Time Restriction of Food Intake During the Circadian Cycle Is a Possible Regulator of Reproductive Function in Postadolescent Female Rats

Desynchronization between Food Intake and Light Stimulations Induces Uterine Clock Quiescence in Female Mice

BACKGROUND

Dysmenorrhea is associated with breakfast skipping in young women, suggesting that fasting in the early active phase disrupts uterine functions.

OBJECTIVES

To investigate the possible involvement of the uterine clock system in fasting-induced uterine dysfunction, we examined core clock gene expressions in the uterus using a 28-h interval-fed mouse model.

METHODS

Young female mice (8 wk of age) were divided into 3 groups: group I (ad libitum feeding), group II (time-restricted feeding, initial 4 h of the active period every day), and group III (time-restricted feeding for 8 h with a 28-h cycle). Groups II and III have the same fasting interval of 20 h. After analyzing feeding and wheel running behaviors during 2 wk of dietary restriction, mice were sacrificed at 4-h intervals, and the expression profiles of clock genes in the uterus and liver were examined by qPCR.

RESULTS

The mice in group I took food mainly during the dark phase and those in group II during the initial 4 h of the dark phase, whereas those in group III delayed feeding time by 4 h per cycle. In all groups, spontaneous wheel running was observed during the dark phase. There was no difference in the quantity of feeding and the amount of running exercise among the 3 groups during the second week. The mRNA expressions of peripheral clock genes, Bmal1, Clock, Per1, Per2, Cry1, Nr1d1, and Dbp and a clock-controlled gene, Fabp1, in the uterus showed rhythmic oscillations with normal sequential expression cascade in groups I and II, whereas their expressions decreased and circadian cycles disappeared in group III. In contrast, liver core clock genes in group III showed clear circadian cycles.

CONCLUSIONS

Fluctuations in the timing of the first food intake impair the uterine clock oscillator system to reduce clock gene expressions and abolish their circadian rhythms.

The Circadian Clock, Nutritional Signals and Reproduction: A Close Relationship

The circadian rhythm, which is necessary for reproduction, is controlled by clock genes. In the mouse uterus, the oscillation of the circadian clock gene has been observed. The transcription of the core clock gene period (Per) and cryptochrome (Cry) is activated by the heterodimer of the transcription factor circadian locomotor output cycles kaput (Clock) and brain and muscle Arnt-like protein-1 (Bmal1). By binding to E-box sequences in the promoters of Per1/2 and Cry1/2 genes, the CLOCK-BMAL1 heterodimer promotes the transcription of these genes. Per1/2 and Cry1/2 form a complex with the Clock/Bmal1 heterodimer and inactivate its transcriptional activities. Endometrial BMAL1 expression levels are lower in human recurrent-miscarriage sufferers. Additionally, it was shown that the presence of BMAL1-depleted decidual cells prevents trophoblast invasion, highlighting the importance of the endometrial clock throughout pregnancy. It is widely known that hormone synthesis is disturbed and sterility develops in Bmal1-deficient mice. Recently, we discovered that animals with uterus-specific Bmal1 loss also had poor placental development, and these mice also had intrauterine fetal death. Furthermore, it was shown that time-restricted feeding controlled the uterine clock's circadian rhythm. The uterine clock system may be a possibility for pregnancy complications, according to these results. We summarize the most recent research on the close connection between the circadian clock and reproduction in this review.

Skipping the first active meal appears to adversely alter reproductive function in female than male rats

There is a growing consciousness about chrono-nutrition and its physiological functions. The human feeding pattern establishes three meals a day, meal timing however may not be adhered to. Previous studies have reported ovarian dysfunctions in breakfast skipping among females. In this study, the investigation was carried out on the effects of breakfast skipping on reproductive functions in the male rat and comparison, to the female rat. Eight-week-old animals (10 rats per group) were used to mimic post-adolescence. Rats are active at night thus the meal model was divided as follows. Female rats who had all three meals (Control_F), Female rats who had a no-first-active meal (NFAM_F), Male rats who had all three meals (Control_M), and Male rats who had a no-first-active meal (NFAM_M). All animals were fed the same amount of food every day. After the expiration of the four weeks experiment, serum testosterone, estrogen, Luteinising Hormone (LH) Follicle Stimulating Hormone (FSH), and prolactin (PRL) were quantified using ELISA. Sperm was also analyzed. There was a significant increase (p < 0.05) in the testosterone level and sperm count in the NFAM_M compared to the Control_M while the estrogen level was significantly reduced in the NFAM_F compared to the Control_F. LH, FSH, and PRL levels were significantly reduced in the NFAM_F compared to the NFAM_M. These findings further confirm that post-adolescent females are prone to breakfast skipping. The increase in testosterone levels and sperm count in the males establish that breakfast skipping might not interfere with the reproductive physiology in males as it does in females.

