The bone anabolic effect of rhFGF2 is attributed to activation of proliferation and differentiation of osteoblasts. Concomitant up-regulation of Runx2 and Bmp2 implies a coordinative function of FGF/FGFR signaling on osteoblast differentiation.
Introduction: Duration and tissue concentration of growth factor exposure are important in tissue regeneration. This study analyzed the availability of rhFGF2 using a sustained release gelatin hydrogel system. To examine biological aspects of the bone anabolic effect, we carried out morphological and cell proliferation assays together with gene expression analyses of osteoblast related genes induced by rhFGF2 using localizing and quantifying procedures in vivo.
Materials and methods: Bone formation induced by implantation of gelatin hydrogel impregnated with 20 microg rhFGF2 (rhFGF2(+)) onto mice maxillae was analyzed by micro computed tomography, proliferating cell nuclear antigen (PCNA) immunohistochemistry, in situ hybridization and quantitative real time polymerase chain reaction combined with laser microdissection (LMD-QPCR).
Results: The bony maxilla was augmented to 1.58 times its original volume (p=0.002) by the implantation of rhFGF2(+) gelatin hydrogel. An increased number of PCNA-positive nuclei were observed among differentiated osteoblasts as well as undifferentiated mesenchymal cells. Fgfr1, Fgfr2 and Runx2 were shown to be co-expressed mainly in differentiated osteoblasts but also in osteoblast marker-negative spindle-shaped cells that were scattered within the outer layer of hyperplastic periosteum. LMD-QPCR revealed up-regulation of Bmp2 expression accompanied by increased transcription of Fgfr1, Fgfr2 and Runx2 by rhFGF2 controlled release.
Conclusions: rhFGF2 sustained release results in bone formation on the maxilla by positively regulating the expansion and differentiation of osteoblastic cells. It is suggested that FGF/FGFR signaling coordinates a bone anabolic effect by simultaneously activating RUNX2 and BMP2 pathways. The gelatin hydrogel system, which enables a sustained slow rate of release of rhFGF2 in tissue has advantages of optimizing bone regeneration.