A novel role of periostin in postnatal tooth formation and mineralization

Periostin plays multiple functions during development. Our previous work showed a critical role of this disulfide-linked cell adhesion protein in maintenance of periodontium integrity in response to occlusal load. In this study, we attempted to address whether this mechanical response molecule played a direct role in postnatal tooth development. Our key findings are 1) periostin is expressed in preodontoblasts, and odontoblasts; and the periostin-null incisor displayed a massive increase in dentin formation after mastication; 2) periostin is also expressed in the ameloblast cells, and an enamel defect is identified in both the adult-null incisor and molar; 3) deletion of periostin leads to changes in expression profiles of many non-collagenous protein such as DSPP, DMP1, BSP, and OPN in incisor dentin; 4) the removal of a biting force leads to reduction of mineralization, which is partially prevented in periostin-null mice; and 6) both in vitro and in vivo data revealed a direct regulation of periostin by TGF-β1 in dentin formation. In conclusion, periostin plays a novel direct role in controlling postnatal tooth formation, which is required for the integrity of both enamel and dentin.     

α11β1 integrin‐mediated MMP‐13‐dependent collagen lattice contraction by fibroblasts: Evidence for integrin‐coordinated collagen proteolysis

We have previously determined that integrin α11β1 is required on mouse periodontal ligament (PDL) fibroblasts to generate the force needed for incisor eruption. As part of the phenotype of α11^?/? mice, the incisor PDL (iPDL) is thickened, due to disturbed matrix remodeling. To determine the molecular mechanism behind the disturbed matrix dynamics in the PDL we crossed α11^?/? mice with the Immortomouse and isolated immortalized iPDL cells. Microarray analysis of iPDL cells cultured inside a 3D collagen gel demonstrated downregulated expression of a number of genes in α11‐deficient iPDL cells, including matrix metalloproteinase‐13 (MMP‐13) and cathepsin K. α11^?/? iPDL cells in vitro displayed disturbed interactions with collagen I during contraction of attached and floating collagen lattices and furthermore displayed reduced MMP‐13 protein expression levels. The MMP‐13 specific inhibitor WAY 170523 and the Cathepsin K Inhibitor II both blocked part of the α11 integrin‐mediated collagen remodeling. In summary, our data demonstrate that in iPDL fibroblasts the mechanical strain generated by α11β1 integrin regulates molecules involved in collagen matrix dynamics. The positive regulation of α11β1‐dependent matrix remodeling, involving MMP‐13 and cathepsin K, might also occur in other types of fibroblasts and be an important regulatory mechanism for coordinated extracellular and intracellular collagen turnover in tissue homeostasis. J. Cell. Physiol. © 2012 Wiley Periodicals, Inc.     

Periostin is required for matricellular localization of CCN3 in periodontal ligament of mice

CCN3 is a matricellular protein that belongs to the CCN family. CCN3 consists of 4 domains: insulin-like growth factor-binding protein-like domain (IGFBP), von Willebrand type C-like domain (VWC), thrombospondin type 1-like domain (TSP1), and the C-terminal domain (CT) having a cysteine knot motif. Periostin is a secretory protein that binds to extracellular matrix proteins such as fibronectin and collagen. In this study, we found that CCN3 interacted with periostin. Immunoprecipitation analysis revealed that the TSP1-CT interacted with the 4 repeats of the Fas 1 domain of periostin. Immunofluorescence analysis showed co-localization of CCN3 and periostin in the periodontal ligament of mice. In addition, targeted disruption of the periostin gene in mice decreased the matricellular localization of CCN3 in the periodontal ligament. Thus, these results indicate that periostin was required for the matricellular localization of CCN3 in the periodontal ligament, suggesting that periostin mediated an interaction between CCN3 and the extracellular matrix.     

