Localization of bone sialoprotein (BSP) expression to sites of mineralized tissue formation in fetal rat tissues by in situ hybridization

Combination of a Synthetic Bioceramic Associated with a Polydioxanone-Based Membrane as an Alternative to Autogenous Bone Grafting

The purpose of this study was to evaluate the repair process in rat calvaria filled with synthetic biphasic bioceramics (Plenum® Osshp-70:30, HA:βTCP) or autogenous bone, covered with a polydioxanone membrane (PDO). A total of 48 rats were divided into two groups (n = 24): particulate autogenous bone + Plenum® Guide (AUTOPT+PG) or Plenum® Osshp + Plenum® Guide (PO+PG). A defect was created in the calvaria, filled with the grafts, and covered with a PDO membrane, and euthanasia took place at 7, 30, and 60 days. Micro-CT showed no statistical difference between the groups, but there was an increase in bone volume (56.26%), the number of trabeculae (2.76 mm), and intersection surface (26.76 mm2) and a decrease in total porosity (43.79%) in the PO+PG group, as well as higher values for the daily mineral apposition rate (7.16 µm/day). Histometric analysis presented material replacement and increased bone formation at 30 days compared to 7 days in both groups. Immunostaining showed a similar pattern between the groups, with an increase in proteins related to bone remodeling and formation. In conclusion, Plenum® Osshp + Plenum® Guide showed similar and sometimes superior results when compared to autogenous bone, making it a competent option as a bone substitute.

Multimodal spatiotemporal transcriptomic resolution of embryonic palate osteogenesis

The terminal differentiation of osteoblasts and subsequent formation of bone marks an important phase in palate development that leads to the separation of the oral and nasal cavities. While the morphogenetic events preceding palatal osteogenesis are well explored, major gaps remain in our understanding of the molecular mechanisms driving the formation of this bony union of the fusing palate. Through bulk, single-nucleus, and spatially resolved RNA-sequencing analyses of the developing secondary palate, we identify a shift in transcriptional programming between embryonic days 14.5 and 15.5 pinpointing the onset of osteogenesis. We define spatially restricted expression patterns of key osteogenic marker genes that are differentially expressed between these developmental timepoints. Finally, we identify genes in the palate highly expressed by palate nasal epithelial cells, also enriched within palatal osteogenic mesenchymal cells. This investigation provides a relevant framework to advance palate-specific diagnostic and therapeutic biomarker discovery.

Divergent Expression of SPARC, SPARC-L, and SCPP Genes During Jawed Vertebrate Cartilage Mineralization

While cartilage is an ancient tissue found both in protostomes and deuterostomes, its mineralization evolved more recently, within the vertebrate lineage. SPARC, SPARC-L, and the SCPP members (Secretory Calcium-binding PhosphoProtein genes which evolved from SPARC-L) are major players of dentine and bone mineralization, but their involvement in the emergence of the vertebrate mineralized cartilage remains unclear. We performed in situ hybridization on mineralizing cartilaginous skeletal elements of the frog Xenopus tropicalis (Xt) and the shark Scyliorhinus canicula (Sc) to examine the expression of SPARC (present in both species), SPARC-L (present in Sc only) and the SCPP members (present in Xt only). We show that while mineralizing cartilage expresses SPARC (but not SPARC-L) in Sc, it expresses the SCPP genes (but not SPARC) in Xt, and propose two possible evolutionary scenarios to explain these opposite expression patterns. In spite of these genetic divergences, our data draw the attention on an overlooked and evolutionarily conserved peripheral cartilage subdomain expressing SPARC or the SCPP genes and exhibiting a high propensity to mineralize.

An In Vitro and In Vivo Comparison of Osteogenic Differentiation of Human Mesenchymal Stromal/Stem Cells

The use of stem cells in regenerative medicine, including tissue engineering and transplantation, has generated a great deal of enthusiasm. Mesenchymal stromal/stem cells (MSCs) can be isolated from various tissues, most commonly, bone marrow but more recently adipose tissue, dental pulp, and Wharton's jelly, to name a few. MSCs display varying phenotypic profiles and osteogenic differentiating capacity depending and their site of origin. MSCs have been successfully differentiated into osteoblasts both in vitro an in vivo but discrepancies exist when the two are compared: what happens in vitro does not necessarily happen in vivo, and it is therefore important to understand why these differences occur. The osteogenic process is a complex network of transcription factors, stimulators, inhibitors, proteins, etc., and in vivo experiments are helpful in evaluating the various aspects of this osteogenic process without distractions and confounding variables. With that in mind, the results of in vitro experiments need to be carefully considered and interpreted with caution as they do not perfectly replicate the conditions found within living organisms. This is where in vivo experiments help us better understand interactions that might occur in the osteogenic process that cannot be replicated in vitro. Potentially, these differences could also be exploited to develop an optimal MSC cell therapeutic product that can be used for bone disorders. There are many bone disorders, most of which cause a great deal of discomfort. Clinically acceptable protocols could be developed in which MSCs are used to aid in bone regeneration providing relief for patients with chronic pain. The aim of this review is to examine the differences between studies conducted in vitro and in vivo with regard to the osteogenic process to better define the gaps in current osteogenic research. By better understanding osteogenic differentiation, we can better define treatment strategies for various bone disorders.

Synergistic effect of electromagnetic fields and nanomagnetic particles on osteogenesis through calcium channels and p-ERK signaling

Electromagnetic fields (EMFs) are widely used in a number of cell therapies and bone disorder treatments, and nanomagnetic particles (NMPs) also promote cell activity. In this study, we investigated the synergistic effects of EMFs and NMPs on the osteogenesis of the human Saos-2 osteoblast cell line and in a rat calvarial defect model. The Saos-2 cells and critical-size calvarial defects of the rats were exposed to EMF (1 mT, 45 Hz, 8 h/day) with or without Fe₃ O₄ NMPs. Biocompatibility was evaluated with MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and LDH (lactate dehydrogenase) assays. This analysis showed that NMP and EMF did not induce cell toxicity. Quantitative reverse-transcription polymerase chain reaction indicated that the osteogenesis-related markers were highly expressed in the NMP-incorporated Saos-2 cells after exposure to EMF. Also, the expression of gene-encoding proteins involved in calcium channels was activated and the calcium concentration of the NMP-incorporated + EMF-exposed group was increased compared with the control group. In particular, in the NMP-incorporated + EMF-exposed group, all osteogenic proteins were more abundantly expressed than in the control group. This indicated that the NMP incorporation + EMF exposure induced a signaling pathway through activation of p-ERK and calcium channels. Also, in vivo evaluation revealed that rat calvarial defects treated with EMFs and NMPs had good regeneration results with new bone formation and increased mineral density after 6 weeks. Altogether, these results suggest that NMP treatment or EMF exposure of Saos-2 cells can increase osteogenic activity and NMP incorporation following EMF exposure which is synergistically efficient for osteogenesis.

