Sirt1与生物钟的相互调控

生物钟调控机制广泛存在于各种类型的细胞中,控制着细胞代谢的节律性变化.最近的研究发现,NAD+依赖的组蛋白去乙酰化酶Sirt1参与了生物钟调控过程,对维持正常的生物钟节律具有重要作用;另一方面,Sirt1的表达也受到生物钟系统的调控,呈现出昼夜节律性的表达.因此Sirt1能与生物钟进行相互调控,并且这一作用机制很可能广泛参与了不同类型细胞内的信号转导和能量代谢过程.本文总结了Sirt1与生物钟之间相互调控的一些研究进展,对它们之间的分子调控机制进行了概述.     

The Impact of HIF1α on the Per2 Circadian Rhythm in Renal Cancer Cell Lines

In mammals, the circadian rhythm central generator consists of interactions among clock genes, including Per1/2/3, Cry1/2, Bmal1, and Clock. Circadian rhythm disruption may lead to increased risk of cancer in humans, and deregulation of clock genes has been implicated in many types of cancers. Among these genes, Per2 is reported to have tumor suppressor properties, but little is known about the correlation between Per2 and HIF, which is the main target of renal cell carcinoma (RCC) therapy. In this study, the rhythmic expression of the Per2 gene was not detectable in renal cancer cell lines, with the exception of Caki-2 cells. In Caki-2 cells, HIF1α increased the amplitude of Per2 oscillation by directly binding to the HIF-binding site located on the Per2 promoter. These results indicate that HIF1α may enhance the amplitude of the Per2 circadian rhythm.     

Quercetin,caffeic acid and resveratrol regulate circadian clock genes and aging-related genes in young and old human lung fibroblast cells

The circadian timing system of mammals is synchronized in concert with a central clock, but is also influenced by additional stimuli, including nutrients. However, little research has been done on polyphenols other than resveratrol and there seem to be no studies on their influence on young and old cells. The purpose of this study was to analyse the potential effects of quercetin, caffeic acid, and resveratrol on young and old fibroblast cells in the expressions of different clock genes and aging-related genes, and further investigate the mechanism. The mRNA expression of different clock genes and aging-related genes was assessed by quantitative real-time PCR. The protein levels of clock genes (BMAL1, PER1 and SIRT1) and glucocorticoid receptor α (GRα) were assessed by ELISA. Quercetin and caffeic acid in old fibroblast cells showed higher clock gene expression than resveratrol, quercetin increased Sirt1 expression, and caffeic acid increased Sirt6 expression indicating the possibility of an anti-aging effect. Also, quercetin and caffeic acid showed higher clock-controlled gene (Sirt1 and NR1D1) expression than resveratrol in young fibroblast cells. It appears that caffeic acid acts on NRF2 expression, and in turn to the actions of GRα, GDF11, Sirt1, and Sirt6. Regarding the increased expression of Per1, the activation effect on NR1D1 was confirmed only for caffeic acid in young fibroblast cells. Our results have confirmed the interplay of the circadian clock genes and cellular aging.

     

Influence of the estrous cycle on clock gene expression in reproductive tissues: Effects of fluctuating ovarian steroid hormone levels

Circadian rhythms in physiology and behavior are known to be influenced by the estrous cycle in female rodents. The clock genes responsible for the generation of circadian oscillations are widely expressed both within the central nervous system and peripheral tissues, including those that comprise the reproductive system. To address whether the estrous cycle affects rhythms of clock gene expression in peripheral tissues, we first examined rhythms of clock gene expression (Per1, Per2, Bmal1) in reproductive (uterus, ovary) and non-reproductive (liver) tissues of cycling rats using quantitative real-time PCR (in vivo) and luminescent recording methods to measure circadian rhythms of PER2 expression in tissue explant cultures from cycling PER2::LUCIFERASE (PER2::LUC) knockin mice (ex vivo). We found significant estrous variations of clock gene expression in all three tissues in vivo, and in the uterus ex vivo. We also found that exogenous application of estrogen and progesterone altered rhythms of PER2::LUC expression in the uterus. In addition, we measured the effects of ovarian steroids on clock gene expression in a human breast cancer cell line (MCF-7 cells) as a model for endocrine cells that contain both the steroid hormone receptors and clock genes. We found that progesterone, but not estrogen, acutely up-regulated Per1, Per2, and Bmal1 expression in MCF-7 cells. Together, our findings demonstrate that the timing of the circadian clock in reproductive tissues is influenced by the estrous cycle and suggest that fluctuating steroid hormone levels may be responsible, in part, through direct effects on the timing of clock gene expression.     

Bmal1-deficient mouse fibroblast cells do not provide premature cellular senescence in vitro

Bmal1 is a core circadian clock gene. Bmal1^?/? mice show disruption of the clock and premature aging phenotypes with a short lifespan. However, little is known whether disruption of Bmal1 leads to premature aging at cellular level. Here, we established primary mouse embryonic fibroblast (MEF) cells derived from Bmal1^?/? mice and investigated its effects on cellular senescence. Unexpectedly, Bmal1^?/? primary MEFs that showed disrupted circadian oscillation underwent neither premature replicative nor stress-induced cellular senescence. Our results therefore uncover that Bmal1 is not required for in vitro cellular senescence, suggesting that circadian clock does not control in vitro cellular senescence.     

Clock controls angiogenesis

Circadian rhythms control multiple physiological and pathological processes, including embryonic development in mammals and development of various human diseases. We have recently, in a developing zebrafish embryonic model, discovered that the circadian oscillation controls developmental angiogenesis. Disruption of crucial circadian regulatory genes, including Bmal1 and Period2, results in marked impairment or enhancement of vascular development in zebrafish. At the molecular level, we show that the circadian regulator Bmal1 directly targets the promoter region of the vegf gene in zebrafish, leading to an elevated expression of VEGF. These findings can reasonably be extended to developmental angiogenesis in mammals and even pathological angiogenesis in humans. Thus, our findings, for the first time, shed new light on mechanisms that underlie circadian clock-regulated angiogenesis.     

