FTO-mediated m6A demethylation of FN1 mRNA modulates S. aureus adhesion and host cell death.

Bovine mastitis caused by Staphylococcus aureus leads to major economic losses, largely due to the pathogen's ability to establish persistent and recurrent infections. The strategies it uses to subvert host defenses, especially those involving epitranscriptomic regulation, are not well defined. Infection by S. aureus is shown to remodel the host N6-methyladenosine (m6A) epitranscriptome, characterized by upregulation of the eraser fat mass and obesity-associated protein (FTO) and downregulation of the reader YTH domain-containing family protein 2 (YTHDF2). This remodeling targets fibronectin (FN1), a key host matrix protein, where FTO-mediated m6A demethylation stabilizes FN1 mRNA and increases its expression. Unexpectedly, functional manipulation of FTO revealed a bidirectional regulatory outcome: FTO knockdown enhanced FN1-mediated S. aureus adhesion and suppressed host cell death, whereas FTO overexpression reduced adhesion but exacerbated cell death. In a mammary epithelial-specific Fto knockout mouse model, FTO deficiency attenuated S. aureus-induced tissue damage and inflammation, phenocopying the protective effects observed in vitro. These results identify the FTO-m6A-FN1 axis as a critical modulator of S. aureus-host interactions, with FTO deficiency enhancing bacterial adhesion while protecting host cells from death, and FTO overexpression exerting opposing effects. This bidirectional regulation reveals an epitranscriptomic trade-off in the host response to mastitis and highlights potential targets for genetic improvement of disease resistance in dairy cattle.