Hepatoprotective effects of oligochitosan on hybrid groupers (Epinephelus lanceolatu ♂ x Epinephelus fuscoguttatus ♀) against Vibrio harvey infection via suppressing apoptosis-related pathways

Oligochitosan (OCS) has many vital bioactive functions; however, its underlying mechanisms in the liver of hybrid grouper (Epinephelus fuscoguttatus female x Epinephelus lanceolatu male) are not well studied. A comprehensive study is currently focused on the systematic effects of OCS on hybrid grouper liver, particularly their effects on transcriptome profiles, toxicity, and apoptosis. With the control diet supplemented with OCS at different dosages (0, 200, 400, 800, or 1600 mg/kg), the 30-day feeding trial was randomized to 360 fish in triplicate. The findings revealed that liver and body weight are not impacted by OCS after a 4-week feeding trial. To characterize the liver transcriptome by high-throughput sequencing, KEGG analysis showed that OCS feeding activated apoptosis-related signaling pathways. The five DEG levels, namely CYC, GADD45, PAI1, CDKN1A, and BCL2L1, were downregulated in apoptosis-related pathways for clarifying the transcriptomic data. To elucidate the immune responses stimulated by OCS by qRT-PCR, inflammation-associated cytokines' mRNA expression levels, such as TNF-alpha and IL-1 beta, were significantly upregulated in the 800 mg/kg group in contrast to the control. At the same time, OCS significantly improved antioxidant capacity by significantly decreasing apoptosis-related genes' expression and considerably enhancing CAT and GPx expression. To further test the antibacterial ability of OCS-fed hybrid groupers, the liver morphology of hybrid groupers was significantly improved after infection with Vibrio harvey, and apoptosis was significantly reduced in grouper liver according to TUNEL results. Overall, appropriate dietary OCS could improve immune responses and attenuate apoptosis-related signaling pathways in the liver of hybrid grouper, thus playing a role in bacterial resistance.