Inhibition of expression of the circadian clock gene Period causes metabolic abnormalities including repression of glycometabolism in Bombyx mori cells

The specificities, influencing factors, and medical implications of bone circadian rhythms

Physiological processes within the human body are regulated in approximately 24-h cycles known as circadian rhythms, serving to adapt to environmental changes. Bone rhythms play pivotal roles in bone development, metabolism, mineralization, and remodeling processes. Bone rhythms exhibit cell specificity, and different cells in bone display various expressions of clock genes. Multiple environmental factors, including light, feeding, exercise, and temperature, affect bone diurnal rhythms through the sympathetic nervous system and various hormones. Disruptions in bone diurnal rhythms contribute to the onset of skeletal disorders such as osteoporosis, osteoarthritis and skeletal hypoplasia. Conversely, these bone diseases can be effectively treated when aimed at the circadian clock in bone cells, including the rhythmic expressions of clock genes and drug targets. In this review, we describe the unique circadian rhythms in physiological activities of various bone cells. Then we summarize the factors synchronizing the diurnal rhythms of bone with the underlying mechanisms. Based on the review, we aim to build an overall understanding of the diurnal rhythms in bone and summarize the new preventive and therapeutic strategies for bone disorders.

Advancements in research on the association between the biological CLOCK and type 2 diabetes

Due to the Earth's rotation, the natural environment exhibits a light-dark diurnal cycle close to 24 hours. To adapt to this energy intake pattern, organisms have developed a 24-hour rhythmic diurnal cycle over long periods, known as the circadian rhythm, or biological clock. With the gradual advancement of research on the biological clock, it has become increasingly evident that disruptions in the circadian rhythm are closely associated with the occurrence of type 2 diabetes (T2D). To further understand the progress of research on T2D and the biological clock, this paper reviews the correlation between the biological clock and glucose metabolism and analyzes its potential mechanisms. Based on this, we discuss the potential factors contributing to circadian rhythm disruption and their impact on the risk of developing T2D, aiming to explore new possible intervention measures for the prevention and treatment of T2D in the future. Under the light-dark circadian rhythm, in order to adapt to this change, the human body forms an internal biological clock involving a variety of genes, proteins and other molecules. The main mechanism is the transcription-translation feedback loop centered on the CLOCK/BMAL1 heterodimer. The expression of important circadian clock genes that constitute this loop can regulate T2DM-related blood glucose traits such as glucose uptake, fat metabolism, insulin secretion/glucagon secretion and sensitivity in various peripheral tissues and organs. In addition, sleep, light, and dietary factors under circadian rhythms also affect the occurrence of T2DM.

The circadian clock affects starvation resistance through the pentose phosphate pathway in silkworm, Bombyx mori

Disruption of the circadian clock can affect starvation resistance, but the molecular mechanism is still unclear. Here, we found that starvation resistance was significantly reduced in the core gene BmPer deficient mutant silkworms (Per-/-), but the mutant's starvation resistance increased with larval age. Under natural physiological conditions, the weight of mutant 5th instar larvae was significantly increased compared to wild type, and the accumulation ability of triglycerides and glycogen in the fat bodies was upregulated. However, under starvation conditions, the weight consumption of mutant larvae was increased and cholesterol utilization was intensified. Transcriptome analysis showed that beta-oxidation was significantly upregulated under starvation conditions, fatty acid synthesis was inhibited, and the expression levels of genes related to mitochondrial function were significantly changed. Further investigations revealed that the redox balance, which is closely related to mitochondrial metabolism, was altered in the fat bodies, the antioxidant level was increased, and the pentose phosphate pathway, the source of reducing power in cells, was activated. Our findings suggest that one of the reasons for the increased energy burden observed in mutants is the need to maintain a more robust redox balance in metabolic tissues. This necessitates the diversion of more glucose into the pentose phosphate pathway to ensure an adequate supply of reducing power.

The clock gene, period, influences migratory flight and reproduction of the oriental armyworm, Mythimna separata (Walker)

The oriental armyworm, Mythimna separata, is a major long-distance migratory insect pest of grain crops in China and other Asian countries. Migratory flights and reproductive behavior usually occur at night, regulated by a circadian rhythm. However, knowledge about the linkages between adult flight, reproduction, and clock genes is still incomplete. To fill this important gap in our knowledge, a clock gene (designated Msper) was identified and phylogenetic analysis indicated that the encoded protein (MsPER) was highly similar to PER proteins from other insect species. Quantitative RT-PCR assays demonstrated that significantly different spatiotemporal and circadian rhythmic accumulations of mRNA encoding MsPER occurred during development under steady 14 h : 10 h light : dark conditions. The highest mRNA accumulation occurred in adult antennae and the lowest in larvae. Msper was expressed rhythmically in adult antennae, relatively less in photophase and more entering scotophase. Injecting small interference RNA (siRNA) into adult heads effectively knocked down Msper mRNA levels within 72 h. Most siRNA-injected adults reduced their evening flight activity significantly and did not exhibit a normal evening peak of flight activity. They also failed to mate and lay eggs within 72 h. Adult mating behavior was restored to control levels by 72 h post injection. We infer that Msper is a prominent clock gene that acts in regulating adult migratory flight and mating behaviors of M. separata. Because of its influence on migration and mating, Msper may be a valuable gene to target for effective management of this migratory insect.

