Primary structure of matrilin-3, a new member of a family of extracellular matrix proteins related to cartilage matrix protein (matrilin-1) and von Willebrand factor

Matrilin-3 supports neuroprotection in ischemic stroke by suppressing astrocyte-mediated neuroinflammation

In the brain, the role of matrilin-3, an extracellular matrix component in cartilage, is unknown. Here, we identify that matrilin-3 decreased in reactive astrocytes but was unchanged in neurons after ischemic stroke in animals. Importantly, it declined in serum of patients with acute ischemic stroke. Genetic or pharmacological inhibition or supplementation of matrilin-3 aggravates or reduces brain injury, astrocytic cell death, and glial scar, respectively, but has no direct effect on neuronal cell death. RNA sequencing demonstrates that Matn3-/- mice display an increased inflammatory response profile in the ischemic brain, including the nuclear factor κB (NF-κB) signaling pathway. Both endogenous and exogenous matrilin-3 reduce inflammatory mediators. Mechanistically, extracellular matrilin-3 enters astrocytes via caveolin-1-mediated endocytosis. Cytoplasmic matrilin-3 translocates into the nucleus by binding to NF-κB p65, suppressing inflammatory cytokine transcription. Extracellular matrilin-3 binds to BMP-2, blocking the BMP-2/Smads pathway. Thus, matrilin-3 is required for astrocytes to exert neuroprotection, at least partially, by suppressing astrocyte-mediated neuroinflammation.

Curcumin Reduces Pathological Endoplasmic Reticulum Stress through Increasing Proteolysis of Mutant Matrilin-3

The intracellular retention of mutant cartilage matrix proteins and pathological endoplasmic reticulum (ER) stress disrupts ossification and has been identified as a shared disease mechanism in a range of skeletal dysplasias including short limbed-dwarfism, multiple epiphyseal dysplasia type 5 (EDM5). Although targeting ER stress is an attractive avenue for treatment and has proven successful in the treatment of a related skeletal dysplasia, to date no drugs have proven successful in reducing ER stress in EDM5 caused by the retention of mutant matrilin-3. Our exciting findings show that by using our established luciferase ER stress screening assay, we can identify a "natural" chemical, curcumin, which is able to reduce pathological ER stress in a cell model of EDM5 by promoting the proteasomal degradation mutant matrilin-3. Therefore, this is an important in vitro study in which we describe, for the first time, the success of a naturally occurring chemical as a potential treatment for this currently incurable rare skeletal disease. As studies show that curcumin can be used as a potential treatment for range of diseases in vitro, current research is focused on developing novel delivery strategies to enhance its bioavailability. This is an important and exciting area of research that will have significant clinical impact on a range of human diseases including the rare skeletal disease, EDM5.

Molecular Typing of Gastric Cancer Based on Invasion-Related Genes and Prognosis-Related Features

Background

This study aimed to construct a prognostic stratification system for gastric cancer (GC) using tumour invasion-related genes to more accurately predict the clinical prognosis of GC.

Methodology

Tumour invasion-related genes were downloaded from CancerSEA, and their expression data in the TCGA-STAD dataset were used to cluster samples via non-negative matrix factorisation (NMF). Differentially expressed genes (DEGs) between subtypes were identified using the limma package. KEGG pathway and GO functional enrichment analyses were conducted using the WebGestaltR package (v0.4.2). The immune scores of molecular subtypes were evaluated using the R package ESTIMATE, MCPcounter and the ssGSEA function of the GSVA package. Univariate, multivariate and lasso regression analyses of DEGs were performed using the coxph function of the survival package and the glmnet package to construct a RiskScore model. The robustness of the model was validated using internal and external datasets, and a nomogram was constructed based on the model.

Results

Based on 97 tumour invasion-related genes, 353 GC samples from TCGA were categorised into two subtypes, thereby indicating the presence of inter-subtype differences in prognosis. A total of 569 DEGs were identified between the two subtypes; of which, four genes were selected to construct the risk model. This four-gene signature was robust and exhibited stable predictive performance in different platform datasets (GSE26942 and GSE66229), indicating that the established model performed better than other existing models.

Conclusion

A prognostic stratification system based on a four-gene signature was developed with a desirable area under the curve in the training and independent validation sets. Therefore, the use of this system as a molecular diagnostic test is recommended to assess the prognostic risk of patients with GC.

Diagnostic and prognostic value of MATN3 expression in gastric carcinoma: TCGA database mining

Backgrounds

Globally, the high morbidity and mortality of gastric carcinoma (GC) have been one of the great challenges facing humanity. However, the early diagnosis of GC is still unknown. Matrilin-3 (MATN3) is a member of the extracellular matrix (ECM) protein family. Previous studies have reported a correlation between the expression of MATN3 and bone disease. However, the role of MATN3 in GC has not been reported in depth, which can have a possible far-reaching implication for GC.

Methods

We explored the diagnostic and prognostic value and pathway enrichment of MATN3 expression in GC. Limma package conducted by R was used to analysis the difference expression data of MATN3 from The Cancer Genome Atlas (TCGA). The receiver operating characteristic (ROC) curve analysis was used to estimate the diagnostic value of MATN3 expression. univariate and multivariate analysis were used to assess the prognostic value of MATN3, and gene set enrichment analysis (GSEA) to identify the enriched signaling pathways.

Results

MATN3 was found to be significantly higher in GC tissue samples. GC patients with high MATN3 expression had poor prognosis. Then, GSEA showed that the gene sets were correlated with signaling pathways including ECM receptor interaction, hypertrophic cardiomyopathy (HCM), and glycosaminoglycan biosynthesis chondroitin sulfate, among others.

Conclusions

The study suggests that MATN3 can serve as a potential diagnostic and prognostic biomarker for GC.

Identification of an EMT-Related Gene Signature for Predicting Overall Survival in Gastric Cancer

Background

It has been widely reported that epithelial-mesenchymal transition (EMT) is associated with malignant progression in gastric cancer (GC). Integration of the molecules related to EMT for predicting overall survival (OS) is meaningful for understanding the role of EMT in GC. Here, we aimed to establish an EMT-related gene signature in GC.

Methods

Transcriptional profiles and clinical data of GC were downloaded from The Cancer Genome Atlas (TCGA). We constructed EMT-related gene signature for predicting OS by using univariate Cox regression and least absolute shrinkage and selection operator (LASSO) regression analyses. Time-dependent receiver operating characteristic (ROC), Kaplan-Meier analysis were performed to assess its predictive value. A nomogram combining the prognostic signature with clinical characteristics for OS prediction was established. And its predictive power was estimated by concordance index (C-index), time-dependent ROC curve, calibration curve and decision curve analysis (DCA). GSE62254 dataset from Gene Expression Omnibus (GEO) was used for external validation. Quantitative real-time PCR (qRT-PCR) was used to detected the mRNA expression of the five EMT-related genes in human normal gastric mucosal and GC cell lines. To further understand the potential mechanisms of the signature, Gene Set Enrichment Analysis (GSEA), pathway enrichment analysis, predictions of transcription factors (TFs)/miRNAs were performed.

Results

A novel EMT-related gene signature (including ITGAV, DAB2, SERPINE1, MATN3, PLOD2) was constructed for OS prediction of GC. With external validation, ROC curves indicated the signature’s good performance. Patients stratified into high- and low-risk groups based on the signature yielded significantly different prognosis. Univariate and multivariate Cox regression suggested that the signature was an independent prognostic variable. Nomogram for prognostication including the signature presented better predictive accuracy and clinical usefulness than the similar model without risk score to some extent with external validation. The qRT-PCR assays suggested that high expression of the five EMT-related genes could be found in human GC cell lines compared with normal gastric mucosal cell line. GSEA and pathway enrichment analysis revealed that focal adhesion and ECM-receptor interaction might be the two important pathways to the signature.

Conclusion

Our EMT-related gene signature may have practical application as an independent prognostic factor in GC.

The Matrilin-3 T298M mutation predisposes for post-traumatic osteoarthritis in a knock-in mouse model

OBJECTIVE

The human matrilin-3 T303M (in mouse T298M) mutation has been proposed to predispose for osteoarthritis, but due to the lack of an appropriate animal model this hypothesis could not be tested. This study was carried out to identify pathogenic mechanisms in a transgenic mouse line by which the mutation might contribute to disease development.

METHODS

A mouse line carrying the T298M point mutation in the Matn3 locus was generated and features of skeletal development in ageing animals were characterized by immunohistology, micro computed tomography, transmission electron microscopy and atomic force microscopy. The effect of transgenic matrilin-3 was also studied after surgically induced osteoarthritis.

RESULTS

The matrilin-3 T298M mutation influences endochondral ossification and leads to larger cartilage collagen fibril diameters. This in turn leads to an increased compressive stiffness of the articular cartilage, which, upon challenge, aggravates osteoarthritis development.

CONCLUSIONS

The mouse matrilin-3 T298M mutation causes a predisposition for post-traumatic osteoarthritis and the corresponding knock-in mouse line therefore represents a valid model for investigating the pathogenic mechanisms involved in osteoarthritis development.

A novel p.A191D matrilin-3 variant in a Vietnamese family with multiple epiphyseal dysplasia: a case report

Background

Multiple epiphyseal dysplasia (MED) is a common skeletal dysplasia that is characterized by variable degrees of epiphyseal abnormality primarily involving the hip and knee joints. Mutations in a gene encoding matrilin-3 (MATN3) have been reported as disease causing of autosomal dominant MED. The current study identified a novel c.572 C > A variant (p.A191D) in exon 2 of MATN3 in a Vietnamese family with MED.