Molecular Aspects of Thyroid Calcification

In thyroid cancer, calcification is mainly present in classical papillary thyroid carcinoma (PTC) and in medullary thyroid carcinoma (MTC), despite being described in benign lesions and in other subtypes of thyroid carcinomas. Thyroid calcifications are classified according to their diameter and location. At ultrasonography, microcalcifications appear as hyperechoic spots ≤ 1 mm in diameter and can be named as stromal calcification, bone formation, or psammoma bodies (PBs), whereas calcifications > 1 mm are macrocalcifications. The mechanism of their formation is still poorly understood. Microcalcifications are generally accepted as a reliable indicator of malignancy as they mostly represent PBs. In order to progress in terms of the understanding of the mechanisms behind calcification occurring in thyroid tumors in general, and in PTC in particular, we decided to use histopathology as the basis of the possible cellular and molecular mechanisms of calcification formation in thyroid cancer. We explored the involvement of molecules such as runt-related transcription factor-2 (Runx-2), osteonectin/secreted protein acidic and rich in cysteine (SPARC), alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteopontin (OPN) in the formation of calcification. The present review offers a novel insight into the mechanisms underlying the development of calcification in thyroid cancer.

Carboxy-Terminal Cementum Protein 1-Derived Peptide 4 (cemp1-p4) Promotes Mineralization through wnt/β-catenin Signaling in Human Oral Mucosa Stem Cells

Human cementum protein 1 (CEMP1) is known to induce cementoblast and osteoblast differentiation and alkaline phosphatase (ALP) activity in human periodontal ligament-derived cells in vitro and promotes bone regeneration in vivo. CEMP1's secondary structure analysis shows that it has a random-coiled structure and is considered an Intrinsic Disordered Protein (IDP). CEMP1's short peptide sequences mimic the biological capabilities of CEMP1. However, the role and mechanisms of CEMP1's C-terminal-derived synthetic peptide (CEMP1-p4) in the canonical Wnt/β-catenin signaling pathway are yet to be described. Here we report that CEMP1-p4 promotes proliferation and differentiation of Human Oral Mucosa Stem Cells (HOMSCs) by activating the Wnt/β-catenin pathway. CEMP1-p4 stimulation upregulated the expression of β-catenin and glycogen synthase kinase 3 beta (GSK-3B) and activated the transcription factors TCF1/7 and Lymphoid Enhancer binding Factor 1 (LEF1) at the mRNA and protein levels. We found translocation of β-catenin to the nucleus in CEMP1-p4-treated cultures. The peptide also penetrates the cell membrane and aggregates around the cell nucleus. Analysis of CEMP1-p4 secondary structure revealed that it has a random-coiled structure. Its biological activities included the induction to nucleate hydroxyapatite crystals. In CEMP1-p4-treated HOMSCs, ALP activity and calcium deposits increased. Expression of Osterix (OSX), Runt-related transcription factor 2 (RUNX2), Integrin binding sialoproptein (IBSP) and osteocalcin (OCN) were upregulated. Altogether, these data show that CEMP1-p4 plays a direct role in the differentiation of HOMSCs to a "mineralizing-like" phenotype by activating the β-catenin signaling cascade.

Label-free quantitative mass spectrometry analysis of differential protein expression in the developing cochlear sensory epithelium

Background

The sensory epithelium of the inner ear converts the mechanical energy of sound to electro-chemical energy recognized by the central nervous system. This process is mediated by receptor cells known as hair cells that express proteins in a timely fashion with the onset of hearing.

Methods

The proteomes of 3, 14, and 30 day-old mice cochlear sensory epithelia were revealed, using label-free quantitative mass spectrometry (LTQ-Orbitrap). Statistical analysis using a one-way ANOVA followed by Bonferroni’s post-hoc test was used to show significant differences in protein expression. Ingenuity Pathway Analysis was used to observe networks of differentially expressed proteins, their biological processes, and associated diseases, while Cytoscape software was used to determine putative interactions with select biomarker proteins. These candidate biomarkers were further verified using Western blotting, while coimmunoprecipitation was used to verify putative partners determined using bioinformatics.

Results

We show that a comparison across all three proteomes shows that there are 447 differentially expressed proteins, with 387 differentially expressed between postnatal day 3 and 30. Ingenuity Pathway Analysis revealed ~ 62% of postnatal day 3 downregulated proteins are involved in neurological diseases. Several proteins are expressed exclusively on P3, including Parvin α, Drebrin1 (Drb1), Secreted protein acidic and cysteine rich (SPARC), Transmembrane emp24 domain-containing protein 10 (Tmed10). Coimmunoprecipitations showed that Parvin and SPARC interact with integrin-linked protein kinase and the large conductance calcium-activated potassium channel, respectively.

Conclusions

Quantitative mass spectrometry revealed the identification of numerous differentially regulated proteins over three days of postnatal development. These data provide insights into functional pathways regulating normal sensory and supporting cell development in the cochlea that include potential biomarkers. Interacting partners of two of these markers suggest the importance of these complexes in regulating cellular structure and synapse development.

Electronic supplementary material

The online version of this article (10.1186/s12953-018-0144-6) contains supplementary material, which is available to authorized users.

Aluminum Trichloride Inhibits the Rat Osteoblasts Mineralization In Vitro

Aluminum (Al) is an accumulative toxic metal. Excessive Al accumulation inhibits osteoblasts mineralization and induces osteoporosis. However, the inhibition mechanism of Al on the mineralization is not fully understood. Thus, in this study, the rat osteoblasts were cultured and exposed to 0 mmol L^-1 (control group, CG) and 0.52 mmol L^-1 aluminum trichloride (AlCl₃, treatment group, TG) for 7, 14, and 21 days, respectively. We found that mineralized matrix nodules, the activity of bone alkaline phosphatase, the concentration of extracellular calcium, the mRNA expression of type-I collagen, the mRNA and protein expressions of osteopontin, osteocalcin, and bone sialoprotein were all decreased, while the concentration of extracellular phosphorus was increased in TG compared with CG with time prolonged. Taken together, these results indicated that AlCl₃ inhibited osteoblasts mineralization in vitro.

