Sodium butyrate promotes lipopolysaccharide-induced innate immune responses by enhancing mitogen-activated protein kinase activation and histone acetylation in bovine mammary epithelial cells.

The innate immune response plays a crucial role in recovery from infectious diseases by promoting the clearance of pathogens. Sodium butyrate (NaB) is an energy source for cellular processes with the potential to regulate the innate immune response. The present study aimed to evaluate the effect of NaB on the innate immune response in a bovine mammary alveolar cell line (MAC-T) initiated by lipopolysaccharides (LPS). Thus, treatments were conducted as follows: treated with 1× PBS for 24 h (control), pretreated with 1 mM NaB (optimized by cell viability assays and dose-dependent experiment) for 18 h followed by treatment of 1× PBS for 6 h (NaB), pretreated with 1× PBS for 18 h followed by stimulation with LPS (1 µg/mL) for 6 h (LPS), and pretreated with 1 mM NaB for 18 h followed by stimulation with LPS (1 µg/mL) for 6 h (NaB + LPS). Different inhibitors were also used to elucidate the underlying mechanism. Furthermore, cells were treated with NaB and heat-inactivated Escherichia coli to test the effect of NaB on transcription of genes related to the innate immune response triggered by the major causative pathogen of mastitis. Each treatment had 3 replicates and was repeated 3 times. Proinflammatory cytokines, chemokines, and β-defensins are crucial secretion factors in innate immunity, and transcription of these factors was increased by NaB during challenge with LPS or heat-inactivated E. coli in MAC-T cells. Acetylation of histone H3 protein, which promotes gene expression by affecting the structure of chromatin, was also upregulated by NaB in response to LPS stimulation. P38 mitogen-activated protein kinases (MAPK), JNK, and Erk 1 and 2 are key upstream regulators of the expression of proinflammatory cytokines, chemokines, and β-defensins, and their activity was enhanced by NaB during LPS stimulation. Furthermore, inhibitors were used to assess the role of MAPK signaling in the effects of NaB. The results showed that inhibitors of p38 MAPK, Erk, and JNK attenuated the NaB-induced upregulation of TNF and β-defensin 5 (DEFB5) transcription, and that the inhibitor of Erk attenuated the NaB-induced upregulation of IL1B transcription during LPS challenge. Enhanced transcription of CXCL8 by NaB was blocked by the inhibitor of Erk and p38 MAPK during LPS stimulation. Overall, NaB boosted the LPS-induced innate immune response by promoting the expression of proinflammatory cytokines, chemokines, and β-defensins, which was associated with enhanced MAPK signaling activation and histone H3 acetylation.