Anderson R A, Zwain I H, Arroyo A, Mellon P L, Yen S S
Department of Reproductive Medicine, University of California San Diego, La Jolla, Calif., USA.
Neuroendocrinology. 1999 Nov;70(5):353-9. doi: 10.1159/000054496.
Evidence suggests that insulin-like growth factors (IGFs; IGF-I and IGF-II) are involved in the regulation of reproductive function including the development of the gonadotropin-releasing hormone (GnRH) neuronal system and the modulation of GnRH secretory activities. To further characterize the regulatory role of the IGF system on GnRH neuronal function, we have examined the gene expression of IGF-I, IGF-II, IGF-I receptor (IGF-IR), and IGF-binding proteins (IGFBPs) in a GnRH neuronal cell line (GT1-7 cells). The relative effects of IGFs and insulin on GnRH secretion by these cells was also investigated. RT-PCR analysis demonstrated IGF-I, IGF-II and IGF-IR mRNAs in GT1-7 cells. The mRNAs for IGFBP-2, -3, -4, -5 and -6 but not IGFBP-1 were also detected. Immunoreactive protein bands for IGFBP-2, -4 and -5 but not for other IGFBPs were demonstrated by Western blot with IGFBP-5 appearing to be the most abundant IGFBP secreted by GT1-7 cells. IGFBP-5 production by GT1-7 cells was stimulated by both IGF-I and IGF-II in a dose-dependent manner with approximately equal potency, whereas insulin caused no significant effect. GnRH secretion by GT1-7 cells treated with IGF-I or IGF-II but not insulin showed an increase (80-100%) at 2 h of treatment followed by a decrease (46%) at 6 h that continued up to 24 h. We conclude that the expression of IGFs, IGF-IR and IGFBPs and their interactions in the regulation of GnRH secretion by GT1-7 cells as demonstrated by our study provide a basis for an autocrine regulatory role for the IGF system in GnRH neuronal secretory activities.
有证据表明，胰岛素样生长因子（IGF；IGF-I和IGF-II）参与生殖功能的调节，包括促性腺激素释放激素（GnRH）神经元系统的发育以及GnRH分泌活动的调节。为了进一步阐明IGF系统对GnRH神经元功能的调节作用，我们检测了GnRH神经元细胞系（GT1-7细胞）中IGF-I、IGF-II、IGF-I受体（IGF-IR）和IGF结合蛋白（IGFBP）的基因表达。我们还研究了IGF和胰岛素对这些细胞分泌GnRH的相对影响。RT-PCR分析显示GT1-7细胞中有IGF-I、IGF-II和IGF-IR mRNA。还检测到了IGFBP-2、-3、-4、-5和-6的mRNA，但未检测到IGFBP-1的mRNA。用IGFBP-5进行的蛋白质免疫印迹显示，GT1-7细胞分泌的最丰富的IGFBP是IGFBP-2、-4和-5，而其他IGFBP未显示免疫反应性蛋白条带。IGF-I和IGF-II均以剂量依赖性方式刺激GT1-7细胞产生IGFBP-5，二者效力大致相同，而胰岛素无显著影响。用IGF-I或IGF-II而非胰岛素处理GT1-7细胞后，GnRH分泌在处理2小时时增加（80-100%），随后在6小时时下降（46%），并持续至24小时。我们得出结论，我们的研究表明，IGF、IGF-IR和IGFBP在GT1-7细胞分泌GnRH的调节中的表达及其相互作用为IGF系统在GnRH神经元分泌活动中的自分泌调节作用提供了依据。
