D-sodium lactate promotes the activation of NF-κB signaling pathway induced by lipopolysaccharide via histone lactylation in bovine mammary epithelial cells.

Lactate is a glycolytic end product that is further metabolized as an energy source. This end product has been associated with certain diseases, including sepsis and tumors, and it can regulate the transition of macrophages to an anti-inflammatory state. This study aimed to explore the effects of lactate on the inflammatory responses of mammary gland epithelial cells, which constitute the first line of defense against pathogens in mammary glands. Bovine mammary epithelial cells (BMECs) were challenged with lipopolysaccharide (LPS) in the presence or absence of D-sodium lactate (D-nala). LPS exposure increased the concentration of lactate both inside and outside the cells. Further, inhibiting glycolysis diminished the LPS-induced production of proinflammatory cytokines. Treatment with LPS, exogenous D-nala, and their combination upregulated the expression levels of MCT1, increased the intracellular levels of lactate and histone H3 lysine 18 lactylation (H3K18la), and activated the nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) signaling pathway. The lactylation of H3K18 was mediated by p300/CBP. The p300/CBP inhibitor C646 decreased the level of H3K18la, reversing the activation of the NF-κB signaling pathway and release of proinflammatory cytokines. Therefore, LPS increased the intracellular level of lactate by upregulating MCT1 and glycolysis. D-nala exacerbated the LPS-induced inflammatory responses in BMECs. Moreover, intracellular lactate enhanced the activation of the NF-κB signaling pathway through the p300/CBP-mediated lactylation of H3K18. Thus, the findings of this study expand our understanding of lactate function in immune regulation.