Nio-Kobayashi Junko, Miyazaki Kaya, Hashiba Kazuhisa, Okuda Kiyoshi, Iwanaga Toshihiko
Laboratory of Histology and Cytology, Hokkaido University Graduate School of Medicine, Kita 15-Nishi 7, Kita-ku, Sapporo, 060-8638, Japan.
Laboratory of Reproductive Physiology, Graduate School of Environmental and Life Science, Okayama University, Tsushima Naka Kita-ku 1-1-1, Okayama, 700-8530, Japan.
J Ovarian Res. 2016 Oct 19;9(1):67. doi: 10.1186/s13048-016-0277-0.
The mechanisms regulating the function and regression of the corpus luteum (CL) have not yet been elucidated in detail. The regressed CL of cows was previously reported to be filled with unusual vessels like arteriovenous anastomosis (AVA); however how these vessels are being established during luteolysis remains unknown.
The bovine CL at different luteal stages and regressing bovine CL induced by prostaglandin F (PGF) were histologically analyzed using light and electron microscopic levels. The changes in mRNA expression of genes encoding α-smooth muscle actin (SMA; Acta2) and transforming growth factor β1 (Tgfb1) in luteal tissues were analyzed by quantitative RT-PCR.
AVA-like vessels appeared in the regressed CL with a diameter less than 1.5 cm in which no functional luteal cells and macrophages were observed. Epithelioid cells in the AVA-like vessel wall were immunoreactive for SMA, and the lumen of the vessels were narrow. Immunoreaction for SMA was found in the tunica media of typical arteries and arterioles, and pericytes around capillary vessel. Cells with elongated cytoplasmic processes -resident fibroblasts expressing vimentin- distributed in the CL parenchyma without any association with blood vessels are also immunoreactive for SMA, and accumulated around arteries and arterioles during the late-luteal stage. In the regressed CL, walls of arteries and arterioles consisted of more than two layers of epithelioid cells positive for both SMA and desmin, suggesting that they are myofibroblasts transformed from fibroblasts. The percentage of the area positive for SMA and the mRNA expression of Acta2 were significantly increased in the regressed CL; however, they did not alter when a luteolytic dose of PGF was injected in vivo and collected within 24 h after the injection. On the other hand, Tgfb1, a known regulator for myofibroblast transformation, was significantly increased in PGF-induced regressing CL as well as in the CL during the late-luteal stage.
SMA-positive myofibroblasts accumulates around the arteries and arterioles to form AVA-like vessels during luteolysis in cows. PGF indirectly regulates myofibroblast transformation through enhancing the expression of TGFβ1. These peculiar AVA-like vessels may be involved in the regulation of blood flow in the bovine CL during luteolysis.
调节黄体（CL）功能及退化的机制尚未完全阐明。先前报道，母牛退化的黄体中充满了诸如动静脉吻合（AVA）之类的异常血管；然而，在黄体溶解过程中这些血管是如何形成的仍不清楚。
利用光学显微镜和电子显微镜对处于不同黄体期的牛黄体以及由前列腺素F（PGF）诱导的退化牛黄体进行组织学分析。通过定量RT-PCR分析黄体组织中编码α-平滑肌肌动蛋白（SMA；Acta2）和转化生长因子β1（Tgfb1）的基因的mRNA表达变化。
在直径小于1.5厘米的退化黄体中出现了类似AVA的血管，其中未观察到功能性黄体细胞和巨噬细胞。类似AVA血管壁中的上皮样细胞对SMA呈免疫反应，且血管腔狭窄。在典型动脉和小动脉的中膜以及毛细血管周围的周细胞中发现了对SMA的免疫反应。具有细长细胞质突起的细胞——表达波形蛋白的驻留成纤维细胞——分布在黄体实质中，与血管无任何关联，对SMA也呈免疫反应，并在黄体后期聚集在动脉和小动脉周围。在退化黄体中，动脉和小动脉壁由两层以上对SMA和结蛋白均呈阳性的上皮样细胞组成，表明它们是由成纤维细胞转化而来的肌成纤维细胞。在退化黄体中，SMA阳性面积百分比和Acta2的mRNA表达显著增加；然而，当在体内注射黄体溶解剂量的PGF并在注射后24小时内收集时，它们并未改变。另一方面，Tgfb1是一种已知的肌成纤维细胞转化调节因子，在PGF诱导的退化黄体以及黄体后期的黄体中显著增加。
在母牛黄体溶解过程中，SMA阳性肌成纤维细胞在动脉和小动脉周围聚集，形成类似AVA的血管。PGF通过增强TGFβ1的表达间接调节肌成纤维细胞转化。这些特殊的类似AVA的血管可能参与了母牛黄体溶解过程中黄体血流的调节。
