Effect of 3D-Fibroblast Dermis Constructed by Layer-by-Layer Cell Coating Technique on Tight Junction Formation and Function in Full-Thickness Skin Equivalent

Human skin equivalents (HSEs) consisting of an epidermis and dermis have been used as promising tools for drug evaluation and for clinical applications in regenerative medicine. Normal human dermal fibroblasts (NHDFs) are essential for the fabrication of HSEs because they play an important role in the maturation of the epidermis. Recently, epidermal tight junctions (TJs), which are complex cell-cell junctions, have attracted much attention as a second barrier and regulator for other barrier functions. In a previous study, we revealed the expression of TJ-related proteins and the time course of formation of TJ structure in the HSE (layer-by-layer (LbL)-three-dimensional (3D) Skin) constructed by layer-by-layer (LbL) cell coating technique that have a unique dermis consisting of NHDFs only (3D-fibroblast dermis). However, the effect of the 3D-fibroblast dermis on the formation of functional epidermal TJs is unknown. In this study, we investigated the effect of the 3D-fibroblast dermis on the expression of TJ-related proteins and TJ function in LbL-3D Skin. We demonstrated that the 3D-fibroblast dermis affects the long-term expression of TJ-related proteins and the formation of TJ with barrier function in the epidermis. These results show that the 3D-fibroblast dermis in LbL-3D Skin contributes to the formation and maintenance of functional TJs as in native human skin by direct contact with KCs.

Observation of a tight junction structure generated in LbL-3D skin reconstructed by layer-by-layer cell coating technique

Tissue-engineered skin equivalents are reconstructed the functions of human skin and can be used as an alternative to animal experiments in basic study or as cultured skin for regenerative medicine. Recent studies confirmed that epidermal tight junctions (TJs), which are complex intercellular junctions formed in the stratum granulosum of human skin, play an important part in the formation of the skin barrier function. In well-formed reconstructed human skin models, there are several reports on the expression of TJ proteins and their localization in epidermal layer, however, the morphological features of TJ, showing tight junctional contacts and the process of TJ formation have yet to be investigated. In this study, we systematically examined and identified TJ-related proteins and TJ structure in three-dimensional (3D) human skin equivalents reconstructed by layer-by-layer (LbL) cell coating technique (LbL-3D Skin). We demonstrate localization of TJ-related proteins and time course of formation of TJ structure with typical junctional morphology in LbL-3D Skin. These data provide evidence that the LbL-3D Skin is an in vitro model with structure and function extremely similar to living skin.

Calcification during bone healing in a standardised rat calvarial defect assessed by micro-CT and SEM-EDX

OBJECTIVE

The study was designed to investigate the process of calcification during bone healing in a standardized rat calvarial bone defect model, measured by bone mineral density and the concentrations and distributions of calcium, phosphorus and carbon in the bone matrix.

MATERIALS AND METHODS

A standard defect was made on the parietal bone of 12-week-old rats under anaesthesia. The rats were fixed in weeks 1, 2, 4 and 8,and the calvaria were resected and examined with microcomputed tomography, then frozen and sectioned for histology and analysed with energy-dispersive X-ray spectroscopy (EDX). Parietal bone of 12-week-old control rats was processed similarly.

RESULTS

The mineral density of healing bone increased with time. The healing bone became thicker and denser with time in histology. The distributions of Ca and P expanded over the bone matrix, whereas that of C became localised and complemented that of C and P. The Ca/P concentration ratio increased, whereas the C/Ca and C/P ratios decreased in the healing bone matrix.

CONCLUSION

Healing bone is immaturely calcified initially and proceeds calcification gradually, that is, as the bone volume increases, mineral increases in density and matures in quality, while organic components decrease.

Functional and direct interaction between the RNA binding protein HuD and active Akt1

The RNA binding protein HuD plays essential roles in neuronal development and plasticity. We have previously shown that HuD stimulates translation. Key for this enhancer function is the linker region and the poly(A) binding domain of HuD that are also critical for its function in neurite outgrowth. Here, we further explored the underlying molecular interactions and found that HuD but not the ubiquitously expressed HuR interacts directly with active Akt1. We identify that the linker region of HuD is required for this interaction. We also show by using chimeric mutants of HuD and HuR, which contain the reciprocal linker between RNA-binding domain 2 (RBD2) and RBD3, respectively, and by overexpressing a dominant negative mutant of Akt1 that the HuD–Akt1 interaction is functionally important, as it is required for the induction of neurite outgrowth in PC12 cells. These results suggest the model whereby RNA-bound HuD functions as an adapter to recruit Akt1 to trigger neurite outgrowth. These data might also help to explain how HuD enhances translation of mRNAs that encode proteins involved in neuronal development.

