Transcription and immunolocalization of Runx2/Cbfa1/Pebp2alphaA in developing rodent and human craniofacial tissues: further evidence suggesting osteoclasts phagocytose osteocytes

Bone marrow mesenchymal stem cells' osteogenic potential: superiority or non-superiority to other sources of mesenchymal stem cells?

Skeletal problems are an increasing issue due to the increase in the global aging population. Different statistics reports show that today, the global population is aging that results in skeletal problems, increased health system costs, and even higher mortality associated with skeletal problems. Common treatments such as surgery and bone grafts are not always effective and in some cases, they can even cause secondary problems such as infections or improper repair. Cell therapy is a method that can be utilized along with common treatments independently. Mesenchymal stem cells (MSCs) are a very important and efficient source in terms of different diseases, especially bone problems. These cells are present in different tissues such as bone marrow, adipose tissue, umbilical cord, placenta, dental pulp, peripheral blood, amniotic fluid and others. Among the types of MSCs, bone marrow mesenchymal stem cells (BMMSCs) are the most widely used source of these cells, which have appeared to be very effective and promising in terms of skeletal diseases, especially compared to the other sources of MSCs. This study focuses on the specific potential and content of BMMSCs from which the specific capacity of these cells originates, and compares their osteogenic potential with other types of MSCs, and also the future directions in the application of BMMSCs as a source for cell therapy.

Biological effect of bone marrow mesenchymal stem cell- derived extracellular vesicles on the structure of alveolar bone in rats with glucocorticoid-induced osteoporosis

BACKGROUND

Glucocorticoids are used for the treatment of autoimmune disorders; however, they can elicit several side effects such as osteoporosis. Several approaches can be made to treat glucocorticoid-induced osteoporosis, including the use of stem cells. However, the therapeutic effect of mesenchymal stem cells depends on its released factors, including extracellular vesicles. Extracellular vesicles have been recognized as important mediators of intercellular communication as they participate in many physiological processes. The present study was designed to investigate the effect of bone marrow mesenchymal stem cells derived extracellular vesicles on the structure of alveolar bone in rats with glucocorticoid-induced osteoporosis.

METHODS

Thirty adult albino male rats were divided into 3 groups: control group (CG), glucocorticoid-induced osteoporosis (GOG) and extracellular vesicles treated group (ExTG). Rats in the GOG and ExTG groups were injected with methylprednisolone acetate (40 mg/kg) intramuscularly in the quadriceps muscle 3 times per week for three weeks in the early morning. Afterwards, the rats in GOG group received a single vehicle injection (PBS) while each rat in the ExTG group received a single injection of extracellular vesicles (400 μg/kg suspended in 0.2 ml PBS) in the tail vein. Rats were euthanized 1 month after injection. Mandibles were dissected and the molar segments were prepared for histological preparation, scanning electron microscopy (SEM), and energy dispersive x-ray (EDX).

RESULTS

Histology and scanning electron microscopyof bone tissue showed alveolar bone loss and bone resorption in the GOG group. while in the ExTG group, alveolar bone demostrated normal bone architecture. EDX showed that calcium percentage in GOG group was lower than ExTG group,which showed no statistically significant difference from the control group.

CONCLUSIONS

Extracellular vesicles may be a promising treatment modality in the treatment of bone diseases and in bone regeneration. However, further research is needed before stating that extracellular vesicles s can be used to treat bone disorders especially when translating to humans.

Spatio-temporal immunolocalization of VEGF-A, Runx2, and osterix during the early steps of intramembranous ossification of the alveolar process in rat embryos

