Gene expression in a 3D skin tissue subjected to bystander alpha-particle irradiation

The radiation bystander effect has been documented with multiple endpoints in various models. While many of the factors regulating this response are known, the mechanisms are still not well understood, and even less is known about signaling of bystander responses in 3-dimensional (3D) tissues. We have used the EPI-200 3D epidermal tissue model to measure global gene expression changes in bystander tissue in order to gain insight into the molecular pathways involved. We identified 187 genes with significantly altered expression in the region between 250 μm and 1 mm from the site of irradiation four hours after exposure. Gene expression at 250-500 μm and 500-750 μm was similar to that within the first 250 μm, the region that also included the directly irradiated tissue. Gene expression, although still significantly altered, began to return toward control levels in the region between 750 μm and 1 mm, however, suggesting a spatial limit to the bystander signal. The 3D bystander genes were concentrated in gene ontology classifications associated with direct irradiation, such as regulation of cell cycle progression and cell death, as well as categories previously associated with bystander responses, such as extracellular signaling, inflammatory processes, and terminal differentiation. A 25-micron wide strip across the center of a 3D skin tissue model was exposed to either 0 or 0.5 Gy alpha particles, and gene expression was analyzed in slices of tissue located at various distances away from the site of irradiation 16 hours after exposure. Three biological repeats were performed for each condition