Abstract
Orthodontic force-induced osteogenic differentiation and bone formation at tension side play a pivotal role in orthodontic tooth movement (OTM). Platelet-derived growth factor-BB (PDGF-BB) is a clinically proven growth factor during bone regeneration process with unclear mechanisms. Fibroblasts in periodontal ligament (PDL) are considered to be mechanosensitive under orthodontic force. Thus, we established OTM model to investigate the correlation between PDGF-BB and fibroblasts during bone regeneration at tension side. We confirmed that tensile force stimulated PDL cells to induce osteogenic differentiation via Runx-2, OCN up-regulation, and to accelerate new bone deposition along the periodontium and the alveolar bone interface. Interestingly, PDGF-BB level was remarkably enhanced at tension side during OTM in parallel with up-regulated PDGFRβ+/α-SMA+ fibroblasts in PDL by immunohistochemistry. Moreover, orthodontic force-treated primary fibroblasts from PDL were isolated and, cultured in vitro, which showed similar morphology and phenotype with control fibroblasts without OTM treatment. PDGFRβ expression was confirmed to be increased in orthodontic force-treated fibroblasts by immunofluorescence and flow cytometry. Bioinformatics analysis identified that PDGF-BB/PDGFRβ signals were relevant to the activation of JAK/STAT3 signals. The protein expression of JAK2 and STAT3 was elevated in PDL of tension side. Importantly, in vivo, the treatment of the inhibitors (imatinib and AG490) for PDGFRβ and JAK–STAT signals were capable of attenuating the tooth movement. The osteogenic differentiation and bone regeneration in tension side were down-regulated upon the treatment of inhibitors during OTM. Meanwhile, the expressions of PDGFRβ, JAK2 and STAT3 were inhibited by imatinib and AG490. Thus, we concluded that tensile force-induced PDGF-BB activated JAK2/STAT3 signals in PDGFRβ+ fibroblasts in bone formation during OTM.
Highlights
Mechanical forces are integral to bone homeostasis and bone regeneration by driving cell d ifferentiation[1]
We previously demonstrated that recombinant human Platelet-derived growth factor-BB (PDGF-BB) promoted adipose derived stem cells (ADSCs) proliferation and osteogenic differentiation and suppressed adipogenic differentiation in vitro via ERK pathway and that ADSCs associated with rhPDGF-BB could be a promising tissue-engineered construct for craniofacial bone regeneration in vivo[15]
The local administration of the inhibitors of PDGFRβ and JAK/STAT signals during orthodontic tooth movement (OTM) restricted tooth movement compared with the vehicle-injected OTM group by down-regulating the osteogenic differentiation and new bone formation via suppressing the PDGFRβ/JAK2/STAT3 signals. These results demonstrated that tensile force-induced PDGF-BB activated JAK2/STAT3 signals in PDGFRβ+ fibroblasts in bone formation during OTM
Summary
Mechanical forces are integral to bone homeostasis and bone regeneration by driving cell d ifferentiation[1]. When the mechanical force is applied in vivo, periodontal ligament cells on the tension side synthesize and secrete cytokines, growth and differentiation factors, such as runt-related transcription factor-2 (Runx-2), osteoprotegerin (OPG), bone morphogenetic proteins (BMPs), to regulate bone synthesis[4,11,12]. PDGF-BB binds to the extracellular domains of PDGF receptors including PDGFRα and PDGFRβ, leading to the activation of multiple signaling pathways[16]. It is not clear whether PDGF-BB/ PDGFR signals plays a role in bone regeneration at tension side during OTM. It is well known that PDGFRβ is almost exclusively expressed in fibroblasts[17,18], but whether fibroblasts in PDL response to PDGF-BB, and participate in bone regeneration at tension side during OTM remains elusive
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