Effects of combined exposure to polystyrene microplastics and 17α-Methyltestosterone on the reproductive system of zebrafish.

Polystyrene microplastics (PS-MPs) are important carriers of pollutants in water. 17α-Methyltestosterone (MT) is a synthetic environmental endocrine disrupting chemical (EDC) with androgenic effects. To study the effects of PS-MPs and MT on zebrafish reproductive systems, zebrafish were exposed to 0 or 50 ng L-1 MT, 0.5 mg∙L-1 PS-MPs, or 50 ng∙L-1 MT + 0.5 mg∙L-1 PS-MPs for 21 d. The results showed that the different exposure reagents caused varying degrees of damage to the reproductive systems in zebrafish, with the extent of damage increasing as the exposure duration increased. Histological analysis of the gonads revealed that the ratio of mature oocytes and mature spermatozoa in the gonad decreased gradually with increased exposure time, with the ratio being Control > PS-MPs > MT > MT + PS-MPs in decreasing order. The results of quantitative real-time PCR (qRT‒PCR) showed that in female fish treated for 7 d, the expression of cyp11a mRNA was significantly reduced in all three treatment groups(MT, PS-MPs, and MT + PS-MPs), while in the group treated for 14 d with MT + PS-MPs, the expression of cyp19a1a and StAR mRNA was significantly increased. In male fish exposed for 21 d, the expression of cyp11a, cyp17a1, cyp19a1a, StAR, 3ß-HSD, and 17ß-HSD3 mRNA was significantly decreased in MT + PS-MPs. ELISA results showed that after 14 d of exposure, the levels of E2, LH, and FSH in the ovaries of female fish were significantly reduced in all three treatment groups. Similarly, the levels of T, E2, LH, and FSH in the testis of male fish were significantly reduced after 14 d of exposure to PS-MPs and MT + PS-MPs. Offspring of zebrafish exposed to MT and MT + PS-MPs exhibited delayed incubation time and slow development. The cross-generational toxicity of PS-MPs themselves may be negligible, but it can exacerbate the toxicity of MT, making the cross-generational effects more pronounced in the offspring, causing offspring mortality and malformations. Offspring of zebrafish exposed to MT and MT + PS-MPs exhibited delayed incubation time and slow development. In addition, MT caused malformations such as pericardial edema, yolk cysts, and spinal deformities in zebrafish during the incubation period.

Effects of 17α-Methyltestosterone on the Transcriptome and Sex Hormones in the Brain of Gobiocypris rarus.

17α-Methyltestosterone (MT), a synthetic environmental endocrine disruptor with androgenic effects, has been shown to disrupt the reproductive system and inhibit germ cell maturation in Gobiocypris rarus. To further investigate the regulation of gonadal development by MT through the hypothalamic-pituitary-gonadal (HPG) axis, G. rarus were exposed to 0, 25, 50, and 100 ng/L of MT for 7, 14, and 21 days. We analyzed its biological indicators, gonadotropin-releasing hormone (GnRH), gonadotropins, reproduction-related gene expression, and brain tissue transcriptome profiles. We found a significant decrease in the gonadosomatic index (GSI) in G. rarus males exposed to MT for 21 days compared to the control group. GnRH, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) levels, as well as the expressions of the gnrh3, gnrhr1, gnrhr3, fshß, and cyp19a1b genes, were significantly reduced in the brains of both male and female fish when exposed to 100 ng/L MT for 14 days compared to the controls. Therefore, we further constructed four RNA-seq libraries from 100 ng/L MT-treated groups of male and female fish, obtaining 2412 and 2509 DEGs in male and female brain tissue, respectively. Three common pathways were observed to be affected in both sexes after exposure to MT, namely, nicotinate and nicotinamide metabolism, focal adhesion, and cell adhesion molecules. Furthermore, we found that MT affected the PI3K/Akt/FoxO3a signaling pathway through the upregulation of foxo3 and ccnd2, and the downregulation of pik3c3 and ccnd1. Therefore, we hypothesize that MT interferes with the levels of gonadotropin-releasing hormone (GnRH, FSH, and LH) in G. rarus brains through the PI3K/Akt/FoxO3a signaling pathway, and affects the expression of key genes in the hormone production pathway (gnrh3, gnrhr1 and cyp19a1b) to interfere with the stability of the HPG axis, thus leading to abnormal gonadal development. This study provides a multidimensional perspective on the damaging effects of MT on fish and confirms that G. rarus is a suitable model animal for aquatic toxicology.