Vascular endothelial growth factor A (VEGF-A) is expressed by several cell types and is a crucial factor for angiogenic-osteogenic coupling. However, the immunolocalization of VEGF-A during the early stages of the alveolar process formation remains underexplored. Thus, we analyzed the spatio-temporal immunolocalization of VEGF-A and its relationship with Runt-related transcription factor 2 (Runx2) and osterix (Osx) during the early steps of intramembranous ossification of the alveolar process in rat embryos. Embryo heads (E) of 16, 18 and 20-day-old rats were processed for paraffin embedding. Histomorphometry and immunohistochemistry to detect VEGF-A, Runx2, and Osx (osteoblast differentiation markers) were performed. The volume density of bone tissue including bone cells and blood vessels increased significantly in E18 and E20. Cells showing high VEGF-A immunoreactivity were initially observed within a perivascular niche in the ectomesenchyme; afterwards, these cells were diffusely located near bone formation sites. Runx2-and Osx-immunopositive cells were observed in corresponded regions of cells showing strong VEGF-A immunoreactivity. Although these immunostained cells were observed in all specimens, this immunolocalization pattern was more evident in E16 specimens and gradually decreased in E18 and E20 specimens. Double immunofluorescence labelling showed intracellular co-localization of Osx and VEGF-A in cells surrounding the developing alveolar process, indicating a crucial role of VEGF-A in osteoblast differentiation. Our results showed VEGF-A immunoexpression in osteoblasts and its precursors during the maxillary alveolar process formation of rat embryos. Moreover, the VEGF-A-positive cells located within a perivascular niche at the early stages of the alveolar process development suggest a crosstalk between endothelium and ectomesenchymal cells, reinforcing the angiogenic-osteogenic coupling in this process.

Differentiation of Bone Marrow Mesenchymal Stem Cells in Osteoblasts and Adipocytes and its Role in Treatment of Osteoporosis

Osteoporosis is a systemic metabolic bone disorder characterized by a decrease in bone mass and degradation of the bone microstructure, leaving bones that are fragile and prone to fracture. Most osteoporosis treatments improve symptoms, but to date there is no quick and effective therapy. Bone marrow mesenchymal stem cells (BMMSCs) have pluripotent potential. In adults, BMMSCs differentiate mainly into osteoblasts and adipocytes in the skeleton. However, if this differentiation is unbalanced, it may lead to a decrease in bone mass. If the number of adipocyte cells increases and that of osteoblast cells decreases, osteoporosis can result. A variety of hormones and cytokines play an important role in the regulation of BMMSCs bidirectional differentiation. Therefore, a greater understanding of the regulation mechanism of BMMSC differentiation may provide new methods to prevent and treat osteoporosis. In addition, autologous, allogeneic BMMSCs or genetically modified BMMSC transplantation can effectively increase bone mass and density, increase bone mechanical strength, correct the imbalance in bone metabolism, and increase bone formation, and is expected to provide a new strategy and method for the treatment of osteoporosis.

Estrogens antagonize RUNX2-mediated osteoblast-driven osteoclastogenesis through regulating RANKL membrane association

In addition to its thoroughly investigated role in bone formation, the osteoblast master transcription factor RUNX2 also promotes osteoclastogenesis and bone resorption. Here we demonstrate that 17β-estradiol (E2), strongly inhibits RUNX2-mediated osteoblast-driven osteoclastogenesis in co-cultures. Towards deciphering the underlying mechanism, we induced premature expression of RUNX2 in primary murine pre-osteoblasts, which resulted in robust differentiation of co-cultured splenocytes into mature osteoclasts. This was attributable to RUNX2-mediated increase in RANKL secretion, determined by ELISA, as well as to RUNX2-mediated increase in RANKL association with the osteoblast membrane, demonstrated using confocal fluorescence microscopy. The increased association with the osteoblast membrane was recapitulated by transiently expressed GFP-RANKL. E2 abolished the RUNX2-mediated increase in membrane-associated RANKL and GFP-RANKL, as well as the concomitant osteoclastogenesis. RUNX2-mediated RANKL cellular redistribution was attributable in part to a decrease in Opg expression, but E2 did not influence Opg expression either in the presence or absence of RUNX2. Diminution of RUNX2-mediated osteoclastogenesis by E2 occurred regardless of whether the pre-osteoclasts were derived from wild type or estrogen receptor alpha (ERα)-knockout mice, suggesting that activated ERα inhibited osteoblast-driven osteoclastogenesis by acting in osteoblasts, possibly targeting RUNX2. Indeed, microarray analysis demonstrated global attenuation of the RUNX2 response by E2, including abrogation of Pstpip2 expression, which likely plays a critical role in membrane trafficking. Finally, the selective ER modulators (SERMs) tamoxifen and raloxifene mimicked E2 in abrogating the stimulatory effect of osteoblastic RUNX2 on osteoclast differentiation in the co-culture assay. Thus, E2 antagonizes RUNX2-mediated RANKL trafficking and subsequent osteoclastogenesis. Targeting RUNX2 and/or downstream mechanisms that regulate RANKL trafficking may lead to the development of improved SERMs and possibly non-hormonal therapeutic approaches to high turnover bone disease.

