Genomics of osteoarthritis

Articular cartilage gene expression patterns in the tissue surrounding the impact site following applications of shear and axial loads

BACKGROUND

Osteoarthritis is a degradative joint disease found in humans and commercial swine which can develop from a number of factors, including prior joint trauma. An impact injury model was developed to deliver in vitro loads to disease-free porcine patellae in a model of OA.

METHODS

Axial impactions (2000 N normal) and shear impactions (500 N normal with induced shear forces) were delivered to 48 randomly assigned patellae. The patellae were then cultured for 0, 3, 7, or 14 days following the impact. Specimens in the tissue surrounding the loading site were harvested and expression of 18 OA related genes was studied via quantitative PCR. The selected genes were previously identified from published work and fell into four categories: cartilage matrix, degradative enzymes, inflammatory response, and apoptosis.

RESULTS

Type II collagen (Col2a1) showed significantly lower expression in shear vs. axial adjacent tissue at day 0 and 7 (fold changes of 0.40 & 0.19, respectively). In addition, higher expression of degradative enzymes and Fas, an apoptosis gene, was observed in the shear specimens.

CONCLUSIONS

The results suggest that a more physiologically valid shear load may induce more damage to surrounding articular cartilage than a normal load alone.

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.

Inhibitory effects of EGb761 on the expression of matrix metalloproteinases (MMPs) and cartilage matrix destruction

Cytokines such as tumor necrosis factor alpha (TNF-α)-induced expression of matrix metalloproteinase (MMP) play a pivotal role in the destruction of articular cartilage in patients who are suffering from osteoarthritis (OA). Collagen type II, the basis for articular cartilage, can be degraded by MMP-1, MMP-3, and 13. EGb761, the standardized extract of Ginkgo biloba produced by Dr. Willar Schwabe Pharmaceuticals, has shown its anti-inflammatory capacity. This study aimed to determine a mechanism whereby EGb761 may inhibit cartilage degradation. Our results indicated that pretreatment with EGb761 abolishes MMP-1, MMP-3, and MMP-13 gene expression and protein expression induced by TNF-α in human chondrocyte monolayer. In addition, the reduction of the tissue inhibitor of metalloproteinase-1(TIMP-1) and metalloproteinase-2 gene expression induced by TNF-α was rescued by pretreatment with EGb761. Importantly, TNF-α-induced degradation of collagen type II was ameliorated by EGb761 in a dose-dependent manner. Mechanistically, our results indicated that EGb761 treatment attenuated TNF-α-induced NF-κB activation. These actions of EGb761 suggest a mechanism by which EGb761 may act to prevent cartilage breakdown in arthritis.

Progression of Gene Expression Changes following a Mechanical Injury to Articular Cartilage as a Model of Early Stage Osteoarthritis

An impact injury model of early stage osteoarthritis (OA) progression was developed using a mechanical insult to an articular cartilage surface to evaluate differential gene expression changes over time and treatment. Porcine patellae with intact cartilage surfaces were randomized to one of three treatments: nonimpacted control, axial impaction (2000 N), or a shear impaction (500 N axial, with tangential displacement to induce shear forces). After impact, the patellae were returned to culture for 0, 3, 7, or 14 days. At the appropriate time point, RNA was extracted from full-thickness cartilage slices at the impact site. Quantitative real-time PCR was used to evaluate differential gene expression for 18 OA related genes from four categories: cartilage matrix, degradative enzymes and inhibitors, inflammatory response and signaling, and cell apoptosis. The shear impacted specimens were compared to the axial impacted specimens and showed that shear specimens more highly expressed type I collagen (Col1a1) at the early time points. In addition, there was generally elevated expression of degradative enzymes, inflammatory response genes, and apoptosis markers at the early time points. These changes suggest that the more physiologically relevant shear loading may initially be more damaging to the cartilage and induces more repair efforts after loading.

