Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Illinois, USA.
Biol Reprod. 2012 Mar 22;86(3):86. doi: 10.1095/biolreprod.111.095927. Print 2012 Mar.
Prolactin (PRL), a pleiotropic hormone essential for maintenance of corpus luteum (CL) function and pregnancy, transduces its signal through two types of receptors, a short form (PRLR-S) and a long form (PRLR-L). Both types of receptors are expressed in the CL, yet their individual roles are not well defined. We have shown previously that female transgenic mice expressing only PRLR-S display total infertility characterized by defective follicular development and early degeneration of CL, suggesting that expression of PRLR-L is a prerequisite for normal follicular development and maintenance of CL. To determine whether PRLR-L alone is the sole receptor required to maintain normal CL formation, differentiation, and progesterone secretion, we generated two transgenic mice which express only PRLR-L, either ubiquitously (Tg-RL) or in a CL-specific manner (CL-RL). To generate CL-specific expression, we used the HSD17B7 promoter. We found both transgenic mice models cycled normally, displayed no apparent defect in follicular development, and had normal ovulation rates. The STAT5 signaling pathway, considered essential for luteinization and progesterone production, was activated by PRL in both transgenic mice models. However, soon after mating, Tg-RL and CL-RL mice showed early regression of CL, lack of progesterone production, and implantation failure that rendered them totally infertile. Embryo transfer studies demonstrated no embryo abnormalities, and supplementation with progesterone rescued implantation failure in these mice. Close observation revealed lack of luteinization and reduced expression of proteins involved in progesterone biosynthesis despite normal levels of LHCGR (LH-R), ESR1 (ER-alpha), CEBPB (C/EBP-beta) and CDKN1B (p27), proteins essential for luteinization. However, we found VEGFA, a key regulator of angiogenesis and vascularization, to be dramatically reduced in both Tg-RL and CL-RL mice. We also found collagen IV, a marker for the basal lamina of endothelial cells, aberrantly expressed and a discordant organization of endothelial cells in CL. Although luteinization did not occur in vivo, granulosa cells isolated from these mice luteinized in culture. Taken together, these results suggest that a vascularization defect in the CL may be responsible for lack of luteinization, progesterone production, and infertility in mice expressing only PRLR-L. This investigation therefore demonstrates that in contrast to earlier presumptions that PRLR-L alone is able to support normal CL formation and function, both isoforms of the PRL receptor are required in the CL for normal female fertility.
催乳素（PRL）是一种多功能激素，对于维持黄体（CL）功能和妊娠至关重要，它通过两种受体传递信号，一种是短型（PRLR-S），另一种是长型（PRLR-L）。这两种受体都在 CL 中表达，但它们的各自作用尚未明确。我们之前已经表明，仅表达 PRLR-S 的雌性转基因小鼠表现出完全不孕的特征，其特征是卵泡发育缺陷和 CL 的早期退化，这表明 PRLR-L 的表达是正常卵泡发育和 CL 维持所必需的。为了确定 PRLR-L 是否是维持正常 CL 形成、分化和孕激素分泌所必需的唯一受体，我们生成了两种仅表达 PRLR-L 的转基因小鼠，一种是在全身表达（Tg-RL），另一种是在 CL 特异性表达（CL-RL）。为了实现 CL 特异性表达，我们使用了 HSD17B7 启动子。我们发现这两种转基因小鼠模型都正常循环，卵泡发育没有明显缺陷，排卵率正常。PRL 激活了 STAT5 信号通路，该通路被认为对于黄体化和孕激素产生至关重要，在这两种转基因小鼠模型中都被激活。然而，在交配后不久，Tg-RL 和 CL-RL 小鼠的 CL 迅速退化，缺乏孕激素产生，并且植入失败，导致完全不孕。胚胎移植研究表明这些小鼠没有胚胎异常，孕激素补充挽救了它们的植入失败。仔细观察发现，尽管黄体生成素受体（LH-R）、雌激素受体 1（ER-alpha）、CEBPB（C/EBP-beta）和 CDKN1B（p27）等蛋白的水平正常，这些蛋白对于黄体化是必需的，但黄体化蛋白的表达减少，并且孕激素生物合成相关蛋白的表达减少。然而，我们发现血管内皮生长因子 A（VEGFA），一种血管生成和血管形成的关键调节剂，在 Tg-RL 和 CL-RL 小鼠中均显著减少。我们还发现胶原 IV，一种内皮细胞基底膜的标志物，在 CL 中异常表达，并且内皮细胞的组织排列不一致。尽管体内未发生黄体化，但从这些小鼠中分离的颗粒细胞在培养中黄体化。综上所述，这些结果表明，CL 中的血管生成缺陷可能是导致这些小鼠缺乏黄体化、孕激素产生和不孕的原因。因此，这项研究表明，与之前的假设相反，即仅 PRLR-L 能够支持正常 CL 的形成和功能，PRL 受体的两种同工型在 CL 中对于正常雌性生育力都是必需的。
