PubMed Health⌕ Search

Biomedical subjects

Toshihisa Komori

Publications and source records attributed to Toshihisa Komori.

At least 19 recordsLinked to original sources
PubMed2007

BMP-2 promotes differentiation of osteoblasts and chondroblasts in Runx2-deficient cell lines.

To investigate the molecular mechanism underlying the differentiation of osteoblasts and chondroblasts, we established a clonal cell lines, RD-C6, from Runx2-deficient mouse embryos. RD-C6 cells expressed almost undetectable levels of phenotypes related to osteoblast and chondroblast differentiation at basal culture condition, whereas treatment with recombinant human bone morphogenetic protein-2 (rhBMP-2) or transduction of BMP-2 by adenovirus effectively induced this cell line to express mRNA related to the differentiation of osteoblasts and chondroblasts including alkaline phosphatase, osteocalcin, and osterix. Transduction of Runx2 also induced the expression of these mRNA in RD-C6 cells. BMP-2 transduction increased expression levels of mRNA for Msx2 and Dlx5, but Runx2 transduction induced no significant increases in expression levels of these mRNA. Microarray analysis using RD-C6 cells with or without rhBMP-2 treatment demonstrated that BMP-2 upregulated 66 genes including 13 transcription-related molecules such as Id1, Id2, Id4, Hey1, Smad6, Smad7, and Msx2. To confirm bone and cartilage formation ability of RD-C6 cells, we transplanted RD-C6 cells into the peritoneal cavity of athymic mice using diffusion chambers with rhBMP-2. RD-C6 cells generated unmineralized cartilage but not bone. These results indicate that BMP-2 induces Runx2-deficient cells to express markers related to osteoblast and chondroblast differentiation using a Runx2-independent pathway, but it failed to induce these cells to differentiate into bone-forming osteoblasts and mature chondrocytes.

Animals↗
PubMed2006

Characterization of GATA-1(+) hemangioblastic cells in the mouse embryo.

Hemangioblasts are thought to be one of the sources of hematopoietic progenitors, yet little is known about their localization and fate in the mouse embryo. We show here that a subset of cells co-expressing the hematopoietic marker GATA-1 and the endothelial marker VE-cadherin localize on the yolk sac blood islands at embryonic day 7.5. Clonal analysis demonstrated that GATA-1(+) cells isolated from E7.0-7.5 embryos include a common precursor for hematopoietic and endothelial cells. Moreover, this precursor possesses primitive and definitive hematopoietic bipotential. By using a transgenic complementation rescue approach, GATA-1(+) cell-derived progenitors were selectively restored in Runx1-deficient mice. In the rescued mice, definitive erythropoiesis was recovered but the rescued progenitors did not display multilineage hematopoiesis or intra-aortic hematopoietic clusters. These results provide evidence of the presence of GATA-1(+) hemangioblastic cells in the extra-embryonic region and also their functional contribution to hematopoiesis in the embryo.

Animals↗
PubMed2006

Regulation of osteoblast differentiation by transcription factors.

Runx2, osterix, and beta-catenin are essential for osteoblast differentiation. Runx2 directs multipotent mesenchymal cells to an osteoblastic lineage, and inhibits them from differentiating into the adipocytic and chondrocytic lineages. After differentiating to preosteoblasts, beta-catenin, osterix, and Runx2 direct them to immature osteoblasts, which produce bone matrix proteins, blocking their potential to differentiate into the chondrocytic lineage. Runx2 inhibits osteoblast maturation and the transition into osteocytes, keeping osteoblasts in an immature stage. Other transcription factors including Msx1, Msx2, Dlx5, Dlx6, Twist, AP1(Fos/Jun), Knox-20, Sp3, and ATF4 are also involved in osteoblast differentiation. To gain an understanding of bone development, it is important to position these transcription factors to the right places in the processes of osteoblast differentiation.

Animals↗
PubMed2006

Cbf beta regulates Runx2 function isoform-dependently in postnatal bone development.