Microtubule association of a neuronal RNA-binding protein HuD through its binding to the light chain of MAP1B

RNA-binding proteins (RBPs) play a vital role in the post-transcriptional regulation of gene expression during neuronal differentiation and synaptic plasticity. One such RBP family, the neuronal Hu protein family, serves as an early marker of neuronal differentiation and targets several mRNAs containing adenine/uridine-rich elements. Recently, we reported that one of the neuronal Hu proteins, HuD stimulates cap-dependent translation through interactions with eIF4A and poly (A) tail. Nevertheless, little is known with respect to how neuronal Hu proteins contribute to the local translation of target mRNAs in neuronal differentiation. Here, we found that neuronal Hu proteins, but not the ubiquitously expressed HuR protein, directly interact with the light chain of microtubule-associated proteins MAP1B (LC1). We also show that HuD simultaneously binds both RNA and LC1 in vitro and that it tightly associates with microtubules in cells in an LC1-dependent manner, raising the possibility that HuD recruits target mRNAs to microtubules. These results uncover the neuronal binding partners for neuron-specific Hu proteins and suggest the involvement of Hu proteins in microtubule-mediated regulation of mRNA expression within neuronal processes.

Root and periodontal tissue development after allogenic tooth transplantation between rat littermates

OBJECTIVE

The study was designed to investigate the development of roots and periodontal tissues after allogenic tooth transplantation between rat littermates by micro-computed tomography (micro-CT) and histology.

MATERIALS AND METHODS

The upper right second molars in 2-week-old rats were extracted and immediately transplanted into the upper right first molar socket of rat littermates under anesthesia. The upper left second molars in 2-week-old recipient rats were used as a control. The rats were fixed and tissues analyzed at 0, 4, 8, or 12 weeks after transplantation. Root development of seven rats in each group was analyzed quantitatively using micro-CT. Periodontal tissue formation was examined qualitatively by histologic methods.

RESULTS

Roots developed after allogenic transplantation, but they were significantly shorter than control roots. The number of roots varied from one to four in transplanted teeth, while it was consistently four in control teeth. Periodontal tissue formation in transplanted teeth was equivalent to that of the control teeth.

CONCLUSION

Allogenic transplantation between rat littermates permits root development and periodontal tissue formation.

A small nucleolar RNA functions in rRNA processing in Caenorhabditis elegans

CeR-2 RNA is one of the newly identified Caenorhabditis elegans noncoding RNAs (ncRNAs). The characterization of CeR-2 by RNomic studies has failed to classify it into any known ncRNA family. In this study, we examined the spatiotemporal expression patterns of CeR-2 to gain insight into its function. CeR-2 is expressed in most cells from the early embryo to adult stages. The subcellular localization of this RNA is analogous to that of fibrillarin, a major protein of the nucleolus. It was observed that knockdown of C/D small nucleolar ribonucleoproteins (snoRNPs), but not of H/ACA snoRNPs, resulted in the aberrant nucleolar localization of CeR-2 RNA. A mutant worm with a reduced amount of cellular CeR-2 RNA showed changes in its pre-rRNA processing pattern compared with that of the wild-type strain N2. These results suggest that CeR-2 RNA is a C/D snoRNA involved in the processing of rRNAs.

WDR55 is a nucleolar modulator of ribosomal RNA synthesis, cell cycle progression, and teleost organ development

The thymus is a vertebrate-specific organ where T lymphocytes are generated. Genetic programs that lead to thymus development are incompletely understood. We previously screened ethylnitrosourea-induced medaka mutants for recessive defects in thymus development. Here we report that one of those mutants is caused by a missense mutation in a gene encoding the previously uncharacterized protein WDR55 carrying the tryptophan-aspartate-repeat motif. We find that WDR55 is a novel nucleolar protein involved in the production of ribosomal RNA (rRNA). Defects in WDR55 cause aberrant accumulation of rRNA intermediates and cell cycle arrest. A mutation in WDR55 in zebrafish also leads to analogous defects in thymus development, whereas WDR55-null mice are lethal before implantation. These results indicate that WDR55 is a nuclear modulator of rRNA synthesis, cell cycle progression, and embryonic organogenesis including teleost thymus development.

Analysis of appositional bone formation using a novel rat experimental model

AIM

To analyze the process of appositional bone formation using our original rat experimental model.

MATERIALS AND METHODS

Rats were anesthetized and a ring made of polytetrafluorethylene was placed on the parietal bone surface in the surgical procedure. The time course of appositional bone formation was analyzed with histomorphometry and in situ hybridization for type I collagen and bone sialoprotein.

RESULTS

The rat experimental model allowed new bone to be formed on the pre-existing bone surface and persist for 12 weeks. We demonstrated that bone is apposed actively for the first 4 weeks and less actively thereafter.

CONCLUSIONS

The experimental model may contribute to biological analysis for appositional bone formation expected to occur in clinical procedures such as alveolar bone augmentation and sinus lifting.

Mutual induction of noncollagenous bone proteins at the interface between epithelial cells and fibroblasts from human periodontal ligament

BACKGROUND AND OBJECTIVE

Epithelial-mesenchymal interactions are responsible for cell differentiation during periodontal regeneration. The present study was undertaken to examine the expression of alkaline phosphatase and noncollagenous bone proteins, such as osteopontin, osteocalcin and bone sialoprotein, with respect to interaction between the cells of the epithelial rests of Malassez and fibroblasts from human periodontal ligament.

MATERIAL AND METHODS

Explants of human periodontal ligament tissues produced outgrowths containing both putative epithelial rests of Malassez cells and human periodontal ligament fibroblasts in a modified serum-free medium. Putative epithelial rests of Malassez cells cultured alone, and human periodontal ligament fibroblasts cultured alone, were used as controls. The expression levels of amelogenin were analyzed by in situ hybridization. The expression and distribution of alkaline phosphatase and noncollagenous bone proteins in both cell populations at the interface between putative epithelial rests of Malassez cells and human periodontal ligament fibroblasts were analyzed by immunohistochemistry, in situ hybridization and reverse transcription-polymerase chain reaction.

