Daily rhythms of glycerophospholipid synthesis in fibroblast cultures involve differential enzyme contributions

A Cross Talking between the Gut Microbiota and Metabolites of Participants in a Confined Environment

Certain workplaces, like deep-sea voyages, subject workers to chronic psychological stress and circadian rhythm disorders due to confined environments and frequent shifts. In this study, participants lived in a strictly controlled confined environment, and we analyzed the effects of a confined environment on gut microbiota and metabolites. The results showed that living in confined environments can significantly alter both the gut microbiota and the gut metabolome, particularly affecting lipid metabolism pathways like glycerophospholipid metabolism. There was a significant reduction in the abundance of Faecalibacterium and Bacteroides, while Blautia, Bifidobacterium, and Collinsella showed significant increases. An association analysis revealed a strong correlation between changes in the gut microbiota and the metabolome. Four upregulated lipid metabolites may serve as biomarkers for damage induced by confined environments, and certain gut microbiota alterations, such as those involving Faecalibacterium and Bacteroides, could be potential psychobiotics or therapeutic targets for enhancing mental health in a confined environment.

Lipid metabolism around the body clocks

Lipids play important roles in energy metabolism along with diverse aspects of biological membrane structure, signaling and other functions. Perturbations of lipid metabolism are responsible for the development of various pathologies comprising metabolic syndrome, obesity, and type 2 diabetes. Accumulating evidence suggests that circadian oscillators, operative in most cells of our body, coordinate temporal aspects of lipid homeostasis. In this review we summarize current knowledge on the circadian regulation of lipid digestion, absorption, transportation, biosynthesis, catabolism, and storage. Specifically, we focus on the molecular interactions between functional clockwork and biosynthetic pathways of major lipid classes comprising cholesterol, fatty acids, triacylglycerols, glycerophospholipids, glycosphingolipids, and sphingomyelins. A growing body of epidemiological studies associate a socially imposed circadian misalignment common in modern society with growing incidence of metabolic disorders, however the disruption of lipid metabolism rhythms in this connection has only been recently revealed. Here, we highlight recent studies that unravel the mechanistic link between intracellular molecular clocks, lipid homeostasis and development of metabolic diseases based on animal models of clock disruption and on innovative translational studies in humans. We also discuss the perspectives of manipulating circadian oscillators as a potentially powerful approach for preventing and managing metabolic disorders in human patients.

Metabolomic Analysis of Plasma in Huntington's Disease Transgenic Sheep (Ovis aries) Reveals Progressive Circadian Rhythm Dysregulation

BACKGROUND

Metabolic abnormalities have long been predicted in Huntington's disease (HD) but remain poorly characterized. Chronobiological dysregulation has been described in HD and may include abnormalities in circadian-driven metabolism.

OBJECTIVE

Here we investigated metabolite profiles in the transgenic sheep model of HD (OVT73) at presymptomatic ages. Our goal was to understand changes to the metabolome as well as potential metabolite rhythm changes associated with HD.

METHODS

We used targeted liquid chromatography mass spectrometry (LC-MS) metabolomics to analyze metabolites in plasma samples taken from female HD transgenic and normal (control) sheep aged 5 and 7 years. Samples were taken hourly across a 27-h period. The resulting dataset was investigated by machine learning and chronobiological analysis.

RESULTS

The metabolic profiles of HD and control sheep were separable by machine learning at both ages. We found both absolute and rhythmic differences in metabolites in HD compared to control sheep at 5 years of age. An increase in both the number of disturbed metabolites and the magnitude of change of acrophase (the time at which the rhythms peak) was seen in samples from 7-year-old HD compared to control sheep. There were striking similarities between the dysregulated metabolites identified in HD sheep and human patients (notably of phosphatidylcholines, amino acids, urea, and threonine).

CONCLUSION

This work provides the first integrated analysis of changes in metabolism and circadian rhythmicity of metabolites in a large animal model of presymptomatic HD.

