Extracellular vesicles containing microbial DNA contribute to ruminal dysbiosis-induced mastitis by activating cGAS-STING-NF-κB/NLRP3 pathway

Background: An imbalance in the rumen microbiota caused by high-concentrate diets (HCD) is a significant endogenous trigger of mastitis. However, the underlying mechanisms remain largely unknown. Microbial extracellular vesicles (mEVs) are critical mediators of microbe-host communication. However, the role of mEVs in rumen microbiota-mediated mastitis has not yet been reported. In this study, we used an HCD-induced rumen microbiota dysbiosis model to investigate the role of mEVs-derived from rumen microbiota in the pathogenesis of mastitis.

Results: Our results indicate that HCD leads to mastitis and systemic inflammation. Meanwhile, HCD-fed goats exhibited substantial rumen microbiota dysbiosis and the disruption of the rumen barrier. Transplanting rumen microbiota from HCD goats into mice induced both mastitis and systemic inflammation in the recipients. Specifically, HCD increases the production of mEVs carrying microbial DNA, which can translocate across the compromised rumen barrier to the mammary gland, triggering a mammary inflammatory response via activation of the cGAS-STING-NF-κB/NLRP3 pathway. Furthermore, treating mice with mEVs isolated from the rumen fluid of HCD goats directly induced mastitis, whereas depletion of microbial DNA attenuated mEVs-induced mastitis.

Conclusion: Our findings suggest that HCD induces rumen microbiota dysbiosis and impairs rumen barrier function. This dysfunction leads to an increase in microbial DNA-containing mEVs, which subsequently leak into the mammary gland. Once there, these mEVs activate the cGAS-STING-NF-κB/NLRP3 signaling pathway, ultimately inducing mastitis. This study provides a new perspective on the "rumen microbiota-mammary gland axis" and enhances the understanding of the pathogenesis of mastitis.

CGAS-STING-NF-κB/NLRP3; Extracellular vesicles; Mastitis; Microbial DNA; Rumen microbiota.