Nuciferine Ameliorates Ovariectomy-Induced Bone Loss via TFEB-Mediated Autophagy-Lysosomal Pathway

Background: Postmenopausal osteoporosis is a common metabolic bone disease that leads to reduced bone formation and increased fracture risk. Nuciferine, an aporphine alkaloid from the lotus leaf, can regulate the TFEB-mediated autophagy-lysosomal pathway. This pathway is critical for osteogenic differentiation. However, it remains unclear whether nuciferine promotes bone formation and alleviates bone loss through this pathway. We therefore hypothesized that nuciferine activates the TFEB-mediated autophagy-lysosomal pathway to promote osteogenic differentiation, thereby counteracting estrogen deficiency-induced bone loss. Methods: We established an OVX rat model (6-month-old females, 24.0 ± 1.0 weeks, n = 10/group), treated the rats with nuciferine via oral gavage for 12 weeks, and used rat BMSCs for mechanistic studies in vitro. Results: Nuciferine significantly increased bone mineral density (BMD) and improved bone microarchitecture in OVX rats; upregulated serum levels of the bone turnover markers bone-specific alkaline phosphatase (BALP), procollagen type I N-terminal propeptide (PINP) and osteocalcin (BGP); and downregulated serum tartrate-resistant acid phosphatase (TRAP), as measured via ELISA. Nuciferine also restored the expression of osterix (OSX) and transcription factor EB (TFEB) in bone tissue, as detected via TSA staining. Furthermore, it increased the microtubule-associated protein 1 light chain 3 (LC3)-II/LC3-I ratio and decreased p62 expression, as determined through Western blotting, indicating the activation of autophagy. In vitro, nuciferine promoted osteogenic differentiation and TFEB nuclear translocation in BMSCs, whereas TFEB silencing suppressed both, an effect partially reversed by nuciferine, as shown via ALP/ARS staining, Western blotting, RT-qPCR, and immunofluorescence. Conclusions: In conclusion, nuciferine ameliorates bone loss in OVX rats and promotes the osteogenic differentiation of BMSCs. Activation of the TFEB-mediated autophagy-lysosomal pathway is a key mechanism underlying its improvement of bone metabolism.