Evolution of the osteoblast: skeletogenesis in gar and zebrafish

BACKGROUND

Although the vertebrate skeleton arose in the sea 500 million years ago, our understanding of the molecular fingerprints of chondrocytes and osteoblasts may be biased because it is informed mainly by research on land animals. In fact, the molecular fingerprint of teleost osteoblasts differs in key ways from that of tetrapods, but we do not know the origin of these novel gene functions. They either arose as neofunctionalization events after the teleost genome duplication (TGD), or they represent preserved ancestral functions that pre-date the TGD. Here, we provide evolutionary perspective to the molecular fingerprints of skeletal cells and assess the role of genome duplication in generating novel gene functions. We compared the molecular fingerprints of skeletogenic cells in two ray-finned fish: zebrafish (Danio rerio)--a teleost--and the spotted gar (Lepisosteus oculatus)--a "living fossil" representative of a lineage that diverged from the teleost lineage prior to the TGD (i.e., the teleost sister group). We analyzed developing embryos for expression of the structural collagen genes col1a2, col2a1, col10a1, and col11a2 in well-formed cartilage and bone, and studied expression of skeletal regulators, including the transcription factor genes sox9 and runx2, during mesenchymal condensation.

RESULTS

Results provided no evidence for the evolution of novel functions among gene duplicates in zebrafish compared to the gar outgroup, but our findings shed light on the evolution of the osteoblast. Zebrafish and gar chondrocytes both expressed col10a1 as they matured, but both species' osteoblasts also expressed col10a1, which tetrapod osteoblasts do not express. This novel finding, along with sox9 and col2a1 expression in developing osteoblasts of both zebrafish and gar, demonstrates that osteoblasts of both a teleost and a basally diverging ray-fin fish express components of the supposed chondrocyte molecular fingerprint.

CONCLUSIONS

Our surprising finding that the "chondrogenic" transcription factor sox9 is expressed in developing osteoblasts of both zebrafish and gar can help explain the expression of chondrocyte genes in osteoblasts of ray-finned fish. More broadly, our data suggest that the molecular fingerprint of the osteoblast, which largely is constrained among land animals, was not fixed during early vertebrate evolution.

Phenotypic characterization of osteoarthritic osteocytes from the sclerotic zones: a possible pathological role in subchondral bone sclerosis

Subchondral bone sclerosis is a well-recognised manifestation of osteoarthritis (OA). The osteocyte cell network is now considered to be central to the regulation of bone homeostasis; however, it is not known whether the integrity of the osteocyte cell network is altered in OA patients. The aim of this study was to investigate OA osteocyte phenotypic changes and its potential role in OA subchondral bone pathogenesis. The morphological and phenotypic changes of osteocytes in OA samples were investigated by micro-CT, SEM, histology, immunohistochemistry, TRAP staining, apoptosis assay and real-time PCR studies. We demonstrated that in OA subchondral bone, the osteocyte morphology was altered showing rough and rounded cell body with fewer and disorganized dendrites compared with the osteocytes in control samples. OA osteocyte also showed dysregulated expression of osteocyte markers, apoptosis, and degradative enzymes, indicating that the phenotypical changes in OA osteocytes were accompanied with OA subchondral bone remodelling (increased osteoblast and osteoclast activity) and increased bone volume with altered mineral content. Significant alteration of osteocytes identified in OA samples indicates a potential regulatory role of osteocytes in subchondral bone remodelling and mineral metabolism during OA pathogenesis.

Histomorphometric and immunohistochemical analysis of human maxillary sinus-floor augmentation using porous β-tricalcium phosphate for dental implant treatment

OBJECTIVES

This study utilized the constitution and expression of Runx2/Cbfa1 to conduct 6-month-post-operation histomorphometrical and histochemical analysis of osteocalcin in bone regeneration following sinus-floor augmentation procedures using β-tricalcium phosphate (β-TCP) and autogenous cortical bone.

MATERIAL AND METHODS

Thirteen sinuses of nine patients were treated with sinus-floor augmentation using 50% β-TCP and 50% autogenous cancellous bone harvested from the ramus of the mandible. Biopsies of augmented sinuses were taken at 6 months for histomorphometric and immunohistochemical measurements.

