Therapeutic implications of circadian clocks in neurodegenerative diseases

Cell-type specific circadian transcription factor BMAL1 roles in excitotoxic hippocampal lesions to enhance neurogenesis

Circadian clocks, generating daily rhythms in biological processes, maintain homeostasis in physiology, so clock alterations are considered detrimental. Studies in brain pathology support this by reporting abnormal circadian phenotypes in patients, but restoring the abnormalities by light therapy shows no dramatic effects. Recent studies on glial clocks report the complex effects of altered clocks by showing their beneficial effects on brain repairs. However, how neuronal clocks respond to brain pathology is elusive. This study shows that neuronal BMAL1, a core of circadian clocks, reduces its expression levels in neurodegenerative excitotoxicity. In the dentate gyrus of excitotoxic hippocampal lesions, reduced BMAL1 in granule cells precedes apoptosis. This subsequently reduces BMAL1 levels in neighbor neural stem cells and progenitors in the subgranular zone, enhancing proliferation. This shows the various BMAL1 roles depending on cell types, and its alterations can benefit brain repair. Thus, cell-type-specific BMAL1 targeting is necessary to treat brain pathology.

Circadian disruption and sleep disorders in neurodegeneration

Disruptions of circadian rhythms and sleep cycles are common among neurodegenerative diseases and can occur at multiple levels. Accumulating evidence reveals a bidirectional relationship between disruptions of circadian rhythms and sleep cycles and neurodegenerative diseases. Circadian disruption and sleep disorders aggravate neurodegeneration and neurodegenerative diseases can in turn disrupt circadian rhythms and sleep. Importantly, circadian disruption and various sleep disorders can increase the risk of neurodegenerative diseases. Thus, harnessing the circadian biology findings from preclinical and translational research in neurodegenerative diseases is of importance for reducing risk of neurodegeneration and improving symptoms and quality of life of individuals with neurodegenerative disorders via approaches that normalize circadian in the context of precision medicine. In this review, we discuss the implications of circadian disruption and sleep disorders in neurodegenerative diseases by summarizing evidence from both human and animal studies, focusing on the bidirectional links of sleep and circadian rhythms with prevalent forms of neurodegeneration. These findings provide valuable insights into the pathogenesis of neurodegenerative diseases and suggest a promising role of circadian-based interventions.

Aging, circadian disruption and neurodegeneration: Interesting interplay

The circadian system is an intricate molecular network of coordinating circadian clocks that organize the internal synchrony of the organism in response to the environment. These rhythms are maintained by genetically programmed positive and negative auto-regulated transcriptional and translational feedback loops that sustain 24-hour oscillations in mRNA and protein components of the endogenous circadian clock. Since inter and intracellular activity of the central pacemaker appears to reduce with aging, the interaction between the circadian clock and aging continues to elude our understanding. In this review article, we discuss circadian clock components at the molecular level and how aging adversely affects circadian clock functioning in rodents and humans. The natural decline in melatonin levels with aging strongly contributes to circadian dysregulation resulting in the development of neurological anomalies. Additionally, inappropriate environmental conditions such as Artificial Light at Night (ALAN) can cause circadian disruption or chronodisruption (CD) which can result in a variety of pathological diseases, including premature aging. Furthermore, we summarize recent evidence suggesting that CD may also be a predisposing factor for the development of age-related neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), although more investigation is required to prove this link. Finally, certain chrono-enhancement approaches have been offered as intervention strategies to prevent, alleviate, or mitigate the impacts of CD. This review thus aims to bring together recent advancements in the chronobiology of the aging process, as well as its role in NDDs.

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.

Expression profile of circular RNAs in continuous light-induced ovarian dysfunction

PURPOSE

This study aims to elucidate the underlying relationship between the expression profiles of circular RNAs (circRNAs) and the ovarian dysfunction induced by continuous light.

METHODS

High-throughput sequencing was used to profile the transcriptome of differentially expressed circRNAs (DEcircRNAs) in rat ovary under continuous light exposure (12 h:12 h light/light cycle, L/L group) and a control cycle (12 h:12 h light/dark cycle, L/D group). Gene ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and circRNAs-microRNAs-messenger RNAs networks were performed to predict the role of DEcircRNAs in biological processes and pathways. A quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) assay was conducted to verify the high-throughput sequencing results and the expression level of circadian rhythm genes.

