Activating transcription factor 4 (ATF4) is a critical transcription factor involved in stress response. It exerts essential regulatory effects on cellular metabolism. Zebrafish genome contains two ATF4 paralogs, atf4a and atf4b. The function of Atf4a has been documented previously while that of Atf4b remains elusive. To investigate the impact of Atf4b on zebrafish development and metabolism, we generated an atf4b knockout zebrafish using CRISPR/Cas9. Sequence alignment revealed that zebrafish Atf4b shares conserved domains only in the leucine zipper and DNA-binding regions with mammalian ATF4. Morphological examination showed no apparent deformities in atf4b^-/- embryos while body length was significantly reduced. Metabolomic profiling demonstrated the elevated citrate level accompanied by reduced downstream metabolites like oxoglutarate, malate and succinate in the tricarboxylic acid (TCA) cycle with a marked decrease in ATP production. Atf4b deficiency induced mitochondrial damage and significantly compromised survival under acidic stress conditions. These findings evidenced the crucial role of Atf4b in zebrafish growth, energy metabolism and stress adaptation, and provided novel insights into the integrated mechanism coupling developmental processes, metabolic homeostasis and stress response.

Microplastics and nanoplastics have become important factors threatening the health of aquatic organisms. In this study, zebrafish (Danio rerio) larvae were used as model organisms to investigate the short-term effects of nanoplastic exposure on the behavior and metabolism of juvenile fish. The larvae were exposed to environments containing fluorescent polystyrene nanoplastics (PSNP), 25 nm and 80 nm in diameter, respectively, to detect nanoplastic accumulation and assess their effects on zebrafish larval behavior and metabolism. The results showed that after 9 hours of treatment, 25 nm PSNP specifically accumulated in the brain tissues of zebrafish while 80 nm PSNP tended to accumulate on the surface of zebrafish larvae. The 25 nm PSNP significantly inhibited the touch-evoked reponse of zebrafish larvae; and significantly reduced the contents of glucose thus inhibited glycolysis and the tricarboxylic acid cycle metabolic pathways. Additionally, 25 nm PSNP significantly reduced the level of adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH). These results indicated that bioaccumulation of nanoplastics is related to their particle size, and nanoplastics significantly inhibit the energy metabolism of zebrafish larvae. Our findings provided important insights for assessing the impact of nanoplastic pollutant on the behavior and metabolism of juvenile fish.