A Narrative Review of the Roles of Chondromodulin-I (Cnmd) in Adult Cartilage Tissue.

Articular cartilage is crucial for joint function but its avascularity limits intrinsic repair, leading to conditions like osteoarthritis (OA). Chondromodulin-I (Cnmd) has emerged as a key molecule in cartilage biology, with potential implications for OA therapy. Cnmd is primarily expressed in cartilage and plays an important role in chondrocyte proliferation, cartilage homeostasis, and the blocking of angiogenesis. In vivo and in vitro studies on Cnmd, also suggest an involvement in bone repair and in delaying OA progression. Its downregulation correlates with OA severity, indicating its potential as a therapeutic target. Further research is needed to fully understand the mode of action of Cnmd and its beneficial implications for managing OA. This comprehensive review aims to elucidate the molecular characteristics of Cnmd, from its expression pattern, role in cartilage maintenance, callus formation during bone repair and association with OA.

Clostridium folliculivorans sp. nov., isolated from soil samples of an organic paddy in Japan.

Two Gram-stain-negative, terminal endospore-forming, rod-shaped and aerotolerant bacterial strains designated D1-1T and B3 were isolated from soil samples of an organic paddy in Japan. Strain D1-1T grew at 15-37 °C, pH 5.0-7.3, and with up to 0.5 % (w/v) NaCl. Phylogenetic analysis of the 16S rRNA gene revealed that strain D1-1T belonged to the genus Clostridium and was closely related to Clostridium zeae CSC2T (99.7 % sequence similarity), Clostridium fungisolvens TW1T (99.7 %) and Clostridium manihotivorum CT4T (99.3 %). Strains D1-1T and B3 were whole-genome sequenced and indistinguishable, with an average nucleotide identity value of 99.7 %. The average nucleotide identity (below 91.1 %) and digital DNA-DNA hybridization (below 43.6 %) values between the two novel isolates and their corresponding relatives showed that strains D1-1T and B3 could be readily distinguished from their closely related species. A novel Clostridium species, Clostridium folliculivorans sp. nov., with type strain D1-1T (=MAFF 212477T=DSM 113523T), is proposed based on genotypic and phenotypic data.

Functional Investigation of a Non-coding Variant Associated with Adolescent Idiopathic Scoliosis in Zebrafish: Elevated Expression of the Ladybird Homeobox Gene Causes Body Axis Deformation.

Previously, we identified an adolescent idiopathic scoliosis susceptibility locus near human ladybird homeobox 1 (LBX1) and FLJ41350 by a genome-wide association study. Here, we characterized the associated non-coding variant and investigated the function of these genes. A chromosome conformation capture assay revealed that the genome region with the most significantly associated single nucleotide polymorphism (rs11190870) physically interacted with the promoter region of LBX1-FLJ41350. The promoter in the direction of LBX1, combined with a 590-bp region including rs11190870, had higher transcriptional activity with the risk allele than that with the non-risk allele in HEK 293T cells. The ubiquitous overexpression of human LBX1 or either of the zebrafish lbx genes (lbx1a, lbx1b, and lbx2), but not FLJ41350, in zebrafish embryos caused body curvature followed by death prior to vertebral column formation. Such body axis deformation was not observed in transcription activator-like effector nucleases mediated knockout zebrafish of lbx1b or lbx2. Mosaic expression of lbx1b driven by the GATA2 minimal promoter and the lbx1b enhancer in zebrafish significantly alleviated the embryonic lethal phenotype to allow observation of the later onset of the spinal curvature with or without vertebral malformation. Deformation of the embryonic body axis by lbx1b overexpression was associated with defects in convergent extension, which is a component of the main axis-elongation machinery in gastrulating embryos. In embryos overexpressing lbx1b, wnt5b, a ligand of the non-canonical Wnt/planar cell polarity (PCP) pathway, was significantly downregulated. Injection of mRNA for wnt5b or RhoA, a key downstream effector of Wnt/PCP signaling, rescued the defective convergent extension phenotype and attenuated the lbx1b-induced curvature of the body axis. Thus, our study presents a novel pathological feature of LBX1 and its zebrafish homologs in body axis deformation at various stages of embryonic and subsequent growth in zebrafish.

A Functional SNP in BNC2 Is Associated with Adolescent Idiopathic Scoliosis.

