P-501 Superovulation alters telomere length and telomerase expression in mouse oocytes, possibly by changing estradiol and progesterone levels
Authors: Tire B , Talibova G , Bilmez Y , Ozturk S 
Published: July 2024

Abstract

Study question
How does the single and repeated superovulation affect the telomerase components expression and telomere length in mouse GV and MII oocytes?

Summary answer
Superovulation significantly altered the expression of the telomerase components Tert and Terc genes, TERT protein levels, and telomere length in the GV and MII oocytes.

What is known already
Assisted reproductive technologies (ARTs) are commonly used to treat infertility problems. One of the basic ART steps is controlled ovarian stimulation, also known as superovulation. Superovulation can lead to several adverse effects, such as increased oxidative stress, decreased oocyte and embryo quality, and mitochondrial dysfunction. These effects of superovulation largely overlap with those that causing telomere shortening.

Study design, size, duration
The effect of superovulation on the telomerase expression and telomere length of GV and MII oocytes is not fully addressed yet. In this study, we investigated the potential effects of single and repeated superovulation on telomerase expression and telomere length in mouse oocytes at germinal vesicle (GV) and metaphase II (MII) stages. In addition, we measured the estradiol and progesterone as well as oxidant and antioxidant capacity in serum samples of the oocytes-collected mice.

Participants/materials, setting, methods
Four groups of female Balb/C mice were formed: Control (C; n = 12), superovulated once (1S; n = 12), superovulated three times (3S; n = 12), and superovulated five times (5S; n = 12) at one-week intervals. The Tert and Terc gene expression, TERT protein levels, and telomere length in the mouse oocytes were assessed by RT-qPCR, immunofluorescence, and q-PCR, respectively. The hormone levels were analyzed by ELISA, and oxidant-antioxidant capacities were measured. All the ovarian follicles were counted in the H&E stained-sections.

Main results and the role of chance
We found that superovulation (1S, 3S, and 5S) significantly altered expression of the telomerase components Tert and Terc genes, TERT protein levels, and telomere length in the GV and MII oocytes (P&lt;0.05). While estradiol levels in GV oocyte-collected and progesterone levels of GV and MII oocyte-collected mice were higher in the 1S, 3S, and 5S groups compared with the C group (P&lt;0.01), the estradiol levels in MII oocyte-collected mice decreased progressively from C to 5S groups (P&lt;0.01). However, no significant changes were found in the total oxidant status (TOS), antioxidant status (TAS), and oxidative stress index (OSI) between the groups. Also, primordial and atretic follicle numbers in the ovaries of 3S and 5S groups were significantly decreased compared to the control and 1S groups (P&lt;0.05).

Limitations, reasons for caution
The limitation of this study is that we could not evaluate telomerase activity and oxidative stress levels in the mouse oocytes.

Wider implications of the findings
All these results suggest that altered telomerase expression and telomere length in GV and MII oocytes, possibly due to changed estradiol and progesterone levels, may be associated with adverse effects of superovulation on oocyte maturation and even preimplantation embryo development.

Trial registration number
not applicaple