Abstract

There is only one known portal system in the mammalian brain – that of the pituitary gland, first identified in 1933 by Popa and Fielding. Here we describe a second portal pathway in the mouse linking the capillary vessels of the brain’s clock suprachiasmatic nucleus (SCN) to those of the organum vasculosum of the lamina terminalis (OVLT), a circumventricular organ. The localized blood vessels of portal pathways enable small amounts of important secretions to reach their specialized targets in high concentrations without dilution in the general circulatory system. These brain clock portal vessels point to an entirely new route and targets for secreted SCN signals, and potentially restructures our understanding of brain communication pathways.

https://www.nature.com/articles/s41467-021-25793-z

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Abstract

Declining female fertility has become a global health concern. It results partially from an abnormal circadian clock caused by unhealthy diet and sleep habits in modern life. The circadian clock system is a hierarchical network consisting of central and peripheral clocks. It not only controls the sleep–wake and feeding–fasting cycles but also coordinates and maintains the required reproductive activities in the body. Physiologically, the reproductive processes are governed by the hypothalamic–pituitary–gonadal (HPG) axis in a time-dependent manner. The HPG axis releases hormones, generates female characteristics, and achieves fertility. Conversely, an abnormal daily rhythm caused by aberrant clock genes or abnormal environmental stimuli contributes to disorders of the female reproductive system, such as polycystic ovarian syndrome and premature ovarian insufficiency. Therefore, breaking the “time code” of the female reproductive system is crucial. In this paper, we review the interplay between circadian clocks and the female reproductive system and present its regulatory principles, moving from normal physiology regulation to disease etiology.

Extract only, for the full study https://academic.oup.com/endo/article/162/8/bqab117/6298422

Remaining Questions and Future Direction

The normal routine of working at sunrise and resting at sunset has been gradually eroded in the social development process. Instead, high-intensity working patterns along with consequent eating and sleeping disorders and other “modern diseases” are becoming the main theme of daily life. Therefore, larger population studies are needed to characterize this remolding of the circadian rhythm. On this basis, chronobiology can help reverse poor physical conditions and improve existing treatment methods.

As early as 1994, the United Nations highlighted the importance of reproductive health in human development. The decline in female fertility resulting from abnormal circadian rhythms caused by unhealthy diet and sleep habits in modern life has become a global health concern (124, 125). Therefore, breaking the “time code” of the female reproductive system is an urgent task. Despite a large number of studies at present, most studies confine the role of a certain clock gene to a specific cell. As the female reproductive system is by no means a simple superposition of cells and tissues, future chronobiology studies are encouraged from a holistic perspective. Furthermore, constructing and improving the circadian clock network of the female reproductive system is needed to help determine biomarkers that could detect and diagnose circadian rhythm disturbances.

https://academic.oup.com/endo/article/162/8/bqab117/6298422

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Abstract 

Chronobiology is the scientific discipline which considers biological phenomena in relation to time, which assumes itself biological identity. Many physiological processes are cyclically regulated by intrinsic clocks and many pathological events show a circadian time-related occurrence. Even the pituitary–thyroid axis is under the control of a central clock, and the hormones of the pituitary–thyroid axis exhibit circadian, ultradian and circannual rhythmicity. This review, after describing briefly the essential principles of chronobiology, will be focused on the results of personal experiences and of other studies on this issue, paying particular attention to those regarding the thyroid implications, appearing in the literature as reviews, metanalyses, original and observational studies until 28 February 2021 and acquired from two databases (Scopus and PubMed). The first input to biological rhythms is given by a central clock located in the suprachiasmatic nucleus (SCN), which dictates the timing from its hypothalamic site to satellite clocks that contribute in a hierarchical way to regulate the physiological rhythmicity. Disruption of the rhythmic organization can favor the onset of important disorders, including thyroid diseases. Several studies on the interrelationship between thyroid function and circadian rhythmicity demonstrated that thyroid dysfunctions may affect negatively circadian organization, disrupting TSH rhythm. Conversely, alterations of clock machinery may cause important perturbations at the cellular level, which may favor thyroid dysfunctions and also cancer.