Cancer Secretome May Influence BSP and DSP Expression in Human Salivary Gland Cells

One of the biggest challenges in managing head and neck cancers, especially salivary gland cancers, is the identification of secreted biomarkers of the disease that can be evaluated noninvasively. A relevant source of enriched tumor markers could potentially be found in the tumor secretome. Although numerous studies have evaluated secretomes from various cancers, the influence of the cancer secretome derived from salivary gland cancers on the behavior of normal cells has not yet been elucidated. Our data indicate that secretome derived from salivary gland cancer cells can influence the expression of two potential biomarkers of oral cancer-namely, bone sialoprotein (BSP) and dentin sialoprotein (DSP)-in normal salivary gland cells. Using routine immunohistochemistry, immunofluorescence, and immunoblotting techniques, we demonstrate an enrichment of BSP and DSP in human salivary gland (HSG) cancer tissue, unique localizations of BSP and DSP in HSG cancer cells, and enriched expression of BSP and DSP in normal salivary gland cells exposed to a cancer secretome. The secretome domain of the cancer microenvironment could alter signaling cascades responsible for normal cell proliferation, migration, and invasion, thus enhancing cancer cell survival and the potential for cancer progression. The cancer secretome may be critical in maintaining and stimulating "cancer-ness," thus potentially promoting specific hallmarks of metastasis.

A combined series of Fgf9 and Fgf18 mutant alleles identifies unique and redundant roles in skeletal development

Fibroblast growth factor (FGF) signaling is a critical regulator of skeletal development. Fgf9 and Fgf18 are the only FGF ligands with identified functions in embryonic bone growth. Mice lacking Fgf9 or Fgf18 have distinct skeletal phenotypes; however, the extent of overlapping or redundant functions for these ligands and the stage-specific contributions of FGF signaling to chondrogenesis and osteogenesis are not known. To identify separate versus shared roles for FGF9 and FGF18, we generated a combined series of Fgf9 and Fgf18 null alleles. Analysis of embryos lacking alleles of Fgf9 and Fgf18 shows that both encoded ligands function redundantly to control all stages of skeletogenesis; however, they have variable potencies along the proximodistal limb axis, suggesting gradients of activity during formation of the appendicular skeleton. Congenital absence of both Fgf9 and Fgf18 results in a striking osteochondrodysplasia and revealed functions for FGF signaling in early proximal limb chondrogenesis. Additional defects were also noted in craniofacial bones, vertebrae, and ribs. Loss of alleles of Fgf9 and Fgf18 also affect the expression of genes encoding other key intrinsic skeletal regulators, including IHH, PTHLH (PTHrP), and RUNX2, revealing potential direct, indirect, and compensatory mechanisms to coordinate chondrogenesis and osteogenesis.

Cementoblastic lineage formation in the cross-talk between stem cells of human exfoliated deciduous teeth and epithelial rests of Malassez cells

OBJECTIVES

The purpose of this study was to evaluate the synergistic effect of epithelial rests of Malassez cells (ERM) and transforming growth factor-β1 (TGF-β1) on proliferation, cementogenic and osteogenic differentiation of stem cells derived from human exfoliated deciduous teeth (SHED).

MATERIALS AND METHODS

SHED were co-cultured with ERM with/without TGF-β1. Then, SHED proliferation, morphological appearance, alkaline phosphatase (ALP) activity, mineralization behaviour and gene/protein expression of cemento/osteoblastic phenotype were evaluated.

RESULTS

TGF-β1 enhanced SHED proliferation when either cultured alone or co-cultured with ERM. ERM induced the cementoblastic differentiation of SHED which was significantly accelerated when treated with TGF-β1. This activity was demonstrated by high ALP activity, strong mineral deposition and upregulation of cementum/bone-related gene and protein expressions (i.e. ALP, collagen type I, bone sialoprotein, osteocalcin and cementum attachment protein).

CONCLUSIONS

ERM were able to induce SHED differentiation along the cemento/osteoblastic lineage that was triggered in the presence of TGF-β1.

CLINICAL RELEVANCE

The cemento/osteoblastic differentiation capability of SHED possesses a therapeutic potential in endodontic and periodontal tissue engineering.

Cementoblastic lineage formation in the cross-talk between stem cells of human exfoliated deciduous teeth and epithelial rests of Malassez cells

OBJECTIVES

The purpose of this study was to evaluate the synergistic effect of epithelial rests of Malassez cells (ERM) and transforming growth factor-β1 (TGF-β1) on proliferation, cementogenic and osteogenic differentiation of stem cells derived from human exfoliated deciduous teeth (SHED).

MATERIALS AND METHODS

SHED were co-cultured with ERM with/without TGF-β1. Then, SHED proliferation, morphological appearance, alkaline phosphatase (ALP) activity, mineralization behaviour and gene/protein expression of cemento/osteoblastic phenotype were evaluated.

RESULTS

TGF-β1 enhanced SHED proliferation when either cultured alone or co-cultured with ERM. ERM induced the cementoblastic differentiation of SHED which was significantly accelerated when treated with TGF-β1. This activity was demonstrated by high ALP activity, strong mineral deposition and upregulation of cementum/bone-related gene and protein expressions (i.e. ALP, collagen type I, bone sialoprotein, osteocalcin and cementum attachment protein).

CONCLUSIONS

ERM were able to induce SHED differentiation along the cemento/osteoblastic lineage that was triggered in the presence of TGF-β1.

CLINICAL RELEVANCE

The cemento/osteoblastic differentiation capability of SHED possesses a therapeutic potential in endodontic and periodontal tissue engineering.

The synergistic effect of micro-topography and biochemical culture environment to promote angiogenesis and osteogenic differentiation of human mesenchymal stem cells

Critical failures associated with current engineered bone grafts involve insufficient induction of osteogenesis of the implanted cells and lack of vascular integration between graft scaffold and host tissue. This study investigated the combined effects of surface microtextures and biochemical supplements to achieve osteogenic differentiation of human mesenchymal stem cells (hMSCs) and revascularization of the implants in vivo. Cells were cultured on 10μm micropost-textured polydimethylsiloxane (PDMS) substrates in either proliferative basal medium (BM) or osteogenic medium (OM). In vitro data revealed that cells on microtextured substrates in OM had dense coverage of extracellular matrix, whereas cells in BM displayed more cell spreading and branching. Cells on microtextured substrates in OM demonstrated a higher gene expression of osteoblast-specific markers, namely collagen I, alkaline phosphatase, bone sialoprotein, and osteocalcin, accompanied by substantial amount of bone matrix formation and mineralization. To further investigate the osteogenic capacity, hMSCs on microtextured substrates under different biochemical stimuli were implanted into subcutaneous pockets on the dorsal aspect of immunocompromised mice to study capacity for ectopic bone formation. In vivo data revealed greater expression of osteoblast-specific markers coupled with increased vascular invasion on microtextured substrates with hMSCs cultured in OM. Together, these data represent a novel regenerative strategy that incorporates defined surface microtextures and biochemical stimuli to direct combined osteogenesis and re-vascularization of engineered bone scaffolds for musculoskeletal repair and relevant bone tissue engineering applications.