RESULTS

Amelogenin mRNA was detected at high levels only in putative epithelial rests of Malassez cells at the interface. Alkaline phosphatase and bone sialoprotein mRNAs were detected significantly at the interface between putative epithelial rests of Malassez cells and human periodontal ligament fibroblast cells. In particular, bone sialoprotein and its mRNA were expressed significantly in human periodontal ligament fibroblasts at the interface between putative epithelial rests of Malassez cells and human periodontal ligament fibroblast cells. The expressions of osteopontin and its mRNA were not different between putative epithelial rests of Malassez cells and human periodontal ligament fibroblasts at the interface. Osteocalcin and its mRNA were expressed strongly in putative epithelial rests of Malassez cells at the interface between putative epithelial rests of Malassez cells and human periodontal ligament fibroblasts.

CONCLUSION

These findings indicate that the epithelial-mesenchymal interaction modulates the expression of alkaline phosphatase, osteocalcin and bone sialoprotein in putative epithelial rests of Malassez cells and human periodontal ligament fibroblasts, suggesting that epithelial-mesenchymal interactions play a role in the maintenance of periodontal ligament.

Proliferation and adhesion of periodontal ligament cells on synthetic biominerals

OBJECTIVE

Hydroxiapatite (HA) has been suggested as a useful biomaterial to support the regeneration of tissues. In this study, we investigated the adhesion of periodontal ligament (PDL) cells on octacalcium phosphate (OCP) and its hydrolyzed apatitic product (HL), which are known precursors of HA.

METHODS

Rat PDL cells were cultured on OCP or HL-coated dishes. Cell proliferation and adhesion and mRNA expression of collagen I, fibronectin integrin subunits were examined. Cell adhesion inhibition assays were carried out by GRGDSPK (Gly-Arg-Gly-Asp-Ser-Pro-Lys).

RESULTS

In early culture period, the cell number of PDL cells was lower on OCP and HL than that on control without any coating. However, the cell number on OCP or HL caught up with control later period. mRNA expression level of collagen I and fibronectin on OCP and HL were similar among OCP HL and control, although they differed early in the culture period. Integrin subunits were expressed on both OCP and HL as well as on control. Cell adhesion was inhibited by RGD inhibitor peptide.

CONCLUSION

Our findings indicated that rat PDL cells produce collagen I and fibronectin on OCP and HL, and then show increased cell numbers depending on adhesion to the matrices through integrins.

In vitro differentiation of epithelial cells cultured from human periodontal ligament

BACKGROUND AND OBJECTIVE

Alkaline phosphatase and noncollagenous bone proteins are produced prior to cementum formation. While it has been suggested that epithelial rests of Malassez are involved in cementum formation, little is known about the relationship between epithelial rests of Malassez and cementum formation. The purpose of the present study was to determine whether the epithelial rests of Malassez cells cultured from human periodontal ligament can produce alkaline phosphatase and noncollagenous bone proteins, such as osteopontin, osteocalcin and bone sialoprotein.

MATERIAL AND METHODS

An outgrowth of putative epithelial rests of Malassez cells was produced from periodontal ligament explant, and second passage cultures were used in the experiments. Human gingival epithelial cells and periodontal ligament fibroblasts were used as controls. The expression levels of amelogenin were analyzed by immunostaining and in situ hybridization. Furthermore, the expression levels of alkaline phosphatase and noncollagenous bone proteins were assessed by immunostaining and reverse transcription-polymerase chain reaction.

RESULTS

Amelogenin, alkaline phosphatase and osteopontin proteins and their corresponding mRNAs were detected at high levels in putative epithelial rests of Malassez cells. Osteocalcin and bone sialoprotein were not expressed in putative epithelial rests of Malassez cells. Alkaline phosphatase and noncollagenous bone proteins were seen in periodontal ligament fibroblasts, but not in gingival epithelial cells.

CONCLUSION

Our results suggest that putative epithelial rests of Malassez cells cultured alone do not transform into maturing cells to form the cementum, but may play a potential role in the mineralization process.

Characterization of dentin formed in transplanted rat molars by electron probe microanalysis

The present study was designed to characterize dentin formed in transplanted rat molars by investigating calcium (Ca), phosphorus (P), and magnesium (Mg) concentrations using electron probe microanalysis (EPMA) as well as examining the rate of dentin matrix formation by vital staining. The unerupted immature lower right second molar in 2-week-old rats was transplanted into the upper right first molar socket. Rats were injected with oxytetracycline, calcein, and alizarin intraperitoneally at 1 day before and 1 and 2 weeks after transplantation, respectively, for vital staining. The maxillae and mandibles were fixed 3 weeks after transplantation, resected, and embedded in resin. Undemineralized sections were cut and examined by fluorescent microscopy and EPMA. The thickness of dentin formed in the first week after transplantation was significantly less than that of dentin formed in any other 1-week period in the transplanted tooth and was about one-fifth the thickness of dentin formed in control teeth. Formation of dentin recovered in the third week after transplantation. In the first week after transplantation, EPMA demonstrated a sharp increase in Mg concentration with a slight decrease in Ca concentration. Thereafter, no significant difference was identified among Ca, P, or Mg concentrations or the Ca/P ratio between transplanted and control teeth. These results suggest that disruption of the circulation and innervation by transplantation cause a temporary change in the matrix formation rate and elemental distribution of dentin, which is subsequently restored within 2 weeks after transplantation.