Evaluating the clinical relevance of codon 594 (g>a) polymorphism of estrogen receptor alpha in knee osteoarthritis

It has been reported that oestrogen receptor alpha (ER-α) polymorphisms are associated with knee osteoarthritis (OA). In this study, we assessed whether there was any association between the codon 594 (G>A) polymorphism in ER-α and radiographic features of OA or patient function. Radiographs, WOMAC score and patient reported time of symptom onset were assessed in 194 patients presenting for total knee replacement at Ramathibodi hospital over a one year period. ESR-1 genotyping was assessed. There were 107 (55.15%) patients with common homozygote (GG), 78 (40.20%) patients with heterozygote (GA) and nine (4.65%) patients with rare homozygote (AA). There was poor correlation (r = <0.2) between group difference in the radiographic parameters, time of onset of symptom , or in WOMAC scores. This polymorphism is not associated with the clinical features of knee osteoarthritis. The role of this polymorphism is unlikely then to be used as a biological marker predicting the progression of knee OA.

Role of hormones in cartilage and joint metabolism: understanding an unhealthy metabolic phenotype in osteoarthritis

OBJECTIVE

Joint health is affected by local and systemic hormones. It is well accepted that systemic factors regulate the metabolism of joint tissues, and that substantial cross-talk between tissues actively contributes to homeostasis. In the current review, we try to define a subtype of osteoarthritis (OA), metabolic OA, which is dependent on an unhealthy phenotype.

METHODS

Peer-reviewed research articles and reviews were reviewed and summarized. Only literature readily available online, either by download or by purchase order, was included.

RESULTS

OA is the most common joint disease and is more common in women after menopause. OA is a disease that affects the whole joint, including cartilage, subchondral bone, synovium, tendons, and muscles. The clinical endpoints of OA are pain and joint space narrowing, which is characterized by cartilage erosion and subchondral sclerosis, suggesting that cartilage is a central tissue of joint health. Thus, the joint, more specifically the cartilage, may be considered a target of endocrine function in addition to the well-described traditional risk factors of disease initiation and progression such as long-term loading of the joint due to obesity. Metabolic syndrome affects a range of tissues and may in part be molecularly described as a dysregulation of cytokines, adipokines, and hormones (e.g., estrogen and thyroid hormone). Consequently, metabolic imbalance may both directly and indirectly influence joint health and cartilage turnover, altering the progression of diseases such as OA.

CONCLUSIONS

There is substantial evidence for a connection between metabolic health and development of OA. We propose that more focus be directed to understanding this connection to improve the management of menopausal health and associated comorbidities.

Human YKL39 (chitinase 3-like protein 2), an osteoarthritis-associated gene, enhances proliferation and type II collagen expression in ATDC5 cells

Human YKL39 (chitinase 3-like protein 2/CHI3L2) is a secreted 39kDa protein produced by articular chondrocytes and synoviocytes. Recent studies showed that hYKL-39 expression is increased in osteoarthritic articular chondrocytes suggesting the involvement of hYKL-39 in the progression of osteoarthritis (OA). However little is known regarding the molecular function of hYKL-39 in joint homeostasis. Sequence analyses indicated that hYKL-39 has significant identity with the human chitotorisidase family molecules, although it is considered that hYKL-39 has no enzymatic activity since it lacks putative chitinase catalytic motif. In this study, to examine the molecular function of hYKL-39 in chondrocytes, we overexpressed hYKL-39 in ATDC5 cells. Here we report that hYKL-39 enhances colony forming activity, cell proliferation, and type II collagen expression in these cells. These data suggest that hYKL-39 is a novel growth and differentiation factor involved in cartilage homeostasis.

Rs143383 in the growth differentiation factor 5 (GDF5) gene significantly associated with osteoarthritis (OA)-a comprehensive meta-analysis

Family, twin, adoption studies show osteoarthritis (OA) has a substantial genetic component. Several studies have shown an association between OA and Growth Differentiation Factor 5 (GDF5), some others have not. Thus, the status of the OA-GDF5 association is uncertain. This meta-analysis was applied to case-control studies of the association between OA and GDF5 to assess the joint evidence for the association, the influence of individual studies, and evidence for publication bias. Relevant studies were identified from the following electronic databases: MEDLINE and current contents before Feb. 2012. For the case-control studies, the authors found 1) support for the association between OA and GDF5. The rs143383 polymorphism was significantly associated with OA [fixed: OR and 95% CI: 1.193 (1.139-1.249), p < 0.001; random: OR and 95% CI: 1.204 (1.135-1.276), p < 0.001], 2) no evidence that this association was accounted for by any one study, and 3) no evidence for publication bias. Although the effect size of the association between OA and GDF5 is small, there is suggestive evidence for an association. Further studies are needed to clarify what variant of GDF5 (or some nearby gene) accounts for this association.

