Chondromodulin I is dispensable during enchondral ossification and eye development

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.

Shedding light on myopia by studying complete congenital stationary night blindness

Myopia is the most common eye disorder, caused by heterogeneous genetic and environmental factors. Rare progressive and stationary inherited retinal disorders are often associated with high myopia. Genes implicated in myopia encode proteins involved in a variety of biological processes including eye morphogenesis, extracellular matrix organization, visual perception, circadian rhythms, and retinal signaling. Differentially expressed genes (DEGs) identified in animal models mimicking myopia are helpful in suggesting candidate genes implicated in human myopia. Complete congenital stationary night blindness (cCSNB) in humans and animal models represents an ON-bipolar cell signal transmission defect and is also associated with high myopia. Thus, it represents also an interesting model to identify myopia-related genes, as well as disease mechanisms. While the origin of night blindness is molecularly well established, further research is needed to elucidate the mechanisms of myopia development in subjects with cCSNB. Using whole transcriptome analysis on three different mouse models of cCSNB (in Gpr179^-/-, Lrit3^-/- and Grm6^-/-), we identified novel actors of the retinal signaling cascade, which are also novel candidate genes for myopia. Meta-analysis of our transcriptomic data with published transcriptomic databases and genome-wide association studies from myopia cases led us to propose new biological/cellular processes/mechanisms potentially at the origin of myopia in cCSNB subjects. The results provide a foundation to guide the development of pharmacological myopia therapies.

Limiting angiogenesis to modulate scar formation

Angiogenesis, the process of new blood vessel formation from existing blood vessels, is a key aspect of virtually every repair process. During wound healing an extensive, but immature and leaky vascular plexus forms which is subsequently reduced by regression of non-functional vessels. More recent studies indicate that uncontrolled vessel growth or impaired vessel regression as a consequence of an excessive inflammatory response can impair wound healing, resulting in scarring and dysfunction. However, in order to elucidate targetable factors to promote functional tissue regeneration we need to understand the molecular and cellular underpinnings of physiological angiogenesis, ranging from induction to resolution of blood vessels. Especially for avascular tissues (e.g. cornea, tendon, ligament, cartilage, etc.), limiting rather than boosting vessel growth during wound repair potentially is beneficial to restore full tissue function and may result in favourable long-term healing outcomes.

Tenogenic modulating insider factor: Systematic assessment on the functions of tenomodulin gene

Tenomodulin (TNMD, Tnmd) is a gene highly expressed in tendon known to be important for tendon maturation with key implications for the residing tendon stem/progenitor cells as well as for the regulation of endothelial cell migration in chordae tendineae cordis in the heart and in experimental tumour models. This review aims at providing an encompassing overview of this gene and its protein. In addition, its known expression pattern as well as putative signalling pathways will be described. A chronological overview of the discovered functions of this gene in tendon and other tissues and cells is provided as well as its use as a tendon and ligament lineage marker is assessed in detail and discussed. Last, information about the possible connections between TNMD genomic mutations and mRNA expression to various diseases is delivered. Taken together this review offers a solid synopsis on the up-to-date information available about TNMD and aids at directing and focusing the future research to fully uncover the roles and implications of this interesting gene.

Defects in tendon, ligament, and enthesis in response to genetic alterations in key proteoglycans and glycoproteins: a review

This review summarizes the genetic alterations and knockdown approaches published in the literature to assess the role of key proteoglycans and glycoproteins in the structural development, function, and repair of tendon, ligament, and enthesis. The information was collected from (i) genetically altered mice, (ii) in vitro knockdown studies, (iii) genetic variants predisposition to injury, and (iv) human genetic diseases. The genes reviewed are for small leucine-rich proteoglycans (lumican, fibromodulin, biglycan, decorin, and asporin); dermatan sulfate epimerase (Dse) that alters structure of glycosaminoglycan and hence the function of small leucine-rich proteoglycans by converting glucuronic to iduronic acid; matricellular proteins (thrombospondin 2, secreted phosphoprotein 1 (Spp1), secreted protein acidic and rich in cysteine (Sparc), periostin, and tenascin X) including human tenascin C variants; and others, such as tenomodulin, leukocyte cell derived chemotaxin 1 (chondromodulin-I, ChM-I), CD44 antigen (Cd44), lubricin (Prg4), and aggrecan degrading gene, a disintegrin-like and metallopeptidase (reprolysin type) with thrombospondin type 1 motif, 5 (Adamts5). Understanding these genes represents drug targets for disrupting pathological mechanisms that lead to tendinopathy, ligamentopathy, enthesopathy, enthesitis and tendon/ligament injury, that is, osteoarthritis and ankylosing spondylitis.