Osteoclastogenic activity during mandibular distraction osteogenesis

Mandibular distraction osteogenesis is a well-developed clinical modality for the treatment of craniofacial deformities and dental arch discrepancies, in combination with orthodontic treatment. However, in our previous study, orthodontic tooth movement into the distraction gap caused severe root resorption. The present study aimed to clarify the osteoclastogenic activity of cells in the distraction gap. We hypothesized that the gene expression of osteoclastogenic- and osteoclast-supporting molecules in osteoblasts and stromal cells would increase at distraction sites during the consolidation period. An animal model experiment involving rabbits was designed for mandibular distraction osteogenesis and subjected to in situ hybridization analysis. The number of osteoclasts was larger in the distraction gap during the early consolidation period than in normal controls, due to an increase of gene expression for osteoclastogenic cytokines in osteoblasts. It was concluded that osteoclastogenic and osteoclastic activities are stimulated at distraction sites during the early consolidation period.

New scaffold for recombinant human bone morphogenetic protein-2

A bioactive and resorbable scaffold is necessary to exhibit the osteoinductive potency of recombinant human bone morphogenetic protein-2 (rhBMP-2). In a previous study, we found that synthetic octacalcium phosphate (OCP) enhances bone regeneration and is replaced by newly formed bone after it is resorbed. We hypothesized that OCP may be useful as an effective scaffold for rhBMP-2 to enhance bone regeneration. To test this hypothesis, the present study was designed to investigate whether an OCP/BMP composite implant could more effectively enhance bone regeneration. A critical-sized defect was made in a rat calvarium and 1. 15 mg of OCP combined with 10 microg of rhBMP-2 (OCP/BMP 10 microg), 2. 15 mg of OCP combined with 1 microg of rhBMP-2 (OCP/BMP 1 microg), or 3. OCP (OCP alone) was implanted into the defect and fixed at 4 or 8 weeks after implantation. The percentage of newly formed bone (n-Bone%) in the defect was determined by a histomorphometrical analysis. A statistical analysis showed that n-Bone% with OCP/BMP was significantly higher than that with OCP at both time points, whereas the difference in n-Bone% between OCP/BMP 10 microg and OCP/BMP 1 microg was not significant. The present results suggest that OCP can be used as an effective scaffold for rhBMP-2 and this OCP delivery system may be able to reduce the standard effective dose of rhBMP-2, which would be beneficial because low doses (<100 microg/g OCP) of rhBMP-2 enhance bone regeneration.

Expression of MMP-8 and MMP-13 genes in the periodontal ligament during tooth movement in rats

Periodontal ligament tissue is remodeled on both the tension and compression sides of moving teeth during orthodontic tooth movement. The present study was designed to clarify the hypothesis that the expression of MMP-8 and MMP-13 mRNA is promoted during the remodeling of periodontal ligament tissue in orthodontic tooth movement. We used the in situ hybridization method and semi-quantitative reverse-transcription/polymerase chain-reaction analysis to elucidate the gene expression of MMP-8 and MMP-13 mRNA. Expression of MMP-8 and MMP-13 mRNA transiently increased on both the compression and tension sides during active tooth movement in vivo. The gene expression of MMP-8 and MMP-13 was induced by tension, while compression indirectly promoted the gene expression of MMP-8 and MMP-13 through soluble factors in vitro. Thus, we concluded that the expression of MMP-8 and MMP-13 is differentially regulated by tension and compression, and plays an important role in the remodeling of the periodontal ligament.

Expression of MMP-8 and MMP-13 mRNAs in rat periodontium during tooth eruption

The present study was designed to investigate mRNA expression of matrix metalloproteinase-8 (MMP-8) and MMP-13 in forming periodontium during tooth eruption in the rat. RT-PCR for the decalcified paraffin sections indicated expression of MMP-8 and MMP-13 in the periodontal tissues. In situ hydridization demonstrated expression of MMP-8 in osteoblasts, osteocytes, periodontal ligament cells, cementoblasts, and cementocytes along with collagen types I and III. In contrast, transcripts of MMP-13 were confined to a small population of osteoblasts and osteocytes in alveolar bone. The results suggested that MMP-8 may be involved in remodeling the periodontium during tooth eruption, and its expression may be coordinated with that of collagen types I and III, whereas the participation of MMP-13 may be rather limited.

