Aging, circadian disruption and neurodegeneration: Interesting interplay

Exploring nightly variability and clinical influences on sleep measures: insights from a digital brain health platform

BACKGROUND

Digital technology offers a convenient way to continuously monitor sleep and assess night-to-night variability, particularly in aging populations where traditional self-reported sleep assessments may be limited.

AIMS

This study aimed to investigate nightly variability in sleep measures obtained via a ring oximeter sensor in older adults and to explore the influence of demographic and cognitive factors on the stability of these metrics.

METHODS

The study included 62 participants (mean age 74, 67.7 % women, 90.3 % White) from the Boston University Alzheimer's Disease Research Center (BU ADRC) cohort. Each participant wore a SleepImage Ring for at least three consecutive nights. Thirty-four continuous sleep measures, such as mean SpO2 and apnea-hypopnea index within unstable sleep, were analyzed. Night-to-night variability was assessed using intraclass correlation coefficients (ICC) based on a two-way random-effects model. Subgroup analyses examined variability by sex, age, and cognitive status. Group-level changes were assessed using one-way repeated measures ANOVA.

RESULTS

Seven sleep measures demonstrated high stability across nights (ICC: 0.70-0.88), with average heart rate being the most stable, followed by mean SpO2 and apnea-hypopnea indices. Sleep latency exhibited the highest variability. Stability improved between the second and third nights compared to the first and second nights. Women and participants under 75 years old showed greater stability in several metrics, while cognitively intact individuals exhibited more consistent breathing-related measures.

CONCLUSION

At least three nights of monitoring are required for reliable estimates of key sleep metrics. Expanding studies with larger samples and extended monitoring periods could further elucidate sleep variability as a potential non-invasive marker for general health.

Altered Structure-Function Coupling Associated with Attention Decline in Shift Work Disorder

Introduction

Previous studies on shift work disorder (SWD) have revealed altered functional and structural brain networks underlying attention decline. However, changes in structure-function coupling (SFC) and their relationship with attention decline remain unknown. This study aimed to examine the role of changed SFC in abnormal attentional network function in SWD.

Methods

Thirty-four patients with SWD and thirty-two healthy controls were recruited. All participants underwent resting-state functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) scans. All participants underwent an attentional network test to evaluate their functions. Finally, Pearson's correlation analysis was conducted to analyze the association between aberrant attentional network function and altered structural and functional connectivity (SC-FC) coupling in patients with SWD.

Results

Compared to healthy subjects, decreased alerting and executive functions were found in patients with SWD. In addition, we observed decreased SC-FC coupling in patients with SWD, specifically in the left anterior cingulate gyrus (T = -3.6449, P = 0.0003), central opercular cortex (T = -3.7187, P = 0.0002), middle frontal gyrus (T = -3.8342, P = 0.0001), and parietal operculum cortex (T = -3.6121, P = 0.0003), compared with healthy subjects. Better altering performance was significantly associated with lower SC-FC coupling in the anterior cingulate gyrus of patients with SWD (r = -0.51, P = 0.002).

Discussion

Our findings unravel that the decreased SC-FC coupling in the anterior cingulate gyrus may contribute to the impaired altering network function in SWD, which can further understand the neural mechanisms of impaired attention in SWD and inform a potentially therapeutic intervention for SWD patients.

Oral supplement in healthy older adults to support physical fitness and mental wellbeing

Introduction

Cucumbers have been anecdotally credited with anti-inflammatory properties. IdoBR1 [(2R,3R,4R,5S)-3,4,5-trihydroxypiperidine-2-carboxylic acid], an iminosugar amino acid isolated from the fruits of certain cucumbers (Cucumis sativus, Cucurbitaceae), has been demonstrated to possess anti-inflammatory activity. Q-actin™ is a quality-controlled cucumber extract containing measured idoBR1, which has shown promising results in the treatment of osteoarthritis through oral administration.

Methods

A healthy middle-aged and older adult population was recruited and randomized to receive either Q-actin™ (2 × gummies containing 10 mg Q-actin™ daily) or matched placebo gummies for 12 weeks. Physical strength and finger dexterity were assessed using hand grip strength and the Nine-Hole Peg Test, respectively. We evaluated diet choices with the Prime Diet Quality Score and sleep quality with the Pittsburgh Sleep Quality Index and collected first-morning urine samples for chemical composition analysis using Flow Infusion Electrospray Ionization Mass Spectrometry (FIE-MS).

