Study On The Role Of Cholesterol Trafficking Genes Related To Steroid Hormones Synthesis In Goose Follicles

It is well known that steroid hormones are mainly secreted from avian ovary and follicles, which are regulated by gonadotrophins. As the precursor of steroid hormone synthesis, the metabolic balance of cholesterol in cells can also regulate the content and bioactivity of steroid hormones. Transporting of cholesterols during the synthesis of steroid hormones in ovarian follicles is mediated by proteins. Early studies have established that STARD4, which is regulated by SREBP-2and cholesterol, is able to transport intracellular cholesterols to outer mitochondrial membrane, and then to the inner mitochondrial membrane by StAR, which are converted as steroid hormones further. The present study was conducted to investigate the roles of four genes during the synthesis of steroid hormones, including SREBP-2、STARD4、StAR、P450scc, thus, we detected the expression patterns of these genes during follicle development, and well as the contents of steroid hormones in follicles. Additionally, in order to further research the functions of these genes in the synthesis of steroid hormones in goose follicles, we investigated the effects of cholesterol,25-hydroxycholesterol and Mevinolin on cholesterol metabolisms in goose follicles, as well as the expression levels of these genes and contents of extracellular progesterone. The results are listed as follows:(1) Partial CDs sequences of STARD4, StAR and P450scc were obtained, which was655bp,512bp, and574bp, respectively. All the three genes showed highest homologies with Gallus, which was89%,88%, and90%, respectively.(2) SREBP-2, STARD4, StAR, and P450scc could express during follicle development, which reached the peak point at preovulatory follicles and2～4mm follicles, and lowest point at atretic and postovulatory follicles.(3) When goose F1granulosa cells were treated with different concentration of cholesterol, we found that15μg/mL cholesterol could promote the activity of granulosa cells, and25μg/mL cholesterol may depress the secretion of progesterone from granulocytes. Compared with the control group, expression levels of StAR and P450scc increased with the increasing contents of cholesterol (P<0.05). However, situations of SREBP-2and STARD4were opposite, expression of SREBP-2was inhibited when cells were treated with15μg/mL cholesterol, while expression of STARD4was depressed with25μg/mL cholesterol)(4)25-hydroxycholesterol could significantly inhibit the activity of granulosa cells, which had no significant effects on secretion of progesterone from granulocytes (P>0.05). In addition,25-hydroxycholesterol was able to suppress expression levels of StAR and SREBP-2. There was no significant effects of different concentration of25-hydroxycholesterol on P450scc expression. As a whole,25-hydroxycholesterol could slightly decrease the expression of P450scc, but increase expression of STARD4.(5) Mevinolin could suppress the activity of granulosa cells without significant effects on secretion of progesterone from granulocytes (P>0.05). Compared with the control group, mevinolin was able to significantly inhibit the expression level of STAR (P<0.05), but situations were different in P450scc expression:0.1μg/mL Mevinolin depressed expression of P450scc,1μ/mL Mevinolin increased its expression and10μg/mL Mevinolin decreased its expression (P<0.05) again. Moreover, expression of both SREBP-2and STARD4were promoted by mevinolin, which showed most significant effects when the concentration was1μg/mL (P<0.05)...