Changes in Telomerase Activity in Experimentally Induced Atretic Follicles of Immature Rats.

Abstract

Follicular atresia is characterized by apoptosis of granulosa cells, and telomerase plays an important role in the apoptotic process. To study the relationship between follicular atresia and telomerase activity, we investigated changes in telomerase activity and localization in experimentally induced atretic follicles of immature rats. Immature female Sprague-Dawley rats received 15 IU equine CG (eCG) by subcutaneous injection. Rats were killed under ether anesthesia at 2, 3, 4, or 5 days after eCG injection. Telomerase activity in granulosa cells was measured by telomeric repeat amplification protocol (TRAP) assay, and telomerase localization in the ovary was examined by in situ TRAP assay. Telomerase activity was detected at high levels in granulosa cells on day 2 after eCG injection regardless of follicle size, and levels were significantly decreased in large follicles, with atretic changes, on days 4 and 5. No such decrease was observed in granulosa cells of small follicles. In the next experiment, rats received subcutaneous injections of estradiol (1, 10, or 50 microg/rat) to prevent follicular atresia or sesame oil as a control from day 2 to day 4 after eCG injection and were killed under ether anesthesia on day 5 after eCG injection. The changes observed in the large follicles on days 4 and 5 in oil treated rats were not observed with estradiol treatment. These findings suggest that the telomerase in granulosa cells is likely to play an important role for healthy follicle life and that loss of its activity may be associated with follicular atresia.

Effect of aromatase inhibitor (fadrozole) on proliferation, estradiol production and telomerase activity in pig granulosa cells in vitro

“…Similar results were obtained by Yamagata et al (2002), who observed a higher level of telomerase activity in healthy, preovulatory follicles as a result of estradiol application to female rats. Estradiol produced by growing follicles is an antiatretic factor, increasing the survivability of the follicular cells.…”

“…Telomerase activity was also detected in the human endometrium, and its level correlated with estrogen changes, being the highest in the follicular phase of the estrus cycle (Kyo et al, 1997;Yokoyama et al, 1998). Application of estradiol to female rats prevented decrease of telomerase activity in granulosa cells (Yamagata et al, 2002). The role of estrogens in telomerase activity regulation in pig granulosa cells is not fully understood.…”

Plasticity of granulosa cells: on the crossroad of stemness and transdifferentiation potential

“…Interestingly, it was shown that there is no significant difference between pig small antral and large antral follicles in telomerase activity of granulosa cells [74]. Additionally, a significantly decreased telomerase activity was observed in large and atretic follicles in comparison to small and healthy follicles in rat [83]. In human the low level of telomerase activity in the ovary was found to be related to the age-related primordial follicle depletion and it was speculated that telomerase activity could be used as a marker of the ovarian functional age [35].…”

Quantitative analysis of oestrogen receptor α and β gene expression during prolonged culture of pig granulosa cells

“…In the present study we focused on the expression of genes for two subtypes of oestrogen receptor in pig granulosa cells cultured in the presence of LIF, bFGF, or SCF. The rationale behind undertaking this study is the well-established role of oestrogens in maintaining granulosa cell survivability (Yamagata et al, 2002). Therefore, it was interesting to elucidate if and how the level of oestrogen receptors is changed under the influence of different growth factors during prolonged culture of GC obtained from follicles of different sizes.…”

“…Its production in atretic follicles is significantly decreased. Yamagata et al (2002) found a decreased level of telomerase activity in experimentally induced atretic rat follicles. Administration of oestradiol to female rats prevented both follicular atresia as well as a decrease of telomerase activity in granulosa cells.…”