Molecular mechanism of apoptosis induced by 4-tBP in common carp (Cyprinus carpio L.) head kidneys was explored from various angles: Hippo pathway, miR-203a, oxidative stress, ER stress, and mitochondrial pathway

4-tert butylphenol (4-tBP), a toxic environmental pollutant estrogen, received widespread attention due to its widespread presence, environmental persistence, and toxic effect. Common carp (Cyprinus carpio L.) is the most important freshwater economic animal in China and is also a model animal for the study on molecular mechanisms of poisoning. Head kidney is a target organ attacked by environmental pollutants. Here, we established a common carp 4-tBP poisoning model. The results showed that exposure to 4-tBP resulted in mitochondrial damage, endoplasmic reticulum damage, and apoptotic damage in head kidneys of common carps using microstructure and ultrastructure observations, as well as TUNEL kit methods. Furthermore, we found at transcriptional level from three perspectives that 4-tBP induced apoptosis in common carp head kidney cells: Hippo pathway, mitochondrial pathway, and ER stress. Hippo pathway formed a complex network, in which LATS1 was a core gene. It's noteworthy that Hippo pathway triggered mitochondrial pathway through YAP/NR4A1/Bcl-2 and YAP/BIRC5/Caspase-9 pathways under 4-tBP-induced apoptosis. PERK-eIF2α-ATF4-Caspase-3 pathway was involved in 4-tBP-induced apoptosis via ER stress. Moreover, miR-203a mediated 4-tBP-induced apoptosis through targeting MST1, MAP4K4, and NR4A1. In addition, 4-tBP disrupted balance between oxidants and antioxidants, and caused oxidative stress, and oxidative stress mediated ER stress under 4-tBP-caused apoptosis via via H2O2-PERK-eIF2α-ATF4-Caspase-3 pathway. miR-203a and oxidative stress participated in 4-tBP-induced apoptosis in common carp head kidney cells. For the first time, we found that Hippo pathway took part in molecular mechanism of fish poisoning, which needs to be investigated in the future. Our research provided foundational knowledge for exploring toxic effects of estrogen on fish and provided new insights into a theoretical basis for safety risk assessment for humans and fish, which deserves further profound exploration in the future. Moreover, the insights we generated help inform new strategies for preventing toxic injury in fish.