DTPA disrupts development of preantral ovarian follicles in vitro

Dietary zinc deficiency disrupts fertility in vivo by impairing oocyte and embryo development near ovulation. Acute treatment of newborn ovaries with a strong intracellular chelator (TPEN), which preferentially binds zinc, disrupts follicular development. However, the chronic effects of transition metal chelation on preantral follicle development are not known. In this study, the effect of the extracellular transition metal chelator, diethylenetriaminepentaacetic acid (DTPA), was used to examine more prolonged effects on preantral follicle development. Preantral granulosa cell-oocyte complexes from 14-day-old mice were cultured under control, chelated (DTPA), or rescue (DTPA + ZnSO4) conditions for up to 10 days. Preantral follicles cultured in DTPA alone showed impaired growth, disrupted nucleolar morphology, and impaired meiotic progression. The granulosa cells in DTPA-treated follicles underwent apoptosis at a higher rate than controls, had fewer physical connections to the oocyte, and reduced activation of pSMAD2 signaling. Moreover, Lhcgr and Ar transcripts were higher in cumulus cells, and Figla was lower in oocytes from DTPA-treated follicles. These data support a role for transition metals in general, and zinc in particular, in proper development of preantral ovarian follicles. The loss of somatic support cells explains some or all of the growth and developmental deficits seen in the DTPA-treated oocytes. DTPA preferentially binds zinc. Therefore, these results support growing evidence that a proper supply of transition metals, including zinc, is essential for optimal ovarian function.

The roles the mineral zinc plays in the ovary are not yet clear. The present study used follicles from mouse ovaries that were grown in the lab for up to 10 days. Follicles are round structures that contain a large egg cell at the center, surrounded by smaller cells called granulosa cells. Follicles were either grown with adequate zinc or insufficient zinc levels. The findings show that follicles require sufficient zinc to form connections between the egg and granulosa cells, which are essential for growth of both the egg and the granulosa cells. When there is insufficient zinc, loss of these connections leads to more granulosa cells dying and smaller follicles. These results show that zinc is important for growth of ovarian follicles, which could be important for treating infertility by supplying adequate levels of zinc in the diet.