0025 Circadian Dysregulation of Human DNA Repair Genes and Elevated DNA Damage in Simulated Night Shift Schedule. (25th May 2022) - Van Dongen, Hans
Abstract: Introduction: Circadian misalignment from night shift (NS) work is associated with increased risk of cancer. In a simulated NS study, we sought to investigate the potential role of circadian disruption of cancer hallmark pathway genes. Methods: N=14 healthy adults (aged 22-34) participated in a laboratory study. Seven were assigned to a simulated day shift (DS) schedule involving 3 days of daytime wakefulness (06:00-22:00); the other seven were assigned to a simulated NS schedule involving 3 days of nighttime wakefulness (18:00-10:00). Subjects then underwent a 24-hour constant routine protocol, during which blood was collected at 3-hour intervals. Leukocytes extracted from blood were subjected to transcriptomics using the NanoString nCounter PanCancer Pathways panel augmented with canonical clock genes. Statistical analysis involved mixed-effects cosinor analysis followed by functional enrichment analysis of rhythmic genes. Leukocytes were also subjected to endogenous DNA damage assessment through alkaline comet and immunofluorescence assays. Furthermore, exogenous DNA damage from exposure to ionizing radiation was investigated for blood collected at opposite times of day (07:30 and 19:30) based on DNA damage biomarkers assessed with immunofluorescence and immunoblot assays. Results: Transcriptomics data showed that the simulated NS schedule, as compared to the simulated DS schedule, significantly altered the endogenous circadian rhythmicity of genes involved in cancer hallmark pathways, as measured under constant routine. A DNA repair pathway showed enrichment of rhythmic genes following the DS schedule (P<0.05), but not following the NS schedule. Functional assessments revealed that the NS schedule was associated with increased endogenous DNA damage, as evidenced by alkaline comet assay (P<0.001) and increased BRCA1 foci (P<0.01) and γH2AX foci by immunofluorescence assay (P<0.001). After exposure to ionizing radiation, there were increased BRCA1 foci (P<0.01) and γH2AX foci by immunofluorescence assay (P<0.005) and elevated DNA damage response signaling biomarkers by immunoblot assay, especially in the samples collected at 19:30. Conclusion: These results suggest that a NS schedule causes circadian dysregulation of DNA repair genes and increases DNA damage – a primary hallmark of carcinogenesis – which may underlie the elevated cancer risk in NS workers. Support (If Any): WSU, CHHE P30ES025128, USAMRDC W81XWH-18-1-0100, NIH R01ES030113 and R21CA227381, CDMRP CA171123, DOE BRAVE DE-AC05-76RL01830.