Mitochondrial DNA contributes to dysbiosis-associated mastitis via activation of the cGAS-STING pathway

Bovine mastitis is widely recognized as being primarily caused by exogenous pathogens. However, in clinical settings, pathogenic bacteria are frequently undetectable in the milk of affected cows. Recent studies have shown that gastrointestinal disorders, such as subacute ruminal acidosis (SARA), which disturb the balance of the gut microbiota, commonly occur as secondary conditions in conjunction with mastitis. The microbiota-gut-mammary axis is increasingly acknowledged as a key contributor to the progression of mastitis; however, the precise underlying mechanisms remain to be fully elucidated. In this study, we established a SARA-associated mastitis model in dairy goats by administering a high-concentrate diet (HCD). Our findings demonstrated that HCD feeding led to disruption of the rumen microbiota and structural damage to the rumen epithelium. Moreover, serum lipopolysaccharide (LPS) levels were significantly elevated, accompanied by increased systemic inflammation and damage to the blood-milk barrier. Notably, mitochondrial DNA (mtDNA) levels were elevated in both the rumen and mammary gland tissues. We further observed activation of the cGAS-STING signaling pathway, which subsequently triggered the NF-κB and NLRP3 inflammatory pathways, resulting in increased production of pro-inflammatory cytokines, including TNF-α and IL-1β. Importantly, mice that received rumen microbiota transplants (RMT) from SARA-affected goats developed mastitis with pathological features closely resembling those observed in the goat model. Additionally, mtDNA isolated from the mammary glands of SARA-associated mastitis goats induced inflammatory responses in recipient mammary tissues, as evidenced by increased tissue damage and elevated inflammatory markers. Our results collectively confirm that gut microbiota dysbiosis leads to elevated mammary mtDNA levels, which activate the cGAS-STING signaling pathway and contribute to the inflammatory processes underlying mastitis. These findings highlight a promising strategy for mastitis management through targeted regulation of the gut microbiota.

Gut microbiota; Mastitis; Mitochondrial DNA; cGAS-STING.