Role and regulation of vascularization processes in endochondral bones

Adequate vascularization is an absolute requirement for bone development, growth, homeostasis, and repair. Endochondral ossification during fetal skeletogenesis is typified by the initial formation of a prefiguring cartilage template of the future bone, which itself is intrinsically avascular. When the chondrocytes reach terminal hypertrophic differentiation they become invaded by blood vessels. This neovascularization process triggers the progressive replacement of the growing cartilage by bone, in a complex multistep process that involves the coordinated activity of chondrocytes, osteoblasts, and osteoclasts, each standing in functional interaction with the vascular system. Studies using genetically modified mice have started to shed light on the molecular regulation of the cartilage neovascularization processes that drive endochondral bone development, growth, and repair, with a prime role being played by vascular endothelial growth factor and its isoforms. The vasculature of bone remains important throughout life as an intrinsic component of the bone and marrow environment. Bone remodeling, the continual renewal of bone by the balanced activities of osteoclasts resorbing packets of bone and osteoblasts building new bone, takes place in close spatial relationship with the vascular system and depends on signals, oxygen, and cellular delivery via the bloodstream. Conversely, the integrity and functionality of the vessel system, including the exchange of blood cells between the hematopoietic marrow and the circulation, rely on a delicate interplay with the cells of bone. Here, the current knowledge on the cellular relationships and molecular crosstalk that coordinate skeletal vascularization in bone development and homeostasis will be reviewed.

Antiangiogenic and anticancer molecules in cartilage

Cartilage is one of the very few naturally occurring avascular tissues where lack of angiogenesis is the guiding principle for its structure and function. This has attracted investigators who have sought to understand the biochemical basis for its avascular nature, hypothesising that it could be used in designing therapies for treating cancer and related malignancies in humans through antiangiogenic applications. Cartilage encompasses primarily a specialised extracellular matrix synthesised by chondrocytes that is both complex and unique as a result of the myriad molecules of which it is composed. Of these components, a few such as thrombospondin-1, chondromodulin-1, the type XVIII-derived endostatin, SPARC (secreted protein acidic and rich in cysteine) and the type II collagen-derived N-terminal propeptide (PIIBNP) have demonstrated antiangiogenic or antitumour properties in vitro and in vivo preclinical trials that involve several complicated mechanisms that are not completely understood. Thrombospondin-1, endostatin and the shark-cartilage-derived Neovastat preparation have also been investigated in human clinical trials to treat several different kinds of cancers, where, despite the tremendous success seen in preclinical trials, these molecules are yet to show success as anticancer agents. This review summarises the current state-of-the-art antiangiogenic characterisation of these molecules, highlights their most promising aspects and evaluates the future of these molecules in antiangiogenic applications.

Perlecan modulates VEGF signaling and is essential for vascularization in endochondral bone formation

Perlecan (Hspg2) is a heparan sulfate proteoglycan expressed in basement membranes and cartilage. Perlecan deficiency (Hspg2(-/-)) in mice and humans causes lethal chondrodysplasia, which indicates that perlecan is essential for cartilage development. However, the function of perlecan in endochondral ossification is not clear. Here, we report the critical role of perlecan in VEGF signaling and angiogenesis in growth plate formation. The Hspg2(-/-) growth plate was significantly wider but shorter due to severely impaired endochondral bone formation. Hypertrophic chondrocytes were differentiated in Hspg2(-/-) growth plates; however, removal of the hypertrophic matrix and calcified cartilage was inhibited. Although the expression of MMP-13, CTGF, and VEGFA was significantly upregulated in Hspg2(-/-) growth plates, vascular invasion into the hypertrophic zone was impaired, which resulted in an almost complete lack of bone marrow and trabecular bone. We demonstrated that cartilage perlecan promoted activation of VEGF/VEGFR by binding to the VEGFR of endothelial cells. Expression of the perlecan transgene specific to the cartilage of Hspg2(-/-) mice rescued their perinatal lethality and growth plate abnormalities, and vascularization into the growth plate was restored, indicating that perlecan in the growth plate, not in endothelial cells, is critical in this process. These results suggest that perlecan in cartilage is required for activating VEGFR signaling of endothelial cells for vascular invasion and for osteoblast migration into the growth plate. Thus, perlecan in cartilage plays a critical role in endochondral bone formation by promoting angiogenesis essential for cartilage matrix remodeling and subsequent endochondral bone formation.

