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

MATN4 as a target gene of HIF-1α promotes the proliferation and metastasis of osteosarcoma

BACKGROUND

Osteosarcoma is a highly malignant bone tumor that exhibits rapid growth and early metastasis. Hypoxia plays a pivotal role in promoting the proliferation and metastasis of osteosarcoma through a series of molecular events, which are partially mediated and regulated by HIF-1α. However, the regulatory network associated with HIF-1α in osteosarcoma remains limited. Therefore, the objective of this study was to identify critical hypoxia-associated genes and investigate their effects and molecular mechanisms in osteosarcoma cells.

METHODS

Through bioinformatics analysis, matrilin-4 (MATN4) was identified as a crucial gene associated with hypoxia. The expression of MATN4 and HIF-1α was assessed using immunohistochemistry, RT-qPCR, and western blotting. The proliferative capacity of osteosarcoma cells was assessed through the utilization of CCK-8, EDU staining, and colony formation assays. The effects of MATN4 on the mobility of OS cells were evaluated using wound-healing assays and transwell assays. The interaction between MATN4 and HIF-1α was detected through chromatin immunoprecipitation.

RESULTS

MATN4 is overexpressed in osteosarcoma tissue and cells, particularly in osteosarcoma cells with high metastatic potential. Knockdown of MATN4 inhibits the proliferation, migration, and invasion abilities of osteosarcoma cells and reverses the promoting effects of hypoxia on these functions. Additionally, HIF-1α binds to MATN4 and upregulates its expression. Interestingly, knockdown of HIF-1α reduces the stimulatory effects of MATN4 overexpression on the proliferation, migration, and invasion of osteosarcoma cells under hypoxic conditions.

CONCLUSIONS

Taken together, our results suggest that MATN4 is regulated by HIF-1α and confers a more aggressive phenotype on OS cells. This evidence suggests that MATN4 may act as a potential target for OS diagnosis and treatment.

CCN Proteins (Cellular Communication Network Factors): Expanding Their Repertoire Toward a New Concept

I herein report the general structures and functions of CCN proteins and possible molecular mechanisms involved in the unique biological actions of this family of intercellular signaling regulators, which are considered matricellular proteins and were once referred to as "signal conductors" but have recently been renamed "Cellular Communication Network Factors." Their repertoire of functions beyond their role as matricellular proteins is also described to aid in future studies. Advanced research concerning their relevance to pathology is briefly introduced as well. The information provided in this chapter is expected to be useful for readers of subsequent chapters.

Differences in stromal component of chordoma are associated with contrast enhancement in MRI and differential gene expression in RNA sequencing

Chordoma is a malignant bone neoplasm demonstrating notochordal differentiation and it frequently involves axial skeleton. Most of chordomas are conventional type with varying amount of myxoid stroma. Previously known prognostic factors for conventional chordoma are not specific for chordoma: old age, metastasis, tumor extent, and respectability. Here, we aimed to investigate the histologic, radiologic, and transcriptomic differences in conventional chordoma based on the stromal component. A total of 45 patients diagnosed with conventional chordoma were selected between May 2011 and March 2020 from a single institution. Electronic medical records, pathology slides, and pretreatment magnetic resonance imaging (MRI) scans were reviewed. Of the 45 patients, ten cases (4 stroma-rich and 6 stroma-poor tumor) were selected for RNA sequencing, and available cases in the remainder were used for measuring target gene mRNA expression with qPCR for validation. Differential gene expression and gene set analysis were performed. Based on histologic evaluation, there were 25 (55.6%) stroma-rich and 20 (44.4%) stroma-poor cases. No clinical differences were found between the two groups. Radiologically, stroma-rich chordomas showed significant signal enhancement on MRI (72.4% vs 27.6%, p = 0.002). Upregulated genes in stroma-rich chordomas were cartilage-, collagen/extracellular matrix-, and tumor metastasis/progression-associated genes. Contrarily, tumor suppressor genes were downregulated in stroma-rich chordomas. On survival analysis, Kaplan–Meier plot was separated that showed inferior outcome of stroma-rich group, although statistically insignificant. In conclusion, the abundant stromal component of conventional chordoma enhanced well on MRI and possibly contributed to the biological aggressiveness that supported by transcriptomic characteristics. Further extensive investigation regarding radiologic-pathologic-transcriptomic correlation in conventional chordoma in a larger cohort could verify additional clinical significance.