Runx2 and Cbfbeta are essential for skeletal development during the embryonic stage. Runx2 has two isoforms with different N-termini. We examined the functions of the Runx2 isoforms and Cbfbeta in postnatal bone development. On luciferase and electrophoretic mobility shift assays, Runx2-I was less active than Runx2-II in the absence of Cbfb, but the two Runx2 isoforms had similar activity levels in the presence of Cbfb. We generated Runx2-I transgenic mice under the control of Col1a1 promoter and Runx2-I/Cbfb and Runx2-II/Cbfb double transgenic mice. Runx2-I transgenic mice showed less severe osteopenia and fragility than Runx2-II transgenic mice due to milder inhibition of both osteoblast maturation and transition to osteocytes, even though the former mice showed higher transgene expression. However, Runx2-I/Cbfb and Runx2-II/Cbfb double transgenic mice had enhanced inhibition of osteoblast maturation, resulting in similar severity of osteopenia and fragility, although the latter mice had less osteocytes. These findings indicate that (1) Runx2-II more strongly inhibits osteoblast maturation and transition to osteocytes than Runx2-I; (2) Cbfbeta regulates Runx2 function isoform-dependently; and (3) Runx2-I activity is highly dependent on Cbfbeta. These findings demonstrate that Runx2 isoforms exert their functions through at least partly different mechanisms and Cbfbeta regulates bone development by regulating Runx2 function isoform-dependently.

Animals↗
PubMed2006

Runx2 is a target of mechanical unloading to alter osteoblastic activity and bone formation in vivo.

Molecular mechanisms underlying unloading-induced reduction of bone formation have not yet been fully understood. In vitro, Runx2 has been suggested to be involved in mechanical signaling in osteoblasts. However, the roles of Runx2 in vivo during the bone response to mechanical stimuli have not yet been known. The purpose of this paper was to examine the roles of Runx2 in unloading-induced bone loss in vivo. Tail suspension was conducted for 2 wk using 9- to 11-wk-old Runx2 heterozygous knockout mice (Runx2(+/-)) and wild-type (Wt) littermates. Bones were subjected to two-dimensional micro-x-ray computed tomography, bone histomorphometry and RT-PCR analyses. Loss of half Runx2 gene dosage-exacerbated unloading-induced bone loss in trabecular and cortical envelopes. Unloading-induced reduction in mineral apposition rate and bone formation rate in cortical bone as well as trabecular bone was exacerbated in Runx2(+/-) mice, compared with Wt mice. Bone resorption parameters were not significantly affected by unloading or Runx2(+/-) genotype. Basal Runx2 and osterix mRNA levels in bone were reduced by 50% in Wt, whereas unloading in Runx2(+/-) mice did not further alter Runx2 and osterix mRNA levels. In contrast, osteocalcin mRNA levels were reduced by unloading, regardless of Runx2 gene dosage. These data demonstrated that full Runx2 gene dosage is required for maintaining normal function of osteoblasts in mechanical unloading or nonphysiological condition. Finally, we propose Runx2 as a critical target gene in unloading to alter osteoblastic activity and bone formation in vivo.

Amino Acids↗
PubMed2006

Contribution of runt-related transcription factor 2 to the pathogenesis of osteoarthritis in mice after induction of knee joint instability.

OBJECTIVE: By producing instability in mouse knee joints, we attempted to determine the involvement of runt-related transcription factor 2 (RUNX-2), which is required for chondrocyte hypertrophy, in the development of osteoarthritis (OA). METHODS: An experimental mouse OA model was created by surgical transection of the medial collateral ligament and resection of the medial meniscus of the knee joints of heterozygous RUNX-2-deficient (Runx2+/-) mice and wild-type littermates. Cartilage destruction and osteophyte formation in the medial tibial cartilage were compared by histologic and radiographic analyses. Localization of type X collagen and matrix metalloproteinase 13 (MMP-13) was examined by immunohistochemistry. Localization of RUNX-2 was determined by X-Gal staining in heterozygous RUNX-2-deficient mice with the lacZ gene insertion at the Runx2-deletion site (Runx2+/lacZ). Messenger RNA levels of type X collagen, MMP-13, and RUNX-2 were examined by real-time reverse transcriptase-polymerase chain reaction analysis. RESULTS: RUNX-2 was induced in the articular cartilage of wild-type mice at the early stage of OA, almost simultaneously with type X collagen but earlier than MMP-13. Runx2+/- and Runx2+/lacZ mice showed normal skeletal development and articular cartilage; however, after induction of knee joint instability, they exhibited decreased cartilage destruction and osteophyte formation, along with reduced type X collagen and MMP-13 expression, as compared with wild-type mice. CONCLUSION: RUNX-2 contributes to the pathogenesis of OA through chondrocyte hypertrophy and matrix breakdown after the induction of joint instability.

