Xu Shaohua, Zhou Lingling, Guo Shuming, Hu Qiongyao, Shi Xuetao, Xia Chuanhui, Zhang Huiying, Ye Cheng, Jia Yongyi, Hu Guangfu
College of Fisheries, Huazhong Agricultural University, Wuhan 430070, China.
Agriculture Ministry Key Laboratory of Healthy Freshwater Aquaculture, Key Laboratory of Fish Health and Nutrition of Zhejiang Province, Zhejiang Institute of Freshwater Fisheries, Huzhou 313001, China.
Gen Comp Endocrinol. 2021 Nov 1;313:113829. doi: 10.1016/j.ygcen.2021.113829. Epub 2021 Jun 2.
In mammals, NK3R is the specific receptor for NKB, which played an important role in reproduction. Recently, two NK3R isoforms, namely NK3Ra and NK3Rb, have been identified in fish. However, little is known about the pituitary actions of the two NK3R isoforms in fish. In this study, both NK3Ra and NK3Rb were isolated from grass carp pituitary. Although their sequence similarity was only 61.6%, the two NK3R isoforms displayed similar ligand selectivity and binding affinity to TAC3 gene products (NKBa, NKBRPa and NKBRPb). In addition, both NK3Ra and NK3Rb displayed similar signaling pathways, including PKA, PKC, MAPK and Ca cascades. Tissue distribution indicated that both NK3Ra and NK3Rb were highly detected in grass carp pituitary. Further study found that NK3Ra was mainly located in pituitary LHβ cells, while NK3Rb was only detected in pituitary SLα cells. Furthermore, NK3Ra and NK3Rb activation could induce LHβ and SLα promoter activity, respectively. These results suggested that the two NK3R isoforms displayed different pituitary actions in fish. Using grass carp pituitary cells as model, we found that PACAP could significantly reduce NK3Ra, but induce NK3Rb mRNA expression coupled with cAMP/PKA and PLC/PKC pathways. Interestingly, PACAP could also significantly inhibit LHβ, but stimulate SLα mRNA expression in grass carp pituitary cells. Furthermore, NK3R antagonist could not only inhibit LHβ mRNA expression, but also block PACAP-induced SLα mRNA expression in grass carp pituitary cells. These results suggested that NK3Ra and NK3Rb could mediate PACAP-reduced LHβ and -induced SLα mRNA expression in grass carp pituitary, respectively.
在哺乳动物中，NK3R是神经激肽B（NKB）的特异性受体，其在生殖过程中发挥重要作用。最近，在鱼类中鉴定出了两种NK3R亚型，即NK3Ra和NK3Rb。然而，关于这两种NK3R亚型在鱼类垂体中的作用知之甚少。在本研究中，从草鱼垂体中分离出了NK3Ra和NK3Rb。尽管它们的序列相似性仅为61.6%，但这两种NK3R亚型对促甲状腺激素释放激素前体3（TAC3）基因产物（NKBa、神经激肽B相关肽a [NKBRPa]和神经激肽B相关肽b [NKBRPb]）表现出相似的配体选择性和结合亲和力。此外，NK3Ra和NK3Rb均表现出相似的信号通路，包括蛋白激酶A（PKA）、蛋白激酶C（PKC）、丝裂原活化蛋白激酶（MAPK）和钙信号通路。组织分布表明，在草鱼垂体中均能高度检测到NK3Ra和NK3Rb。进一步研究发现，NK3Ra主要位于垂体促黄体生成素β（LHβ）细胞中，而NK3Rb仅在垂体促生长激素释放激素α（SLα）细胞中被检测到。此外，NK3Ra和NK3Rb的激活分别可诱导LHβ和SLα启动子活性。这些结果表明，这两种NK3R亚型在鱼类垂体中表现出不同的作用。以草鱼垂体细胞为模型，我们发现垂体腺苷酸环化酶激活肽（PACAP）可显著降低NK3Ra的表达，但通过环磷酸腺苷/蛋白激酶A（cAMP/PKA）和磷脂酶C/蛋白激酶C（PLC/PKC）信号通路诱导NK3Rb的mRNA表达。有趣的是，PACAP还可显著抑制草鱼垂体细胞中LHβ的表达，但刺激SLα的mRNA表达。此外，NK3R拮抗剂不仅可抑制草鱼垂体细胞中LHβ的mRNA表达，还可阻断PACAP诱导的SLα的mRNA表达。这些结果表明，NK3Ra和NK3Rb可分别介导PACAP降低草鱼垂体中LHβ的表达和诱导SLα的mRNA表达。
