促性腺激素调节C-型钠肽及其受体表达的分子机理

Fully grown mammalian oocytes in Graafian follicles are maintained in meiotic prophase arrest until the preovulatory surge of luteinizing hormone (LH) triggers the resumption of meiosis and ovulation. The mature oocytes (eggs) are then available for fertilization within the oviduct. The granulosa cell ligand C-type natriuretic peptide (CNP/NPPC) and its receptor NPR2 in cumulus cells prevent precocious meiotic maturation, which is critical for maturation and ovulation synchrony and for normal female fertility. Further study shows that FSH down-regulates, but LH up-regulates their expression. However, the molecular mechanism is not clear. The objective of the present project is to study the mechanism of reproductive hormones (FSH,LH), sex hormones, transcription factor, oocyte-derived paracrine factors on the expression of CNP and NPR2 in mouse follicles, their role in LH-induced oocyte maturation, and the relationship with cGMP levels in the follicle. These results will further understand the mechanism of FSH-induced follicular development and LH-induced oocyte maturation, reinforce the theory of mammalian oocyte maturation, and provide foundation for the pathogenesis of polycystic ovary syndrome.

C-型钠肽（CNP/NPPC）及其受体NPR2维持卵母细胞减数分裂的阻滞,其在FSH促进卵泡发育时高表达,而在LH诱导卵母细胞成熟和排卵时低表达。但是其表达调节的分子机理还不清楚。本项目以已取得的研究成果和最新的研究进展为依据，应用体外培养卵母细胞和卵泡，以及基因突变小鼠为模型，主要研究促性腺激素、性激素、旁分泌因子和转录因子对CNP及其受体在卵巢中表达调节的分子机理；CNP及其受体功能性变化与促性腺激素诱导卵母细胞成熟之间的相关性；CNP及其受体的表达与卵泡中cGMP水平变化之间的关系。研究结果可进一步了解FSH和LH在卵泡发育与卵母细胞成熟过程中的不同作用、性激素在卵母细胞成熟中的作用机理，补充和完善卵母细胞成熟理论，对进一步完善促性腺激素诱导卵母细胞成熟中的分子机制、阐明多囊卵巢综合征的发病机理具有重要的理论和实际意义。

前期研究表明，由颗粒细胞分泌的C-型钠肽NPPC与卵丘细胞中的受体NPR2结合，产生了cGMP。cGMP通过缝隙连接，进入到卵母细胞中，抑制了磷酸二酯酶PDE3A的活性和cAMP的水解，维持了减数分裂阻滞。在此基础上本项目研究了促性腺激素、性激素、旁分泌因子和转录因子对NPPC以及NPR2表达调节，以及NPPC/NPR2在卵泡发育、卵母细胞成熟中的作用机制。研究发现FSH通过雌激素、TGF-beta信号上调NPPC/NPR2的表达，从而维持了卵母细胞减数分裂阻滞；LH通过转录因子CREB诱导表皮样生子因子的表达，转激活卵丘细胞中的表皮生长因子受体；激活卵丘细胞中的EGF受体导致鞘氨醇激酶（SphK）的激活，引起鞘氨醇1磷酸（S1P）水平增加，钙离子水平升高；钙离子水平增加导致NPPC与NPRR2的亲和性下降，NPR2失活，从而诱导卵母细胞减数分裂恢复。研究结果阐明了FSH和LH，通过调节NPPC/NPR2的表达，在卵泡发育与卵母细胞成熟过程中的不同作用机制，进一步补充和完善卵母细胞成熟理论，为家畜繁殖及临床应用奠定了理论基础。相关研究结果发表在Endocrinology、Biol Reprod、Mol Reprod Dev等杂志上。