Abstract
The circadian clock plays a critical role in synchronizing the inner molecular, metabolic and physiological processes to environmental cues that cycle with a period of 24 h. Non-24 h and shift schedules are commonly used in maritime operations, and both of which can disturb circadian rhythms. In this study, we first conducted an experiment in which the volunteers followed a 3-d rotary schedule with consecutive shift in sleep time (rotatory schedule), and analyzed the changes in salivary cortisol rhythms and blood variables. Next we conducted another experiment in which the volunteers followed an 8 h-on and 4-h off schedule (non-24-h schedule) to compare the changes in blood/serum variables. The rotatory schedule led to elevated levels of serum cortisol during the early stage, and the phase became delayed during the early and late stages. Interestingly, both of the schedules caused comprehensive changes in blood/serum biochemical variables and increased phosphate levels. Furthermore, transcriptomic analysis of the plasma miRNAs from the volunteers following the rotatory schedule identified a subset of serum miRNAs targeting genes involved in circadian rhythms, sleep homeostasis, phosphate transport and multiple important physiological processes. Overexpression of miRNAs targeting the phosphate transport associated genes, SLC20A1 and SLC20A2, showed altered expression due to rotary schedule resulted in attenuated cellular levels of phosphate, which might account for the changed levels in serum phosphate. These findings would further our understanding of the deleterious effects of shift schedules and help to optimize and enhance the performances and welfare of personnel working on similar schedules.
Highlights
Circadian clock plays a critical role in synchronizing the inner molecular, metabolic and physiological processes to the environmental cues which cycle with a period of 24 h
These findings would help understand the deleterious effects of shift schedules and optimize to enhance performance and welfare of the personnel working with similar schedules
The results revealed that the serum cortisol levels displayed daily rhythms in both control and experiment periods (Fig. 1B,C)
Summary
Circadian clock plays a critical role in synchronizing the inner molecular, metabolic and physiological processes to the environmental cues which cycle with a period of 24 h. Misalignment in the circadian rhythms leads to decrease in adaptation, performance and increased risk of associated disorders. Circadian clocks are ubiquitous in most of the organisms on earth, which play critical roles in synchronizing the internal physiology with the external cycling environment cues with a period of 24 h [1]. Circadian clock controls a broad variety of physiological, cognitive, emotional and behavioral features, and misalignment in circadian rhythms leads to detrimental effects on health and performance [3]. The oscillation of many human physiological variables is governed by circadian clock [4, 5]. The level of plasma phosphate displays an overt diurnal rhythmicity with the nadir approximately at 11:00 AM, and the peak approximately at 12:30 AM [7]
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