Adolescent idiopathic scoliosis (AIS) is the most common spinal deformity. We previously conducted a genome-wide association study (GWAS) and detected two loci associated with AIS. To identify additional loci, we extended our GWAS by increasing the number of cohorts (2,109 affected subjects and 11,140 control subjects in total) and conducting a whole-genome imputation. Through the extended GWAS and replication studies using independent Japanese and Chinese populations, we identified a susceptibility locus on chromosome 9p22.2 (p = 2.46 × 10(-13); odds ratio = 1.21). The most significantly associated SNPs were in intron 3 of BNC2, which encodes a zinc finger transcription factor, basonuclin-2. Expression quantitative trait loci data suggested that the associated SNPs have the potential to regulate the BNC2 transcriptional activity and that the susceptibility alleles increase BNC2 expression. We identified a functional SNP, rs10738445 in BNC2, whose susceptibility allele showed both higher binding to a transcription factor, YY1 (yin and yang 1), and higher BNC2 enhancer activity than the non-susceptibility allele. BNC2 overexpression produced body curvature in developing zebrafish in a gene-dosage-dependent manner. Our results suggest that increased BNC2 expression is implicated in the etiology of AIS.

THRAP3 interacts with and inhibits the transcriptional activity of SOX9 during chondrogenesis.

Sex-determining region Y (Sry)-box (Sox)9 is required for chondrogenesis as a transcriptional activator of genes related to chondrocyte proliferation, differentiation, and cartilage-specific extracellular matrix. Although there have been studies investigating the Sox9-dependent transcriptional complexes, not all their components have been identified. In the present study, we demonstrated that thyroid hormone receptor-associated protein (THRAP)3 is a component of a SOX9 transcriptional complex by liquid chromatography mass spectrometric analysis of FLAG-tagged Sox9-binding proteins purified from FLAG-HA-tagged Sox9 knock-in mice. Thrap3 knockdown in ATDC5 chondrogenic cells increased the expression of Collagen type II alpha 1 chain (Col2a1) without affecting Sox9 expression. THRAP3 and SOX9 overexpression reduced Col2a1 levels to a greater degree than overexpression of SOX9 alone. The negative regulation of SOX9 transcriptional activity by THRAP3 was mediated by interaction between the proline-, glutamine-, and serine-rich domain of SOX9 and the innominate domain of THRAP3. These results indicate that THRAP3 negatively regulates SOX9 transcriptional activity as a cofactor of a SOX9 transcriptional complex during chondrogenesis.

Metre-long cell-laden microfibres exhibit tissue morphologies and functions.

Artificial reconstruction of fibre-shaped cellular constructs could greatly contribute to tissue assembly in vitro. Here we show that, by using a microfluidic device with double-coaxial laminar flow, metre-long core-shell hydrogel microfibres encapsulating ECM proteins and differentiated cells or somatic stem cells can be fabricated, and that the microfibres reconstitute intrinsic morphologies and functions of living tissues. We also show that these functional fibres can be assembled, by weaving and reeling, into macroscopic cellular structures with various spatial patterns. Moreover, fibres encapsulating primary pancreatic islet cells and transplanted through a microcatheter into the subrenal capsular space of diabetic mice normalized blood glucose concentrations for about two weeks. These microfibres may find use as templates for the reconstruction of fibre-shaped functional tissues that mimic muscle fibres, blood vessels or nerve networks in vivo.

Sclerostin modulates mineralization degree and stiffness profile in the fibrocartilaginous enthesis for mechanical tissue integrity.

Fibrocartilaginous entheses consist of tendons, unmineralized and mineralized fibrocartilage, and subchondral bone, each exhibiting varying stiffness. Here we examined the functional role of sclerostin, expressed in mature mineralized fibrochondrocytes. Following rapid mineralization of unmineralized fibrocartilage and concurrent replacement of epiphyseal hyaline cartilage by bone, unmineralized fibrocartilage reexpanded after a decline in alkaline phosphatase activity at the mineralization front. Sclerostin was co-expressed with osteocalcin at the base of mineralized fibrocartilage adjacent to subchondral bone. In Scx-deficient mice with less mechanical loading due to defects of the Achilles tendon, sclerostin+ fibrochondrocyte count significantly decreased in the defective enthesis where chondrocyte maturation was markedly impaired in both fibrocartilage and hyaline cartilage. Loss of the Sost gene, encoding sclerostin, elevated mineral density in mineralized zones of fibrocartilaginous entheses. Atomic force microscopy analysis revealed increased fibrocartilage stiffness. These lines of evidence suggest that sclerostin in mature mineralized fibrochondrocytes acts as a modulator for mechanical tissue integrity of fibrocartilaginous entheses.

