Accelerated fracture healing in transgenic mice overexpressing an anabolic isoform of fibroblast growth factor 2

Abstract

The effect of targeted expression of an anabolic isoform of basic fibroblast growth factor (FGF2) in osteoblastic lineage on tibial fracture healing was assessed in mice. Closed fracture of the tibiae was performed in Col3.6-18 kDaFgf2-IRES-GFPsaph mice in which a 3.6 kb fragment of type I collagen promoter (Col3.6) drives the expression of only the 18 kD isoform of FGF2 (18 kDaFgf2/LMW) with green fluorescent protein-sapphire (GFPsaph) as well as Vector mice (Col3.6-IRES-GFPsaph, Vector) that did not harbor the FGF2 transgene. Radiographic, micro-CT, DEXA, and histologic analysis of fracture healing of tibiae harvested at 3, 10 and 20 days showed a smaller fracture callus but accelerated fracture healing in LMWTg compared with Vector mice. At post fracture day 3, FGF receptor 3 and Sox 9 mRNA were significantly increased in LMWTg compared with Vector. Accelerated fracture healing was associated with higher FGF receptor 1, platelet derived growth factors B, C, and D, type X collagen, vascular endothelial cell growth factor, matrix metalloproteinase 9, tartrate resistant acid phosphatase, cathepsin K, runt-related transcription factor-2, Osterix and Osteocalcin and lower Sox9, and type II collagen expression at 10 days post fracture. We postulate that overexpression of LMW FGF2 accelerated the fracture healing process due to its effects on factors that are important in chondrocyte and osteoblast differentiation and vascular invasion.

Acceleration of Fracture Healing by Overexpression of Basic Fibroblast Growth Factor in the Mesenchymal Stromal Cells

“…We found that treatment of OVX rats with bFGF or hPTH (1-34) for 6 weeks both increased trabecular bone mass, but hPTH (1-34) increased trabecular thickness whereas bFGF increased trabecular number and connectivity [38][39][40]. Transgenic mice overexpressing bFGF had higher levels of osteoblast maturation and vascular invasion during the early fracture repair period [24]. Previous studies have shown that short-term bFGF injection induces profound de novo bone formation in rodents [25,26].…”

Cellular biology of fracture healing

“…Early fracture healing in IL6‐null mice is marked by decreases in osteocytes and callus strength . In addition to providing inflammatory cytokines, inflammatory cells also produce growth factors such as Fibroblast Growth Factors (FGF), Platelet‐Derived Growth Factor (PDGF) and Transforming Growth Factor beta (TGF‐beta), which initiate the repair process by facilitating proliferation and differentiation of the stem cells that give rise to the fracture callus …”

“…28 In addition to providing inflammatory cytokines, inflammatory cells also produce growth factors such as Fibroblast Growth Factors (FGF), Platelet-Derived Growth Factor (PDGF) and Transforming Growth Factor beta (TGF-beta), which initiate the repair process by facilitating proliferation and differentiation of the stem cells that give rise to the fracture callus. 4,29,30 The multifactorial role of the acute pro-inflammatory response together contributes to its significance in healing and inhibition of inflammation is associated with delays in fracture repair. 14,[18][19][20][21][22]31 For example, depletion of macrophages during the early phases of fracture repair has been shown to reduce both callus size and chondrogenesis resulting in impaired fracture union.…”

Platelet-Rich Fibrin and Its Usage in Orthopaedic Surgery: Review

“…Büyüme faktörleri yaralanma sonrasında çevre dokularda iyileşmeyi başlatmak-tadır. 25,26 İn vitro çalışmalarda, PDGF'nin fibroblastların üzerinde proliferatif ve kemotaktik etki yaptığı, kollajen ve protein sentezini artırarak kemik iyileşmesine katkıda bulunduğu belirlenmiştir. 26,27 TZF içerisinde lökositler tarafından salgılanıp polimorfonükleer lökosit, makrofaj gibi hücrelerin aktive edilip, inflamasyon kontrolünde görev alan sitokinler de saptanmıştır.…”

“…37,38 Osteoblastlar organik matriks proteinlerini sentezlerken IGF-I, IGF-II, TGF-β, fibroblast büyüme faktörü [fibroblast growth factor (FGF)], PDGF ve kemik morfojenik protein [bone morphogenetic protein (BMP)]'leri gibi osteoblastlar tarafından üretilen büyüme faktörleri-nin yapısal matriks proteinlerine katılarak büyüme faktörü etkisinin devam etmesini sağla-dığı bildirilmiştir. 19,26 TZF'nin kemik defektlerinin onarımı ile ilgili deneysel çalışmalar yapılarak olumlu sonuç alındı-ğını bildiren raporlar bulunmaktadır. 24,39 Shah ve ark., periodontal rejenerasyon için TZF ve dondurulmuş, kurutulmuş demineralize kemik allogreftlerini kullanmışlar ve TZF'nin birçok avantajı olduğunu ve kemik defektlerinin onarımında kullanılabileceğini bildirmişlerdir.…”