Animals↗
PubMed2006

Sp1 family of transcription factors regulates the human alpha2 (XI) collagen gene (COL11A2) in Saos-2 osteoblastic cells.

UNLABELLED: Genes encoding type XI collagen, normally associated with chondrogenesis, are also expressed by osteoblasts. By studying Saos-2 cells, we showed that the transcription factors, Sp1, Sp3, and Sp7 (Osterix), regulate COL11A2 expression through its proximal promoter. The findings indicate both ubiquitous and osteoblast-specific mechanisms of collagen gene regulation. INTRODUCTION: Type XI collagen is essential for skeletal morphogenesis. Collagen XI gene regulation has been studied in chondrocytes but not in osteoblasts. MATERIALS AND METHODS: We cultured Saos-2 cells, a human osteosarcoma-derived line of osteoblasts, and analyzed them for alpha2(XI) protein and COL11A2 regulatory mechanisms. RESULTS AND CONCLUSIONS: Although types I and V were the dominant collagens deposited by Saos-2 cells, they expressed COL11A2 mRNA, and alpha2(XI) chains were present in the extracellular matrix. The COL11A2 promoter region (from -149 to -40) containing three Sp1 binding sites was required for promoter activity in transient transfection assays. All three Sp1 sites were critical for binding by nuclear proteins in electrophoretic mobility shift assays. Further analysis using consensus oligonucleotides and specific antibodies as well as chromatin immunoprecipitation assay implicated Sp1 and Sp3 in binding to this promoter region. Overexpressing Sp1 or Sp3 significantly increased COL11A2 promoter activity and endogenous COL11A2 gene expression, an effect that was suppressed by the Sp1-binding inhibitor mithramycin A. Further experiments showed that Sp1, Sp3, CREB-binding protein (CBP), p300, and histone deacetylase (HDAC) were physically associated and HDAC inhibitors (trichostatin A or NaB) upregulated COL11A2 promoter activity and endogenous gene expression. Another Sp1 family member, Sp7 (Osterix), was expressed in Saos-2 cells, but not in chondrocytes, and was shown by chromatin immunoprecipitation to occupy the COL11A2 promoter. Overexpressing Sp7 increased COL11A2 promoter activity and endogenous gene expression, an effect also blocked by mithramycin A. Using siRNA to knockdown Sp1, Sp3, or Sp7, it was shown that depression of any of them decreased COL11A2 promoter activity and endogenous gene expression. Finally, primary cultures of osteoblasts expressed COL11A2 and Sp7, upregulated COL11A2 promoter activity and endogenous gene expression when Sp1, Sp3, or Sp7 were overexpressed, and downregulated them when Sp1, Sp3, or Sp7 were selectively depressed. The results establish that Sp1 proteins regulate COL11A2 transcription by binding to its proximal promoter and directly interacting with CBP, p300, and HDAC.

Base Sequence↗
PubMed2006

[Mechanism of transcriptional regulation by Runx2 in osteoblasts].

Runt-related transcription factor 2 (Runx2) is an essential transcription factor for osteoblast differentiation, and the expression is regulated by many factors including bone morphogenetic protein (BMP). Core binding factorbeta (Cbf beta) is required for DNA binding of Runx2 and Runx2-dependent transcription, and Cbf beta regulates Runx2 function isoform-dependently. Further, ability of Runx2 for transcriptional activation is regulated by many molecules. Phosphoinositide 3-kinase (PI3K)-Akt signaling enhances DNA binding of Runx2 and Runx2-dependent transcription, and Runx2 upregulates PI3K subunits (p85 and p110 beta) and Akt. Therefore, Runx2 and PI3K-Akt signaling are mutually dependent each other in the regulation of osteoblast and chondrocyte differentiation and their migration.

