Low dose rate effects on VH10 fibroblasts
Experimental studies complement epidemiological data on the biological effects of low doses and dose rates of ionizing radiation and help in determining the dose and dose rate effectiveness factor. Here, human VH10 skin fibroblasts exposed to 25, 50 and 100 mGy of 137Cs gamma radiation at 1.6, 8, 12 mGy/h, and at a high dose rate of 23.4 Gy/h were analyzed for radiation-induced short- and long-term effects. Two sample cohorts, i.e. discovery (n=30) and validation (n=12), were subjected to RNA sequencing. Results from the pool of those samples with shared conditions among six experiments constituted a third cohort (n=12). The 100 mGy-exposed cells at all the abovementioned dose rates, harvested at early and late time points after exposure, showed no strong gene expression changes. DMXL2, involved in regulating the NOTCH signaling pathway, presented a consistent upregulation among the discovery and validation cohorts. Gene set enrichment analysis revealed that the NOTCH pathway was upregulated in the pooled cohort (p=0.76, NES=0.86). Apart from upregulated apical junction and downregulated DNA repair, few pathways were consistently changed across exposed cohorts. In agreement, cell viability assays, performed 1-, 3-, and 6-days post-irradiation, and colony forming assay, seeded just after exposure, did not reveal any statistically significant early effects in cell growth or survival patterns. Tendencies of increased growth and reduced colony size were observed at 12 mGy/h and 23.4 Gy/min. Furthermore, no long-term changes were observed in cell growth curves generated up to 70 days after exposure. In conclusion, low doses of gamma radiation given at low dose rates had no strong cytotoxic effects on VH10 cells.