Limb Mesoderm and Head Ectomesenchyme Both Express a Core Transcriptional Program During Chondrocyte Differentiation

To explain how cartilage appeared in different parts of the vertebrate body at discrete times during evolution, we hypothesize that different embryonic populations co-opted expression of a core gene regulatory network (GRN) driving chondrocyte differentiation. To test this hypothesis, laser-capture microdissection coupled with RNA-seq was used to reveal chondrocyte transcriptomes in the developing chick humerus and ceratobranchial, which are mesoderm- and neural crest-derived, respectively. During endochondral ossification, two general types of chondrocytes differentiate. Immature chondrocytes (IMM) represent the early stages of cartilage differentiation, while mature chondrocytes (MAT) undergo additional stages of differentiation, including hypertrophy and stimulating matrix mineralization and degradation. Venn diagram analyses generally revealed a high degree of conservation between chondrocyte transcriptomes of the limb and head, including SOX9, COL2A1, and ACAN expression. Typical maturation genes, such as COL10A1, IBSP, and SPP1, were upregulated in MAT compared to IMM in both limb and head chondrocytes. Gene co-expression network (GCN) analyses of limb and head chondrocyte transcriptomes estimated the core GRN governing cartilage differentiation. Two discrete portions of the GCN contained genes that were differentially expressed in limb or head chondrocytes, but these genes were enriched for biological processes related to limb/forelimb morphogenesis or neural crest-dependent processes, respectively, perhaps simply reflecting the embryonic origin of the cells. A core GRN driving cartilage differentiation in limb and head was revealed that included typical chondrocyte differentiation and maturation markers, as well as putative novel "chondrocyte" genes. Conservation of a core transcriptional program during chondrocyte differentiation in both the limb and head suggest that the same core GRN was co-opted when cartilage appeared in different regions of the skeleton during vertebrate evolution.

Identification of MATN3 as a Novel Prognostic Biomarker for Gastric Cancer through Comprehensive TCGA and GEO Data Mining

Gastric cancer (GC) is still a vital malignant cancer across the world with unsatisfactory prognostic results. Matrilin-3 (MATN3) is a member of the extracellular matrix (ECM) protein family. The present research intends to explore the expression level of MATN3 in patients with GC and to explore the prognosis significance of MATN3. In this study, we observed that the MATN3 expression was remarkably upregulated in GC samples in contrast to noncancer samples. Clinical analyses unveiled that high MATN3 expression was related to age, tumor status, and clinical stages. Survival analyses unveiled that patients with high MATN3 expression displayed a poorer overall survival and progression-free survival than those with low MATN3 expression. The AUC of the relevant ROC curve for 1 year, 3 years, and 5 years of survival is 0.571, 0.596, and 0.720, separately. Multivariate assays revealed that MATN3 expression and stage were independent predictors of poor prognosis of GC patients. A meta-analysis unveiled that high MATN3 expression was tightly associated with better overall survival. Overall, our data indicated that MATN3 may have a diagnostic and prognostic value for patients with advanced gastric cancer and assist to improve clinical outcomes for GC patients.

Mice Lacking the Matrilin Family of Extracellular Matrix Proteins Develop Mild Skeletal Abnormalities and Are Susceptible to Age-Associated Osteoarthritis

Matrilins (MATN1, MATN2, MATN3 and MATN4) are adaptor proteins of the cartilage extracellular matrix (ECM), which bridge the collagen II and proteoglycan networks. In humans, dominant-negative mutations in MATN3 lead to various forms of mild chondrodysplasias. However, single or double matrilin knockout mice generated previously in our laboratory do not show an overt skeletal phenotype, suggesting compensation among the matrilin family members. The aim of our study was to establish a mouse line, which lacks all four matrilins and analyze the consequence of matrilin deficiency on endochondral bone formation and cartilage function. Matn1-4^−/− mice were viable and fertile, and showed a lumbosacral transition phenotype characterized by the sacralization of the sixth lumbar vertebra. The development of the appendicular skeleton, the structure of the growth plate, chondrocyte differentiation, proliferation, and survival were normal in mutant mice. Biochemical analysis of knee cartilage demonstrated moderate alterations in the extractability of the binding partners of matrilins in Matn1-4^−/− mice. Atomic force microscopy (AFM) revealed comparable compressive stiffness but higher collagen fiber diameters in the growth plate cartilage of quadruple mutant compared to wild-type mice. Importantly, Matn1-4^−/− mice developed more severe spontaneous osteoarthritis at the age of 18 months, which was accompanied by changes in the biomechanical properties of the articular cartilage. Interestingly, Matn4^−/− mice also developed age-associated osteoarthritis suggesting a crucial role of MATN4 in maintaining the stability of the articular cartilage. Collectively, our data provide evidence that matrilins are important to protect articular cartilage from deterioration and are involved in the specification of the vertebral column.

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.

Clinical significance of Matrilin-3 gene polymorphism in Egyptian patients with primary knee osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is a multifactorial, degenerative, and inflammatory disorder of joints causing damage of the articular cartilage, formation of osteophytes, and eburination of the subchondral bone. Matrilin-3 (MATN-3) is a non-collagenous oligomeric extracellular matrix protein (ECM), which is the smallest member of the matrilin family. This study was conducted to identify the potential association and clinical significance of MATN-3 rs8176070 (SNP6) polymorphism in a series of Egyptian patients with primary knee OA.

