Thematic Issue: Biological Rhythms 2019
December 2019
Just in time for the holidays, read our special collection of journal articles, published in 2018-2019, focused on biological rhythms! Curation of the collection was guided by Altmetric Attention Scores and Featured Article designations.
Recent years have seen a huge increase in the research focus on rhythms typically driven by interlinked biological clocks and influencing a plethora of endocrine processes. As their disruption is linked to metabolic disease, increased understanding of their roles holds promise for treatments.
This article in Endocrinology by Nathan Skinner and others shows that mice exposed to a chronically shifting light environment have a decrease in central leptin signaling and an increase in fasting blood glucose levels not accompanied by an increase in insulin levels, which may be linked to their weight gain. Su Young Han and colleagues describe a powerful technique, GCaMP6 fiber photometry technology, for making long-term recordings of the activity of specific populations of neurons in freely behaving mice and use it to support the role of arcuate nucleus kisspeptin neurons as the GnRH pulse generator.
Karen Tonsfeldt and co-workers show in Journal of the Endocrine Society that the disruption of fertility in mice lacking the important clock gene Bmal1 is unexpectedly not the result of a lack of endogenous clocks in kisspeptin or GnRH neurons. William Engeland and associates, writing in Endocrinology, show, in contrast, that Bmal1 is needed in the adrenals for persistence of circadian corticosterone rhythms under light disruption.
On the clinical side, the article by Shadab Rahman and others in JCEM demonstrates that female reproductive hormones are under endogenous circadian regulation: 24-hour rhythms persist in the absence of external time cues. Stacey Simon and colleagues find that adolescent girls with PCOS have substantial circadian misalignment, with later melatonin offset compared to obese controls, and this correlates with worse insulin sensitivity. Sleep deprivation in healthy men caused by perturbation of 24-hour rhythms “dramatically blunted morning-to-evening” white adipose tissue transcriptome variations, according to the findings of Britta Wilms et al.
Froy and Garaulet provide a fine review of the role of the circadian clock in adipose tissue in Endocrine Reviews, where Pureum Kim et al. also review the role of the core clockwork gene Period1 and its analogues, which are functionally closely linked to Bmal1. In the same journal, Cipolla-Neto and do Amaral discuss the far-reaching importance of melatonin, a “biological time-domain-acting” molecule that primes the body for not only the daily light/dark cycle but also the cycle of the seasons, soon to turn at this writing. In a fascinating mini-review of the “Musica Universalis” of the cell in Journal of the Endocrine Society, Bokai Zhu and his colleagues discuss the prevalence and history of biological 12-hour rhythms and other harmonics of the circadian rhythm. They suggest that 12-hour rhythms may have originated from the circatidal clock and so derive not from the sun, but from the moon. Happy holiday reading!
The Journal of Clinical Endocrinology & Metabolism
Endogenous Circadian Regulation of Female Reproductive Hormones
Studies suggest that female reproductive hormones are under circadian regulation, although methodological differences have led to inconsistent findings.
Morning Circadian Misalignment Is Associated With Insulin Resistance in Girls With Obesity and Polycystic Ovarian Syndrome
To our knowledge, circadian rhythms have not been examined in girls with polycystic ovarian syndrome (PCOS), despite the typical delayed circadian timing of adolescence, which is an emerging link between circadian health and insulin sensitivity (SI), and decreased SI in PCOS.
Sleep Loss Disrupts Morning-to-Evening Differences in Human White Adipose Tissue Transcriptome
Chronodisruption, as caused by such conditions as perturbations of 24-hour rhythms of physiology and behavior, may promote the development of metabolic diseases.
Journal of the Endocrine Society
The Contribution of the Circadian Gene Bmal1 to Female Fertility and the Generation of the Preovulatory Luteinizing Hormone Surge
In rodents, the preovulatory LH surge is temporally gated, but the timing cue is unknown.
Unveiling “Musica Universalis” of the Cell: A Brief History of Biological 12-Hour Rhythms
“Musica universalis” is an ancient philosophical concept claiming the movements of celestial bodies follow mathematical equations and resonate to produce an inaudible harmony of music, and the harmonious sounds that humans make were an approximation of this larger harmony of the universe.
Endocrine Reviews
The Circadian Clock in White and Brown Adipose Tissue: Mechanistic, Endocrine, and Clinical Aspects
Obesity is a major risk factor for the development of illnesses, such as insulin resistance and hypertension, and has become a serious public health problem.
Melatonin as a Hormone: New Physiological and Clinical Insights
Melatonin is a ubiquitous molecule present in almost every live being from bacteria to humans.
Coupling the Circadian Clock to Homeostasis: The Role of Period in Timing Physiology
A plethora of physiological processes show stable and synchronized daily oscillations that are either driven or modulated by biological clocks.
Endocrinology
Characterization of GnRH Pulse Generator Activity in Male Mice Using GCaMP Fiber Photometry
Kisspeptin neurons located in the hypothalamic arcuate nucleus are thought to represent the GnRH pulse generator responsible for driving pulsatile LH secretion.
Chronic Light Cycle Disruption Alters Central Insulin and Leptin Signaling as well as Metabolic Markers in Male Mice
Recent evidence suggests that the circadian timing system plays a role in energy and glucose homeostasis, and disruptions to this system are a risk factor for the development of metabolic disorders.
The Adrenal Clock Prevents Aberrant Light-Induced Alterations in Circadian Glucocorticoid Rhythms
The glucocorticoid (GC) rhythm is entrained to light-dark (LD) cycles via a molecular clock in the suprachiasmatic nucleus (SCN) and is maintained by an adrenal clock synchronized by SCN-dependent signals.
