Fibroblast growth factor 2 stimulation of osteoblast differentiation and bone formation is mediated by modulation of the Wnt signaling pathway

Fibroblast growth factor 2 (FGF2) positively modulates osteoblast differentiation and bone formation. However, the mechanism( s) is not fully understood. Because the Wnt canonical pathway is important for bone homeostasis, this study focuses on modulation of Wnt/β-catenin signaling using Fgf2 ^-/- mice (FGF2 all isoforms ablated), both in the absence of endogenous FGF2 and in the presence of exogenous FGF2. This study demonstrates a role of endogenous FGF2 in bone formation through Wnt signaling. Specifically, mRNA expression for the canonical Wnt genes Wnt10b, Lrp6, and β-catenin was decreased significantly in Fgf2 ^-/- bone marrow stromal cells during osteoblast differentiation. In addition, a marked reduction of Wnt10b and β-catenin protein expression was observed in Fgf2 ^-/- mice. Furthermore, Fgf2 ^-/- osteoblasts displayed marked reduction of inactive phosphorylated glycogen synthase kinase-3β, a negative regulator of Wnt/β-catenin pathway as well as a significant decrease of Dkk2 mRNA, which plays a role in terminal osteoblast differentiation. Addition of exogenous FGF2 promoted β-catenin nuclear accumulation and further partially rescued decreased mineralization in Fgf2 ^-/- bone marrow stromal cell cultures. Collectively, our findings suggest that FGF2 stimulation of osteoblast differentiation and bone formation is mediated in part by modulating the Wnt pathway.