RESULTS

Runx2/Cbfa1- and osteocalcin-positive cells were found around TCP particles and on the bone surface. Approximately 60% of cells found around TCP particles stained positive for Runx2/Cbfa1. Fewer cells stained positive for osteocalcin. These positive cells decreased apically with increasing vertical distance from the maxillary bone surface. Histomorphometric analysis showed that the augmented site close to residual bone and periosteum contained approximately 42% bony tissue and 42% soft connective tissue, and the remaining 16% consisted of TCP particles. On the other hand, the augmented bone far from residual bone and periosteum contained 35% bony tissue and 50% soft connective tissue.

CONCLUSIONS

Our data suggest that TCP particles attract osteoprogenitor cells that migrate into the interconnecting micropores of the bone-substitute material by 6 months. The augmented site close to residual bone contained a higher proportion of bony tissue and a lower proportion of soft connective tissue than did the augmented site far from residual bone.

RUNX2 expression in developing human bones and various bone tumors

The heterozygous germline mutation of runt-related protein 2 (RUNX2) causes cleidocranial dysplasia. To clarify the involvement of RUNX2 in human osteogenesis, fetal bones and various bone tumors were immunohistochemically examined. During both membranous and endochondral ossification in the fetus (n= 8), RUNX2 was expressed not only in osteoblastic cells but also in surrounding mesenchymal cells and early stage chondrocytes. Such an expression pattern was recapitulated in bone tumors: RUNX2 was unequivocally expressed in osteosarcoma (n= 20) and fibrous dysplasia (n= 10), regardless of the site of occurrence, cell morphology or amount of neoplastic osteoid. RUNX2 expression was limited to less differentiated cells in chondrogenic tumors (n= 20). We further analyzed whether RUNX2 expression was regulated by bone morphogenetic protein-2 (BMP-2), which is critical for osteoblastic differentiation. With real-time polymerase chain reaction, the RUNX2 mRNA level was correlated with BMP-2 mRNA level, and both levels were significantly higher in three osteosarcoma cell lines than in three chondrosarcoma cell lines. With treatment of recombinant BMP-2, the RUNX2 mRNA level was significantly altered in these cell lines. RUNX2 expression is constitutive in developing and neoplastic human osteogenesis, and is most likely to be regulated by BMP-2.

Osteopontin is up-regulated and associated with neutrophil and macrophage infiltration in glioblastoma

Osteopontin (OPN) is a glycophosphoprotein with multiple intracellular and extracellular functions. In vitro, OPN enhances migration of mouse neutrophils and macrophages. In cancer, extracellular OPN facilitates migration of cancer cells via its RGD sequence. The present study was designed to investigate whether osteopontin is responsible for neutrophil and macrophage infiltration in human cancer and in particular in glioblastoma. We found that in vitro mouse neutrophil migration was RGD-dependent. In silico, we found that the OPN gene was one of the 5% most highly expressed genes in 20 out of 35 cancer microarray data sets in comparison with normal tissue in at least 30% of cancer patients. In some types of cancer, such as ovarian cancer, lung cancer and melanoma, the OPN gene was one of those with the highest expression levels in at least 90% of cancer patients. In glioblastoma, the most invasive type of brain tumours/glioma, but not in lower grades of glioma it was one of the 5% highest expressed genes in 90% of patients. In situ, we found increased protein levels of OPN in human glioblastoma versus normal human brain confirming in silico results. OPN protein expression was co-localized with neutrophils and macrophages. In conclusion, OPN in tumours not only induces migration of cancer cells but also of leucocytes.

Bone formation in a rat calvarial defect model after transplanting autogenous bone marrow with beta-tricalcium phosphate

In the present study, we evaluated the osteogenic potential of an autogenous bone marrow graft combined with beta-tricalcium phosphate (beta-TCP) in a rat calvarial bone defect model. The bone marrow harvested from the tibia of 7-week-old rats was grafted autogenously in a calvarial defect together with beta-TCP (=BTG group, n=16) or without beta-TCP (=BG group, n=16). Groups of animals were also treated with beta-TCP alone (=TG group, n=16) and control animals (n=8) received no graft implanted into the defect. We then observed the process of bone formation by histology, enzyme histochemistry and immunohistochemistry. Five days after grafting, in the BTG and BG groups, cell proliferation and osteogenic differentiation were observed. From 5 to 10 days after surgery, active Runx2, osteopontin (OPN), and TRAP- positive cells appeared in the BTG and BG groups. New bone formation started in the defect in both the BTG and BG groups. At 30 days after grafting, the BTG group showed new bone development and replacement of beta-TCP to fill the bone defect. New bone formation in the BTG group was significantly greater than in the BG group (P<0.01). The TG group showed no marked bone formation in the defect. The combination graft of bone marrow with beta-TCP showed marked bone formation in rat calvarial defects. Our results indicate that the combination grafts of bone marrow with beta-TCP may be an effective technique for repairing bone defects Beta-TCPgraft (TG) group.

