Instituto de Biología y Medicina Experimental (IBYME), CONICET, Buenos Aires, Argentina.
Facultad de Medicina, Instituto de Investigaciones Biomédicas (INBIOMED), UBA-CONICET, Buenos Aires, Argentina.
J Neuroendocrinol. 2018 Sep;30(9):e12614. doi: 10.1111/jne.12614. Epub 2018 Aug 7.
The membrane progesterone receptors (mPRα, mPRβ, mPRγ, mPRδ and mPRε) are known to mediate rapid nongenomic progesterone functions in different cell types. However, the functions of these receptors in the pituitary have not been reported to date. In the present study, we show that the expression of mPRα was the highest among the mPRs in the rat anterior pituitary gland. Immunostaining of mPRα was detected in somatotrophs, gonadotrophs and lactotrophs. Interestingly, 63% of mPRα-positive cells within the pituitary were lactotrophs, suggesting that mPRα is involved in controlling prolactin (PRL) secretion in the pituitary. To test this hypothesis, rat pituitaries were incubated (1 hour) with either progesterone (P4) or the mPRα-specific agonist Org OD 02-0. PRL secretion was then measured by radioimmunoassay. The results of this experiment revealed that both P4 and Org OD 02-0 decreased PRL secretion. Moreover, the results from the GH3 cell line (CCL-82.1) showed that P4 and Org OD 02-0 inhibited PRL release, although the nuclear PR agonist R5020 was ineffective. Our investigation of the cellular mechanisms behind mPRα activity indicated that both P4 and Org OD 02-0 decreased cAMP accumulation, whereas R5020 was ineffective. In addition, the Org OD 02-0-effect on PRL release was blocked by pretreatment with pertussis toxin, an inhibitor of Go/Gi proteins. Because transforming growth factor (TGF)β1 is a potent inhibitor of PRL secretion in lactotrophs, we lastly evaluated whether TGFβ1 was activated by progesterone and whether this effect was mediated by mPRα. Our results showed that P4 and Org OD 02-0, but not R5020, increased active TGFβ1 levels. This effect was not observed when cells were transfected with mPRα-small interfering RNA. Taken together, these data provide new evidence suggesting that mPRα mediates the progesterone inhibitory effect on PRL secretion through both decreases in cAMP levels and activation of TGFβ1 in the lactotroph population.
膜孕激素受体（mPRα、mPRβ、mPRγ、mPRδ 和 mPRε）已知在不同细胞类型中介导孕激素的快速非基因组功能。然而，迄今为止，这些受体在垂体中的功能尚未报道。在本研究中，我们显示 mPRα 的表达在大鼠前垂体中是 mPR 中最高的。mPRα 的免疫染色在生长激素细胞、促性腺激素细胞和催乳素细胞中检测到。有趣的是，垂体中 mPRα 阳性细胞的 63%是催乳素细胞，这表明 mPRα 参与控制垂体中的催乳素（PRL）分泌。为了验证这一假设，将大鼠垂体孵育（1 小时）用孕激素（P4）或 mPRα 特异性激动剂 Org OD 02-0。然后通过放射免疫测定法测量 PRL 分泌。该实验的结果表明，P4 和 Org OD 02-0 均降低 PRL 分泌。此外，来自 GH3 细胞系（CCL-82.1）的结果表明，P4 和 Org OD 02-0 抑制 PRL 释放，尽管核 PR 激动剂 R5020 无效。我们对 mPRα 活性的细胞机制的研究表明，P4 和 Org OD 02-0 均降低 cAMP 积累，而 R5020 无效。此外，Org OD 02-0 对 PRL 释放的作用被百日咳毒素预处理阻断，百日咳毒素是 Go/Gi 蛋白的抑制剂。因为转化生长因子（TGF）β1 是催乳素细胞中 PRL 分泌的有效抑制剂，所以我们最后评估了孕激素是否激活 TGFβ1，以及这种作用是否由 mPRα 介导。我们的结果表明，P4 和 Org OD 02-0，但不是 R5020，增加了活性 TGFβ1 水平。当细胞用 mPRα 小干扰 RNA 转染时，没有观察到这种效应。总之，这些数据提供了新的证据表明，mPRα 通过降低催乳素细胞中 cAMP 水平和激活 TGFβ1 来介导孕激素对 PRL 分泌的抑制作用。
