Exosomal miRNAs Mediate Immune–Metabolic Interactions in the Hemocytes of the Pearl Oyster Pinctada fucata martensii

Mollusks, such as bivalves, face increasing threats, such as disease, in aquaculture. Exosomes, widely derived from living cells carrying diverse bioactive molecules, affect the immune response. To overcome these challenges, bivalves utilize exosomal miRNAs as critical regulators of immune responses. This study investigates the role of exosomal miRNAs in modulating immune and metabolic responses in Pinctada fucata martensii following lipopolysaccharide (LPS) stimulation. Exosomes (75–150 nm) were isolated from hemolymph and characterized. High-throughput sequencing identified 30 differentially expressed miRNAs (DEMs) and 1349 differentially expressed genes (DEGs) in LPS-treated oysters, with significant enrichment in TNF, TLR/NF-κB, and metabolic pathways. This study revealed exosomal miRNA-mediated regulation of immune genes (IκBα, TRAF6, IRAK1, and BIRC2/3) and metabolic enzymes (PCK and CYP2J), demonstrating their role in apoptosis, inflammation, and metabolic reprogramming. Network analysis highlighted miRNA–mRNA interactions, including miR-7/IκBα (TNF pathway) and miR-34_5/IRAK1 (TLR pathway). Additionally, exosomal miRNAs (miR-92_2 and novel_mir5) were found to regulate oxidative stress (SOD1) and gluconeogenesis (PCK), linking immune defense with metabolic adaptation. These findings provide novel insights into exosomal miRNA-mediated immune regulation in bivalves, revealing conserved mechanisms with potential implications for molluscan health and disease management.