Low-intensity pulsed ultrasound affects RUNX2 immunopositive osteogenic cells in delayed clinical fracture healing

INTRODUCTION

Osteogenic cell proliferation and differentiation play an important role in adequate fracture healing, and is target for osteoinductive therapies in delayed fracture healing. The aim of this study was to investigate whether low-intensity pulsed ultrasound enhances fracture healing at the tissue level in patients with a delayed union of the osteotomized fibula through an effect on the presence of RUNX2 immunopositive osteogenic cells. The effect was studied in both atrophic and hypertrophic delayed unions.

MATERIALS AND METHODS

Biopsies were obtained from 6 female and 1 male patient (age 43-63) with a delayed union of the osteotomized fibula after a high tibial osteotomy treated for 2-4 months with or without low-intensity pulsed ultrasound in a randomized prospective double-blind placebo-controlled trial. Immunolocalization of RUNX2 protein was performed to identify osteogenic cells. Histomorphometrical analysis was performed to determine the number of cells expressing RUNX2 located within and around the newly formed woven bone at the fracture end (area of new bone formation), and up to 3 mm distant from the fracture end.

RESULTS

Cells expressing RUNX2 were present in all histological sections of control and low-intensity pulsed ultrasound-treated bone evaluated. Within the area of new bone formation, RUNX2 immunopositive cells were found in the undifferentiated soft connective tissue, at the bone surface (presumably osteoblasts), and within the newly formed woven bone. Low-intensity pulsed ultrasound treatment of fibula delayed unions significantly reduced the number of RUNX2 immunopositive cells within the soft connective tissue at the fracture ends, whereas the number of RUNX2 immunopositive cells at the bone surface was not affected. The number of RUNX2 immunopositive cells was similar for the atrophic and hypertrophic delayed unions.

CONCLUSIONS

Immunolocalization of RUNX2 positive cells in delayed unions of the fibula reveals that delayed clinical fracture healing does not result in impairment of osteogenic cell proliferation and/or differentiation at the tissue level, even if delayed unions are clinically regarded as atrophic. Reduced number of osteogenic RUNX2 immunopositive cells within the soft connective tissue, and unchanged number of RUNX2 immunopositive cells at the bone surface, implicate that low-intensity pulsed ultrasound does not increase osteogenic cell presence, but likely affects osteogenic cell differentiation.

Catabolic properties of microdissected human endosteal bone lining cells

Bone lining cells cover > 80% of endosteal surfaces of human cancellous bone. Current research assigns to them a dual role: (1) as a biological membrane regulating exchange of substrates between the bone fluid compartment and the extracellular fluid of bone marrow and (2) as a signaling link between the osteocytic network as mechanical receptor and the osteoclastic cell pool for local induction of bone resorption. Furthermore, a catabolic role has been considered. We therefore examined the presence of matrix-metalloproteinases (MMPs) and their physiological tissue inhibitors (TIMPs) as putative proteolytic elements. Firstly, human cancellous bone from 60 patients was examined by immunofluorescence with antibodies against MMPs and TIMPs. Secondly, we applied laser-assisted microdissection (LMD) to isolate bone lining cells from frozen sections of human trabecular bone. mRNA analysis was performed using a single-cell PCR protocol. Three laser microdissection systems were tested: the new generation of Leica LMD and P.A.L.M. laser pressure catapulting (LPC) were compared to P.A.L.M. laser microdissection and micromanipulation (LMM). In a few pooled cell profiles, mRNA of MMP13, MMP14, TIMP1, and CBFA-1 was clearly detected. By immunofluorescence MMP13 and -14 as well as TIMP1 and -2 were strongly present in lining cells, while MMP2, TIMP3, and TIMP4 showed weak or negative signals. Although the functional impact of these enzymatic components remains open, there is additional evidence for a catabolic function of lining cells. The new diode-laser microdissection with LMD and LPC proved to be especially suitable to gain new insights into the properties of bone lining cells.

