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, 15 (1), 78

Effects of Melatonin Administration on Embryo Implantation and Offspring Growth in Mice Under Different Schedules of Photoperiodic Exposure

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Effects of Melatonin Administration on Embryo Implantation and Offspring Growth in Mice Under Different Schedules of Photoperiodic Exposure

Lu Zhang et al. Reprod Biol Endocrinol.

Abstract

Background: Embryo implantation is crucial for animal reproduction. Unsuccessful embryo implantation leads to pregnancy failure, especially in human-assisted conception. Environmental factors have a profound impact on embryo implantation. Because people are being exposed to more light at night, the influence of long-term light exposure on embryo implantation should be explored.

Methods: The effects of long photoperiodic exposure and melatonin on embryo implantation and offspring growth were examined. Long photoperiodic exposure (18:6 h light:dark) was selected to resemble light pollution. Melatonin (10-2, 10-3, 10-4, 10-5 M) was added to the drinking water of mice starting at Day 1 (vaginal plugs) until delivery.

Results: Melatonin treatment (10-4,10-5 M) significantly increased litter sizes compared to untreated controls (12.9 ± 0.40 and 12.2 ± 1.01 vs. 11.5 ± 0.43; P < 0.05). The most effective concentration of melatonin (10-4 M) was selected for further investigation. No remarkable differences were found between melatonin-treated mice and controls in terms of the pups' birth weights, weaning survival rates, and weaning weights. Long photoperiodic exposure significantly reduced the number of implantation sites in treated mice compared to controls (light/dark, 12/12 h), and melatonin rescued this negative effect. Mechanistic studies revealed that melatonin enhanced the serum 17β-estradiol (E2) levels in the pregnant mice and upregulated the expression of the receptors MT1 and MT2 and p53 in uterine tissue. All of these factors may contribute to the beneficial effects of melatonin on embryo implantation in mice.

Conclusion: Melatonin treatment was associated with beneficial effects in pregnant mice, especially those subjected to long photoperiodic exposure. This was achieved by enhanced embryo implantation. At the molecular level, melatonin administration probably increases the E2 level during pregnancy and upregulates p53 expression by activating MT1/2 in the uterus. All of the changes may improve the microenvironment of the uterus and, thus, the outcomes of pregnancy.

Keywords: Embryo implantation; MT1; MT2; Melatonin; p53.

Conflict of interest statement

Ethics approval

All experimental protocols concerning the handling and care of mice were in accordance with the requirements of the Institutional Animal Care Committee and were approved by the Ethics Committee of the Agriculture University of China.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
Effects of different concentrations of melatonin on offspring development and growth in mice. a The average litter sizes for 10−2, 10−3, 10−4 and 10−5 M melatonin-treated groups and the control group (10.97 ± 1.453, 12.00 ± 0.92, 12.9 ± 0.40 and 12.2 ± 1.01 vs. 11.5 ± 0.43, respectively). b The survival rates of pups at weaning in the melatonin (10−4 M) and control group (95.6 ± 1.78% vs. control 92.9 ± 2.62%, respectively; P˃0.05). c The average litter weight at birth in the melatonin (10−4 M) and control group (23.24 ± 0.65 vs. control 20.95 ± 0.72, respectively; P < 0.05). d The birth weight and 3rd week weaning weight per pup in the melatonin treated group (10−4 M) and the control group (1.8 ± 0.20 g vs. control 1.8 ± 0.17 g; 11.5 ± 0.43 g vs. control 12.0 ± 0.41 g, respectively; P>0.05). Data are expressed as the means ± SEM (N = 10 litters/group). Different superscript letters indicate statistically significant differences (P < 0.05)
Fig. 2
Fig. 2
The implantation sites on Days 5.5 and 7.5 of pregnancy. MT: melatonin group; C: control group; LE: light extended group; LE + MT: light extended group treated with melatonin (10−4 M). a Implantation sites on Day 5.5 (14. 8 ± 0.62, 14.0 ± 0.67, 11.2 ± 0.43 and 13.4 ± 0.48 in the MT, C, LE and LE + MT groups, respectively) and on Day 7.5 (12.0 ± 0.37, 11.7 ± 1.48, 10.0 ± 0.58 and 11.4 ± 0.40 in the MT, C, LE and LE + MT groups, respectively). b Representative images of uterine implantation sites on Day 5.5 (up) and Day 7.5 (down) of pregnancy. Data are expressed as the means ± SEM (N = 9). Different superscript letters indicate statistically significant differences (P < 0.05)
Fig. 3
Fig. 3
Serum P4 and E2 contents on Days 4 and 4.5 of pregnancy. The levels of P4 and E2 were determined. a Serum E2 content showed significant differences on both day 4 (59.68 ± 8.59 pg/ml vs. control 16.71 ± 1.48 pg/ml; P < 0.05) and day 4.5 (33.62 ± 5.34 pg/ml vs. control 12.16 ± 1.49 pg/ml; P < 0.5). Data are expressed as the means ± SEM (N = 9) Different superscript letters indicate statistically significant differences (P < 0.05). b No significant difference was found in serum P4 content between the control group and melatonin group on day 4 (9.12 ± 1.31 ng/ml vs. control 8.27 ± 0.73 ng/ml; P > 0.05) and day 4.5 (18.82 ± 2.31 ng/ml vs. control 17.76 ± 2.05 ng/ml; P > 0.05)
Fig. 4
Fig. 4
Effects of melatonin on the protein expression of MT1, MT2 and p53 on Day 4.5 in uterine tissue. (a1) On Day 4.5, MT1 and MT2 receptor expression in the uterus was significantly higher in melatonin (10−4 M)-treated samples than in control samples (MT1: 27.8 ± 3.23% vs. control 10.7 ± 5.38% and MT2: 50.5 ± 3.41% vs. control 26.6 ± 5.29%; P < 0.05), and MT2 expression was higher than MT1 expression. (b1) Uterine p53 expression significantly increased in melatonin-treated group (38.3 ± 3.69% vs. control 26.4 ± 2.65%; P < 0.05). (c1) The relative protein expression level of LIF. There was no significant difference between the melatonin and control group (26.9 ± 6.50% vs. control 26.3 ± 4.73%; P > 0.05). (a2, b2 & c2) Western blotting results of uterine MT1, MT2, p53 and LIF protein expression. Different superscript letters indicate statistically significant differences (P < 0.05). Data are expressed as the means ± SEM (N = 8). Different superscript letters indicate statistically significant differences (P < 0.05)

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