Spatiotemporal single-cell tracking analysis in 3D tissues to reveal heterogeneous cellular response to mechanical stimuli.

Mechanical stimuli have been recognized as important for tissue maturation, homeostasis and constructing engineered three-dimensional (3D) tissues. However, we know little about the cellular mechanical response in tissues that could be considerably heterogeneous and spatiotemporally dynamic due to the complex structure of tissues. Here, we report a spatiotemporal single-cell tracking analysis of in vitro 3D tissues under mechanical stretch, to reveal the heterogeneous cellular behavior by using a developed stretch and optical live imaging system. The system could affect the cellular orientation and directly measure the distance of cells in in vitro 3D myoblast tissues (3DMTs) at the single-cell level. Moreover, we observed the spatiotemporal heterogeneous cellular locomotion and shape changes under mechanical stretch in 3DMTs. This single-cell tracking analysis can become a principal method to investigate the heterogeneous cellular response in tissues and provide insights that conventional analyses have not yet offered.

Small-artery-mimicking multi-layered 3D co-culture in a self-folding porous graphene-based film.

In vitro vessel-mimicking models have been spotlighted as a powerful tool for investigating cellular behaviours in vascular development and diseases. However, it is still challenging to create micro-scale tubular tissues while mimicking the structural features of small arteries. Here, we propose a 3D culture model of small vascular tissue using a self-folding graphene-based porous film. Vascular endothelial cells were encapsulated within the self-folding film to create a cellular construct with a controlled curvature radius ranging from 10 to 100 µm, which is comparable to the size of a human arteriole. Additionally, vascular endothelial cells and smooth muscle cells were separately co-cultured on the inner and outer surfaces of the folded film, respectively. The porous wall worked as a permeable barrier between them, affecting the cell-cell communications like the extracellular layer in the artery wall. Thus, the culture model recapitulates the structural features of a small artery and will help us better understand intercellular communications at the artery wall in physiological and pathological conditions.

Synthetic disulfide-bridged cyclic peptides mimic the anti-angiogenic actions of chondromodulin-I.

Chondromodulin-I (ChM-I) is a 25-kDa glycoprotein in cartilage matrix that inhibits angiogenesis. It contains two distinctive structural domains: the N-terminal third of the molecule is a hydrophilic domain that contains O-linked and N-linked oligosaccharide chains, and the C-terminal two-thirds is a hydrophobic domain that contains all of the cysteine residues. In the present study, we have attempted to further uncover the structural requirements for ChM-I to exert anti-angiogenic activity by monitoring its inhibition of the vascular endothelial growth factor (VEGF)-A-induced migration of HUVEC in vitro. Site-directed mutagenesis experiments revealed that the cyclic structure formed by the disulfide bridge between Cys(83) and Cys(99) in human ChM-I is indispensable for its anti-angiogenic function. Moreover, the C-terminal hydrophobic tail (from Trp(111) to Val(120) ) was found to play an important role in ensuring the effectiveness of ChM-I activity on HUVEC. A synthetic cyclic peptide corresponding to the ChM-I region between Ile(82) to Arg(100) also inhibited the migration of HUVEC, while replacing the Cys(83) and Cys(99) residues in this peptide with Ser completely negated this inhibitory activity. An additional synthetic cyclic peptide harboring the hydrophobic C-terminal tail of ChM-I clearly mimicked the inhibitory action of this protein on the migration of HUVEC and successfully inhibited tumor angiogenesis and growth in a xenograft mouse model of human chondrosarcoma.

Functional analysis of human brain endothelium using a microfluidic device integrating a cell culture insert.

