Exosomal circRNA Transcriptome Analysis of Porcine Intestinal Epithelial Cells Under E. coli F18 Infection

Enterotoxigenic Escherichia coli F18 (E. coli F18) ranks as the leading bacterial cause of diarrhea in piglets. Exosomes and other extracellular vesicles ferry diverse RNA species, among them mRNAs and non-coding RNAs, and act as central intermediaries in intercellular communication. Their contribution to the biology of E. coli F18-infected IPEC-J2 cells, however, has received no attention. In this study, we characterized the morphology, particle dimensions, and output of exosomes secreted by control and E. coli F18-infected cells, then profiled their circRNA cargo by RNA-seq. Nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM), and Western blotting verified that the vesicle-like particles recovered from IPEC-J2 cultures were bona fide exosomes. We then catalogued the circRNAs within IPEC-J2-derived exosomes during E. coli F18 infection. Comparing the two groups yielded 280 differentially expressed circRNAs (DECs), of which circCHUK displayed the largest shift. circCHUK abundance rose sharply in E. coli F18-treated IPEC-J2 cells. Knocking down or overexpressing circCHUK markedly altered the adherence of E. coli F18 to IPEC-J2 cells. ceRNA network construction pinpointed the exo-circCHUK/ssc-miR-339-3p/FUT2 as candidate axis. Collectively, we speculated that exo-circCHUK is a new biomarker that regulates E. coli F18 susceptibility, offering a conceptual framework for tackling bacterial diarrhea in piglets.