ROS Induced by Streptococcus agalactiae Activate Inflammatory Responses via the TNF-α/NF-κB Signaling Pathway in Golden Pompano Trachinotus ovatus (Linnaeus, 1758)

Abstract

Streptococcus agalactiae is common pathogenic bacteria in aquaculture and can cause mass mortality after fish infection. This study aimed to investigate the effects of S. agalactiae infection on the immune and antioxidant regulatory mechanisms of golden pompano (Trachinotus ovatus). Serum and liver samples were obtained at 0, 6, 12, 24, 48, 96, and 120 h after golden pompano infection with S. agalactiae for enzyme activity and gene expression analyses. After infection with S. agalactiae, the content of reactive oxygen species (ROS) in serum was significantly increased (p < 0.05). Serum levels of glucose (GLU), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and malondialdehyde (MDA) increased and then decreased (p < 0.05), reaching a maximum at 6 h. Serum antioxidant enzyme (LZM) activity increased significantly (p < 0.05) and reached a maximum at 120 h. In addition, the mRNA expression levels of antioxidant genes (SOD, CAT, and GPx) in the liver increased and then decreased, reaching the maximum at 24 h, 48 h, and 24 h, respectively. During the experimental period, the mRNA expression levels of NF-κB-related genes of the inflammatory signaling pathway inhibitory κB (IκB) showed an overall decreasing trend (p < 0.05) and the lowest expression at 120 h, whereas the mRNA expression levels of tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), IκB kinase (IKK), and nuclear factor NF-κB increased significantly (p < 0.05) and the highest expression was at 120 h. In conclusion, these results showed that S. agalactiae could activate internal regulatory signaling in the liver of golden pompano to induce defense and immune responses. This study is expected to lay a foundation to develop the healthy aquaculture of golden pompano and promote a more comprehensive understanding of its disease resistance mechanisms.

Effects of cysteine addition to low-fishmeal diets on the growth, anti-oxidative stress, intestine immunity, and Streptococcus agalactiae resistance in juvenile golden pompano (Trachinotus ovatus)

“…Infectious diseases caused by S. agalactiae have frequently erupted in recent years in large-scale aquacultures of marine fish because of high culture densities ( 34 ). Therefore, we also examined the protective effect of cysteine during an S. agalactiae challenge in golden pompano.…”

“…The RNA extraction, cDNA production, and qPCR methods were based on a previous study ( 34 ). In brief, total RNA was extracted from the intestine of golden pompano using a HiPure Universal RNA Mini kit (Magen Biotech Co., Ltd., Guangzhou, China) according to the manufacturer’s instructions.…”

“…To complement the impact of cysteine on golden pompano immunity, we conducted an S. agalactiae challenge experiment following the feeding trial. The S. agalactiae concentration of 2.0 × 10 7 CFU/fish was the LD50 of golden pompano challenged by S. agalactiae for 120 h, as determined previously by our lab ( 34 ). After sample collection, we stochastically selected 20 fish per cage with similar size and healthy condition, injected 200 μL of the bacterial suspension at a concentration of 2.0 × 10 7 CFU/fish into the peritoneal cavity of each fish using a sterile syringe and returned the fish to their respective cages for continued feeding for 120 h. The remaining number of fish in each group was recorded every 12 h, and dead fish were removed.…”

“…Nevertheless, diets with lower fishmeal content tend to reduce the immune capacity of fish ( 8 , 9 ). Infectious diseases caused by Streptococcus agalactiae frequently broke out in recent years in large-scale cultures of marine fish due to excessive farming density and increasing environmental pollution ( 34 ). Therefore, we explored the effects of cysteine-supplemented low-fishmeal diets (containing 20% fishmeal) on growth performance, intestine immunity, and resistance against S. agalactiae in juvenile golden pompano in order to provide further insights into the mechanism of cysteine regulation of the intestine immunity of fish and to identify a solution for future usage of low-fishmeal diets.…”

Effects of exogenous taurine supplementation on the growth, antioxidant capacity, intestine immunity, and resistance against Streptococcus agalactiae in juvenile golden pompano (Trachinotus ovatus) fed with a low-fishmeal diet

“…Golden pompano (Trachinotus ovatus) has a wide distribution, high adaptability, and tasty meat. Owing to the maturation of artificial broodstock and culture techniques, it has become one of the most essential marine fish in China for largescale culture (24,25). However, golden pompano fed lowfishmeal feed are prone to decreased growth performance, oxidative stress, intestinal structural damage, dysbiosis, and reduced intestine immunity (26)(27)(28).…”