Expression of BmDHFR is up-regulated to trigger an increase in the BH4/BH2 ratio when the de novo synthesis of BH4 is blocked in silkworm, Bombyx mori

Tetrahydrobiopterin (BH4) is a vital coenzyme for several enzymes involved in diverse enzymatic reactions in animals. BH4 deficiency can lead to metabolic and neurological disorders due to dysfunction in its metabolism. Sepiapterin reductase (SPR) and dihydrofolate reductase (DHFR) are crucial enzymes in the BH4 de novo synthesis pathway and salvage pathway, respectively. Dihydrobiopterin (BH2) is an oxidized product of BH4 metabolism. The ratio of BH4/BH2 is a key indicator of the stability of BH4 levels. The de novo pathway of BH4 synthesis is well-defined; however, little is known about the mechanisms of the salvage pathway in insects. Herein, we used the natural BmSPR mutant silkworm (lem) as a resource material. Our results reveal that the BmDHFR expression and the BH4/BH2 ratio were remarkably higher in lem as compared to the wild-type silkworm. In BmN cells, knockdown of BmSpr showed increased BmDHFR expression, while the BH4/BH2 ratio decreased after BmDhfr knockdown by RNAi. Furthermore, simultaneous RNAi of BmSpr and BmDhfr showed a further decrease in the BH4/BH2 ratio. These manifest that the expression of BmDHFR is up-regulated to trigger an increase in the BH4/BH2 ratio when the de novo synthesis of BH4 is blocked in silkworm. Additionally, the knockdown of BmSpr in wild-type silkworms also showed an increased BmDHFR level and BH4/BH2 ratio. Taken together, when the silkworm BH4 de novo synthesis pathway is blocked, the salvage pathway is activated, and BmDHFR plays an important role in maintaining the metabolic balance of silkworm BH4. This study enriches our understanding of the molecular mechanism of the BH4 salvage pathway and lays a good foundation for further studies on BH4 using the silkworm as a model insect.

Potential Effect of the Circadian Clock on Erectile Dysfunction

The circadian rhythm is an internal timing system, which is generated by circadian clock genes. Because the circadian rhythm regulates numerous cellular, behavioral, and physiological processes, organisms have evolved with intrinsic biological rhythms to adapt the daily environmental changes. A variety of pathological events occur at specific times, while disturbed rhythms can lead to metabolic syndrome, vascular dysfunction, inflammatory disorders, and cancer. Therefore, the circadian clock is considered closely related to various diseases. Recently, accumulated data have shown that the penis is regulated by the circadian clock, while erectile function is impaired by an altered sleep-wake cycle. The circadian rhythm appears to be a novel therapeutic target for preventing and managing erectile dysfunction (ED), although research is still progressing. In this review, we briefly summarize the superficial interactions between the circadian clock and erectile function, while focusing on how disturbed rhythms contribute to risk factors of ED. These risk factors include NO/cGMP pathway, atherosclerosis, diabetes mellitus, lipid abnormalities, testosterone deficiency, as well as dysfunction of endothelial and smooth muscle cells. On the basis of recent findings, we discuss the potential role of the circadian clock for future therapeutic strategies on ED, although further relevant research needs to be performed.

Circadian rhythms affect bone reconstruction by regulating bone energy metabolism

Metabolism is one of the most complex cellular biochemical reactions, providing energy and substances for basic activities such as cell growth and proliferation. Early studies have shown that glucose is an important nutrient in osteoblasts. In addition, amino acid metabolism and fat metabolism also play important roles in bone reconstruction. Mammalian circadian clocks regulate the circadian cycles of various physiological functions. In vertebrates, circadian rhythms are mediated by a set of central clock genes: muscle and brain ARNT like-1 (Bmal1), muscle and brain ARNT like-2 (Bmal2), circadian rhythmic motion output cycle stagnates (Clock), cryptochrome 1 (Cry1), cryptochrome2 (Cry2), period 1 (Per1), period 2 (Per2), period 3 (Per3) and neuronal PAS domain protein 2 (Npas2). Negative feedback loops, controlled at both the transcriptional and posttranslational levels, adjust these clock genes in a diurnal manner. According to the results of studies on circadian transcriptomic studies in several tissues, most rhythmic genes are expressed in a tissue-specific manner and are affected by tissue-specific circadian rhythms. The circadian rhythm regulates several activities, including energy metabolism, feeding time, sleeping, and endocrine and immune functions. It has been reported that the circadian rhythms of mammals are closely related to bone metabolism. In this review, we discuss the regulation of the circadian rhythm/circadian clock gene in osteoblasts/osteoclasts and the energy metabolism of bone, and the relationship between circadian rhythm, bone remodeling, and energy metabolism. We also discuss the therapeutic potential of regulating circadian rhythms or changing energy metabolism on bone development/bone regeneration.

