Microarray analysis reveals the involvement of beta-2 microglobulin (B2M) in human osteoarthritis

CTGF regulates mineralization in human mature chondrocyte by controlling Pit-1 and modulating ANK via the BMP/Smad signalling

OBJECTIVE

Connective tissue growth factor (CTGF) exhibits potent proliferative, differentiated, and mineralizing effects, and is believed to be contribute to cartilage mineralization in Osteoarthritis (OA). However, the underlying mechanism of chondrocyte mineralization induced by CTGF remains obscure. As a key regulator of mineral responses, type III phosphate transporter 1 (Pit-1) has been associated with the pathogenesis of articular mineralization. Therefore, the primary objective of this study was to investigate whether CTGF influences the development of mature chondrocyte mineralization and the underlying mechanisms governing such mineralization.

METHODS

The effect of Connective tissue growth factor (CTGF) on human C-28/I2 chondrocytes were investigated. The chondrocytes were treated with CTGF or related inhibitors, and transfected with Overexpression and siRNA transfection of Type III Phosphate Transporter 1(Pit-1). Subsequently, the cells were subjected to Alizarin red S staining, PiPer Phosphate Assay Kit, Alkaline Phosphatase Diethanolamine Activity Kit, ELISA, RT-PCR or Western blot analysis.

RESULTS

Stimulation with Connective tissue growth factor (CTGF) significantly upregulated the expression of the Type III Phosphate Transporter 1(Pit-1) and mineralization levels in chondrocytes through activation of α5β1 integrin and BMP/Samd1/5/8 signaling pathways. Furthermore, treatment with overexpressed Pit-1 markedly increased the expression of Multipass Transmembrane Ankylosis (ANK) transporter in the cells. The inhibitory effect of CTGF receptor blockade using α5β1 Integrin blocking antibody was demonstrated by significantly suppressed the expression of Pit-1 and ANK transporter, as well as chondrocyte mineralization.

CONCLUSIONS

Our data indicate that Connective tissue growth factor (CTGF) plays a critical role inchondrocyte mineralization, which is dependent on the expression of the Type III Phosphate Transporter 1(Pit-1) and Multipass Transmembrane Ankylosis (ANK) transporter. Consequently, inhibition of CTGF activity may represent a novel therapeutic approach for the management of Osteoarthritis (OA).

β2-Microglobulin Elevates COL5A1 mRNA in the Subsynovial Connective Tissue of Patients Receiving Hemodialysis With Carpal Tunnel Syndrome

Background Although carpal tunnel syndrome (CTS) is frequently observed in patients undergoing long-term hemodialysis (HD), exactly how CTS arises is unknown. Here, we examined levels of COL5A1 in the subsynovial connective tissue (SSCT) of patients receiving HD and studied its potential regulation by β2-microglobulin (Β2-MG) in SSCT-derived cells (SSCTCs). Methods We extracted SSCT samples from 67 patients with CTS (49 non-HD and 18 HD) during carpal tunnel release. The samples were subjected to quantitative polymerase chain reaction (qPCR) to determine COL5A1 expression. Further, to examine the potential regulation of COL5A1 expression by Β2-MG, SSCTCs were stimulated in the absence (control) or presence of 10 µg/ml Β2-MG. Results The HD group showed significantly elevated COL5A1 levels compared to the non-HD group (P=0.027). Moreover, treating SSCTCs with Β2-MG for 24 h increased the mRNA expression of COL5A1 relative to control conditions (P=0.013). Conclusions Elevated COL5A1 expression may form part of the mechanism underlying the development of CTS, and Β2-MG may play a role in promoting COL5A1 expression in HD patients.

Identification of crucial salivary proteins/genes and pathways involved in pathogenesis of temporomandibular disorders

Temporomandibular disorder (TMD) is a collective term for a group of conditions that lead to impairment of the function of the temporomandibular joint. The proteins/genes and signaling pathways associated with TMD are still poorly understood. The aim of this study was to identify key differentially expressed salivary proteins/genes (DEGs) associated with TMD progression using LC-MS/MS coupled with a bioinformatics approach. The protein–protein interaction network was obtained from the STRING database and the hub genes were identified using Cytoscape including cytoHubba and MCODE plug-ins. In addition, enrichment of gene ontology functions and the Reactome signaling pathway was performed. A total of 140 proteins/genes were differentially expressed. From cluster analysis, a set of 20 hub genes were significantly modulated: ALB, APOA1, B2M, C3, CAT, CLU, CTSD, ENO1, GSN, HBB, HP, HSPA8, LTF, LYZ, MMP9, S100A9, SERPINA1, TF, TPI1, and TXN. Two enriched signaling pathways, glycolysis and gluconeogenesis, and tryptophan signaling pathway involving the hub genes CAT, ENO1, and TPI1 have been identified. The rest of the hub genes were mainly enriched in the innate immune system and antimicrobial peptides signaling pathways. In summary, hub DEGs and the signaling pathways identified here have elucidated the molecular mechanisms of TMD pathogenesis.

