Endocrine-disrupting Effects Of Cypermethrin On Synthesis Of Gonadotropin Hormons In Mouse Pituitary Cells

Background:Pyrethroids pesticides are widely and frequently used in agriculture and home. The residues of pyrethroids have been extensively detected in agricultural products and indoor environment. Cypermethrin is the most widely used type II pyrethroid. Pyrethroids have been considered as endocrine disruption chemicals (EDCs) and they have been shown to affect mammalian hypothalamus-pituitary-gonad (HPG) axis. HPG axis plays an important role in development, sexual maturity and reproduction of human and mammal. Gonadotropin hormones, which are synthesized and secreted by pituitary, are essential for sexual maturity and reproduction. Gonadotropin hormones include follicle stimulation hormone (FSH) and luteinizing hormone (LH). FSH and LH are composed of a common α subunit (also known as chorionic gonadotropin alpha, Cga) dimerized with unique β subunits (FSHP and LHP). Previsous studies have shown that pyrethroids, including cypermethrin, induced serum FSH and LH levels in male mouse or rat. Epidemiological investigation found the statistically significant positive associations between the levels of pyrethroid metabolites and FSH, as well as LH in man. However, the mechanism of endocrine-disrupting effects of pyrethroids on pituitary gonadotropin synthesis remains unclear.Methods:In this study, the immortalized mouse gonadotrope cell line LβT2was utilized to characterize the mechanism of effects of cypermethrin on gonadotropin synthesis. We analyzed the mRNA and protein levels of FSHβ, LHβ and Cga in LβT2cells exposed to cypermethrin by using Real time-PCR, ELISA and Western Blotting. The signaling pathways involved in the regulation of gonadotropins by cypermethrin were determined by using specific inhibitors.Results:LβT2cells were exposed to cypermethrin at concentrations of1nM, lOnM or100nM for24h. The MTS assay results indicated that cypermethrin at concentrations tested in this study had no effects on LβT2cell viability. Cypermethrin stimulated the mRNA and protein levels of FSHp, LHp and Cga in a dose-dependent manner. GnRH receptor/PLC/IP3pathway is not involved in cypermethrin-induced gonadotropin gene expression. Cypermethrin modified voltage-sensitive calcium channels (VSCCs) and inhibited Ca2+-ATPase activity, which led to elevation of intracellular Ca2+levels, activation of protein kinase C (PKC), c-Raf, Calmodulin and ERK, increased expression of c-Fos, c-Jun and Egr-1, to regulate the synthesis of gonadotropins.Conclusion:Cypermethrin induced gonadotropin gene expression through Ca2+/PKC/c-raf/Calmodulin/ERK/Egr-1, c-Fos, c-Jun signaling pathways. This study reveals the mechanism of endocrine-disrupting effects of pyrethroids, such as cypermethrin, on pituitary gonadotropin synthesis.