Changes in Gut Microbiota Structure: A Potential Pathway for Silver Nanoparticles to Affect the Host Metabolism

Silver nanoparticles (AgNPs) are one of the most widely used NPs. Their adverse effects on either the host or its gut microbiota (GM) have been examined. Nevertheless, whether the GM plays any role in AgNP toxicity to the host remains unclear. In the present study, AgNPs were administered to mice by oral gavage once a day for 120 days. A significant dose-dependent accumulation of Ag in the liver was observed, with a steady state reached within 21 days. The AgNPs changed the structure of the GM, mainly with respect to microorganisms involved in the metabolism of energy, amino acids, organic acids, and lipids, as predicted in a PICRUST analysis. Effects of the AgNPs on liver metabolism were also demonstrated, as a KEGG pathway analysis showed the enrichment of pathways responsible for the metabolism of amino acids, purines and pyrimidine, lipids, and energy. More interestingly, the changes in GM structure and liver metabolism were highly correlated, evidenced by the correlation between ∼23% of the differential microorganisms at the genus level and ∼60% of the differential metabolites. This implies that the metabolic variations in liver as affected by AgNPs were partly attributable to NP-induced changes of GM structure. Therefore, our results demonstrate the importance of considering the roles of GM in the toxicity of NPs to the host in evaluations of the health risks of NPs.

Circadian Regulation and Clock-Controlled Mechanisms of Glycerophospholipid Metabolism from Neuronal Cells and Tissues to Fibroblasts

Along evolution, living organisms developed a precise timekeeping system, circadian clocks, to adapt life to the 24-h light/dark cycle and temporally regulate physiology and behavior. The transcriptional molecular circadian clock and metabolic/redox oscillator conforming these clocks are present in organs, tissues, and even in individual cells, where they exert circadian control over cellular metabolism. Disruption of the molecular clock may cause metabolic disorders and higher cancer risk. The synthesis and degradation of glycerophospholipids (GPLs) is one of the most highly regulated metabolisms across the 24-h cycle in terms of total lipid content and enzyme expression and activity in the nervous system and individual cells. Lipids play a plethora of roles (membrane biogenesis, energy sourcing, signaling, and the regulation of protein-chromatin interaction, among others), making control of their metabolism a vital checkpoint in the cellular organization of physiology. An increasing body of evidence clearly demonstrates an orchestrated and sequential series of events occurring in GPL metabolism across the 24-h day in diverse retinal cell layers, immortalized fibroblasts, and glioma cells. Moreover, the clock gene Per1 and other circadian-related genes are tightly involved in the regulation of GPL synthesis in quiescent cells. However, under proliferation, the metabolic oscillator continues to control GPL metabolism of brain cancer cells even after molecular circadian clock disruption, reflecting the crucial role of the temporal metabolism organization in cell preservation. The aim of this review is to examine the control exerted by circadian clocks over GPL metabolism, their synthesizing enzyme expression and activities in normal and tumorous cells of the nervous system and in immortalized fibroblasts.

Temporal regulation of tumor growth in nocturnal mammals: In vivo studies and chemotherapeutical potential

Tumors of the nervous system including glioblastoma multiforme (GBM) are the most frequent and aggressive form of brain tumors; however, little is known about the impact of the circadian timing system on the formation, growth, and treatment of these tumors. We investigated day/night differences in tumor growth after injection of A530 glioma cells isolated from malignant peripheral nerve sheath tumor (MPNSTs) of NPcis (Trp53+/- ; Nf1+/- ) mice. Synchronized A530 cell cultures expressing typical glial markers were injected at the beginning of the day or night into the sciatic nerve zone of C57BL/6 mice subject to a 12:12 hours light/dark (LD) cycle or after being released to constant darkness (DD). Tumors generated in animals injected early at night in the LD cycle or in DD showed higher growth rates than in animals injected diurnally. No differences were found when animals were injected at the same time with cultures synchronized 12 hours apart. Similar experiments performed with B16 melanoma cells showed higher tumor growth rates in animals injected at the beginning of the night compared to those injected in the daytime. A higher tumor growth rate than that in controls was observed when mice were injected with knocked-down clock gene Bmal1 cells. Finally, when we compared day/night administration of different doses of the proteasome inhibitor Bortezomib (0.5-1.5 mg/kg) in tumor-bearing animals, we found that low-dose chemotherapy displayed higher efficacy when administered at night. Results suggest the existence of a precise temporal control of tumor growth and of drug efficacy in which the host state and susceptibility are critical.

Chemotherapeutic Effect of SR9009, a REV-ERB Agonist, on the Human Glioblastoma T98G Cells

