Uncovering the protective mechanisms of Bacillus subtilis fmbj against LPS-induced hepatic immune stress and redox imbalance in broilers through transcriptomic profiling

This study investigated the protective effects of Bacillus subtilis fmbj (BS) in alleviating hepatic immune stress and redox imbalance induced by lipopolysaccharide (LPS) in broilers. A total of 240 chickens were randomly assigned to three groups, each consisting of ten replicates with eight birds per replicate. Birds in the LPS and BSLPS groups received intraperitoneal injections of LPS (1 mg/kg body weight), whereas the CON group was administered an equivalent volume of 0.9 % NaCl solution from day 14 to day 20. LPS exposure reduced growth performance and caused pronounced histopathological alterations and mitochondrial swelling in the liver compared with the CON group (P < 0.05). The LPS challenge also elevated immune stress markers (IL-1β, IL-6, IL-10, and IFN-γ) in both serum and liver, disrupted hepatic redox balance (SOD, T-AOC, POD, GSH-Px, GSH, GR, MDA), and impaired mitochondrial antioxidant capacity (MnSOD, GPx, GSH, GR, GST, γ-GCL, ROS, PC, 8-OHdG, MMP) (P < 0.05). Furthermore, LPS altered the expression of redox- and immune-related genes and proteins, particularly Nrf2 and NF-κB (P < 0.05). Although broilers in the BSLPS group still exhibited hepatic morphological damage, redox imbalance in hepatic tissue and mitochondria, and elevated immune stress indicators compared with the CON group (P < 0.05), BS supplementation attenuated liver injuries relative to the LPS group (P < 0.05). Transcriptomic analysis further demonstrated that BS modulated multiple signaling pathways, including the Toll-like receptor pathway, NF-κB pathway, cell adhesion molecules, and osteoclast differentiation. These findings suggest that the protective role of BS may be mediated, at least in part, through the regulation of the Nrf2/NF-κB signaling axis. In conclusion, this study highlights the potential of Bacillus subtilis fmbj as a functional feed additive for improving liver health and enhancing immune resilience in poultry industry.