Results

We recruited a cohort of 47 healthy middle-aged and older adults (ages 50-78; 15 men and 32 women). FIE-MS analysis on urines was conducted and we tentatively identified elevated melatonin derivatives after Q-actin™ supplementation, suggesting a positive effect on sleep quality, which correlated with self-reported Pittsburgh Sleep Quality Index. The relative m/z-transition areas of melatonin and its two main biotransformation products in selected urine samples after Q-actin™ supplementation were confirmed following LC-MS/MS fragmentation.

Conclusion

Q-actin™ demonstrated potential benefits in a healthy middle-aged and older adult population by improving sleep quality, as evidenced by elevated melatonin derivatives identified in urine samples and self-reported improvements on the Pittsburgh Sleep Quality Index and improved finger dexterity. These findings support the hypothesis that Q-actin™ may have positive effects on overall wellbeing, as shown here in healthy older people, and could be rated to enhanced sleep quality.

Clinical trial registration

ISRCTN registry ISRCTN28705061 and clinicaltrials.gov/ NCT05878847.

Disruption of circadian rhythm as a potential pathogenesis of nocturia

Increasing evidence suggested the multifactorial nature of nocturia, but the true pathogenesis of this condition still remains to be elucidated. Contemporary clinical medications are mostly symptom based, aimed at either reducing nocturnal urine volume or targeting autonomic receptors within the bladder to facilitate urine storage. The day-night switch of the micturition pattern is controlled by circadian clocks located both in the central nervous system and in the peripheral organs. Arousal threshold and secretion of melatonin and vasopressin increase at night-time to achieve high-quality sleep and minimize nocturnal urine production. In response to the increased vasopressin, the kidney reduces the glomerular filtration rate and facilitates the reabsorption of water. Synchronously, in the bladder, circadian oscillation of crucial molecules occurs to reduce afferent sensory input and maintain sufficient bladder capacity during the night sleep period. Thus, nocturia might occur as a result of desynchronization in one or more of these circadian regulatory mechanisms. Disrupted rhythmicity of the central nervous system, kidney and bladder (known as the brain-kidney-bladder circadian axis) contributes to the pathogenesis of nocturia. Novel insights into the chronobiological nature of nocturia will be crucial to promote a revolutionary shift towards effective therapeutics targeting the realignment of the circadian rhythm.

Circadian rhythm, hypoxia, and cellular senescence: From molecular mechanisms to targeted strategies

Cellular senescence precipitates a decline in physiological activities and metabolic functions, often accompanied by heightened inflammatory responses, diminished immune function, and impaired tissue and organ performance. Despite extensive research, the mechanisms underpinning cellular senescence remain incompletely elucidated. Emerging evidence implicates circadian rhythm and hypoxia as pivotal factors in cellular senescence. Circadian proteins are central to the molecular mechanism governing circadian rhythm, which regulates homeostasis throughout the body. These proteins mediate responses to hypoxic stress and influence the progression of cellular senescence, with protein Brain and muscle arnt-like 1 (BMAL1 or Arntl) playing a prominent role. Hypoxia-inducible factor-1α (HIF-1α), a key regulator of oxygen homeostasis within the cellular microenvironment, orchestrates the transcription of genes involved in various physiological processes. HIF-1α not only impacts normal circadian rhythm functions but also can induce or inhibit cellular senescence. Notably, HIF-1α may aberrantly interact with BMAL1, forming the HIF-1α-BMAL1 heterodimer, which can instigate multiple physiological dysfunctions. This heterodimer is hypothesized to modulate cellular senescence by affecting the molecular mechanism of circadian rhythm and hypoxia signaling pathways. In this review, we elucidate the intricate relationships among circadian rhythm, hypoxia, and cellular senescence. We synthesize diverse evidence to discuss their underlying mechanisms and identify novel therapeutic targets to address cellular senescence. Additionally, we discuss current challenges and suggest potential directions for future research. This work aims to deepen our understanding of the interplay between circadian rhythm, hypoxia, and cellular senescence, ultimately facilitating the development of therapeutic strategies for aging and related diseases.