MATN3 gene polymorphism is associated with osteoarthritis in Chinese Han population: a community-based case-control study

Background. The matrilin, especially matrilin-3 (MATN3), are reported to play important roles in the pathophysiology of osteoarthritis (OA). To explore the relationship between MATN3 SNP6 (rs8176070) and primary OA, we conducted a community-based case-control study. Methods. A total of 732 community residents aged 40–84 years participated in the community-based study in Northeast China. After taking physical and radiographic examinations, 420 of the residents were diagnosed OA (216 women and 204 men). The other 312 individuals without any symptoms of osteoarthritis or signs in the radiographs (156 women and 156 men) were considered as healthy controls. After obtaining the DNA of case and control groups, genotypes of the MATN3 SNP6 were determined by polymerase chain reaction followed by restriction enzyme digestion. The numbers of patients with different OA subtypes were also calculated. Results. The distribution of genotypes and alleles of the MATN3 SNP6 between OA patients and controls was different significantly. The BB carrier tends to be associated with the increased osteoarthritis (P = 0.025, OR = 1.724, 95% CI = 1.071–2.77), especially the knee osteoarthritis (P = 0.021, OR = 2.402, 95% CI = 1.141–5.060) and lumber osteoarthritis (P = 0.020, OR = 1.880, 95% CI = 1.103–3.204). Bb carrier increased hand osteoarthritis risk (P = 0.002, OR = 5.380, 95% CI = 1.828–15.835). The B allele might have an effect on the increased knee osteoarthritis (P = 0.000, OR = 3.143, 95% CI = 2.283–4.328). Conclusion. These findings suggest that the MATN3 gene polymorphism might be associated with osteoarthritis in the Chinese Han population.

A genetic association study between growth differentiation factor 5 (GDF 5) polymorphism and knee osteoarthritis in Thai population

Objective

Osteoarthritis (OA) is a multi-factorial disease and genetic factor is one of the important etiologic risk factors. Various genetic polymorphisms have been elucidated that they might be associated with OA. Recently, several studies have shown an association between Growth Differentiation Factor 5(GDF5) polymorphism and knee OA. However, the role of genetic predisposing factor in each ethnic group cannot be replicated to all, with conflicting data in the literatures. Therefore, the aim of this study was to investigate the association between GDF5 polymorphism and knee OA in Thai population.

Materials and Methods

One hundred and ninety three patients aged 54-88 years who attended Ramathibodi Hospital were enrolled. Ninety cases with knee OA according to American College of Rheumatology criteria and one hundred and three cases in control group gave informed consent. Blood sample (5 ml) were collected for identification of GDF5 (rs143383) single nucleotide polymorphism by PCR/RFLP according to a standard protocol. This study protocol was approved by the Ethics Committee on human experimentation of Ramathibodi Hospital Faculty of Medicine, Mahidol University. Odds ratios (OR) and 95% confidence intervals were calculated for the risk of knee OA by genotype (TT, TC and CC) and allele (T/C) analyses.

Results

The baseline characteristics between two groups including job, smoking and activity were not different, except age and BMI. The entire cases and controls were in Hardy-Weinberg equilibrium (p > 0.05). The OA knee group (n = 90) had genotypic figure which has shown by TT 42.2% (n = 38), TC 45.6% (n = 41) and CC 12% (n = 11), whereas the control group (n = 103) revealed TT 32% (n = 33), TC 45.6% (n = 47), and CC 22.3% (n = 23), respectively. Genotypic TT increased risk of knee OA as compared to CC [OR = 2.41 (P = 0.04, 95%CI = 1.02-5.67)]. In the allele analysis, the T allele was found to be significantly associated with knee OA [OR = 1.53 (P = 0.043, 95%CI = 1.01-2.30)].

