Disrupted Circadian Rhythms as a Novel Driver of Sarcopenia: Mechanisms, Evidence, and Future Directions

361 Circadian Rhythm Disruption in Emergency Medicine Residents

Melatonin, circadian rhythms and glaucoma: current perspective.

Circadian molecular clock disruption in chronic pulmonary diseases.

Preface

Circadian rhythms are evolutionarily created cycles programmed to integrate human behavior, physiology, and metabolism with the surrounding environment. The core clock machinery is composed of an autoregulatory network. The positive components of the loop are CLOCK and BMAL transcription factors, which heterodimerize to regulate expression of key circadian genes through E-box elements. CLOCK/BMAL regulate expression of cryptochrome (CRY1 and CRY2) and period (PER1, PER2, and PER3) genes, which are the negative components of the circadian loop. CRYs and PERs repress CLOCK/BMAL activity, thus conferring daily rhythmicity of cellular, metabolic, and physiological functions for homeostatic maintenance. Disruption to these rhythms, via nighttime light exposure or other forms of desynchronization, has been linked to poor health outcomes. Specifically, circadian disruption is designated as a probable carcinogen by the World Health Organization. Subsequent epidemiology research identified pilots and other shift workers have an increased risk of prostate cancer (PCa). Additional genomic studies identified multiple core clock genes (CCGs) with associated upregulation and/or downregulation in prostatic tumor tissues compared to benign samples. CCGs have also been found to impact several key oncogenic pathways including cell cycle control, apoptosis, DNA repair, and metabolic regulation. In order to further clarify the risk of an altered circadian genome, we analyzed multiple publicly available human PCa datasets to identify clinical correlates in both primary and metastatic disease. Intriguingly, we found genomic alterations in circadian rhythm were associated with increased Gleason score, cancer staging, and positive node status in primary disease. Furthermore, within a subset of patients with castrate-resistant prostate cancer (CRPC), those with concurrent altered CCGs had a decreased survival compared to patients without altered CCGs. This data further emphasizes the importance of circadian rhythm consideration in the context of malignancy and preventative medicine. With so many unknown questions and a high potential to identify subtypes of tumors with altered CCGs and aggressive disease, future studies are needed to improve therapeutic efficacy. Analysis of circadian genomic alterations with subsequent comparison of demographics including ethnicity, occupation, and sleep habits would expand the understanding of everyday variables on circadian disruption. Additionally, the comparison of short-term versus long-term circadian synchronizations should be analyzed to identify higher-risk populations. Lastly, the long-term goal should be to discover potential circadian targeted treatments or to identify ways of involvement of circadian rhythmicity in cancer treatment, including chronotherapy (i.e., time of day of treatment) to optimize the impact of cancer therapeutics to enhance patient outcome. Citation Format: Sierra T. Pence, Ayesha A. Shafi. The importance of time: Circadian rhythm disruption and prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A048.

Disruption of circadian rhythms and the condition of frailty are believed to be interrelated. Various manifestations of sleep disturbances, including insomnia, disrupted sleep-wake cycles, and alterations in sleep timing, are considered integral components of circadian rhythm disruption, which are also observed in individuals with frailty. Extensive research has established a connection between gut microbiota and both frailty and circadian rhythm disruption. However, prior studies have predominantly focused on investigating isolated links between gut microbiota and its metabolites with either frailty or circadian rhythm disruption, often neglecting the significant role that gut microbiota and its metabolites may play in the bidirectional relationship between circadian rhythms and frailty. Consequently, we propose the hypothesis that circadian rhythm disruption may induce frailty by altering the composition and structure of gut microbiota metabolites, and conversely, frailty may influence circadian rhythm disruption through similar mechanisms. The aim of our hypothesis is to emphasize the important role of gut microbiota metabolites in the bidirectional communication between circadian disruption and frailty and to speculate on the relevant mechanisms by which gut microbiota metabolites mediate the bidirectional communication between circadian disruption and frailty, rather than being solely related to frailty or circadian disorders.

Losing Sleep Over Cancer

ABSTRACTObjectiveAnorexia nervosa (AN) is an eating disorder characterized by severe weight loss and associated with hyperactivity and circadian rhythm disruption. However, the cellular basis of circadian rhythm disruption is poorly understood. Glial cells in the suprachiasmatic nucleus (SCN), the principal circadian pacemaker, are involved in regulating circadian rhythms. We hypothesize that the circadian rhythm disruption in AN patients is associated with glial cell changes in the SCN.MethodIn the starvation‐induced hyperactivity mouse model, mice had free access to a running wheel and received a restricted amount of food once a day, until a 25% body weight loss was reached and maintained their weight loss for two weeks. This was followed by a refeeding phase. Different daily periods of running wheel activity were defined, such as food anticipatory activity up to 4 h before feeding. Circadian rhythmicity was analyzed using the cosinor method. Gene expression was evaluated using real‐time polymerase chain reaction. Immunohistochemistry was used to quantify astrocytes, microglia, and oligodendrocytes.ResultsStarvation induced changes in circadian rhythm, as indicated by changes in cosinor‐based characteristics. Refeeding reversed these effects. Additionally, there was an increase in cryptochrome circadian regulator 1 expression and a decrease in the density of astrocytes and oligodendrocytes in the SCN after chronic starvation.DiscussionStarvation‐induced alterations in circadian rhythms are associated with molecular, and cellular changes in the hypothalamus. Reduced astrocytes and oligodendrocytes in the SCN in a mouse model of AN suggest that glial pathophysiology may play a role in circadian rhythm disruption.