Case presentation

A standard clinical tests and radiological examination were performed in an 8-year-old Vietnamese girl patient. The clinical examination showed that patient height was under average, with bent lower limbs, limited mobility and dislocation of the joints at both knees. Radiological documentation revealed abnormal cartilage development at the epiphysis of the femur and patella. The patient has a varus deformity of the lower limbs. The patient was diagnosed with autosomal dominant MED using molecular testing in the order of the coding sequences and flanking sequences of five genes: COMP (exons 8–19), MATN3 (exon 2), COL9A2 (exon 3), COL9A3 (exon 3), COL9A1 (exon 8) by Sanger sequencing. A novel heterozygous missense variant (c.572 C > A, p.A191D) in MATN3 was identified in this family, which were not inherited from parents. The p.A191D was predicted and classified as a pathogenic variant. When the two predicted structures of the wild type and mutant matrilin-3 were compared, the p.A191D substitution caused conformational changes near the substitution site, resulting in deformity of the β-sheet of the single A domain of matrilin- 3.

Conclusions

This is the first Vietnamese MED family attributed to p.A191D matrilin-3 variant, and our clinical, radiological and molecular data suggest that the novel de novo missense variant in MATN3 contributed to MED.

Alu-Alu mediated intragenic duplications in IFT81 and MATN3 are associated with skeletal dysplasias

Skeletal dysplasias are a diverse group of rare Mendelian disorders with clinical and genetic heterogeneity. Here, we used targeted copy number variant (CNV) screening and identified intragenic exonic duplications, formed through Alu-Alu fusion events, in two individuals with skeletal dysplasia and negative exome sequencing results. First, we detected a homozygous tandem duplication of exon 9 and 10 in IFT81 in a boy with Jeune syndrome, or short-rib thoracic dysplasia (SRTD) (MIM# 208500). Western blot analysis did not detect any wild-type IFT81 protein in fibroblasts from the patient with the IFT81 duplication, but only a shorter isoform of IFT81 that was also present in the normal control samples. Complementary zebrafish studies suggested that loss of full-length IFT81 protein but expression of a shorter form of IFT81 protein affects the phenotype while being compatible with life. Second, a de novo tandem duplication of exons 2 to 5 in MATN3 was identified in a girl with multiple epiphyseal dysplasia (MED) type 5 (MIM# 607078). Our data highlights the importance of detection and careful characterization of intragenic duplication CNVs, presenting them as a novel and very rare genetic mechanism in IFT81-related Jeune syndrome and MATN3-related MED.

Suppressing mesenchymal stem cell hypertrophy and endochondral ossification in 3D cartilage regeneration with nanofibrous poly(l-lactic acid) scaffold and matrilin-3

Articular cartilage has a very limited ability to self-heal after injury or degeneration due to its low cellularity, poor proliferative activity, and avascular nature. Current clinical options are able to alleviate patient suffering, but cannot sufficiently regenerate the lost tissue. Biomimetic scaffolds that recapitulate the important features of the extracellular matrix (ECM) of cartilage are hypothesized to be advantageous in supporting cell growth, chondrogenic differentiation, and integration of regenerated cartilage with native cartilage, ultimately restoring the injured tissue to its normal function. It remains a challenge to support and maintain articular cartilage regenerated by bone marrow-derived mesenchymal stem cells (BMSCs), which are prone to hypertrophy and endochondral ossification after implantation in vivo. In the present work, a nanofibrous poly(l-lactic acid) (NF PLLA) scaffold developed by our group was utilized because of the desired highly porous structure, high interconnectivity, and collagen-like NF architecture to support rabbit BMSCs for articular cartilage regeneration. We further hypothesized that matrilin-3 (MATN3), a non-collagenous, cartilage-specific ECM protein, would enhance the microenvironment of the NF PLLA scaffold for cartilage regeneration and maintain the cartilage property. To test this hypothesis, we seeded BMSCs on the NF PLLA scaffold with or without MATN3. We found that MATN3 suppresses hypertrophy in this 3D culture system in vitro. Subcutaneous implantation of the chondrogenic cell/scaffold constructs in a nude mouse model showed that pretreatment with MATN3 was able to maintain chondrogenesis and prevent hypertrophy and endochondral ossification in vivo. These results demonstrate that the porous NF PLLA scaffold treated with MATN3 represents an advantageous 3D microenvironment for cartilage regeneration and phenotype maintenance, and is a promising strategy for articular cartilage repair.

STATEMENT OF SIGNIFICANCE

Articular cartilage defects, caused by trauma, inflammation, or joint instability, may ultimately lead to debilitating pain and disability. Bone marrow-derived mesenchymal stem cells (BMSCs) are an attractive cell source for articular cartilage tissue engineering. However, chondrogenic induction of BMSCs is often accompanied by undesired hypertrophy, which can lead to calcification and ultimately damage the cartilage. Therefore, a therapy to prevent hypertrophy and endochondral ossification is of paramount importance to adequately regenerate articular cartilage. We hypothesized that MATN3 (a non-collagenous ECM protein expressed exclusively in cartilage) may improve regeneration of articular cartilage with BMSCs by maintaining chondrogenesis and preventing hypertrophic transition in an ECM mimicking nanofibrous scaffold. Our results showed that the administration of MATN3 to the cell/nanofibrous scaffold constructs favorably maintained chondrogenesis and prevented hypertrophy/endochondral ossification in the chondrogenic constructs in vitro and in vivo. The combination of nanofibrous PLLA scaffolds and MATN3 treatment provides a very promising strategy to generate chondrogenic grafts with phenotypic stability for articular cartilage repair.

The distribution patterns of COMP and matrilin-3 in septal, alar and triangular cartilages of the human nose

The biomechanical characteristics of septal cartilage depend strongly on the distinct extracellular matrix of cartilage tissue; therefore, it is essential that the components of this matrix are identified and understood. Cartilage oligomeric matrix protein (COMP) and matrilin-3 are localised in articular cartilage. This study was the first to examine all subtypes of mature human nasal cartilages (alar, triangular and septal) with specific attention to the distribution of COMP and matrilin-3. Three whole fresh-frozen noses from human donors were dissected, and exemplary biopsies were examined using histochemical staining (haematoxylin and eosin and Alcian blue) and immunohistochemistry (collagen II, COMP and matrilin-3). The following three zones within the nasal cartilage were identified: superficial, intermediate and central. COMP was detected as highest in the intermediate zones in all three subtypes of nasal cartilage, whereas matrilin-3 was detected with pericellular deposition mainly within septal cartilage predominantly in the superficial zones. The distinct staining patterns of COMP and matrilin-3 underscore the different functional roles of both proteins in nasal cartilage. According to the literature, COMP might be involved with collagen II in the formation of networks, whereas matrilin-3 is reported to prevent ossification or regulate mechanosensitivity. The predominant staining observed in septal cartilage suggests matrilin-3's modulatory role because of its presence in the osteochondral junctional zone and given that the biomechanical load in septal cartilage is different from that in alar or triangular cartilage. In conclusion, COMP and matrilin-3 were detected in mature human nasal cartilage but displayed different staining patterns that might be explained by the functional roles of the respective matrix protein; however, further research is necessary to identify and define the functional aspects of this morphological difference.

Downregulation of microRNA-448 inhibits IL-1β-induced cartilage degradation in human chondrocytes via upregulation of matrilin-3

Background

Osteoarthritis is characterized by the continuous degradation of the articular cartilage. The microRNA miR-448 has been found to be broadly involved in cellular processes, including proliferation, apoptosis, invasion and EMT. While aberrant expression of miR-448 has been found in multiple cancers, its level in osteoarthritis cartilage and its role in the progression of this disease are still unknown. Here, we examined the functional roles of miR-448 and its expression in osteoarthritis tissues, including IL-1β-stimulated osteoarthritis chondrocytes.

Methods

Chondrocytes were isolated from human articular cartilage and stimulated with IL-1β. The expression levels of miR-448 in the cartilage and chondrocytes were both determined. After transfection with an miR-448 mimic or inhibitor, the mRNA levels of aggrecan, type II collagen and MMP-13 were determined. Luciferase reporter assay, qRT-PCR and western blot were performed to explore whether matrilin-3 was a target of miR-448. Furthermore, we co-transfected chondrocytes with miR-448 inhibitor and siRNA for matrilin-3 and then stimulated them with IL-1β to determine whether miR-448-mediated IL-1β-induced cartilage matrix degradation resulted from directly targeting matrilin-3.

Results

The level of miR-448 was significantly higher and matrilin-3 expression was significantly lower in osteoarthritis cartilage and IL-1β-induced chondrocytes than in normal tissues and cells. Furthermore, matrilin-3 expression was reduced by miR-448 overexpression. MiR-448 downregulation significantly alleviated the IL-1β-induced downregulation of aggrecan and type II collagen expression, and upregulation of MMP-13 expression. MiR-448 overexpression had the opposite effects. Knockdown of matrilin-3 reversed the effects of the miR-448 inhibitor on the expressions of aggrecan, type II collagen and MMP-13.