Loss of bone sialoprotein leads to impaired endochondral bone development and mineralization

Bone sialoprotein (BSP) is an anionic phosphoprotein in the extracellular matrix of mineralized tissues, and a promoter of biomineralization and osteoblast development. Previous studies on the Bsp-deficient mouse (Bsp(-/-)) have demonstrated a significant bone and periodontal tissue phenotype in adulthood. However, the role of BSP during early long bone development is not known. To address this, early endochondral ossification in the Bsp(-/-) mouse was studied. Embryonic day 15.5 (E15.5) wild-type (WT) tibiae showed early stages of ossification that were absent in Bsp(-/-) mice. At E16.5, mineralization had commenced in the Bsp(-/-) mice, but staining for mineral was less intense and more dispersed compared with that in WT controls. Tibiae from Bsp(-/-) mice also demonstrated decreased mineralization and shortened length at postnatal day 0.5 (P0.5) compared to WT bones. There was no detectable difference in the number of tartrate-resistant acid phosphatase-positive foci at P0.5, although the P0.5 Bsp(-/-) tibiae had decreased Vegfα expression compared with WT tissue. Due to the shortened tibiae the growth plates were examined and determined to be of normal overall length. However, the length of the resting zone was increased in P0.5 Bsp(-/-) tibiae whereas that of the proliferative zone was decreased, with no change in the hypertrophic zone length of Bsp(-/-) mice. A reduction in cells positive for Ki-67, an S-phase cell-cycle marker, was noted in the proliferative zone. Decreased numbers of TUNEL-positive hypertrophic chondrocytes were also apparent in the Bsp(-/-) tibial growth plates, suggesting decreased apoptosis. Expression of the osteogenic markers Alp1, Col1a1, Sp7, Runx2, and Bglap was reduced in the endochondral bone of the neonatal Bsp(-/-) compared to WT tibiae. These results suggest that BSP is an important and multifaceted protein that regulates both chondrocyte proliferation and apoptosis as well as transition from cartilage to bone during development of endochondral bone.

Poly(vinylidene-trifluoroethylene)/barium titanate composite for in vivo support of bone formation

In this study, we evaluated the effect of poly(vinylidene fluoride-trifluoroethylene)/barium titanate (P(VDF-TrFE)/BT) membrane on in vivo bone formation. Rat calvarial bone defects were implanted with P(VDF-TrFE)/BT and polytetrafluoroethylene (PTFE) membranes, and at 4 and 8 weeks, histomorphometric and gene expression analyses were performed. A higher amount of bone formation was noticed on P(VDF-TrFE)/BT compared with PTFE. The gene expression of RUNX2, bone sialoprotein, osteocalcin, receptor activator of nuclear factor-kappa B ligand, and osteoprotegerin indicates that P(VDF-TrFE)/BT favored the osteoblast differentiation compared with PTFE. These results evidenced the benefits of using P(VDF-TrFE)/BT to promote new bone formation, which may represent a promising alternative to be employed in guided bone regeneration.

Recent developments of functional scaffolds for craniomaxillofacial bone tissue engineering applications

Autogenous bone grafting remains a gold standard for the reconstruction critical-sized bone defects in the craniomaxillofacial region. Nevertheless, this graft procedure has several disadvantages such as restricted availability, donor-site morbidity, and limitations in regard to fully restoring the complicated three-dimensional structures in the craniomaxillofacial bone. The ultimate goal of craniomaxillofacial bone reconstruction is the regeneration of the physiological bone that simultaneously fulfills both morphological and functional restorations. Developments of tissue engineering in the last two decades have brought such a goal closer to reality. In bone tissue engineering, the scaffolds are fundamental, elemental and mesenchymal stem cells/osteoprogenitor cells and bioactive factors. A variety of scaffolds have been developed and used as spacemakers, biodegradable bone substitutes for transplanting to the new bone, matrices of drug delivery system, or supporting structures enhancing adhesion, proliferation, and matrix production of seeded cells according to the circumstances of the bone defects. However, scaffolds to be clinically completely satisfied have not been developed yet. Development of more functional scaffolds is required to be applied widely to cranio-maxillofacial bone defects. This paper reviews recent trends of scaffolds for crania-maxillofacial bone tissue engineering, including our studies.

Human serine protease HTRA1 positively regulates osteogenesis of human bone marrow-derived mesenchymal stem cells and mineralization of differentiating bone-forming cells through the modulation of extracellular matrix protein

Mammalian high-temperature requirement serine protease A1 (HTRA1) is a secreted member of the trypsin family of serine proteases which can degrade a variety of bone matrix proteins and as such has been implicated in musculoskeletal development. In this study, we have investigated the role of HTRA1 in mesenchymal stem cell (MSC) osteogenesis and suggest a potential mechanism through which it controls matrix mineralization by differentiating bone-forming cells. Osteogenic induction resulted in a significant elevation in the expression and secretion of HTRA1 in MSCs isolated from human bone marrow-derived MSCs (hBMSCs), mouse adipose-derived stromal cells (mASCs), and mouse embryonic stem cells. Recombinant HTRA1 enhanced the osteogenesis of hBMSCs as evidenced by significant changes in several osteogenic markers including integrin-binding sialoprotein (IBSP), bone morphogenetic protein 5 (BMP5), and sclerostin, and promoted matrix mineralization in differentiating bone-forming osteoblasts. These stimulatory effects were not observed with proteolytically inactive HTRA1 and were abolished by small interfering RNA against HTRA1. Moreover, loss of HTRA1 function resulted in enhanced adipogenesis of hBMSCs. HTRA1 Immunofluorescence studies showed colocalization of HTRA1 with IBSP protein in osteogenic mASC spheroid cultures and was confirmed as being a newly identified HTRA1 substrate in cell cultures and in proteolytic enzyme assays. A role for HTRA1 in bone regeneration in vivo was also alluded to in bone fracture repair studies where HTRA1 was found localized predominantly to areas of new bone formation in association with IBSP. These data therefore implicate HTRA1 as having a central role in osteogenesis through modification of proteins within the extracellular matrix.

The importance of the SIBLING family of proteins on skeletal mineralisation and bone remodelling

The small integrin-binding ligand N-linked glycoprotein (SIBLING) family consists of osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein. These proteins share many structural characteristics and are primarily located in bone and dentin. Accumulating evidence has implicated the SIBLING proteins in matrix mineralisation. Therefore, in this review, we discuss the individual role that each of the SIBLING proteins has in this highly orchestrated process. In particular, we emphasise how the nature and extent of their proteolytic processing and post-translational modification affect their functional role. Finally, we describe the likely roles of the SIBLING proteins in clinical disorders of hypophosphataemia and their potential therapeutic use.

Quantification of Changes in Morphology, Mechanotransduction, and Gene Expression in Bovine Articular Chondrocytes in Response to 2-Dimensional Culture Indicates the Existence of a Novel Phenotype

OBJECTIVE

Matrix-induced autologous chondrocyte implantation (ACI) offers a potential solution for cartilage repair but is currently hindered by loss of the chondrocyte differentiated phenotype. To further our understanding of the mechanism of dedifferentiation, changes in the phenotype in relation to mechanotransduction were recorded in response to monolayer culture.

