Department of Veterinary Clinical Sciences, The Royal Veterinary College, Hatfield, Hertfordshire, United Kingdom.
Theriogenology. 2010 Apr 15;73(7):856-72. doi: 10.1016/j.theriogenology.2009.10.011. Epub 2009 Dec 29.
Healthy follicles are highly vascularized whereas those undergoing atresia have poor vascularity, suggesting a relationship between follicular vascularization and follicular function. Vascularization is regulated by angiogenic factors, and among them vascular endothelial growth factor (VEGF) and angiopoietin-Tie (Ang-Tie) systems are of central importance. The objectives of this study were to determine if VEGF, VEGF receptor-2 (VEGFR-2), and components of the Ang-Tie system are expressed in ovarian follicles at both the protein and mRNA levels and to explore if their expression is related to the stage of the estrous cycle in the ewe. Ovaries from cyclic ewes were collected during the luteal phase (n=5) or before (n=5), during (n=4), and after (n=4) the preovulatory luteinizing hormone (LH) surge. After fixation, ovaries were wax-embedded, serially sectioned, and analyzed for both protein and mRNA expression of VEGF, VEGFR-2, angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), Tie-1 (mRNA only), and Tie-2. mRNA was studied by in situ hybridization using digoxigenin-11-UTP-labeled ovine riboprobes. A similar pattern of expression was observed for mRNA and protein for all of the factors. Both mRNA and protein expression of VEGF, VEGFR-2, Ang-1, Ang-2, Tie-1 (mRNA only), and Tie-2 in the granulosa and theca cells of follicles >or=2mm in diameter was significantly different among the stages of the estrous cycle, with the highest expression detected at the post-LH surge stage. Theca cells expressed significantly greater levels of the six angiogenic factors compared with granulosa cells at all stages of the estrous cycle. Expression levels in granulosa and theca cells were comparable between small (2.0 to 2.5mm) and medium (2.5 to 4.0mm) follicles, but large follicles (>4.0mm) expressed higher mRNA and protein levels (all P<0.05) for all factors at all stages of the estrous cycle. These data show (i) that VEGF, VEGFR-2, and the Ang-Tie system are present in both granulosa and theca cells of the ovarian follicle, (ii) that thecal cells consistently express greater levels of all of these factors compared with granulosa cells, and (iii) that their levels of expression are related to the stage of the estrous cycle and to follicle size.
健康的卵泡具有高度的血管生成能力，而正在发生闭锁的卵泡则血管生成能力较差，这表明卵泡血管生成与卵泡功能之间存在关系。血管生成受到血管生成因子的调节，其中血管内皮生长因子 (VEGF) 和血管生成素- Tie (Ang-Tie) 系统是最重要的。本研究的目的是确定 VEGF、VEGF 受体-2 (VEGFR-2) 和 Ang-Tie 系统的组成部分是否在蛋白质和 mRNA 水平上在卵巢卵泡中表达，并探讨其表达是否与绵羊发情周期的阶段有关。在黄体期 (n=5) 或发情前 (n=5)、发情期 (n=4) 和发情后 (n=4) 期间收集发情周期绵羊的卵巢。固定后，将卵巢包埋在蜡中，进行连续切片，并分析 VEGF、VEGFR-2、血管生成素-1 (Ang-1)、血管生成素-2 (Ang-2)、Tie-1（仅 mRNA）和 Tie-2 的蛋白质和 mRNA 表达。使用 DIG-11-UTP 标记的绵羊 RNA 探针进行原位杂交研究。所有因子的 mRNA 和蛋白质表达均表现出相似的模式。直径≥2mm 的卵泡的颗粒细胞和膜细胞中 VEGF、VEGFR-2、Ang-1、Ang-2、Tie-1（仅 mRNA）和 Tie-2 的 mRNA 和蛋白质表达在发情周期的各个阶段均有显著差异，在 LH 后阶段检测到最高表达。在发情周期的各个阶段，与颗粒细胞相比，膜细胞表达的六种血管生成因子水平均显著较高。在小（2.0 至 2.5mm）和中（2.5 至 4.0mm）卵泡中，颗粒细胞和膜细胞的表达水平相当，但大卵泡（>4.0mm）在发情周期的各个阶段均表达更高的 mRNA 和蛋白水平（所有 P<0.05）所有因素。这些数据表明：(i) VEGF、VEGFR-2 和 Ang-Tie 系统存在于卵巢卵泡的颗粒细胞和膜细胞中；(ii) 与颗粒细胞相比，膜细胞始终表达更高水平的所有这些因子；(iii) 它们的表达水平与发情周期阶段和卵泡大小有关。