Targeted transcriptomic analyses of RNA isolated from formalin-fixed and paraffin-embedded human menisci

Formalin-fixed and paraffin-embedded (FFPE) biospecimens are a valuable and widely-available resource for diagnostic and research applications. With biobanks of tissue samples available in many institutions, FFPE tissues could prove to be a valuable resource for translational orthopaedic research. The purpose of this study was to characterize the molecular profiles and degree of histologic degeneration on archival fragments of FFPE human menisci obtained during arthroscopic partial meniscectomy. We used FFPE menisci for multiplexed gene expression analysis using the NanoString nCounter® platform, and for histological assessment using a quantitative scoring system. In total, 17 archival specimens were utilized for integrated histologic and molecular analyses. The median patient age was 22 years (range: 14-62). We found that the genes with the highest normalized counts were those typically expressed in meniscal fibrocartilage. Gene expression differences were identified in patient cohorts based on age (≤40 years), including genes associated with the extracellular matrix and tissue repair. The majority of samples showed mild to moderate histologic degeneration. Based on these data, we conclude that FFPE human menisci can be effectively utilized for molecular evaluation following a storage time as long as 11 years. Statement of Clinical Significance: The integration of histological and transcriptomic analyses described in this study will be useful for future studies investigating the basis for biological classification of meniscus specimens in patients. Further exploration into the genes and pathways uncovered by this study may suggest targets for biomarker discovery and identify patients at greater risk for osteoarthritis once the meniscus is torn.

A Review of Emerging Tear Proteomics Research on the Ocular Surface in Ocular Allergy

Ocular allergy is an immunoglobulin E-mediated Type I hypersensitivity reaction localised to the ocular surface and surrounding tissues. Primary signs and symptoms of ocular allergy include itching, redness, irritation and inflammation. Eye-rubbing caused by itching has been shown to alter ocular surface protein concentrations in conditions linked to ocular allergy such as keratoconus. In keratoconus, the cornea begins to thin and sag over time, leading to progressive vision loss and blindness in severe conditions. Due to the high incidence of ocular allergy sufferers rubbing their eyes in response to symptoms of itching, the protein landscape of the ocular surface may be significantly altered. Differential protein expression caused by long-term inflammation and eye-rubbing may lead to subsequent changes in ocular surface structure and function over time. This review aims to summarise and explore the findings of current ocular allergy proteome research conducted using techniques such as gel electrophoresis, mass spectrometry and lab-on-a-chip proteomics. Proteins of interest for this review include differentially expressed immunoglobulins, mucins, functional proteins, enzymes and proteins with previously uncharacterised roles in ocular allergy. Additionally, potential applications of this research are addressed in terms of diagnostics, drug development and future research prospects.

Identification of Common Pathogenic Pathways Involved in Hemochromatosis Arthritis and Calcium Pyrophosphate Deposition Disease: a Review

OBJECTIVES

Arthritis is a common clinical manifestation of hereditary hemochromatosis (HH), and HH is one of a handful of conditions linked to calcium pyrophosphate deposition (CPPD) in joints. The connection between these two types of arthritis has not yet been fully elucidated. In light of new pathogenic pathways recently implicated in CPPD involving bone, we reviewed the literature on the etiology of hemochromatosis arthropathy (HHA) seeking shared pathogenic mechanisms.

RESULTS

Clinical observations reinforce striking similarities between HHA and CPPD even in the absence of CPP crystals. They share a similar joint distribution, low grade synovial inflammation, and generalized bone loss. Excess iron damages chondrocytes and bone cells in vitro. While direct effects of iron on cartilage are not consistently seen in animal models of HH, there is decreased osteoblast alkaline phosphatase activity, and increased osteoclastogenesis. These abnormalities are also seen in CPPD. Joint repair processes may also be impaired in both CPPD and HHA.

CONCLUSIONS

Possible shared pathogenic pathways relate more to bone and abnormal damage/repair mechanisms than direct damage to articular cartilage. While additional work is necessary to fully understand the pathogenesis of arthritis in HH and to firmly establish causal links with CPPD, this review provides some plausible hypotheses explaining the overlap of these two forms of arthritis.

Caspase Inhibition Affects the Expression of Autophagy-Related Molecules in Chondrocytes

Objective. Caspases, cysteine proteases traditionally associated with apoptosis and inflammation, have recently been identified as important regulators of autophagy and reported within the growth plate, a cartilaginous part of the developing bone. The aim of this research was to identify novel autophagy-related molecules affected by inhibition of pro-apoptotic caspases in chondrocytes. Design. Chondrocyte micromasses derived from mouse limb buds were treated with pharmacological inhibitors of caspases. Autophagy-related gene expression was examined and possible novel molecules were confirmed by real-time polymerase chain reaction and immunocytofluorescence. Individual caspases inhibitors were used to identify the effect of specific caspases. Results. Chondrogenesis accompanied by caspase activation and autophagy progression was confirmed in micromass cultures. Expression of several autophagy-associated genes was significantly altered in the caspases inhibitors treated groups with the most prominent decrease for Pik3cg and increase of Tnfsf10. The results showed the specific pro-apoptotic caspases that play a role in these effects. Importantly, use of caspase inhibitors mimicked changes triggered by an autophagy stimulator, rapamycin, linking loss of caspase activity to an increase in autophagy. Conclusion. Caspase inhibition significantly affects regulation of autophagy-related genes in chondrocytes cultures. Detected markers are of importance in diagnostics and thus the data presented here open new perspectives in the field of cartilage development and degradation.

