Expressions Of RUNX2，OSX And OPN In Periodontal Ligament During Orthodontic Tooth Movement

The periodontal tissues are remodeled by the applied mechanical force duringorthodontic tooth movement, and finally the teeth are moved to the purpose of thedirection. Therefore, it is important to find out the effect of orthodontic force on theperiodontal tissue and to investigate the relationship between the mechanical forceand bone remodeling. Periodontal ligament (PDL) is the connective tissue locatedbetween the root and alveolar bone. The transmission of the force applied to the teethand the alveolar bone is mediated by the response of PDL. PDL has the ability ofbone resorption and formation during orthodontic tooth movement, resulting inperiodontal tissues remodeled.PDLCs have been suggested to be multipotent cells and be composed ofheterogenous cell populations, which can differentiate into either osteoblasts orcementoblasts depending on the microenvironment. These cells are respondeddirectly to orthodontic force and mechanical stimulation, and could be differentiatedto osteoblast-like cells, suggesting that they are involved in the process ofmechanical stress-induced bone remodeling. However, the molecular mechanism ofmechanical stress enhancing osteoblast proliferation and differentiation is stillunclear. In this mechanism, many signaling molecules and pathways were involved,such as bone morphogenetic protein-2(BMP-2), insulin-like growth factor-I (IGF-I), transforming growth factor-β1(TGF-β1), vasoactive peptide, nitric oxide,prostaglandin E2and E12(PGE2and PGl2), pertussis toxin-sensitive heterotrimeric Gproteins, stretch activated ion channels, integrins. Recent data indicate thatintranuclear transcription factors are associated with the intracellular regulatorypathways that convert extracellular physical or mechanical stimuli into a coordinatedcellular response.Runx-related transcription factor (Runx) are transcription factor proteins. Amongthese proteins, RUNX2was first discovered in1997. The ability of RUNX2tocontrol bone formation and growth is closely related to its structure, which has aRunt domain,3transcriptional activation zone (AD),1transcriptional inhibitionzone (RD).The appropriate expression of RUNX2can promote early differentiationof osteoblasts. And RUNX2could be expressed during each stage in the embryodevelops into a bone, showing that RUNX2is related to the growth and developmentof bone.Osterix (OSX) was first discovered by Kazuhisa in2002. Osterix is a novelosteoblast-specific internuclear transcription factor belonging to the Sp/XKLF family,which contains three C2C12-type zinc fingers at its cterminus. There are increasingevidences indicating that OSX acts downstream of RUNX2/Cbfal and plays anessential role in osteogenic differentiation and bone formation. Recent studies showthat OSX plays a key role in the osteoblast differentiation and bone development,and OSX also plays an important role in the development of the tooth and theperiodontal tissue.Osteopontin (OPN) was first discovered in1983by Herring, Laterly, OPN weredetected in the different tissues, such as the kidney, inner ear, smooth muscle,macrophages, etc. OPN is a secreted phosphorylated glycoprotein (secretedphosphoprotein,SPP), belonging to a kind of non-collagenous proteins, and is also one of the osteoblast phenotype. OPN can be detected in bone tissue, osteoblasts,osteoclasts and osteoblasts. In mature bone tissue, OPN mainly exsists in the areas ofnew bone formation, activing bone remodeling, resorption and matrix mineralizationand plays a crucial role in the integrity of the bone and the surrounding tissues.Therefore, the aim of the study is to observe the expressions of RUNX2, OSX andOPN at the tension side of the periodontal ligament during orthodontic toothmovement, and to investigate the roles of RUNX2, OSX and OPN duringorthodontic periodontium remodeling. This study can help us better understand themolecular biology mechanism of periodontal tissue bone remodeling duringorthodontic tooth movement which may accumulating new data for clinical work.Objective: The purpose of this research is to observe the expressions of RUNX2,OSX and OPN at the tensile side of periodontal ligament during orthodontic toothmovement.Methods: Forty SD rats were randomly grouped according to the experimental timeof tooth movement (8h,24h,3d and7d). The orthodontic appliance, titanium-nickelclosed-coil spring was placed between the upper incisors and the upper left firstmolar of each rat. While the upper right first molar without any orthodonticappliance as the control group. The coil spring was kept constant and recorded for8h,24h,3d and7d. After the experiment, the maxillae were removed. The specimenswere fixed in4%paraformaldehyde in0.1M phosphate for12h and decalcified in10%ethylene diaminetetraacetic acid at4°C for8weeks. After being dehydrated,cleared in xylene, and embedded in paraffin,5μm erial sections were cutparasagittally. Immunohistochemical staining was carried out to examine theexpressions of RUNX2, OSX and OPN.Results: The width of PDL was approximately increased in a time-dependentmanner and the blood capillaries were mostly detected near the alveolar bone. Positive cells and areas were seldom observed in8h and24h. RUNX2-positive cellswere detected in the PDL in24h and on day3and were lined up separately in themargin of the cementum and alveolar bone adjacent to the PDL on day7.OSX-positive cells were strongly detected in the PDL, especially on the surface ofthe newly formed alveolar bone and cementum on day3and day7. OPN-positiveareas were clearly evident throughout the entire PDL, especially on the surface of thenewly formed alveolar bone on day3and day7.Conclusion: RUNX2, OSX and OPN are involved in the periodontal tissueremodeling during orthodontic tooth movements and play a key role in alveolar boneremodeling. This study help us better understand the molecular mechanism of boneremodeling during orthodontic tooth movement.