miR-9394b from Lactobacillus paracasei extracellular vesicles targets iNOS to reprogram host NO-ornithine metabolism and ameliorate DSS-induced murine colitis

Ulcerative colitis (UC) is a growing global health burden, creating an urgent need for new therapies. While extracellular vesicles (EVs) from probiotic bacteria show therapeutic potential, their molecular mechanisms are largely unknown. This study reveals that Lactobacillus paracasei (LPC) and its EVs (LPC-EVs) alleviate Dextran Sulfate Sodium Salt (DSS)-induced colitis in mice through a multi-faceted mechanism involving partial reshaping of the gut microbiota, suppression of TLR4/NF-κB signaling, and reinforcement of tight junctions. We found that miR-9394b carried by LPC-EVs plays a central role in this effect. In MODE-K cells, miR-9394b directly targets iNOS, shifting arginine metabolism away from nitric oxide (NO) production toward ornithine-associated metabolism. The increased ornithine served as a downstream mediator linking epithelial metabolic remodeling to macrophage polarization. Collectively, these findings support a model in which bacterial EVs mediate the transfer of miR-9394b to coordinate a metabolic-immune response, highlighting a potential avenue for miRNA-guided intervention in experimental colitis.