Spicer L J, Aad P Y
Department of Animal Science, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
Biol Reprod. 2007 Jul;77(1):18-27. doi: 10.1095/biolreprod.106.058230. Epub 2007 Mar 14.
Little is known regarding the role of insulin-like growth factor 2 (IGF2) and the regulation of the IGF2 receptor (IGF2R) during follicular development. Granulosa cells were collected from small (1-5 mm) and large (8-22 mm) bovine follicles and were treated with IGF2 for 1-2 days in serum-free medium, and steroid production, cell proliferation, specific (125)I-IGF2 binding, and gene expression were quantified. IGF2 increased both estradiol and progesterone production by granulosa cells, and cells from large follicles were more responsive to the effects of IGF2 than those from small follicles. Abundance of aromatase (CYP19A1) mRNA was stimulated by IGF2 and IGF1. The effective dose (ED(50)) of IGF2 stimulating 50% of the maximal estradiol production was 63 ng/ml for small follicles and 12 ng/ml for large follicles, and these values were not affected by FSH. The ED(50) of IGF2 for progesterone production was 20 ng/ml for both small and large follicles. IGF2 also increased proliferation of granulosa cells by 2- to 3-fold, as determined by increased cell numbers and (3)H-thymidine incorporation into DNA. Treatment with IGF1R antibodies reduced the stimulatory effect of IGF2 and IGF1 on estradiol production and cell proliferation. Specific receptors for (125)I-IGF2 existed in granulosa cells, and 2-day treatment with estradiol, FSH, or cortisol had no significant effect on specific (125)I-IGF2 binding. Also, FSH treatment of small- and large-follicle granulosa cells had no effect on IGF2R mRNA levels, whereas IGF1 decreased IGF2R mRNA and specific (125)I-IGF2 binding. Granulosa cell IGF2R mRNA abundance was 3-fold greater in small than in large follicles. These findings support the hypothesis that both IGF2 and its receptor may play a role in granulosa cell function during follicular development. In particular, increased free IGF1 in developing follicles may decrease synthesis of IGF2R, thereby allowing for more IGF2 to be bioavailable (free) for induction of steroidogenesis and mitogenesis via the IGF1R.
关于胰岛素样生长因子2（IGF2）在卵泡发育过程中的作用以及IGF2受体（IGF2R）的调节，目前所知甚少。从小（1 - 5毫米）和大（8 - 22毫米）的牛卵泡中收集颗粒细胞，并在无血清培养基中用IGF2处理1 - 2天，然后对类固醇生成、细胞增殖、特异性（125）I - IGF2结合以及基因表达进行定量分析。IGF2增加了颗粒细胞的雌二醇和孕酮生成，并且来自大卵泡的细胞比来自小卵泡的细胞对IGF2的作用更敏感。芳香化酶（CYP19A1）mRNA的丰度受到IGF2和IGF1的刺激。刺激50%最大雌二醇生成的IGF2有效剂量（ED50），小卵泡为63纳克/毫升，大卵泡为12纳克/毫升，且这些值不受促卵泡激素（FSH）影响。IGF2对孕酮生成的ED50，小卵泡和大卵泡均为20纳克/毫升。IGF2还使颗粒细胞增殖增加2至3倍，这通过细胞数量增加以及（3）H - 胸腺嘧啶掺入DNA来确定。用IGF1R抗体处理可降低IGF2和IGF1对雌二醇生成和细胞增殖的刺激作用。颗粒细胞中存在特异性的（125）I - IGF2受体，用雌二醇、FSH或皮质醇处理2天对特异性（125）I - IGF2结合无显著影响。此外，FSH处理小卵泡和大卵泡颗粒细胞对IGF2R mRNA水平无影响，而IGF1可降低IGF2R mRNA和特异性（125）I - IGF2结合。小卵泡颗粒细胞中IGF2R mRNA丰度比大卵泡高3倍。这些发现支持了以下假设：IGF2及其受体在卵泡发育过程中可能对颗粒细胞功能起作用。特别是，发育中的卵泡中游离IGF1增加可能会减少IGF2R的合成，从而使更多的IGF2可通过IGF1R用于诱导类固醇生成和有丝分裂。