The Common Hallmarks and Interconnected Pathways of Aging, Circadian Rhythms, and Cancer: Implications for Therapeutic Strategies

The intricate relationship between cancer, circadian rhythms, and aging is increasingly recognized as a critical factor in understanding the mechanisms underlying tumorigenesis and cancer progression. Aging is a well-established primary risk factor for cancer, while disruptions in circadian rhythms are intricately associated with the tumorigenesis and progression of various tumors. Moreover, aging itself disrupts circadian rhythms, leading to physiological changes that may accelerate cancer development. Despite these connections, the specific interplay between these processes and their collective impact on cancer remains inadequately explored in the literature. In this review, we systematically explore the physiological mechanisms of circadian rhythms and their influence on cancer development. We discuss how core circadian genes impact tumor risk and prognosis, highlighting the shared hallmarks of cancer and aging such as genomic instability, cellular senescence, and chronic inflammation. Furthermore, we examine the interplay between circadian rhythms and aging, focusing on how this crosstalk contributes to tumorigenesis, tumor proliferation, and apoptosis, as well as the impact on cellular metabolism and genomic stability. By elucidating the common pathways linking aging, circadian rhythms, and cancer, this review provides new insights into the pathophysiology of cancer and identifies potential therapeutic strategies. We propose that targeting the circadian regulation of cancer hallmarks could pave the way for novel treatments, including chronotherapy and antiaging interventions, which may offer important benefits in the clinical management of cancer.

Circadian Clock Disruption and Growth of Kidney Cysts in Autosomal Dominant Polycystic Kidney Disease

Key Points

Lack of Bmal1 , a circadian clock protein in renal collecting ducts disrupted the clock and increased cyst growth and fibrosis in an autosomal dominant polycystic kidney disease mouse model. Bmal1 gene deletion increased cell proliferation by increasing lipogenesis in kidney cells. Thus, circadian clock disruption could be a risk factor for accelerated disease progression in patients with autosomal dominant polycystic kidney disease.

Background

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in the PKD1 and PKD2 genes and often progresses to kidney failure. ADPKD progression is not uniform among patients, suggesting that factors secondary to the PKD1/2 gene mutation could regulate the rate of disease progression. Here, we tested the effect of circadian clock disruption on ADPKD progression. Circadian rhythms are regulated by cell-autonomous circadian clocks composed of clock proteins. BMAL1 is a core constituent of the circadian clock.

Methods

To disrupt the circadian clock, we deleted Bmal1 gene in the renal collecting ducts of the Pkd1 RC/RC (RC/RC) mouse model of ADPKD (RC/RC;Bmal1 f/f;Pkhd1 cre, called double knockout [DKO] mice) and in Pkd1 knockout mouse inner medullary collecting duct cells (Pkd1Bmal1 KO mouse renal inner medullary collecting duct cells). Only male mice were used.

Results

Human nephrectomy ADPKD kidneys showed altered clock gene expression when compared with normal control human kidneys. When compared with RC/RC kidneys, DKO kidneys showed significantly altered clock gene expression, increased cyst growth, cell proliferation, apoptosis, and fibrosis. DKO kidneys also showed increased lipogenesis and cholesterol synthesis–related gene expression and increased tissue triglyceride levels compared with RC/RC kidneys. Similarly, in vitro , Pkd1Bmal1 KO cells showed altered clock genes, increased lipogenesis and cholesterol synthesis–related genes, and reduced fatty acid oxidation–related gene expression compared with Pkd1KO cells. The Pkd1Bmal1 KO cells showed increased cell proliferation compared with Pkd1KO cells, which was rescued by pharmacological inhibition of lipogenesis.

Conclusions

Renal collecting duct–specific Bmal1 gene deletion disrupted the circadian clock and triggered accelerated ADPKD progression by altering lipid metabolism–related gene expression.

Circulating biomarkers and neuroanatomical brain structures differ in older adults with and without post-traumatic stress disorder

The aim of this study was to advance post-traumatic stress disorder (PTSD) understanding in older adults (48-77 years) by determining if circulating cytokines (IL-1β, IL-2, IL-4, IL-6, IL-12p70, IL17A and TNFα), brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF-A) and neuroanatomical brain volumes (grey and white matter, hippocampus, and amygdala) significantly differed in those with versus without PTSD. While none of the tested cytokines showed a significant difference, serum BDNF and VEGF-A levels were found to be significantly higher in the PTSD cohort. The assay used for BDNF quantification was important, with differences in general BDNF detected, but not when pro- and mature BDNF were measured specifically. Additionally, BDNF genotyping revealed a significant difference in Val66Met genotype distribution by PTSD diagnosis, with Val66Met carriers generally having lower circulating levels of BDNF compared to their Val66Val counterparts, regardless of PTSD diagnosis. Neuroanatomically, an all-female subset was examined to find total grey and white matter volumes and left and right hippocampal volumes were significantly smaller in those with PTSD. Collectively, these results show that both novel (VEGF-A) and established targets (BDNF and neuroimaging) may serve as useful biomarkers for older adults with PTSD.

