Butyrate-induced trained immunity enhances bacterial killing ability of head kidney macrophages in turbot (Scophthalmus maximus L.)

Abstract

Trained immunity represents an evolutionarily conserved form of innate immune memory established through epigenetic and metabolic reprogramming. This study has demonstrated for the first time that butyrate, a key gut microbiota-derived metabolite, induces trained immunity in teleost macrophages. Our results revealed that priming head kidney macrophages (HKMs) from turbot (Scophthalmus maximus L.) with 1 μM of sodium butyrate (NaB) for 24 h followed by a 5-day training period, established a durable memory phenotype of HKMs. Importantly, the bactericidal capacity against Edwardsiella tarda (E. tarda) infection was significantly enhanced in butyrate-trained HKMs, accompanied by the elevated pro-inflammatory response with significantly elevated expression of il-1β and tnf-α. Mechanistically, butyrate training activated the HIF-1α signaling pathway, modulated a late-phase metabolic shift towards anaerobic glycolysis and TCA cycle, evidenced by altered citrate metabolism and glutamine pathway activation. Furthermore, the gene expression of acly, acss1 and acss2 was increased, while the expression of acc1 was suppressed, leading to the increased acetyl-CoA pools. On the other hand, butyrate induced persistent epigenetic remodeling, evidenced by increased expression of histone acetyltransferase CBP/P300, HDAC3 suppression, and a robust accumulation of H3K27 acetylation. Remarkably, in vivo pretreatment with butyrate at a low dose conferred a 20 % survival advantage against a lethal E. tarda challenge in juvenile turbot after 14 days post-exposure to butyrate compared to that in control group. These findings have established that butyrate drives innate immune memory in fish, offering novel insights and a promising candidate for prophylactic strategies against pathogenic infection in aquaculture.