Dietary supplementation with milk-derived Bifidobacterium animalis subsp. lactis relieves colitis-linked reproductive disorders via gut-testis axis

Rapid urbanization, medication, and modern dietary patterns are the main challenges leading to impaired fertility, with a lack of effective therapies. Emerging evidence suggests that reproductive disorders may be closely associated with intestinal damage or occasionally worsen by the side effects of medications. Therefore, the development of dietary supplements as alternatives is crucial for intestinal-linked reproductive health. Milk and dairy products are essential in dietary nutrition with great potential functional ingredients. Bifidobacterium animalis subsp. lactis NJ241 (NJ241), a promising probiotic isolated from naturally fermented bovine milk, remains underexplored. This study aims to investigate the molecular mechanisms of NJ241 on colitis and its associated reproductive disorders. The biomarker microbes and their correlated metabolites were further explored by 16S rRNA sequencing and metabolomics. Hematological analysis and histopathological examination were applied for conjoined identification. Results indicated that NJ241 effectively restored the expression levels of Claudin-2 and MLCK1, reducing intestinal permeability. Multi-omics results further revealed that NJ241 may effectively improve gut barrier integrity by increasing the abundance of Akkermansia muciniphila and its metabolite trans-ferulic acid. This effect was accompanied by a reduction in the pro-inflammatory cytokine IL-6 in both serum and testicular tissue, mediated through the TLR4 signaling pathway. Consequently, the restoration of microbiota homeostasis and a systemic reduction in inflammation rescued testicular spermatogenesis, which was impaired by colitis. The current findings consistently elucidated the potential molecular mechanism by which NJ241 ameliorates colitis-linked reproductive disorders through the gut-testis axis. Additionally, NJ241 demonstrates promise as a probiotic supplement for the development of fortified dairy products and provides strong evidence for the potential reproductive health benefits of naturally fermented bovine milk.