We investigated the relationship between oxidative stress and poor oocyte quality and whether the antioxidant melatonin improves oocyte quality. Follicular fluid was sampled at oocyte retrieval during in vitro fertilization and embryo transfer (IVF-ET). Intrafollicular concentrations of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in women with high rates of degenerate oocytes were significantly higher than those with low rates of degenerate oocytes. As there was a negative correlation between intrafollicular concentrations of 8-OHdG and melatonin, 18 patients undergoing IVF-ET were given melatonin (3 mg/day), vitamin E (600 mg/day) or both melatonin and vitamin E. Intrafollicular concentrations of 8-OHdG and hexanoyl-lysine adduct were significantly reduced by these antioxidant treatments. One hundred and fifteen patients who failed to become pregnant with a low fertilization rate (< or =50%) in the previous IVF-ET cycle were divided into two groups during the next IVF-ET procedure; 56 patients with melatonin treatment (3 mg/day) and 59 patients without melatonin treatment. The fertilization rate was improved by melatonin treatment compared to the previous IVF-ET cycle. However, the fertilization rate was not significantly changed without melatonin treatment. Oocytes recovered from preovulatory follicles in mice were incubated with H2O2 for 12 hr. The percentage of mature oocytes with a first polar body was significantly reduced by addition of H2O2 (300 microm). The inhibitory effect of H2O2 was significantly blocked by simultaneous addition of melatonin. In conclusion, oxidative stress causes toxic effects on oocyte maturation and melatonin protects oocytes from oxidative stress. Melatonin is likely to improve oocyte quality and fertilization rates.

This review summarizes new findings related to beneficial effects of melatonin (N-acetyl-5-methoxytryptamine) on reproductive physiology. Recently many researchers have begun to study the local role of melatonin as an antioxidant. We focused on intra-follicular role of melatonin in the ovary. Melatonin, secreted by the pineal gland, is taken up into the follicular fluid from the blood. Reactive oxygen species (ROS) are produced within the follicles, during the ovulatory process. Melatonin reduces oxidative stress as an antioxidant, and contribute to oocyte maturation, embryo development and luteinization of granulosa cells. Our clinical study demonstrated that melatonin treatment for infertile women increases intra-follicular melatonin concentrations, reduces intra-follicular oxidative damage, and elevates fertilization and pregnancy rates. Melatonin treatment also improves progesterone production by corpus luteum in infertile women with luteal phase defect. Melatonin treatment could become a new cure for improving oocyte quality and luteal function in infertile women.

Dramatic changes of gene expressions occur in human endometrial stromal cells (ESCs) during decidualization. The changes in gene expression are associated with changes of chromatin structure, which are regulated by histone modifications. Here we investigated genome-wide changes in histone modifications associated with decidualization in human ESCs using chromatin immunoprecipitation combined with next-generation sequencing. ESCs were incubated with estradiol and medroxyprogesterone acetate for 14 days to induce decidualization. The chromatin immunoprecipitation-sequence data showed that induction of decidualization increased H3K27ac and H3K4me3 signals in many genomic regions but decreased in only a few regions. Most of the H3K27ac-increased regions (80%) and half of the H3K4me3-increased regions were located in the distal promoter regions (more than 3 kb upstream or downstream of the transcription start site). RNA sequence showed that induction of decidualization up-regulated 881 genes, 223 of which had H3K27ac- or H3K4me3-increased regions in the proximal and distal promoter regions. Induction of decidualization increased the mRNA levels of these genes more than it increased the mRNA levels of genes without H3K27ac- or H3K4me3-increased regions. Pathway analysis revealed that up-regulated genes with the H3K27ac- or H3K4me3-increased regions were associated with the insulin signaling, which may be involved in glucose uptake that is necessary for ESCs to undergo decidualization. These results show that histone modification statuses on a genome-wide basis change in human ESCs during decidualization. The main changes of histone modifications are increases of H3K27ac and H3K4me3 in both the proximal and distal promoter regions, which are involved in the up-regulation of gene expression that occurs during decidualization.

DNMT mRNAs declined in the human endometrium during the secretory phase, and E + MPA down-regulated DNMT3a and DNMT3b mRNAs in ESC in culture. These results suggest that DNMTs have regulatory functions in gene expression that is associated with decidualization.

The change in Ang expression is closely associated with angiogenesis, blood vessel stabilization, and blood vessel regression during the divergent phases of luteal formation, luteal regression, and luteal rescue by pregnancy.