The circadian clock plays a critical role in regulating various physiological processes, including gene expression, metabolic regulation, immune response, and the sleep-wake cycle in living organisms. Post-translational modifications (PTMs) are crucial regulatory mechanisms to maintain the precise oscillation of the circadian clock. By modulating the stability, activity, cell localization and protein-protein interactions of core clock proteins, PTMs enable these proteins to respond dynamically to environmental and intracellular changes, thereby sustaining the periodic oscillations of the circadian clock. Different types of PTMs exert their effects through distincting molecular mechanisms, collectively ensuring the proper function of the circadian system. This review systematically summarized several major types of PTMs, including phosphorylation, acetylation, ubiquitination, SUMOylation and oxidative modification, and overviewed their roles in regulating the core clock proteins and the associated pathways, with the goals of providing a theoretical foundation for the deeper understanding of clock mechanisms and the treatment of diseases associated with circadian disruption.
Protein Processing, Post-Translational/physiology* ; Circadian Rhythm/physiology* ; Humans ; Animals ; CLOCK Proteins/physiology* ; Circadian Clocks/physiology* ; Phosphorylation ; Acetylation ; Ubiquitination ; Sumoylation

The circadian rhythm regulates the 24-hour physiological and behavioral cycles through endogenous molecular clocks governed by core clock genes via the transcription-translation feedback loop (TTFL). In mammals, the suprachiasmatic nucleus (SCN) serves as the central pacemaker, coordinating the timing of physiological processes throughout the body by regulating clock genes such as CLOCK, BMAL1, PER, and CRY. The molecular clocks of peripheral tissues and cells are synchronized by the SCN through TTFLs to regulate metabolism, immunity, and energy homeostasis. Numerous studies indicate that circadian rhythm disruption is closely related to obesity, type 2 diabetes, metabolic syndrome and other diseases, and the mechanism involves the dysregulation of glucose and lipid metabolism, abnormal insulin signaling and low-grade inflammation. In recent years, small-molecule compounds targeting the core clock components such as CRY, REV-ERB, and ROR have been identified and shown potential to modulate metabolic diseases by stabilizing or inhibiting the activity of key clock proteins. This review summarizes the mechanisms and advances in these compounds, and explores the challenges and future directions for their clinical translation, providing insights for chronotherapy-based metabolic disease interventions.
Humans ; Metabolic Diseases/physiopathology* ; Animals ; Circadian Rhythm/physiology* ; Biological Clocks/drug effects* ; CLOCK Proteins/physiology* ; Circadian Clocks/physiology* ; Suprachiasmatic Nucleus/physiology*

The renin-angiotensin-aldosterone system (RAAS) is crucial for regulating blood pressure and maintaining fluid balance, while clock genes are essential for sustaining biological rhythms and regulating metabolism. There exists a complex interplay between RAAS and clock genes that may significantly contribute to the development of various cardiovascular and metabolic diseases. Although current literature has identified correlations between these two systems, the specific mechanisms of their interaction remain unclear. Moreover, the interaction patterns under different physiological and pathological conditions need further investigation. This review summarizes the synergistic roles of the RAAS and clock genes in cardiovascular diseases, explores their molecular mechanisms and pathophysiological connections, discusses the application of chronotherapy, and highlights potential future research directions, aiming to provide novel insights for the prevention and treatment of related diseases.
Humans ; Renin-Angiotensin System/genetics* ; Cardiovascular Diseases/genetics* ; CLOCK Proteins/physiology* ; Animals

Recently, male reproductive health has attracted extensive attention, with the adverse effects of circadian disruption on male fertility gradually gaining recognition. However, the mechanism by which circadian disruption leads to damage to male reproductive system remains unclear. In this review, we first summarized the dual regulatory roles of circadian clock genes on the male reproductive system: (1) circadian regulation of testosterone synthesis via the hypothalamic-pituitary-testicular (HPT) and hypothalamic-pituitary-adrenal (HPA) axes; (2) non-circadian regulation of spermatogenesis. Next, we further listed the possible mechanisms by which circadian disruption impairs male fertility, including interference with the oscillatory function of the reproductive system, i.e., synchronization of the HPT axis, crosstalk between the HPT axis and the HPA axis, as well as direct damage to germ cells by disturbing the non-oscillatory function of the reproductive system. Future research using spatiotemporal omics, epigenomic assays, and neural circuit mapping in studying the male reproductive system may provide new clues to systematically unravel the mechanisms by which circadian disruption affects male reproductive system through circadian clock genes.
Male ; Humans ; Animals ; Circadian Clocks/physiology* ; Hypothalamo-Hypophyseal System/physiology* ; Circadian Rhythm/genetics* ; Spermatogenesis/physiology* ; Pituitary-Adrenal System/physiology* ; Testis/physiology* ; Testosterone/biosynthesis* ; CLOCK Proteins ; Infertility, Male/physiopathology*

