Metagenome of intestinal flora in retinoic acid-induced osteoporotic mice after Bifidobacterium longum intervention

The elderly population is prone to osteoporosis owing to the deterioration of skin, liver, and kidney functions. Vitamin D (VD) supplementation has a limited effect, and VD deficiency is mostly treated with medication. Several studies have shown that the gut microbiota alters intestinal VD metabolism and that probiotic supplements can influence circulating VD levels. Therefore, in the present study, we screened a strain of Bifidobacterium longum FSHHK13M1 that can increase the level of VD metabolites in the fermented supernatant species in vitro by modeling fecal bacterial fermentation. The results showed that FSHHK13M1 intervention significantly increased the serum levels of 1,25-dihydroxy VD and osteocalcin. It activated the expression of the VDR, OPG, Wnt10b/b-catenin and Runx2/Osterix pathways and inhibited the expression of RANKL/RANK pathway. Furthermore, there was an enhancement in the quantity of bone trabeculae and the proportion of bone volume. Concurrently, the gut microbiota in mice with osteoporosis exhibited signs of imbalance. FSHHK13M1 intervention increased the relative abundance of specific bacteria, such as Faecalibaculum rodentium, Limosilactobacillus fermentum, Bifidobacterium pseudolongum, and Akkermansia muciniphila. These results suggest that B. longum FSHHK13M1 alleviates retinoic acid-induced osteoporosis symptoms by modulating related genes, regulating the intestinal flora and increasing the level of active VD.