Time-Restricted Feeding Regulates Circadian Rhythm of Murine Uterine Clock

BACKGROUND

Skipping breakfast is associated with dysmenorrhea in young women. This suggests that the delay of food intake in the active phase impairs uterine functions by interfering with circadian rhythms.

OBJECTIVES

To examine the relation between the delay of feeding and uterine circadian rhythms, we investigated the effects of the first meal occasion in the active phase on the uterine clock.

METHODS

Zeitgeber time (ZT) was defined as ZT0 (08:45) with lights on and ZT12 (20:45) with lights off. Young female mice (8 wk of age) were divided into 3 groups: group I (ad libitum consumption), group II (time-restricted feeding during ZT12-16, initial 4 h of the active period), and group III (time-restricted feeding during ZT20-24, last 4 h of the active period, a breakfast-skipping model). After 2 wk of dietary restriction, mice in each group were killed at 4-h intervals and the expression profiles of uterine clock genes, Bmal1 (brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein 1), Per1 (period circadian clock 1), Per2, and Cry1 (cryptochrome 1), were examined.

RESULTS

qPCR and western blot analyses demonstrated synchronized circadian clock gene expression within the uterus. Immunohistochemical analysis confirmed that BMAL1 protein expression was synchronized among the endometrium and myometrium. In groups I and II, mRNA expression of Bmal1 was elevated after ZT12 at the start of the active phase. In contrast, Bmal1 expression was elevated just after ZT20 in group III, showing that the uterine clock rhythm had shifted 8 h backward. The changes in BMAL1 protein expression were confirmed by western blot analysis.

CONCLUSIONS

This study is the first to indicate that time-restricted feeding regulates a circadian rhythm of the uterine clock that is synchronized throughout the uterine body. These findings suggest that the uterine clock system is a new candidate to explain the etiology of breakfast skipping-induced uterine dysfunction.

Breakfast Skipping in Female College Students Is a Potential and Preventable Predictor of Gynecologic Disorders at Health Service Centers

Inadequate dietary habits in youth are known to increase the risk of onset of various diseases in adulthood. Previously, we found that female college students who skipped breakfast had higher incidences of dysmenorrhea, suggesting that breakfast skipping interferes with ovarian and uterine functions. Since dietary habits can be managed by education, it is preferable to establish a convenient screening system for meal skipping that is associated with dysmenorrhea as part of routine services of health service centers. In this study, we recruited 3172 female students aged from 18 to 25 at Kanazawa University and carried out an annual survey of the status of students’ health and lifestyle in 2019, by a questionnaire. We obtained complete responses from 3110 students and analyzed the relationship between dietary habits, such as meal skipping and history of dieting, and menstrual disorders, such as troubles or worries with menstruation, menstrual irregularity, menstrual pain, and use of oral contraceptives. The incidence of troubles or worries with menstruation was significantly higher in those with breakfast skipping (p < 0.05) and a history of dieting (p < 0.001). This survey successfully confirmed the positive relationship between breakfast skipping and menstrual pain (p < 0.001), indicating that this simple screening test is suitable for picking up breakfast skippers who are more prone to gynecologic disorders. In conclusions, since dysmenorrhea is one of the important clinical signs, breakfast skipping may become an effective marker to predict the subsequent onset of gynecological diseases at health service centers. Considering educational correction of meal skipping, breakfast skipping is a potential and preventable predictor that will contribute to managing menstrual disorders from a preventive standpoint in the future.

Adolescent Dietary Habit-induced Obstetric and Gynecologic Disease (ADHOGD) as a New Hypothesis-Possible Involvement of Clock System

There are growing concerns that poor dietary behaviors at young ages will increase the future risk of chronic diseases in adulthood. We found that female college students who skipped breakfast had higher incidences of dysmenorrhea and irregular menstruation, suggesting that meal skipping affects ovarian and uterine functions. Since dysmenorrhea is more prevalent in those with a past history of dieting, we proposed a novel concept that inadequate dietary habits in adolescence become a trigger for the subsequent development of organic gynecologic diseases. Since inadequate feeding that was limited during the non-active phase impaired reproductive functions in post-adolescent female rats, we hypothesize that circadian rhythm disorders due to breakfast skipping disrupts the hypothalamic–pituitary–ovarian axis, impairs the reproductive rhythm, and leads to ovarian and uterine dysfunction. To explain how reproductive dysfunction is memorized from adolescence to adulthood, we hypothesize that the peripheral clock system also plays a critical role in the latent progression of reproductive diseases together with the central system, and propose naming this concept “adolescent dietary habit-induced obstetric and gynecologic disease (ADHOGD)”. This theory will contribute to analyzing the etiologies of and developing prophylaxes for female reproductive diseases from novel aspects. In this article, we describe the precise outline of the above hypotheses with the supporting evidence in the literature.