Immunolocalization and activity of the MMP-9 and MMP-2 in odontogenic region of the rat incisor tooth after post shortening procedure

MMP-9 and MMP-2 are metalloproteinases which degrade the denatured collagen fibers. However, there is no report about roles of these MMPs in the odontogenic region of the adult rat incisor tooth under different eruption conditions. Male Wistar rats were divided in a normofunctional group (NF) in which their lower teeth remained in a normal eruption. In a hypofunctional group (HP) rats underwent shortening of their lower left incisor tooth every 2 days during 12 days. The eruption rate as well as the expression and activities of MMP-9 and MMP-2 were evaluated using imunohistochemistry and zymography. Although the shortening increased the eruption rate, no changes in the MMP-9 and MMP-2 were observed. We conclude that in adult rats, in opposite to development of tooth, the MMP-9 and MMP-2 present in the odontogenic region does not seem to play a direct role in the remodeling matrix, even after post-shortening procedures which to lead an acceleration of the eruption process in the incisor.     

Periostin regulates collagen fibrillogenesis and the biomechanical properties of connective tissues

Periostin is predominantly expressed in collagen-rich fibrous connective tissues that are subjected to constant mechanical stresses including: heart valves, tendons, perichondrium, cornea, and the periodontal ligament (PDL). Based on these data we hypothesize that periostin can regulate collagen I fibrillogenesis and thereby affect the biomechanical properties of connective tissues. Immunoprecipitation and immunogold transmission electron microscopy experiments demonstrate that periostin is capable of directly interacting with collagen I. To analyze the potential role of periostin in collagen I fibrillogenesis, gene targeted mice were generated. Transmission electron microscopy and morphometric analyses demonstrated reduced collagen fibril diameters in skin dermis of periostin knockout mice, an indication of aberrant collagen I fibrillogenesis. In addition, differential scanning calorimetry (DSC) demonstrated a lower collagen denaturing temperature in periostin knockout mice, reflecting a reduced level of collagen cross-linking. Functional biomechanical properties of periostin null skin specimens and atrioventricular (AV) valve explant experiments provided direct evidence of the role that periostin plays in regulating the viscoelastic properties of connective tissues. Collectively, these data demonstrate for the first time that periostin can regulate collagen I fibrillogenesis and thereby serves as an important mediator of the biomechanical properties of fibrous connective tissues.     

Periostin localizes to cells in normal skin, but is associated with the extracellular matrix during wound repair

Epidermal tissue repair represents a complex series of temporal and dynamic events resulting in wound closure. Matricellular proteins, not normally expressed in quiescent adult tissues, play a pivotal role in wound repair and associated extracellular matrix remodeling by modulating the adhesion, migration, intracellular signaling, and gene expression of inflammatory cells, pericytes, fibroblasts and keratinocytes. Several matricellular proteins show temporal expression during dermal wound repair, but the expression pattern of the recently identified matricellular protein, periostin, has not yet been characterized. The primary aim of this study was to assess whether periostin protein is present in healthy human skin or in pathological remodeling (Nevus). The second aim was to determine if periostin is expressed during dermal wound repair. Using immunohistochemistry, periostin reactivity was detected in the keratinocytes, basal lamina, and dermal fibroblasts in healthy human skin. In pathological nevus samples, periostin was present in the extracellular matrix. In excisional wounds in mice, periostin protein was first detected in the granulation tissue at day 3, with levels peaking at day 7. Periostin protein co-localized with α-smooth muscle actin-positive cells and keratinocytes, but not CD68 positive inflammatory cells. We conclude that periostin is normally expressed at the cellular level in human and murine skin, but additionally becomes extracellular during tissue remodeling. Periostin may represent a new therapeutic target for modulating the wound repair process.     