Conclusion

The findings showed that miR-448 contributed to the progression of osteoarthritis by directly targeting matrilin-3. This indicates that it has potential as a therapeutic target for the treatment of osteoarthritis.

Martrilin-3 (MATN3) Overexpression in Gastric Adenocarcinoma and its Prognostic Significance

BACKGROUND The aim of this study was to investigate the expression level of martrilin-3 (MATN3) in patients with gastric adenocarcinoma (GAC) and to investigate the prognostic significance of MATN3. MATERIAL AND METHODS Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) data were used to predict the expression and prognostic value of MATN3 mRNA in GAC patients. Seventy-six GAC patients had GAC tissue samples and paired adjacent normal tissue samples collected retrospectively to examine the MATN3 protein expression level by immunohistochemical staining. Furthermore, Kaplan-Meier univariate and Cox multivariate analyses were used to verify the correlation between MATN3 expression and clinicopathological parameters of GAC patients and the prognostic significance of MATN3. RESULTS The GEO and TCGA data predicted that MATN3 mRNA levels were significantly higher in GAC tissue compared to normal tissue (all p<0.05). Further survival analyses showed that GAC patients with high mRNA expression of MATN3 had significantly lower disease-free survival (DFS) and overall survival (OS) time than those with low mRNA expression of MATN3 (all p<0.05). Subsequent immunohistochemical staining results confirmed that the MATN3 protein levels in GAC tissues were highly expressed (p=0.000) compared to normal tissues. In addition, GAC patients with high protein expression of MATN3 had remarkably decreased OS compared to patients with low protein expression of MATN3 (p=0.000). Univariate and multivariate survival analyses revealed that MATN3 high expression could be used as an independent predictor of poor prognosis in GAC patients (all p=0.000). CONCLUSIONS This study confirmed that MATN3 protein was highly expressed in GAC patients, and MATN3 overexpression could be used as an independent predictor of poor prognosis in GAC patients.

Matrilins

Marilins mediate interactions between macromolecular components of the extracellular matrix, e.g., collagens and proteoglycans. They are composed of von Willebrand factor type A and epidermal growth factor-like domains and the subunits oligomerize via coiled-coil domains. Matrilin-1 and -3 are abundant in hyaline cartilage, whereas matrilin-2 and -4 are widespread but less abundant. Mutations in matrilin genes have been linked to chondrodysplasias and osteoarthritis and recently characterization of matrilin-deficient mice revealed novel functions in mechanotransduction, regeneration, or inflammation. Due to their intrinsic adhesiveness and partially also low abundance, the study of matrilins is cumbersome. In this chapter, we describe methods for purification of matrilins from tissue, analysis of matrilins in tissue extracts, recombinant expression, and generation of matrilin-specific antibodies.

Fibulins and matrilins are novel structural components of the periodontium in the mouse

Periodontitis refers to inflammatory disease of the periodontal structures (the gingiva, dental cementum, periodontal ligament (PDL) and alveolar bone) that ultimately leads to their destruction. Whereas collagens are well-examined main components of the periodontium, little is known about the other structural proteins that make up this tissue. The aim of this study was to identify new extracellular matrix (ECM) components, including fibulins and matrilins, in the periodontium of mice. After sacrificing 14 mice (Sv/129 strain), jaws were prepared. Each tissue sample contained a molar and its surrounding alveolar bone. Immunohistochemistry was carried out on paraffin-embedded sections. Our results show that mice exhibit fibulin-3, -4 and -5 and matrilin-1, -2, -3 and -4 in PDL and in blood vessels of alveolar bone and PDL as well as in the pericellular matrix of osteocytes and cementocytes. In dental cementum, only fibulin-4 is expressed. For the first time, we show that fibulin-3, -4 and -5 and matrilin-1, -2, -3 and -4 are essential components of the periodontal tissues. Our findings indicate an association of these proteins with collagens and oxytalan fibers that might be of future interest in regenerative periodontitis therapy.

Neutral sphingomyelinase (SMPD3) deficiency disrupts the Golgi secretory pathway and causes growth inhibition

Systemic loss of neutral sphingomyelinase (SMPD3) in mice leads to a novel form of systemic, juvenile hypoplasia (dwarfism). SMPD3 deficiency in mainly two growth regulating cell types contributes to the phenotype, in chondrocytes of skeletal growth zones to skeletal malformation and chondrodysplasia, and in hypothalamic neurosecretory neurons to systemic hypothalamus–pituitary–somatotropic hypoplasia. The unbiased smpd3−/− mouse mutant and derived smpd3−/− primary chondrocytes were instrumental in defining the enigmatic role underlying the systemic and cell autonomous role of SMPD3 in the Golgi compartment. Here we describe the unprecedented role of SMPD3. SMPD3 deficiency disrupts homeostasis of sphingomyelin (SM), ceramide (Cer) and diacylglycerol (DAG) in the Golgi SMPD3-SMS1 (SM-synthase1) cycle. Cer and DAG, two fusogenic intermediates, modify the membrane lipid bilayer for the initiation of vesicle formation and transport. Dysproteostasis, unfolded protein response, endoplasmic reticulum stress and apoptosis perturb the Golgi secretory pathway in the smpd3−/− mouse. Secretion of extracellular matrix proteins is arrested in chondrocytes and causes skeletal malformation and chondrodysplasia. Similarly, retarded secretion of proteo-hormones in hypothalamic neurosecretory neurons leads to hypothalamus induced combined pituitary hormone deficiency. SMPD3 in the regulation of the protein vesicular secretory pathway may become a diagnostic target in the etiology of unknown forms of juvenile growth and developmental inhibition.

Association of Matrilin-3 Gene Polymorphism with Temporomandibular Joint Internal Derangement

AIMS

Temporomandibular joint internal derangement (TMJ ID) is a multifactorial complex disease characterised by articular disc degeneration. Matrilin-3 is a cartilage and bone-specific adaptor protein, and amino-acid substitutions in the protein are associated with skeletal diseases and joint disorders. We aimed to detect the variants of Matrilin-3 gene (MATN3) in a TMJ ID case-control group and to investigate the risk association of the detected variants with TMJ ID.

MATERIALS AND METHODS

A case control study was conducted consisting of 57 unrelated TMJ ID patients (32.7 ± 8.2) and 96 unrelated healthy controls (26.63 ± 3.05) without TMJ ID to look for associations with variants of the MATN3 gene. DNA from individual subjects was extracted and each of the eight exons was amplified by polymerase chain reaction using and analyzed by single-strand conformational polymorphism (SSCP) analysis. SSCP variants were subjected to DNA sequence analysis, which yielded band pattern variations in exon 2 of the gene. We further analyzed exon 2 by DNA sequencing to determine the sequence of these variants.

RESULTS

We identified SSCP band patterns variants in exon 2 of the MATN3 gene which upon sequencing revealed a single C to T transition mutation (rs28598872) c.447 C>T (g.11608 C>T). This polymorphism is predicted to result in a synonymous mutation (pAla149 = ). The TT and CT genotypes were more prevalent than the CC genotype in TMJ ID patients compared to the control group with a risk factor of 2.12 (confidence intervals [CI] :0.88-5.08) and 2.0 (CI:0.726-5.508). In addition, TMJ ID patients were divided into two groups as anterior disc displacement with reduction (ADDWR) and anterior disc displacement without reduction (ADDWOR) and compared with the controls. The TT and CT genotypes were more prevalent than the CC genotype in ADDWR patients compared to the control group with a risk factor of 3.85 (CI:0.927-16.048) and 3.75 (1.02-13.786), respectively. We found that, among ADDWR patients, the T allele is a risk factor both in homozygous and heterozygous carriers (p < 0.052, p < 0.036).

CONCLUSION

The results of the study indicate a potential role for the MATN3 rs28598872 polymorphism in the pathogenesis of TMJ ID.

Matrilin-3 Role in Cartilage Development and Osteoarthritis

The extracellular matrix (ECM) of cartilage performs essential functions in differentiation and chondroprogenitor cell maintenance during development and regeneration. Here, we discuss the vital role of matrilin-3, an ECM protein involved in cartilage development and potential osteoarthritis pathomechanisms. As an adaptor protein, matrilin-3 binds to collagen IX to form a filamentous network around cells. Matrilin-3 is an essential component during cartilage development and ossification. In addition, it interacts directly or indirectly with transforming growth factor β (TGF-β), and bone morphogenetic protein 2 (BMP2) eventually regulates chondrocyte proliferation and hypertrophic differentiation. Interestingly, matrilin-3 increases interleukin receptor antagonists (IL-Ra) in chondrocytes, suggesting its role in the suppression of IL-1β-mediated inflammatory action. Matrilin-3 downregulates the expression of matrix-degrading enzymes, such as a disintegrin metalloproteinase with thrombospondin motifs 4 (ADAMTS4) and ADAMTS5, matrix metalloproteinase 13 (MMP13), and collagen X, a hypertrophy marker during development and inflammatory conditions. Matrilin-3 essentially enhances collagen II and aggrecan expression, which are required to maintain the tensile strength and elasticity of cartilage, respectively. Interestingly, despite these attributes, matrilin-3 induces osteoarthritis-associated markers in chondrocytes in a concentration-dependent manner. Existing data provide insights into the critical role of matrilin-3 in inflammation, matrix degradation, and matrix formation in cartilage development and osteoarthritis.

