokeratin? epidermal cells upregulated genes related to cellular stress and damage (e.g., Usp19, Adam25), as well as structural remodeling and apoptosis (e.g., Krt18, Phlda1). Single-cell RNA sequencing (scRNA-seq) conducted 12 hours after UVR exposure identified 4,849 differentially expressed genes (DEGs), with the epidermis and endothelial cells showing the highest DEG counts. Pathway analysis of upregulated genes in the epidermis revealed enrichment in VEGF, HIPPO, complement, IL-6, and apoptosis signaling pathways. In endothelial cells, UVR induced expression of multiple chemokines and cytokines. Notably, receptor-ligand analysis highlighted endothelial cells as key targets of CXCL chemokines and complement component C3. In fibroblasts, UVR triggered upregulation of inflammatory activation markers (Osmr, Cux1) alongside genes associated with glucose metabolism (Hif1a, Pkm). Cross-species comparison of UVR-responsive DEGs between mice and humans revealed strong concordance, particularly in TGF-ß and TNF-associated pathways. Overall design: Mice used in this study were 12-16 week old C57BL/6 (B6, wild type) females. Mice were anesthetized with isoflurane and a single dose of UVB (500 mJ/cm2) was delivered to the shaved whole back using FS40T12/UVB bulbs (National Biological Corporation) as described previously (Skopelja-Gardner et al., 2021). The narrow band UVB light energy (290-320 nm) at the dorsal surface was measured with Photolight IL1400A radiometer with a SEL240/UVB detector (International Light Technologies). Biopsies were taken at times 0, 6, and 24 hours after UVB exposure (n=3 per group) for spatial transcriptome analysis.