Fusobacterium nucleatum Extracellular Vesicles Promote Experimental Colitis by Modulating Autophagy via the miR-574-5p/CARD3 Axis

Background Ulcerative colitis (UC) may be exacerbated by Fusobacterium nucleatum (Fn) infection. However, the mechanism underlying Fn-mediated progression of UC has yet to be established. Here, we aimed to establish whether and how Fn-derived extracellular vesicles (Fn-EVs) participate in the development of experimental colitis through microRNAs (miRNAs). Methods EVs were isolated and purified by ultracentrifugation from Fn and Escherichia coli culture supernatants. Differentially expressed miRNAs in control intestinal epithelial cells (IECs) and Fn-EV-treated IECs were identified by miRNA sequencing. EVs were cocultured with IECs or administered to CARD3(wt)/CARD3(-/-) mice by gavage to assess inflammatory responses to and the mechanism of action of Fn-EVs. Results Fn-EVs promoted upregulation of proinflammatory cytokines (interleukin [IL]-1 beta, IL-6, tumor necrosis factor alpha), downregulation of anti-inflammatory IL-10 and intercellular tight junction proteins ZO-1 and occludin, and epithelial barrier dysfunction in IECs. Fn-EVs significantly aggravated experimental colitis in mice associated with Fn-EV-mediated downregulation of miR-574-5p expression and autophagy activation. Blockade of autophagy using chloroquine alleviates barrier damage exacerbated by Fn-EVs in vitro and in vivo. Inhibition of the miR-574-5p/CARD3 axis reduced the severity of colitis, epithelial barrier damage, and autophagy activation induced by Fn-EVs. Conclusions Here, we describe a new mechanism by which Fn-EVs mediate experimental colitis severity through miR-574-5p/CARD3-dependent autophagy activation, providing a novel target for UC monitoring and targeted therapy. Lay Summary Fusobacterium nucleatum-derived extracellular vesicles (Fn-EVs) alter the microRNA profile of intestinal epithelial cells and colitis tissues, especially the expression of miR-574-5p. Fn-EVs mediate experimental colitis severity through miR-574-5p/CARD3-dependent autophagy activation. Hence, inhibiting Fn-EV-activated autophagy or targeting the miR-574-5p/CARD3 axis may be potential new therapeutic strategies in ulcerative colitis.