Connective Tissue Growth Factor: From Molecular Understandings to Drug Discovery

Connective tissue growth factor (CTGF) is a key signaling and regulatory molecule involved in different biological processes, such as cell proliferation, angiogenesis, and wound healing, as well as multiple pathologies, such as tumor development and tissue fibrosis. Although the underlying mechanisms of CTGF remain incompletely understood, a commonly accepted theory is that the interactions between different protein domains in CTGF and other various regulatory proteins and ligands contribute to its variety of functions. Here, we highlight the structure of each domain of CTGF and its biology functions in physiological conditions. We further summarized main diseases that are deeply influenced by CTGF domains and the potential targets of these diseases. Finally, we address the advantages and disadvantages of current drugs targeting CTGF and provide the perspective for the drug discovery of the next generation of CTGF inhibitors based on aptamers.

Knockout of beta-2 microglobulin reduces stem cell-induced immune rejection and enhances ischaemic hindlimb repair via exosome/miR-24/Bim pathway

Generating universal human umbilical mesenchymal stem cells (UMSCs) without immune rejection is desirable for clinical application. Here we developed an innovative strategy using CRISPR/Cas9 to generate B2M^‐UMSCs in which human leucocyte antigen (HLA) light chain β2‐microglobulin (B2M) was deleted. The therapeutic potential of B2M^‐UMSCs was examined in a mouse ischaemic hindlimb model. We show that B2M^‐UMSCs facilitated perfusion recovery and enhanced running capability, without inducing immune rejection. The beneficial effect was mediated by exosomes. Mechanistically, microRNA (miR) sequencing identified miR‐24 as a major component of the exosomes originating from B2M^‐UMSCs. We identified Bim as a potential target of miR‐24 through bioinformatics analysis, which was further confirmed by loss‐of‐function and gain‐of‐function approaches. Taken together, our data revealed that knockout of B2M is a convenient and efficient strategy to prevent UMSCs‐induced immune rejection, and it provides a universal clinical‐scale cell source for tissue repair and regeneration without the need for HLA matching in the future.

The pathogenic role of connective tissue growth factor in osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis, and connective tissue growth factor (CTGF) is found to be up-regulated in adjacent areas of cartilage surface damage. CTGF is present in osteophytes of late stage OA. In the present study, we have reviewed association of CTGF in the development and progression of OA and the potential effects of CTGF as a therapeutic agent for the treatment of OA. We have reviewed the recent articles on CTGF and OA in databases like PubMed, google scholar, and SCOPUS and collected the information for the articles. CTGF is usually up-regulated in synovial fluid of OA that stimulates the production of inflammatory cytokines. CTGF also activates nuclear factor-κB, increases the production of chemokines and cytokines, and up-regulates matrix metalloproteinases-3 (MMP-3) that in turn leads to the reduction in proteoglycan contents in joint cartilage. Consequently, cartilage homeostasis is imbalanced that might contribute to the pathogenesis of OA by developing synovial inflammation and cartilage degradation. CTGF might serve as a useful biomarker for the prognosis and treatment of OA, and recent studies have taken attempt to use CTGF as therapeutic target of OA. However, more investigations with clinical trials are necessary to validate the possibility of use of CTGF as a biomarker in OA diagnosis and therapeutic target for OA treatment.

The unresolved problem of beta-2 microglobulin amyloid deposits in the intervertebral discs of long-term dialysis patients

BACKGROUND

Dialysis-related destructive spondyloarthropathy caused by beta-2 microglobulin (β2M) amyloid deposits in intervertebral discs is a major burden for patients undergoing long-term dialysis. This study aimed to quantify the presence of β2M amyloid deposits in the intervertebral disc tissue of such patients and analyze whether there was a significant correlation between β2M accumulation and the duration of dialysis.

METHODS

Two groups of patients who had undergone surgery for degenerative spinal pathologies were selected: the dialysis group (n = 29) with long-term dialysis and the control group (n = 10) with no renal impairment. Tissue sections were prepared from specimens of intervertebral disc tissue obtained during spinal surgery and analyzed via histological staining, including immunohistochemistry (IHC) and Congo red.

RESULTS

There was a statistically significant multifold increase of β2M expression in the disc tissue of long-term dialysis patients when compared to non-dialysis patients, as shown by both IHC (0.019 ± 0.023 μm² vs. 0.00020 ± 0.00033 μm², respectively; p = 0.012) and Congo red staining (0.027 ± 0.041 μm² vs. 9.240 × 10^-5 ± 5.261 × 10^-5 μm², respectively; p = 0.047). We also note a moderate strength positive correlation between the duration of dialysis and positive IHC (r = 0.39; p = 0.015) and Congo-red staining (r = 0.42; p = 0.007).

CONCLUSIONS

The problem of β2M amyloidosis in long-term dialysis patients remains unresolved even with predominant use of high-flux dialysis membranes. This highlights the insufficiency of current dialysis modalities to effectively filter β2M.