The circadian clock is a highly conserved timekeeping system in organisms, which maintains physiological homeostasis by precisely regulating periodic fluctuations in gene expression. Substantial clinical and experimental evidence has established a close association between circadian rhythm disruption and the development of various malignancies. Research has revealed characteristic alterations in the circadian gene expression profiles in tumor tissues, primarily manifested as a dysfunction of core clock components (particularly circadian locomotor output cycles kaput (CLOCK) and brain and muscle ARNT-like 1 (BMAL1)) and the widespread dysregulation of their downstream target genes. Notably, CLOCK demonstrates non-canonical oncogenic functions, including epigenetic regulation via histone acetyltransferase activity and the circadian-independent modulation of cancer pathways. This review systematically elaborates on the oncogenic mechanisms mediated by CLOCK/BMAL1, encompassing multidimensional effects such as cell cycle control, DNA damage response, metabolic reprogramming, and tumor microenvironment (TME) remodeling. Regarding the therapeutic strategies, we focus on cutting-edge approaches such as chrononutritional interventions, chronopharmacological modulation, and treatment regimen optimization, along with a discussion of future perspectives. The research breakthroughs highlighted in this work not only deepen our understanding of the crucial role of circadian regulation in cancer biology but also provide novel insights for the development of chronotherapeutic oncology, particularly through targeting the non-canonical functions of circadian proteins to develop innovative anti-cancer strategies.
Humans ; ARNTL Transcription Factors/physiology* ; Neoplasms/therapy* ; CLOCK Proteins/physiology* ; Circadian Clocks/genetics* ; Animals ; Circadian Rhythm/genetics* ; Tumor Microenvironment ; Epigenesis, Genetic ; Gene Expression Regulation, Neoplastic

OBJECTIVETo study the changes of miRNA expression in the pineal gland of neonatal rats with hypoxic-ischemic brain damage (HIBD) and the possible roles of miRNA in the pathogenesis of circadian rhythm disturbance after HIBD.

METHODSSeven-day-old Sprague-Dawley (SD) rats were randomly divided into 2 groups: HIBD and sham-operated. HIBD was induced according to the Rice-Vannucci method. The pineal glands were obtained 24 hours after the HIBD event. The expression profiles of miRNAs were determined using GeneChip technigue and quantitative real-time PCR (RT-PCR). Then the miRNA which was highly expressed was selected. The expression levels of the chosen miRNA were detected in different tissues (lungs, intestines, stomach, kidneys, cerebral cortex, pineal gland). RT-PCR analysis was performed to measure the expression profiles of the chosen miRNA and the targeted gene Clock mRNA in the pineal gland at 0, 24, 48 and 72 hours after HIBD.

RESULTSmiRNA-182 that met the criteria was selected by GeneChip and RT-PCR. miRNA-182 was highly expressed in the pineal gland. Compared with the sham-operated group, the expression of miRNA-182 was significantly up-regulated in the pineal gland at 24 and 48 hours after HIBD (P<0.05). Compared with the sham-operated group, Clock mRNA expression in the HIBD group increased at 0 hour after HIBD, decreased at 48 hours after HIBD and increased at 72 hours after HIBD (P<0.05).

CONCLUSIONSmiRNA-182 may be involved in the pathogenesis of circadian rhythm disturbance after HIBD.

Animals ; Animals, Newborn ; CLOCK Proteins ; genetics ; Circadian Rhythm ; physiology ; Female ; Gene Expression Regulation ; Hypoxia-Ischemia, Brain ; physiopathology ; Male ; MicroRNAs ; analysis ; physiology ; Pineal Gland ; metabolism ; RNA, Messenger ; analysis ; Rats ; Rats, Sprague-Dawley ; Real-Time Polymerase Chain Reaction

By means of a circadian clock system, all the living organisms on earth including human beings can anticipate the environmental rhythmic changes such as light/dark and warm/cold periods in a daily as well as in a yearly manner. Anticipating such environmental changes provide organisms with survival benefits via manifesting behavior and physiology at an advantageous time of the day and year. Cell-autonomous circadian oscillators, governed by transcriptional feedback loop composed of positive and negative elements, are organized into a hierarchical system throughout the organisms and generate an oscillatory expression of a clock gene by itself as well as clock controlled genes (ccgs) with a 24 hr periodicity. In the feedback loop, hetero-dimeric transcription factor complex induces the expression of negative regulatory proteins, which in turn represses the activity of transcription factors to inhibit their own transcription. Thus, for robust oscillatory rhythms of the expression of clock genes as well as ccgs, the precise control of subcellular localization and/or timely translocation of core clock protein are crucial. Here, we discuss how sub-cellular localization and nuclear translocation are controlled in a time-specific manner focusing on the negative regulatory clock proteins.
Circadian Clocks* ; Circadian Rhythm ; CLOCK Proteins ; Humans ; Periodicity ; Phosphorylation ; Physiology ; Protein Processing, Post-Translational ; Repressor Proteins* ; Transcription Factors

OBJECTIVETo study the effects of biological clock protein on circadian disorders in hypoxic-ischemic brain damage (HIBD) by examining levels of CLOCK and BMAL1 proteins in the pineal gland of neonatal rats.

