ABSTRACT: Transcriptomic profiling of normal mouse thyroid tissue following 211At irradiation Introduction The cellular response to stimuli can be studied on different molecular levels, including gene expression regulation. RNA microarray is a high-throughput technique that enables comparison of genome-wide transcriptional status between samples. 211At-labeled radiopharmaceuticals are potentially useful for tumor therapy. Metabolically released 211At accumulates in the thyroid gland, which is one of the main critical organs for such therapy. The aim of this study was to determine the effect of absorbed dose, dose-rate, and time after 211At exposure on transcriptional expression in mouse thyroid gland. Method BALB/c mice were i.v. injected with 1.7, 7.5 or 100 kBq 211At. Animals injected with 1.7 kBq were killed after 1, 6, or 168 h with mean absorbed doses to thyroid of 0.023, 0.32, and 1.4 Gy, respectively. Animals injected with 7.5 and 100 kBq were killed after 6 and 1 h, respectively, resulting in mean absorbed doses to thyroid of 1.4 Gy. Animals were killed through cardiac puncture under anesthesia, and thyroids were removed and snap-frozen. Total RNA was extracted from pooled thyroid tissue samples and mRNA levels were determined with the Illumina RNA microarray platform. Nexus Expression 3.0 was used to identify differentially expressed transcripts (adjusted p-value <0.01, fold change >1.5) and enriched GO terms (p-value <0.05) between irradiated groups and controls. Results In total, 1232 differentially expressed transcripts were detected after 211At administration, demonstrating a profound effect on gene regulation. The number of regulated transcripts increased with higher initial dose-rate/absorbed dose when the exposure time was 1 or 6 h. However, the number of regulated transcripts decreased with mean absorbed dose/time after 1.7 kBq 211At administration. This suggests that initial dose-rate (thus injected activity) is an important parameter in radiation-induced responses. Furthermore, the regulation profiles of groups administered 1.7 kBq were similar. Few previously proposed radiation responsive genes were identified in the present study, but, e.g. Gadd45g and Cdkn1a were among the regulated genes identified in the present study. A response involving immunological processes was identified especially at 1, 6, and 168 h after 1.7 kBq administration (0.023, 0.32, 1.8 Gy). Conclusion The present study allowed a comprehensive assessment of how variations in exposure parameters affect transcriptional regulation. The regulation profiles were dependent on both absorbed dose and time after exposure, but, initial dose-rate was the most influential parameter. Functional annotation of regulated genes revealed exposure-specific effects on biological processes. Additionally, we have identified several recurrently regulated genes after 211At exposure that may play a role in how mouse thyroid tissue responds to 211At exposure. Introduction The cellular response to stimuli can be studied on different molecular levels, including gene expression regulation. RNA microarray is a high-throughput technique that enables comparison of genome-wide transcriptional status between samples. 211At-labeled radiopharmaceuticals are potentially useful for tumor therapy. Metabolically released 211At accumulates in the thyroid gland, which is one of the main critical organs for such therapy. The aim of this study was to determine the effect of absorbed dose, dose-rate, and time after 211At exposure on transcriptional expression in mouse thyroid gland. Method BALB/c mice were i.v. injected with 1.7, 7.5 or 100 kBq 211At. Animals injected with 1.7 kBq were killed after 1, 6, or 168 h with mean absorbed doses to thyroid of 0.023, 0.32, and 1.4 Gy, respectively. Animals injected with 7.5 and 100 kBq were killed after 6 and 1 h, respectively, resulting in mean absorbed doses to thyroid of 1.4 Gy. Animals were killed through cardiac puncture under anesthesia, and thyroids were removed and snap-frozen. Total RNA was extracted from pooled thyroid tissue samples and mRNA levels were determined with the Illumina RNA microarray platform. Nexus Expression 3.0 was used to identify differentially expressed transcripts (adjusted p-value <0.01, fold change >1.5) and enriched GO terms (p-value <0.05) between irradiated groups and controls. Results In total, 1232 differentially expressed transcripts were detected after 211At administration, demonstrating a profound effect on gene regulation. The number of regulated transcripts increased with higher initial dose-rate/absorbed dose when the exposure time was 1 or 6 h. However, the number of regulated transcripts decreased with mean absorbed dose/time after 1.7 kBq 211At administration. This suggests that initial dose-rate (thus injected activity) is an important parameter in radiation-induced responses. Furthermore, the regulation profiles of groups administered 1.7 kBq were similar. Few previously proposed radiation responsive genes were identified in the present study, but, e.g. Gadd45g and Cdkn1a were among the regulated genes identified in the present study. A response involving immunological processes was identified especially at 1, 6, and 168 h after 1.7 kBq administration (0.023, 0.32, 1.8 Gy). Conclusion The present study allowed a comprehensive assessment of how variations in exposure parameters affect transcriptional regulation. The regulation profiles were dependent on both absorbed dose and time after exposure, but, initial dose-rate was the most influential parameter. Functional annotation of regulated genes revealed exposure-specific effects on biological processes. Additionally, we have identified several recurrently regulated genes after 211At exposure that may play a role in how mouse thyroid tissue responds to 211At exposure. Total RNA was isolated from fresh-frozen tissue samples (Normal balb/c mouse thyroids)