Quantitative proteomics reveals regulatory differences in the chondrocyte secretome from human medial and lateral femoral condyles in osteoarthritic patients

Background

Osteoarthritis (OA) is a destructive joint disease and there are no known biomarkers available for an early diagnosis. To identify potential disease biomarkers and gain further insight into the disease mechanisms of OA we applied quantitative proteomics with SILAC technology on the secretomes from chondrocytes of OA knees, designated as high Mankin (HM) scored secretome. A quantitative comparison was made between the secretomes of the medial and lateral femur condyle chondrocytes in the same knee since the medial femur condyle is usually more affected in OA than the lateral condyle, which was confirmed by Mankin scoring. The medial/lateral comparison was also made on the secretomes from chondrocytes taken from one individual with no clinically apparent joint-disease, designated as low Mankin (LM) scored secretome.

Results

We identified 825 proteins in the HM secretome and 69 of these showed differential expression when comparing the medial and lateral femoral compartment. The LM scored femoral condyle showed early signs of OA in the medial compartment as assessed by Mankin score. We here report the identification and relative quantification of several proteins of interest for the OA disease mechanism e.g. CYTL1, DMD and STAB1 together with putative early disease markers e.g. TIMP1, PPP2CA and B2M.

Conclusions

The present study reveals differences in protein abundance between medial/lateral femur condyles in OA patients. These regulatory differences expand the knowledge regarding OA disease markers and mechanisms.

Molecular regulation of CCN2 in the intervertebral disc: lessons learned from other connective tissues

Connective tissue growth factor (CCN2/CTGF) plays an important role in extracellular matrix synthesis, especially in skeletal tissues such as cartilage, bone, and the intervertebral disc. As a result there is a growing interest in examining the function and regulation of this important molecule in the disc. This review discusses the regulation of CCN2 by TGF-β and hypoxia, two critical determinants that characterize the disc microenvironment, and discusses known functions of CCN2 in the disc. The almost ubiquitous regulation of CCN2 by TGF-β, including that seen in the disc, emphasizes the importance of the TGF-β-CCN2 relationship, especially in terms of extracellular matrix synthesis. Likewise, the unique cross-talk between CCN2 and HIF-1 in the disc highlights the tissue and niche specific mode of regulation. Taken together the current literature supports an anabolic role for CCN2 in the disc and its involvement in the maintenance of tissue homeostasis during both health and disease. Further studies of CCN2 in this tissue may reveal valuable targets for the biological therapy of disc degeneration.

Hyaluronic acid modulates gene expression of connective tissue growth factor (CTGF), transforming growth factor-beta1 (TGF-beta1), and vascular endothelial growth factor (VEGF) in human fibroblast-like synovial cells from advanced-stage osteoarthritis in vitro

Intraarticular injection of hyaluronan (hyaluronic acid; HA) is the common way to treat osteoarthritis (OA) of knees. This treatment cannot only maintain the viscoelastic properties of knee but also release the OA pain. However, the exact molecular mechanism is unknown. In this study, after human synovial cells were stimulated with HA and Hylan (Synvisc) for 24 h, real-time polymerase chain reaction (real-time PCR) was used to detect the alteration of connective tissue growth factor (CTGF), transforming growth factor-beta1 (TGF-beta1), and vascular endothelial growth factor (VEGF) gene expression, which were specific genes related to pathogenesis of OA knees. Our results illustrated that both HA and Hylan might not cause cytotoxicity or apoptosis of synovial cells in serum deprivation environment. The gene expressions of TGF-beta1 and VEGF were significantly increased at the concentration of 0.1 mg/mL HA and 0.1 mg/mL Hylan, respectively (alpha < 0.05). The synovial cells with treatment of 0.1 mg/mL Hylan decreased the CTGF gene expression (0.66-fold) and VEGF (0.78-fold) compared to 0.1 mg/mL HA (alpha < 0.05). We suggested that the profile of CTGF, TGF-beta1, and VEGF gene expressions in our study might provide the rational mechanism for the therapeutic effect of hyaluronan on OA knees.

Cartilage biomarkers in hemodialysis patients and the effect of beta2-microglobulin on articular chondrocytes

OBJECTIVE

Dialysis-related amyloidosis (DRA) is a severe complication of maintenance hemodialysis (HD). Given the predominant deposition of beta(2)-microglobulin (beta2m) fibrils on articular cartilage in early DRA, we investigated the significance of beta2m and its relationship to distinct cartilage biomarkers in early DRA diagnosis in HD patients. Furthermore, we assessed the effects of beta2m on articular chondrocytes in vitro.

METHODS

Serum samples from 133 patients were collected before and after HD. Type II collagen cleavage product (C2C), procollagen II c-propeptide (CPII), aggrecan chondroitin sulfate 846 epitope (CS-486) and cartilage oligomeric matrix protein (COMP) levels were determined by enzyme-linked immunosorbent assay. Primary bovine articular chondrocytes were cultured as monolayers and incubated with beta2m at 1.5mg/l and 20mg/l. Cartilage glucosaminoglycan synthesis was measured by [(35)S]sulfate incorporation. mRNA expression of interleukin (IL)-1beta, matrix metalloproteinases (MMPs)-3 and -9 was measured by reverse-transcriptase polymerase chain reaction (RT-PCR).