Hesperidin modulates the rhythmic proteomic profiling in Drosophila melanogaster under oxidative stress

The circadian clock regulates vital aspects of physiology including protein synthesis and oxidative stress response. In this investigation, we performed a proteome-wide scrutiny of rhythmic protein accrual in Drosophila melanogaster on exposure to rotenone, rotenone + hesperidin and hesperidin in D. melanogaster. Total protein from fly samples collected at 6 h intervals over the 24 h period was subjected to two-dimensional gel electrophoresis and mass spectrometry. Bioinformatics tool, Protein ANalysis THrough Evolutionary Relationships classification system was used to the determine the biological processes of the proteins of altered abundance. Conspicuous variations in the proteome (151 proteins) of the flies exposed to oxidative stress (by rotenone treatment) and after alleviating oxidative stress (by hesperidin treatment) were observed during the 24 h cycle. Significantly altered levels of abundance of a wide variety of proteins under oxidative stress (rotenone treatment) and under alleviation of oxidative stress (rotenone + hesperidin treatment) and hesperidin (alone) treatment were observed. These proteins are involved in metabolism, muscle activity, heat shock response, redox homeostasis, protein synthesis/folding/degradation, development, ion-channel/cellular transport, and gustatory and olfactory function of the flies. Our data indicates that numerous cellular processes are involved in the temporal regulation of proteins and widespread modulations happen under rotenone treatment and, action of hesperidin could also be seen on these categories of proteins.

Circadian rhythm and atherosclerosis (Review)

Atherosclerosis is the leading cause of morbidity and mortality worldwide. The underlying pathogenesis involves multiple metabolic disorders, endothelial dysfunction and a maladaptive immune response, and leads to chronic arterial wall inflammation. Numerous normal physiological activities exhibit daily rhythmicity, including energy metabolism, vascular function and inflammatory immunoreactions, and disrupted or misaligned circadian rhythms may promote the progression of atherosclerosis. However, the association between the circadian rhythm and atherosclerosis remains to be fully elucidated. In the present review, the effects of the circadian rhythm on atherosclerosis progression are discussed.

Gas Chromatography-Mass Spectrometry Based Midgut Metabolomics Reveals the Metabolic Perturbations under NaF Stress in Bombyx mori

Fluoride tolerance is an important economic trait in sericulture, especially in some industrial development regions. Analyses of physiological changes involving structural damage to the insect body and molecular analyses of some related genes have focused on this area; however, the changes that occur at the metabolic level of silkworms after eating fluoride-contaminated mulberry leaves remain unclear. Here, metabonomic analysis was conducted using gas chromatography-mass spectrometry (GC-MS) to analyze the changes in midgut tissue after NaF stress using silkworm strains 733xin (susceptible stain) and T6 (strain resistant to fluoride), which were previously reported by our laboratory. Differential metabolomics analysis showed that both T6 and 733xin strains displayed complex responses after exposure to 200 mg/kg NaF. The purine metabolism and arginine and proline metabolic pathways of fluoride-tolerant strains reached significant levels, among which 3′-adenylic acid and hypoxanthine were significantly upregulated, whereas guanine, allantoic acid, xanthine, N-acetyl-L-glutamic acid, and pyruvate were significantly downregulated. These metabolic pathways may be related to the fluoride tolerance mechanism of NaF poisoning and tolerant strains.

Inhibition of Period Gene Expression Causes Repression of Cell Cycle Progression and Cell Growth in the Bombyx mori Cells

Circadian clock system disorders can lead to uncontrolled cell proliferation, but the molecular mechanism remains unknown. We used a Bombyx mori animal model of single Period gene (BmPer) expression to investigate this mechanism. A slow growing developmental cell model (Per-KD) was isolated from a B. mori ovarian cell line (BmN) by continuous knock down of BmPer expression. The effects of BmPer expression knockdown (Per-KD) on cell proliferation and apoptosis were opposite to those of m/hPer1 and m/hPer2 in mammals. The knockdown of BmPer expression led to cell cycle deceleration with shrinking of the BmN cell nucleus, and significant inhibition of nuclear DNA synthesis and cell proliferation. It also promoted autophagy via the lysosomal pathway, and accelerated apoptosis via the caspase pathway.

