Contents lists available at ScienceDirect Bone Reports journal homepage: www.elsevier.com/locate/bonr FGF2 crosstalk with Wnt signaling in mediating the anabolic action of PTH on bone formation Liping Xiao, Yurong Fei 1 , Marja M. Hurley ⁎ Department of Medicine, UConn Health, Farmington, CT 06030, USA ARTICLE INFO Keywords: PTH FGF2 Wnt signaling Bone ABSTRACT The mechanisms of the anabolic effect of parathyroid hormone (PTH) in bone are not fully defined. The bone anabolic effects of PTH require fibroblast growth factor 2 (FGF2) as well as Wnt signaling and FGF2 modulates Wnt signaling in osteoblasts. In vivo PTH administration differentially modulated Wnt signaling in bones of wild type (WT) and in mice that Fgf2 was knocked out (Fgf2KO). PTH increased Wnt10b mRNA and protein in WT but not in KO mice. Wnt antagonist SOST mRNA and protein was significantly higher in KO group. However, PTH decreased Sost mRNA significantly in WT as well as in Fgf2KO mice, but to a lesser extent in Fgf2KO. Dickhopf 2 (DKK2) is critical for osteoblast mineralization. PTH increased Dkk2 mRNA in WT mice but the response was impaired in Fgf2KO mice. PTH significantly increased Lrp5 mRNA and phosphorylation of Lrp6 in WT but the increase was markedly attenuated in Fgf2KO mice. PTH increased β-catenin expression and Wnt/β-catenin transcriptional activity significantly in WT but not in Fgf2KO mice. These data suggest that the impaired bone anabolic response to PTH in Fgf2KO mice is partially mediated by attenuated Wnt signaling. 1. Introduction Osteoporosis is a disease characterized by low bone mass and a deterioration in the micro-architecture of bone tissue, which leads to bone fractures (Holroyd et al., 2008). In year 2025 an estimated 44 million Americans are threatened by osteoporosis and the cost for os- teoporosis-related fractures is predicted to be $25.3 billion (NOF, 2013). Therefore, osteoporosis is an enormous health and economic problem. Parathyroid hormone (PTH) is currently the only anabolic agent for treatment of osteoporosis in the U.S. Since 2002, when the FDA approved intermittent PTH administration, great progress has been made in understanding how intermittent PTH treatment mediates its anabolic bone response. However, the detailed mechanisms of PTH actions are not fully defined. We previously showed that maximal bone anabolic effects of PTH require fibroblast growth factor 2 (FGF2). PTH induced FGF2 and FGF receptor mRNA expression in osteoblast cells (Hurley et al., 1999). In addition, PTH treatment increased serum FGF2 in osteoporotic subjects together with enhanced bone formation (Hurley et al., 2005). However, the anabolic response of PTH on bone formation in mice was impaired in the absence of endogenous FGF2 (Hurley et al., 2006)(Fei et al., 2011b). These data suggest that endogenous FGF2 is required for maximal bone anabolic response of PTH. FGF2 is one member of the FGF family. It is expressed in osteoblasts and stored in the extracellular matrix (Ornitz and Marie, 2015). FGF2 stimulates osteoblast precursor proliferation (Fei and Hurley, 2012; Hurley et al., 2002). Although continuous administration of FGF2 de- creases osteoblast differentiation markers, intermittent FGF2 treatment stimulates osteoblast differentiation and bone formation in vitro and in vivo (Hurley et al., 2002; Montero et al., 2000). Fgf2KO mice further reveal the importance of FGF2 in bone. There is markedly reduced plate-like trabecular structures and loss of connecting rods of trabecular bone in the absence of endogenous FGF2 (Montero et al., 2000). In- terestingly, we observed that FGF2 expression decreased in osteoblasts from aged subjects compared to cells from young subjects (Hurley et al., 2016). Clinical trials demonstrate that local application of FGF2 sti- mulates periodontal regeneration (Kitamura et al., 2011) and accel- erates healing of tibial shaft fractures (Kawaguchi et al., 2010). These data support that FGF2 positively regulates osteoblast differentiation and bone formation. Bone anabolic response of PTH also requires the Wnt signaling pathway (Fei and Hurley, 2012; Jilka, 2007). Wnt signaling can occur either through the non-canonical pathway or the canonical Wnt/β-ca- tenin signaling. Non-canonical pathway includes the Wnt/calcium pathway and the Wnt/planar cell polarity pathway (Piters et al., 2008). The canonical Wnt/β-catenin pathway is well studied in bone. To https://doi.org/10.1016/j.bonr.2018.09.003 Received 9 May 2018; Received in revised form 30 July 2018; Accepted 20 September 2018 ⁎ Corresponding author at: Department of Medicine, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT 06030, USA. 1 Current address: Springer Nature, New York, NY, 10013. E-mail address: hurley@uchc.edu (M.M. Hurley). Bone Reports 9 (2018) 136–144 Available online 21 September 2018 2352-1872/ © 2018 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/). T