Vascular endothelial growth factor-A is a survival factor for nucleus pulposus cells in the intervertebral disc

The intervertebral disc (IVD) is composed of two avascular tissue types, the nucleus pulposus (NP) and the annulus fibrosus (AF). IVDs is the largest avascular tissue in the human body, however, how these tissues are maintained without a blood supply is poorly understood. Here we show that vascular endothelial growth factor-A (VEGF-A) is highly expressed in NP and that VEGF-A plays a role in NP survival. High VEGF-A expression in NP was detected by microarray analysis, and NP was positive for the hypoxic probe pimonidazole and hypoxia-responsive genes. VEGF-A expression in NP was promoted by hypoxic conditions in vitro. NP cells also expressed the membrane-bound VEGF receptor-1 (VEGFR-1), and the number of apoptotic cells in cultured cell model of NP increased following treatment with VEGFR-1-Fc, which traps VEGF-A in NP. These results indicate that NP is a hypoxic tissue, and that VEGF-A functions in NP survival in an autocrine/paracrine manner.

Biological roles of carboxymethyl-chitin associated for the growth factor production

Many techniques to restore cartilage defection have been tried. However, the development is still under way because of problems, including loosening of artificial joint, degenerative change of compensated tissue, risk of viral transmission via allograft/autograft, and cost of therapeutic materials for repair. In the previous research, we found that complementing cartilage defective part with carboxymethyl-chitin (CM-chitin)/beta-tricalcium phosphate composite induced regeneration of cartilage in rabbits in vivo, and it is presumable that CM-chitin plays a key role in chondrogenesis causing the regeneration of cartilage. However, the induction mechanism of chondrogenesis with CM-chitin is still unclear. In this study, we investigated the cell responses to CM-chitin by using peritoneal exudate cell (PEC) in mice and found that CM-chitin induced the expression of inflammatory cytokines and growth factors, both of which are both considered to correlate with chondrogenesis. After intraperitoneal injection CM-chitin showed enhanced expressions of mRNA of interleukin-1beta (IL-1beta), interleukin-6 (IL-6), keratinocyte-derived chemokine, tumor necrosis factor-alpha, and transforming growth factor-beta1 (TGF-beta1) in PEC as observed by reverse transcriptase polymerase chain reaction. Productions of TGF-beta1 protein were confirmed by enzyme linked immunosorbant assay. It was also shown that mononuclear cells in PEC were responsible for the TGF-beta1 production. These results suggest that CM-chitin is an inductor of inflammatory cytokines and growth factors and may contribute to regeneration of cartilage.

Focal adhesions: what's new inside

The cytoplasmic side of focal adhesions is comprised of large molecular complexes that link transmembrane receptors, such as integrins, to the actin cytoskeleton and mediate signals modulating cell attachment, migration, proliferation, differentiation, and gene expression. These complexes are heterogeneous and dynamic structures that are apparent targets of regulatory signals that control the function of focal adhesions. Recent studies using genetic approaches in invertebrate and vertebrate systems have begun to reveal the structure and function of these complexes in vivo.

Effect of TGF-beta inducible early gene deficiency on flexor tendon healing

The role of transforming growth factor beta (TGF-beta) in tendon healing is still not clearly established. TGF-beta affects gene expression primarily through the activation of the Smad signaling pathway. The first step in the Smad pathway is the expression of TGF-beta inducible early gene (TIEG). Recently, a TIEG knockout mouse has been developed. The purpose of this study was to examine the healing potential of flexor tendons in mice lacking the TIEG gene, and to further examine what role the TIEG pathway plays in flexor tendon repair. Twenty-two mice, consisting of 11 normal wild-type mice and 11 TIEG knockout mice, were euthanized at 8 to 12 weeks of age. The second through fifth FDL tendons of both hind feet were transected and repaired in zone 2. The repaired tendons were removed from the mice and placed into tissue culture. Tendons were then examined at days 3, 7, 14, 21, and 42 after surgery. Hematoxylin and eosin (HE) staining and immunohistochemical staining for TGF-beta, collagen type I, and collagen type III were performed. Reverse transcriptase polymerase chain reaction (RT-PCR) was performed to examine expression of TGF-beta1, beta2, beta3, and collagen type I and III. At 42 days after surgery, HE staining showed coaptation of lacerated tendon ends in both groups. Both groups showed healing of the lacerated tendon, but the chronologic expression pattern of TGF-beta was different between the knockout and normal tendons. TIEG deficient tendons had delayed expression of TGF-beta when compared with control tendons. The collagen mRNA expression pattern was similar with both groups, but the expression level was different, with TIEG knockout tendons having a lower expression of collagen type I mRNA (p < 0.001). TGF-beta is thought to play a major role in tendon healing. Healing of tendons in the TIEG knockout mouse suggests the possibility of tendon healing in the absence of the Smad pathway. The knockout mouse model described in the present study provides a novel means for further understanding of the tendon healing process through isolated deletion of specific growth factors.

