Staphylococcus aureus rewires arginine metabolism to drive mammary aging via macrophage–epithelial crosstalk

As a common opportunistic pathogen, Staphylococcus aureus ( S. aureus ) can rapidly adapt to the host immune system and cause chronic infections. Currently, such chronic infections are extremely difficult to eliminate, severely impairing the function of tissues and organs. We observed localized tissue senescence in the mammary glands of mice with chronic S. aureus infection; however, the mechanism driving this senescence remains unclear. To address this, we employed a mouse model of chronic S. aureus -induced mastitis and an in vitro model of mouse mammary epithelial cells (mMECs) to confirm the inductive effect of S. aureus on tissue and cellular senescence. Through integrated analysis of the transcriptome and metabolome of mouse mammary tissues, it was found that the ornithine cycle was significantly disordered following S. aureus infection, wherein Arginase 1 (Arg1) serves as a key metabolic regulator. Notably, stimulation by S. aureus induces mammary epithelial cells to produce cytokines, thereby promoting the massive release of Arg1 by macrophages into the microenvironment, which constitutes one of the sources of abnormally elevated Arg1 in mammary tissue. This extracellular Arg1 is subsequently taken up by mammary epithelial cells, further accelerating the intracellular conversion of arginine to ornithine. The accumulation of ornithine and its downstream metabolites drives the occurrence of senescence in epithelial cells. Importantly, supplementation with excess arginine or ornithine can mimic this senescence phenotype, while knocking down Arg1 in epithelial cells can reverse this phenomenon. In summary, this study reveals a novel immunometabolic cross-regulation mechanism, specifically that Arg1 released by macrophages—triggered by mammary epithelial cells under S. aureus stimulation—acts as a paracrine senescence-inducing factor that acts back on mammary epithelial cells. The Arg1—ornithine axis holds promise as a potential therapeutic target for chronic infection-associated tissue senescence. This study found that S. aureus stimulation induces senescence in mouse mammary glands and mMECs. In mMECs, S. aureus directly induces senescence-associated changes, including activation of p53/p21, DNA damage, and SASP-related inflammatory responses, despite reduced endogenous Arg1 expression. Meanwhile, the compensatory upregulation of Arg2 and other ornithine-cycle enzymes suggests that arginine/ornithine metabolism is remodeled in epithelial cells. In the tissue microenvironment, epithelial-derived inflammatory mediators further stimulate macrophages to express and release Arg1. This macrophage-derived Arg1 can be taken up by mMECs and may amplify epithelial senescence by promoting arginine-to-ornithine metabolic dysregulation. Therefore, macrophage-derived Arg1 promotes epithelial senescence but is not the sole initiator of this process.