Autophagy-induced osteoblast-derived exosomes maintain bone formation and prevent osteoporosis by remodeling gut microbiota-metabolism.

BACKGROUND: Osteoporosis is a chronic disease of bone metabolism with high incidence rates. Recently, exosome therapy has emerged as a promising avenue for the treatment of osteoporosis. However, the role of autophagy-induced osteoblast-derived exosomes (Auto-exo) in osteoporosis has yet to be elucidated. METHODS: The effect of Auto-exo on bone formation was assessed in vivo. The composition of gut microbiota was determined through 16S rDNA sequencing, and metabolite profiles were analyzed using liquid chromatography-mass spectrometry (LC-MS). Cell experiments were conducted to explore the role of bilirubin in bone formation. RESULTS: Auto-exo were successfully isolated and identified. Auto-exo promoted bone formation and alleviated osteoporosis progression in a mouse model of osteoporosis. 16S rDNA sequencing revealed that Auto-exo changed diversity and composition of gut microbiota in osteoporotic mice, with a notable increase in Lactobacillus and a decrease in Dubosiella and Faecalibaculum. LC-MS analysis indicated that Auto-exo treatment reduced the elevated levels of bilirubin in osteoporotic mice. Cell experiments uncovered that bilirubin remarkably inhibited osteoblast differentiation. Furthermore, Auto-exo promoted osteoblast differentiation via inhibiting bilirubin production. CONCLUSIONS: Our findings demonstrated that Auto-exo promoted bone formation by modulating the gut microbiota-metabolite bilirubin axis, thereby alleviating osteoporosis progression. This discovery provides a novel perspective on the mechanism underlying the therapeutic effects of Auto-exo on osteoporosis.