Background: Burnout among healthcare professionals is increasingly recognized as a syndrome with biological correlations. Beyond psychosocial factors, circadian misalignment, sleep disturbances, and hormonal dysregulation—particularly involving melatonin and cortisol—are emerging as relevant mechanisms. Methods: We systematically reviewed studies published between 2015 and 2025 examining associations between burnout, melatonin, circadian disruption, sleep quality, and related biomarkers in healthcare workers. Results: Across 14 included studies, burnout was associated with suppressed melatonin secretion, cortisol dysregulation, and circadian misalignment, including social jet lag and poor sleep quality. Night-shift nurses consistently displayed greater circadian disruption and higher burnout scores than day-shift colleagues. Evidence also suggests that environmental and interventional approaches—such as optimizing daylight exposure and melatonin supplementation to improve sleep quality and cognitive performance—may mitigate circadian disruption and occupational fatigue. Conclusions: Burnout should be recognized as a biopsychosocial syndrome with measurable chronobiological correlates. Future research should integrate circadian biomarkers into occupational health assessments and evaluate preventive strategies aimed at preserving circadian health in healthcare professionals.

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.

Circadian rhythms are endogenous biological cycles that regulate essential cardiovascular functions, including blood pressure, heart rate, vascular tone, and metabolic homeostasis. Disruption of these rhythms due to factors such as shift work, artificial light at night, irregular sleep–wake cycles, or mistimed eating has been increasingly recognized as an independent risk factor for cardiovascular disease. A growing body of evidence links circadian misalignment to key pathophysiological mechanisms, including endothelial dysfunction, oxidative stress, inflammation, and autonomic imbalance. Melatonin, a hormone produced primarily by the pineal gland, plays a central role in circadian regulation and exhibits potent antioxidant, anti-inflammatory, and cardiometabolic properties. This narrative review synthesizes current findings on the interplay between circadian disruption and cardiovascular risk, with a particular emphasis on the mechanistic and therapeutic role of melatonin. We also highlight the potential of chronotherapeutic strategies, such as timed melatonin supplementation, antihypertensive dosing, and time-restricted eating, to restore circadian alignment and improve cardiovascular outcomes. Despite promising data, translation into clinical practice remains limited. Future research should focus on identifying practical circadian biomarkers, refining chronotherapy protocols, and integrating circadian variables into risk models and clinical workflows.

This review delved into the intricate relationship between circadian clocks and physiological processes, emphasizing their critical role in maintaining homeostasis. Orchestrated by interlocked clock genes, the circadian timekeeping system regulates fundamental processes like the sleep-wake cycle, energy metabolism, immune function, and cell proliferation. The central oscillator in the hypothalamic suprachiasmatic nucleus synchronizes with light-dark cycles, while peripheral tissue clocks are influenced by cues such as feeding times. Circadian disruption, linked to modern lifestyle factors like night shift work, correlates with adverse health outcomes, including metabolic syndrome, cardiovascular diseases, infections, and cancer. We explored the molecular mechanisms of circadian clock genes and their impact on metabolic disorders and cancer pathogenesis. Specific associations between circadian disruption and endocrine tumors, spanning breast, ovarian, testicular, prostate, thyroid, pituitary, and adrenal gland cancers, are highlighted. Shift work is associated with increased breast cancer risk, with PER genes influencing tumor progression and drug resistance. CLOCK gene expression correlates with cisplatin resistance in ovarian cancer, while factors like aging and intermittent fasting affect prostate cancer. Our review underscored the intricate interplay between circadian rhythms and cancer, involving the regulation of the cell cycle, DNA repair, metabolism, immune function, and the tumor microenvironment. We advocated for integrating biological timing into clinical considerations for personalized healthcare, proposing that understanding these connections could lead to novel therapeutic approaches. Evidence supports circadian rhythm-focused therapies, particularly chronotherapy, for treating endocrine tumors. Our review called for further research to uncover detailed connections between circadian clocks and cancer, providing essential insights for targeted treatments. We emphasized the importance of public health interventions to mitigate lifestyle-related circadian disruptions and underscored the critical role of circadian rhythms in disease mechanisms and therapeutic interventions.