Alpha11 beta1 integrin-dependent regulation of periodontal ligament function in the erupting mouse incisor

The fibroblast integrin alpha11beta1 is a key receptor for fibrillar collagens. To study the potential function of alpha11 in vivo, we generated a null allele of the alpha11 gene. Integrin alpha11(-/-) mice are viable and fertile but display dwarfism with increased mortality, most probably due to severely defective incisors. Mutant incisors are characterized by disorganized periodontal ligaments, whereas molar ligaments appear normal. The primary defect in the incisor ligament leads to halted tooth eruption. alpha11beta1-defective embryonic fibroblasts displayed severe defects in vitro, characterized by (i) greatly reduced cell adhesion and spreading on collagen I, (ii) reduced ability to retract collagen lattices, and (iii) reduced cell proliferation. Analysis of matrix metalloproteinase in vitro and in vivo revealed disturbed MMP13 and MMP14 synthesis in alpha11(-/-) cells. We show that alpha11beta1 is the major receptor for collagen I on mouse embryonic fibroblasts and suggest that alpha11beta1 integrin is specifically required on periodontal ligament fibroblasts for cell migration and collagen reorganization to help generate the forces needed for axial tooth movement. Our data show a unique role for alpha11beta1 integrin during tooth eruption.     

Deletion of epithelial cell-specific Cdc42 leads to enamel hypermaturation in a conditional knockout mouse model

Recent evidence suggests that GTPases Rho family plays an important role in tooth development; however, the role of Cdc42 in tooth development remains unclear. We aimed to investigate the function of Cdc42 in tooth development and amelogenesis. We generated an epithelial cell-specific K5-Cdc42 knockout (KO) mouse to evaluate post-eruption dental phenotypes using a K5-Cre driver line. This model overcomes the previously reported perinatal lethality. Tooth phenotypes were analyzed by micro X-ray, micro-computed tomography (CT), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), wear rate, shear strength, and a microhardness test. Enamel matrix protein expression was determined by immunohistochemistry.KO mice displayed a hypomaturation phenotype, including incisors that lacked yellow pigmentation and were abnormally white, rapid attrition of molars following eruption, and decreased micro-hardness and shearing strength. Micro-CT data revealed that of incisor and molar enamel volumes were smaller in the KO than in wild-type (WT) mice. SEM analysis showed that the enamel prism structure was disordered. In addition, HE staining indicated a remarkable difference in the ameloblast morphology and function between KO and WT mice, and immunohistochemistry showed increased expression of amelogenin, ameloblastin, matrix metallopeptidase 20, kallikrein-related peptidase 4 and amelotin in the KO mice teeth.Our results suggest epithelium cell-specific Cdc42 deletion leads to tooth hypomaturation and transformation of the enamel prism structure that is likely due to altered ameloblast morphology and the secretion of enamel matrix proteins and proteases. This is the first in vivo evidence suggesting that Cdc42 is essential for proper tooth development and amelogenesis.     

Periostin and matrix stiffness combine to regulate myofibroblast differentiation and fibronectin synthesis during palatal healing

Although the matricellular protein periostin is prominently upregulated in skin and gingival healing, it plays contrasting roles in myofibroblast differentiation and matrix synthesis respectively. Palatal healing is associated with scarring that can alter or restrict maxilla growth, but the expression pattern and contribution of periostin in palatal healing is unknown. Using periostin-knockout (Postn^−/−) and wild-type (WT) mice, the contribution of periostin to palatal healing was investigated through 1.5 mm full-thickness excisional wounds in the hard palate. In WT mice, periostin was upregulated 6 days post-wounding, with mRNA levels peaking at day 12. Genetic deletion of periostin significantly reduced wound closure rates compared to WT mice. Absence of periostin reduced mRNA levels of pivotal genes in wound repair, including α-SMA/acta2, fibronectin and βigh3. Recruitment of fibroblasts and inflammatory cells, as visualized by immunofluorescent staining for fibroblast specific factor-1, vimentin, and macrophages markers Arginase-1 and iNOS was also impaired in Postn^−/−, but not WT mice. Palatal fibroblasts isolated from the hard palate of mice were cultured on collagen gels and prefabricated silicon substrates with varying stiffness. Postn^−/− fibroblasts showed a significantly reduced ability to contract a collagen gel, which was rescued by the exogenous addition of recombinant periostin. As the stiffness increased, Postn^−/− fibroblasts increasingly differentiated into myofibroblasts, but not to the same degree as the WT. Pharmacological inhibition of Rac rescued the deficient myofibroblastic phenotype of Postn^−/− cells. Low stiffness substrates (0.2 kPa) resulted in upregulation of fibronectin in WT cells, an effect which was significantly reduced in Postn^−/− cells. Quantification of immunostaining for vinculin and integrinβ1 adhesions revealed that Periostin is required for the formation of focal and fibrillar adhesions in mPFBs. Our results suggest that periostin modulates myofibroblast differentiation and contraction via integrinβ1/RhoA pathway, and fibronectin synthesis in an ECM stiffness dependent manner in palatal healing.     