Glioblastoma multiforme is the most aggressive brain tumor, and human T98G cells constitute a useful glioblastoma multiforme model to evaluate the chemotherapeutic agents. Modern life (shiftwork, jetlag, etc.) may cause circadian disorganization promoting higher cancer risk and metabolic disorders. Although little is known about the tumor-intrinsic circadian clock function, pharmacological modulation of circadian components may offer selective anticancer strategies. REV-ERBs are heme-binding circadian clock components acting as repressors of processes involved in tumorigenesis such as metabolism, proliferation, and inflammation. A synthetic pyrrole derivative (SR9009) that acts as REV-ERBs-specific agonists exhibits potent in vivo activity on metabolism and tumor cell viability. Here, we investigated SR9009 effects on T98G cell viability, differential chemotherapy time responses, and underlying metabolic processes (reactive oxygen species [ROS] and lipid droplets [LDs]) and compared it with the proteasome inhibitor Bortezomib treatment. SR9009-treated cells exhibited significant reduction in cell viability with consequences on cell cycle progression. Dexamethasone synchronized cells displayed differential time responses to SR9009 treatment with highest responses 18 to 30 h after synchronization. SR9009 treatment decreased ROS levels while Bortezomib increased them. However, both treatments significantly increased LD levels, whereas the combined treatment showed additive or synergistic effects between both drugs. In addition, we extended these studies to HepG2 cells which also showed a significant decrease in cell viability and ROS levels and the increase in LD levels after SR9009 treatment. Our results suggest that the pharmacological modulation of the tumor-intrinsic clock by REV-ERB agonists severely affects cell metabolism and promotes cytotoxic effects on cancer cells.

Circadian Clock Regulation on Lipid Metabolism and Metabolic Diseases

The basic helix-loop-helix-PAS transcription factor (CLOCK, Circadian locomotor output cycles protein kaput) was discovered in 1994 as a circadian clock. Soon after its discovery, the circadian clock, Aryl hydrocarbon receptor nuclear translocator-like protein 1 (ARNTL, also call BMAL1), was shown to regulate adiposity and body weight by controlling on the brain hypothalamic suprachiasmatic nucleus (SCN). Farther, circadian clock genes were determined to exert several of lipid metabolic and diabetes effects, overall indicating that CLOCK and BMAL1 act as a central master circadian clock. A master circadian clock acts through the neurons and hormones, with expression in the intestine, liver, kidney, lung, heart, SCN of brain, and other various cell types of the organization. Among circadian clock genes, numerous metabolic syndromes are the most important in the regulation of food intake (via regulation of circadian clock genes or clock-controlled genes in peripheral tissue), which lead to a variation in plasma phospholipids and tissue phospholipids. Circadian clock genes affect the regulation of transporters and proteins included in the regulation of phospholipid metabolism. These genes have recently received increasing recognition because a pharmacological target of circadian clock genes may be of therapeutic worth to make better resistance against insulin, diabetes, obesity, metabolism syndrome, atherosclerosis, and brain diseases. In this book chapter, we focus on the regulation of circadian clock and summarize its phospholipid effect as well as discuss the chemical, physiology, and molecular value of circadian clock pathway regulation for the treatment of plasma lipids and atherosclerosis.

Proliferative Glioblastoma Cancer Cells Exhibit Persisting Temporal Control of Metabolism and Display Differential Temporal Drug Susceptibility in Chemotherapy

Even in immortalized cell lines, circadian clocks regulate physiological processes in a time-dependent manner, driving transcriptional and metabolic rhythms, the latter being able to persist without transcription. Circadian rhythm disruptions in modern life (shiftwork, jetlag, etc.) may lead to higher cancer risk. Here, we investigated whether the human glioblastoma T98G cells maintained quiescent or under proliferation keep a functional clock and whether cells display differential time responses to bortezomib chemotherapy. In arrested cultures, mRNAs for clock (Per1, Rev-erbα) and glycerophospholipid (GPL)-synthesizing enzyme genes, ³²P-GPL labeling, and enzyme activities exhibited circadian rhythmicity; oscillations were also found in the redox state/peroxiredoxin oxidation. In proliferating cells, rhythms of gene expression were lost or their periodicity shortened whereas the redox and GPL metabolisms continued to fluctuate with a similar periodicity as under arrest. Cell viability significantly changed over time after bortezomib treatment; however, this rhythmicity and the redox cycles were altered after Bmal1 knock-down, indicating cross-talk between the transcriptional and the metabolic oscillators. An intrinsic metabolic clock continues to function in proliferating cells, controlling diverse metabolisms and highlighting differential states of tumor suitability for more efficient, time-dependent chemotherapy when the redox state is high and GPL metabolism low.