RESULTS

In total, 305 circRNAs were differentially expressed between the L/L and L/D groups. Among these, 211 circRNAs were up regulated, while 94 were down regulated. Eight candidate circRNAs from 305 DEcircRNAs were verified by qRT-PCR. Further bioinformatics analysis revealed that interactions between DEcircRNAs and a set of microRNAs involved in ovarian dysfunction-related pathways, such as regulation of androgen receptors, gonadotrophin releasing hormone signaling pathway, endocrine resistance, etc. Subsequently, we identified rno_circ:chr2:86868285-86964272 and rno_circ:chr1:62330221-62360073 may participate in the pathophysiology of ovarian dysfunction by constructing circRNAs-microRNAs-messenger RNAs networks. Meanwhile, constant light reduced the expression of circadian rhythm genes CLOCK, BAML1, PER1, and PER2 compared with that of controls. Caspase3 and Bax were up regulated in the L/L group compared with the L/D group, while Bcl-2 was down regulated.

CONCLUSIONS

In summary, the results reveal that the expression profiles and potential functions of DEcircRNAs in rat ovaries may play important roles in continuous light-induced ovarian dysfunction. These findings provide novel clues and molecular targets for studying the mechanisms and clinical therapy of ovarian dysfunction.

Functional Medicine Approaches to Neurodegeneration

Neurodegenerative diseases impact more than 6 million Americans, and current predictions estimate the rates of neurodegenerative diseases will double in the next 30 years. These diseases are progressive with increasing loss of brain function throughout their course. Overtime, those suffering from neurodegenerative diseases will lose their ability to work and function efficiently in society. Families and society are burdened with skyrocketing costs to provide care for those who are unable to perform activities of daily living. There is an urgent need to develop treatment strategies to both reduce the incidence of neurodegenerative diseases and to delay the progression of the disease.

Attention to time-of-day variability improves the reproducibility of gene expression patterns in multiple sclerosis

Low reproducibility in gene expression profiles has been observed in transcriptome studies, and this often limits applying findings to clinical practice. Here, we show time-of-day effects on gene expression and analytical schemes to increase the reproducibility in expression patterns. We recruited patients with relapsing-remitting multiple sclerosis (RRMS) and healthy subjects and collected blood from individuals twice a day, day (2 pm) and night (9 pm). RNA sequencing analyses found that gene expression in RRMS in relapse (Relapse) is significantly changed at night compared with either Relapse at day or RRMS in remission (Remission). Gene set overrepresentation analysis demonstrated that gene sets significantly changed in Relapse at night are enriched to immune responses related to MS pathology. In those gene sets, 68 genes are significantly changed expression in Relapse at night compared with Relapse at day and Remission. This supports that times of sample collections should be standardized to obtain reproducible gene expression patterns.

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Times of day affect gene expression patterns in patients with RRMS in relapse

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Transcriptome profiles in Relapse are changed from day to night

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In Relapse, immune response-related genes change the expression at night

Mammalian circadian networks mediated by the suprachiasmatic nucleus

The brain has a complex structure composed of hundreds of regions, forming networks to cooperate body functions. Therefore, understanding how various brain regions communicate with each other and with peripheral organs is important to understand human physiology. The suprachiasmatic nucleus (SCN) in the brain is the circadian pacemaker. The SCN receives photic information from the environment and conveys this to other parts of the brain and body to synchronize all circadian clocks. The circadian clock is an endogenous oscillator that generates daily rhythms in metabolism and physiology in almost all cells via a conserved transcriptional-translational negative feedback loop. So, the information flow from the environment to the SCN to other tissues synchronizes locally distributed circadian clocks to maintain homeostasis. Thus, understanding the circadian networks and how they adjust to environmental changes will better understand human physiology. This review will focus on circadian networks mediated by the SCN to understand how the environment, brain, and peripheral tissues form networks for cooperation.

Applying real-time monitoring of circadian oscillations in adult mouse brain slices to study communications between brain regions

This protocol combines a protective cutting method to prepare various brain slices from adult mice and real-time monitoring of circadian oscillations to measure circadian rhythmicity in various brain slices. This protocol can be applied to studies of how brain damages affect local circadian clocks and subsequent circadian variations in nearby areas. Further functional analyses with in vivo systems will determine whether these circadian variations are detrimental or beneficial to the brain.

For complete details on the use and execution of this protocol, please refer to Huang et al. (2020).

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Protective cutting method of the adult brain to minimize neural cell damages

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Co-culture system to study communications between different brain areas

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Monitoring circadian oscillations in non-SCN brain areas