Excerpt

Introduction

From ancient hourglasses to sophisticated modern clocks, the measurement of time has been considered indispensable by man for the verification of the flow of natural and human phenomena. The earliest recorded recognition of the importance of biological rhythms in plants and animal dates back to at least 5000 BC. Light/darkness-correlated variations in leaf movements in some plants had been already observed by Androstene during the Empire of Alexander the Great, and the importance of temporal factors was even recognized in biblical times as stated in Ecclesiastes: “To everything there is a season and a time to every purpose under Heaven: a time to be born and a time to die; a time to plant and a time to harvest”. Moreover, as reported in Genesis, the light was created by God first of all, and this is of particular significance, since, as we will see later on, the alternation of light/darkness is the main synchronizing factor in the circadian rhythm [1]

5. Conclusions

Knowledge and respect of biological rhythms and of their endogenous and environmental synchronizing factors is mandatory not only for physicians but also for patients, to ensure the best conditions for the lives of human beings. This is particularly important for the HPT axis, as the knowledge and respect of the reciprocal relationship between the secretions of this axis and the circadian machinery may avoid, on the one hand, the disruption of the circadian rhythmic organization of the subjects and, on the other hand, the consequences of this disruption, which can cause not only thyroid dysfunction but also thyroid cancer. Further studies have to be encouraged to better clarify physiological and pathophysiological aspects of this issue and to search for more appropriate preventive choices to avoid circadian but also ultradian and infradian rhythm disruption of the HPT axis and to search for more effective therapeutic options to promptly correct these alterations, when they have already occurred.

https://www.mdpi.com/2075-1729/11/5/426

The post Chronothyroidology: Chronobiological Aspects in Thyroid Function and Diseases appeared first on EMFSA.

Abstract

The molecular circadian clock and symbiotic host-microbe relationships both evolved as mechanisms that enhance metabolic responses to environmental challenges. The gut microbiome benefits the host by breaking down diet-derived nutrients indigestible by the host and generating microbiota-derived metabolites that support host metabolism. Similarly, cellular circadian clocks optimize organismal physiology to the environment by influencing the timing and coordination of metabolic processes. Host-microbe interactions are influenced by dietary quality and timing, as well as daily light/dark cycles that entrain circadian rhythms in the host. Together, the gut microbiome and the molecular circadian clock play a coordinated role in neural processing, metabolism, adipogenesis, inflammation, and disease initiation and progression. This review examines the bidirectional interactions between the circadian clock, gut microbiota, and host metabolic systems and their effects on obesity and energy homeostasis. Directions for future research and the development of therapies that leverage these systems to address metabolic disease are highlighted.

Extract:

Our findings support the hypothesis that poor host metabolic outcomes are the result of asynchronous feeding signals, out of coordination with the light entrained circadian clock-driven anticipatory mechanisms regulating nutrient absorption and utilization, which may indirectly affect GM composition throughout the day. Small, achievable changes in behavior (e.g., changing timing of macronutrient consumption and improved sleep hygiene) that modulate GM signaling may harness innate biology to overcome the obesogenic environment that imposes a potential detriment to human health.

Publication History

Published online: March 30, 2021

Identification

DOI: https://doi.org/10.1016/j.cmet.2021.03.015

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Abstract

Circadian rhythms are ~24 h cycles of behavior and physiology that are generated by a network of molecular clocks located in nearly every tissue in the body. In mammals, the circadian system is organized hierarchically such that the suprachiasmatic nucleus (SCN) is the main circadian clock that receives light information from the eye and entrains to the light-dark cycle. The SCN then coordinates the timing of tissue clocks so internal rhythms are aligned with environmental cycles. Estrogens interact with the circadian system to regulate biological processes. At the molecular level, estrogens and circadian genes interact to regulate gene expression and cell biology. Estrogens also regulate circadian behavior across the estrous cycle. The timing of ovulation during the estrous cycle requires coincident estrogen and SCN signals. Studies using circadian gene reporter mice have also elucidated estrogen regulation of peripheral tissue clocks and metabolic rhythms. This review synthesizes current understanding of the interplay between estrogens and the circadian system, with a focus on female rodents, in regulating molecular, physiological, and behavioral processes.

https://pubmed.ncbi.nlm.nih.gov/33975754/

Copyright © 2021 Elsevier Ltd. All rights reserved.

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