Circadian Clocks, Daily Stress, and Neurodegenerative Disease

Disrupted circadian or 24-h rhythms are among the most common early findings in a wide range of neurodegenerative disorders. Once thought to be a mere consequence of the disease process, increasing evidence points toward a causal or contributory role of the circadian clock in neurodegenerative disease. Circadian clocks control many aspects of cellular biochemistry, including stress pathways implicated in neuronal survival and death. Given the dearth of disease-modifying therapies for these increasingly prevalent disorders, this understanding may lead to breakthroughs in the development of new treatments. In this review, we provide a background on circadian clocks and focus on some potential mechanisms that may be pivotal in neurodegeneration.

Age- and sex-associated alterations in hypothalamic mitochondrial bioenergetics and inflammatory-associated signaling in the 3xTg mouse model of Alzheimer's disease

Mitochondrial dysfunction and associated inflammatory signaling are pivotal in both aging and in Alzheimer's disease (AD). Studies have also shown that hypothalamic function is affected in AD. The hypothalamus may be a target for AD drugs given that mitochondrial alterations are observed in the hypothalamus. This study investigated how age and sex affect mitochondrial bioenergetics and inflammatory signaling in the hypothalamic mitochondria of 3xTg and control mice at 2, 6, and 13 months, aiming to enhance our understanding of these processes in aging and AD. Parameters included oxygen consumption rates, expression levels of subunits comprising mitochondrial complexes I-V, the enzymatic activity of cytochrome c oxidase (COX), transcription factors associated with inflammation such as NF-κB, pIκB-α, Nrf2, and other inflammatory biomarkers. Hypothalamic mitochondrial dysfunction was observed in 3xTg females as early as 2 months, but no changes were detected in 3xTg males until 6 months of age. In 3xTg mice, subunit expression levels for mitochondrial complexes I-II were significantly reduced in both sexes. Significant sex-based differences in COX activity were also observed at 13 months of age, with levels being lower in females compared to males. In addition, significant sex differences were indicated in NF-κB, pIκB-α, Nrf2, and other inflammatory biomarkers at different age groups during normal aging and AD progression. These findings highlight important sex differences in hypothalamic bioenergetics and inflammation, offering insights into potential new targets for preventing and/or treating AD.

Changing dynamics in daily rhythms of oxidative stress indicators in SCN and extra-SCN brain regions with aging in male Wistar rats

The suprachiasmatic nucleus (SCN) in the hypothalamus regulates circadian timing system (CTS) by co-ordinating peripheral tissue clocks and extra-SCN oscillators in the brain. Aging disrupts the CTS, impairing physiological functions and reducing antioxidant defences, which contribute to neurodegeneration. The brain is vulnerable to oxidative damage due to its high metabolic activity, oxygen consumption, and levels of iron and lipids. Antioxidant enzymes, such as catalase (CAT), glutathione S-transferase (GST), superoxide dismutase (SOD), and lipid peroxidation (LPO), help against oxidative damage. In this study, we examined the temporal patterns of these antioxidant stress indicators in the SCN and extra-SCN brain regions (frontal cortex, cerebellum, and hippocampus) at various time points in male Wistar rats 3, 12, and 24 months. The rhythmicity of GST and LPO levels persisted across brain regions with aging, while CAT rhythmicity was lost in the SCN and hippocampus of older rats. SOD rhythmicity persisted in cortex, cerebellum, and hippocampus but was lost in the SCN. The daily rhythm parameters of CAT were affected most significantly, followed by SOD, GST, and LPO. Our findings demonstrate that aging leads to desynchronization of oxidative stress indicators potentially contributing to neurodegeneration and circadian dysfunction with varying effects across different brain tissues.