Implanted octacalcium phosphate is more resorbable than beta-tricalcium phosphate and hydroxyapatite

Our previous studies have suggested that synthetic octacalcium phosphate (OCP) could be resorbed and replaced by newly formed bone if implanted in rat skull defects. We hypothesized that the implanted OCP is more resorbable than other commonly used bone graft substitutes of calcium phosphate compounds, such as hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP). To test the hypothesis, the present study was designed to compare histomorphometrically resorption of the implanted OCP, HA, and beta-TCP, which were kept in the experimental cranial defect of rats for a long term. A full thickness of standardized trephine defect was made in the rat parietal bone, and the same volume of granules of OCP, HA, and beta-TCP were implanted into the defect. Five specimens of each group were fixed 6 months after implantation. The percentage of remaining implants (r-Imp%) and newly formed bone (n-Bone%) in the defect was analyzed histomorphometrically. The statistical analysis showed that the r-Imp% of OCP was significantly lower than that of HA and beta-TCP. In contrast, the n-Bone% of OCP was significantly higher than that of HA and beta-TCP. The present study has shown that the implanted OCP in the rat cranial defect is more resorbable than the implanted beta-TCP and HA, whereas the implanted OCP enhances bone formation more than the implanted beta-TCP and HA.

Implantation of octacalcium phosphate combined with transforming growth factor-beta1 enhances bone repair as well as resorption of the implant in rat skull defects

In our previous study, we reported that synthetic octacalcium phosphate (OCP) enhances bone repair if implanted in rat skull defects. We hypothesized that OCP can be used as an effective carrier for transforming growth factor-beta1 (TGF-beta1) to promote bone repair. We designed the present study to investigate histomorphometrically whether combination with recombinant human TGF-beta1 could promote bone repair caused by OCP per se (Control/OCP). A full-thickness standardized trephine defect was made in the rat parietal bone and OCP combined with recombinant human TGF-beta1 (TGF-beta1/OCP) or Control/OCP was implanted into the defect. Four rats from each group were fixed at 2, 4, and 8 weeks after implantation. Histomorphometrical analysis of the percentage of newly formed bone (n-Bone %) and remaining implants (r-Imp %) in the defect was performed. The statistical analysis showed the n-Bone % of TGF-beta1/OCP was significantly higher than that of the Control/OCP in week 4, whereas the r-Imp % of TGF-beta1/OCP was significantly lower than that of the Control/OCP. The present study demonstrated that OCP can be used as an effective carrier for TGF-beta1 and their combination enhances bone repair as well as resorption of the carrier OCP in the early stage of bone formation.

Temporal and spatial gene expression of major bone extracellular matrix molecules during embryonic mandibular osteogenesis in rats

It is not known how gene expression of bone extracellular matrix molecules is controlled temporally and spatially, or how it is related with morphological differentiation of osteoblasts during embryonic osteogenesis in vivo. The present study was designed to examine gene expressions of type I collagen, osteonectin, bone sialoprotein, osteopontin, and osteocalcin during mandibular osteogenesis using in situ hybridization. Wistar rat embryos 13-20 days post coitum were used. The condensation of mesenchymal cells was formed in 14-day rat embryonic mandibles and expressed genes of pro-alpha 1 (I) collagen, osteonectin, bone sialoprotein and osteopontin. Cuboidal osteoblasts surrounding the uncalcified bone matrix were seen as early as in 15-day embryonic mandibles, while flat osteoblasts lining the surface of the calcified bone were seen from 16-day embryonic mandibles. Cuboidal osteoblasts expressed pro-alpha 1(I) collagen, osteonectin and bone sialoprotein intensely but osteopontin very weakly. In contrast, flat osteoblasts expressed osteopontin very strongly. Osteocytes expressed the extracellular matrix molecules actively, in particular, osteopontin. The present study demonstrated the distinct gene expression pattern of type I collagen, osteonectin, bone sialoprotein, osteopontin and osteocalcin during embryonic mandibular osteogenesis in vivo.

Osteoblastic differentiation of periosteum-derived cells is promoted by the physical contact with the bone matrix in vivo

The periosteum contains osteoprogenitors that differentiate to osteoblasts in bone growth or repair. Our previous studies suggested the hypothesis that the physical contact of the periosteum with the bone matrix is requisite for the differentiation of osteoblasts. To test the hypothesis, the present study was designed to investigate how the contact between the periosteum and the bone matrix influences the osteoblastic differentiation of periosteal cells with establishing a new experimental model in vivo. Differentiation of osteoblasts was assessed by gene expression of type I collagen, osteocalcin and bone sialoprotein using in situ hybridization. A barrier was designed to prevent periosteal cells from contacting the bone matrix using the membrane filter. The membrane filter was inserted surgically between the surface of rat parietal bone and the periosteum after being punched out with pin holes. Periosteal cells were allowed to contact with the bone surface only through the pin holes. The pin hole was filled with cells derived from the periosteum 1 week after inserting the filter. Differentiation of osteoblasts in week 2 and noticeable bone formation in week 3 were identified on the bone surface only under the pin hole but not under the filter. The present study demonstrated that the physical contact with the bone matrix promotes osteoblastic differentiation of periosteum-derived cells in vivo.

Implantation of octacalcium phosphate nucleates isolated bone formation in rat skull defects

OBJECTIVE

Our previous radiographic examinations have indicated that the synthetic octacalcium phosphate (OCP) may provide the core for nucleating multiple osteogenic sites in the experimentally created cranial defect.

DESIGN

The present study was designed to confirm the possibility that the implanted OCP causes the osteoinduction as well as the osteoconduction in the rat cranial defect.