Matrilin-3 inhibits chondrocyte hypertrophy as a bone morphogenetic protein-2 antagonist

Increased chondrocyte hypertrophy is often associated with cartilage joint degeneration in human osteoarthritis patients. Matrilin-3 knock-out (Matn3 KO) mice exhibit these features. However, the underlying mechanism is unknown. In this study, we sought a molecular explanation for increased chondrocyte hypertrophy in the mice prone to cartilage degeneration. We analyzed the effects of Matn3 on chondrocyte hypertrophy and bone morphogenetic protein (Bmp) signaling by quantifying the hypertrophic marker collagen type X (Col X) gene expression and Smad1 activity in Matn3 KO mice in vivo and in Matn3-overexpressing chondrocytes in vitro. The effect of Matn3 and its specific domains on BMP activity were quantified by Col X promoter activity containing the Bmp-responsive element. Binding of MATN3 with BMP-2 was determined by immunoprecipitation, solid phase binding, and surface plasmon resonance assays. In Matn3 KO mice, Smad1 activity was increased more in growth plate chondrocytes than in wild-type mice. Conversely, Matn3 overexpression in hypertrophic chondrocytes led to inhibition of Bmp-2-stimulated, BMP-responsive element-dependent Col X expression and Smad1 activity. MATN3 bound BMP-2 in a dose-dependent manner. Multiple epidermal growth factor (EGF)-like domains clustered together by the coiled coil of Matn3 is required for Smad1 inhibition. Hence, as a novel BMP-2-binding protein and antagonist in the cartilage extracellular matrix, MATN3 may have the inherent ability to inhibit premature chondrocyte hypertrophy by suppressing BMP-2/Smad1 activity.

Matrilin-2 is proteolytically cleaved by ADAMTS-4 and ADAMTS-5

Matrilin-2 is a widely distributed, oligomeric extracellular matrix protein that forms a filamentous network by binding to a variety of different extracellular matrix proteins. We found matrilin-2 proteolytic products in transfected cell lines in vitro and in mouse tissues in vivo. Two putative cleavage sites were identified in the unique domain of matrilin-2; the first site was located between D⁸⁵¹ and L⁸⁵² in the middle of the domain and the second, at the boundary with the coiled-coil domain at the C-terminus. Deletion of the entire unique domain eliminated the proteolysis of matrilin-2. While the first cleavage site was present in all matrilin-2 oligomers, the second cleavage site became apparent only in the matrilin-2 hetero-oligomers with matrilin-1 or matrilin-3. Analysis using a variety of extracellular protease inhibitors suggested that this proteolytic activity was derived from a member or several members of the ADAMTS family. Recombinant human ADAMTS-4 (aggrecanase-1) and ADAMTS-5 (aggrecanase-2), but not ADAMTS-1, cleaved recombinant matrilin-2, thereby yielding matrilin-2 proteolytic peptides at the predicted sizes. These results suggest that ADAMTS-4 and ADAMTS-5 may destabilize the filamentous network in the extracellular matrix by cleaving matrilin-2 in both homo-oligomers and hetero-oligomers.

Matrilin-2 is a widely distributed extracellular matrix protein and a potential biomarker in the early stage of osteoarthritis in articular cartilage

In this study, we first generated and characterized a polyclonal antibody against unique domain of matrlin-2 and then used this specific antibody to assess the expression pattern of matrilin-2 by immunohistochemistry. We found that marilin-2 is widely distributed in the connective tissues of many mouse tissues including heart, colon, penis, esophagus, lung, kidney, tracheal cartilage, developmental bone, and adult bone. The expression level of matrilin-2 was remarkably increased in the tissues of osteoarthritis developmental articular cartilage, compared to normal healthy tissues. Furthermore, we determined matrilin-2 expression in specific epithelial cells in stomach and ductal epithelial cells of salivary gland. In other tissues, the positive signals were mainly located around cardiac muscle cells and Purkinje fibers in the heart; corpus spongiosum in the penis; submucosa in the colon and esophagus; extracellular matrix of cartilage in the tracheal cartilage; and, glomerulus, the basement membrane of distal convoluted tubule and renal matrix in kidney. These observations indicated that the distribution pattern of matrilin-2 is heterogeneous in each tissue. Matrilin-2 may play an important role in the communication of matrix to matrix and matrix to cells and will be used as a potential biomarker in the early stage of osteoarthritis of articular cartilage.

Matrilin-3 induction of IL-1 receptor antagonist is required for up-regulating collagen II and aggrecan and down-regulating ADAMTS-5 gene expression

Introduction

Deletion or mutation of the gene encoding the cartilage extracellular matrix (ECM) protein matrilin-3 (MATN3) results in the early onset of osteoarthritis (OA), suggesting chondroprotective properties of MATN3. To understand the mechanisms underlying these properties, we determined the effects of MATN3 protein on the expression of several key anabolic and catabolic genes involved in chondrocyte homeostasis, and the dependence of such regulation on the anti-inflammatory cytokine: IL-1 receptor antagonist (IL-1Ra).

Methods

The effects of recombinant human (rh) MATN3 protein were examined in C28/I2 immortalized human chondrocytes, primary human chondrocytes (PHCs), and primary mouse chondrocytes (PMCs). Messenger RNA levels of IL-1Ra, COL2A1, ACAN, MMP-13, and ADAMTS-4 and -5 were determined using real-time RT-PCR. Knocking down IL-1Ra was achieved by siRNA gene silencing. IL-1Ra protein levels were quantified by ELISA and the Bio-Plex Suspension Array System. COL2A1 protein level was quantified using Western blot analysis. Statistic analysis was done using the two-tailed t-test or one-way ANOVA.

Results

rhMATN3 protein induced gene expression of IL-1Ra in C28/I2 cells, PHCs, and PMCs in a dose- and time-dependent manner. Treatment of C28/I2 cells and PHCs with MATN3 protein stimulated gene expression of COL2A1 and ACAN. Conversely, mRNA levels of COL2A1 and ACAN were decreased in MATN3 KO mice. MATN3 protein treatment inhibited IL-1β-induced MMP-13, ADAMTS-4 and ADAMTS-5 in C28/I2 cells and PHCs. Knocking down IL-1Ra abolished the MATN3-mediated stimulation of COL2A1 and ACAN and inhibition of ADAMTS-5, but had no effect on MATN3 inhibition of MMP-13 mRNA.

Conclusion

Our findings point to a novel regulatory role of MATN3 in cartilage homeostasis due to its capacity to induce IL-1Ra, to upregulate gene expression of the major cartilage matrix components, and to downregulate the expression of OA-associated matrix-degrading proteinases in chondrocytes. The chondroprotective properties of endogenous MATN3 depend partly on its induction of IL-1Ra. Our findings raise a possibility to use rhMATN3 protein for anti-inflammatory and chondroprotective therapy.

Matrilin-3 switches from anti- to pro-anabolic upon integration to the extracellular matrix

The extracellular matrix (ECM) has long been viewed primarily as an organized network of solid-phase ligands for integrin receptors. During degenerative processes, such as osteoarthritis, the ECM undergoes deterioration, resulting in its remodeling and in the release of some of its components. Matrilin-3 (MATN3) is an almost cartilage specific, pericellular protein acting in the assembly of the ECM of chondrocytes. In the past, MATN3 was found required for cartilage homeostasis, but also involved in osteoarthritis-related pro-catabolic functions. Here, to better understand the pathological and physiological functions of MATN3, its concentration as a circulating protein in articular fluids of human osteoarthritic patients was determined and its functions as a recombinant protein produced in human cells were investigated with particular emphasis on the physical state under which it is presented to chondrocytes. MATN3 down-regulated cartilage extracellular matrix (ECM) synthesis and up-regulated catabolism when administered as a soluble protein. When artificially immobilized, however, MATN3 induced chondrocyte adhesion via a α5β1 integrin-dependent mechanism, AKT activation and favored survival and ECM synthesis. Furthermore, MATN3 bound directly to isolated α5β1 integrin in vitro. TGFβ1 stimulation of chondrocytes allowed integration of exogenous MATN3 into their ECM and ECM-integrated MATN3 induced AKT phosphorylation and improved ECM synthesis and accumulation. In conclusion, the integration of MATN3 to the pericellular matrix of chondrocytes critically determines the direction toward which MATN3 regulates cartilage metabolism. These data explain how MATN3 plays either beneficial or detrimental functions in cartilage and highlight the important role played by the physical state of ECM molecules.

A haplotype of MATN3 is associated with vertebral fracture in Chinese postmenopausal women: Peking Vertebral Fracture (PK-VF) study

The Matrilin3 gene (MATN3) encodes an extracellular matrix protein, which modulates chondrocyte differentiation. The aim of this study was to test for association of MATN3 polymorphisms with bone mineral density (BMD), fracture, vertebral fracture, bone turnover or 25-hydroxyvitamin D [25(OH)D] in postmenopausal women. A community-based population of 1488 postmenopausal women was randomly selected in Beijing. The history of fracture and vertebral fracture was obtained via questionnaire and vertebral X-ray respectively. BMD of lumbar spine (2-4), femoral neck and total hip were measured by dual energy X-ray absorptiometry. Serum N-terminal procollagen of type 1 collagen (P1NP), β-isomerized type I collagen C-telopeptide breakdown products (β-CTX) and 25(OH)D were quantified. Binary logistic regression revealed that Haplotype-4 was significantly associated with vertebral fracture risk in both additive model (p=0.023, OR=1.521) and dominant model (p=0.028, OR=1.623). The significance remained after 10,000 permutation tests to correct multiple testing (p=0.042). Re-selected age matched vertebral fracture case-control groups revealed similar associations in additive model (p=0.014, OR=1.927, 95%CI=1.142-3.253) and in dominant model (p=0.011, OR=2.231, 95%CI=1.200-4.148). However, no significant association was found between MATN3 polymorphisms and serum β-CTX, P1NP, 25(OH)D levels, or BMD. In linear regression, Haplotype-2 approached marginal significance in association with femoral neck BMD T-score (p=0.050), but this would account for only 0.2% of BMD variation in our sample. This study suggests that Haplotype-4 of MATN3 is associated with vertebral fracture risk independent of BMD in Chinese postmenopausal women. Efforts should be made to replicate our finding in other, similar and ethnically diverse, populations.

