The cost of the circadian desynchrony on the Leydig cell function

Regulation of testosterone synthesis by circadian clock genes and its research progress in male diseases

ABSTRACT

The circadian clock is an important internal time regulatory system for a range of physiological and behavioral rhythms within living organisms. Testosterone, as one of the most critical sex hormones, is essential for the development of the reproductive system, maintenance of reproductive function, and the overall health of males. The secretion of testosterone in mammals is characterized by distinct circadian rhythms and is closely associated with the regulation of circadian clock genes. Here we review the central and peripheral regulatory mechanisms underlying the influence of circadian clock genes upon testosterone synthesis. We also examined the specific effects of these genes on the occurrence, development, and treatment of common male diseases, including late-onset hypogonadism, erectile dysfunction, male infertility, and prostate cancer.

Light pollution: time to consider testicular effects

Technological advances have led to a modern-day lighting and smartphone revolution, with artificial light exposure at night increasing to levels never before seen in the evolutionary history of living systems on Earth. Light as a pollutant, however, remains largely unrecognized, and the reproductive effects of light pollution are mostly if not entirely unconsidered. This is despite the reproductive system being intricately linked to metabolism and the circadian system, both of which can be disturbed even by low levels of light. Here, we aim to change this perspective by reviewing the physiological and pathophysiological mechanisms by which light exposure alters the intricate hormonal, metabolic and reproductive networks that are relevant to reproductive toxicology. Nascent human studies have recently identified the photoreceptors responsible for the light dose relationship with melatonin suppression and circadian re-entrainment, directly shown the association between the alignment of light-dark cycles with activity-rest cycles on metabolic health and provided proof-of-principle that properly timed blue light-enriched and blue light-depleted delivery can accelerate circadian re-entrainment. With these advances, there is now a need to consider testicular effects of light pollution.

REVERBA couples the circadian clock to Leydig cell steroidogenesis

The involvement of the molecular clock in regulating cell physiological processes on a specific time scale is a recognized concept, yet its specific impact on optimizing androgen production in Leydig cells has been unclear. This study aimed to confirm the role of the REVERBA (NR1D1) gene in controlling the transcription of key genes related to Leydig cell steroid production. We investigated daily variations by collecting Leydig cells from rats at various times within a 24-h period. Chromatin immunoprecipitation study showed a time-dependent pattern for genes linked to steroid production (Nur77, Star, Cyp11a1, and Cyp17a1), which closely matched the 24-h REVERBA levels in Leydig cells, peaking between zeitgeber time (ZT) 7-11. To understand the physiological significance of REVERBA's interaction with promoters of steroidogenesis-related genes, Leydig cells from rats at two different times (ZT7 and ZT16; chosen based on REVERBA expression levels), were treated with either an agonist (GSK4112) or an antagonist (SR8278). The results revealed that the REVERBA agonist stimulated gene transcription, while the antagonist inhibited it, but only when REVERBA was sufficiently present, indicating a reliance on REVERBA's circadian fluctuation. Moreover, this REVERBA-dependent stimulation had a clear impact on testosterone production in the culture medium, underscoring REVERBA's involvement in the circadian regulation of testosterone. This study indicates that REVERBA, in addition to being a core component of the cellular clock, plays a key role in regulating androgen production in Leydig cells by influencing the transcription of critical steroidogenesis-related genes.

Association of sleep traits with male fertility: a two-sample Mendelian randomization study

Background: Previous observational studies have investigated the association between sleep-related traits and male fertility; however, conclusive evidence of a causal connection is lacking. This study aimed to explore the causal relationship between sleep and male fertility using Mendelian randomisation. Methods: Eight sleep-related traits (chronotype, sleep duration, insomnia, snoring, dozing, daytime nap, oversleeping, and undersleeping) and three descriptors representing male fertility (male infertility, abnormal sperm, and bioavailable testosterone levels) were selected from published Genome-Wide Association Studies. The causal relationship between sleep-related traits and male fertility was evaluated using multiple methods, including inverse variance weighting (IVW), weighted median, Mendelian randomisation-Egger, weighted model, and simple model through two-sample Mendelian randomisation analysis. Mendelian randomisation-Egger regression was used to assess pleiotropy, Cochrane's Q test was employed to detect heterogeneity, and a leave-one-out sensitivity analysis was conducted. Results: Genetically-predicted chronotype (IVW,OR = 1.07; 95%CL = 1.04-1.12; p = 0.0002) was suggestively associated with bioavailable testosterone levels. However, using the IVW method, we found no evidence of a causal association between other sleep traits and male fertility. Conclusion: This study found that chronotype affects testosterone secretion levels. However, further studies are needed to explain this mechanism.

