Melatonin improves pregnancy outcomes in adenomyosis mice by restoring endometrial receptivity via NF-kappa B/apoptosis signaling

Background: Adenomyosis is a common gynecological disease which seriously impacts female fertility and is increasing in incidence in women of childbearing age. Melatonin has beneficial effects on reproductive processes. However, its impact on the uterine receptivity of patients with adenomyosis remains unclear. In this study, we investigated the effect of melatonin on uterine receptivity and pregnancy outcomes in an adenomyosis mouse model. Methods: We induced an adenomyosis mouse model by oral administration of tamoxifen to neonatal female CD-1 mice, then conducted a melatonin injection experiment to investigate its effect on implantation rates (n=6 each). In a second experiment, the endometrium in the implantation state was collected to identify the local action of melatonin on adenomyosis mice (n=6 each), and in a parallel study, the pregnancy rate and number of offspring were recorded (n=6 each). Results: The number of implantation sites in the adenomyosis model mice was much less than in control group (5.0 +/- 2.10 vs. 13.3 +/- 2.38, P<0.0001), and 30 mg/kg of melatonin significantly improved this (9.0 +/- 0.63 vs. 5.0 +/- 2.10, P=0.002). Additionally, melatonin administration ameliorated the impaired endometrial receptivity [leukemia inhibitory factor (LIF), integrin beta 3, homeobox A10 (HoxA10), and HoxA11], and improved the endometrium development [endometrial area (EA) and endometrial thickness index (ETI)] and pregnancy outcomes. Furthermore, the expression of implantation-related genes (Era, Pra, and P53), inflammatory factors [tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta)], oxidative stress associated genes (Gpx1 and Sod1), and apoptosis-related genes or proteins (Bax, Bcl-2, caspase-3, and cleaved caspase-3) was detected. The results showed higher local levels of reactive oxygen species (ROS) and inflammatory cytokines in the uterus of an adenomyosis model mice induced endometrial cells apoptosis and tissue damage, changed the uterine microenvironment, affected embryo implantation, and reduced the fertility of adenomyosis. Interestingly, melatonin significantly mitigated adenomyosis-induced changes by inhibiting the nuclear factor kappa B (NF-kappa B) signaling pathway, increasing the vascular endothelial growth factor (VEGF) expression, decreasing the endometrial cells apoptosis, and improving pregnancy outcomes. Conclusions: Melatonin treatment restored impaired uterine development and endometrial receptivity of adenomyosis mice by improving the endometrial microenvironment via the NF-kappa B/apoptosis signaling pathway. Our results provided new insight into melatonin-based therapy for adenomyosis-related infertility.