METHODS

Bovine cartilage explants were excised and chondrocytes cultured for 9 days (P1), 14 days (P2), and 21 (P3) days. Changes in morphology and regulatory volume increase (RVI; a mechanotransduction response) were determined by the expression of key genes by RT-PCR and confocal microscopy, respectively.

RESULTS

A loss of a differentiated phenotype was observed in P1 with a reduction in sphericity and an overall increase in cell volume from 474.7 ± 32.1 µm(3) to 725.2 ± 35.6 µm(3). Furthermore, the effect of 2-dimensional (2-D) culture-induced dedifferentiation on mechanotransduction was investigated, whereby RVI and Gd(3+)-sensitive REV5901-induced calcium rise were only observed in 2-D cultured chondrocytes. A significant up-regulation of types I and II collagens and Sox9 was observed in P1 chondrocytes and no further significant change in type I collagen but a return to baseline levels of type II collagen and Sox9 upon further culture.

CONCLUSION

These data indicated the presence of an intermediate, mesodifferentiated phenotype and highlight the importance of mechanotransduction as a marker of the chondrocytic cell type.

Effect of vitronectin bound to insulin-like growth factor-I and insulin-like growth factor binding protein-3 on porcine enamel organ-derived epithelial cells

The aim of this paper was to determine whether the interaction between IGF, IGFBP, and VN modulates the functions of porcine EOE cells. Enamel organs from 6-month-old porcine third molars were dissociated into single epithelial cells and subcultured on culture dishes pretreated with VN, IGF-I, and IGFBP-3 (IGF-IGFBP-VN complex). The subcultured EOE cells retained their capacity for ameloblast-related gene expression, as shown by semiquantitative reverse transcription-polymerase chain reaction. Amelogenin expression was detected in the subcultured EOE cells by immunostaining. The subcultured EOE cells were then seeded onto collagen sponge scaffolds in combination with fresh dental mesenchymal cells and transplanted into athymic rats. After 4 weeks, enamel-dentin-like complex structures were present in the implanted constructs. These results show that EOE cells cultured on IGF-IGFBP-VN complex differentiated into ameloblasts-like cells that were able to secrete amelogenin proteins and form enamel-like tissues in vivo. Functional assays demonstrated that the IGF/IGFBP/VN complex significantly enhanced porcine EOE cell proliferation and tissue forming capacity for enamel. This is the first study to demonstrate a functional role of the IGF-IGFBP-VN complex in EOE cells. This application of the subculturing technique provides a foundation for further tooth-tissue engineering and for improving our understanding of ameloblast biology.

Determination of osteogenic or adipogenic lineages in muscle-derived stem cells (MDSCs) by a collagen-binding peptide (CBP) derived from bone sialoprotein (BSP)

Bone sialoprotein (BSP) is a mineralized, tissue-specific, non-collagenous protein that is normally expressed only in mineralized tissues such as bone, dentin, cementum, and calcified cartilage, and at sites of new mineral formation. The binding of BSP to collagen is thought to be important for initiating bone mineralization and bone cell adhesion to the mineralized matrix. Several recent studies have isolated stem cells from muscle tissue, but their functional properties are still unclear. In this study, we examined the effects of a synthetic collagen-binding peptide (CBP) on the differentiation efficiency of muscle-derived stem cells (MDSCs). The CBP sequence (NGVFKYRPRYYLYKHAYFYPHLKRFPVQ) corresponds to residues 35-62 of bone sialoprotein (BSP), which are located within the collagen-binding domain in BSP. Interestingly, this synthetic CBP inhibited adipogenic differentiation but increased osteogenic differentiation in MDSCs. The CBP also induced expression of osteoblastic marker proteins, including alkaline phosphatase (ALP), type I collagen, Runt-related transcription factor 2 (Runx2), and osteocalcin; prevented adipogenic differentiation in MDSCs; and down-regulated adipose-specific mRNAs, such as adipocyte protein 2 (aP2) and peroxisome proliferator-activated receptor γ. The CBP increased Extracellular signal-regulated kinases (ERK) 1/2 protein phosphorylation, which is important in lineage determination. These observations suggest that this CBP determines the osteogenic or adipogenic lineage in MDSCs by activating ERK1/2. Taken together, a novel CBP could be a useful candidate for regenerating bone and treating osteoporosis, which result from an imbalance in osteogenesis and adipogenesis differentiation.

Transcriptional regulation of bone sialoprotein gene by interleukin-11

Interleukin-11 (IL-11) is a stromal cell-derived cytokine that belongs to the interleukin-6 family of cytokines. IL-11 has many biological activities and has roles in hematopoiesis, immune responses, the nervous system and bone metabolism. Bone sialoprotein (BSP) is a mineralized tissue-specific protein expressed in differentiated osteoblasts that appears to function in the initial mineralization of bone. IL-11 (20 ng/ml) increased BSP mRNA and protein levels at 12h in osteoblast-like ROS 17/2.8 cells. In a transient transfection assay, IL-11 (20 ng/ml) increased luciferase activity of the construct (-116 to +60) in ROS 17/2.8 cells and rat bone marrow stromal cells. Introduction of 2 bp mutations to the luciferase constructs showed that the effects of IL-11 were mediated by a cAMP response element (CRE), a fibroblast growth factor 2 response element (FRE) and a homeodomain protein-binding site (HOX). Luciferase activities induced by IL-11 were blocked by protein kinase A inhibitor, tyrosine kinase inhibitor and ERK1/2 inhibitor. Gel shift analyses showed that IL-11 (20 ng/ml) increased nuclear protein binding to CRE, FRE and HOX. CREB1, phospho-CREB1, c-Fos, c-Jun, JunD and Fra2 antibodies disrupted the formation of CRE-protein complexes. Dlx5, Msx2, Runx2 and Smad1 antibodies disrupted FRE- and HOX-protein complex formations. These studies demonstrate that IL-11 stimulates BSP transcription by targeting CRE, FRE and HOX sites in the proximal promoter of the rat BSP gene. Moreover, phospho-CREB1, c-Fos, c-Jun, JunD, Fra2, Dlx5, Msx2, Runx2 and Smadl transcription factors appear to be key regulators of IL-11 effects on BSP transcription.