Animals↗
PubMed2005

Regulation of skeletal development by the Runx family of transcription factors.

The Runx (runt-related protein) family of transcription factors plays important roles in different tissues and cell lineages. Runx1 determines commitment to the hematopoietic cell lineage and Runx2 determines commitment to the osteoblastic lineage. Cbfbeta is required for Runx1- and Runx2-dependent transcriptional regulation. Runx2 interacts with many other transcription factors and co-regulators in the transcriptional regulation of its target genes. Runx2 is essential for the commitment of multipotent mesenchymal cells into the osteoblastic lineage and inhibits adipocyte differentiation. Runx2 induces the gene expression of bone matrix proteins, while keeping the osteoblastic cells in an immature stage. Runx2 and Runx3 have redundant functions in chondrocytes, and they are essential for chondrocyte maturation. Runx2 directly induces Indian hedgehog (Ihh) expression and co-ordinates the proliferation and differentiation of chondrocytes. Therefore, elucidation of the signaling pathways through Runx2 and Runx3 will unravel the complex mechanism of skeletal development.

Animals↗
PubMed2005

Developmental regulation of Wnt/beta-catenin signals is required for growth plate assembly, cartilage integrity, and endochondral ossification.

Studies have suggested that continuous Wnt/beta-catenin signaling in nascent cartilaginous skeletal elements blocks chondrocyte hypertrophy and endochondral ossification, whereas signaling starting at later stages stimulates hypertrophy and ossification, indicating that Wnt/beta-catenin roles are developmentally regulated. To test this conclusion further, we created transgenic mice expressing a fusion mutant protein of beta-catenin and LEF (CA-LEF) in nascent chondrocytes. Transgenic mice had severe skeletal defects, particularly in limbs. Growth plates were totally disorganized, lacked maturing chondrocytes expressing Indian hedgehog and collagen X, and failed to undergo endochondral ossification. Interestingly, the transgenic cartilaginous elements were ill defined, intermingled with surrounding connective and vascular tissues, and even displayed abnormal joints. However, when activated beta-catenin mutant (delta-beta-catenin) was expressed in chondrocytes already engaged in maturation such as those present in chick limbs, chondrocyte maturation and bone formation were greatly enhanced. Differential responses to Wnt/beta-catenin signaling were confirmed in cultured chondrocytes. Activation in immature cells blocked maturation and actually de-stabilized their phenotype, as revealed by reduced expression of chondrocyte markers, abnormal cytoarchitecture, and loss of proteoglycan matrix. Activation in mature cells instead stimulated hypertrophy, matrix mineralization, and expression of terminal markers such as metalloprotease (MMP)-13 and vascular endothelial growth factor. Because proteoglycans are crucial for cartilage function, we tested possible mechanisms for matrix loss. Delta-beta-catenin expression markedly increased expression of MMP-2, MMP-3, MMP-7, MMP-9, MT3-MMP, and ADAMTS5. In conclusion, Wnt/beta-catenin signaling regulates chondrocyte phenotype, maturation, and function in a developmentally regulated manner, and regulated action by this pathway is critical for growth plate organization, cartilage boundary definition, and endochondral ossification.

ADAM Proteins↗
PubMed2005

Mammalian polycomb-mediated repression of Hox genes requires the essential spliceosomal protein Sf3b1.

