Comprehensive Analysis of Exosomal microRNAs in Buffalo Milk Across the Early Postpartum Transition

Milk-derived exosomes (MDEs) are bioactive nanocarriers rich in microRNAs (miRNAs) that play critical roles in post-transcriptional regulation during neonatal development and immune adaptation. However, the dynamic changes in miRNA expression across lactation stages and their biological functions remain insufficiently explored. We hypothesized that the miRNA cargo of buffalo MDEs exhibits temporal specificity, thereby dynamically matching the immune requirements of the neonatal calves. Therefore, the present study aimed to systematically characterize the miRNA expression profiles of MDEs derived from colostrum, transitional milk, and mature milk. MDEs were isolated, purified using differential ultracentrifugation, and characterized via transmission electron microscopy, Western blotting, and nanoparticle-tracking analysis. A total of 370 miRNAs were identified in the MDEs, with 220 (59.5%) co-expressed across colostrum, transitional milk, and mature milk. Comparative analysis revealed that colostrum MDEs exhibited the greatest miRNA diversity. Expression patterns of miRNAs showed distinct stage-specific clustering as lactation progressed. Compared to mature milk, 100 differentially expressed miRNAs (DE-miRNAs) were identified in colostrum MDEs, including 39 upregulated and 61 downregulated miRNAs. Bioinformatics analyses indicated that predicted target genes were associated with transmembrane transport, immune response, cell development, and apoptosis. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis identified pathways involved in immune regulation, inflammation, and apoptosis. Moreover, macrophages incubated with buffalo colostrum MDEs showed upregulation of proliferation-related genes and downregulation of pro-inflammatory factors, suggesting an anti-inflammatory effect through activation of the phosphoinositide 3-kinase-protein kinase B (PI3K-Akt) signaling pathway. These findings offer new insights into miRNA profiles of buffalo MDEs across the early postpartum transition and provide a preliminary basis for exploring immunomodulatory potential of buffalo MDEs.