Conclusion

These data suggested that GDF5 polymorphism has an association with knee OA in Thai ethnic. This finding also supports the hypothesis that OA has an important genetic component in its etiology, and GDF5 protein might play important role in the pathophysiology of the disease.

Regulation of SOX9 in normal and osteoarthritic equine articular chondrocytes by hyperosmotic loading

OBJECTIVES

SOX9 is a transcription factor that is essential for cartilage extracellular matrix (ECM) formation. Osteoarthritis (OA) is characterised by a loss of cartilage ECM. In chondrocytes SOX9 gene expression is regulated by osmotic loading. Here we characterise SOX9 mRNA regulation through static and cyclical application of hyperosmotic conditions in normal and OA monolayer equine chondrocytes. Furthermore, we investigate whether extracellular signal-regulated protein kinase (ERK)1/2 mitogen-activated protein kinases (MAPK) pathways have a role in this regulation of SOX9.

METHODS

Equine chondrocytes harvested from normal or OA joints were subjected to different osmotic loading patterns as either primary (P0) or passaged (P2) cells. The involvement of MEK-ERK signalling was demonstrated by using pharmacological inhibitors. In addition SOX9 gene stability was determined. Levels of transcripts encoding SOX9, Col2A1 and aggrecan were measured using qRT-PCR. De novo glycosaminoglycan synthesis of explants was determined with (35)S sulphate during static hyperosmolar loading.

RESULTS

MEK-ERK signalling increases glycosaminoglycans (GAG) synthesis in explants. Static hyperosmotic conditions significantly reduced SOX9 mRNA in normal P2 and OA P0 but not normal P0 chondrocytes. SOX9 mRNA was stabilised by hyperosmotic conditions. Cyclical loading of normal P2 and OA P0 but not normal P0 cells led to an increase in SOX9 gene expression and this was prevented by MEK1/2 inhibition.

CONCLUSIONS

The response to osmotic loading of SOX9 mRNA is dependent on the nature of the osmotic stimulation and the chondrocyte phenotype. This variation may be important in disease progression.

Heritability estimates and linkage analysis of 23 short tandem repeat loci on chromosomes 2, 11, and 12 in an endemic osteochondropathy in China

OBJECTIVE

To estimate the heritability of Kashin-Beck disease (KBD) in first-degree relatives and to identify chromosome regions likely to contain susceptibility loci for KBD.

METHODS

A total of 331 probands with confirmed KBD in their pedigrees were selected from 9331 residents in 17 KBD villages of Linyou county, northwestern China. The heritability (h(2)) in first-degree relatives was estimated by using Falconer's formula. The segregation ratio was calculated by the Li-Mantel-Gart method. A total of 23 short tandem repeat (STR) loci on chromosomes 2, 11, and 12 were used to identify the susceptibility genes for KBD by linkage analysis using the GENEHUNTER program in 19 KBD pedigrees.

RESULTS

The general prevalence rate of KBD was 13.75% in the 17 KBD villages, lower than that of 20.88% in the first-degree relatives of the KBD probands. In the first-degree relatives, the heritability was 0.064 and the segregation ratio 35.10% (p < 0.05). Slight evidence for heritability was detected only in locus D12S1725 with a logarithm of odds (LOD) score of 1.95. However, the nonparametric linkage (NPL) scores showed no linkage between KBD and the 23 loci; the maximum NPL score was 1.59 for locus D12S1725.

CONCLUSIONS

Our results show that 35.10% of the heritability is attributable to genetic variation for the KBD phenotype among individuals of Linyou county, and the segregation ratio supports a multifactorial inheritance of KBD. There is no significant linkage between KBD and the 23 markers in the Linyou population examined; however, markers near the locus D12S1725 may indicate loci for further study.