An update on the role and potential mechanisms of clock genes regulating spermatogenesis: A systematic review of human and animal experimental studies

Circadian clocks can be traced in nearly all life kingdoms, with the male reproductive system no exception. However, our understanding of the circadian clock in spermatogenesis seems to fall behind other scenarios. The present review aims to summarize the current knowledge about the role and especially the potential mechanisms of clock genes in spermatogenesis regulation. Accumulating studies have revealed rhythmic oscillation in semen parameters and some physiological events of spermatogenesis. Disturbing the clock gene expression by genetic mutations or environmental changes will also notably damage spermatogenesis. On the other hand, the mechanisms of spermatogenetic regulation by clock genes remain largely unclear. Some recent studies, although not revealing the entire mechanisms, indeed attempted to shed light on this issue. Emerging clues hinted that gonadal hormones, retinoic acid signaling, homologous recombination, and the chromatoid body might be involved in the regulation of spermatogenesis by clock genes. Then we highlight the challenges and the promising directions for future studies so as to stimulate attention to this critical field which has not gained adequate concern.

Circadian desynchrony disturbs the function of rat spermatozoa

Decreased male fertility is a growing health problem that requires a better understanding of molecular events regulating reproductive competence. Here the effects of circadian desynchrony on the rat spermatozoa functionality were studied. Circadian desynchrony was induced in rats that lived for 2 months under disturbed light conditions designed to mimic shiftwork in humans (two days of constant light, two days of continual dark, and three days of 14:10 h light:dark schedule). Such a condition abolished circadian oscillations in the rats' voluntary activity, followed by a flattened transcriptional pattern of the pituitary gene encoding follicle stimulating hormone subunit (Fshb), and genes important for germ cell maturation (Tnp1 and Prm2) as well as the clock in seminiferous tubules. However, the number of spermatozoa isolated from the epididymis of the rats suffering from circadian desynchrony did not deviate from the controls. Nevertheless, spermatozoa functionality, estimated by motility and progesterone-induced acrosome reaction, was reduced compared to the control. These changes were associated with the altered level of main markers of mitochondrial biogenesis (Pprgc1a/PGC1A, Nrf1/NRF1, Tfam, Cytc), decreased mitochondrial DNA copy number, ATP content, and clock genes (Bmal1/BMAL1, Clock, Cry1/2, and Reverba). The principal-component-analysis (PCA) points to a positive association of the clock and mitochondrial biogenesis-related genes in spermatozoa from rats suffering circadian desynchrony. Altogether, the results show the harmful effect of circadian desynchrony on spermatozoa functionality, targeting energetic homeostasis.

Alterations in Pregnenolone and Testosterone Levels in Male Shift Workers

Steroid hormone levels are closely related to the endogenous circadian rhythm induced by sleep-wake and dark-light cycles. Shift work that disrupts the circadian rhythm may influence the levels of steroid hormones. The association between shift work and alterations in female sex steroid hormone levels has been studied, but little is known about testosterone and its precursor pregnenolone levels in male shift workers. The present study investigated serum pregnenolone and testosterone levels in a group of shift and daytime male workers. All participants were sampled at the beginning of the morning shift. Lower levels of serum pregnenolone and total testosterone were found in the shift workers compared to the daytime workers. Variations in pregnenolone levels may have consequences for well-being, and they might produce consequences for the levels of hormones downstream of the steroid hormone cascade, such as testosterone. The low levels of testosterone found in shift workers demonstrate the perturbative effect of shift work on testosterone serum levels, which may be independent and/or related to pregnenolone synthesis.