MATERIALS AND METHODS

Standardized defects were created in male Wistar rat calvaria, and the OCP granules were implanted into the defect. The sham operated rats were processed in the same way except that nothing was implanted. The rats were fixed at 4 weeks after implantation of OCP or the sham operation. We examined bone formed on the implanted OCP, analyzing serial sections histologically combined with immunohistochemistry for the bone specific protein, osteocalcin.

RESULTS

In the defects treated with OCP, the radiopacity was scattered throughout the defect besides being observed along the defect margin of the parietal bone. Examination of the serial sections showed that some of new bones on the implanted OCP were formed away from the defect margin of the parietal bone with regard to both histological identification and specific molecular marker.

CONCLUSIONS

The present study suggested that the implanted OCP can serve as a core for initiating bone formation and cause the osteoinduction as well as the osteoconduction in the defect.

Gene and protein expressions of type I collagen are regulated tissue-specifically in rat hyaline cartilages in vivo

The present study was designed to investigate how rat hyaline cartilages at various sites in vivo express the gene and protein of type I collagen using in situ hybridization and immunohistochemistry. The gene of pro alpha 1(I) collagen was expressed by chondrocytes in articular cartilage, and the protein of type I collagen was identified in the cartilage matrix. In contrast, growth plate cartilage expressed the gene of pro alpha 1(I) collagen, but no protein of type I collagen. Neither gene nor protein of type I collagen was expressed in cartilages of trachea and nasal septum. The present study suggested that expression of type I collagen in hyaline cartilages may be regulated tissue-specifically at gene and/or protein levels.

Characterization of interglobular dentin and Tomes' granular layer in dog dentin using electron probe microanalysis in comparison with predentin

The interglobular dentin (IG) and the Tomes' granular layer (TGL) as well as predentin are hypomineralized regions in dentin. Some previous studies proposed that the IG and the TGL are identical with difference only in size, whereas other suggested that they are distinct structures. In order to characterize their matrix components, the present study was designed to analyze the elements of calcium (Ca), phosphorus (P), and sulfur (S) in the IG and the TGL in comparison with predentin using the Electron Probe Microanalysis (EPMA). The TGL was highest in the concentration of both Ca and P among the hypomineralized regions followed by the IG and predentin, whereas predentin was the highest in the concentration of S followed by the IG and the TGL. Alcian blue staining suggested that the S elements identified with the EPMA are incorporated into the sulfated glycosaminoglycan chains of proteoglycans. The present study first demonstrated distinct characteristics of matrix components in the IG and the TGL, i.e., the IG is poorer in mineralization but much richer in a proteoglycan content than the TGL. The IG may originate from predentin because of their analogy, whereas the TGL may follow a different ontogeny.

Distinctive expression of extracellular matrix molecules at mRNA and protein levels during formation of cellular and acellular cementum in the rat

Little is known about differential expression of extracellular matrices secreted by cementoblasts between cellular and acellular cementum. We hypothesize that cementoblasts lining acellular cementum express extracellular matrix genes differently from those lining cellular cementum, thereby forming two distinct types of extracellular matrices. To test this hypothesis, we investigated spatial and temporal gene expression of selected extracellular matrix molecules, that is type I collagen, bone sialoprotein, osteocalcin and osteopontin, during formation of both cellular and acellular cementum using in situ hybridization. In addition, their extracellularly deposited and accumulated proteins were examined immunohistochemically. The mRNA transcripts of pro-alpha1 (I) collagen were primarily localized in cementoblasts of cellular cementum and cementocytes, while those of bone sialoprotein were predominantly seen in cementoblasts lining acellular cementum. In contrast, osteocalcin was expressed by both types of cementoblasts and cementocytes and so was osteopontin but only transiently. Our immunohistochemical examination revealed that translated proteins were localized extracellularly where the genes had been expressed intracellularly. The present study demonstrated the distinctive expression of genes and proteins of the extracellular matrix molecules between cellular and acellular cementum.

Compressive force promotes chondrogenic differentiation and hypertrophy in midpalatal suture cartilage in growing rats

Midpalatal suture cartilage (MSC) is secondary cartilage located between the bilateral maxillary bones and has been utilized in the analysis of the biomechanical characteristics of secondary cartilage. The present study was designed to investigate the effects of compressive force on the differentiation of cartilage in midpalatal suture cartilage in rats. Forces of various magnitudes were applied to the midpalatal suture cartilage in 4-week-old male Wistar rats for 1, 2, 4, 7, or 14 days, mediated through the bilateral 1st molars using orthodontic wires. The differentiation pathways in the MSC cells were examined by immunohistochemistry for the differentiation markers type I, type II and type X collagen, and glycosaminoglycans (GAGs), chondroitin-4-sulfate, chondroitin-6-sulfate and keratan sulfate. Histologically and immunohistochemically, the midpalatal suture cartilage in control rats had the characteristic appearance of secondary cartilage. In the experimental groups, the center of the midpalatal suture cartilage that contained osteo-chondro progenitor cells seemed to become mature cartilage and its immuno-reaction to type II and X collagen and GAGs increased as the experiment progressed. This differentiation was dependent upon the magnitude and duration of the force applied to the midpalatal suture cartilage; i.e., cartilaginous differentiation progressed more rapidly as the applied force increased. The present results suggest that the differentiation of osteo-chondro progenitor cells into mature and hypertrophic chondrocytes in the precartilaginous cell layer is promoted by compressive force.

