Abstract
BackgroundEmbryo 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.MethodsThe 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.ResultsMelatonin 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.ConclusionMelatonin 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.
Highlights
Embryo implantation is crucial for animal reproduction
Luminex xMAP - EMD Millipore (MA, USA), goat antirabbit IgG (H + L), goat anti-mouse IgG (H + L), HRP and rabbit anti-goat IgG (H + L) were from Jackson Immunoresearch Laboratories (PA, USA); protein extraction RIPA was from Thermo Fisher Scientific (MA, USA); the Melatonin receptor type 1 (MT1) antibody (SC-390328; Santa Cruz Bio Inc., Santa Cruz, CA, USA), Melatonin receptor type 2 (MT2) antibody (SC-13177; Santa Cruz Bio Inc.) and p53 antibody (SC-47698; Santa Cruz Bio Inc.) were from Santa Cruz Biotechnology; the protein marker was from Thermo Fisher Scientific; and the separation gel buffer, stacking gel buffer, 20% Tween 20 and protein sample buffer were from Bio-Rad Lab (CA, USA)
The current study showed that melatonin at 10−5 to 10−4 M increased the number of embryo implantation sites in pregnant mice
Summary
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. Implantation is a crucial process that involves an intricate interaction between the embryo and uterus. The defects that occur before, during or immediately after implantation are responsible for early pregnancy loss in animals, including humans. An embryo needs to be developed to the blastocyst phase and the uterus must be in a receptive state, which allows the blastocyst to communicate with the luminal epithelium [1]. Progesterone (P4) and E2 are master regulators of implantation in both mice and humans because P4 and E2 modify the receptive status of the uterus and promote embryo implantation [3,4,5]. P53 regulates both the basal and inducible transcription of LIF to regulate the process of implantation [9, 12, 13]
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