Synchronized oscillation of the segmentation clock gene in vertebrate development

In vertebrate somitogenesis, “segmentation clock” genes (her in zebrafish, hes in mouse, and hairy in chick) show oscillation, synchronized over nearby cells through intercellular interaction. In zebrafish, neighboring cells interact by Delta-Notch signaling to realize synchronization. Under Delta-Notch, however, a cell with a high expression of the segmentation clock gene tends to suppress its expression in adjacent cells, which might produce spatial heterogeneity instead of synchronized oscillation. Here we studied the conditions under which pre-somitic mesoderm cells show synchronized oscillation of gene expression mathematically. We adopted a model that explicitly considers the kinetics of the mRNA and proteins of the segmentation clock gene and cell–cell interaction via Delta-Notch signaling. From statistical study of a model with randomly generated parameters, we revealed how the likelihood that the system generates stable synchronized oscillation depends on the rate of each reaction in the gene–protein kinetics.     

Reduced Histone H3K9 Acetylation of Clock Genes and Abnormal Glucose Metabolism in ob/ob Mice

Recent chronobiological studies found significant correlation between lack of clock function and metabolic abnormalities. We previously showed that clock gene expressions were dampened in the peripheral tissues of obese and diabetic ob/ob mice. However, the molecular mechanism of the disturbance remained to be determined. In this study, we demonstrated for the first time that acetylation levels of histone H3 lysine 9 (H3K9) at the promoter regions of clock genes, such as Dbp, Per2, and Bmal1, in the adipose tissue of ob/ob mice were significantly reduced compared with those of its control C57BL/6J mice. Treatment with histone deacetylase (HDAC) inhibitors increased Dbp, but not Per2 or Bmal1, mRNA expression in adipose tissue, and it decreased blood glucose in these animals. In addition, 2-deoxyglucose uptake activity was significantly suppressed by silencing Dbp expression in cultured adipocytes. These results suggest that reduced H3K9 acetylation and subsequent decreased mRNA expression of the Dbp gene in adipose tissue are involved in the mechanism of development of abnormal glucose metabolism in ob/ob mice. (Author correspondence: akiofuji@jichi.ac.jp ).     

Altered cellular redox status,sirtuin abundance and clock gene expression in a mouse model of developmentally primed NASH

BackgroundWe have previously shown that high fat (HF) feeding during pregnancy primes the development of non-alcoholic steatohepatits (NASH) in the adult offspring. However, the underlying mechanisms are unclear.AimsSince the endogenous molecular clock can regulate hepatic lipid metabolism, we investigated whether exposure to a HF diet during development could alter hepatic clock gene expression and contribute to NASH onset in later life.MethodsFemale mice were fed either a control (C, 7% kcal fat) or HF (45% kcal fat) diet. Offspring were fed either a C or HF diet resulting in four offspring groups: C/C, C/HF, HF/C and HF/HF. NAFLD progression, cellular redox status, sirtuin expression (Sirt1, Sirt3), and the expression of core clock genes (Clock, Bmal1, Per2, Cry2) and clock-controlled genes involved in lipid metabolism (Rev-Erbα, Rev-Erbβ, RORα, and Srebp1c) were measured in offspring livers.ResultsOffspring fed a HF diet developed NAFLD. However HF fed offspring of mothers fed a HF diet developed NASH, coupled with significantly reduced NAD⁺/NADH (p < 0.05, HF/HF vs C/C), Sirt1 (p < 0.001, HF/HF vs C/C), Sirt3 (p < 0.01, HF/HF vs C/C), perturbed clock gene expression, and elevated expression of genes involved lipid metabolism, such as Srebp1c (p < 0.05, C/HF and HF/HF vs C/C).ConclusionOur results suggest that exposure to excess dietary fat during early and post-natal life increases the susceptibility to develop NASH in adulthood, involving altered cellular redox status, reduced sirtuin abundance, and desynchronized clock gene expression.     

Chronic treatment with prednisolone represses the circadian oscillation of clock gene expression in mouse peripheral tissues

Although altered homeostatic regulation, including disturbance of 24-h rhythms, is often observed in the patients undergoing glucocorticoid therapy, the mechanisms underlying the disturbance remains poorly understood. We report here that chronic treatment with a synthetic glucocorticoid, prednisolone (PSL), can cause alteration of circadian clock function at molecular level. Treatment of cultured hepatic cells (HepG2) with PSL induced expression of Period1 (Per1), and the PSL treatment also attenuated the serum-induced oscillations in the expression of Period2 (Per2), Rev-erbalpha, and Bmal1 mRNA in HepG2 cells. Because the attenuation of clock gene oscillations was blocked by pretreating the cells with a Per1 antisense phosphothioate oligodeoxynucleotide, the extensive expression of Per1 induced by PSL may have resulted in the reduced amplitude of other clock gene oscillations. Continuous administration of PSL into mice constitutively increased the Per1 mRNA levels in liver and skeletal muscle, which seems to attenuate the oscillation in the expressions of Per2, Rev-erbalpha, and Bmal1. However, a single daily administration of PSL at the time of day corresponding to acrophase of endogenous glucocorticoid levels had little effect on the rhythmic expression of clock genes. These results suggest a possible pharmacological action by PSL on the core circadian oscillation mechanism and indicate the possibility that the alteration of clock function induced by PSL can be avoided by optimizing the dosing schedule.