The blood-brain barrier (BBB) is a specialized brain endothelial barrier structure that regulates the highly selective transport of molecules under continuous blood flow. Recently, various types of BBB-on-chip models have been developed to mimic the microenvironmental cues that regulate the human BBB drug transport. However, technical difficulties in complex microfluidic systems limit their accessibility. Here, we propose a simple and easy-to-handle microfluidic device integrated with a cell culture insert to investigate the functional regulation of the human BBB endothelium in response to fluid shear stress (FSS). Using currently established immortalized human brain microvascular endothelial cells (HBMEC/ci18), we formed a BBB endothelial barrier without the substantial loss of barrier tightness under the relatively low range of FSS (0.1-1 dyn/cm2). Expression levels of key BBB transporters and receptors in the HBMEC/ci18 cells were dynamically changed in response to the FSS, and the effect of FSS reached a plateau around 1 dyn/cm2. Similar responses were observed in the primary HBMECs. Taking advantage of the detachable cell culture insert from the device, the drug efflux activity of P-glycoprotein (P-gp) was analyzed by the bidirectional permeability assay after the perfusion culture of cells. The data revealed that the FSS-stimulated BBB endothelium exhibited the 1.9-fold higher P-gp activity than that of the static culture control. Our microfluidic system coupling with the transwell model provides a functional human BBB endothelium with secured transporter activity, which is useful to investigate the bidirectional transport of drugs and its regulation by FSS.

Localization of chondromodulin-I at the feto-maternal interface and its inhibitory actions on trophoblast invasion in vitro.

BACKGROUND: Chondromodulin-I (ChM-I) is an anti-angiogenic glycoprotein that is specifically localized at the extracellular matrix of the avascular mesenchyme including cartilage and cardiac valves. In this study, we characterized the expression pattern of ChM-I during early pregnancy in mice in vivo and its effect on invasion of trophoblastic cells into Matrigel in vitro. RESULTS: Northern blot analysis clearly indicated that ChM-I transcripts were expressed in the pregnant mouse uterus at 6.5-9.5 days post coitum. In situ hybridization and immunohistochemistry revealed that ChM-I was localized to the mature decidua surrounding the matrix metalloproteinase-9 (MMP-9)-expressing trophoblasts. Consistent with this observation, the expression of ChM-I mRNA was induced in decidualizing endometrial stromal cells in vitro, in response to estradiol and progesterone. Recombinant human ChM-I (rhChM-I) markedly inhibited the invasion through Matrigel as well as the chemotactic migration of rat Rcho-1 trophoblast cells in a manner independent of MMP activation. CONCLUSIONS: This study demonstrates the inhibitory action of ChM-I on trophoblast migration and invasion, implying the potential role of the ChM-I expression in decidual cells for the regulated tissue remodeling and angiogenesis at feto-maternal interface.

A functional role of the glycosylated N-terminal domain of chondromodulin-I.

Chondromodulin-I (ChM-I) is a 25-kDa glycoprotein that specifically localizes in the extracellular matrix of cartilage and negatively regulates angiogenesis. ChM-I comprises two domains: an N-terminal hydrophilic domain (domain 1) containing an N-linked glycosylation site and a C-terminal hydrophobic domain (domain 2) with all four disulfide bonds that are present in this protein. We generated a nonglycosylated recombinant human ChM-I (NG-hChM-I) and compared its bioactivity with that of the glycosylated form of human ChM-I (G-hChM-I) expressed in Chinese hamster ovary cells in vitro. NG-hChM-I exhibited the growth factor/inhibitor activity in the cultures of chondrocytes and vascular endothelial cells but required markedly higher doses. Although domain 1 is predicted to be hydrophilic per se on the basis of its amino acid sequence, NG-hChM-I remains insoluble in aqueous solution as much as ΔN-hChM-I that lacks the N-terminal 37 amino acids containing an N-glycosylation site. Circular dichroism measurements revealed that the content of α-helix was calculated to be 34% in G-hChM-I, whereas the content of the characteristic secondary structures in NG-hChM-I was distinctly lower than those in G-hChM-I. These results indicate that glycosylation in domain 1 is critical for the structural integrity for biological functions of ChM-I in vitro.

Impairment of VEGF-A-stimulated lamellipodial extensions and motility of vascular endothelial cells by chondromodulin-I, a cartilage-derived angiogenesis inhibitor.