Atrophic jaw reconstruction by means of calvarial bone graft: long-term results

The aim of this work was to investigate the immunohistochemical and histologic patterns occurring in samples obtained from sites reconstructed with calvarial bone graft, 4 months (T1) and 10 years (T2) after grafting, in comparison to those observed in samples from the calvaria taken from the donor sites at the moment of withdrawal for the grafting (T0).Samples underwent immunohistochemical analysis for bone sialoprotein, matrix metalloproteinases 2 and 9, vascular endothelial growth factor, and Bax expressions; terminal-deoxynucleotidyl-transferase-mediated dUTP nick end-labeling analysis to evaluate the number of apoptotic samples; and morphologic evaluation after hematoxylin and eosin staining.The expression levels of all the investigated molecules, such as the apoptotic cells' count, showed a significant (P < 0.05) increase in T1 samples, that is, 4 months after grafting, although their expression levels recorded after 10 years seemed to be comparable to those in the native bone. Moreover, at observation under the light microscope, T1 samples showed a nonuniform morphology, with mineralized areas surrounded by connective tissues where blood vessels could be distinguished. On the other hand, T0 and T2 samples showed a similar aspect, characterized by uniform areas of mineralized extracellular matrix with cavities containing osteocytes.These data suggest that, after approximately 4 months, it is possible to highlight stronger remodeling phenomena, accompanied by new bone formation and new blood vessel proliferation, which are necessary to the host tissue for graft integration. On the contrary, these phenomena could not be observed in samples obtained after a long period (T2), which reveal a morphologic and an immunohistochemical pattern comparable to that recorded in calvarial native bone (T0).

Modification of polymer networks with bone sialoprotein promotes cell attachment and spreading

Biomaterials used for tissue engineering scaffolds act as temporary substrates, on which cells deposit newly synthesized extracellular matrix. In cartilage tissue engineering, polycaprolactone/poly(2-hydroxyethyl methacrylate) (PCL/pHEMA) polymer blends have been used as scaffold materials, but their use in osseous tissue engineering has been more limited. The objective of this study was to evaluate modification of PCL/pHEMA surfaces with bone sialoprotein (BSP), an extracellular matrix protein important in regulating osseous tissue formation. Modification of surfaces with BSP significantly enhanced osteoblastic cell attachment and spreading, without compromising proliferation. Thus, BSP-immobilization may be a useful strategy for optimizing scaffolds for skeletal tissue engineering.

How does bone sialoprotein promote the nucleation of hydroxyapatite? A molecular dynamics study using model peptides of different conformations

Bone sialoprotein (BSP) is a highly phosphorylated, acidic, noncollagenous protein in bone matrix. Although BSP has been proposed to be a nucleator of hydroxyapatite (Ca(5)(PO(4))(3)OH), the major mineral component of bone, no detailed mechanism for the nucleation process has been elucidated at the atomic level to date. In the present work, using a peptide model, we apply molecular dynamics (MD) simulations to study the conformational effect of a proposed nucleating motif of BSP (a phosphorylated, acidic, 10 amino-acid residue sequence) on controlling the distributions of Ca(2+) and inorganic phosphate (Pi) ions in solution, and specifically, we explore whether a nucleating template for orientated hydroxyapatite could be formed in different peptide conformations. Both the alpha-helical conformation and the random coil structure have been studied, and inorganic solutions without the peptide are simulated as reference. Ca(2+) distributions around the peptide surface and interactions between Ca(2+) and Pi in the presence of the peptide are examined in detail. From the MD simulations, although in some cases for the alpha-helical conformation, we observe that a Ca(2+) equilateral triangle forms around the surface of peptide, which matches the distribution of Ca(2+) ions on the (001) face of the hydroxyapatite crystal, we do not consistently find a stable nucleating template formation in general for either the helical conformation or the random coil structure. Therefore, independent of conformations, the BSP nucleating motif is more likely to help nucleate an amorphous calcium phosphate cluster, which ultimately converts to crystalline hydroxyapatite.

A microarray based identification of osteoporosis-related genes in primary culture of human osteoblasts

Genetic factors influencing the pathogenesis of osteoporosis are still largely unknown. We employed genome-wide gene expression approach in order to discover novel genes involved in the pathogenesis of osteoporosis. To this end, primary cultures of osteoblasts isolated from osteoporotic and non-osteoporotic human bone tissue samples were prepared. One thousand six hundred six genes were found to be differentially expressed, indicating increased demand for protein synthesis and decreased cell proliferation rate in osteoblasts from osteoporotic tissue as compared to osteoblasts from non-osteoporotic tissue. At first, top four genes, based on the microarray data and potential role in bone metabolism, were further studied in bone tissue samples of 55 patients. PTN and COL15A1 were both downregulated in osteoporotic bone tissue (6.2- and 3.4-fold, respectively, both p<0.05), while IBSP and CXCL2 were both upregulated (5.7-fold, p<0.05, and 2.1-fold, p>0.05). Further biostatistical analysis of the microarray data by gene set enrichment analysis suggested oxidative stress may have an important part in the pathogenesis of osteoporosis. Thus, secondly, we tested it by an in vitro assay on human osteosarcoma cell line cells treated with hydrogen peroxide. After 72 h of treatment with 500 microM hydrogen peroxide, the upregulation of the same genes involved in the response to oxidative stress as on the microarrays was observed: MT1G (metallothionein 1G, 22.1-fold, p<0.05), TXNRD1 (thioredoxin reductase 1, 3.7-fold, p<0.05), AOX1 (aldehyde oxidase 1, 24.5-fold, p<0.05) and GSR (glutathione reductase, 4.7-fold, p<0.05). Our results present a novel list of genes and metabolic pathways that may be associated with the pathogenesis of osteoporosis. PTN, CXCL2, COL15A1, IBSP, AOX1, MT1G, GSR and TXNRD1 are candidate genes for further studies in the assessment of the genetic susceptibility to osteoporosis. In addition, differences in protein synthesis, cell proliferation rate and response to oxidative stress may also be involved in the pathogenesis of osteoporosis.

Conditionally replicating adenovirus therapy utilizing bone sialoprotein promoter (Ad-BSP-E1a) in an in vivo study of treating androgen-independent intraosseous prostate cancer

BACKGROUND

Adenoviral based gene therapy has been used in clinical trials in control of advanced prostate cancer. In this study, a promising conditionally replicating adenovirus (CRAd) driven by a tissue specific bone sialoprotein promoter in controlling prostate cancer both in vitro and in vivo is demonstrated.

METHODS

C4-2B, an androgen-independent prostate cancer cell line, was treated with PBS, Ad-BSP-TK, or the Ad-BSP-E1a in vitro, and in subcutaneous and intraosseous xenographs. Cell proliferation, PSA level in condition medium, tumor volume, and/or serum PSA were followed.

RESULTS

The growth of C4-2B and the PSA production was dramatically suppressed by Ad-BSP-E1a at very low dosage (0.3 MOI) compared with PBS and Ad-BSP-TK treatment in vitro. In the subcutaneous model, the tumor volume was significantly lower statistically in the Ad-BSP-E1a treated group than the Ad-BSP-TK control group (P = 0.02). In the intraosseous model, the mice treated in the Ad-BSP-E1a treatment group demonstrated a significant lower PSA compared to that in the control group (P < 0.01) at week 8 and week 16 post-treatment.