Epithelial rests colocalize with cementoblasts forming acellular cementum but not with cementoblasts forming cellular cementum

Epithelial rests of Malassez and cementoblasts were examined in the rat molars during the early stages of root formation using an antilaminin antibody and/or peanut agglutinin (PNA), and an antiosteocalcin (OC) antibody, respectively. The roots of the first molars were used for study. The antilaminin antibody stained the basement membrane surrounding the epithelial root sheath and epithelial rests. The basement membrane of the epithelial root sheath was continuous, but that of the epithelial rests was discontinuous. The cells of epithelial rests and epithelial root sheath were positive for PNA. The structural characteristics of the epithelial rests were seen in the sections stained doubly with PNA and the antilaminin antibody. The cells of epithelial rests were fibroblast-like and formed a fine mesh in 2-week-old rats. In 3-week-old rats, the epithelial rests were also present at the coronal half of root surface, showing typical cell cords, but were not present at the apical part of the root surface where the cellular cementum covered the root dentin. At the root apex of 3-week-old rats, the cells of epithelial rests forming fine meshes were seen near the epithelial root sheath. The anti-OC antibody stained cementoblasts lining acellular and cellular cementum. The sections doubly stained with the anti-OC and the antilaminin antibodies or PNA further revealed the close relation between epithelial rests and cementoblasts. The OC-positive cells lining acellular cementum or dentin were localized very close to the epithelial rests. In contrast, the OC-positive cells lining cellular cementum did not show close association with the epithelial cells, except the cells located most apically where the basement membrane of the epithelial root sheath is disrupted and the initial cellular cementum begins to be formed. The present results suggest that the epithelial rests and/or the discontinuous basement membrane of them may have a role for the acellular cementum formation at least in the early stage of root formation.

Immunohistochemical localization of type I collagen, fibronectin and tenascin C during embryonic osteogenesis in the dentary of mandibles and tibias in rats

Type I collagen, fibronectin and tenascin C play an important role in regulating early osteoblast differentiation, but the temporal and spatial relationship of their localization during embryonic osteogenesis in vivo is notknown. The present study was designed to localize these three molecules in the dentary of mandibles and tibias in rat embryos using immunohistochemistry. Serial paraffin sections were cut and adjacent sections were processed for von Kossa staining or immunohistochemistry for type I collagen, fibronectin and tenascin C. In the dentary, tenascin C was localized within and around the mesenchymal cell condensation in embryos at 14 days in utero. The bone matrix at 15 days showed immunoreactivity for both type I collagen and fibronectin. The immunoreactivity of type I collagen was persistent, whereas that of fibronectin decreased with age of embryos. In tibias, tenascin C was localized in the perichondral mesenchymal tissue at 17 days. Immunoreactivity for type I collagen was persistent in the bone matrix, whereas the tibial bone showed little immunoreactivity for fibronectin at any embryonic age examined. The present study demonstrated characteristic localization of type I collagen, fibronectin and tenascin C during embryonic osteogenesis in the dentary of mandibles and tibias.

[Cementum formation in rat molar roots]

Cementum is the calcified tissue covering roots of teeth and serves as attachment sites of the periodontal ligament. Although recent studies have suggested that extracellular matrix of cementum is very similar to that of bone, cementogenesis on a biological basis is still poorly understood. There are variations in the distribution and mineral contents of cementum depending on animal age, tooth species and position within the tooth roots. This paper reviews the formation and age-related changes of cellular and acellular cementum in rat molar roots, and discusses the effect of mechanical stress to the cementum formation.

Expression of major bone extracellular matrix proteins during embryonic osteogenesis in rat mandibles

It is not known how bone proteins appear in the matrix before and after calcification during embryonic osteogenesis. The present study was designed to investigate expressions of the five major bone extracellular matrix proteins--i.e. type I collagen, osteonectin, osteopontin, bone sialoprotein and osteocalcin--during osteogenesis in rat embryonic mandibles immunohistochemically, and their involvement in calcification demonstrated by von Kossa staining. Wistar rat embryos 14 to 18 days post coitum were used. Osteogenesis was not seen in 14-day rat embryonic mandibles. Type I collagen was localized in the uncalcifed bone matrix in 15-day mandibles, where no other bone proteins showed immunoreactivity. Osteonectin, osteopontin, bone sialoprotein and osteocalcin appeared almost simultaneously in the calcified bone matrix of 16-day mandibles and accumulated continuously in 18-day mandibles. The present study suggested that type I collagen constitutes the basic framework of the bone matrix upon which the noncollagenous proteins are oriented to lead to calcification, whereas the noncollagenous proteins are deposited simultaneously by osteoblasts and are involved in calcification cooperatively.