Loss of the clock gene PER2 is associated with cancer development and altered expression of important tumor-related genes in oral cancer

Recent studies have demonstrated that abnormal expression of the clock gene PER2 is closely associated with the development of a variety of cancer types. However, the expression of PER2 in oral squamous cell carcinoma (OSCC), a common malignant tumor in humans, and its correlations with the clinicopathological parameters and survival time of OSCC patients and the altered expression of important tumor-related genes remain unclear. In the present study, we detected the mRNA and protein expression levels of PER2, PIK3CA, PTEN, P53, P14ARF and caspase‑8 in OSCC tissues and cancer-adjacent oral mucosa by reverse transcription-quantitative PCR (RT-qPCR), western blotting and immunohistochemistry. The results showed that the PER2, PTEN, P53, P14ARF and caspase‑8 mRNA and protein expression levels in OSCC were significantly reduced compared with those in cancer-adjacent tissues. Additionally, the PIK3CA protein expression level was significantly increased in OSCC tissues, whereas the mRNA level was not. Decreased expression of PER2 was significantly associated with advanced clinical stage and the presence of lymphatic metastasis in OSCC patients. Patients with PER2‑negative expression had a significantly shorter survival time than those with PER2‑positive expression. PER2 expression was negatively correlated with PIK3CA and P53 levels, and positively correlated with PTEN, P14ARF and caspase‑8 levels. In summary, the results of this study suggest that loss of PER2 expression is closely associated with the genesis and development of OSCC and that PER2 may be an important prognostic biomarker in OSCC. PER2 may serve an antitumor role via the P53/P14ARF, PIK3CA/AKT and caspase‑8 pathways.

Metabolomics differences between silkworms (Bombyx mori) reared on fresh mulberry (Morus) leaves or artificial diets

Silkworms (Bombyx mori) reared on artificial diets have great potential applications in sericulture. However, the mechanisms underlying the enhancement of metabolic utilization by altering silkworm nutrition are unclear. The aim of this study was to investigate the mechanisms responsible for the poor development and low silk protein synthesis efficiency of silkworms fed artificial diets. After multi-generational selection of the ingestive behavior of silkworms to artificial diets, we obtained two strains, one of which developed well and another in which almost all its larvae starved to death on the artificial diets. Subsequently, we analyzed the metabolomics of larval hemolymph by gas chromatography/liquid chromatography–mass spectrometry, and the results showed that vitamins were in critically short supply, whereas the nitrogen metabolic end product of urea and uric acid were enriched substantially, in the hemolymph of the silkworms reared on the artificial diets. Meanwhile, amino acid metabolic disorders, as well as downregulation of carbohydrate metabolism, energy metabolism, and lipid metabolism, co-occurred. Furthermore, 10 male-dominant metabolites and 27 diet-related metabolites that differed between male and female silkworms were identified. These findings provide important insights into the regulation of silkworm metabolism and silk protein synthesis when silkworms adapt to an artificial diet.

Networks Underpinning Symbiosis Revealed Through Cross-Species eQTL Mapping

Organisms engage in extensive cross-species molecular dialog, yet the underlying molecular actors are known for only a few interactions. Many techniques have been designed to uncover genes involved in signaling between organisms. Typically, these focus on only one of the partners. We developed an expression quantitative trait locus (eQTL) mapping-based approach to identify cause-and-effect relationships between genes from two partners engaged in an interspecific interaction. We demonstrated the approach by assaying expression of 98 isogenic plants (Medicago truncatula), each inoculated with a genetically distinct line of the diploid parasitic nematode Meloidogyne hapla With this design, systematic differences in gene expression across host plants could be mapped to genetic polymorphisms of their infecting parasites. The effects of parasite genotypes on plant gene expression were often substantial, with up to 90-fold (P = 3.2 × 10-52) changes in expression levels caused by individual parasite loci. Mapped loci included a number of pleiotropic sites, including one 87-kb parasite locus that modulated expression of >60 host genes. The 213 host genes identified were substantially enriched for transcription factors. We distilled higher-order connections between polymorphisms and genes from both species via network inference. To replicate our results and test whether effects were conserved across a broader host range, we performed a confirmatory experiment using M. hapla-infected tomato. This revealed that homologous genes were similarly affected. Finally, to validate the broader utility of cross-species eQTL mapping, we applied the strategy to data from a Salmonella infection study, successfully identifying polymorphisms in the human genome affecting bacterial expression.