Circadian clock disruption and growth of kidney cysts in autosomal dominant polycystic kidney disease

Background

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in the PKD1 and PKD2 genes, and often progresses to kidney failure. ADPKD progression is not uniform among patients, suggesting that factors secondary to the PKD1/2 gene mutation could regulate the rate of disease progression. Here we tested the effect of circadian clock disruption on ADPKD progression. Circadian rhythms are regulated by cell-autonomous circadian clocks composed of clock proteins. BMAL1 is a core constituent of the circadian clock.

Methods

To disrupt the circadian clock, we deleted Bmal1 gene in the renal collecting ducts of the Pkd1 RC/RC (RC/RC) mouse model of ADPKD (RC/RC; Bmal1 f/f ; Pkhd1 cre , called DKO mice), and in Pkd1 knockout mouse inner medullary collecting duct cells ( Pkd1Bmal1 KO mIMCD3 cells). Only male mice were used.

Results

Human nephrectomy ADPKD kidneys and Pkd1 KO mIMCD3 cells showed reduced Bmal1 gene expression compared to normal controls. When compared to RC/RC kidneys, DKO kidneys showed significantly altered clock gene expression, increased cyst growth, cell proliferation, apoptosis and fibrosis. DKO kidneys also showed increased lipogenesis and cholesterol synthesis-related gene expression, and increased tissue triglyceride levels compared to RC/RC kidneys. Similarly, in vitro, Pkd1Bmal1 KO cells showed altered clock genes, increased lipogenesis and cholesterol synthesis-related genes, and reduced fatty-acid oxidation-related gene expression compared to Pkd1KO cells. The Pkd1Bmal1 KO cells showed increased cell proliferation compared to Pkd1KO cells, which was rescued by pharmacological inhibition of lipogenesis.

Conclusion

Renal collecting duct specific Bmal1 gene deletion disrupts the circadian clock and triggers accelerated ADPKD progression by altering lipid metabolism-related gene expression.

Key points

Lack of BMAL1, a circadian clock protein in renal collecting ducts disrupted the clock and increased cyst growth and fibrosis in an ADPKD mouse model.BMAL1 gene deletion increased cell proliferation by increasing lipogenesis in kidney cells.Thus, circadian clock disruption could be a risk factor for accelerated disease progression in patients with ADPKD.

Louis EK, Ruoff CM, Kolla BP. Aging and sex are associated with multiple sleep latency test findings and their relationship with self-reported sleepiness

The aim of this study was to assess age- and sex-related differences in multiple sleep latency test (MSLT) results and in the performance of the Epworth Sleepiness Scale (ESS) at classifying objective hypersomnia (mean sleep latency (MSL) ≤ 8 min). We studied 480 consecutive adults (39.3 ± 15.3 years old [18-93], 67.7% female) who underwent hypersomnia evaluation. We fit linear regression models to investigate associations between age and sex and sleep latencies (mean and for every nap), after adjusting for total sleep time and sleep efficiency (on polysomnography), and REM-suppressing antidepressant effect. A logistic regression was performed to assess whether age and sex were associated with sleep-onset REM period (SOREMP) occurrence. ROC analysis assessed the diagnostic performance of ESS scores to identify a MSL ≤ 8 min in different age/sex groups. For every 10 years of age, there was 0.41 (95% CI 0.11-0.72, p = 0.008) min reduction in MSL. Objectively (MSL ≤ 8 min) sleepy patients had shortening of latencies in naps 4 and 5 with aging. Female sex was associated with a higher MSL only in patients with MSL > 8 min. A 2.4% reduction in the odds of SOREMP occurrence was observed for every year of age in objectively sleepy patients (p = 0.045). ESS scores had a better diagnostic performance in older (≥ 50 years old) men than younger (< 50 years old) women (p < 0.05). Older patients with objectively confirmed hypersomnia may be sleepier in later naps, possibly due to less restorative naps and/or circadian rhythm factors. Self-reported sleepiness is more predictive of objective sleepiness in older men than younger women.

