Mechanical Tension-Stress Induces Expression of Bone Morphogenetic Protein (BMP)-2 and BMP-4, but Not BMP-6, BMP-7, and GDF-5 mRNA, During Distraction Osteogenesis

Abstract

Bone lengthening with osteotomy and gradual distraction was achieved in 57 rats, and the effect of mechanical tension-stress on gene expression of bone morphogenetic proteins (BMPs) was investigated by in situ hybridization and Northern blot analysis using probes of BMP-2, BMP-4, BMP-6, BMP-7, and growth/differentiation factor (GDF)-5. There was a lag phase for 7 days after femoral osteotomy until gradual distraction was carried out for 21 days at a rate of 0.25 mm/12 h using a small external fixator. The signals of the above BMPs mRNA were not detected in the intact rat bone but they were induced after osteotomy except those for BMP-7. By 4 days after osteotomy, BMP-2 and BMP-4 mRNAs were detected in chondrogenic precursor cells in the subperiosteal immature callus. BMP-6 and GDF-5 mRNA were detected in more differentiated cells in chondroid bone. By 7 days after osteotomy, cartilaginous external callus and bony endosteal callus were formed. Meanwhile, the signals of BMP-2 and BMP-4 mRNAs declined to preoperative levels, whereas the signals of BMP-6 and GDF-5 mRNAs were rather elevated. As distraction was started, the callus elongated and eventually separated into proximal and distal segments forming a fibrous interzone in the middle. Expression of BMP-2 and BMP-4 mRNAs was markedly induced at this stage. Their signals were detected widely among chondrogenic and osteogenic cells and their precursor cells sustaining mechanical tension-stress at the fibrous interzone. BMP-6 and GDF-5 mRNAs were detected exclusively in chondrogenic cells at both ends of the fibrous interzone, where endochondral ossification occurred. But neither mRNA was detected in terminally differentiated hypertrophic chondrocytes. As distraction advanced, the cartilage was progressively resorbed from both ends and new bone was formed directly by intramembranous ossification. There was no new cartilage formation in the advanced stage of distraction. The signals of BMP-6 and GDF-5 mRNA declined by this stage, while those of BMP-2 and BMP-4 were maintained at high level for as long as distraction was continued. After completion of distraction, the fibrous interzone fused and the lengthened segment was consolidated. BMP-2, BMP-4, BMP-6, nor GDF-5 was expressed at this stage. The signals of BMP-7 were not detected throughout the experiment. The present results suggest that excellent and uninterrupted bone formation during distraction osteogenesis owes to enhanced expression of BMP-2 and BMP-4 genes by mechanical tensionstress. Abundant gene products of BMP-2 and BMP-4 could induce in situ bone formation by paracrine and autocrine

Periosteum-derived cells respond to mechanical stretch and activate Wnt andBMP signaling pathways

“…IL-1β and IL-6 cause inflammatory responses and promote osteoclast differentiation and bone resorption (23,25). BMP-6, which promotes osteogenesis mentioned above, induces IL-1β and IL-6 expression, and osteoclast differentiation (4,19,28). In this study, we found that expression levels of BMP-2 and BMP-4 were increased, and that of BMP-6 was decreased as well as IL-1β and IL-6 in stretch-stimulated HJBPCs.…”

“…In contrast, identically treated HGFs showed no significant changes in sion and osteoclast differentiation (4,19,28). The observed increase in BMP-2 and BMP-4 expression and reduction in BMP-6 expression may represent a unique profile associated with the mechanical stressdriven bone remodeling.…”

Sequential changes in vessel formation and micro-vascular function during bone repair

“…The lack of complete regeneration might be due to a prolonged ossification process, but also because of the missing mechanical loading (Simpson et al 1996, Sato et al 1999, Weiss et al 2002.…”

Design, characterisation and in vivo testing of a new, adjustable stiffness, external fixator for the rat femur

“…The novel fi xator is based upon external fi xation, which is widely used for distraction osteogenesis (Pacicca et al, 2002;Radomisli et al, 2001;Richards et al, 1999;Sato et al, 1999;Sato et al, 1998;Seebach et al, 2004;Sojo et al, 2005;Yasui et al, 1997), fracture fi xation (Harrison et al, 2003;Kaspar et al, 2007;Mark et al, 2003;Mark et al, 2004;Mark and Rydevik, 2005;McCann et al, 2008;Smith-Adaline et al, 2004) and large defect models in experimental animals (Betz et al, 2006;Cullinane et al, 2002;Cullinane et al, 2003;Dickson et al, 2008;Jager et al, 2005). As well as imposing a controlled and reproducible local mechanical environment, its accessibility allows the modulation of this environment at different stages of healing.…”