Periostin is expressed in pericryptal fibroblasts and cancer-associated fibroblasts in the colon.

Periostin is a unique extracellular matrix protein, deposition of which is enhanced by mechanical stress and the tissue repair process. Its significance in normal and neoplastic colon has not been fully clarified yet. Using immunohistochemistry and immunoelectron microscopy with a highly specific monoclonal antibody, periostin deposition was observed in close proximity to pericryptal fibroblasts of colonic crypts. The pericryptal pattern of periostin deposition was decreased in adenoma and adenocarcinoma, preceding the decrease of the number of pericryptal fibroblasts. Periostin immunoreactivity appeared again at the invasive front of the carcinoma and increased along the appearance of cancer-associated fibroblasts. ISH showed periostin signals in cancer-associated fibroblasts but not in cancer cells. Ki-67-positive epithelial cells were significantly decreased in the colonic crypts of periostin-/- mice (approximately 0.6-fold) compared with periostin+/+ mice. In three-dimensional co-culture within type I collagen gel, both colony size and number of human colon cancer cell line HCT116 cells were significantly larger ( approximately 1.5-fold) when cultured with fibroblasts derived from periostin+/+ mice or periostin-transfected NIH3T3 cells than with those from periostin-/- mice or periostin-non-producing NIH3T3 cells, respectively. Periostin is secreted by pericryptal and cancer-associated fibroblasts in the colon, both of which support the growth of epithelial components.     

Neonatal periostin knockout mice are protected from hyperoxia-induced alveolar simplication

In bronchopulmonary dysplasia (BPD), alveolar septae are thickened with collagen and α-smooth muscle actin, transforming growth factor (TGF)-β-positive myofibroblasts. Periostin, a secreted extracellular matrix protein, is involved in TGF-β-mediated fibrosis and myofibroblast differentiation. We hypothesized that periostin expression is required for hypoalveolarization and interstitial fibrosis in hyperoxia-exposed neonatal mice, an animal model for this disease. We also examined periostin expression in neonatal lung mesenchymal stromal cells and lung tissue of hyperoxia-exposed neonatal mice and human infants with BPD. Two-to-three day-old wild-type and periostin null mice were exposed to air or 75% oxygen for 14 days. Mesenchymal stromal cells were isolated from tracheal aspirates of premature infants. Hyperoxic exposure of neonatal mice increased alveolar wall periostin expression, particularly in areas of interstitial thickening. Periostin co-localized with α-smooth muscle actin, suggesting synthesis by myofibroblasts. A similar pattern was found in lung sections of infants dying of BPD. Unlike wild-type mice, hyperoxia-exposed periostin null mice did not show larger air spaces or α-smooth muscle-positive myofibroblasts. Compared to hyperoxia-exposed wild-type mice, hyperoxia-exposed periostin null mice also showed reduced lung mRNA expression of α-smooth muscle actin, elastin, CXCL1, CXCL2 and CCL4. TGF-β treatment increased mesenchymal stromal cell periostin expression, and periostin treatment increased TGF-β-mediated DNA synthesis and myofibroblast differentiation. We conclude that periostin expression is increased in the lungs of hyperoxia-exposed neonatal mice and infants with BPD, and is required for hyperoxia-induced hypoalveolarization and interstitial fibrosis.     

