Sph-mediated mtDNA release and autophagy-dependent ferroptosis contribute to Staphylococcus aureus-induced mastitis

Staphylococcus aureus (S. aureus), a major pathogen of mastitis, employs a diverse arsenal of virulence factors to invade and disrupt mammary tissues, thereby eliciting a complex and dysregulated inflammatory response. Sphingomyelin phosphodiesterase (Sph) has emerged as a key virulence determinant of S. aureus; however, its potential role and underlying mechanisms in mastitis remain elusive. In this study, we demonstrate that Sph deficiency significantly suppresses S. aureus-induced ferroptosis. Mechanistically, Sph disrupts mitochondrial cristae through interaction with Mic60, a core component of the mitochondrial contact site and cristae-organizing system (MICOS). Sph-mediated cytosolic mitochondrial DNA (mtDNA) released is sensed by cyclic GMP-AMP synthase (cGAS), leading to activation of the STING signaling pathway, which further triggers the recruitment of GPX4 into the autophagy-lysosome pathway for degradation. Collectively, our study unveils a novel pathogenic mechanism whereby the S. aureus virulence factor Sph perturbs mitochondrial homeostasis, and engages the cGAS-STING axis to promote GPX4 degradation and ferroptosis, highlighting Sph as a potential therapeutic target for S. aureus-associated mastitis.