Polycomb group (PcG) proteins are responsible for the stable repression of homeotic (Hox) genes by forming multimeric protein complexes. We show (1) physical interaction between components of the U2 small nuclear ribonucleoprotein particle (U2 snRNP), including Sf3b1 and PcG proteins Zfp144 and Rnf2; and (2) that Sf3b1 heterozygous mice exhibit skeletal transformations concomitant with ectopic Hox expressions. These alterations are enhanced by Zfp144 mutation but repressed by Mll mutation (a trithorax-group gene). Importantly, the levels of Sf3b1 in PcG complexes were decreased in Sf3b1-heterozygous embryos. These findings suggest that Sf3b1-PcG protein interaction is essential for true PcG-mediated repression of Hox genes.

Animals↗
PubMed2005

Runx2 regulates FGF2-induced Bmp2 expression during cranial bone development.

Calvarial bone is formed by the intramembranous bone-forming process, which involves many signaling molecules. The constitutive activation of the fibroblast growth factor (FGF) signaling pathway accelerates osteoblast differentiation and results in premature cranial suture closure. Bone morphogenetic protein (BMP) signaling pathways, which involve the downstream transcription factors Dlx5 and Msx2, are also involved in the bone-forming processes. However, the relationships between these two main signaling cascades are still unclear. We found that FGF2 treatment of developing bone fronts stimulated Bmp2 gene expression but that BMP2 treatment could not induce Fgf2 expression. Moreover, the disruption of the Runx2 gene completely eliminated the expression of Bmp2 and its downstream genes Dlx5 and Msx2 in the developing primordium of bone, while the expression of Fgf2 was maintained. In addition, cultured Runx2-/- cells expressed very low baseline levels of Bmp2 that were up-regulated by transfection with a Runx2-expressing plasmid. These levels in turn were markedly elevated by FGF2 treatment. FGF2 treatment also strongly enhanced the Bmp2 expression in MC3T3-E1 cells, whose endogenous Runx2 gene is intact and which express Bmp2 at low baseline levels as well. These results indicate that Runx2 is an important mediator of the expression of Bmp2 in response to FGF stimulation in cranial bone development.

Animals↗
PubMed2005

Inhibition of Cdk6 expression through p38 MAP kinase is involved in differentiation of mouse prechondrocyte ATDC5.

Because a temporal arrest in the G1-phase of the cell cycle is a prerequisite for cell differentiation, this study investigated the involvement of cell cycle factors in the differentiation of cultured mouse prechondrocyte cell line ATDC5. Among the G1 cell cycle factors examined, both protein and mRNA levels of cyclin-dependent kinase (Cdk6) were downregulated during the culture in a differentiation medium. The protein degradation of Cdk6 was not involved in this downregulation because proteasome inhibitors did not reverse the protein level. When inhibitors of p38 MAPK, ERK-1/2, and PI3K/Akt were added to the culture, only a p38 MAPK inhibitor SB203580 blocked the decrease in the Cdk6 protein level by the differentiation medium, indicating that the Cdk6 inhibition was mediated by p38 MAPK pathway. In fact, p38 MAPK was confirmed to be phosphorylated during differentiation of ATDC5 cells. Enforced expression of Cdk6 in ATDC5 cells blocked the chondrocyte differentiation and inhibited Sox5 and Sox6 expressions. However, the Cdk6 overexpression did not affect the proliferation or the cell cycle progression, suggesting that the inhibitory effect of Cdk6 on the differentiation was exerted by a mechanism largely independent of its cell cycle regulation. These results indicate that Cdk6 may be a regulator of chondrocyte differentiation and that its p38-mediated downregulation is involved in the efficient differentiation.

Animals↗
PubMed2005

Role of Runx proteins in chondrogenesis.

The mammalian RUNX protein family comprises three transcription factorsRUNX1, RUNX2, and RUNX3. RUNX1 is involved in hematopoiesis, RUNX2 has multiple roles in osteogenesis and RUNX3 is associated with neural and gut development. In addition, all RUNX proteins are expressed during chondrogenesis, the process by which cartilage is formed. This review describes the involvement of Runx proteins in chondrogenesis, delineating their expression pattern and emphasizing their active roles in mesenchymal condensation, chondrocyte proliferation, and chondrocyte maturation. It also highlights how Runx proteins regulate transcription of target genes and how Runx proteins are regulated in the cartilaginous skeleton.

