Abstract
The role of the 18-kDa isoform of fibroblast growth factor-2 (FGF2) in the maintenance of bone mass was examined in Col3.6-18-kDa FGF2-IRES-GFPsaph transgenic (18-kDa TgFGF2) mice in which a 3.6-kb fragment of the type I collagen 5'-regulatory region (Col3.6) drives the expression of only the 18-kDa isoform of FGF2 with green fluorescent protein-sapphire (GFPsaph). Vector only transgenic mice (Col3.6-IRES-GFPsaph, VTg) were also developed as a control, and mice specifically deficient in 18-kDa FGF2 (FGF2(lmw)(-/-)) were also examined. Bone mineral density, femoral bone volume, trabecular thickness, and cortical bone area and thickness were significantly increased in 18-kDa TgFGF2 mice compared with VTg. Bone marrow cultures (BMSC) from 18-kDa TgFGF2 mice produced more mineralized nodules than VTg. Increased bone formation was associated with reduced expression of the Wnt antagonist secreted frizzled receptor 1 (sFRP-1). In contrast to 18-kDa TgFGF2 mice, FGF2(lmw)(-/-) mice have significantly reduced bone mineral density and fewer mineralized nodules, coincident with increased expression of sFRP-1 in bones and BMSC. Moreover, silencing of sFRP-1 in BMSC from FGF2(lmw)(-/-) mice reversed the decrease in beta-catenin and Runx2 mRNA. Assay of Wnt/beta-catenin-mediated transcription showed increased and decreased TCF-luciferase activity in BMSC from 18-kDa TgFGF2 and FGF2(lmw)(-/-) mice, respectively. Collectively, these results demonstrate that the 18-kDa FGF2 isoform is a critical determinant of bone mass in mice by modulation of the Wnt signaling pathway.
Highlights
A variety of tissues, including bone, produce FGF22 where osteoblasts deposit it in newly forming bone matrix [1]
Previous studies showed that constitutive overexpression of all the human fibroblast growth factor-2 (FGF2) protein isoforms in transgenic (TgFGF2) mice resulted in chondrodysplasia [5], decreased bone mineral density (BMD), and decreased bone mass [6]
We examined whether differential expression of secreted frizzled receptor 1 (sFRP-1) altered -catenin that is important in osteoblast differentiation
Summary
A variety of tissues, including bone, produce FGF22 where osteoblasts deposit it in newly forming bone matrix [1]. FGFr3 mRNA expression was increased at 3 weeks of culture but was similar in BMSC from VTg and 18-kDa TgFGF2 mice (supplemental Fig. 5).
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