Immunolocalization of sibling and RUNX2 proteins during vertical distraction osteogenesis in the human mandible

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.

Targeted bone remodeling involves BMU steering as well as activation

Microdamage removal is an important function of bone remodeling. Experiments have repeatedly shown that remodeling of cortical bone by Basic Multicellular Units (BMUs) is initiated in response to microdamage, and this has become known as "targeted remodeling". This paper considers the possibility that microdamage is not only able to activate new BMUs, but may also attract or "steer" existing BMUs as they continue to tunnel through the bone matrix. An initial analysis of the relationship of between mean microcrack length and BMU resorption space density in cortical bone indicates that BMUs have an effective area about 40 times greater than their actual cross-section. Interpreting this as evidence that the osteoclasts in a tunneling BMU are able to sense and steer toward microdamage, a model is developed for "BMU steering" based on the hypothesis that osteoclasts are guided not only in the principal stress direction, as proposed by Burger et al. (Burger, E.H., Klein-Nulend, J., Smit, T.H. Strain-derived canalicular fluid flow regulates osteoclast activity in a remodelling osteon-a proposal. J. Biomech 36 (2003) 1453-1459), but also toward microdamage, depending on its proximity.

Gene expression in skeletal tissues: application of laser capture microdissection

Tissue differentiation is based on the expression of transcription factors, receptors for cytokines, and nuclear receptors that regulate a specific phenotype. The purpose of this study was to select cells from various skeletal tissues in order to analyse differential gene expression of cells in the native environment in vivo. It is a difficult task to obtain cells from skeletal tissues, such as cartilage, periost, bone and muscle, that are structured together and do not exist as individual organs. We used laser capture microdissection which permits the selection and isolation of individual cells from tissue sections. The RNA isolated from these tissues was used for reverse transcriptase-polymerase chain reactions for molecular analysis. We analysed the expression of transcription factors (cFOS, cbfa1, MyoD), receptors for cytokines, nuclear receptors, alkaline phosphatase and the structural proteins osteocalcin and collagen II. The results obtained demonstrate differential patterns of gene expression according to the tissue arrangement in their native in vivo environment, with reliable interpretation of the functions of the analysed genes in the context of intact skeletal tissue physiology.

[Anomalies of the skull in cleidocranial dysplasia]

BACKGROUND

The description of the otorhinolaryngeal and craniofacial anomalies in patients with cleidocranial dysplasia.

METHODS

For this study, 26 patients with cleidocranial dysplasia were examined after their medical history had been recorded. The main focus was placed on otorhinolaryngological and orthodontic findings.

RESULTS

The portion of spontaneous mutations in our patient population was 46.1%. All patients exhibited otorhinolaryngological and craniofacial anomalies. While single ENT-anomalies were expressed in 76.9%-92.3% of the patients, the craniofacial findings were distributed over 84.6%-92.3%.

CONCLUSION

The expression of this rare disorder is variable and its symptomatology not always distinct. Otorhinolaryngological and craniofacial anomalies are often apparent. Appropriate treatment can significantly contribute to an improvement in the patient's quality of life. In cases of ambiguous findings, we recommend consultation with an experienced clinician as well as genetic counselling.

Localisation of osteogenic and osteoclastic cells in porous β-tricalcium phosphate particles used for human maxillary sinus floor elevation

We and others have shown earlier that porous beta-tricalcium phosphate (TCP) (Cerasorb) can be used in patients to augment the maxillary sinus floor prior to placement of oral dental implants. To better understand the transformation of TCP particles into bone tissue, we analyse here the appearance of cells with osteogenic or osteoclastic potential in relation to these particles. In biopsies taken at 6 months after sinus floor augmentation we observed bone growth into the TCP particles but also replacement by soft connective tissue. To identify possible osteoprogenitor cells in this tissue, histological sections were immunostained with an antibody to Runx2/Cbfa1, an essential and early transcription factor for osteoblast differentiation. The osteogenic potential of cells was further confirmed by immunostaining for bone sialoprotein (BSP) and osteopontin (OPN). Other sections were stained for Tartrate Resistant Acid Phosphatase (TRAP) activity to identify cells with osteoclastic capacity. Runx2/Cbfa1 positive connective tissue cells were found in abundance throughout and around the TCP particles, even at a distance of several millimetres from the maxillary bone surface. About 95% of the cells found within TCP particles stained positive for Runx2/Cbfa1. Fewer cells stained positive for BSP and OPN, suggesting more mature osteoblastic properties. Mono- and binucleate TRAP-positive cells, but no multinucleate TRAP-positive osteoclasts, were found in the soft tissue infiltrating the TCP and at the surface of the TCP particles. Both the Runx2/Cbfa1 positive and the TRAP-positive cells decreased apically with increasing vertical distance from the maxillary bone surface. This data suggests that the TCP particles attract osteoprogenitor cells that migrate into the interconnecting micropores of the bone substitute material by 6 months. The lack of large multinucleate TRAP positive cells suggests that resorption of the TCP material by osteoclasts plays only a minor role in its replacement by bone. Chemical dissolution, possibly favoured by a high cell metabolism in the particles, seems the predominant cause of TCP degradation. The abundance of Runx2/Cbfa1 positive cells would indicate that with a greater time of healing there will be further bone deposition into these particles.

