Abm Rabie

VEGF: an Essential Mediator of Both Angiogenesis and Endochondral Ossification

During bone growth, development, and remodeling, angiogenesis as well as osteogenesis are closely associated processes, sharing some essential mediators. Vascular endothelial growth factor (VEGF) was initially recognized as the best-characterized endothelial-specific growth factor, which increased vascular permeability and angiogenesis, and it is now apparent that this cytokine regulates multiple biological functions in the endochondral ossification of mandibular condylar growth, as well as long bone formation. The complexity of VEGF biology is paralleled by the emerging complexity of interactions between VEGF ligands and their receptors. This narrative review summarizes the family of VEGF-related molecules, including 7 mammalian members, namely, VEGF, placenta growth factor (PLGF), and VEGF-B, -C, -D, -E, and -F. The biological functions of VEGF are mediated by at least 3 corresponding receptors: VEGFR-1/Flt-1, VEGFR-2/Flk-1, VEGFR-3/Flt-4 and 2 co-receptors of neuropilin (NRP) and heparan sulfate proteoglycans (HSPGs). Current findings on endochondral ossification are also discussed, with emphasis on VEGF-A action in osteoblasts, chondroblasts, and chondroclasts/osteoclasts and regulatory mechanisms involving oxygen tension, and some growth factors and hormones. Furthermore, the therapeutic implications of recombinant VEGF-A protein therapy and VEGF-A gene therapy are evaluated. Abbreviations used: VEGF, Vascular endothelial growth factor; PLGF, placenta growth factor; NRP, neuropilin; HSPGs, heparan sulfate proteoglycans; FGF, fibroblast growth factor; TGF, transforming growth factor; HGF, hepatocyte growth factor; TNF, tumor necrosis factor; ECM, extracellular matrix; RTKs, receptor tyrosine kinases; ERK, extracellular signal kinases; HIF, hypoxia-inducible factor

Indian Hedgehog: A Mechanotransduction Mediator in Condylar Cartilage

Indian hedgehog (Ihh) is a critical mediator transducing mechanical signals to stimulate chondrocyte proliferation. To clarify the cellular signal transduction pathway that senses and converts mechanical signals into tissue growth in mandibular condyle, we evaluated Ihh expression and its relation to the kinetics of replicating mesenchymal cells in condylar cartilage during natural growth and mandibular advancement. Thirty-five-day-old Sprague-Dawley rats were fitted with functional appliances. Experimental animals with matched controls were doubly labeled with iododeoxyuridine and bromodeoxyuridine so that we could evaluate the cycles of the proliferative mesenchymal cells. Mandibular advancement triggered Ihh expression in condylar cartilage. A higher level of Ihh expression coincided with the increase of the replicating mesenchymal cells’ population and the shortening of the turnover time. These findings suggested that Ihh acts as a mediator of mechanotransduction that converts mechanical signals resulting from anterior mandibular displacement to stimulate cellular proliferation in condylar cartilage.

PTHrP Regulates Chondrocyte Maturation in Condylar Cartilage

PTHrP is a key factor regulating the pace of endochondral ossification during skeletal development. Mandibular advancement solicits a cascade of molecular responses in condylar cartilage. However, the pace of cellular maturation and its effects on condylar growth are still unknown. The purpose of this study was to evaluate the pattern of expression of PTHrP and correlate it to cellular dynamics of chondrocytes in condylar cartilage during natural growth and mandibular advancement. We fitted 35-day-old Sprague-Dawley rats with functional appliances. Experimental animals with matched controls were labeled with bromodeoxyuridine 3 days before their death, so that mesenchymal cell differentiation could be traced. Mandibular advancement increased the number of differentiated chondroblasts and subsequently increased the cartilage volume. Higher levels of PTHrP expression in experimental animals coincided with the slowing of chondrocyte hypertrophy. Thus, mandibular advancement promoted mesenchymal cell differentiation and triggered PTHrP expression, which retarded their further maturation to allow for more growth.