RESULTS

Incubation with beta2m at 20mg/l significantly decreased matrix biosynthesis. PCR analysis revealed an increase of IL-1beta, as well as MMPs-3 and -9 on the mRNA level. C2C/CPII, CS-486 and COMP levels were increased only in a subset of patients without a significant correlation with beta2m concentrations. A subgroup analysis elucidated an increase in type II collagen degradation during the first years of HD, as shown by the elevation of C2C/CPII ratio.

CONCLUSION

beta2m exerted anti-anabolic effects on articular chondrocytes in vitro and might be involved in cartilage degradation in HD patients. beta2m serum levels, however, did not reflect cartilage degradation in DRA. The assessment of C2C/CPII, CS-486 or COMP concentrations apparently has minor relevance in DRA diagnosis in HD patients. However, the increased type II collagen breakdown within 5 years after HD onset possibly mirrors the early stages of DRA. Thus, the C2C/CPII ratio could be employed in longitudinal studies, since it may reflect a risk for DRA related arthropathy development in a subset of patients.

Molecular network of cartilage homeostasis and osteoarthritis

This review article presents the current understanding of the molecular basis of articular cartilaginous homeostasis, and outlines potential areas to focus on within the developing field of therapeutics for cartilage disorders. Articular cartilage, an integral component of joints in extremities and the vertebral column, is essential for locomotion. Disturbance of joint development or cartilage homeostasis causes congenital osteocartilaginous dysplasia or osteoarthritic diseases, respectively. Symptomatic treatments and surgical replacement of joints are effective but can also be problematic in terms of quality of life over time. Recently, new insights into the molecular biological basis of chondrocyte differentiation and cartilage homeostasis have been reported. While joint formation is regulated by several growth factors such as Wnts (wingless-related MMTV integration site) and Gdfs (growth and differentiation factors), the pathology of osteoarthritis is now interpreted as the disruption of balance between anabolic and catabolic signals. Current findings in molecular biology on joint development are reviewed concisely to aid in the understanding of the molecular network that governs articular cartilage development and homeostasis.

Functional genomics, evo-devo and systems biology: a chance to overcome complexity?

PURPOSE OF REVIEW

This review addresses the key question of how to integrate a high complexity of processes and data to a unifying picture of disease processes and progression relevant for osteoarthritis.

RECENT FINDINGS

Many research efforts in the last few years have resulted in the accumulation of a huge amount of data. To date, however, these data have not led to a unifying concept of the pathogenesis and progression of the osteoarthritic disease process. Methods to integrate a lot of information are needed, therefore, in order to progress from experimental findings to practical knowledge. Several such strategies have been followed up in the past: in-vitro models, large-scale gene expression analysis/functional genomics, and an attempt to interpret gene expression patterns on the basis of developmental chondrocyte differentiation. A novel approach is systems biology, which promises to overcome issues of complexity using appropriate models and quantitative simulation.

SUMMARY

Efforts are required to integrate a continuously growing high complexity of experimental data into an understanding of the joint system and its derangement in osteoarthritis. Modelling of the 'whole' picture appears to be needed so that we do not get lost in the plethora of details.

Large-scale gene expression profiles, differentially represented in osteoarthritic synovium of the knee joint using cDNA microarray technology

Osteoarthritis (OA) is one of the most common age-related chronic disorders of articular cartilage, joints and bone tissue. Diagnosis of OA commonly depends on clinical and radiographic findings. However, changes in cartilage associated with the early stage of OA cannot be detected using radiographs, because significant cartilage degeneration must occur before radiographic findings show alterations of the appearance of cartilage. To identify new biomarkers of OA, we analysed gene expression profiles of synovium from 43 patients with OA, ten patients with rheumatoid arthritis (RA), and eight non-OA/non-RA patients using a novel cDNA microarray chip. We identified 21 genes with simultaneous significant differences in expression between OA and non-OA/non-RA groups and between OA and RA groups. Linear discriminant analysis showed that the three groups could be well separated using those 21 genes. Statistical analysis also revealed that several of the 21 genes were associated with disease progression and clinical presentation. The graphical modelling method indicated that some of the 21 genes are significantly associated with a particular clinical presentation, suggesting biological relationships among those genes. This is the first report of the use of cDNA microarray technology to create large-scale gene expression profiles differentially expressed in situ in OA synovium of the knee joint.

Growth plate zonal microarray analysis shows upregulation of extracellular matrix genes and downregulation of metalloproteinases and cathepsins following irradiation

Although the growth plate matrix area fraction increases after irradiation, extracellular matrix (ECM) gene expression in this context has not been studied. The hypothesis was that normally expressed ECM genes would be upregulated after irradiation. The right limbs of six Sprague-Dawley 5-week-old rats were irradiated with the left limbs as controls. Half of the animals were harvested after 1 week and half after 2. Microarray was conducted from normal and irradiated tibial growth plate proliferative zone (PZ) and hypertrophic zone (HZ) chondrocytes separated by laser microdissection at each time point. In situ hybridization (ISH) and real-time polymerase chain reaction (PCR) were used to confirm expression of selected genes. At 1 and 2 weeks after irradiation, both normally expressed ECM genes and others not highly expressed in the normal growth plate showed upregulation. Metalloproteinases and cathepsins were downregulated. PZ gene expression after irradiation exhibited features of the normal HZ, suggesting premature terminal differentiation. ECM genes not highly expressed in the normal growth plate included several members of the small leucine-rich proteins and the ezrin-radixin-moesin family. The effects of irradiation on cathepsin K (Ctsk), integrin binding sialoprotein (Ibsp), and procollagen II alpha 1 (Col2a1), as determined by ISH and real-time PCR, were highly correlated with the microarray results. Accumulation of matrix following radiation injury to the growth plate correlated well with changes in gene expression. Upregulation of genes not normally highly expressed in the noninjured growth plate suggests their importance in the injury and repair response.