Amino Acid Sequence↗
PubMed2005

[Functions of BMPs, Runx2, and osterix in the development of bone and cartilage].

BMP signaling plays important roles in craniofacial development, limb development, and joint formation. BMPs enhance chondrocyte differentiation and proliferation but inhibit the terminal differentiation of chondrocytes. Runx2 and Runx3 are essential for chondrocyte maturation, and Runx2 and Osterix are essential for osteoblast differentiation. Runx2 and Runx3 induce Ihh, which enhances chondrocyte proliferation and inhibits chondrocyte maturation, in prehypertrophic chondrocytes, and Ihh induces Runx2 in the perichondrial cells leading to their differentiation into osteoblasts.

Animals↗
PubMed2004

Dexamethasone inhibits insulin-induced chondrogenesis of ATDC5 cells by preventing PI3K-Akt signaling and DNA binding of Runx2.

Glucocorticoids play important roles in cell growth and differentiation. In this study, we investigated the effect of application of dexamethasone (DEX) at the early stage of chondrogenesis using the prechondrogenic cell line, ATDC5, which differentiates into chondrocytes in the presence of insulin. When ATDC5 cells were cultured in the presence of DEX and insulin, DEX inhibited insulin-induced cellular condensation and subsequent cartilaginous nodule formation, and reduced proteoglycan synthesis and type II collagen expression dose-dependently. Pretreatment with 10(-8) M DEX for 1 day inhibited insulin-induced Akt phosphorylation, but not ERK1/2 phosphorylation, in ATDC5 cells. Treatment of ATDC5 cells with insulin for more than 2 days upregulated the levels of phosphatidylinositol 3-kinase (PI3K) subunit proteins, p85 and p110, and Akt, whereas the upregulation was inhibited in the presence of 10(-8) M DEX. In electrophoresis mobility shift assays (EMSAs), treatment with 10(-8) M DEX inhibited DNA binding of Runx2 during culture of ATDC5 cells with insulin. Reporter assays using osteocalcin promoter showed that DEX inhibited Runx2-dependent transcription dose-dependently. Adenoviral introduction of dominant-negative (dn)-Akt or dn-Runx2 into ATDC5 cells inhibited cellular condensation and reduced proteoglycan synthesis upon incubation with insulin, whereas adenoviral introduction of Akt or Runx2 prevented the inhibition of chondrogenesis by DEX. These findings indicate that DEX inhibits chondrogenesis of ATDC5 cells at the early stage by downregulating Akt phosphorylation as well as the protein levels of PI3K subunits and Akt, thereby suppressing PI3K-Akt signaling, and by inhibiting DNA binding of Runx2 and Runx2-dependent transcription.

Adenoviridae↗
PubMed2004

Runx2 induces osteoblast and chondrocyte differentiation and enhances their migration by coupling with PI3K-Akt signaling.

Runx2 and phosphatidylinositol 3-kinase (PI3K)-Akt signaling play important roles in osteoblast and chondrocyte differentiation. We investigated the relationship between Runx2 and PI3K-Akt signaling. Forced expression of Runx2 enhanced osteoblastic differentiation of C3H10T1/2 and MC3T3-E1 cells and enhanced chondrogenic differentiation of ATDC5 cells, whereas these effects were blocked by treatment with IGF-I antibody or LY294002 or adenoviral introduction of dominant-negative (dn)-Akt. Forced expression of Runx2 or dn-Runx2 enhanced or inhibited cell migration, respectively, whereas the enhancement by Runx2 was abolished by treatment with LY294002 or adenoviral introduction of dn-Akt. Runx2 up-regulated PI3K subunits (p85 and p110beta) and Akt, and their expression patterns were similar to that of Runx2 in growth plates. Treatment with LY294002 or introduction of dn-Akt severely diminished DNA binding of Runx2 and Runx2-dependent transcription, whereas forced expression of myrAkt enhanced them. These findings demonstrate that Runx2 and PI3K-Akt signaling are mutually dependent on each other in the regulation of osteoblast and chondrocyte differentiation and their migration.

Adenoviridae↗