Role Of Kisspeptins/GPR54 System In Zearalenone-induced Advance Of Puberty Onset Induced In Female Rats

Zearalenone(ZEA) toxin, also known as F-2 toxin, it first isolated from gibberellic disease corn,it is a Fusarium toxin which is non-steroid and have estrogen like effect mainly produced by Fusarium graminearum, Fusarium roseum and other fungus. ZEA is distributed extensivelly in mouldy wheat, corn, sorghum and other grain crops and milk, which are the world’s widest range of pollution in fusarium toxins. According to the research report, ZEA can affect rodents, primates, humans puberty and reproductive function, but the exact mechanism is unclear. The onset and development of puberty is mainly affected by hypothalamic-pituitary-gonadal axis(HPGA), This axis mainly driven by the pulsed release of gonadotropin-releasing hormone(Gn RH) by hypothalamus. Kisspeptins / G protein coupled receptor 54(GPR54) system in the regulation of puberty and reproductive function played an integral role has been clarified, Kisspeptins and its ligand GPR54 can activate the pulsed release of Gn RH by hypothalamus, and be considerd as the key target of puberty development and onset. The subject use the female juvenile Sprague-Dawley(SD) rats exposed ZEA to establish ZEA-induced puberty onset and development induced in preadolescence female rats, to clarify the role Kisspeptins/ GPR54 in Zearalenone-induced advance of puberty onset induced in female rats, and to investigate the mechanism of estrogen-like effect of exogenous substances and to provide reference of Fusarium toxins induced advance of puberty onset.150 female juvenile SD rats at postnatal day 18(PND18) according to the way of litter block and weight random allocation methods were grouped into 5 groups: vehicle control group(corn oil), 50 g kg-1 E2 positive control group, 0.2 mg kg-1 ZEA exposure group, 1 mg kg-1 exposure group ZEA, 5 mg kg-1 ZEA exposure group. A daily intragastric administration for consecutive 5 days. After the administration finish, according to litter block method at random choose 15 rats from each group which at PND24 were executed, the remaining rats in each group were observed to PND52 and executed at PND52. Using observed mass and general clinical signs in rats to test the effects of comprehensive toxicity on prepubertal rats after exposure ZEA, using observed rats’ vaginal opening time to test the effects of puberty onset time on prepubertal rats after exposure ZEA, using vaginal smear method to observed estrous cycle’s cell morphology of each phase and calculated the duration of estrous cycle to test the effects of ovary and even HPGA function on prepubertal rats after exposure ZEA, Using calculated the indice of uterus and ovary to test the effects of uterus and ovary’s development on prepubertal rats after exposure ZEA, using observed uterus and ovary’s tissue slice to test the effects of uterus,ovary and follicle’s development on prepubertal rats after exposure ZEA. The results showed that 0.2,1,5 mg kg-1 ZEA have no significant effect on prepubertal rats’ mass with the extension of contamination and feeding’s time, suggests that 0.2,1,5 mg kg-1 ZEA have no comprehensive toxicity effect on prepubertal rats; 1,5 mg kg-1 ZEA advanced the rats’ vaginal opening time in a dose-dependent way, suggests that1,5 mg kg-1 ZEA could advance the prepubertal rats’ puberty onset; 0.2,1,5 mg kg-1 ZEA have no significant effect on vaginal exfoliated cell morphology but 1,5 mg kg-1 ZEA could prolong the duration of the estrous cycle, suggests that 1,5 mg kg-1 ZEA could effect prepubertal rats’ ovary and even HPGA function; 0.2,1,5 mg kg-1 ZEA have no significant effect on indice of ovary but 1,5 mg kg-1 ZEA could increase the indice of uterus in a dose-dependent way, suggests that 1,5 mg kg-1 ZEA could promote prepubertal rats’ uterus development; cellular morphology of uterus and ovary’s tissue slice in 0.2,1,5 mg kg-1 ZEA groups’ were normal, 1 mg kg-1 ZEA group follicle development appeared at secondary follicle to follicle mature follicle stage, 5 mg kg-1 ZEA group follicle development appeared at ovulation and the luteal phase, suggests that 0.2,1,5 mg·kg-1ZEA have no toxicity effect on uterus and ovary of prepubertal rats and could promote the development of prepubertal rats’ uterus and ovary. In summary, a certain dose of ZEA could induce the advance of puberty onset and development of female prepubertal SD rats, but the exact mechanism of action of ZEA need further study.Using Western blot method to test the protein expression levels of Gn RH, GPR54, PLC, PKC, ERK, p38 in the hypothalamus homogenate of female prepubertal SD rats in 5 treatment groups. The results showed that 0.2,1,5 mg kg-1 ZEA could promote the expression of Gn RH, suggests that a certain dose of ZEA induce the onset of puberty by the affect HPGA early start and trigger hypothalamus synthesis and secretion Gn RH; 0.2 mg kg-1 ZEA could promote the expression of Gn RH, suggests that a certain dose of ZEA induce the onset of puberty by regulated Gn RH secretion may through GPR54; 0.2,1,5 mg kg-1 ZEA could promote the expression of PLC,PKC, suggests that a certain dose of ZEA induce the onset of puberty may through GPR54 regulate and control the expression of PLC,PKC, and then causing the secretion of Gn RH; the hypothalamus ERK1/2 expression levels were significantly lower in 1,5 mg kg-1 ZEA groups, 0.2 mg kg-1 ZEA group’s p38 expression levels were significantly increased, suggests that ERK1/2 and p38 may be involved in the control process which ZEA induce the onset of puberty may through GPR54 regulate and control the Gn RH, but the specific regulatory mechanisms still need to be further explored.Conclusions: In summary, a certain dose of ZEA could induced the advance of puberty onset and development, Kisspeptins / GPR54 system plays an important role in the ZEA-induced advance of puberty onset and development induced in female prepubertal SD rats, hypothalamus GPR54 regulate and control the Gn RH protein expression levels increased may through increase the expression to further increase the PLC,PKC, p38 expression and lowered ERK1/2 expression, the advanced of puberty onset and development of female prepubertal SD rats caused by Gn RH priming the HPGA. However, the regulation of puberty is a very complex neuroendocrine network, there are many regulatory pathways and mechanism needs further study in ZEA-induced advance of puberty onset and development and the role of Kisspeptins/GPR54 system in Zearalenone-induced advance of puberty onset and development.