Expression stability of commonly used reference genes in canine articular connective tissues

Background

The quantification of gene expression in tissue samples requires the use of reference genes to normalise transcript numbers between different samples. Reference gene stability may vary between different tissues, and between the same tissue in different disease states. We evaluated the stability of 9 reference genes commonly used in human gene expression studies. Real-time reverse transcription PCR and a mathematical algorithm were used to establish which reference genes were most stably expressed in normal and diseased canine articular tissues and two canine cell lines stimulated with lipolysaccaride (LPS).

Results

The optimal reference genes for comparing gene expression data between normal and diseased infrapatella fat pad were RPL13A and YWHAZ (M = 0.56). The ideal reference genes for comparing normal and osteoarthritic (OA) cartilage were RPL13A and SDHA (M = 0.57). The best reference genes for comparing normal and ruptured canine cranial cruciate ligament were B2M and TBP (M = 0.59). The best reference genes for normalising gene expression data from normal and LPS stimulated cell lines were SDHA and YWHAZ (K6) or SDHA and HMBS (DH82), which had expression stability (M) values of 0.05 (K6) and 0.07 (DH82) respectively. The number of reference genes required to reduce pairwise variation (V) to <0.20 was 4 for cell lines, 5 for cartilage, 7 for cranial cruciate ligament and 8 for fat tissue. Reference gene stability was not related to the level of gene expression.

Conclusion

The reference genes demonstrating the most stable expression within each different canine articular tissue were identified, but no single reference gene was identified as having stable expression in all different tissue types. This study underlines the necessity to select reference genes on the basis of tissue and disease specific expression profile evaluation and highlights the requirement for the identification of new reference genes with greater expression stability for use in canine articular tissue gene expression studies.

Analysis of normal and osteoarthritic canine cartilage mRNA expression by quantitative polymerase chain reaction

The molecular basis to mammalian osteoarthritis (OA) is unknown. We hypothesised that the expression of selected proteases, matrix molecules, and collagens believed to have a role in the pathogenesis of OA would be changed in naturally occurring canine OA cartilage when compared to normal articular cartilage. Quantitative (real-time) reverse transcriptase-polymerase chain reaction assays were designed measuring the expression of selected matrix molecules (collagens and small leucine-rich proteoglycans), key mediators of the proteolytic degradation of articular cartilage (metalloproteinases, cathepsins), and their inhibitors (tissue inhibitors of matrix metalloproteinases). All data were normalised using a geometric mean of three housekeeping genes, and the results subjected to power calculations and corrections for multiple hypothesis testing. We detected increases in the expression of BGN, COL1A2, COL2A1, COL3A1, COL5A1, CSPG2, CTSB, CTSD, LUM, MMP13, TIMP1, and TNC in naturally occurring canine OA. The expression of TIMP2 and TIMP4 was significantly reduced in canine OA cartilage. The patterns of gene expression change observed in naturally occurring canine OA were similar to those reported in naturally occurring human OA and experimental canine OA. We conclude that the expression profiles of matrix-associated molecules in end-stage mammalian OA may be comparable but that the precise aetiologies of OA affecting specific joints in different species are presently unknown.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Chondrocyte genomics: implications for disease modification in osteoarthritis

Advances in genomic technologies have made genome-wide-association and gene-expression studies a reality. Despite technical and analytical challenges, the application of genomic technologies to osteoarthritis research will lead to a better understanding of the disease at the molecular level. Functional genomics will identify genes involved in the chondrocyte response to cartilage injury and cartilage repair, and will help clarify the role of chondrocytes in arthritis onset, progression and outcome. Systems biology will enable researchers to develop a full portrait of osteoarthritis, a complex and multifactorial disease that involves not only articular cartilage but also synovium, synovial fluid, subchondral bone and peripheral blood. Ultimately such an approach will result in novel diagnostic and therapeutic targets and better disease management.

Connective tissue growth factor/CCN2 overexpression in mouse synovial lining results in transient fibrosis and cartilage damage

OBJECTIVE

Characteristics of osteoarthritis (OA) include cartilage damage, fibrosis, and osteophyte formation. Connective tissue growth factor (CTGF; also known as CCN2), is found in high levels in OA chondrocytes and is frequently involved in fibrosis, bone formation, and cartilage repair. The present study was therefore undertaken to investigate the potential role of CTGF in OA pathophysiology.

METHODS

We transfected the synovial lining of mouse knee joints with a recombinant adenovirus expressing human CTGF and measured synovial fibrosis and proteoglycan content in cartilage on days 1, 3, 7, 14, and 28. Messenger RNA (mRNA) expression in synovium and cartilage was measured on days 3, 7, and 21.