Expression of mouse HtrA1 serine protease in normal bone and cartilage and its upregulation in joint cartilage damaged by experimental arthritis

Levels of HtrA1 protein in cartilage have been reported to elevate in joints of human osteoarthritis patients. To understand roles of HtrA1 in normal osteogenesis as well as in pathogenesis of arthritis, we examine HtrA1 expression pattern during bone and cartilage development and in articular cartilage affected by experimental arthritis. HtrA1 is not expressed in mesenchymal or cartilage condensations before initiation of ossification. When ossification begins in the condensations, the expression of HtrA1 starts in chondrocytes undergoing hypertrophic differentiation near the ossification center. Hypertrophic chondrocytes found in adult articular cartilage and epiphyseal growth plates also express HtrA1. When arthritis is induced by injection of anti-collagen antibodies and lipopolysaccharide, resting chondrocytes proceed to terminal hypertrophic differentiation and start expressing HtrA1. These data suggest that hypertrophic change induces HtrA1 expression in chondrocytes both in normal and pathological conditions. HtrA1 has been reported to inhibit TGF-beta signaling. We show that HtrA1 digests major components of cartilage, such as aggrecan, decorin, fibromodulin, and soluble type II collagen. HtrA1 may, therefore, promote degeneration of cartilage by inducing terminal hypertrophic chondrocyte differentiation and by digesting cartilage matrix though its TGF-beta inhibitory activity and protease activity, respectively. In bone, active cuboidal osteoblasts barely express HtrA1, but osteoblasts which flatten and adhere to the bone matrix and osteocytes embedded in bone are strongly positive for HtrA1 production. The bone matrix shows a high level of HtrA1 protein deposition akin to that of TGF-beta, suggesting a close functional interaction between TGF-beta and HtrA1.

The transcriptome's drugable frequenters

Microarray studies are widely employed in the exploratory phase of the drug discovery process. Expectations raised by the genomics revolution led to the belief that they would rapidly lead to the identification of novel drug targets. However, a few basic questions were often overlooked. Are members of drugable gene families properly represented in the transcriptome? Or are they poorly expressed and below the detection limit of the microarray technology? This review explores the representation of drug targets and components of downstream cellular signaling pathways in the transcriptome. It appears that members of drugable gene families are underrepresented in the transcriptomes of non-pathological human tissues. But, they are represented at or above the expected frequency in the differential transcriptome (i.e. the set of genes that changes expression upon a change in cellular environment). Analysis of differential gene expression on a genome-wide scale will therefore give a comprehensive overview of cellular pathways and possible drug targets.

Tenomodulin is necessary for tenocyte proliferation and tendon maturation

Tenomodulin (Tnmd) is a member of a new family of type II transmembrane glycoproteins. It is predominantly expressed in tendons, ligaments, and eyes, whereas the only other family member, chondromodulin I (ChM-I), is highly expressed in cartilage and at lower levels in the eye and thymus. The C-terminal extracellular domains of both proteins were shown to modulate endothelial-cell proliferation and tube formation in vitro and in vivo. We analyzed Tnmd function in vivo and provide evidence that Tnmd is processed in vivo and that the proteolytically cleaved C-terminal domain can be found in tendon extracts. Loss of Tnmd expression in gene targeted mice abated tenocyte proliferation and led to a reduced tenocyte density. The deposited amounts of extracellular matrix proteins, including collagen types I, II, III, and VI and decorin, lumican, aggrecan, and matrilin-2, were not affected, but the calibers of collagen fibrils varied significantly and exhibited increased maximal diameters. Tnmd-deficient mice did not have changes in tendon vessel density, and mice lacking both Tnmd and ChM-I had normal retinal vascularization and neovascularization after oxygen-induced retinopathy. These results suggest that Tnmd is a regulator of tenocyte proliferation and is involved in collagen fibril maturation but do not confirm an in vivo involvement of Tnmd in angiogenesis.

Chondromodulin-I expression in the growth plate of young uremic rats

BACKGROUND

Growth retardation of chronic renal failure is associated with alterations in the growth plate suggestive of a disturbed chondrocyte maturation process and abnormal vascular invasion at the chondro-osseous interphase. Chondromodulin I (ChM-I) is a potent cartilage-specific angiostatic factor. Its pattern of expression in the uremic rat growth plate is unknown. Persistence of ChM-I synthesis and/or imbalance between ChM-I and vascular endothelial growth factor (VEGF) expressions might play a role in the alterations of uremic growth plate.

