Dexamethasone reduces osteogenic potential through suppressing retinoic acid signaling via NF-κB/CYP26B1 axis in mesenchymal stem cells

Glucocorticoid-induced osteoporosis (GIOP) is the most common secondary osteoporosis, which characterized by the decreased bone strength and increased fracture risk. But the pathogenic causes of GIOP remains not completely yet. In this study, we investigated the effect of Cyp26b1 , a key enzyme for all-trans retinoic acid (ATRA) degradation, on the osteogenic inhibitory effect of dexamethasone (DEX) in mesenchymal stem cells (MSCs) and revealed the possible mechanism through which DEX regulates the expression of Cyp26b1 . MSCs were induced with osteogenic induction medium in vitro to establish the osteogenic model, and high concentration (10 − 6 M) of DEX was utilized to treat MSCs to exert its osteogenic inhibitory effect. ATRA content was detected with ELISA, real-time polymerase chain reaction (RT-PCR), western blot, and immunofluorescence staining were employed to detect hall markers for osteogenic differentiation. Chromatin immunoprecipitation (ChIP) assay was used to detect the binding of promoter region of target gene. The rat GIOP model was constructed by intraperitoneal injection of DEX, and the adeno-associated virus was injected via tail vein after the model was constructed. The bone samples were subjected with µ-CT scanning, H&E, and Masson trichrome staining, respectively. DEX (10 − 6 M) decreased the levels of osteogenic markers induced by osteogenic induction medium (OIM) in MSCs, and it was almost reversed by ATRA. But this effect of ATRA was obviously eliminated by overexpression of Cyp26b1 . The mRNA expression level of Cyp26b1 was significantly increased by DEX (10 − 6 M), and the content of retinoic acid was decreased in cells. Osteogenic markers decreased by DEX (10 − 6 M) were recovered by Cyp26b1 knockdown, whereas Cyp26b1 overexpression exerted the opposite effect. DEX (10 − 6 M) increased the activation of NF-κB signaling, and the osteogenic inhibitory effects of DEX were ameliorated by NF-κB inhibitors which was almost abolished by Cyp26b1 overexpression. The mRNA level of Cyp26b1 was up-regulated by DEX (10 − 8 M and 10 − 6 M), but the degradation of Cyp26b1 was promoted by DEX (10 − 8 M) only via the lysosomal pathway. The osteogenic inhibitory effect of high concentration of DEX may be resulted from the disturbance of retinoic acid signaling. The expression of Cyp26b1 can be up-regulated by either low or high concentration of DEX, but its degradation can only be inhibited by high concentration of DEX. The effect of DEX on Cyp26b1 expression was partially mediated by activating NF-κB signaling in MSCs.