RESULTS

CTGF induced synovial fibrosis, as indicated by accumulation of extracellular matrix and an increase in procollagen type I-positive cells. The fibrosis reached a maximum on day 7 and had reversed by day 28. Levels of mRNA for matrix metalloproteinase 3 (MMP-3), MMP-13, ADAMTS-4, ADAMTS-5, tissue inhibitor of metalloproteinases 1 (TIMP-1), and transforming growth factor beta were elevated in the fibrotic tissue. TIMP-1 expression was elevated on day 3, while expression of other genes did not increase until day 7 or later. CTGF induced proteoglycan depletion in cartilage as early as day 1. Maximal depletion was observed on days 3-7. Cartilage damage was reduced by day 28. A high level of MMP-3 mRNA expression was found in cartilage. CTGF overexpression did not induce osteophyte formation.

CONCLUSION

CTGF induces transient fibrosis that is reversible within 28 days. Overexpression of CTGF in knee joints results in reversible cartilage damage, induced either by the high CTGF levels or via factors produced by the CTGF-induced fibrotic tissue.

Microarray analysis of differential gene expression in temporomandibular joint condylar cartilage after experimentally induced osteoarthritis

OBJECTIVE

To identify the gene expression profile of mandibular condylar cartilage after experimentally induced osteoarthritis (OA).

DESIGN

We studied the gene expression levels in temporomandibular joint (TMJ) condylar cartilage during different stages of experimentally induced OA. The pathological characteristics of normal, early-stage and late-stage osteoarthritic TMJ cartilage were verified by histological techniques. The gene expression profiles in normal and osteoarthritic cartilage were measured by Affymetrix RAE230A microarrays. Some of the gene transcripts were confirmed by quantitative real-time reverse-transcription PCR analysis.

RESULTS

A comprehensive, differentially expressed, gene profile was obtained in TMJ cartilage during the progression of OA. In total, 138 genes and expressed sequence tags were up- or down-regulated at least 2-fold. Some of these genes have been shown to play a role in OA, including matrix-degrading proteases, protease inhibitors and genes involved in cell growth, apoptosis and bone remodeling. However, some genes that had never been reported to be related with OA, such as AQP3, SPP2, NOV, DKK3 and EGLN3, were consistently observed to be up-regulated in this study, suggesting they may be involved in OA progression.

CONCLUSION

This study provides a new gene expression profile of the progression of OA. Further study of these OA-related genes may provide new insights into understanding the molecular mechanisms underlying OA.

Blood-based biomarkers for detecting mild osteoarthritis in the human knee

OBJECTIVE

This study was designed to test the utility of a blood-based approach to identify mild osteoarthritis (OA) of the knee.

METHODS

Blood samples were drawn from 161 subjects, including 85 subjects with arthroscopically diagnosed mild OA of the knee and 76 controls. Following RNA isolation, an in-house custom cDNA microarray was used to screen for differentially expressed genes. A subset of selected genes was then tested using real-time RT-PCR. Logistic regression analysis was used to evaluate linear combinations of the biomarkers and receiver operating characteristic curve analysis was used to assess the discriminatory power of the combinations.

RESULTS

Genes differentially expressed (3543 genes) between mild knee OA and control samples were identified through microarray analysis. Subsequent real-time RT-PCR verification identified six genes significantly down-regulated in mild OA: heat shock 90kDa protein 1, alpha; inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase complex-associated protein; interleukin 13 receptor, alpha 1; laminin, gamma 1; platelet factor 4 (also known as chemokine (C-X-C motif) ligand 4) and tumor necrosis factor, alpha-induced protein 6. Logistic regression analysis identified linear combinations of nine genes--the above six genes, early growth response 1; alpha glucosidase II alpha subunit; and v-maf musculoaponeurotic fibrosarcoma oncogene homolog B (avian)--as discriminatory between subjects with mild OA and controls, with a sensitivity of 86% and specificity of 83% in a training set of 78 samples. The optimal biomarker combinations were then evaluated using a blind test set (67 subjects) which showed 72% sensitivity and 66% specificity.

CONCLUSIONS

Linear combinations of blood RNA biomarkers offer a substantial improvement over currently available diagnostic tools for mild OA. Blood-derived RNA biomarkers may be of significant clinical value for the diagnosis of early, asymptomatic OA of the knee.

First comprehensive mapping of cartilage transcripts to the human genome

We present the first comprehensive transcriptome-to-genome mapping for human cartilage. First, we determined that the cartilage transcriptome represents between 13,200 and 15,800 unique genes. Next, a subset of approximately 10,000 of the best characterized cartilage-expressed transcripts (CETs) was selected and mapped to the human genome. The distribution of CETs across the genome was found to be significantly different compared to the expected distribution. Furthermore, clusters of adjacent coordinately transcribed genes, as well as numerous "hot spots" and "cold spots" for transcription in cartilage, were identified. We propose that transcriptional control in cartilage can be exerted over genomic domains containing as few as four neighboring genes. Our findings, which are consistent with recent "chromatin domain" models of transcription, are further supported by our identification of CETs that putatively encode components of the HDAC- and Swi/SNF-mediated chromatin remodeling pathways. Our study illustrates the value of comprehensive high-resolution scans to detect transcription patterns within the human genome.