CONCLUSIONS

The CRAd Ad-BSP-E1a revealed potential in treating prostate cancer in this model system. Using viral or none-viral mediated gene therapy to treat prostate carcinoma continues to be a potential avenue to treat afflicted men with prostate cancer.

Osteocalcin secretion as an early marker of in vitro osteogenic differentiation of rat mesenchymal stem cells

Osteocalcin (OC) is a bone-specific protein synthesized by osteoblasts that represents a good marker for osteogenic maturation. We examined whether in vitro osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (MSCs) could be simply assessed at earlier stages by monitoring OC secretion into the conditioned medium, rather than measuring OC deposition on the extracellular matrix (ECM), using a sandwich enzyme immunoassay system involving a specific anti-rat OC monoclonal antibody. During a 16-day culture, OC was secreted into the medium of MSCs from day 8 and increased substantially until day 16. In contrast, OC deposition on the ECM was low, even at day 13, when calcium deposition was at high levels. The histological expression pattern of OC messenger RNA provided in situ evidence that osteoblastic cells appeared at the early stages of 6 to 9 days and matured over time in vitro. Furthermore, the temporal expression of osteogenesis-specific genes, such as the transcriptional factors core-binding factor 1 and osterix, followed by increases in secretory OC proved the commitment of MSCs to osteoblastic differentiation. These results revealed that biomineralization followed secretion of OC, which may reflect early osteoblastic differentiation of cultured MSCs under osteoinductive conditions. We ascertained the osteogenic differentiation capacity of cultured MSCs in a non-destructive manner by monitoring OC secretion into the culture medium and proved that secretory OC could represent a reliable marker for predicting in vivo osteogenic potential in bone tissue engineering.

Influence of ADAM28 on biological characteristics of human dental follicle cells

OBJECTIVES

The aim of this study was to investigate the effects of a disintegrin and metalloproteinase 28 (ADAM28) on the biological characteristics of human dental follicle cells (HDFCs) and possible action mechanism.

METHODS

Eukaryotic expression plasmid containing ADAM28 coding region and ADAM28 antisense oligodeoxynucleotides (AS-ODN) with FITC labelling were constructed and synthesised by gene clone and recombination. Then we respectively transfected them into HDFCs by Lipofectamine 2000 system and detected their effects on proliferation, differentiation and apoptosis of HDFCs by MTT assay, cell cycle detection, ALP activity and Annexin V-FITC/PI analysis. Finally we observed the effects of ADAM28 AS-ODN on HDFCs expressing extracellular matrix (ECM) proteins by immunocytochemical staining.

RESULTS

ADAM28 eukaryotic plasmid was constructed and identified successfully, and could be correctly translated and expressed in HDFCs, furthermore overexpression of ADAM28 promoted the HDFCs proliferation and inhibited specific differentiation of HDFCs, while inhibition of ADAM28 exerted the opposite effects and induced apoptosis. Moreover ADAM28 could significantly inhibit the secretion of OPN and type III collagen of HDFCs.

CONCLUSIONS

ADAM28 might actively participate in the network regulation which associates HDFCs proliferation, differentiation, apoptosis with matrix mineralisation during tooth development by interacting with multiple signal molecules.

Fibroblast growth factor expression during skeletal fracture healing in mice

Fibroblast growth factors (FGFs) are important signaling molecules that regulate many stages of endochondral bone development. During the healing of a skeletal fracture, several features of endochondral bone development are reactivated. To better understand the role of FGFs in skeletal fracture healing, we quantitatively evaluated the temporal expression patterns of Fgfs, Fgf receptors (Fgfrs), and molecular markers of bone development over a 14-day period following long bone fracture in a mouse model. These studies identify distinct groups of FGFs that are differentially expressed and suggest active stage-specific roles for FGF signaling during the fracture repair process.

A BAC-bacterial recombination method to generate physically linked multiple gene reporter DNA constructs

BACKGROUND

Reporter gene mice are valuable animal models for biological research providing a gene expression readout that can contribute to cellular characterization within the context of a developmental process. With the advancement of bacterial recombination techniques to engineer reporter gene constructs from BAC genomic clones and the generation of optically distinguishable fluorescent protein reporter genes, there is an unprecedented capability to engineer more informative transgenic reporter mouse models relative to what has been traditionally available.

RESULTS

We demonstrate here our first effort on the development of a three stage bacterial recombination strategy to physically link multiple genes together with their respective fluorescent protein (FP) reporters in one DNA fragment. This strategy uses bacterial recombination techniques to: (1) subclone genes of interest into BAC linking vectors, (2) insert desired reporter genes into respective genes and (3) link different gene-reporters together. As proof of concept, we have generated a single DNA fragment containing the genes Trap, Dmp1, and Ibsp driving the expression of ECFP, mCherry, and Topaz FP reporter genes, respectively. Using this DNA construct, we have successfully generated transgenic reporter mice that retain two to three gene readouts.

CONCLUSION

The three stage methodology to link multiple genes with their respective fluorescent protein reporter works with reasonable efficiency. Moreover, gene linkage allows for their common chromosomal integration into a single locus. However, the testing of this multi-reporter DNA construct by transgenesis does suggest that the linkage of two different genes together, despite their large size, can still create a positional effect. We believe that gene choice, genomic DNA fragment size and the presence of endogenous insulator elements are critical variables.

Overexpression of bone sialoprotein leads to an uncoupling of bone formation and bone resorption in mice

The purpose of this study was to determine the effects of bone sialoprotein (BSP) overexpression in bone metabolism in vivo by using a homozygous transgenic mouse line that constitutively overexpresses mouse BSP cDNA driven by the cytomegalovirus (CMV) promoter. CMV-BSP transgenic (TG) mice and wildtype mice were weighed, and their length, BMD, and trabecular bone volume were measured. Serum levels of RANKL, osteocalcin, osteoprotegerin (OPG), TRACP5b, and PTH were determined. Bone histomorphometry, von Kossa staining, RT-PCR analysis, Western blot, MTS assay, in vitro mineralization assay, and TRACP staining were also performed to delineate phenotypes of this transgenic mouse line. Compared with wildtype mice, adult TG mice exhibit mild dwarfism, lower values of BMD, and lower trabecular bone volume. TG mice serum contained increased calcium levels and decreased PTH levels, whereas the levels of phosphorus and magnesium were within normal limits. TG mice serum also exhibited lower levels of osteoblast differentiation markers and higher levels of markers, indicating osteoclastic activity and bone resorption. H&E staining, TRACP staining, and bone histomorphometry showed that adult TG bones were thinner and the number of giant osteoclasts in TG mice was higher, whereas there were no significant alterations in osteoblast numbers between TG mice and WT mice. Furthermore, the vertical length of the hypertrophic zone in TG mice was slightly enlarged. Moreover, ex vivo experiments indicated that overexpression of BSP decreased osteoblast population and increased osteoclastic activity. Partly because of its effects in enhancing osteoclastic activity and decreasing osteoblast population, BSP overexpression leads to an uncoupling of bone formation and resorption, which in turn results in osteopenia and mild dwarfism in mice. These findings are expected to help the development of therapies to metabolic bone diseases characterized by high serum level of BSP.