Distribution of interglobular dentine in human tooth roots

The present study was designed to examine the distribution of interglobular dentine in human tooth roots. The material comprised 17 teeth, of which 3 were premolars extracted for orthodontic reasons from children 10-12 years of age and the other teeth (4 incisors, 3 canines and 7 molars) were extracted for periodontitis from individuals aged 32-63 years. All teeth were free of caries and cervical dentine defects. Ground sections of the teeth cut longitudinally were stained with basic fuchsin and observed by fluorescence and confocal microscopy as well as transmitted light microscopy. Basic fuchsin stained the dentinal tubules, interglobular dentine and the granular layer of Tomes. These structures appeared intense blue to faint violet with transmitted light microscopy, whereas their staining displayed intense fluorescence with fluorescence microscopy. Therefore, the interglobular dentine could be detected more sensitively with fluorescence and confocal microscopy than with transmitted light microscopy. Typical interglobular dentine was present in coronal dentine in most of the teeth. In the radicular dentin, position and size of the interglobular dentine was different among the teeth examined. Most of the teeth had the interglobular dentine in the cervical part of the roots (type A). Two premolars displayed the interglobular dentine in the coronal half of the root (type B). The types A and B contained large interglobular areas. A small amount of interglobular dentine was restricted to the apical half of the roots of two canines and one molar (type C). In contrast to types A and B which were seen at both labial or buccal and lingual sides of roots, the interglobular dentine of type C was seen only at one side, labial or lingual. Some of the tooth roots did not show any interglobular dentine (type D). Most of the incisors, canines and premolar were types A, B, and C, respectively, and the molars were mixed types A, C, and D. These results suggest that the factors affecting dentinogenesis during root formation are unique for each tooth.

Confocal microscopy of Tomes' granular layer in dog premolar teeth

Tomes' granular layer is the hypomineralized area of radicular dentin, but knowledge concerning it is limited. The present study was designed to investigate the structural characteristics of Tomes' granular layer in the dog's teeth by confocal microscopy. Permanent premolars of four beagles, two at 7 months and the other two at 14 months of age, were used for observation. During premolar root formation, the 7-month-old dogs were injected with calcein and alizarin red S for vital staining of dentin, and ground sections of the teeth were prepared. Both ground and decalcified-paraffin sections were made from the teeth of the 14-month-old dogs and stained with basic fuchsin or with hematoxylin and eosin. All sections were examined by fluorescence and confocal microscopy. In the ground sections, granules of Tomes' layer and dentinal tubules were stained with basic fuchsin and with calcein. The granules of Tomes' layer stained with calcein were seen only near the labeling lines by calcein. The granules of Tomes' layer appeared as bright spots in cross sections, and as lines in longitudinal sections. When the sections were cut tangentially through the surface of dentin, the granules of Tomes' layer showed a reticular structure. Most of the dentinal tubules were seen to pass between the granules and terminated in the dentin-cementum junction. Looped tubules were not found in this area. In the paraffin sections stained with hematoxylin and eosin, extracellular matrix of dentin showed fluorescence of various intensities and dentinal tubules appeared dark. At the surface of the radicular dentin, the granules of Tomes' layer appeared as fluorescent fibers running parallel to the surface of dentin in the longitudinal sections. The fibers appeared as bright spots in the cross sections and as a mesh in the tangential sections. In the periodontal ligament, collagen fibers showed intense fluorescence, whereas most cells were negative. From these results we conclude that Tomes' granular layer of dog's teeth may be the collagen fiber bundles that remained uncalcified or hypocalcified within the radicular dentin.

Implantation of octacalcium phosphate (OCP) in rat skull defects enhances bone repair

Synthetic octacalcium phosphate (OCP) enhances bone formation if implanted into the subperiosteal region of murine bone. Such implanted OCP may be resorbed and replaced by bone with time. We hypothesized that OCP could be used as an effective bone substitute. To test this hypothesis, we designed the present study to investigate if bone repair in a rat skull defect is enhanced by the implantation of OCP. Rats were divided into two groups: OCP-treated animals and untreated controls. Six rats from each group were fixed at 4, 12, and 24 weeks after implantation. A full-thickness standardized trephine defect was made in the parietal bone, and synthetic OCP was implanted into the defect. After being examined radiographically, the specimens were decalcified and processed for histology. OCP implantation significantly promoted bone repair compared with the controls. A statistical analysis showed an increase in the area of radiopacity within the skull defect between week 4 and week 12. Histologically, bone was formed on the implanted OCP and along the defect margin at week 4. At week 12, the implanted OCP was surrounded by newly formed bone. At week 24, the defect was almost completely filled with bone. In the control, bone formation was observed only along the defect margin. The present results demonstrate that OCP could be used as an effective bone substitute.

Implanted octacalcium phosphate (OCP) stimulates osteogenesis by osteoblastic cells and/or committed osteoprogenitors in rat calvarial periosteum

Our previous studies demonstrated that the octacalcium phosphate (OCP) causes new appositional bone formation on the OCP when implanted into the subperiosteal region of murine calvaria. The OCP may stimulate the cell population committed to the osteoblastic differentiation in the periosteum and have them express the phenotype. The present study was designed to investigate which periosteal cell population is involved in bone formation on the OCP with applying the OCP implants on top of and underneath the periosteum. The periosteum of the rat parietal bones was flapped and the OCP was implanted on top of or underneath the periosteum, in which the implantation sites were defined using the membrane filter. The histology was examined to see if new appositional bone formation occurs on the OCP implant under each condition. New bone was deposited on the OCP on the bone surface separated from the periosteum by the filter, whereas no bone was formed either under the periosteum separated from the bone surface by the filter or on the periosteum. The present study suggests that the OCP acts on osteoblasts, bone lining cells and/or their closely committed progenitors on the bone surface to express the phenotype and deposit new bone on the OCP implant.