Brain activity and transcriptional profiling in mice under chronic jet lag

Frequent Shifts During Chronic Jet Lag Uncouple Liver Rhythms From the Light Cycle in Male Mice

Circadian disruption is pervasive in modern society and associated with increased risk of disease. Chronic jet lag paradigms are popular experimental tools aiming to emulate human circadian disruption experienced during rotating and night shift work. Chronic jet lag induces metabolic phenotypes tied to liver and systemic functions, yet lack of a clear definition for how rhythmic physiology is impaired under these conditions hinders the ability to identify the underlying molecular mechanisms. Here, we compared 2 common chronic jet lag paradigms and found that neither induced arrythmicity of the liver and each had distinct effects on rhythmicity. Instead, more frequent 8-h forward shifts of the light schedule induced more severe misalignment and non-fasted hyperglycemia. Every other day shifts eventually uncoupled behavioral and hepatic rhythms from the light cycle, reminiscent of free-running conditions. These results point to misalignment, not arrhythmicity, as the initial disturbance tied to metabolic dysfunction in environmental circadian disruption and highlight considerations for the interpretation and design of chronic jet lag studies.

Circadian disruption promotes the neurotoxicity of oligomeric alpha-synuclein in mice

Circadian disruption often arises prior to the onset of typical motor deficits in patients with Parkinson's disease (PD). It remains unclear whether such a prevalent non-motor manifestation would contribute to the progression of PD. Diffusible oligomeric alpha-synuclein (O-αSyn) is perceived as the most toxic and rapid-transmitted species in the early stages of PD. Exploring the factors that influence the spread and toxicity of O-αSyn should be helpful for developing effective interventions for the disease. The aim of this study was to explore the effects of circadian disruption on PD pathology and parkinsonism-like behaviors in a novel mouse model induced by O-αSyn. We discovered that O-αSyn could enter the brain rapidly following intranasal administration, resulting in the formation of nitrated-αSyn pathology and non-motor symptoms of the mice. Meanwhile, circadian disruption exacerbated the burden of nitrated-αSyn pathology and accelerated the loss of dopaminergic neurons in O-αSyn-treated mice. Subsequent experiments demonstrated that circadian disruption might act via promoting nitrative stress and neuroinflammation. These findings could highlight the circadian rhythms as a potential diagnostic and therapeutic target in early-stage PD.

Chronic jet lag reduces motivation and affects other mood-related behaviors in male mice

Introduction: The circadian system regulates various physiological processes such as sleep-wake cycles, hormone secretion, metabolism, and the reaction to both natural and drug-based rewards. Chronic disruption of the circadian system caused by unsteady synchronization with light-dark (LD) schedules, such as advancing chronic jet lag (CJL), leads to adverse physiological effects and pathologies, and is linked with changes in mood and depressive behaviors in humans and rodent models. Methods: C57BL/6J male mice were subjected to circadian disruption through phase advances of 6 h every 2 days (CJL +6/2). Mice under 12:12-h LD cycle were used as controls. After 8 weeks under these conditions, a battery of behavioral tests was performed to assess if mood-related behaviors were affected. Results: Compared to controls under 24 h LD cycles, mice under CJL presented desynchronization of activity-rest rhythms that led to several behavioral impairments, including a decrease in motivation for food reward, and an increase in anxiety, anhedonia, and depressive-like behavior. Conclusion: Chronic circadian disruption, caused by an experimental CJL protocol, affects mood-related and reward-related behaviors in mice. Understanding the importance of the circadian system and its potential role for disruption due to CJL is important for maintaining good health and well-being.

Chronic jet lag-like conditions dysregulate molecular profiles of neurological disorders in nucleus accumbens and prefrontal cortex

Background

Patients with neurological disorders often display altered circadian rhythms. The disrupted circadian rhythms through chronic jetlag or shiftwork are thought to increase the risk and severity of human disease including, cancer, psychiatric, and related brain diseases.

Results

In this study, we investigated the impact of shiftwork or chronic jetlag (CJL) like conditions on mice's brain. Transcriptome profiling based on RNA sequencing revealed that genes associated with serious neurological disorders were differentially expressed in the nucleus accumbens (NAc) and prefrontal cortex (PFC). According to the quantitative PCR (qPCR) analysis, several key regulatory genes associated with neurological disorders were significantly altered in the NAc, PFC, hypothalamus, hippocampus, and striatum. Serotonin levels and the expression levels of serotonin transporters and receptors were significantly altered in mice treated with CJL.