Expression of matrilin-2 and -4 in human dental pulps during dentin-pulp complex wound healing

INTRODUCTION

Matrilin-2 and matrilin-4 are members of the matrilin family displaying broad tissue distribution. We recently reported that matrilin-2 showed significant down-regulation during the odontogenic differentiation of dental pulp cells (DPCs). It is reported that matrilin-4 was the only extracellular matrix biogenesis and organization-related gene detected in odontoblasts but not DPCs. However, the exact role of matrlin-2 and -4 in dental pulps remains unclear. The aim of our study was to analyze the expression of matrilin-2 and -4 in human dental pulps and their relation to dentin-pulp complex wound healing.

METHODS

Immunohistology was performed on the paraffin-embedded tissue sections of human dental pulps from sound and deep carious teeth. Matrilin-2 and -4 messenger RNAs were detected by quantitative real-time reverse-transcription polymerase chain reaction, and the proteins were shown by immunofluorescence and Western blot during odontogenic differentiation of the DPCs.

RESULTS

In the sound dental pulp, matrilin-2 immunoreactivity was observed throughout the pulp, whereas matrilin-4 was observed only in the odontoblast layer. In deep carious dental pulp, matrilin-2 protein was weakly stained, whereas matrilin-4 was detected in the pulp under the carious lesion. During odontogenic differentiation of DPCs, the expression of matrilin-2 messenger RNA was down-regulated within 14 days followed by a statistical increase on day 21, and the matrilin-2 protein level was down-regulated within the 3 weeks, whereas the messenger RNA and protein expressions of matrilin-4 increased in a time-dependent manner.

CONCLUSIONS

Matrilin-2 and matrilin-4 have been shown in human dental pulps and might be involved in the dentin-pulp complex wound-healing process.

An unfolded protein response is the initial cellular response to the expression of mutant matrilin-3 in a mouse model of multiple epiphyseal dysplasia

Multiple epiphyseal dysplasia (MED) can result from mutations in matrilin-3, a structural protein of the cartilage extracellular matrix. We have previously shown that in a mouse model of MED the tibia growth plates were normal at birth but developed a progressive dysplasia characterised by the intracellular retention of mutant matrilin-3 and abnormal chondrocyte morphology. By 3 weeks of age, mutant mice displayed a significant decrease in chondrocyte proliferation and dysregulated apoptosis. The aim of this current study was to identify the initial post-natal stages of the disease. We confirmed that the disease phenotype is seen in rib and xiphoid cartilage and, like tibia growth plate cartilage is characterised by the intracellular retention of mutant matrilin-3. Gene expression profiling showed a significant activation of classical unfolded protein response (UPR) genes in mutant chondrocytes at 5 days of age, which was still maintained by 21 days of age. Interestingly, we also noted the upregulation of arginine-rich, mutated in early stage of tumours (ARMET) and cysteine-rich with EGF-like domain protein 2 (CRELD2) are two genes that have only recently been implicated in the UPR. This endoplasmic reticulum (ER) stress and UPR did not lead to increased chondrocyte apoptosis in mutant cartilage by 5 days of age. In an attempt to alleviate ER stress, mutant mice were fed with a chemical chaperone, 4-sodium phenylbutyrate (SPB). SPB at the dosage used had no effect on chaperone expression at 5 days of age but modestly decreased levels of chaperone proteins at 3 weeks. However, this did not lead to increased secretion of mutant matrilin-3 and in the long term did not improve the disease phenotype. We performed similar studies with a mouse model of Schmid metaphyseal chondrodysplasia, but again this treatment did not improve the phenotype.

A matrilin-3 mutation associated with osteoarthritis does not affect collagen affinity but promotes the formation of wider cartilage collagen fibrils

Mutations in matrilin-3 have been associated with common skeletal diseases like osteoarthritis as well as with the rare chondrodysplasias MED and SEMD. We have previously shown that the mutations p.R116W and p.C299S, associated with MED and SEMD, respectively, cause retention of matrilin-3 within the endoplasmic reticulum of primary chondrocytes, while the mutation associated with osteoarthritis, p.T298M, does not hinder secretion. The present study focused on the consequences of the p.T298M mutation on the structure of matrilin-3 and on the role of matrilin-3 in the formation of a functional extracellular matrix. Analysis of recombinant full-length matrilin-3 revealed that the p.T298M mutation does not influence oligomerization of matrilin-3 or its proteolytic processing by ADAMTS-4 and -5. Nevertheless, structural analyses indicate local conformational changes. These changes do not affect the affinity for collagens II, IX, XI, or COMP, but have a major impact on the in vitro fibrillogenesis of collagen II/IX/XI heterofibrils.

Increased expression of matrilin-3 not only in osteoarthritic articular cartilage but also in cartilage-forming tumors, and down-regulation of SOX9 via epidermal growth factor domain 1-dependent signaling

OBJECTIVE

To identify regulators of the cartilaginous phenotype, on the basis of their differential expression in human conventional chondrogenic tumors compared with articular cartilage.

METHODS

Differential proteomics analysis revealed matrilin-3 (MATN3) as a candidate regulator of the cartilaginous phenotype. Its capacity to modulate gene expression was investigated in human HCS-2/8 chondrosarcoma cells and transfected chondrocytes, using cell culture fractionation, reverse transcription-polymerase chain reaction, and Western blot analyses.

RESULTS

Increased expression of the cartilage-specific matrix protein MATN3 was specifically observed in enchondromas and conventional chondrosarcomas. A substantial fraction of MATN3 was found in cytoplasmic structures of tumor cells, as demonstrated by immunohistochemistry. Analyses of intracellular MATN3 revealed that it corresponded to an imperfectly maturated MATN3 polypeptide, both in HCS-2/8 human chondrosarcoma cells and in transfected human chondrocytes. Moderately increased expression of MATN3 resulted in its intracellular retention. Antibody-mediated blockade of soluble, extracellular MATN3 in HCS-2/8 cell cultures resulted in increased expression of MATN3 and the chondrogenic transcription factor SOX9. Conversely, increased ectopic expression of MATN3 resulted in decreased expression of MATN3 and SOX9 in primary chondrocytes, while a mutant MATN3 lacking its first epidermal growth factor (EGF)-like domain failed to down-regulate SOX9.

CONCLUSION

Aberrant expression and processing of MATN3 are hallmarks of conventional cartilaginous neoplasms. A particular step in the maturation of MATN3 limits its processing through the secretion machinery, resulting in its intracellular accumulation upon increased expression. Soluble, secreted MATN3, however, down-regulates SOX9 at the messenger RNA and protein levels. The first EGF-like domain of MATN3 is a critical determinant of its regulatory activity toward SOX9. These activities of MATN3 suggest that its increased expression in osteoarthritis might contribute to the degeneration of articular cartilage.

Comprehensive profiling of cartilage extracellular matrix formation and maturation using sequential extraction and label-free quantitative proteomics

Articular cartilage is indispensable for joint function but has limited capacity for self-repair. Engineering of neocartilage in vitro is therefore a major target for autologous cartilage repair in arthritis. Previous analysis of neocartilage has targeted cellular organization and specific molecular components. However, the complexity of extracellular matrix (ECM) development in neocartilage has not been investigated by proteomics. To redress this, we developed a mouse neocartilage culture system that produces a cartilaginous ECM. Differential analysis of the tissue proteome of 3-week neocartilage and 3-day postnatal mouse cartilage using solubility-based protein fractionation targeted components involved in neocartilage development, including ECM maturation. Initially, SDS-PAGE analysis of sequential extracts revealed the transition in protein solubility from a high proportion of readily soluble (NaCl-extracted) proteins in juvenile cartilage to a high proportion of poorly soluble (guanidine hydrochloride-extracted) proteins in neocartilage. Label-free quantitative mass spectrometry (LTQ-Orbitrap) and statistical analysis were then used to filter three significant protein groups: proteins enriched according to extraction condition, proteins differentially abundant between juvenile cartilage and neocartilage, and proteins with differential solubility properties between the two tissue types. Classification of proteins differentially abundant between NaCl and guanidine hydrochloride extracts (n = 403) using bioinformatics revealed effective partitioning of readily soluble components from subunits of larger protein complexes. Proteins significantly enriched in neocartilage (n = 78) included proteins previously not reported or with unknown function in cartilage (integrin-binding protein DEL1; coiled-coil domain-containing protein 80; emilin-1 and pigment epithelium derived factor). Proteins with differential extractability between juvenile cartilage and neocartilage included ECM components (nidogen-2, perlecan, collagen VI, matrilin-3, tenascin and thrombospondin-1), and the relationship between protein extractability and ECM ultrastructural organization was supported by electron microscopy. Additionally, one guanidine extract-specific neocartilage protein, protease nexin-1, was confirmed by immunohistochemistry as a novel component of developing articular cartilage in vivo. The extraction profile and matrix-associated immunostaining implicates protease nexin-1 in cartilage development in vitro and in vivo.

