Methionyl-Methionine Exerts Anti-Inflammatory Effects through the JAK2-STAT5-NF-κB and MAPK Signaling Pathways in Bovine Mammary Epithelial Cells.

Methionyl-methionine (Met-Met) is a functional dipeptide. Although the role of a dipeptide in milk protein synthesis is clearly established, whether Met-Met has an anti-inflammatory effect and a protective mechanism in bovine mammary epithelial cell (MAC-T) inflammation remains unknown. The purpose of this study was to determine the beneficial effects and underlying mechanisms of Met-Met on lipopolysaccharide (LPS)-induced MAC-T cell inflammation. RNA-seq, siRNA interference, and western blotting were performed to determine the anti-inflammatory mechanisms of Met-Met in the context of LPS exposure. Pretreatment with 2 mM Met-Met could reduce the increase in TNF-α (3.14 ± 0.55 vs 1.54 ± 0.26, P < 0.01), IL-1β (2.30 ± 0.21 vs 1.86 ± 0.11, P < 0.05), and IL-8 (3.49 ± 0.29 vs 0.62 ± 0.20, P < 0.01) after 1 μg/mL LPS exposure. RNA-seq analyses indicated that the overlapping genes were primarily enriched in the nuclear factor kappa-B (NF-κB), mitogen-activated protein kinase (MAPK), and IL-17 pathways. The suppression of NF-κB, P38, and JNK by Met-Met was mediated through the Janus kinase 2-signal transducers and activators of transcription 5 (JAK2-STAT5) pathway. Moreover, the Met-Met-mediated decrease in the LPS-induced activation of p-IκB, NF-κB, and JNK was reversed by knocking down JAK2. Collectively, Met-Met has beneficial effects on MAC-T cell inflammation by activating the JAK2-STAT5 pathway and then inhibiting the NF-κB and MAPK signaling pathways.