The Positive Association between Melatonin-Containing Food Consumption and Older Adult Life Satisfaction, Psychoemotional State, and Cognitive Function

The purpose of this study was to test the hypothesis that melatonin-containing food (FMT) consumption is associated with a better sleep schedule and cognitive and psychoemotional state in older adults. A cross-sectional study of 557 (79% females) older adults living in the community with a mean age of 68.9 ± 7.7, ranging from 50 to 90 years, was conducted. The study, conducted in May and September 2023 using a face-to-face interview, collected personal data and assessed FMT intake during the day (FMTday) and for dinner (FMTdinner), life satisfaction, positive and negative affect, depression severity, cognitive functions, and sleep characteristics. Multiple regression and logistic regression analysis, adjusted for co-factors, were used to assess the association between the studied indicators. Multiple regression analysis showed that older adults with higher FMT consumption are more satisfied with life (FMTdinner: β = 0.107; ∆R2 = 0.011; p = 0.020), have a lower level of depression (FMTday: β = -0.124; ∆R2 = 0.015; p = 0.003), and higher scores in positive affect (FMTday: β = 0.169; ∆R2 = 0.016; p = 0.007; FMTdinner: β = 0.136; ∆R2 = 0.019; p = 0.003). Logistic regression analysis showed that older adults with higher FMT consumption are less likely to have depression (FMTday: OR, 0.614; 95% CI, 0.436-0.864; p = 0.005; FMTdinner: OR, 0.671; 95% CI, 0.476-0.945; p = 0.023), and they perform better on logical thinking tests (FMTday: OR, 2.066; 95% CI, 1.131-2.204; p = 0.013; FMTdinner: OR, 1.887; 95% CI, 1.183-2.138; p = 0.033). A greater life satisfaction as well as a decrease in the cognitive impairment and psychoemotional state of older adults is associated with a higher consumption of melatonin-containing foods.

Circadian Rhythms of the Blood-Brain Barrier and Drug Delivery

The blood-brain barrier (BBB) is a critical interface separating the central nervous system from the peripheral circulation, ensuring brain homeostasis and function. Recent research has unveiled a profound connection between the BBB and circadian rhythms, the endogenous oscillations synchronizing biological processes with the 24-hour light-dark cycle. This review explores the significance of circadian rhythms in the context of BBB functions, with an emphasis on substrate passage through the BBB. Our discussion includes efflux transporters and the molecular timing mechanisms that regulate their activities. A significant focus of this review is the potential implications of chronotherapy, leveraging our knowledge of circadian rhythms for improving drug delivery to the brain. Understanding the temporal changes in BBB can lead to optimized timing of drug administration, to enhance therapeutic efficacy for neurological disorders while reducing side effects. By elucidating the interplay between circadian rhythms and drug transport across the BBB, this review offers insights into innovative therapeutic interventions.

Recent advances in understanding the kidney circadian clock mechanism

Circadian rhythms are endogenous biological oscillations that regulate various physiological processes in organisms, including kidney function. The kidney plays a vital role in maintaining homeostasis by regulating water and electrolyte balance, blood pressure, and excretion of metabolic waste products, all of which display circadian rhythmicity. For this reason, studying the circadian regulation of the kidney is important, and the time of day is a biological and experimental variable that must be considered. Over the past decade, considerable progress has been made in understanding the molecular mechanisms underlying circadian regulation within the kidney. In this review, the current knowledge regarding circadian rhythms in the kidney is explored, focusing on the molecular clock machinery, circadian control of renal functions, and the impact of disrupted circadian rhythms on kidney health. In addition, parameters that should be considered and future directions are outlined in this review.

From Chronodisruption to Sarcopenia: The Therapeutic Potential of Melatonin

Sarcopenia is an age-related condition that involves a progressive decline in muscle mass and function, leading to increased risk of falls, frailty, and mortality. Although the exact mechanisms are not fully understood, aging-related processes like inflammation, oxidative stress, reduced mitochondrial capacity, and cell apoptosis contribute to this decline. Disruption of the circadian system with age may initiate these pathways in skeletal muscle, preceding the onset of sarcopenia. At present, there is no pharmacological treatment for sarcopenia, only resistance exercise and proper nutrition may delay its onset. Melatonin, derived from tryptophan, emerges as an exceptional candidate for treating sarcopenia due to its chronobiotic, antioxidant, and anti-inflammatory properties. Its impact on mitochondria and organelle, where it is synthesized and crucial in aging skeletal muscle, further highlights its potential. In this review, we discuss the influence of clock genes in muscular aging, with special reference to peripheral clock genes in the skeletal muscle, as well as their relationship with melatonin, which is proposed as a potential therapy against sarcopenia.