Involvement of extracellular matrix protein matrilin-2 in oval cell-mediated rat liver regeneration

AIM: To investigate possible involvement of extracellular matrix (ECM) protein matrilin-2 in oval cell-mediated liver regeneration in rats.

METHODS: A rat model of hepatic oval cell proliferation was established using the modified Soft-Farber protocol. The control group was fed normal saline. On days 2, 4, 6, 9, 12 and 15 after partial hepatectomy (PH), rat liver tissue samples were collected. The dynamic relationship between matrilin-2 protein expression and oval cell distribution during the proliferation and differentiation of oval cells was analyzed using immunohistochemistry and Western blot.

RESULTS: On day 2 after PH, oval cells began to proliferate around the portal area, and matrilin-2 deposition was observed in the hepatic sinusoids in the periportal area. On day 9, proliferating oval cells were present in the hepatic acini, and matrilin-2 upregulation was noted. On day 12, as oval cells differentiated to form hepatocellular nodules, matrilin-2 was distributed mainly in the periphery of the nodules, and little protein was present in the nodules. The expression level of matrilin-2 protein began to be upregulated on day 2 after PH, and reached the peak on day 9. After day 12, the protein level returned to physiological level.

CONCLUSION: The close relationship between matrilin-2 expression and oval cell distribution suggests a role for the protein in stem cell-fed liver regeneration.

Proteolytic processing causes extensive heterogeneity of tissue matrilin forms

The matrilins are a family of multidomain extracellular matrix proteins with adapter functions. The oligomeric proteins have a bouquet-like structure and bind to a variety of different ligands whereby the avidity of their interactions is dependent on the number of subunits and domains present. Here we show the contribution of post-translational proteolytic processing to the heterogeneity of matrilins seen in tissue extracts and cell culture supernatants. A cleavage site after two glutamate residues in the hinge region close to the C-terminal coiled-coil oligomerization domain is conserved among the matrilins. Cleavage at this site yields molecules that lack almost complete subunits. The processing is least pronounced in matrilin-1 and particularly complex in matrilin-2, which contains additional cleavage sites. Replacement of the hinge region in matrilin-4 by the matrilin-1 hinge region had no marked effect on the processing. A detailed study revealed that matrilin-4 is processed already in the secretory pathway and that the activation of the responsible enzymes is dependent on proprotein convertase activity. Matrilin-3 and -4, but not matrilin-1 subunits present in matrilin-1/-3 hetero-oligomers, were identified as substrates for ADAMTS4 and ADAMTS5, whereas ADAMTS1 did not cleave any matrilin. A neo-epitope antibody raised against the N terminus of the C-terminal cleavage product of matrilin-4 detected processed matrilin-4 in cultures of primary chondrocytes as well as on cartilage sections showing that the conserved cleavage site is used in vivo.

Influence of microvascular endothelial cells on transcriptional regulation of proximal tubular epithelial cells

In the renal cortex the peritubular capillary network and the proximal tubular epithelium cooperate in solute and water reabsorption, secretion, and inflammation. However, the mechanisms by which these two cell types coordinate such diverse functions remain to be characterized. Here we investigated the influence of microvascular endothelial cells on proximal tubule cells, using a filter-based, noncontact, close-proximity coculture of the human microvascular endothelial cell line HMEC-1 and the human proximal tubular epithelial cell line HK-2. With the use of DNA microarrays the transcriptomes of HK-2 cells cultured in mono- and coculture were compared. HK-2 cells in coculture exhibited a differential expression of 99 genes involved in pathways such as extracellular matrix (e.g., lysyl oxidase), cell-cell communication (e.g., IL-6 and IL-1β), and transport (e.g., GLUT3 and lipocalin 2). HK-2 cells also exhibited an enhanced paracellular gating function in coculture, which was dependent on HMEC-1-derived extracellular matrix. We identified a number of HMEC-1-enriched genes that are potential regulators of epithelial cell function such as extracellular matrix proteins (e.g., collagen I, III, IV, and V, laminin-α IV) and cytokines/growth factors (e.g., hepatocyte growth factor, endothelin-1, VEGF-C). This study demonstrates a complex network of communication between microvascular endothelial cells and proximal tubular epithelial cells that ultimately affects proximal tubular cell function. This coculture model and the data described will be important in the further elucidation of microvascular endothelial and proximal tubular epithelial cross talk mechanisms.

Structural and functional characterization of recombinant matrilin-3 A-domain and implications for human genetic bone diseases

Mutations in matrilin-3 result in multiple epiphyseal dysplasia, which is characterized by delayed and irregular bone growth and early onset osteoarthritis. The majority of disease-causing mutations are located within the beta-sheet of the single A-domain of matrilin-3, suggesting that they disrupt the structure and/or function of this important domain. Indeed, the expression of mutant matrilin-3 results in its intracellular retention within the rough endoplasmic reticulum of cells, where it elicits an unfolded protein response. To understand the folding characteristics of the matrilin-3 A-domain we determined its structure using CD, analytical ultracentrifugation, and dual polarization interferometry. This study defined novel structural features of the matrilin-3 A-domain and identified a conformational change induced by the presence or the absence of Zn(2+). In the presence of Zn(2+) the A-domain adopts a more stable "tighter" conformation. However, after the removal of Zn(2+) a potential structural rearrangement of the metal ion-dependent adhesion site motif occurs, which leads to a more "relaxed" conformation. Finally, to characterize the interactions of the matrilin-3 A-domain we performed binding studies on a BIAcore using type II and IX collagen and cartilage oligomeric matrix protein. We were able to demonstrate that it binds to type II and IX collagen and cartilage oligomeric matrix protein in a Zn(2+)-dependent manner. Furthermore, we have also determined that the matrilin-3 A-domain appears to bind exclusively to the COL3 domain of type IX collagen and that this binding is abolished in the presence of a disease causing mutation in type IX collagen.

Neutral sphingomyelinase (SMPD3) deficiency causes a novel form of chondrodysplasia and dwarfism that is rescued by Col2A1-driven smpd3 transgene expression

Neutral sphingomyelinase SMPD3 (nSMase2), a sphingomyelin phosphodiesterase, resides in the Golgi apparatus and is ubiquitously expressed. Gene ablation of smpd3 causes a generalized prolongation of the cell cycle that leads to late embryonic and juvenile hypoplasia because of the SMPD3 deficiency in hypothalamic neurosecretory neurons. We show here that this novel form of combined pituitary hormone deficiency is characterized by the perturbation of the hypothalamus-pituitary growth axis, associated with retarded chondrocyte development and enchondral ossification in the epiphyseal growth plate. To study the contribution by combined pituitary hormone deficiency and by the local SMPD3 deficiency in the epiphyseal growth plate to the skeletal phenotype, we introduced the full-length smpd3 cDNA transgene under the control of the chondrocyte-specific promoter Col2a1. A complete rescue of the smpd3(-/-) mouse from severe short-limbed skeletal dysplasia was achieved. The smpd3(-/-) mouse shares its dwarf and chondrodysplasia phenotype with the most common form of human achondrodysplasia, linked to the fibroblast-growth-factor receptor 3 locus, not linked to deficits in the hypothalamic-pituitary epiphyseal growth plate axis. The rescue of smpd3 in vivo has implications for future research into dwarfism and, particularly, growth and development of the skeletal system and for current screening and future treatment of combined dwarfism and chondrodysplasia.

Pericellular matrilins regulate activation of chondrocytes by cyclic load-induced matrix deformation

Pericellular matrix is at the ideal location to be involved in transmitting mechanical signals from the microenvironment to a cell. We found that changes of the content of matrilins that link various pericellular molecules surrounding chondrocytes affect mechanical stimulation of chondrocyte proliferation and gene expression. Thus, pericellular matrilins may play a role in chondrocyte mechanotransduction.

INTRODUCTION

Chondrocytes reside in a capsule of pericellular matrix (chondron), which has been hypothesized to play a critical role in transducing mechanical signals to the cell. In this study, we test the hypothesis that the levels of matrilin (MATN)-1 and -3, major components of the chondrocyte pericellular matrix network, regulate activation of chondrocyte proliferation and differentiation by cyclic load-induced matrix deformation.

MATERIALS AND METHODS

Functional matrilins were decreased by expressing a dominant negative mini-MATN in primary chondrocytes or by using MATN1-null chondrocytes. The abundance of matrilins was also increased by expressing a wildtype MATN1 or MATN3 in chondrocytes. Chondrocytes were cultured in a 3D sponge subjected to cyclic deformation at 1 Hz. Chondrocyte gene expression was quantified by real-time RT-PCR and by Western blot analysis. Matrilin pericellular matrix assembly was examined by immunocytochemistry.

RESULTS

Elimination of functional matrilins from pericellular matrix abrogated mechanical activation of Indian hedgehog signaling and abolished mechanical stimulation of chondrocyte proliferation and differentiation. Excessive or reduced matrilin content decreased mechanical response of chondrocytes.

