Icariin regulates the Hippo/TAZ signaling pathway to promote osteogenic differentiation and bone remodeling in osteoporosis.

BACKGROUND: Osteoporotic bone defects pose significant clinical challenges. While icariin (ICA) exhibits pro-osteogenic effects in vitro, its capacity to repair osteoporosis (OP)-related bone defects remains unverified. This study investigates ICA' s therapeutic role in bone regeneration and elucidates its molecular mechanisms via the Hippo pathway in bone marrow mesenchymal stem cells (BMSCs) and OP rats.

METHODS: Rat BMSCs were isolated and characterized by flow cytometry (CD29+/CD34-/CD45-). BMSCs were induced under osteogenic conditions with ICA at 25 and 50 mg/L. Osteogenic differentiation and mineralization were assessed by ALP and Alizarin Red staining and by measuring mRNA and protein levels of ALP, Runx2, and OCN. The Hippo/TAZ pathway was evaluated by Western blot and qPCR for MST1, p-MST1, TAZ, and p-TAZ. A rescue experiment employed the Hippo pathway agonist lysophosphatidic acid (LPA). An ovariectomized (OVX) rat model of osteoporosis was established to validate ICA's effects in vivo, examined by micro-CT, histology, and tibial expression analyses of osteogenic markers and Hippo/TAZ signaling components.

RESULTS: ICA promoted osteogenic differentiation and mineralization of BMSCs. Mechanistically, ICA did not alter MST1 or TAZ transcripts but markedly reduced MST1 and TAZ phosphorylation, thereby stabilizing total TAZ and enhancing downstream osteogenesis. Co-treatment with LPA abrogated ICA-induced osteogenesis, confirming Hippo/TAZ pathway dependence. In OVX rats, ICA mitigated bone loss, improved trabecular microarchitecture (BMD, BV/TV, Tb.N), and upregulated tibial expression of ALP, Runx2, and OCN. Consistently, ICA reduced p-MST1 and p-TAZ levels and increased total TAZ in bone tissues.

CONCLUSION: ICA promotes bone formation both in vitro and in vivo by inhibiting Hippo kinase activity and stabilizing TAZ, thereby enhancing osteogenic differentiation. Our findings identify the Hippo/TAZ axis as a potential therapeutic target for OP and support further translational exploration of ICA as an anti-osteoporotic agent.