PARENT SESSION
GRANULOSA CELL FUNCTION AND REGULATION
Laurel
7:30 AM-10:00 AM

(284) INSULIN-LIKE GROWTH FACTOR I REGULATES PREANTRAL FOLLICULAR GROWTH IN VITRO BY STIMULATING PROLIFERATION AND SUPPRESSING APOPTOSIS OF GRANULOSA CELLS.

Mao, Jiude¹, Smith, Michael¹, Rucker, Edmund¹, Wu, Guangming¹, McCauley, Tod¹, Prather, Randall¹, Didion, Brad², Day, Billy¹, ¹ Animal Science Research Center, Columbia, MO² Monsanto, St Louis, MO

ABSTRACT- Insulin-like growth factor I (IGF-I) is reported to stimulate the proliferation and differentiation of granulosa cells (GC). However, few studies have investigated the effects of IGF-I on preantral follicular growth. Follicular growth or atresia depends on a balance between granulosa cell proliferation and cell death (apoptosis). Therefore, the objectives of this study were to determine the effects of different levels of IGF-I on preantral follicular growth in vitro and to investigate the role of IGF-I in regulating granulosa cell proliferation and apoptosis. Porcine preantral follicles (mean diameter = 245.4 ± 2.0 m) were cultured individually for 8 days in Waymouth MB752/1 medium supplemented with 7.5% FCS, 10 g/ml transferrin, 50 g/ml L-ascorbic acid, 2 mIU oFSH/ml and 0, 1, 10, or 100 ng/ml human recombinant IGF-I. Follicular diameter was recorded at the time of collection and every 48 h during culture. On day 8 of culture, cumulus cell-oocyte complexes (COCs) from half of the follicles were collected and morphologically evaluated. The remaining follicles were fixed and processed for the detection of apoptotic and proliferating granulosa cells. Overall, there was no effect of IGF-I on follicular diameter on different days of culture, but there was a significant interaction between IGF-I and day of culture. During the first 4 days of culture, follicular diameter increased in all groups. Thereafter, follicular diameter continued to increase in follicles cultured in 10 and 100 ng/ml IGF-I; however, diameter of follicles cultured in 0 and 1 ng/ml IGF-I decreased after day 4. Compared to the 0 and 1 ng/ml IGF-I groups, addition of 10 and 100 ng/ml IGF-I to the culture medium decreased (P < 0.01) the percentage of apoptotic GCs, and increased (P < 0.01) the proportion of proliferating GCs (apoptotic GCs: 11.6 ± 1.7%, 9.7 ± 2.3%, 2.6 ± 1.6%, and 3.3 ± 1.8%; proliferating GCs: 0.3 ± 0.2%, 0.2 ± 0.1%, 9.5 ± 3.1%, and 6.8 ± 1.4% for 0, 1, 10, and 100 ng/ml IGF-I, respectively). The recovery rate of COCs from follicles cultured in 10 and 100 ng/ml IGF-I was also higher (P < 0.05) than follicles cultured in 0 and 1 ng/ml IGF-I; however, there was no difference among groups in oocyte diameter. In summary, IGF-I stimulated preantral follicular growth by suppressing apoptosis and increasing proliferation of granulosa cells.

KEY WORDS: Preantral follicle, Apoptosis, Cell proliferation, Follicular development