Immunolocalization of Sibling and RUNX2 Proteins During Vertical Distraction Osteogenesis in the Human Mandible

Abstract

S U M M A R Y We tested the hypothesis that mechanical loading of human bone increases expression of the transcription factor RUNX2 and bone matrix proteins osteopontin (OPN), bone sialoprotein (BSP), dentin matrix protein-1 (DMP1), and matrix extracellular phosphoglycoprotein (MEPE). We examined this in tissue sections of atrophic mandibular bone taken from edentulous patients who had undergone distraction osteogenesis. In undistracted bone, weak to moderate staining for OPN and BSP was found in osteoblasts and bone matrix of immature woven bone. RUNX2 was also detectable in osteoblasts and in cells of the periosteum. In woven bone, but not in lamellar bone, a small number of osteocytes stained for all proteins tested. After distraction, staining intensity had increased in the existing old bone and staining was seen in more bone cells than before distraction. We also found a high expression of DMP1 and MEPE in many osteocytes embedded in woven bone and in some osteocytes of lamellar bone not seen before distraction. New bone trabeculae were forming in the fibrous tissue of the distraction gap containing all stages of intramembranous bone formation. Moderate to strong staining was seen for all five proteins tested in osteocytes located in woven bone of these trabeculae and for RUNX2, OPN, and BSP in osteoblasts lining the trabecular surfaces. We conclude that loading of atrophic human jawbone by distraction activates matrix synthesis of bone cells in and around existing bone. Increased staining of DMP1 and MEPE in osteocytes after loading is in line with the concept that these proteins may be involved in signaling the effector cells to adapt the bone structure to its mechanical demands. (J Histochem Cytochem 55:1095-1104, 2007

Transglutaminase-mediated oligomerization promotes osteoblast adhesive properties of osteopontin and bone sialoprotein

“…[60][61][62] For example, thrombin cleavage of OPN reveals a binding site for α 9 β 1 integrin, 61 and non-RGD containing BSP osteoblasts and osteocytes-indicating that these could be the sites that may contain significant levels of TG2-oligomerized proteins. [43][44][45] Electron microscopy and high-resolution immunogold labeling have demonstrated that in extracellular matrix related to osteocytes OPN is localized to a thin, noncollagenous surfacecoating structure termed the lamina limitans often found exactly at the osteocyte-mineralized matrix interface when no intervening unmineralized matrix is present. 44 It is therefore reasonable to consider that in the context of cell adhesion, OPN oligomerization in bone could be related to maintaining osteocyte adhesion to surrounding matrix that is heavily mineralized and perhaps to promoting formation of cellular extensions such as observed in our work here.…”

The Progressive Ankylosis Protein Regulates Cementum Apposition and Extracellular Matrix Composition

“…Under normal conditions, DMP1 production is highest in osteocytes of the bone [Toyosawa et al, 2001] and is found in the similarly embedded cementocytes of the cellular cementum [MacDougall et al, 1998;Feng et al, 2003;Ye et al, 2008]. DMP1 is important for the canalicular systems of both osteocytes and cementocytes [Ye et al, 2008], possibly via its role in response to mechanical loading [Gluhak-Heinrich et al, 2003;Yang et al, 2004Yang et al, , 2005Amir et al, 2007], or by regulating HAP mineralization [Gajjeraman et al, 2007]. Thus, the increase in Dmp1 gene expression and DMP1 protein secretion into cementum matrix in the Ank KO mouse is hypothesized to be the result of more rapid apposition and cell inclusion, i.e.…”

Bone regeneration during distraction osteogenesis

“…24 Also, immunohistochemical evidence in the human jaw indicates that distraction initiates or enhances osteogenic activity (Runx2 expression) and deposition of bone-specifi c proteins such as osteopontin (OPN), bone sialoprotein, dentin matrix protein 1, and matrix extracellular phosphoglycoprotein -all involved in bone matrix formation and bone mineralization -in cells lining the old bone surface as well as in some of its osteocytes. 74 It is furthermore interesting to note that similar activation of bone-specifi c transcription factors (Runx2) and matrix proteins (collagen type I, osteocalcin, OPN) by mechanical stimulation has been reported during loading of human periodontal ligament cells and periosteal cells from alveolar bone in vitro, simulating mechanical loading during tooth movement. [75][76][77] Molecular mechanisms of mechanoloading on adaptation of bone structure An important issue that has not yet been resolved is how mechanoloading is sensed by the bone cells, transduced, and turned into a biochemical response.…”