Mammary Epithelial Cell-Derived Exosomal miR-221-3p Regulates Macrophage Polarization by Targeting Igf2bp2 during Mastitis

Mastitis affects the milk quality and yield and is the most expensive disease in dairy cows. Elucidation of the pathogenesis of mastitis is of great importance for disease control. As a medium of intercellular communication, exosomes play key roles in various inflammatory diseases by regulating macrophage polarization. However, the molecular factors in exosomes that mediate the intercellular communication between mammary epithelial cells and macrophages during mastitis remain to be further explored. In this study, we isolated and identified mammary epithelial cell-derived exosomes from a lipopolysaccharide (LPS)/lipoteichoic acid (LTA)-induced mastitis cell model, and we demonstrated that exosomes from LPS/LTA-stimulated mammary epithelial cells promote M1-type macrophage polarization in vivo and in vitro. Based on the results of high-throughput sequencing, we constructed a differential miRNA (microRNA) expression profile of exosomes and demonstrated that miR-221-3p was highly expressed. Furthermore, in vivo and in vitro experiments, combined with coculture experiments and fluorescence tracing, showed that high miR-221-3p expression promoted M1-type macrophage polarization, demonstrating the transcellular role of miR-221-3p. Mechanistically, dual luciferase reporter gene assays and rescue assays showed that miR-221-3p regulated macrophage polarization by targeting Igf2bp2. The results of this study will deepen our understanding of the pathogenesis of mastitis, and the molecular regulatory axis that was established in this study is expected to be a target for mastitis treatment.