Protective effects of naringin on glucocorticoid-induced osteoporosis through regulating the PI3K/Akt/mTOR signaling pathway

Objective: To investigate the protective effects of Naringin on glucocorticoid-induced osteoporosis (GIOP) through the PI3K/AKT/mTOR signaling pathway in vivo and in vitro. Methods: Osteoblasts were cultured from the differentiated bone marrow mesenchymal stem cells (BM-MSCs) and were grouped as follows: the PBS group (the control group), the model group (Dexamethasone intervention), the LY294002 group (PI3K/AKT/mTOR pathway inhibitor intervention), the Naringin group (Naringin intervention), and the LY294002+ Naringin intervention group. Cell proliferation and differentiation were detected through cell counting kit-8 (CCK8) assay and alkaline phosphatase (ALP) staining, respectively. The formation of autophagosome was observed by Monodansylcadaverine (MDC) staining. Expressions of signaling pathway and autophagy related factors such as Beclin-1 and p62 were detected by qRT-PCR and western blot. Then, the rats were grouped as the PBS group (normal rats injected with PBS), the model group (GIOP rats injected with dexamethasone), the LY294002 group (GIOP rats injected with PI3K/AKT/ mTOR pathway inhibitor LY294002), the Naringin group (GIOP rats injected with Naringin) and the LY294002+ Naringin group (GIOP rats injected with PI3K/AKT/mTOR pathway inhibitor LY294002 and Naringin). Bone mineral density and bone histomorphometry parameters of rats in each group were compared. In addition, the expressions of pathway and autophagy related factors in cartilage tissue of rats in each groups were also detected. Results: The proliferation and differentiation abilities of osteoblasts were increased with an increasing concentration of Naringin in a dose-dependent manner. Compared with the model group, the expression of PI3K/AKT/mTOR pathway related phosphorylated proteins, the proliferation and differentiation abilities of osteoblasts, the expression of autophagosome and autophagy related factors were all increased in the Naringin group, but contrary results were found in the LY294002 group (all P<0.05). In vivo, GIOP rats had improved bone mineral density and bone morphology parameters , and elevated expressions of autophagy related factors in cartilage tissue compared to the model group through Naringin intervention, while LY294002 intervention showed the opposite effects (all P<0.05). What is more, LY294002 partially reversed the effects of Naringin on osteogenic differentiation and bone morphological parameters in GIOP. Conclusion: Naringin exerts protective effects in GIOP by the PI3K/AKT/mTOR pathway, which may be related to autophagy induction and enhanced proliferation of osteoblasts.