The Correlation Between Neovascularization and Bone Formation in the Condyle During Forward Mandibular Positioning

The aim of the present study was to investigate the temporal pattern of expression of VEGF (Vascular Endothelial Growth Factor) and new bone formation in the condyle during forward mandibular positioning. The importance of vascularization during endochondral ossification was investigated during natural growth of the condyle and compared to that after forward mandibular positioning. The goal was to further our understanding of the cellular responses during functional appliance therapy with a view to extending the experiment into maturity. One hundred and fifty 35 days old Sprague-Dawley rats, 100 fitted with a bite-jumping appliance and 50 untreated, were divided into 10 groups. One group was sacrificed on each of experimental days 3, 7, 14, 21, 30, 33, 37, 44, 51 and 60 respectively. Sagittal sections were cut and stained with VEGF antibodies and Periodic acid and Schiffs reagent (PAS). Each section was quantitatively analyzed with a computer assisted analyzing program and the temporal sequence of expression of VEGF and new bone formation during natural growth and after mandibular forward positioning was compared. There was significant increase in both vascularization and mandibular bone growth upon forward mandibular positioning and the highest amount of both were expressed in the posterior region of the condyle. The highest acceleration of vascularization preceded that of new bone formation. Thus, forward mandibular positioning was found to solicit a sequence of cellular events leading to increased vascularization and subsequently new bone formation resulting in enhanced condylar growth.

Runx2 Regulates Endochondral Ossification in Condyle during Mandibular Advancement

Runx2 is a transcription factor prerequisite for chondrocyte maturation and osteoblast differentiation. We tested the hypothesis that Runx2 is responsible for signaling chondrocyte maturation and endochondral ossification in the condyle during mandibular advancement. Fifty 35-day-old Sprague-Dawley rats were fitted with functional appliances for 3, 7, 14, 21, and 30 days. Experimental animals with 50 matched controls were labeled with bromodeoxyuridine for evaluation of the invasion of chondroclasts and osteoblasts into condylar cartilage. Mandibular advancement elicited Runx2 expression in condylar cartilage, and subsequently led to an expansion of type X collagen domain in the hypertrophic layer. Stronger Runx2 mRNA signals in subchondral bone corresponded with the increase in the recruitment of osteoblasts and chondroclasts, which preceded the increase of new bone formation in the condyle. Thus, Runx2 mediates chondrocyte terminal maturation and endochondral ossification in the mandibular condyle in response to mandibular advancement.

Chinese norms of McNamara's cephalometric analysis

OBJECTIVE To establish cephalometric norms of McNamaras analysis in young Chinese and compare them to those of a matched young Caucasian sample. MATERIALS AND METHODS The material comprised lateral cephalometric radiographs of a random sample of 200 male and 205 female 12-year-old southern Chinese children, and an additional sample of 43 male and 43 female 12-year-old British Caucasian children in Hong Kong. The radiographs were digitized twice with the CASSOS program. RESULTS The results showed that there were statistically significant gender differences for six out of the 11 cephalometric variables in the Chinese, but for only one variable in the Caucasians. The size of the statistically significant gender differences varied from -0.3 to 0.4 on SD scores. There were statistically significant ethnic differences for eight variables in males and seven variables in females. The size of the observed statistically significant ethnic differences varied from -1.8 to 1.6 on SD scores. CONCLUSION The use of specific standards for Chinese, separate for gender, for McNamaras cephalometric analysis seems to be justified.

The Effect of Demineralized Bone Matrix on the Healing of Intramembranous Bone Grafts in Rabbit Skull Defects

A clinical dilemma exists regarding the type of bone that should be used to replace diseased or traumatized osseous tissue. Oral, plastic, and orthopedic surgeons normally implant viable mineralized endochondral (EC) autografts or demineralized EC allografts. A few clinicians have recognized the disadvantages of using EC bone in craniofacial surgery and advocated the replacement of intramembranous (IM) bone with healthy IM bone. However, controversy and uncertainty surround our understanding of these matrices to induce bone formation. Recent studies have advocated the use of other materials with osteoinductive properties, such as demineralized bone matrix (DBM). The proposed delivery system used in this study included IM bone grafts, DBM, and fixation of the IM bone graft. The purpose of this work was to gain further insights into the mechanism of healing of IM bone, in both the presence and the absence of DBM, and to compare the healing of IM bone grafts with that of DBM alone. Critical-sized (10 x 5 mm), full-thickness bony defects in rabbit parietal bone, devoid of periosteum, were filled with IM bone graft (mandible) alone, demineralized cortical bone matrix (DBM) alone, or combined DBM-IM bone graft, or were left unfilled. Histologic changes were examined 14 days later. The IM bone graft healed through IM ossification with no intermediate cartilage stage. DBM and composite DBM-IM healed through an EC ossification with an intermediate cartilage stage. It is hypothesized that the role of the IM graft is to induce neovascularization into the defect site, and that the undifferentiated mesenchymal cells in the perivascular region of the new blood vessels are induced by the bone morphogenetic protein(s) in the DBM into bone-forming cells.