MATERIAL AND METHODS

Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to determine genotypes of MATN-3 SNP6 for 50 primary knee OA patients in addition to 50 healthy subjects of the same sex and age range. Full history was obtained from OA patients, followed by clinical examination, together with clinical assessment of the severity of knee OA using Lequesne Algofunctional Index score and radiological grading using the Kellgren-Lawrence grade scale (KL).

RESULTS

With regard to genotypes of MATN-3 gene SNP6 (rs8176070), a statistically significant difference between OA patients and healthy control subjects was found for the B\b genotype and b allele (p=0.046 and 0.042 respectively), with the prevalence being higher in OA patients with a high risk to develop OA (Odds Ratio [OR]=2.250, 95% CI=1.011-5.008). Patients with the B\b genotype had worse clinical and radiological findings than those with B\B and b\b genotypes.

CONCLUSION

The investigated polymorphism in the MATN-3 gene may reflect the risk and severity of knee OA in Egyptian patients, particularly with the B\b genotype.

Chondrocytes Derived From Mesenchymal Stromal Cells and Induced Pluripotent Cells of Patients With Familial Osteochondritis Dissecans Exhibit an Endoplasmic Reticulum Stress Response and Defective Matrix Assembly

: Familial osteochondritis dissecans (FOCD) is an inherited skeletal defect characterized by the development of large cartilage lesions in multiple joints, short stature, and early onset of severe osteoarthritis. It is associated with a heterozygous mutation in the ACAN gene, resulting in a Val-Met replacement in the C-type lectin domain of aggrecan. To understand the cellular pathogenesis of this condition, we studied the chondrogenic differentiation of patient bone marrow mesenchymal stromal cells (BM-MSCs). We also looked at cartilage derived from induced pluripotent stem cells (iPSCs) generated from patient fibroblasts. Our results revealed several characteristics of the differentiated chondrocytes that help to explain the disease phenotype and susceptibility to cartilage injury. First, patient chondrogenic pellets had poor structural integrity but were rich in glycosaminoglycan. Second, it was evident that large amounts of aggrecan accumulated within the endoplasmic reticulum of chondrocytes differentiated from both BM-MSCs and iPSCs. In turn, there was a marked absence of aggrecan in the extracellular matrix. Third, it was evident that matrix synthesis and assembly were globally dysregulated. These results highlight some of the abnormal aspects of chondrogenesis in these patient cells and help to explain the underlying cellular pathology. The results suggest that FOCD is a chondrocyte aggrecanosis with associated matrix dysregulation. The work provides a new in vitro model of osteoarthritis and cartilage degeneration based on the use of iPSCs and highlights how insights into disease phenotype and pathogenesis can be uncovered by studying differentiation of patient stem cells.

SIGNIFICANCE

The isolation and study of patient stem cells and the development of methods for the generation of iPSCs have opened up exciting opportunities in understanding causes and exploring new treatments for major diseases. This technology was used to unravel the cellular phenotype in a severe form of inherited osteoarthritis, termed familial osteochondritis dissecans. The phenotypic abnormalities that give rise to cartilage lesions in these patients were able to be described via the generation of chondrocytes from bone marrow-derived mesenchymal stromal cells and iPSCs, illustrating the extraordinary value of these approaches in disease modeling.

Small-Molecule Inhibition of Rho/MKL/SRF Transcription in Prostate Cancer Cells: Modulation of Cell Cycle, ER Stress, and Metastasis Gene Networks

Metastasis is the major cause of cancer deaths and control of gene transcription has emerged as a critical contributing factor. RhoA- and RhoC-induced gene transcription via the actin-regulated transcriptional co-activator megakaryocytic leukemia (MKL) and serum response factor (SRF) drive metastasis in breast cancer and melanoma. We recently identified a compound, CCG-1423, which blocks Rho/MKL/SRF-mediated transcription and inhibits PC-3 prostate cancer cell invasion. Here, we undertook a genome-wide expression study in PC-3 cells to explore the mechanism and function of this compound. There was significant overlap in the genes modulated by CCG-1423 and Latrunculin B (Lat B), which blocks the Rho/MKL/SRF pathway by preventing actin polymerization. In contrast, the general transcription inhibitor 5,6-dichloro-1-β-d-ribofuranosyl-1H-benzimidazole (DRB) showed a markedly different pattern. Effects of CCG-1423 and Lat B on gene expression correlated with literature studies of MKL knock-down. Gene sets involved in DNA synthesis and repair, G1/S transition, and apoptosis were modulated by CCG-1423. It also upregulated genes involved in endoplasmic reticulum stress. Targets of the known Rho target transcription factor family E2F and genes related to melanoma progression and metastasis were strongly suppressed by CCG-1423. These results confirm the ability of our compound to inhibit expression of numerous Rho/MKL-dependent genes and show effects on stress pathways as well. This suggests a novel approach to targeting aggressive cancers and metastasis.