Association of TIMP-2 with extracellular matrix exposed to mechanical stress and its co-distribution with periostin during mouse mandible development

Matrix remodeling is regulated by matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). Periostin, originally identified in a mouse osteoblastic library, plays a role in cell adhesion and migration and in mechanical stress-induced matrix remodeling. In this study, we analyzed and compared the distribution patterns of TIMP-2 and periostin during mouse mandible development. Immunohistochemical staining for TIMP-2 and periostin was carried out on serial cryosections obtained from mice at embryonic days 13–16, postnatal day 2 (P2), P35, and 12 weeks of age. TIMP-2 and periostin exhibited a strikingly similar protein distribution during mandible development. From bud to early bell stages of molars, TIMP-2 and periostin were highly expressed on the lingual and anterior sides of the basement membrane and on the adjacent jaw mesenchyme. In pre- and postnatal incisors, the basement membrane of the apical loop and dental follicle was immunostained for TIMP-2 and periostin. At postnatal stages, TIMP-2 and periostin were prominently confined to the extracellular matrix (ECM) of gingival tissues, periodontal ligaments, and tendons (all recipients of mechanical strain). However, periostin was solely detected in the lower portion of the inner root sheath of hair follicles. Gingiva of P2 cultured in anti-TIMP-2 antibody-conditioned medium showed markedly reduced staining of periostin. We suggest that TIMP-2 and periostin are co-distributed on ECM exposed to mechanical forces and coordinately function as ECM modulators. This work was supported by the Japanese Ministry of Education, Culture, Sports, Science, and Technology and by Niigata University Research Projects.     

Connective tissue growth factor coordinates chondrogenesis and angiogenesis during skeletal development

Coordinated production and remodeling of the extracellular matrix is essential during development. It is of particular importance for skeletogenesis, as the ability of cartilage and bone to provide structural support is determined by the composition and organization of the extracellular matrix. Connective tissue growth factor (CTGF, CCN2) is a secreted protein containing several domains that mediate interactions with growth factors, integrins and extracellular matrix components. A role for CTGF in extracellular matrix production is suggested by its ability to mediate collagen deposition during wound healing. CTGF also induces neovascularization in vitro, suggesting a role in angiogenesis in vivo. To test whether CTGF is required for extracellular matrix remodeling and/or angiogenesis during development, we examined the pattern of Ctgf expression and generated Ctgf-deficient mice. Ctgf is expressed in a variety of tissues in midgestation embryos, with highest levels in vascular tissues and maturing chondrocytes. We confirmed that CTGF is a crucial regulator of cartilage extracellular matrix remodeling by generating Ctgf(-/-) mice. Ctgf deficiency leads to skeletal dysmorphisms as a result of impaired chondrocyte proliferation and extracellular matrix composition within the hypertrophic zone. Decreased expression of specific extracellular matrix components and matrix metalloproteinases suggests that matrix remodeling within the hypertrophic zones in Ctgf mutants is defective. The mutant phenotype also revealed a role for Ctgf in growth plate angiogenesis. Hypertrophic zones of Ctgf mutant growth plates are expanded, and endochondral ossification is impaired. These defects are linked to decreased expression of vascular endothelial growth factor (VEGF) in the hypertrophic zones of Ctgf mutants. These results demonstrate that CTGF is important for cell proliferation and matrix remodeling during chondrogenesis, and is a key regulator coupling extracellular matrix remodeling to angiogenesis at the growth plate.     

Periostin promotes atrioventricular mesenchyme matrix invasion and remodeling mediated by integrin signaling through Rho/PI 3-kinase

Recent evidence suggests that extracellular matrix components may play a signaling role in embryonic valve development. We have previously identified the spatiotemporal expression patterns of periostin in developing valves, but its function during this process is largely unknown. To evaluate the functional role periostin plays during valvulogenesis, two separate three-dimensional culture assay systems, which model chick atrioventricular cushion development, were employed. These assays demonstrated that cushion mesenchymal cells adhered and spread on purified periostin in a dose-responsive manner, similar to collagen I and fibronectin via alpha(v)beta(3) and beta(1) integrin pairs. Periostin overexpression resulted in enhanced mesenchyme invasion through 3D collagen gels and increased matrix compaction. This invasion was dependent on alpha(v)beta(3) more than beta(1) integrin signaling, and was mediated differentially by Rho kinase and PI 3-kinase. Both matrix invasion and compaction were associated with a colocalization of periostin and beta(1) integrin expression to migratory cell phenotype in both surface and deep cells. The Rho/PI 3-kinase pathway also differentially mediated matrix compaction. Both Rho and PI 3-kinase were involved in normal cushion mesenchyme matrix compaction, but only PI 3-kinase was required for the enhanced matrix compaction due to periostin. Taken together, these results highlight periostin as a mediator of matrix remodeling by cushion mesenchyme towards a mature valve structure.     