METHODSSeventy-two 7-day-old Sprague-Dawley (SD) rats were randomly divided into sham-operated and HIBD groups. HIBD model was prepared according to the modified Levine method. Western blot analysis was used to measure the levels of CLOCK and BMAL1 in the pineal gland at 0, 2, 12, 24, 36 and 48 hours after operation.

RESULTSBoth CLOCK and BMAL levels in the pineal gland increased significantly 48 hours after HIBD compared with the sham-operated group (P<0.05). There were no significant differences in levels of CLOCK and BMAL proteins between the two groups at 0, 2, 12, 24 and 36 hours after operation (P>0.05).

CONCLUSIONSLevels of CLOCK and BMAL1 proteins in the pineal gland of rats increase significantly 48 hours after HIBD, suggesting that both CLOCK and BMAL1 may be involved the regulatory mechanism of circadian disorders in rats with HIBD.

ARNTL Transcription Factors ; analysis ; physiology ; Animals ; Animals, Newborn ; CLOCK Proteins ; analysis ; physiology ; Chronobiology Disorders ; etiology ; Female ; Hypoxia-Ischemia, Brain ; metabolism ; Male ; Pineal Gland ; chemistry ; Rats ; Rats, Sprague-Dawley ; Time Factors

Low density lipoprotein receptor (LDLR) plays an important role in the cholesterol homeostasis. We examined the possible circadian regulation of LDLR and mechanism(s) underlying it. In mice, blood glucose and plasma triglyceride, total and high density lipoprotein cholesterol varied distinctively throughout a day. In addition, LDLR mRNA oscillated in the liver in a functional clock-dependent manner. Accordingly, analysis of human LDLR promoter sequence revealed three putative E-boxes, raising the possible regulation of LDLR expression by E-box-binding transcription factors. To test this possibility, human LDLR promoter reporter constructs were transfected into HepG2 cells and the effects of CLOCK/BMAL1, Hes1, and Hes6 expression were analyzed. It was found that positive circadian transcription factor complex CLOCK/BMAL1 upregulated human LDLR promoter activity in a serum-independent manner, while Hes family members Hes1 and Hes6 downregulated it only under serum-depleted conditions. Both effects were mapped to proximal promoter region of human LDLR, where mutation or deletion of well-known sterol regulatory element (SRE) abolished only the repressive effect of Hes1. Interestingly, hes6 and hes1 mRNA oscillated in an anti-phasic manner in the wild-type but not in the per1-/-per2-/- mouse. Comparative analysis of mouse, rat and human hes6 genes revealed that three E-boxes are conserved among three species. Transfection and site-directed mutagenesis studies with hes6 reporter constructs confirmed that the third E-box in the exon IV is functionally induced by CLOCK/BMAL1. Taken together, these results suggest that LDLR expression is under circadian control involving CLOCK/BMAL1 and Hes family members Hes1 and Hes6.
ARNTL Transcription Factors/physiology ; Animals ; Base Sequence ; Basic Helix-Loop-Helix Transcription Factors/*genetics/metabolism/physiology ; CLOCK Proteins/physiology ; Cholesterol/blood ; *Circadian Rhythm ; E-Box Elements ; Exons ; *Gene Expression Regulation ; Hep G2 Cells ; Homeodomain Proteins/*genetics/metabolism/physiology ; Homeostasis ; Humans ; Liver/metabolism ; Male ; Mice ; Mice, Inbred C57BL ; *Promoter Regions, Genetic ; Receptors, LDL/*genetics/metabolism ; Repressor Proteins/*genetics/metabolism/physiology ; Transcription, Genetic

The sleep-wake cycle displays a characteristic 24-hour periodicity, providing an opportunity to dissect the endogenous circadian clock through the study of aberrant behaviour. This article surveys the properties of circadian clocks, with emphasis on mammals. Information was obtained from searches of peer-reviewed literature in the PUBMED database. Features that are highlighted include the known molecular components of clocks, their entrainment by external time cues and the output pathways used by clocks to regulate metabolism and behaviour. A review of human circadian rhythm sleep disorders follows, including recent discoveries of their genetic basis. The article concludes with a discussion of future approaches to the study of human circadian biology and sleep-wake behaviour.
ARNTL Transcription Factors ; Animals ; Basic Helix-Loop-Helix Transcription Factors ; physiology ; CLOCK Proteins ; Circadian Rhythm ; genetics ; physiology ; Humans ; Neurons, Afferent ; physiology ; Neurons, Efferent ; physiology ; Polymorphism, Single Nucleotide ; Sleep Disorders, Circadian Rhythm ; genetics ; physiopathology ; Suprachiasmatic Nucleus ; cytology ; physiology ; Trans-Activators ; physiology