Genes, genetics, and Class III malocclusion

To present current views that are pertinent to the investigation of the genetic etiology of Class III malocclusion. Class III malocclusion is thought to be a polygenic disorder that results from an interaction between susceptibility genes and environmental factors. However, research on family pedigrees has indicated that Class III malocclusion might also be a monogenic dominant phenotype. Recent studies have reported that genes that encode specific growth factors or other signaling molecules are involved in condylar growth under mechanical strain. These genes, which include Indian hedgehog homolog (IHH), parathyroid-hormone like hormone (PTHLH), insulin-like growth factor-1 (IGF-1), and vascular endothelial growth factor (VEGF), and variations in their levels of expression play an important role in the etiology of Class III malocclusion. In addition, genome-wide scans have revealed chromosomal loci that are associated with Class III malocclusion. It is likely that chromosomal loci 1p36, 12q23, and 12q13 harbor genes that confer susceptibility to Class III malocclusion. In a case-control association study, we identified erythrocyte membrane protein band 4.1 (EPB41) to be a new positional candidate gene that might be involved in susceptibility to mandibular prognathism. Most of the earlier studies on the genetic etiology of Class III malocclusion have focused on the patterns of inheritance of this phenotype. Recent investigations have focused on understanding the genetic variables that affect Class III malocclusion and might provide new approaches to uncovering the genetic etiology of this phenotype.

Correlation between chronological age, cervical vertebral maturation and Fishman's skeletal maturity indicators in southern Chinese.

OBJECTIVE To investigate the correlation between chronological age, cervical vertebral maturation (CVM), and Fishmans hand-wrist skeletal maturity indicators in southern Chinese. MATERIALS AND METHODS Four hundred contemporary hand-wrist and lateral cephalometric radiographs of southern Chinese subjects were randomly selected and analyzed. The female subjects were between 10 and 15 years of age, and the male subjects were between 12 and 17 years of age; all subjects were within the circumpubertal period. The CVM was assessed using the method developed by Baccetti and coworkers, but the hand-wrist maturation was assessed using the method developed by Fishman. These two methods and the chronological age were correlated using the Spearman rank correlation analysis. RESULTS The CVM was significantly correlated with the hand-wrist skeletal age (Spearman r male = 0.9206, female = 0.9363). All patients in the cervical maturation stage (CS3) of CVM were discovered to be in the skeletal maturational indicator (SMI2 or SMI3) stages of hand-wrist maturation (HWM), which was around the peak of the growth spurt. Low correlations were found between the CVM and chronological age (male r = 0.7577; female r = 0.7877) and between the HWM and chronological age (male r = 0.7492; female r = 0.7758). CONCLUSIONS CVM is a valid indicator of skeletal growth during the circumpubertal and has a high correlation with the HWM for the southern Chinese population. However, the low correlations found between the chronological age and both CVM and HWM showed that the chronological age was not suitable to measure skeletal maturity.

Human periodontal ligament cells express osteoblastic phenotypes under intermittent force loading in vitro.

UNLABELLED Mechanical strain applied to bone leads to bone remodeling. In the oral cavity, it is unclear how such mechanical force applied to move teeth orthodontically induces alveolar bone remodeling. It is known that osteoclasts are the only cells that are responsible for bone resorption, while the formation and activity of osteoclasts are regulated by osteoblasts. So it is believed that osteoblasts play an important role not only in bone formation but in bone remodeling as well. Therefore, the purpose of this study was to examine the effect of mechanical force on human periodontal ligament (PDL) cells and whether they express osteoblastic characters in vitro. METHODS Human PDL cells cultured in vitro were loaded with intermittently stretching force for 24 hours. The expression of alkaline phosphatase (ALP), osteocalcin (OCN) and osteoprotegerin (OPG) were detected at mRNA and protein levels at 0, 2nd, 4th, 6th, 12th, 24th hours after intermittent force loading. RESULTS Without any stimulation, ALP and OPG mRNA expressions were detected in human PDL cells by in-situ hybridization, but not that of OCN mRNA. ALP mRNA signal was up-regulated and that of OPG was down-regulated by mechanical force within 24 hours. OCN mRNA expression was induced by mechanical force in the late phase of the 24-hours loading cycle. The changes in secreted proteins showed similar results with those seen at the mRNA level. CONCLUSION Human PDL cells express osteoblastic phenotypes under intermittent force loading and play a role in alveolar bone remodeling.