bims-ciryme 2021-01-17 papers

Nat Commun. 2021 Jan 15. 12(1): 377

Rhythmic glucose metabolism regulates the redox circadian clockwork in human red blood cells.

Ratnasekhar Ch, Guillaume Rey, Sandipan Ray, Pawan K Jha, Paul C Driscoll, Mariana Silva Dos Santos, Dania M Malik, Radoslaw Lach, Aalim M Weljie, James I MacRae, Utham K Valekunja, Akhilesh B Reddy.

Circadian clocks coordinate mammalian behavior and physiology enabling organisms to anticipate 24-hour cycles. Transcription-translation feedback loops are thought to drive these clocks in most of mammalian cells. However, red blood cells (RBCs), which do not contain a nucleus, and cannot perform transcription or translation, nonetheless exhibit circadian redox rhythms. Here we show human RBCs display circadian regulation of glucose metabolism, which is required to sustain daily redox oscillations. We found daily rhythms of metabolite levels and flux through glycolysis and the pentose phosphate pathway (PPP). We show that inhibition of critical enzymes in either pathway abolished 24-hour rhythms in metabolic flux and redox oscillations, and determined that metabolic oscillations are necessary for redox rhythmicity. Furthermore, metabolic flux rhythms also occur in nucleated cells, and persist when the core transcriptional circadian clockwork is absent in Bmal1 knockouts. Thus, we propose that rhythmic glucose metabolism is an integral process in circadian rhythms.

DOI: https://doi.org/10.1038/s41467-020-20479-4

Proc Natl Acad Sci U S A. 2021 Jan 19. pii: e2015803118. [Epub ahead of print]118(3):

Systematic analysis of differential rhythmic liver gene expression mediated by the circadian clock and feeding rhythms.

Benjamin D Weger, Cédric Gobet, Fabrice P A David, Florian Atger, Eva Martin, Nicholas E Phillips, Aline Charpagne, Meltem Weger, Felix Naef, Frédéric Gachon.

The circadian clock and feeding rhythms are both important regulators of rhythmic gene expression in the liver. To further dissect the respective contributions of feeding and the clock, we analyzed differential rhythmicity of liver tissue samples across several conditions. We developed a statistical method tailored to compare rhythmic liver messenger RNA (mRNA) expression in mouse knockout models of multiple clock genes, as well as PARbZip output transcription factors (Hlf/Dbp/Tef). Mice were exposed to ad libitum or night-restricted feeding under regular light-dark cycles. During ad libitum feeding, genetic ablation of the core clock attenuated rhythmic-feeding patterns, which could be restored by the night-restricted feeding regimen. High-amplitude mRNA expression rhythms in wild-type livers were driven by the circadian clock, but rhythmic feeding also contributed to rhythmic gene expression, albeit with significantly lower amplitudes. We observed that Bmal1 and Cry1/2 knockouts differed in their residual rhythmic gene expression. Differences in mean expression levels between wild types and knockouts correlated with rhythmic gene expression in wild type. Surprisingly, in PARbZip knockout mice, the mean expression levels of PARbZip targets were more strongly impacted than their rhythms, potentially due to the rhythmic activity of the D-box-repressor NFIL3. Genes that lost rhythmicity in PARbZip knockouts were identified to be indirect targets. Our findings provide insights into the diurnal transcriptome in mouse liver as we identified the differential contributions of several core clock regulators. In addition, we gained more insights on the specific effects of the feeding-fasting cycle.

Keywords: circadian clock; differential rhythmicity analysis; feeding–fasting cycle; liver metabolism; transcriptomics

DOI: https://doi.org/10.1073/pnas.2015803118

Neurosci Biobehav Rev. 2021 Jan 10. pii: S0149-7634(20)30687-4. [Epub ahead of print]

Distinct feedback actions of behavioural arousal to the master circadian clock in nocturnal and diurnal mammals.

Pawan Kumar Jha, Hanan Bouâouda, Andries Kalsbeek, Etienne Challet.