Gene expression during redifferentiation of human articular chondrocytes

OBJECTIVE

The aim of the present study was to investigate gene expression during the in vitro redifferentiation process of human articular chondrocytes isolated from clinical samples from patient undergoing an autologous chondrocyte transplantation therapy (ACT).

METHOD

Monolayer (ML) expanded human articular chondrocytes from four donors were cultured in a 3D pellet model and the redifferentiation was investigated by biochemistry, histology, immunohistochemistry and microarray analysis.

RESULTS

The culture expanded chondrocytes redifferentiated in the pellet model as seen by an increase in collagen type II immunoreactivity between day 7 and 14. The gene expression from ML to pellet at day 7 included an increase in cartilage matrix proteins like collagen type XI, tenascin C, dermatopontin, COMP and fibronectin. The late phase consisted of a strong downregulation of extracellular signal-regulated protein kinase (ERK-1) and an upregulation of p38 kinase and SOX-9, suggesting that the late phase mimicked parts of the signaling processes involved in the early chondrogenesis in limb bud cells. Other genes, which indicated a transition from proliferation to tissue formation, were the downregulated cell cycle genes GSPT1 and the upregulated growth-arrest-specific protein (gas). The maturation of the pellets included no signs of hypertrophy or apoptosis as seen by downregulation of collagen type X, Matrix Gla protein and increased expression of caspase 3.

CONCLUSION

Our data show that human articular chondrocytes taken from surplus cells of patient undergoing ACT treatment and expanded in ML, redifferentiate and form cartilage like matrix in vitro and that this dynamic process involves genes known to be expressed in early chondrogenesis.

Differential gene expression and regulation of the bone morphogenetic protein antagonists follistatin and gremlin in normal and osteoarthritic human chondrocytes and synovial fibroblasts

OBJECTIVE

To compare gene expression in normal and osteoarthritic (OA) human chondrocytes using microarray technology. Of the novel genes identified, we selected follistatin, a bone morphogenetic protein (BMP) antagonist, and investigated its expression/regulation as well as that of 3 other antagonists, gremlin, chordin, and noggin, in normal and OA chondrocytes and synovial fibroblasts.

METHODS

Basal and induced gene expression were determined using real-time polymerase chain reaction. Gene regulation was monitored following treatment with inflammatory, antiinflammatory, growth, and developmental factors. Follistatin protein production was measured using a specific enzyme-linked immunosorbent assay, and localization of follistatin and gremlin in cartilage was determined by immunohistochemical analysis.

RESULTS

All BMP antagonists except noggin were expressed in chondrocytes and synovial fibroblasts. Follistatin and gremlin were significantly up-regulated in OA chondrocytes but not in OA synovial fibroblasts. Chordin was weakly expressed in normal and OA cells. Production of follistatin protein paralleled the gene expression pattern. Follistatin and gremlin were expressed preferentially by the chondrocytes at the superficial layers of cartilage. Tumor necrosis factor alpha and interferon-gamma significantly stimulated follistatin expression but down-regulated expression of gremlin. Interleukin-1beta (IL-1beta) had no effect on follistatin but reduced gremlin expression. Conversely, BMP-2 and BMP-4 significantly stimulated expression of gremlin but down-regulated that of follistatin. IL-13, dexamethasone, transforming growth factor beta1, basic fibroblast growth factor, platelet-derived growth factor type BB, and endothelial cell growth factor down-regulated the expression of both antagonists.

CONCLUSION

This study is the first to show the possible involvement of follistatin and gremlin in OA pathophysiology. The increased activin/BMP-binding activities of these antagonists could affect tissue remodeling. The data suggest that follistatin and gremlin might appear at different stages during the OA process, making them interesting targets for the treatment of this disease.

Genomics of osteoarthritis

PURPOSE OF REVIEW

This review addresses the progress in three major fields of "genomics of osteoarthritis" over the past year: genetic alterations thought to be important for the initiation and progression of osteoarthritis, differential gene expression analysis, and functional genomics of osteoarthritis.

RECENT FINDINGS

Distinct genetic risk factors may predispose different joint sites to osteoarthritis, and although clear loci for susceptibility genes for common osteoarthritis have yet to emerge from the epidemiological studies, new approaches are narrowing down known loci. The search for specific genes using cDNA array technology has further demonstrated its potential in arthritis research as a powerful tool that could further provide biological insights into disease mechanisms, osteoarthritis polymorphic subtypes, the molecular validation of animal models, and the monitoring of drug activity on gene expression levels. Gene expression analysis has further characterized the striking shift in the gene expression pattern during "dedifferentiation" of chondrocytes in vitro as well as added depth to the phenotype of differentiated versus undifferentiated mesenchymal stem cells. Several new molecules potentially relevant to the disease process were identified, among them beta2-microglobulin (B2M), clusterin, and chitinase-like molecule 2.

SUMMARY

Functional genomic approaches will in the future allow to complement traditional biochemistry and molecular biology. Although there are limitations to cDNA array technology, "molecular portraits" of osteoarthritic chondrocytes in vivo and in vitro can be produced to analyze whole or large biologic systems rather than just single aspects of it. This will stimulate the testing of new markers, which are needed for the diagnosis and monitoring of osteoarthritis.