Expression of Runx2/Cbfa1/Pebp2alphaA during angiogenesis in postnatal rodent and fetal human orofacial tissues

Transient expression of Runx2 is reported in endothelial cells and vascular smooth muscle cells during vessel formation in skin, stroma of forming bones and developing periodontal ligament, developing skeletal muscle cells, and fat tissue. The data suggest that Runx2 is expressed in a multipotential mesenchymal cell population that gives rise to various osseous and nonosseous cell lineages.

INTRODUCTION

Runx2/Cbfa1 is a transcription factor essential for cells of osteogenic and dentinogenic lineages. Here we examined expression of Runx2/Cbfa1 (all isotypes) in several nonskeletal cell types present in developing orofacial tissues of neonatal rodents and human fetuses with special emphasis on vessel formation.

MATERIALS AND METHODS

Sections obtained from heads or jaws of postnatal mice, hamster, and human fetuses were immunostained with monoclonal anti-Pebp2aA antibody. Mouse and human tissues were also examined by in situ hybridization. Sections of Runx2 null mutant mice with a LacZ reporter construct inserted in the Runx2 locus were stained for Runx2 promoter activity with anti-galactosidase.

RESULTS

We found transient mRNA and protein expression in endothelial cells and in vascular smooth muscle cells of forming vessels in skin, alveoli of forming bone, and forming periodontal ligament. We also noticed weak and variable expression in some fibroblasts of embryonic skin, early differentiating cross-striated muscle cells, and differentiating fat cells.

CONCLUSION

Runx2 is not an exclusive marker for chondrogenic, osteogenic, and dentinogenic tissues, but is much more widely present in an early multipotential mesenchymal cell population that gives rise to several other lineages.

A pair of Sox: distinct and overlapping functions of zebrafish sox9 co-orthologs in craniofacial and pectoral fin development

Understanding how developmental systems evolve after genome amplification is important for discerning the origins of vertebrate novelties, including neural crest, placodes, cartilage and bone. Sox9 is important for the development of these features, and zebrafish has two co-orthologs of tetrapod SOX9 stemming from an ancient genome duplication event in the lineage of ray-fin fish. We have used a genotype-driven screen to isolate a mutation deleting sox9b function, and investigated its phenotype and genetic interactions with a sox9a null mutation. Analysis of mutant phenotypes strongly supports the interpretation that ancestral gene functions partitioned spatially and temporally between Sox9 co-orthologs. Distinct subsets of the craniofacial skeleton, otic placode and pectoral appendage express each gene, and are defective in each single mutant. The double mutant phenotype is additive or synergistic. Ears are somewhat reduced in each single mutant but are mostly absent in the double mutant. Loss-of-function animals from mutations and morpholino injections, and gain-of-function animals injected with sox9a and sox9b mRNAs showed that sox9 helps regulate other early crest genes, including foxd3, sox10, snai1b and crestin, as well as the cartilage gene col2a1 and the bone gene runx2a; however, tfap2a was nearly unchanged in mutants. Chondrocytes failed to stack in sox9a mutants, failed to attain proper numbers in sox9b mutants and failed in both morphogenetic processes in double mutants. Pleiotropy can cause mutations in single copy tetrapod genes, such as Sox9, to block development early and obscure later gene functions. By contrast, subfunction partitioning between zebrafish co-orthologs of tetrapod genes, such as sox9a and sox9b, can relax pleiotropy and reveal both early and late developmental gene functions.

