Table_1_Activation of farnesoid X receptor suppresses ER stress and inflammation via the YY1/NCK1/PERK pathway in large yellow croaker (Larimichthys crocea).DOCX

Unfolded protein responses from endoplasmic reticulum (ER) stress have been implicated in inflammatory signaling. The vicious cycle of ER stress and inflammation makes regulation even more difficult. This study examined effects of farnesoid X receptor (FXR) in ER-stress regulation in large yellow croakers. The soybean-oil-diet-induced expression of ER stress markers was decreased in fish with FXR activated. In croaker macrophages, FXR activation or overexpression significantly reduced inflammation and ER stress caused by tunicamycin (TM), which was exacerbated by FXR knockdown. Further investigation showed that the TM-induced phosphorylation of PERK and EIF2α was inhibited by the overexpression of croaker FXR, and it was increased by FXR knockdown. Croaker NCK1 was then confirmed to be a regulator of PERK, and its expression in macrophages is increased by FXR overexpression and decreased by FXR knockdown. The promoter activity of croaker NCK1 was inhibited by yin-yang 1 (YY1). Furthermore, the results show that croaker FXR overexpression could suppress the P65-induced promoter activity of YY1 in HEK293t cells and decrease the TM-induced expression of yy1 in macrophages. These results indicate that FXR could suppress P65-induced yy1 expression and then increase NCK1 expression, thereby inhibiting the PERK pathway. This study may benefit the understanding of ER stress regulation in fish, demonstrating that FXR can be used in large yellow croakers as an effective target for regulating ER stress and inflammation.

内质网应激引发的未折叠蛋白反应与炎症信号传导密切相关。内质网应激与炎症的恶性循环使得其调控愈发复杂。本研究旨在探究在大型黄鱼中，法尼醇X受体（FXR）对内质网应激调控的影响。通过大豆油饲料诱导的表达内质网应激标志物在FXR激活的鱼类中有所降低。在鲈鱼巨噬细胞中，FXR的激活或过表达显著减少了由真菌素（TM）引起的炎症和内质网应激，而FXR敲低则加剧了这种应激。进一步研究显示，TM诱导的PERK和EIF2α的磷酸化被鲈鱼FXR的过表达所抑制，而FXR敲低则导致其增加。鲈鱼NCK1被确认为PERK的调控因子，其表达在巨噬细胞中由FXR过表达所增加，并由FXR敲低所减少。鲈鱼NCK1的启动子活性被阴阳1（YY1）所抑制。此外，结果还显示，鲈鱼FXR的过表达能够抑制HEK293t细胞中P65诱导的YY1启动子活性，并降低巨噬细胞中yy1的TM诱导表达。这些结果表明，FXR可以抑制P65诱导的yy1表达，进而增加NCK1的表达，从而抑制PERK途径。本研究有助于加深对鱼类内质网应激调控机制的理解，证明了FXR可以作为调节大型黄鱼内质网应激和炎症的有效靶点。