Lactococcus lactis and Bifidobacterium bifidum alleviate postmenopausal symptoms by suppressing NF-κB signaling and microbiota dysbiosis.

To understand the action mechanism of probiotics against postmenopausal symptoms, we examined the effects of Lactococcus lactis P32 (P) and Bifidobacterium bifidum P45 (P), which suppressed interleukin (IL)-6 and receptor activator of nuclear factor-κB (RANK) ligand (RNAKL) expression in Gardnerella vaginalis (Gv)-stimulated macrophages, on vaginitis, osteoporosis, and depression/cognitive impairment (DC) in mice with vaginally infected Gv, ovariectomy (Ov), or Ov/Gv (oG). Oral administration of P or P decreased Gv-induced DC-like behavior and tumor necrosis factor (TNF)-α, IL-6, RANK, and/or RANKL expression in the vagina, bone, hypothalamus, hippocampus, and colon, while Gv-suppressed bone osteoprotegerin and brain serotonin and brain-derived neurotrophic factor (BDNF) levels increased. They partially shifted vaginal and gut dysbiosis in Gv-infected mice to the gut microbiota composition in normal control mice. In mice with oG, oral administration of P or P decreased oG-induced DC-like behavior and TNF-α, IL-6, RANK, and/or RANKL expression in the vagina, bone, brain, and colon, while oG-suppressed bone osteoprotegerin and brain serotonin and BDNF levels increased. They also alleviated oG-induced vaginal and gut dysbiosis: they decreased Proteobacteria population. P and P (4:1) mix (P) suppressed DC-like behavior in mice with Gv, Ov, or oG. P also suppressed TNF-α, IL-6, RANK, and/or RANKL expression in the vagina, bone, colon, and brain. P alleviated Gv-induced vaginal and gut dysbiosis: it decreased Proteobacteria population. These findings suggest that P and P, singly or together, can alleviate postmenopausal symptoms including vaginitis, colitis, osteoporosis, and DC by suppressing RANK/RANKL-mediated NF-κB activation and alleviating vaginal/gut microbiota dysbiosis.