Chondromodulin-I (ChM-I) is a cartilage-derived angiogenesis inhibitor that has been identified as inhibitory to the growth activity of vascular endothelial cells. In our present study, we demonstrate the anti-angiogenic activity of recombinant human ChM-I (rhChM-I) in mouse corneal angiogenesis and examine its action. We focus on the VEGF-A-induced migration of vascular endothelial cells, a critical regulatory step in angiogenesis. In a modified Boyden chamber assay, nanomolar concentrations of rhChM-I inhibited the chemotactic migration of human umbilical vein endothelial cells (HUVECs) induced by VEGF-A as well as by FGF-2 and IGF-I. The ChM-I action was found to be endothelial cell-specific and independent of cell adhesions. Time-lapse analysis further revealed that rhChM-I markedly reduces VEGF-A-stimulated motility of HUVECs and causes frequent alterations of the moving front due to the appearance of multiple transient protrusions. This action involved the inhibition of cell spreading and the disrupted reorganization of the actin cytoskeleton upon VEGF-A stimulation. Consistent with these observations, rhChM-I was found to significantly reduce the activity of Rac1/Cdc42 during cell spreading, and the VEGF-A-induced Rac1 activity but not its basal activity in quiescent cells. Taken together, our present data suggest that ChM-I impairs the VEGF-A-stimulated motility of endothelial cells by destabilizing lamellipodial extensions.

Stimulatory actions of lysophosphatidic acid on mouse ATDC5 chondroprogenitor cells.

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are bioactive lysophospholipids that affect various cellular processes through G protein-coupled receptors. In our current study, we found by in situ hybridization that E11.5 mouse embryos strongly expressed the LPA receptor subtype LPA(1) in cartilaginous bone primordia and the surrounding mesenchymal cells. However, despite their wide-ranging actions, the roles of lysophospholipids in chondrogenesis remain poorly understood. The mouse clonal cell line ATDC5 undergoes a sequential differentiation of chondroprogenitor cells in vitro. Undifferentiated and differentiated ATDC5 cells express LPA(1) and other lysophospholipid receptors including S1P receptor S1P(1) and S1P(2). Taking advantage of this cell model, we studied the effects of LPA on the activities of chondroprogenitor cells. LPA markedly stimulates both DNA synthesis and the migration of ATDC5 chondroprogenitor cells in culture, whereas S1P suppresses the migration of these cells. Treatment with Ki16425, an LPA(1)- and LPA(3)-specific receptor antagonist, suppressed the fetal bovine serum-stimulated migration of ATDC5 cells by almost 80%. These results indicate that LPA plays an important role in the activation of chondroprogenitor cells.

Microfluidic Device for the Analysis of Angiogenic Sprouting under Bidirectional Biochemical Gradients.

In this paper, we developed a spheroid culture device that can trap a spheroid in the trapping site sandwiched by two extracellular matrix gels located at the upper and lower side of the spheroid. This device can form different biochemical gradients by applying target biochemicals separately in upper and lower channels, allowing us to study the angiogenic sprouting under various biochemical gradients in different directions. In the experiments, we confirmed the trapping of the spheroids and demonstrate the investigation on the direction and extent of angiogenic sprouts under unidirectional or bidirectional biochemical gradients. We believe our device can contribute to understanding the pathophysiological phenomena driven by chemical gradients, such as tissue development and tumor angiogenesis.

ECM-based microchannel for culturing in vitro vascular tissues with simultaneous perfusion and stretch.

We present an extracellular matrix (ECM)-based stretchable microfluidic system for culturing in vitro three-dimensional (3D) vascular tissues, which mimics in vivo blood vessels. Human umbilical vein endothelial cells (HUVECs) can be cultured under perfusion and stretch simultaneously with real-time imaging by our proposed system. Our ECM (transglutaminase (TG) cross-linked gelatin)-based microchannel was fabricated by dissolving water-soluble sacrificial polyvinyl alcohol (PVA) molds printed with a 3D printer. Flows in the microchannel were analyzed under perfusion and stretch. We demonstrated simultaneous perfusion and stretch of TG gelatin-based microchannels culturing HUVECs. We suggest that our TG gelatin-based stretchable microfluidic system proves to be a useful tool for understanding the mechanisms of vascular tissue formation and mechanotransduction.

Benzene metabolite hydroquinone up-regulates chondromodulin-I and inhibits tube formation in human bone marrow endothelial cells.