Quiescent epithelial cell rests of Malassez can differentiate into ameloblast-like cells

Epithelial cell rests of Malassez (ERM) are quiescent epithelial remnants of Hertwig's epithelial root sheath (HERS) that are involved in the formation of tooth roots. After completion of crown formation, HERS are converted from cervical loop cells, which have the potential to generate enamel for tooth crown formation. Cervical loop cells have the potential to differentiate into ameloblasts. Generally, no new ameloblasts can be generated from HERS, however this study demonstrated that subcultured ERM can differentiate into ameloblast-like cells and generate enamel-like tissues in combination with dental pulp cells at the crown formation stage. Porcine ERM were obtained from periodontal ligament tissue by explant culture and were subcultured with non-serum medium. Thereafter, subcultured ERM were expanded on 3T3-J2 feeder cell layers until the tenth passage. The in vitro mRNA expression pattern of the subcultured ERM after four passages was found to be different from that of enamel organ epithelial cells and oral gingival epithelial cells after the fourth passage using the same expansion technique. When subcultured ERM were combined with subcultured dental pulp cells, ERM expressed cytokeratin14 and amelogenin proteins in vitro. In addition, subcultured ERM combined with primary dental pulp cells seeded onto scaffolds showed enamel-like tissues at 8 weeks post-transplantation. Moreover, positive staining for amelogenin was observed in the enamel-like tissues, indicating the presence of well-developed ameloblasts in the implants. These results suggest that ERM can differentiate into ameloblast-like cells.

Regulation of cartilage formation and maturation by mitogen-activated protein kinase signaling

The majority of bones comprising the adult vertebrate skeleton are generated from hyaline cartilage templates that form during embryonic development. A process known as endochondral ossification is responsible for the conversion of these transient cartilage anlagen into mature, calcified bone. Endochondral ossification is a highly regulated, multistep cell specification program involving the initial differentiation of prechondrogenic mesenchymal cells into hyaline chondrocytes, terminal differentiation of hyaline chondrocytes into hypertrophic chondrocytes, and finally, apoptosis of hypertrophic chondrocytes followed by bone matrix deposition. Recently, extensive research has been carried out describing roles for the three major mitogen-activated protein kinase (MAPK) signaling pathways, the extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and c-jun N-terminal kinase (JNK) pathways, in the successive stages of chondrogenic differentiation. In this review, we survey this research examining the involvement of ERK1/2, p38, and JNK pathway signaling in all aspects of the chondrogenic differentiation program from embryonic through postnatal stages of development. In addition, we summarize evidence from in vitro studies examining MAPK function in immortalized chondrogenic cell lines and adult mesenchymal stem cells. We also provide suggestions for future studies that may help ameliorate existing confusion concerning the specific roles of MAPK signaling at different stages of chondrogenesis.

SCPP gene evolution and the dental mineralization continuum

Many genes critical to vertebrate skeletal mineralization are members of the secretory calcium-binding phosphoprotein (SCPP) gene family, which has evolved by gene duplication from a single ancestral gene. In humans, mutations in some of these SCPP genes have been associated with various diseases related to dentin or enamel hypoplasia. Recently, systematic searches for SCPP genes of various species have allowed us to investigate the history of phylogenetically variable dental tissues as a whole. One important conclusion is that not all disease-associated SCPP genes are present in tetrapods, and teleost fish probably have none, even in toothed species, having acquired their complement of SCPP genes through an independent duplication history. Here, we review comparative analyses of mineralized dental tissues, with particular emphasis on the use of SCPPs, within and between tetrapods and teleosts. Current knowledge suggests a close relationship among bone, dentin, teleost fish enameloid (enamel-like hard tissue), and tetrapod enamel. These tissues thus form a mineralized-tissue continuum. Contemporary dental tissues have evolved from an ancestral continuum through lineage-specific modifications.

Apical tooth germ cell-conditioned medium enhances the differentiation of periodontal ligament stem cells into cementum/periodontal ligament-like tissues

BACKGROUND AND OBJECTIVE

Limitations of current periodontal regeneration modalities in both predictability and extent of healing response, especially on new cementum and attachment formation, underscore the importance of restoring or providing a microenvironment that is capable of promoting the differentiation of periodontal ligament stem cells (PDLSCs) towards cementoblast-like cells and the formation of cementum/periodontal ligament-like tissues. The aim of this study was to investigate the biological effect of conditioned medium from developing apical tooth germ cells (APTG-CM) on the differentiation and cementogenesis of PDLSCs both in vitro and in vivo.

MATERIAL AND METHODS

Using the limiting dilution technique, single-colony-derived human PDLSCs were isolated and expanded to obtain homogeneous populations of PDLSCs. Morphological appearance, cell cycle analysis, bromodeoxyuridine incorporation, alkaline phosphatase (ALP) activity, mineralization behavior, gene expression of cementoblast phenotype and in vivo differentiation capacities of PDLSCs co-cultured with APTG-CM were evaluated.

RESULTS

The induced PDLSCs exhibited several characteristics of cementoblast lineages, as indicated by the morphological changes, increased proliferation, high ALP activity, and the expression of cementum-related genes and calcified nodule formation in vitro. When transplanted into immunocompromised mice, the induced PDLSCs showed tissue-regenerative capacity to produce cementum/periodontal ligament-like structures, characterized by a layer of cementum-like mineralized tissues and associated periodontal ligament-like collagen fibers connecting with the newly formed cementum-like deposits, whereas control, untreated PDLSCs transplants mainly formed connective tissues.

CONCLUSION

Our findings suggest that APTG-CM is able to provide a cementogenic microenvironment and induce differentiation of PDLSCs along the cementoblastic lineage. This has important implications for periodontal engineering.

Gene expression of MC3T3-E1 cells on fibronectin-immobilized titanium using tresyl chloride activation technique

Fibronectin (FN) can be immobilized directly on titanium surfaces using tresyl chloride activation technique. The key advantage of tresyl chloride activation technique lies in its simplicity. In this study, we examined the cell attachment and gene expression of MC3T3-E1 cells on FN-immobilized titanium using GeneChip. Cells attached on FN-immobilized titanium at a higher rate than untreated titanium. FN altered the gene expression profile, whereby 62 genes were found to be up-regulated, while 56 genes were found to down-regulate to over twice the level on day 14. FN not only enhanced the expression levels of IBSP and OMD, but also decreased SULF1 mRNA level. Taken together, the immobilization of FN on tresylated titanium promoted early matrix mineralization and bone formation.