The master clock in the suprachiasmatic nucleus (SCN) of the hypothalamus provides a temporal pattern of sleep and wake that - like many other behavioural and physiological rhythms - is oppositely phased in nocturnal and diurnal animals. The SCN primarily uses environmental light, perceived through the retina, to synchronize its endogenous circadian rhythms with the exact 24 h light/dark cycle of the outside world. The light responsiveness of the SCN is maximal during the night in both nocturnal and diurnal species. Behavioural arousal during the resting period not only perturbs sleep homeostasis, but also acts as a potent non-photic synchronizing cue. The feedback action of arousal on the SCN is mediated by processes involving several brain nuclei and neurotransmitters, which ultimately change the molecular function of SCN pacemaker cells. Arousing stimuli during the sleeping period differentially affect the circadian system of nocturnal and diurnal species, as evidenced by the different circadian windows of sensitivity to behavioural arousal. In addition, arousing stimuli reduce and increase light resetting in nocturnal and diurnal species, respectively. It is important to address further the question of circadian impairments associated with shift work and trans-meridian travel not only in the standard nocturnal laboratory animals, but also in diurnal animal models.

Keywords: Behavioural arousal; Circadian rhythm; Diurnal; Entrainment; Nocturnal; Phase-shifts; Sleep; Suprachiasmatic nucleus

DOI: https://doi.org/10.1016/j.neubiorev.2020.12.011

Neuropharmacology. 2021 Jan 11. pii: S0028-3908(21)00009-5. [Epub ahead of print] 108455

Modulation of single cell circadian response to NMDA by diacylglycerol lipase inhibition reveals a role of endocannabinoids in light entrainment of the suprachiasmatic nucleus.

Martin Sládek, Karolína Liška, Pavel Houdek, Alena Sumová.

Suprachiasmatic nucleus (SCN) of the hypothalamus is the master clock that drives circadian rhythms in physiology and behavior and adjusts their timing to external cues. Neurotransmitter glutamate and glutamatergic receptors sensitive to N-methyl-D-aspartate (NMDA) play a dual role in the SCN by coupling astrocytic and neuronal single cell oscillators and by resetting their phase in response to light. Recent reports suggested that signaling by endogenous cannabinoids (ECs) participates in both of these functions. We have previously shown that ECs, such as 2-arachidonoylglycerol (2-AG), act via CB1 receptors to affect the SCN response to light-mimicking NMDA stimulus in a time-dependent manner. We hypothesized that this ability is linked to the circadian regulation of EC signaling. We demonstrate that circadian clock in the rat SCN regulates expression of 2-AG transport, synthesis and degradation enzymes as well as its receptors. Inhibition of the major 2-AG synthesis enzyme, diacylglycerol lipase, enhanced the phase delay and lowered the amplitude of explanted SCN rhythm in response to NMDAR activation. Using microscopic PER2 bioluminescence imaging, we visualized how individual single cell oscillators in different parts of the SCN respond to the DAGL inhibition/NMDAR activation and shape response of the whole pacemaker. Additionally, we present strong evidence that the zero amplitude behavior of the SCN in response to single NMDA stimulus in the middle of subjective night is the result of a loss of rhythm in individual SCN cells. The paper provides new insights into the modulatory role of endocannabinoid signaling during the light entrainment of the SCN.

Keywords: N-methyl-D-aspartate; PER2::LUC; circadian; endocannabinoids; phase response curve; suprachiasmatic nucleus

DOI: https://doi.org/10.1016/j.neuropharm.2021.108455

Nat Metab. 2021 Jan 11.

Space-time logic of liver gene expression at sub-lobular scale.

Colas Droin, Jakob El Kholtei, Keren Bahar Halpern, Clémence Hurni, Milena Rozenberg, Sapir Muvkadi, Shalev Itzkovitz, Felix Naef.

The mammalian liver is a central hub for systemic metabolic homeostasis. Liver tissue is spatially structured, with hepatocytes operating in repeating lobules, and sub-lobule zones performing distinct functions. The liver is also subject to extensive temporal regulation, orchestrated by the interplay of the circadian clock, systemic signals and feeding rhythms. However, liver zonation has previously been analysed as a static phenomenon, and liver chronobiology has been analysed at tissue-level resolution. Here, we use single-cell RNA-seq to investigate the interplay between gene regulation in space and time. Using mixed-effect models of messenger RNA expression and smFISH validations, we find that many genes in the liver are both zonated and rhythmic, and most of them show multiplicative space-time effects. Such dually regulated genes cover not only key hepatic functions such as lipid, carbohydrate and amino acid metabolism, but also previously unassociated processes involving protein chaperones. Our data also suggest that rhythmic and localized expression of Wnt targets could be explained by rhythmically expressed Wnt ligands from non-parenchymal cells near the central vein. Core circadian clock genes are expressed in a non-zonated manner, indicating that the liver clock is robust to zonation. Together, our scRNA-seq analysis reveals how liver function is compartmentalized spatio-temporally at the sub-lobular scale.

DOI: https://doi.org/10.1038/s42255-020-00323-1