Conclusion

Overall, these results indicate that CJL may increase the risk of neurological disorders by disrupting the key regulatory genes, biological functions, serotonin, and corticosterone. These molecular linkages can further be studied to investigate the mechanism underlying CJL or shiftwork-mediated neurological disorders in order to develop treatment strategies.

Circadian Rhythm Disruption Increases Tumor Growth Rate and Accumulation of Myeloid-Derived Suppressor Cells

Circadian rhythm disruption is implicated in the initiation and progression of many diseases, including cancer. External stimuli, such as sunlight, serve to synchronize physiological processes and cellular functions to a 24-h cycle. The immune system is controlled by circadian rhythms, and perturbation of these rhythms can potentially alter the immune response to infections and tumors. The effect of circadian rhythm disruption on the immune response to tumors remains unclear. Specifically, the effects of circadian disruption (CD) on immunosuppressive cell types within the tumor, such as myeloid-derived suppressor cells (MDSCs), are unknown. In this study, a shifting lighting schedule is used to disrupt the circadian rhythm of mice. After acclimation to lighting schedules, mice are inoculated with 4T1 or B16-F10 tumors. Tumor growth is increased in mice housed under circadian disrupting lighting conditions compared to standard lighting conditions. Analysis of immune populations within the spleen and tumor shows an increased accumulation of MDSCs within these tissues, suggesting that MDSC mediated immunosuppression plays a role in the enhanced tumor growth caused by circadian disruption. This paves the way for future studies of the effects of CD on immunosuppression in cancer.

Disrupting circadian rhythms promotes cancer-induced inflammation in mice

Disruption of circadian rhythms occurs in rotating shift-work, jetlag, and in individuals with irregular sleep schedules. Circadian disruption is known to alter inflammatory responses and impair immune function. However, there is limited understanding of how circadian disruption modulates cancer-induced inflammation. Inflammation is a hallmark of cancer and is linked to worse prognosis and impaired brain function in cancer patients. Here, we investigated the effect of circadian disruption on cancer-induced inflammation in an orthotopic breast cancer model. Using a validated chronic jetlag protocol that advances the light-cycle by 8 ​h every 2 days to disrupt circadian rhythms, we found that circadian disruption alters cancer-induced inflammation in a tissue-specific manner, increasing inflammation in the body and brain while decreasing inflammation within the tumor tissue. Circadian disruption did not affect inflammation in mice without tumors, suggesting that the impact of circadian disruption may be particularly detrimental in the context of underlying inflammatory conditions, such as cancer. Importantly, circadian disruption did not affect tumor burden, suggesting that increased inflammation was not a result of increased cancer progression. Overall, these findings identify the importance of healthy circadian rhythms for limiting cancer-induced inflammation.

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Circadian disruption enhances cancer-induced inflammation in the body and brain.

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The profile of inflammatory cytokines altered by circadian disruption is tissue specific.

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Changes in inflammatory profiles by circadian ​disruption are not due to enhanced tumor burden.

Circadian disruption in mice through chronic jet lag-like conditions modulates molecular profiles of cancer in nucleus accumbens and prefrontal cortex

Biological rhythms regulate physiological activities. Shiftwork disrupts normal circadian rhythms and may increase the risk of cancer through unknown mechanisms. To mimic environmental light/dark changes encountered by shift workers, a protocol called 'chronic jet lag (CJL)' induced by repeatedly shifting light-dark cycles has been used. Here, we subjected mice to CJL by advancing light-dark cycle by 6 h every 2 days, and conducted RNA sequencing to analyze the expression profile and molecular signature in the brain areas of prefrontal cortex and nucleus accumbens. We also performed positron emission tomography (PET) imaging to monitor changes related to glucose metabolism in brain. Our results reveal systematic reprogramming of gene expression associated with cancer-related pathways and metabolic pathways in prefrontal cortex and nucleus accumbens. PET imaging indicates that glucose uptake level was significantly reduced in whole brain as well as the individual brain regions. Moreover, qPCR analysis describes that the expression levels of cancer-related genes were altered in prefrontal cortex and nucleus accumbens. Overall, these results suggest a molecular and metabolic link with CJL-mediated cancer risk, and generate hypotheses on how CJL increases the susceptibility to cancer.