Crosstalk Between Aging, Circadian Rhythm, and Melatonin

Circadian rhythms (CRs) are 24-hour periodic oscillations governed by an endogenous circadian pacemaker located in the suprachiasmatic nucleus (SCN), which organizes the physiology and behavior of organisms. Circadian rhythm disruption (CRD) is also indicative of the aging process. In mammals, melatonin is primarily synthesized in the pineal gland and participates in a variety of multifaceted intracellular signaling networks and has been shown to synchronize CRs. Endogenous melatonin synthesis and its release tend to decrease progressively with advancing age. Older individuals experience frequent CR disruption, which hastens the process of aging. A profound understanding of the relationship between CRs and aging has the potential to improve existing treatments and facilitate development of novel chronotherapies that target age-related disorders. This review article aims to examine the circadian regulatory mechanisms in which melatonin plays a key role in signaling. We describe the basic architecture of the molecular circadian clock and its functional decline with age in detail. Furthermore, we discuss the role of melatonin in regulation of the circadian pacemaker and redox homeostasis during aging. Moreover, we also discuss the protective effect of exogenous melatonin supplementation in age-dependent CR disruption, which sheds light on this pleiotropic molecule and how it can be used as an effective chronotherapeutic medicine.

Targeting the blood-brain barrier to delay aging-accompanied neurological diseases by modulating gut microbiota, circadian rhythms, and their interplays

The blood-brain barrier (BBB) impairment plays a crucial role in the pathological processes of aging-accompanied neurological diseases (AAND). Meanwhile, circadian rhythms disruption and gut microbiota dysbiosis are associated with increased morbidity of neurological diseases in the accelerated aging population. Importantly, circadian rhythms disruption and gut microbiota dysbiosis are also known to induce the generation of toxic metabolites and pro-inflammatory cytokines, resulting in disruption of BBB integrity. Collectively, this provides a new perspective for exploring the relationship among circadian rhythms, gut microbes, and the BBB in aging-accompanied neurological diseases. In this review, we focus on recent advances in the interplay between circadian rhythm disturbances and gut microbiota dysbiosis, and their potential roles in the BBB disruption that occurs in AAND. Based on existing literature, we discuss and propose potential mechanisms underlying BBB damage induced by dysregulated circadian rhythms and gut microbiota, which would serve as the basis for developing potential interventions to protect the BBB in the aging population through targeting the BBB by exploiting its links with gut microbiota and circadian rhythms for treating AAND.

Exploring Astrocyte-Mediated Mechanisms in Sleep Disorders and Comorbidity

Astrocytes, the most abundant cells in the brain, are integral to sleep regulation. In the context of a healthy neural environment, these glial cells exert a profound influence on the sleep-wake cycle, modulating both rapid eye movement (REM) and non-REM sleep phases. However, emerging literature underscores perturbations in astrocytic function as potential etiological factors in sleep disorders, either as protopathy or comorbidity. As known, sleep disorders significantly increase the risk of neurodegenerative, cardiovascular, metabolic, or psychiatric diseases. Meanwhile, sleep disorders are commonly screened as comorbidities in various neurodegenerative diseases, epilepsy, and others. Building on existing research that examines the role of astrocytes in sleep disorders, this review aims to elucidate the potential mechanisms by which astrocytes influence sleep regulation and contribute to sleep disorders in the varied settings of brain diseases. The review emphasizes the significance of astrocyte-mediated mechanisms in sleep disorders and their associated comorbidities, highlighting the need for further research.

Circadian rhythms, gut microbiota, and diet: Possible implications for health

AIMS

Over the past years, interest in chrono-nutrition has grown enormously as the fundamental role of circadian rhythms in regulating most physiological and metabolic processes has become clearer. Recently, the influence of circadian rhythms on the gut microbiota (GM) composition has also emerged, as more than half of the total microbial composition fluctuates rhythmically throughout the day. At the same time, other studies have observed that the GM itself synchronises the host's circadian biological clock through signals of a different nature. Therefore, it has been hypothesised that there is a two-way communication between the circadian rhythms of the host and the GM, but researchers have only just begun to identify some of its action mechanisms. The manuscript aim is, therefore, to gather and combine the latest evidence in the field of chrono-nutrition with the more recent research on the GM, in order to investigate their relationship and their potential impact on human health.

DATA SYNTHESIS

Considering current evidence, a desynchronization of circadian rhythms is closely associated with an alteration in the abundance and functionality of the gut microbiota with consequent deleterious effects on health, such as increased risk of numerous pathologies, including cardiovascular disease, cancer, irritable bowel disease, and depression. A key role in maintaining the balance between circadian rhythms and GM seems to be attributed to meal-timing and diet quality, as well as to certain microbial metabolites, in particular short-chain fatty acids.