The hepatic circadian clock regulates the choline kinase α gene through the BMAL1-REV-ERBα axis

The circadian timing system adapts most of the mammalian physiology and behaviour to the 24 h light/dark cycle. This temporal coordination relies on endogenous circadian clocks present in virtually all tissues and organs and implicated in the regulation of key cellular processes including metabolism, transport and secretion. Environmental or genetic disruption of the circadian coordination causes metabolic imbalance leading for instance to fatty liver, dyslipidaemia and obesity, thereby contributing to the development of a metabolic syndrome state. In the liver, a key metabolic organ, the rhythmic regulation of lipid biosynthesis is known, yet the molecular mechanisms through which the circadian clock controls lipogenesis, in particular, that of phospholipids, is poorly characterised. In this study, we show that the wild-type mice display a rhythmic accumulation of hepatic phosphatidylcholine with a peak at ZT 22-0 while clock-deficient Bmal1(-/-) mice show elevated phosphatidylcholine levels in the liver associated with an atherogenic lipoprotein profile. Profiling of the mRNA expression of enzymes from the Kennedy and phosphatidylethanolamine N-methyltransferase pathways which control the production of hepatic phosphatidylcholine revealed a robust circadian pattern for Chkα while other mRNA showed low amplitude (Chkβ and Pemt) or no rhythm (Cctα and Chpt1). Chkα mRNA expression was increased and no longer rhythmic in the liver from clock-deficient Bmal1(-/-) mice. This change resulted in the upregulation of the CHKα protein in these animals. We further show that the robust circadian expression of Chkα is restricted to the liver and adrenal glands. Analysis of the Chkα gene promoter revealed the presence of a conserved response element for the core clock transcription factors REV-ERB and ROR. Consistent with the antiphasic phase relationship between Chkα and Rev-erbα expression, in cotransfection experiments using HepG2 cells we show that RORα4-dependent transactivation of this element is repressed by REV-ERBα· Correspondingly, Rev-erbα(-/-)mice displayed higher Chkα mRNA levels in liver at ZT 12. Collectively, these data establish that hepatic phosphatidylcholine is regulated by the circadian clock through a Bmal1-Rev-erbα-Chkα axis and suggest that an intact circadian timing system is important for the temporal coordination of phospholipid metabolism.

Variant discovery in a QTL region on chromosome 3 associated with fatness in chickens

Abdominal fat content is an economically important trait in commercially bred chickens. Although many quantitative trait loci (QTL) related to fat deposition have been detected, the resolution for these regions is low and functional variants are still unknown. The current study was conducted aiming at increasing resolution for a region previously shown to have a QTL associated with fat deposition, to detect novel variants from this region and to annotate those variants to delineate potentially functional ones as candidates for future studies. To achieve this, 18 chickens from a parental generation used in a reciprocal cross between broiler and layer lines were sequenced using the Illumina next-generation platform with an initial coverage of 18X/chicken. The discovery of genetic variants was performed in a QTL region located on chromosome 3 between microsatellite markers LEI0161 and ADL0371 (33,595,706-42,632,651 bp). A total of 136,054 unique SNPs and 15,496 unique INDELs were detected in this region, and after quality filtering, 123,985 SNPs and 11,298 INDELs were retained. Of these variants, 386 SNPs and 15 INDELs were located in coding regions of genes related to important metabolic pathways. Loss-of-function variants were identified in several genes, and six of those, namely LOC771163, EGLN1, GNPAT, FAM120B, THBS2 and GGPS1, were related to fat deposition. Therefore, these loss-of-function variants are candidate mutations for conducting further studies on this important trait in chickens.

The mouse liver displays daily rhythms in the metabolism of phospholipids and in the activity of lipid synthesizing enzymes

The circadian system involves central and peripheral oscillators regulating temporally biochemical processes including lipid metabolism; their disruption leads to severe metabolic diseases (obesity, diabetes, etc). Here, we investigated the temporal regulation of glycerophospholipid (GPL) synthesis in mouse liver, a well-known peripheral oscillator. Mice were synchronized to a 12:12 h light-dark (LD) cycle and then released to constant darkness with food ad libitum. Livers collected at different times exhibited a daily rhythmicity in some individual GPL content with highest levels during the subjective day. The activity of GPL-synthesizing/remodeling enzymes: phosphatidate phosphohydrolase 1 (PAP-1/lipin) and lysophospholipid acyltransferases (LPLATs) also displayed significant variations, with higher levels during the subjective day and at dusk. We evaluated the temporal regulation of expression and activity of phosphatidylcholine (PC) synthesizing enzymes. PC is mainly synthesized through the Kennedy pathway with Choline Kinase (ChoK) as a key regulatory enzyme or through the phosphatidylethanolamine (PE) N-methyltransferase (PEMT) pathway. The PC/PE content ratio exhibited a daily variation with lowest levels at night, while ChoKα and PEMT mRNA expression displayed maximal levels at nocturnal phases. Our results demonstrate that mouse liver GPL metabolism oscillates rhythmically with a precise temporal control in the expression and/or activity of specific enzymes.