bims-ciryme Biomed News
on Circadian rhythms and metabolism
Issue of 2020‒06‒28
four papers selected by
Gabriela Da Silva Xavier
University of Birmingham

  1. Sci Rep. 2020 Jun 22. 10(1): 10036
      Circadian rhythms are the product of the interaction of molecular clocks and environmental signals, such as light-dark cycles and eating-fasting cycles. Several studies have demonstrated that the circadian rhythm of peripheral clocks, and behavioural and metabolic mediators are re-synchronized in rodents fed under metabolic challenges, such as hyper- or hypocaloric diets and subjected to time-restricted feeding protocols. Despite the metabolic challenge, these approaches improve the metabolic status, raising the enquiry whether removing progressively the hypocaloric challenge in a  time-restricted feeding protocol leads to metabolic benefits by the synchronizing effect. To address this issue, we compared the effects of two time-restricted feeding protocols, one involved hypocaloric intake during the entire protocol (HCT) and the other implied a progressive intake accomplishing a normocaloric intake at the end of the protocol (NCT) on several behavioural, metabolic, and molecular rhythmic parameters. We observed that the food anticipatory activity (FAA) was driven and maintained in both HCT and NCT. Resynchronization of hepatic molecular clock, free fatty acids (FFAs), and FGF21 was elicited closely by HCT and NCT. We further observed that the fasting cycles involved in both protocols promoted ketone body production, preferentially beta-hydroxybutyrate in HCT, whereas acetoacetate was favoured in NCT before access to food. These findings demonstrate that time-restricted feeding does not require a sustained calorie restriction for promoting and maintaining the synchronization of the metabolic and behavioural circadian clock, and suggest that metabolic modulators, such as FFAs and FGF21, could contribute to FAA expression.
  2. Nat Commun. 2020 Jun 24. 11(1): 3193
      Breast cancer is the most common type of cancer worldwide and one of the major causes of cancer death in women. Epidemiological studies have established a link between night-shift work and increased cancer risk, suggesting that circadian disruption may play a role in carcinogenesis. Here, we aim to shed light on the effect of chronic jetlag (JL) on mammary tumour development. To do this, we use a mouse model of spontaneous mammary tumourigenesis and subject it to chronic circadian disruption. We observe that circadian disruption significantly increases cancer-cell dissemination and lung metastasis. It also enhances the stemness and tumour-initiating potential of tumour cells and creates an immunosuppressive shift in the tumour microenvironment. Finally, our results suggest that the use of a CXCR2 inhibitor could correct the effect of JL on cancer-cell dissemination and metastasis. Altogether, our data provide a conceptual framework to better understand and manage the effects of chronic circadian disruption on breast cancer progression.
  3. J Exp Biol. 2020 Jun 25. pii: jeb.220699. [Epub ahead of print]
      Organisms use changes in photoperiod to anticipate and exploit favourable conditions in a seasonal environment. While species living at temperate latitudes receive day length information as a year-round input, species living in the Arctic may spend as much as two-thirds of the year without experiencing dawn or dusk. This suggests that specialised mechanisms may be required to maintain seasonal synchrony in polar regions.Svalbard ptarmigan (Lagopus muta hyperborea) are resident at 74-81° north latitude. They spend winter in constant darkness (DD) and summer in constant light (LL); extreme photoperiodic conditions under which they do not display overt circadian rhythms.Here we explored how arctic adaptation in circadian biology affects photoperiodic time measurement in captive Svalbard ptarmigan. For this purpose, DD-adapted birds, showing no circadian behaviour, either remained in prolonged DD, were transferred into a simulated natural photoperiod (SNP) or were transferred directly into LL. Birds transferred from DD to LL exhibited a strong photoperiodic response in terms of activation of the hypothalamic thyrotropin-mediated photoperiodic response pathway. This was assayed through expression of the Eya3, Tshβ and deiodinase genes, as well as gonadal development. While transfer to SNP established synchronous diurnal activity patterns, activity in birds transferred from DD to LL showed no evidence of circadian rhythmicity.These data show that the Svalbard ptarmigan does not require circadian entrainment to develop a photoperiodic response involving conserved molecular elements found in temperate species. Further studies are required to define how exactly arctic adaptation modifies seasonal timer mechanisms.
    Keywords:  Circadian; Deiodinase; Eyes absent; Pars tuberalis; Photoperiodism; Seasonal reproduction; Svalbard ptarmigan
  4. Swiss Med Wkly. 2020 Jun 15. pii: Swiss Med Wkly. 2020;150:w20273. [Epub ahead of print]150 w20273
      The discovery and administration of exogenous insulin has revolutionised diabetes treatment and continues, almost 100 years on, to be the basis for the management of insulin deficiency. However, insulin therapy still has potentially life-threatening side effects such as hypoglycaemia and increased risk of cardiovascular disease. So far, improvements in insulin therapy have focused mainly on modulating its pharmacokinetic and pharmacodynamic properties and improving delivery methods, while variations in the insulin sensitivity of peripheral tissues has received relatively little attention. Notably, tissue insulin sensitivity has been shown to vary considerably around the clock, which could contribute greatly to the effect (and risk of side effects) of a given dose of insulin. Recent evidence suggests that photic inputs regulate diurnal variations in the insulin sensitivity of metabolically relevant tissues via a previously unrecognised mechanism involving the ventromedial hypothalamic nucleus. Therefore, understanding the mechanisms underlying photic control of insulin action is of paramount medical importance. In addition, considering “when” (i.e., the time of day) could assist in deciding “how much” insulin should be administered and hence could aid the fine-tuning of insulin dosage, lowering the risk of side effects, and improving the quality of life of patients with insulin deficiency.