Inactivation of Fam20C in Cells Expressing Type I Collagen Causes Periodontal Disease in Mice

Background

FAM20C is a kinase that phosphorylates secretory proteins. Previous studies have shown that FAM20C plays an essential role in the formation and mineralization of bone, dentin and enamel. The present study analyzed the loss-of-function effects of FAM20C on the health of mouse periodontal tissues.

Methods

By crossbreeding 2.3 kb Col 1a1-Cre mice with Fam20C^fl/fl mice, we created 2.3 kb Col 1a1-Cre;Fam20C^fl/fl (cKO) mice, in which Fam20C was inactivated in the cells that express Type I collagen. We analyzed the periodontal tissues in the cKO mice using X-ray radiography, histology, scanning electron microscopy and immunohistochemistry approaches.

Results

The cKO mice underwent a remarkable loss of alveolar bone and cementum, along with inflammation of the periodontal ligament and formation of periodontal pockets. The osteocytes and lacuno-canalicular networks in the alveolar bone of the cKO mice showed dramatic abnormalities. The levels of bone sialoprotein, osteopontin, dentin matrix protein 1 and dentin sialoprotein were reduced in the Fam20C-deficient alveolar bone and/or cementum, while periostin and fibrillin-1 were decreased in the periodontal ligament of the cKO mice.

Conclusion

Loss of Fam20C function leads to periodontal disease in mice. The reduced levels of bone sialoprotein, osteopontin, dentin matrix protein 1, dentin sialoprotein, periostin and fibrillin-1 may contribute to the periodontal defects in the Fam20C-deficient mice.     

uPARAP expression during murine lung development

Lung remodeling requires active collagen deposition and degradation. Urokinase plasminogen activator receptor-associated protein (uPARAP), or Endo 180, is a cell-surface receptor for collagens, which leads to collagen internalization and degradation. Thus, uPARAP-mediated collagen degradation is an additional pathway for matrix remodeling in addition to matrix remodeling mediated by matrix metalloproteinases and cathepsins. Using immunohistochemistry, we demonstrate extensive uPARAP expression in the mesenchyme throughout murine lung development. By immunofluorescence, we demonstrate significant overlap of uPARAP expression with collagen IV expression, but minimal overlap with collagen I expression in the developing murine lung. Finally, we compared lung development between wild-type and uPARAP(-/-) mice, and found no significant histologic differences, indicating the presence of alternative collagen degradation pathways during murine lung development.     

Atrial natriuretic peptide-dependent modulation of hypoxia-induced pulmonary vascular remodeling