Eccentric localization of osteocytes expressing enzymatic activities, protein, and mRNA signals for type 5 tartrate-resistant acid phosphatase (TRAP)

Enzymatic activity of type 5 tartrate-resistant acid phosphatase (TRAP) has been regarded as one of the reliable markers for osteoclasts and their precursors. The presence of TRAP activity in osteocytes near the bone resorbing surface has also been pointed out in some reports. However, the significance of TRAP reactions in osteocytes remains controversial and, in fact, there is no agreement as to whether the histochemical enzyme reactions in osteocytes represent the TRAP enzyme generated by the respective osteocytes or is a mere diffusion artifact of the reaction products derived from the nearby osteoclasts. Current histochemical, immunohistochemical, and in situ hybridization studies of rat and canine bones confirmed TRAP enzyme activity, TRAP immunoreactivity, and the expression of Trap mRNA signals in osteocytes located close to the bone-resorbing surface. TRAP/Trap- positive osteocytes thus identified were confined to the areas no further than 200 microm from the bone-resorbing surface and showed apparent upregulation of TRAP/Trap expression toward the active osteoclasts. Spatial and temporal patterns of TRAP/Trap expression in the osteocytes should serve as a valuable parameter for further analyses of biological interactions between the osteocytes and the osteoclasts associated with bone remodeling.

Cbfa1 couples chondrocytes maturation and endochondral ossification in rat mandibular condylar cartilage

Core binding factor a1 (Cbfa1) is a crucial transcription factor for osteoblasts differentiation and chondrocytes maturation in embryonic skeletal genesis, but little is known about its function in mandibular condylar growth. The aim of this study was to determine the temporal and spatial pattern of Cbfa1 expression in condylar cartilage during natural growth. Mandibular condyles were harvested from 50 female Sprague-Dawley rats at age of 38, 42, 49, 56 and 65 days. Alcian blue and PAS staining was used for histological analysis. Type A antibody raised against Cbfa1 isoform II was observed in the pre-hypertrophic and hypertrophic chondrocytes in condylar cartilage, and in the mature osteocytes in trabecular bone. Type B antibody raised against 17 aa sequence present after the Runt domain was detected in tartrate resistant acid phosphatase (TRAP) positive osteoclasts in the erosive front of cartilage, and also in the osteoblasts on the sub-chondral bone surface. In situ hybridisation was carried out with a probe containing a fragment in exon 8 of the cDNA. Cbfa1 transcripts were localised in the osteoblasts and chondrocytes, but not in osteoclasts. Quantitative analysis demonstrated that both types of Cbfa1 proteins reached their maximum level on day 56, which coincided with the terminal maturation of hypertrophic chondrocytes and the aggregation of mineralisation deposits in extracellular matrix. These results suggest that Cbfa1 is a master gene controlling the functions of all the skeletal cell lineages by synthesising different functional isoforms. Furthermore, Cbfa1 couples the process of chondrocytes maturation, extracellular matrix mineralisation and degradation, as well as osteoblasts invasion during endochondral bone formation. Beyond its function on embryonic development, Cbfa1 regulates the postnatal growth of mandibular condyle.

Pressure simulation of orthodontic force in osteoblasts: a pilot study

OBJECTIVES

To elucidate the RUNX2 gene expression induction in human osteoblasts after mechanical loading.

DESIGN

Using a stringent pulse-chase protocol human osteoblasts were exposed to centrifugal pressure force for 30 and 90 min. Untreated control cells were processed in parallel. Before, and at defined times after centrifugation, total RNA was isolated. RUNX2 gene expression was measured using real-time quantitative reverse transcriptase polymerase chain reaction. The stress/control ratio was used to illustrate possible stimulatory or diminishing effects of force application.

RESULTS

Immediately after 30 min of force application the RUNX2 gene expression was induced by a factor of 1.7 +/- 0.14 as compared with the negative control. This induction decreased rapidly and reached its pre-load levels within 30 min. Longer force applications (up to 90 min) did not change the RUNX2 gene expression.

CONCLUSION

In mature osteoblasts centrifugal pressure force stimulates RUNX2 gene expression within a narrow time frame: loading of mature cells results in a temporary increase of RUNX2 expression and a fast downregulation back to its pre-load expression level. With this pilot study the gene expression behavior after mechanical stimuli could be determined with a simple laboratory setup.