title: Linarin promotes osteogenic differentiation by activating the BMP-2/RUNX2 pathway via protein kinase A signaling.
abstract: Linarin (LIN), a flavonoid which exerts both anti-inflammatory and antioxidative effects, has been found to promote osteogenic differentiation. However, the molecular mechanism of its effect on osteoblast differentiation was unclear. In the present study, LIN from Flos Chrysanthemi Indici (FCI) was isolated in order to investigate the underlying mechanisms of LIN on MC3T3-E1 cells (a mouse osteoblastic cell line) and the osteoprotective effect of LIN in mice which had undergone an ovariectomy (OVX). The results revealed that LIN enhanced osteoblast proliferation and differentiation in MC3T3-E1 cells dose‑dependently, with enhanced alkaline phosphatase (ALP) activity and mineralization of extracellular matrix. LIN upregulated osteogenesis-related gene expression, including that of ALP, runt‑related transcription factor 2 (RUNX2), osteocalcin (OCN), bone sialoprotein (BSP), and type I collagen (COL‑I). Pretreatment with noggin, a bone morphogenetic protein-2 (BMP-2) antagonist, meant that LIN-induced gene expression levels of COL-1, ALP, OCN, BSP and RUNX2 were significantly reduced, as shown by RT-qPCR. Western blot analysis showed that LIN dose‑dependently increased the protein levels of BMP-2 and RUNX2 and enhanced the phosphorylation of SMAD1/5. In addition, LIN dose‑dependently upregulated protein kinase A (PKA) expression. H-89 (a PKA inhibitor) partially blocked the LIN-induced protein increase in BMP-2, p-SMAD1/5 and RUNX2. We noted that LIN preserved the trabecular bone microarchitecture of ovariectomized mice in vivo. Moreover, pretreatment with LIN significantly lowered serum levels of ALP and OCN in ovariectomized mice. Our data indicated that LIN induced the osteogenic differentiation and mineralization of MC3T3-E1 osteoblastic cells by activating the BMP-2/RUNX2 pathway through PKA signaling in vitro and protected against OVX-induced bone loss in vivo. The results strongly suggest that LIN is a useful natural alternative for the management of postmenopausal osteoporosis.
authors.affiliation: Shanghai Engineering Research Center of Tooth Restoration and Regeneration, Department of Prosthodontics, School of Stomatology, Tongji University, Shanghai 200072, P.R. China.
authors.forename: Jia
authors.initials: J
authors.lastname: Li
authors.affiliation: Shanghai Engineering Research Center of Tooth Restoration and Regeneration, Department of Prosthodontics, School of Stomatology, Tongji University, Shanghai 200072, P.R. China.
authors.forename: Lingyu
authors.initials: L
authors.lastname: Hao
authors.affiliation: Shanghai Engineering Research Center of Tooth Restoration and Regeneration, Department of Prosthodontics, School of Stomatology, Tongji University, Shanghai 200072, P.R. China.
authors.forename: Junhua
authors.initials: J
authors.lastname: Wu
authors.affiliation: Ministry of Education, Engineering Research Center of Modern Preparation Technology of TCM, Shanghai University of Traditional Chinese Medicine, Shanghai 201203, P.R. China.
authors.forename: Jiquan
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Shanghai Engineering Research Center of Tooth Restoration and Regeneration, Department of Prosthodontics, School of Stomatology, Tongji University, Shanghai 200072, P.R. China.
authors.forename: Jiansheng
authors.initials: J
authors.lastname: Su
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D031202:Chrysanthemum / Q000737:chemistry; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005260:Female; D006027:Glycosides / Q000737:chemistry / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects*; D010024:Osteoporosis / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control; D015398:Signal Transduction / Q000187:drug effects
chemical_list: C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D050659:Core Binding Factor Alpha 1 Subunit; D006027:Glycosides; C493716:Runx2 protein, mouse; D017868:Cyclic AMP-Dependent Protein Kinases; D000469:Alkaline Phosphatase; C008282:linarin