METHODS

Growth cartilage ChM-I expression was investigated by immunohistochemistry, in situ hybridization, and reverse transcription-polymerase chain reaction (RT-PCR) in growth-retarded young uremic rats (UREM), control rats, fed ad libitum (SAL) or pair-fed with the UREM group (SPF), and uremic rats treated with growth hormone (UREM-GH). VEGF expression was analyzed by immunohistochemistry.

RESULTS

ChM-I and ChM-I mRNA were confined to the proliferative and early hypertrophic zones of growth cartilage. A similar number of chondrocytes per column was positive for ChM-I in the 4 groups. In accordance with the elongation of the hypertrophic stratum in uremia, the distance (X+/-SEM, microm) between the extracellular ChM-I signal and the metaphyseal end of growth cartilage was higher (P < 0.003) in UREM (236 +/- 40) and UREM-GH (297 +/- 17) than in SAL (92 +/- 7) and SPF (113 +/- 6). No differences in ChM-I expression were appreciated by RT-PCR. Similar VEGF positivity was observed in the hypertrophic chondrocytes of all groups.

CONCLUSION

In experimental uremia, expansion of growth cartilage does not result from increased or persistent expression of ChM-I or from reduced VEGF expression at the cartilage-metaphyseal bone interphase. GH treatment does not modify ChM-I and VEGF expressions.

Matrilin-3 is dispensable for mouse skeletal growth and development

Matrilin-3 belongs to the matrilin family of extracellular matrix (ECM) proteins and is primarily expressed in cartilage. Mutations in the gene encoding human matrilin-3 (MATN-3) lead to autosomal dominant skeletal disorders, such as multiple epiphyseal dysplasia (MED), which is characterized by short stature and early-onset osteoarthritis, and bilateral hereditary microepiphyseal dysplasia, a variant form of MED characterized by pain in the hip and knee joints. To assess the function of matrilin-3 during skeletal development, we have generated Matn-3 null mice. Homozygous mutant mice appear normal, are fertile, and show no obvious skeletal malformations. Histological and ultrastructural analyses reveal endochondral bone formation indistinguishable from that of wild-type animals. Northern blot, immunohistochemical, and biochemical analyses indicated no compensatory upregulation of any other member of the matrilin family. Altogether, our findings suggest functional redundancy among matrilins and demonstrate that the phenotypes of MED disorders are not caused by the absence of matrilin-3 in cartilage ECM.

Expression of the chondromodulin-I gene in chondrosarcomas

We investigated the expression of the Chondromodulin-I (ChM-I) gene, a putative tumor suppressor gene in cartilaginous tumors, by quantitative RT-PCR in 15 chondrosarcomas (CSs). Eight CSs expressed the ChM-I gene at the level higher than those in articular cartilage (positive cases), whereas the expression of the ChM-I gene in the remaining seven CSs was lower than those in articular cartilage (negative cases). All of five peripheral CS were positive, and the ChM-I positive tumors shared expression profiles of cartilage-related genes with articular cartilage cells. On the other hand, all of four central CSs without extramedullary lesions were negative, and the ChM-I negative tumors expressed the parathyroid hormone-related peptide gene at the lower level and the COL10A1 genes at the higher level than articular cartilage cells. Neither the histological grade nor the rate of recurrence showed clear association with the level of ChM-I gene expression. These results suggested that the expression of ChM-I gene in CS has no direct role in tumorigenesis but rather reflects the site of tumor development and therefore precursor of tumor cells.

Beta1 integrins regulate chondrocyte rotation, G1 progression, and cytokinesis

Beta1 integrins are highly expressed on chondrocytes, where they mediate adhesion to cartilage matrix proteins. To assess the functions of beta1 integrin during skeletogenesis, we inactivated the beta1 integrin gene in chondrocytes. We show here that these mutant mice develop a chondrodysplasia of various severity. beta1-deficient chondrocytes had an abnormal shape and failed to arrange into columns in the growth plate. This is caused by a lack of motility, which is in turn caused by a loss of adhesion to collagen type II, reduced binding to and impaired spreading on fibronectin, and an abnormal F-actin organization. In addition, mutant chondrocytes show decreased proliferation caused by a defect in G1/S transition and cytokinesis. The G1/S defect is, at least partially, caused by overexpression of Fgfr3, nuclear translocation of Stat1/Stat5a, and up-regulation of the cell cycle inhibitors p16 and p21. Altogether these findings establish that beta1-integrin-dependent motility and proliferation of chondrocytes are mandatory events for endochondral bone formation to occur.