CONCLUSIONS

Future studies are needed to decipher the link between the circadian rhythms and specific microbial patterns in relation to different disease frameworks.

Redefining Autoimmune Disorders' Pathoetiology: Implications for Mood and Psychotic Disorders' Association with Neurodegenerative and Classical Autoimmune Disorders

Although previously restricted to a limited number of medical conditions, there is a growing appreciation that 'autoimmune' (or immune-mediated) processes are important aspects of a wide array of diverse medical conditions, including cancers, neurodegenerative diseases and psychiatric disorders. All of these classes of medical conditions are associated with alterations in mitochondrial function across an array of diverse cell types. Accumulating data indicate the presence of the mitochondrial melatonergic pathway in possibly all body cells, with important consequences for pathways crucial in driving CD8⁺ T cell and B-cell 'autoimmune'-linked processes. Melatonin suppression coupled with the upregulation of oxidative stress suppress PTEN-induced kinase 1 (PINK1)/parkin-driven mitophagy, raising the levels of the major histocompatibility complex (MHC)-1, which underpins the chemoattraction of CD8⁺ T cells and the activation of antibody-producing B-cells. Many factors and processes closely associated with autoimmunity, including gut microbiome/permeability, circadian rhythms, aging, the aryl hydrocarbon receptor, brain-derived neurotrophic factor (BDNF) and its receptor tyrosine receptor kinase B (TrkB) all interact with the mitochondrial melatonergic pathway. A number of future research directions and novel treatment implications are indicated for this wide collection of poorly conceptualized and treated medical presentations. It is proposed that the etiology of many 'autoimmune'/'immune-mediated' disorders should be conceptualized as significantly determined by mitochondrial dysregulation, with alterations in the mitochondrial melatonergic pathway being an important aspect of these pathoetiologies.

Melatonin as a Harmonizing Factor of Circadian Rhythms, Neuronal Cell Cycle and Neurogenesis: Additional Arguments for Its Therapeutic Use in Alzheimer's Disease

The synthesis and release of melatonin in the brain harmonize various physiological functions. The apparent decline in melatonin levels with advanced aging is an aperture to the neurodegenerative processes. It has been indicated that down regulation of melatonin leads to alterations of circadian rhythm components, which further causes a desynchronization of several genes and results in an increased susceptibility to develop neurodegenerative diseases. Additionally, as circadian rhythms and memory are intertwined, such rhythmic disturbances influence memory formation and recall. Besides, cell cycle events exhibit a remarkable oscillatory system, which is downstream of the circadian phenomena. The linkage between the molecular machinery of the cell cycle and complex fundamental regulatory proteins emphasizes the conjectural regulatory role of cell cycle components in neurodegenerative disorders such as Alzheimer's disease. Among the mechanisms intervening long before the signs of the disease appear, the disturbances of the circadian cycle, as well as the alteration of the machinery of the cell cycle and impaired neurogenesis, must hold our interest. Therefore, in the present review, we propose to discuss the underlying mechanisms of action of melatonin in regulating the circadian rhythm, cell cycle components and adult neurogenesis in the context of AD pathogenesis with the view that it might further assist to identify new therapeutic targets.

Different levels of circadian (de)synchrony -- where does it hurt?

A network of cellular timers ensures the maintenance of homeostasis by temporal modulation of physiological processes across the day. These so-called circadian clocks are synchronized to geophysical time by external time cues (or zeitgebers). In modern societies, natural environmental cycles are disrupted by artificial lighting, around-the-clock availability of food or shift work. Such contradictory zeitgeber input promotes chronodisruption, i.e., the perturbation of internal circadian rhythms, resulting in adverse health outcomes. While this phenomenon is well described, it is still poorly understood at which level of organization perturbed rhythms impact on health and wellbeing. In this review, we discuss different levels of chronodisruption and what is known about their health effects. We summarize the results of disrupted phase coherence between external and internal time vs. misalignment of tissue clocks amongst each other, i.e., internal desynchrony. Last, phase incoherence can also occur at the tissue level itself. Here, alterations in phase coordination can emerge between cellular clocks of the same tissue or between different clock genes within the single cell. A better understanding of the mechanisms of circadian misalignment and its effects on physiology will help to find effective tools to prevent or treat disorders arising from modern-day chronodisruptive environments.