CONCLUSIONS

Normal content of matrilins is essential to optimal activation of chondrocytes by mechanical signals. Our data suggest that the sensitivity of chondrocytes to the changes in the microenvironment can be adjusted by altering the content of matrilins in pericellular matrix. This finding supports a critical role of pericellular matrix in chondrocyte mechano-transduction and has important implications in cartilage tissue engineering and mechanical adaptation.

Functional knockout of the matrilin-3 gene causes premature chondrocyte maturation to hypertrophy and increases bone mineral density and osteoarthritis

Mutations in the gene encoding matrilin-3 (MATN3), a noncollagenous extracellular matrix protein, have been reported in a variety of skeletal diseases, including multiple epiphyseal dysplasia, which is characterized by irregular ossification of the epiphyses and early-onset osteoarthritis, spondylo-epimetaphyseal dysplasia, and idiopathic hand osteoarthritis. To assess the role of matrilin-3 in the pathogenesis of these diseases, we generated Matn3 functional knockout mice using embryonic stem cell technology. In the embryonic growth plate of the developing long bones, Matn3 null chondrocytes prematurely became prehypertrophic and hypertrophic, forming an expanded zone of hypertrophy. This expansion was attenuated during the perinatal period, and Matn3 homozygous null mice were viable and showed no gross skeletal malformations at birth. However, by 18 weeks of age, Matn3 null mice had a significantly higher total body bone mineral density than Matn1 null mice or wild-type littermates. Aged Matn3 null mice were much more predisposed to develop severe osteoarthritis than their wild-type littermates. Here, we show that matrilin-3 plays a role in modulating chondrocyte differentiation during embryonic development, in controlling bone mineral density in adulthood, and in preventing osteoarthritis during aging. The lack of Matn3 does not lead to postnatal chondrodysplasia but accounts for higher incidence of osteoarthritis.

Multiple epiphyseal dysplasia mutations in MATN3 cause misfolding of the A-domain and prevent secretion of mutant matrilin-3

Multiple epiphyseal dysplasia (MED) is a relatively common skeletal dysplasia that can present in childhood with a variable phenotype of short stature and pain and stiffness in the large joints, and often progresses to early-onset osteoarthritis in adulthood. Mutations in the matrilin-3 gene (MATN3) have recently been shown to underlie some forms of autosomal dominant MED. To date all MED mutations in matrilin-3 cluster in the single A-domain, suggesting that they may disrupt the structure and/or function of this important domain. To determine the effects of MATN3 mutations on the structure and function of matrilin-3 we expressed both normal and mutant matrilin-3 in mammalian cells. Wild-type (wt) matrilin-3 was efficiently secreted into conditioned medium, whereas mutant matrilin-3 was retained and accumulated within the cell. Furthermore, when the mutant A-domains were examined individually, they existed primarily in an unfolded conformation. Co-immunoprecipitation experiments demonstrated that the mutant A-domains were specifically associated with ERp72, a chaperone protein known to be involved in mediating disulfide bond formation. Light microscopy of cartilage from an MED patient with a MATN3 mutation showed the presence of intracellular material within the chondrocytes, whilst the overall matrix appeared normal. On electron micrographs, the inclusions noted at the light microscopy level appeared to be dilated cisternae of rough endoplasmic reticulum and immunohistochemical analysis confirmed that the retained protein was matrilin-3. In summary, the data presented in this paper suggest that MED caused by MATN3 mutations is the result of an intracellular retention of the mutant protein.

The matrilins--adaptor proteins in the extracellular matrix

The matrilins form a four-member family of modular, multisubunit matrix proteins, which are expressed in cartilage but also in many other forms of extracellular matrix. They participate in the formation of fibrillar or filamentous structures and are often associated with collagens. It appears that they mediate interactions between collagen-containing fibrils and other matrix constituents, such as aggrecan. This adaptor function may be modulated by physiological proteolysis that causes the loss of single subunits and thereby a decrease in binding avidity. Attempts to study matrilin function by gene inactivation in mouse have been frustrating and so far not yielded pronounced phenotypes, presumably because of the extensive redundancy within the family allowing compensation by one family member for another. However, mutations in matrilin-3 in humans cause different forms of chondrodysplasias and perhaps also hand osteoarthritis. As loss of matrilin-3 is not critical in mouse, these phenotypes are likely to be caused by dominant negative effects.

Adaptation of mechanical, morphological, and biochemical properties of the rat growth plate to dose-dependent voluntary exercise

Mechanical loading has been shown to modulate longitudinal bone growth and cellular activity of the growth plate. Nevertheless, limited and controversial results exist regarding the effect of exercise on a physiological level on the growth plate. The present study investigated whether dose-dependent voluntary exercise has an influence on morphological, biochemical, and mechanical factors of the distal femoral growth plate of immature rats. Female growing Sprague-Dawley rats were randomly assigned to a unlimited exercise group (UE, n = 10), a limited exercise group (LE, n = 10), and a sedentary control group (CON, n = 10). The exercise groups were trained voluntarily in a running wheel for 8 weeks. The UE group could use the running wheel every time, whereas the LE group had timely restricted (50%) access. After sacrifice, the right femur was prepared for histomorphometric analysis and immunohistochemical staining of the distal growth plate. Mechanical testing was carried out on the distal growth plate of the left femur in shear direction. At the end of the study, the UE group had a significantly lower body mass than the CON group. There was no significant difference in overall femoral length between the groups. The height of the growth plate and the proliferation zone was significantly greater in the CON group than in both exercise groups. Only the LE group had a significantly lower hypertrophic zone and matrilin-3 staining pattern than the CON group. Osteonectin was located in the matrix of the upper hypertrophic zone in the UE group, whereas the LE and CON group showed more chondrocytes in the hypertrophic and lower proliferation zones stained for osteonectin, suggesting a higher level of mineralization in the growth plate of the UE group. No variations of mechanical properties of the distal femoral growth plate were detected. These results clearly demonstrate adaptations of morphology and biochemical parameters to the dose of running exercise, which do not result in significant differences in mechanical properties or bone length between the UE, LE, and CON groups.

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.

Complexes of matrilin-1 and biglycan or decorin connect collagen VI microfibrils to both collagen II and aggrecan

Native supramolecular assemblies containing collagen VI microfibrils and associated extracellular matrix proteins were isolated from Swarm rat chondrosarcoma tissue. Their composition and spatial organization were characterized by electron microscopy and immunological detection of molecular constituents. The small leucine-rich repeat (LRR) proteoglycans biglycan and decorin were bound to the N-terminal region of collagen VI. Chondroadherin, another member of the LRR family, was identified both at the N and C termini of collagen VI. Matrilin-1, -3, and -4 were found in complexes with biglycan or decorin at the N terminus. The interactions between collagen VI, biglycan, decorin, and matrilin-1 were studied in detail and revealed a biglycan/matrilin-1 or decorin/matrilin-1 complex acting as a linkage between collagen VI microfibrils and aggrecan or alternatively collagen II. The complexes between matrilin-1 and biglycan or decorin were also reconstituted in vitro. Colocalization of collagen VI and the different ligands in the pericellular matrix of cultured chondrosarcoma cells supported the physiological relevance of the observed interactions in matrix assembly.

Comparative genetics and evolution of annexin A13 as the founder gene of vertebrate annexins

Annexin A13 (ANXA13) is believed to be the original founder gene of the 12-member vertebrate annexin A family, and it has acquired an intestine-specific expression associated with a highly differentiated intracellular transport function. Molecular characterization of this subfamily in a range of vertebrate species was undertaken to assess coding region conservation, gene organization, chromosomal linkage, and phylogenetic relationships relevant to its progenitor role in the structure-function evolution of the annexin gene superfamily. Protein diagnostic features peculiar to this subfamily include an alternate isoform containing a KGD motif, an elevated basic amino acid content with polyhistidine expansion in the 5'-translated region, and the conservation of 15% core tetrad residues specific to annexin A13 members. The 12 coding exons comprising the 58-kb human ANXA13 gene were deduced from BAC clone sequencing, whereas internal repetitive elements and neighboring genes in chromosome 8q24.12 were identified by contig analysis of the draft sequence from the human genome project. A unique exon splicing pattern in the annexin A13 gene was corroborated by coanalysis of mouse, rat, zebrafish, and pufferfish genomic DNA and determined to be the most distinct of all vertebrate annexins. The putative promoter region was identified by phylogenetic footprinting of potential binding sites for intestine-specific transcription factors. Mouse annexin A13 cDNA was used to map the gene to an orthologous linkage group in mouse chromosome 15 (between Sdc2 and Myc by backcross analysis), and the zebrafish cDNA permitted its localization to linkage group 24. Comparative analysis of annexin A13 from nine species traced this gene's speciation history and assessed coding region variation, whereas phylogenetic analysis showed it to be the deepest-branching vertebrate annexin, and computational analysis estimated the gene age and divergence rate. The unique, conserved aspects of annexin A13 primary structure, gene organization, and genetic maps identify it as the probable common ancestor of all vertebrate annexins, beginning with the sequential duplication to annexins A7 and A11 approximately 700 MYA, before the emergence of chordates.