Hypoxic stress upsets the balance in the normal relationships between mitogenic and growth inhibiting pathways in lung, resulting in pulmonary vascular remodeling characterized by hyperplasia of pulmonary arterial smooth muscle cells (PASMCs) and fibroblasts and enhanced deposition of extracellular matrix. Atrial natriuretic peptide (ANP) reduces pulmonary vascular resistance and attenuates hypoxia-induced pulmonary hypertension in vivo and PASMC proliferation and collagen synthesis in vitro. The current study utilized an ANP null mouse model (Nppa-/-) to test the hypothesis that ANP modulates the pulmonary vascular and alveolar remodeling response to normobaric hypoxic stress. Nine-10 wk old male ANP null (Nppa-/-) and wild type nontransgenic (NTG) mice were exposed to chronic hypoxia (10% O(2), 1 atm) or air for 6 wks. Measurement: pulmonary hypertension, right ventricular hypertrophy, and pulmonary arterial and alveolar remodeling were assessed. Hypoxia-induced pulmonary arterial hypertrophy and muscularization were significantly increased in Nppa-/- mice compared to NTG controls. Furthermore, the stimulatory effects of hypoxia on alveolar myofibroblast transformation (8.2 and 5.4 fold increases in Nppa-/- and NTG mice, respectively) and expression of extracellular matrix molecule (including osteopontin [OPN] and periostin [PN]) mRNA in whole lung were exaggerated in Nppa-/- mice compared to NTG controls. Combined with our previous finding that ANP signaling attenuates transforming growth factor (TGF)-beta-induced expression of OPN and PN in isolated PASMCs, the current study supports the hypothesis that endogenous ANP plays an important anti-fibrogenic role in the pulmonary vascular adaptation to chronic hypoxia.     

Dmp1-deficient mice display severe defects in cartilage formation responsible for a chondrodysplasia-like phenotype

Understanding the molecular mechanisms by which cartilage formation is regulated is essential toward understanding the physiology of both embryonic bone development and postnatal bone growth. Although much is known about growth factor signaling in cartilage formation, the regulatory role of noncollagenous matrix proteins in this process are still largely unknown. In the present studies, we present evidence for a critical role of DMP1 (dentin matrix protein 1) in postnatal chondrogenesis. The Dmp1 gene was originally identified from a rat incisor cDNA library and has been shown to play an important role in late stage dentinogenesis. Whereas no apparent abnormalities were observed in prenatal bone development, Dmp1-deficient (Dmp1(-/-)) mice unexpectedly develop a severe defect in cartilage formation during postnatal chondrogenesis. Vertebrae and long bones in Dmp1-deficient (Dmp1(-/-)) mice are shorter and wider with delayed and malformed secondary ossification centers and an irregular and highly expanded growth plate, results of both a highly expanded proliferation and a highly expanded hypertrophic zone creating a phenotype resembling dwarfism with chondrodysplasia. This phenotype appears to be due to increased cell proliferation in the proliferating zone and reduced apoptosis in the hypertrophic zone. In addition, blood vessel invasion is impaired in the epiphyses of Dmp1(-/-) mice. These findings show that DMP1 is essential for normal postnatal chondrogenesis and subsequent osteogenesis.     

Impaired capsule formation of tumors in periostin-null mice

Being a secreted protein, periostin is a multifunctional matricellular glycoprotein. In vitro, periostin has the ability to promote the proliferation and migration of fibroblasts. Previously, it was demonstrated that periostin is mainly produced by cancer-associated fibroblasts or tumor stromal cells. In the present study, we show that periostin regulates capsule formation in a positive manner and inhibits tumor growth. Consistent with a previous finding, several tumor cell lines did not exhibit expression of periostin in vitro or in vivo; and the growth of tumors that had been allografted into periostin −/− mice was significantly accelerated compared with that of the same kind of tumors grafted into periostin +/+ mice. Immunostaining and biochemical analyses revealed that mature collagen was detected abundantly in the capsules and interstitium of the wild-type-grafted tumors but not in those of the periostin −/− grafted tumors. Moreover, the number of activated tumor stromal cells was decreased significantly in the periostin −/− grafted tumors. Our studies suggest that host-derived periostin negatively regulates tumor growth by promoting capsule formation and by mediating changes in the deposition and organization of the tumor microenvironment coordinated by periostin-producing stromal cells.     

Relationship between enamel formation and eruption rate in rat mandibular incisors

Summary The relationship between the formation of dental enamel and tooth eruption was investigated. Rat mandibular incisor eruption rate was accelerated by maintaining incisors out of occlusion. Rate of eruption, enamel thickness, secretory zone length and matrix breakdown were measured. Eruption rate increased by 120% in experimental teeth but enamel secretion increased by only 90%. There were no obvious differences between control and experimental teeth in final enamel thickness or in the molecular weight distribution of the enamel matrix proteins.