The role of estrogen receptor α and heat shock protein 90 in the apoptosis of fish liver cells after fipronil exposure.

Fipronil (FPN) as an insecticide can excessively enter aquatic ecosystems and may act as endocrine-disrupting chemicals by binding to estrogen receptor (ER) or aryl hydrocarbon receptor (AhR). Currently, there is limited information on the xenoestrogen role of FPN in the transcriptional modulation of hepatic genes involved in cell apoptosis. Three experiments were used in this study to determine how the FPN interference between the ER, AhR, and intermediate chaperons can induce apoptosis and change the expression of erα, erβ, erβ2, hsp70, hsp90, p53, bad1, bcl2, ahr, cyp1a, and caspase9 genes in common carp (Cyprinus carpio) hepatocytes. The IC values of FPN and 17β estradiol (E2) (positive control) in fish hepatocytes were determined (5 µg/mL). In the first experiment, exposure (6, 24, and 48 h) of hepatocytes to the low (0.1 µg/mL) and high (1 µg/mL) doses of FPN up-regulated apoptosis, pro-apoptotic genes (caspase9 and bad1), and chaperone protein genes (hsp70 and hsp90), while down-regulated anti-apoptotic genes (p53and bcl2). Additionally, there was a significant increase in the expression of the genes erα, ahr, and cyp1a that was dependent on both time and dose. ERα antagonist and a high dose of FPN were administered to the hepatocytes in the second experiment, which reduced cell apoptosis. In the third experiment, anti-apoptotic gene expression increased, and cell apoptosis and ahr and cyp1a gene expression significantly decreased when HSP90 and ERα antagonists were applied in comparison to the control group (P < 0.05). Based on this study, we demonstrate that FPN-induced apoptosis in fish hepatocytes is mediated by erα and hsp90 through transcriptional regulation of pro-apoptotic and anti-apoptotic genes.