Retinoic acid-related orphan nuclear receptor alpha inhibits adipogenic differentiation of bone marrow mesenchymal stem cells via activating WNT/β-catenin signaling pathway.

BACKGROUND: The balance between adipogenic and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) is essential for maintaining bone homeostasis. This study aimed to investigate the role of retinoid-related orphan receptor α (RORα) in the adipogenic differentiation of BMSCs. METHODS: Stable BMSC lines with RORα overexpression or knockdown were established. Adipogenic differentiation was evaluated using Oil Red O staining and by measuring the expression of adipogenic markers, including PPARγ2, LPL, LEP, FABP4, and ADIPOQ. RESULTS: Treatment with the RORα inhibitor SR3335 significantly promoted adipogenic differentiation, whereas the RORα agonist SR1078 exerted the opposite effect. Similarly, RORα-overexpressing (OE-RORα) BMSCs showed reduced adipogenic differentiation, while RORα knockdown BMSCs exhibited enhanced differentiation at 14 days after induction. During adipogenesis, PPARγ2 expression increased significantly, peaking at day 6 before gradually declining. Overexpression and knockdown of RORα accentuated this downregulation and upregulation, respectively, at days 6 and 12. The adipogenic marker genes lipoprotein lipase (LPL), leptin (LEP), fatty acid binding protein 4 (FABP4), and adiponectin C1Q and collagen domain containing (ADIPOQ) were markedly downregulated in RORα-overexpressing BMSCs at day 12. Moreover, RORα overexpression enhanced β-catenin nuclear translocation at day 1 post-induction and upregulated downstream WNT/β-catenin signaling molecules (Axin2, c-Myc, CD44) at day 6. Inhibition of WNT/β-catenin signaling with XAV-939 effectively reversed the suppressive effect of RORα overexpression on adipogenic differentiation and restored the expression of adipogenesis-related genes. CONCLUSION: RORα suppresses adipogenic differentiation of BMSCs, at least in part, by activating WNT/β-catenin signaling.