Bone marrow is a major target of benzene toxicity, and NAD-(P)H:quinone oxidoreductase (NQO1), an enzyme protective against benzene toxicity, is present in human bone marrow endothelial cells, which form the hematopoietic stem cell vascular niche. In this study, we have employed a transformed human bone marrow endothelial cell (TrHBMEC) line to study the adverse effects induced by the benzene metabolite hydroquinone. Hydroquinone inhibited TrHBMEC tube formation at concentrations that were not overtly toxic, as demonstrated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide or sulforhodamine B analysis. Hydroquinone was found to up-regulate chondromodulin-I (ChM-I), a protein that promotes chondrocyte growth and inhibits endothelial cell growth and tube formation. Recombinant human ChM-I protein inhibited tube formation in TrHBMECs, suggesting that up-regulation of ChM-I may explain the ability of hydroquinone to inhibit TrHB-MEC tube formation. To explore this possibility further, anti-ChM-I small interfering RNA (siRNA) was used to deplete ChM-I mRNA and protein. Pretreatment with anti-ChM-I siRNA markedly abrogated hydroquinone-induced inhibition of tube formation in TrHBMECs. Overexpression of the protective enzyme NQO1 in TrHBMECs inhibited the up-regulation of ChM-I and abrogated the inhibition of tube formation induced by hydroquinone. In summary, hydroquinone treatment up-regulated ChM-I and inhibited tube formation in TrHBMECs; NQO1 inhibited hydroquinone-induced up-regulation of ChM-I in TrHB-MECs and protected cells from hydroquinone-induced inhibition of tube formation. This study demonstrates that ChM-I up-regulation is one of the underlying mechanisms of inhibition of tube formation and provides a mechanism that may contribute to benzene-induced toxicity at the level of bone marrow endothelium.

Local tenomodulin absence, angiogenesis, and matrix metalloproteinase activation are associated with the rupture of the chordae tendineae cordis.

BACKGROUND: Rupture of the chordae tendineae cordis (CTC) is a well-known cause of mitral regurgitation. Despite its importance, the mechanisms by which the CTC is protected and the cause of its rupture remain unknown. CTC is an avascular tissue. We investigated the molecular mechanisms underlying the avascularity of CTC and the correlation between avascularity and CTC rupture. METHODS AND RESULTS: We found that tenomodulin, which is a recently isolated antiangiogenic factor, was expressed abundantly in the elastin-rich subendothelial outer layer of normal rodent, porcine, canine, and human CTC. Conditioned medium from cultured CTC interstitial cells strongly inhibited tube formation and mobilization of endothelial cells; these effects were partially inhibited by small-interfering RNA against tenomodulin. The immunohistochemical analysis was performed on 12 normal and 16 ruptured CTC obtained from the autopsy or surgical specimen. Interestingly, tenomodulin was locally absent in the ruptured areas of CTC, where abnormal vessel formation, strong expression of vascular endothelial growth factor-A and matrix metalloproteinases, and infiltration of inflammatory cells were observed, but not in the normal or nonruptured area. In anesthetized open-chest dogs, the tenomodulin layer of tricuspid CTC was surgically filed, and immunohistological analysis was performed after several months. This intervention gradually caused angiogenesis and expression of vascular endothelial growth factor-A and matrix metalloproteinases in the core collagen layer in a time-dependent manner. CONCLUSIONS: These findings provide evidence that tenomodulin is expressed universally in normal CTC in a concentric pattern and that local absence of tenomodulin, angiogenesis, and matrix metalloproteinase activation are associated with CTC rupture.

Scleraxis is a transcriptional activator that regulates the expression of Tenomodulin, a marker of mature tenocytes and ligamentocytes.

Tenomodulin (Tnmd) is a type II transmembrane glycoprotein predominantly expressed in tendons and ligaments. We found that scleraxis (Scx), a member of the Twist-family of basic helix-loop-helix transcription factors, is a transcriptional activator of Tnmd expression in tenocytes. During embryonic development, Scx expression preceded that of Tnmd. Tnmd expression was nearly absent in tendons and ligaments of Scx-deficient mice generated by transcription activator-like effector nucleases-mediated gene disruption. Tnmd mRNA levels were dramatically decreased during serial passages of rat tenocytes. Scx silencing by small interfering RNA significantly suppressed endogenous Tnmd mRNA levels in tenocytes. Mouse Tnmd contains five E-box sites in the ~1-kb 5'-flanking region. A 174-base pair genomic fragment containing a TATA box drives transcription in tenocytes. Enhancer activity was increased in the upstream region (-1030 to -295) of Tnmd in tenocytes, but not in NIH3T3 and C3H10T1/2 cells. Preferential binding of both Scx and Twist1 as a heterodimer with E12 or E47 to CAGATG or CATCTG and transactivation of the 5'-flanking region were confirmed by electrophoresis mobility shift and dual luciferase assays, respectively. Scx directly transactivates Tnmd via these E-boxes to positively regulate tenocyte differentiation and maturation.