Age plays a critical role in disease development and tolerance to cancer treatment, often leading to an increased risk of developing negative symptoms including sleep disturbances. Circadian rhythms and sleep become disrupted as organisms age. In this study, we explored the behavioral alterations in sleep, circadian rhythms, and masking using a novel video system and interrogate the long-term impact of age-based changes in the non-image forming visual pathway on brain anatomy. We demonstrated the feasibility and utility of the novel system and establish that older mice have disruptions in sleep, circadian rhythms, and masking behaviors that were associated with major negative volume alterations in the non-imaging forming visual system, critical for the induction and rhythmic expression of sleep. These results provide important insights into a mechanism, showing brain atrophy is linked to age in distinct non-image forming visual regions, which may predispose older individuals to developing circadian and sleep dysfunction when further challenged by disease or treatment.
Circadian clock genes have been linked to clinical outcomes in cancer, including gliomas. However, these studies have not accounted for established markers that predict the prognosis, including mutations in Isocitrate Dehydrogenase (IDH), which characterize the majority of lower-grade gliomas and secondary high-grade gliomas. To demonstrate the connection between circadian clock genes and glioma outcomes while accounting for the IDH mutational status, we analyzed multiple publicly available gene expression datasets. The unsupervised clustering of 13 clock gene transcriptomic signatures from The Cancer Genome Atlas showed distinct molecular subtypes representing different disease states and showed the differential prognosis of these groups by a Kaplan–Meier analysis. Further analyses of these groups showed that a low period (PER) gene expression was associated with the negative prognosis and enrichment of the immune signaling pathways. These findings prompted the exploration of the relationship between the microenvironment and clock genes in additional datasets. Circadian clock gene expression was found to be differentially expressed across the anatomical tumor location and cell type. Thus, the circadian clock expression is a potential predictive biomarker in glioma, and further mechanistic studies to elucidate the connections between the circadian clock and microenvironment are warranted.
BACKGROUND Radiation therapy is the standard of care for both primary and secondary brain tumors. The majority of patients experience radiation induced hypersomnia (RIH) to varying extents which may impact life quality and treatment tolerance. Previously, we demonstrated that risk is enhanced by presence of select clock gene polymorphisms. The purpose of this study is to establish a mouse model of RIH to test dose effects of cranial irradiation on behavioral sleep and activity prior to introducing tumor in transgenic mice. METHODS Twenty-four non-tumor bearing C57BL/6 mice received whole brain radiation at one of 4 doses (sham, 2Gy, 5Gy, and 15Gy) using a single fraction. Behavior, total activity (distance) and sleep quantity (seconds) were monitored using Phenotyper cages and Ethovision Software with data collected at baseline (10 days) and post-radiation (11 days); percentage of activity was calculated as post-radiation/baseline activity. Blood and tissue samples were collected. RESULTS Baseline activity was not significantly different between groups (F(3.23) = 0.649, p=0.593). Shams and 2Gy mice were not affected by the procedure and activity levels were unchanged, 99.76±1.3% and 103.3±3.5%, respectively. The higher doses, 5Gy and 15Gy, had suppression of general activity compared to baseline with 90.8±2.7% and 88.9±1.3%, respectively. Between the two groups, suppression of activity started after 2 days in 15Gy and 5 days in 5Gy mice. Across three days (8–10), 5Gy and 15Gy (19,872±577sec) had more sleep during their active phase (t=2.27, p=0.03) than sham or 2Gy (17,618±803sec). CONCLUSION Activity and sleep are affected by cranial irradiation in our RIH mouse model in dose dependent manner. This model closely resembles the effects seen in patients and provides a critical tool for interrogating the physiological drivers of RIH. In future studies, we will examine other behaviors and the association between circadian gene variants and RIH susceptibility as previously reported in patients.
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