Chondrons and the pericellular matrix of chondrocytes

In cartilage, chondrocytes are embedded within an abundant extracellular matrix (ECM). A typical chondron consists of a chondrocyte and the immediate surrounding pericellular matrix (PCM). The PCM has a patent structure, defined molecular composition, and unique physical properties that support the chondrocyte. Given this spatial position, the PCM is pivotal in mediating communication between chondrocytes and the ECM and, thus, plays a critical role in cartilage homeostasis. The biological function and mechanical properties of the PCM have been extensively studied, mostly in the form of chondrons. This review intends to summarize recent progress in chondron and chondrocyte PCM research, with emphasis on the re-establishment of the PCM by isolated chondrocytes or mesenchymal stem cells during chondrogenic differentiation, and the effects of the PCM on cartilage tissue formation.

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-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.

Rho/ROCK and MEK/ERK activation by transforming growth factor-alpha induces articular cartilage degradation

Identification and characterization of therapeutic targets for joint conditions, such as osteoarthritis (OA), is exceedingly important for addressing the increasing burden of disease. Transforming growth factor-alpha (TGFalpha) is upregulated by articular chondrocytes in experimentally induced and human OA. To test the potential involvement of TGFalpha, which is an activator of epidermal growth factor receptor (EGFR) signaling, in joint degeneration and to identify signaling mechanisms mediating articular chondrocyte responses to TGFalpha, rat chondrocytes and osteochondral explants were treated with TGFalpha and various inhibitors of intracellular signaling pathways. Stimulation of EGFR signaling in articular chondrocytes by TGFalpha resulted in the activation of RhoA/ROCK (Rho kinase), MEK (MAPK/ERK kinase)/ERK (extracellular-signal-regulated kinase), PI3K (phosphoinositide 3-kinase) and p38 MAPK (mitogen-activated protein kinase) pathways. Modification of the chondrocyte actin cytoskeleton was stimulated by TGFalpha, but inhibition of only Rho or ROCK activation prevented morphological changes. TGFalpha suppressed expression of anabolic genes including Sox9, type II collagen and aggrecan, which were rescued only by inhibiting MEK/ERK activation. Furthermore, catabolic factor upregulation by TGFalpha was prevented by ROCK and p38 MAPK inhibition, including matrix metalloproteinase-13 and tumor necrosis factor-alpha, which are well known to contribute to cartilage digestion in OA. To assess the ability of TGFalpha to stimulate degradation of mature articular cartilage, type II collagen and aggrecan cleavage fragments were analyzed in rat osteochondral explants exposed to exogenous TGFalpha. Normal articular cartilage contained low levels of both cleavage fragments, but high levels were observed in the cartilage treated with TGFalpha. Selective inhibition of MEK/ERK and Rho/ROCK activation greatly reduced or completely prevented excess type II collagen and aggrecan degradation in response to TGFalpha. These data suggest that TGFalpha is a strong stimulator of cartilage degradation and that Rho/ROCK and MEK/ERK signaling have critical roles in mediating these effects.

Analysing the role of endogenous matrix molecules in the development of osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis worldwide. In this condition, damage to the extracellular matrix (ECM) of cartilage occurs, resulting in joint destruction. Factors mediating cartilage damage include mechanical injury, cytokine and superoxide release on a background of genetic susceptibility and obesity. Studies of arthritic cartilage show increased production of ECM molecules including type II collagen, cartilage oligomeric matrix protein, fibronectin (FN) and fibromodulin. Recent reports suggest that ECM proteins may become endogenous catabolic factors during joint damage. Activation of pro-inflammatory pathways by ECM proteins has led to their description as damage-associated molecular patterns (DAMPs). The ECM proteins involved include fibromodulin, which activates the complement pathway and may promote the persistence of joint inflammation. Fragmentation of type II collagen, FN and hyaluronan reveals cryptic epitopes that stimulate proteolytic enzymes including matrix metalloproteinases and aggrecanases (ADAMTSs - a disintegrin and metalloproteinase with thrombospondin type 1 motifs). Proteolytic fragments also stimulate the release of nitric oxide, chemokines and cytokines and activation of the MAP kinases. Reports are emerging that the receptors for the fragments described involve interaction with integrins and toll-like receptors. In this review the contribution of endogenous ECM molecules to joint destruction will be discussed. A deeper understanding of the pathways stimulated by endogenous ligands could offer potential avenues for novel therapies in the future.