Sarcopenia, a musculoskeletal disease characterized by the progressive loss of skeletal muscle mass, strength, and physical performance, presents significant challenges to global public health due to its adverse effects on mobility, morbidity, mortality, and healthcare costs. This comprehensive review explores the intricate connections between sarcopenia and low birth weight (LBW), emphasizing the developmental origins of health and disease (DOHaD) hypothesis, inflammatory processes (inflammaging), mitochondrial dysfunction, circadian rhythm disruptions, epigenetic mechanisms, and genetic variations revealed through genome-wide studies (GWAS). A systematic search strategy was developed using PubMed to identify relevant English-language publications on sarcopenia, LBW, DOHaD, inflammaging, mitochondrial dysfunction, circadian disruption, epigenetic mechanisms, and GWAS. The publications consist of 46.2% reviews, 21.2% cohort studies, 4.8% systematic reviews, 1.9% cross-sectional studies, 13.4% animal studies, 4.8% genome-wide studies, 5.8% epigenome-wide studies, and 1.9% book chapters. The review identified key factors contributing to sarcopenia development, including the DOHaD hypothesis, LBW impact on muscle mass, inflammaging, mitochondrial dysfunction, the influence of clock genes, the role of epigenetic mechanisms, and genetic variations revealed through GWAS. The DOHaD theory suggests that LBW induces epigenetic alterations during foetal development, impacting long-term health outcomes, including the early onset of sarcopenia. LBW correlates with reduced muscle mass, grip strength, and lean body mass in adulthood, increasing the risk of sarcopenia. Chronic inflammation (inflammaging) and mitochondrial dysfunction contribute to sarcopenia, with LBW linked to increased oxidative stress and dysfunction. Disrupted circadian rhythms, regulated by genes such as BMAL1 and CLOCK, are associated with both LBW and sarcopenia, impacting lipid metabolism, muscle mass, and the ageing process. Early-life exposures, including LBW, induce epigenetic modifications like DNA methylation (DNAm) and histone changes, playing a pivotal role in sarcopenia development. Genome-wide studies have identified candidate genes and variants associated with lean body mass, muscle weakness, and sarcopenia, providing insights into genetic factors contributing to the disorder. LBW emerges as a potential early predictor of sarcopenia development, reflecting the impact of intrauterine exposures on long-term health outcomes. Understanding the complex interplay between LBW with inflammaging, mitochondrial dysfunction, circadian disruption, and epigenetic factors is essential for elucidating the pathogenesis of sarcopenia and developing targeted interventions. Future research on GWAS and the underlying mechanisms of LBW-associated sarcopenia is warranted to inform preventive strategies and improve public health outcomes.

In mammals, circadian rhythms in peripheral organs are impaired when animals are maintained in abnormal environmental light-dark cycles such as constant light (LL). This conclusion is based on averaged data from groups of experimental animals sacrificed at each time point. To investigate the effect of LL housing on the peripheral clocks of individual mice, an in vivo imaging system was used to observe the circadian bioluminescence rhythm in peripheral tissues of the liver, kidney, and submandibular salivary gland in PER2::LUCIFERASE knock-in mice. Using this technique, we demonstrated that the majority of individual peripheral tissues still had rhythmic oscillations of their circadian clocks in LL conditions. However, LL housing caused decreased amplitudes and a broad distribution of peak phases in PER2::LUCIFERASE oscillations irrespective of the state of the animals' behavioral rhythmicity. Because both scheduled feeding and scheduled exercise are effective recovery stimuli for circadian clock deficits, we examined whether scheduled feeding or scheduled exercise could reverse this impairment. The results showed that scheduled feeding or exercise could not restore the amplitude of peripheral clocks in LL. On the other hand, the LL-induced broad phase distribution was reversed, and peak phases were entrained to a specific time point by scheduled feeding but only slightly by scheduled exercise. The present results demonstrate that LL housing impairs peripheral circadian clock oscillations by altering both amplitude and phase in individual mice. The broad distribution of clock phases was clearly reversed by scheduled feeding, suggesting the importance of scheduled feeding as an entraining stimulus for impaired peripheral clocks.

Disrupted circadian rhythms and alterations of the gut microbiome composition were proposed to affect host health. Therefore, the aim of this research was to identify whether these events are connected and if circadian rhythm disruption by abnormal light–dark (LD) cycles affects microbial community gene expression and host vulnerability to intestinal dysfunction. Mice were subjected to either a 4-week period of constant 24-h light or of normal 12-h LD cycles. Stool samples were collected at the beginning and after the circadian rhythm disruption. A metatranscriptomic analysis revealed an increase in Ruminococcus torques, a bacterial species known to decrease gut barrier integrity, and a decrease in Lactobacillus johnsonii, a bacterium that helps maintain the intestinal epithelial cell layer, after circadian rhythm disruption. In addition, genes involved in pathways promoting host beneficial immune responses were downregulated, while genes involved in the synthesis and transportation of the endotoxin lipopolysaccharide were upregulated in mice with disrupted circadian cycles. Importantly, these mice were also more prone to dysfunction of the intestinal barrier. These results further elucidate the impact of light-cycle disruption on the gut microbiome and its connection with increased incidence of disease in response to circadian rhythm disturbances.