Expression of matrilin-2 in human skin

The extracellular matrix is composed of a large number of different modular proteins. Matrilin-2 is a newly described member of the protein superfamily with von Willebrand factor A-like modules. To examine the expression of matrilin-2 in human skin, the distribution of protein and mRNA was studied by immunohistochemistry and in situ hybridization. In addition, immunoblotting and real-time reverse transcription polymerase chain reaction were used to investigate the expression of matrilin-2 in keratinocyte and fibroblast cultures. In vivo, keratinocytes and fibroblasts were both found to express matrilin-2 mRNA and deposit the protein at the basal side of the dermal-epidermal basement membrane. Matrilin-2 molecules synthesized by the two cell types in vitro appeared to be processed differently by cell-associated proteases. Transcription of matrilin-2 mRNA in keratinocytes was enhanced by a diffusible factor produced by fibroblasts, suggesting a regulatory mechanism for the production of extracellular matrix at the dermal-epidermal junction. These findings demonstrate that matrilin-2 is expressed in normal skin by keratinocytes and fibroblasts and may thus contribute to cutaneous homeostasis.

Characterization of the matrilin coiled-coil domains reveals seven novel isoforms

Matrilins constitute a family of four oligomeric extracellular proteins that are involved in the development and homeostasis of cartilage and bone. To reveal their homo- and heterotypic oligomerization propensities, we analyzed the four human matrilin coiled-coil domains by biochemical and biophysical methods. These studies not only confirmed the homo- and heterotypic oligomerization states reported for the full-length proteins but revealed seven novel matrilin isoforms. Specific heterotrimeric interactions of variable chain stoichiometries were observed between matrilin-1 and matrilin-2, matrilin-1 and matrilin-4, and matrilin-2 and matrilin-4. In addition, matrilin-1 formed two different specific heterotetramers with matrilin-3. Interestingly, a distinct heterotrimer consisting of three different chains was formed between matrilin-1, matrilin-2, and matrilin-4. No interactions, however, were observed between matrilin-2 and matrilin-3 or between matrilin-3 and matrilin-4. Both homo- and heterotypic oligomers folded into parallel disulfide-linked structures, although coiled-coil formation was not dependent on disulfide bridge formation. Our results indicate that the heterotypic preferences seen for the matrilin coiled-coil domains are the result of the packing of the hydrophobic core rather than ionic interactions. Mass spectrometry revealed that the concentrations of the individual chains statistically determined the stoichiometry of the heteromers, suggesting that formation of the different matrillin chain combinations is controlled by expression levels.

Matrilin-3 in human articular cartilage: increased expression in osteoarthritis

OBJECTIVE

Matrilin-3 is a member of the recently described matrilin family of extracellular matrix proteins containing von Willebrand factor A-like domains. The matrilin-3 subunit can form homo-tetramers as well as hetero-oligomers together with subunits of matrilin-1 (cartilage matrix protein). It has a restricted tissue distribution and is strongly expressed in growing skeletal tissues. Detailed information on expression and distribution of extracellular matrix proteins is important to understand cartilage function in health and in disease like osteoarthritis (OA).

METHODS

Normal and osteoarthritic cartilage were systematically analysed for matrilin-3 expression, using immunohistochemistry, Western blot analysis, in situ hybridization, and quantitative PCR.

RESULTS

Our results indicate that matrilin-3 is a mandatory component of mature articular cartilage with its expression being restricted to chondrocytes from the tangential zone and the upper middle cartilage zone. Osteoarthritic cartilage samples with only moderate morphological osteoarthritic degenerations have elevated levels of matrilin-3 mRNA. In parallel, we found an increased deposition of matrilin-3 protein in the cartilage matrix. Matrilin-3 staining was diffusely distributed in the cartilage matrix, with no cellular staining being detectable. In cartilage samples with minor osteoarthritic lesions, matrilin-3 deposition was restricted to the middle zone and to the upper deep zone. A strong correlation was found between enhanced matrilin-3 gene and protein expression and the extent of tissue damage. Sections with severe osteoarthritic degeneration showed the highest amount of matrilin-3 mRNA, strong signals in in situ hybridization, and prominent protein deposition in the middle and deep cartilage zone.

CONCLUSION

We conclude that matrilin-3 is an integral component of human articular cartilage matrix and that the enhanced expression of matrilin-3 in OA may be a cellular response to the modified microenvironment in the disease.

The occurrence of autoantibodies to matrilin 1 reflects a tissue-specific response to cartilage of the respiratory tract in patients with relapsing polychondritis

OBJECTIVE

Relapsing polychondritis (RP) is an inflammatory disease that mainly affects cartilage tissue in the auricle, nose, and lower respiratory tract. When tracheolaryngeal cartilage is involved, the disease is occasionally fatal. Matrilin 1 is a cartilage-specific protein most prominently expressed in tracheal cartilage, but not in joint cartilage. Immunization with the protein in rats and mice induces respiratory distress and nasal destruction, as seen in RP. We investigated the response to matrilin 1 and other cartilage proteins in sera from patients with RP, 4 additional groups of patients with other major connective tissue diseases, and healthy control subjects.

METHODS

Sera were analyzed by enzyme-linked immunosorbent assay (ELISA) for antibody responses to matrilin 1, types II, IX, and XI collagen, and cartilage oligomeric matrix protein (COMP). Titers above the mean + 3SD of controls were considered positive. Specificity of matrilin 1 recognition was further investigated by the capacity of high-titer sera to block the binding of a matrilin 1-specific monoclonal antibody in inhibition ELISAs. In vivo reactivity and specificity were tested by injecting sera into neonatal mice, and antibody binding was detected by immunohistochemical staining.

RESULTS

Serum antibodies from RP patients bound tracheolaryngeal and nasal cartilage in vivo and inhibited the binding of anti-matrilin 1-specific monoclonal antibodies. Thirteen of the 97 RP patients had increased titers of matrilin 1 antibody. Positive titers correlated with respiratory symptoms in 69% of the cases. Significant responses to type II collagen and COMP were also detected.

CONCLUSION

Antibodies to matrilin 1 bind tracheolaryngeal cartilage in vivo and are correlated with an inflammatory attack on tracheolaryngeal cartilage that is often seen in RP.

Molecular Properties of Matrilin-3 Isolated from Human Growth Cartilage

Matrilin-3 is a recently identified matrix protein of cartilage that shows sequence homology to matrilin-1 (cartilage matrix protein or CMP). Here we identify and characterize the molecular properties of matrilin-3 from human growth cartilage by immunochemical and mass spectrometry methods. Extracts of fetal skeletal cartilage were resolved by SDS-PAGE and candidate matrilin subunits were identified by electrospray mass spectrometry of tryptic peptides. Matrilin-3 and matrilin-1 were both present in disulfide-bonded tetrameric components. Polyclonal antisera to synthetic peptides specific to each subunit confirmed the identities by Western blotting and further demonstrated the existence of several forms of tetramer. A homotetramer (matrilin-3)4 and more than one species of heterotetramer containing matrilin-3 and matrilin-1 chains were resolved. Immunohistochemistry of tissue sections confirmed that both matrilin-1 and matrilin-3 are widely codistributed throughout human skeletal growth cartilage.

Expression of matrilin-1, -2 and -3 in developing mouse limbs and heart

The expression of matrilin-1, -2 and -3 was studied in the heart and limb during mouse development. Matrilin-1 is transiently expressed in the heart between days 9.5 and 14.5 p.c. Matrilin-2 expression was detected in the heart from day 10.5 p.c. onwards. In the developing limb bud, both matrilin-1 and -3 were observed first at day 12.5 p.c. Throughout development matrilin-3 expression was strictly limited to cartilage, while matrilin-1 was also found in some other forms of connective tissue. Matrilin-2, albeit present around hypertrophic chondrocytes in the growth plate, was mainly expressed in non-skeletal structures. The complementary, but in part overlapping, expression of matrilins indicates the possibility for both redundant and unique functions among the members of this novel family of extracellular matrix proteins.

Changes of matrilin forms during endochondral ossification. Molecular basis of oligomeric assembly

To understand the molecular properties of matrilin-3, a newly discovered member of the novel extracellular matrix protein family, we cloned a MAT-3 cDNA from developing chicken sterna. Real time quantitative reverse-transcription polymerase chain reaction indicates that MAT-3 mRNA is mainly expressed in the proliferation zone of a growth plate. It is also expressed in the maturation zone, overlapping with that of the mature chondrocyte-abundant matrilin-1 mRNA. This suggests that matrilin-3 may self-assemble in the proliferation zone, in addition to its co-assembly with matrilin-1 during endochondral ossification. Transfection of a MAT-3 cDNA into COS-7 cells shows that MAT-3 predominantly forms a homotetramer but also a trimer and a dimer. Co-transfection of both MAT-3 and MAT-1 cDNAs results in three major matrilins as follows: (MAT-1)(3), (MAT-3)(4), and (MAT-1)(2)(MAT-3)(2). Thus matrilin-3 may assemble into both homotypic and heterotypic oligomers. Our analysis shows that the assembly of MAT-3 does not depend on the number of epidermal growth factor repeats within the molecule, but the presence of Cys(412) and Cys(414) within the coiled-coil domain, which form covalent disulfide linkage responsible for both homo-oligomerization of MAT-3 and hetero-oligomerization of MAT-3 and MAT-1. Our data suggest that the varying synthetic levels of matrilins in different zones of a growth plate may result in a change of matrilin oligomeric forms during endochondral ossification.