Apert syndrome mutant FGFR2 and its soluble form reciprocally alter osteogenesis of primary calvarial osteoblasts

Apert syndrome mutant FGFR2 and its soluble form reciprocally alter osteogenesis of primary calvarial osteoblasts

Apert syndrome is characterized by craniosynostosis and syndactyly, and is predominantly caused by mutation of either S252W or P253W in the fibroblast growth factor receptor (FGFR) 2 gene. In this study, we characterized the effects of one of the mutations (S252W) using primary calvarial osteoblasts derived from transgenic mice, Ap‐Tg and sAp‐Tg, that expressed an Apert‐type mutant FGFR2 (FGFR2IIIc‐S252W; FGFR2IIIc‐Ap), and the soluble form (extracellular domain only) of the mutant FGFR2 (sFGFR2IIIc‐Ap), respectively. Compared to WT‐derived osteoblasts, osteoblasts from Ap‐Tg mouse showed a higher proliferative activity and enhanced differentiation, while those from sAp‐Tg mouse exhibited reduced potential for proliferation and osteogenic differentiation. When transplanted with β‐tricalcium phosphate (β‐TCP) granules into immunodeficient mice, Ap‐Tg‐derived osteoblasts showed a higher bone forming capacity, whereas sAp‐Tg‐derived osteoblasts were completely deficient for this phenotype. Phosphorylation of extracellular signal‐regulated kinase (ERK), MEK, PLCγ, and p38 was increased in Ap‐Tg‐derived osteoblasts, whereas phosphorylation of these signaling molecules was reduced in sAp‐Tg‐derived osteoblasts. Interestingly, when these experiments were carried out using osteoblasts from the mice generated by crossing Ap‐Tg and sAp‐Tg (Ap/sAp‐Tg), which co‐expressed FGFR2IIIc‐Ap and sFGFR2IIIc‐Ap, the results were comparable to those obtained from WT‐derived osteoblasts. Taken together, these results indicate that osteoblasts expressing FGFR2IIIc‐Ap proliferate and differentiate via highly activated MEK, ERK, and p38 pathways, while these pathways are suppressed in osteoblasts expressing sFGFR2IIIc‐Ap. Our findings also suggest that altered FGFR2IIIc signaling in osteoblasts is mostly responsible for the phenotypes seen in Apert syndrome, therefore these osteoblast cell lines are useful tools for investigating the pathogenesis of Apert syndrome. J. Cell. Physiol. 227: 3267–3277, 2012. © 2011 Wiley Periodicals, Inc.

Apert综合征的特征是颅缝早闭和并指（趾），主要由成纤维细胞生长因子受体2（FGFR2）基因中的S252W或P253W突变引起。在本研究中，我们利用源自转基因小鼠Ap - Tg和sAp - Tg的原代颅盖骨成骨细胞来描述其中一种突变（S252W）的影响，这些小鼠分别表达Apert型突变FGFR2（FGFR2IIIc - S252W；FGFR2IIIc - Ap）以及突变FGFR2的可溶性形式（仅细胞外结构域）（sFGFR2IIIc - Ap）。与野生型（WT）来源的成骨细胞相比，来自Ap - Tg小鼠的成骨细胞显示出更高的增殖活性和增强的分化能力，而来自sAp - Tg小鼠的成骨细胞则表现出增殖和成骨分化潜能降低。当与β - 磷酸三钙（β - TCP）颗粒一起移植到免疫缺陷小鼠体内时，Ap - Tg来源的成骨细胞显示出更高的成骨能力，而sAp - Tg来源的成骨细胞则完全缺乏这种表型。细胞外信号调节激酶（ERK）、MEK、PLCγ和p38的磷酸化在Ap - Tg来源的成骨细胞中增加，而这些信号分子的磷酸化在sAp - Tg来源的成骨细胞中降低。有趣的是，当使用由Ap - Tg和sAp - Tg杂交产生的小鼠（Ap/sAp - Tg）的成骨细胞进行这些实验时，这些小鼠共表达FGFR2IIIc - Ap和sFGFR2IIIc - Ap，结果与从野生型来源的成骨细胞获得的结果相当。综上所述，这些结果表明表达FGFR2IIIc - Ap的成骨细胞通过高度激活的MEK、ERK和p38通路增殖和分化，而这些通路在表达sFGFR2IIIc - Ap的成骨细胞中受到抑制。我们的研究结果还表明，成骨细胞中FGFR2IIIc信号的改变是Apert综合征所见表型的主要原因，因此这些成骨细胞系是研究Apert综合征发病机制的有用工具。《细胞生理学杂志》2012年第227卷第3267 - 3277页。© 2011威利期刊公司