Protective effect of nano-selenium on mercury-induced prehierarchical follicular atresia in laying hens

This study investigated the effect of nano-selenium (nano-Se) in protecting laying hens from mercury (Hg)-induced prehierarchical follicular atresia. Furthermore, the endoplasmic reticulum stress (ERS) was explored to reveal the molecular mechanism. In vivo, 720 Hyline-Brown laying hens were treated with Hg and nano-Se alone or in combination. In vitro, the prehierarchical follicles were treated with Hg, nano-Se and 4-phenyl butyric acid (4-PBA) alone or in combination (Control, 25 μM Hg group, 10 μM nano-Se group, 20 μM nano-Se group, 25 μM Hg + 10 μM nano-Se group, 25 μM Hg + 20 μM nano-Se group, 25 μM Hg + 4-PBA group, and 25 μM Hg + 20 μM nano-Se + 4-PBA group). The GCs were treated with Hg and nano-Se alone or in combination (Control, 15 μM Hg group, 6 μM nano-Se group, 12 μM nano-Se group, 15 μM Hg + 6 μM nano-Se group, 15 μM Hg + 12 μM nano-Se group). The results revealed that dietary Hg significantly reduced laying performance (P < 0.05) and egg quality (P < 0.05), whereas nano-Se addition prevented these reductions (P < 0.05). Hg exposure significantly induced the accumulation of Hg in PHFs (P < 0.05), prehierarchical follicular atresia (P < 0.05) and apoptosis in PHFs, whereas nano-Se addition significantly prevented these effects (P < 0.05). The levels of sex hormones (P < 0.05) were significantly decreased after Hg exposure in vivo and in vitro, while nano-Se addition prevented the reductions. Furthermore, the RNA-Seq results showed that the key factors of the ERS presented differential expression, including C/EBP homologous protein, protein kinase RNA-like endoplasmic reticulum kinase (PERK) and activating transcription factor 6 (ATF6) in GCs. Hg exposure significantly increased the key gene expression of endoplasmic reticulum stress in GCs, whereas nano-Se addition prevented the induction of expression of these genes. In addition, the protein levels of PERK, inositol requiring protein 1α (IRE1α) and ATF6 were significantly increased, whereas nano-Se addition prevented the enhancements of protein expression in GCs. In conclusion, this study shows that Hg exposure can reduce induce prehierarchical follicular atresia, whereas nano-Se can prevent these effects. Our results also elucidate a key role of ERS in these protective effects of nano-Se in laying hens.