Association of the calcitonin gene (CA) polymorphism with osteoarthritis of the knee in a Mexican mestizo population

Osteoarthritis (OA) is the most common form of destructive joint disease that is characterized by the degeneration of the articular cartilage, synovial membrane, joint capsule, and subchondral bone. The knee is a joint commonly affected for OA. Calcitonin (CT) has been suggested to have chondroprotective effects; therefore, could play a role in the pathogenesis of OA of the knee. Genetic variations in or adjacent to the CT gene may be associated with primary OA development. We conducted a case-control association study in which we examined the correlation between a dinucleotide (cytosine-adenine, CA) repeat polymorphism at the CT locus and OA of the knee in 88 patients with OA and in 111 control subjects from the Mexican mestizo population. Allele A and genotype AG frequencies were significantly higher in patients with OA than in control subjects (56.3 vs. 43.2%; p<0.001 and 40.9 vs. 26.1%; p=0.027, respectively), and were associated with the presence of OA of the knee (odds ratio [OR], 2.62; 95% confidence interval [95% CI], 1.30-5.27, and OR, 1.93; 95% CI, 1.04-3.58, respectively) using a logistic regression model adjusted for gender, age and Body mass index (BMI). The GG genotype was associated with a lower risk of OA development of the knee; thus, it may constitute a protective factor against this disease (OR, 0.40; 95% CI, 0.16-0.98). In summary, we conclude that the dinucleotide CA polymorphism in the CT gene may become a useful marker for genetic studies of OA of the knee in Mexican population.

ADAM-8 isolated from human osteoarthritic chondrocytes cleaves fibronectin at Ala(271)

OBJECTIVE

Fibronectin fragments are thought to play a critical role in the initiation and progression of cartilage degradation in arthritis. In a recent study, fibronectin neoepitopes resulting from cleavage of intact fibronectin at the Ala(271)/Val(272) scissile bond, generating an approximately 30-kd fragment with the new C-terminus VRAA(271) and an approximately 50-85-kd fragment with the new N-terminus (272)VYQP, were identified in osteoarthritis (OA) cartilage. The present study was undertaken to isolate the enzymes responsible for this cleavage from human OA chondrocytes.

METHODS

Fibronectin-degrading activity in human OA chondrocyte-conditioned medium (OACCM) was purified using conventional chromatography. A fluorescent peptide was developed based on the fibronectin scissile bond (269)RAA downward arrowVal(272), and this peptide was used to track fibronectinase activity during purification. Western blotting with antibodies that detect the fibronectin neoepitopes VRAA(271) and (272)VYQP was used to confirm cleavage of intact fibronectin by the enzymatically active fractions. Mass spectrometry was used to identify the proteins found in the fibronectinase-enriched fractions, with further confirmation by Western blotting. In addition, a recombinant enzyme identified by mass spectrometry was tested by Western blotting and dimethylmethylene blue assay for its ability to produce fibronectin neoepitopes in OA cartilage.

RESULTS

Purification of OACCM by chromatography resulted in isolation of a fibronectin-degrading enzyme, and mass spectrometry identified ADAM-8 as the fibronectinase present in these preparations. Furthermore, treatment of OA cartilage with recombinant human ADAM-8 promoted cartilage catabolism.

CONCLUSION

The results of this study identify ADAM-8 as a fibronectinase in human OA chondrocytes. Because ADAM-8 is capable of producing the fibronectin neoepitopes VRAA(271) and (272)VYQP in human OA cartilage, this enzyme may be an important mediator of cartilage catabolism.

Genetics in osteoarthritis

Osteoarthritis is a degenerative articular disease with complex pathogeny because diverse factors interact causing a process of deterioration of the cartilage. Despite the multifactorial nature of this pathology, from the 50's it s known that certain forms of osteoarthritis are related to a strong genetic component. The genetic bases of this disease do not follow the typical patterns of mendelian inheritance and probably they are related to alterations in multiple genes. The identification of a high number of candidate genes to confer susceptibility to the development of the osteoarthritis shows the complex nature of this disease. At the moment, the genetic mechanisms of this disease are not known, however, which seems clear is that expression levels of several genes are altered, and that the inheritance will become a substantial factor in future considerations of diagnosis and treatment of the osteoarthritis.

[Genetics in osteoarthritis]

Osteoarthritis is a degenerative articular pathology with complex pathogeny because diverse factors interact causing a process of deterioration of the cartilage. In spite of the multifactorial nature of this pathology, from years 50 one knows that certain forms of osteoarthritis are related to a strong genetic component. The genetic bases of this disease do not follow the typical patterns of mendelian inheritance and probably they are related to alterations in multiple genes. The identification of a high number of candidates genes to confer susceptibility to the development of the osteoarthritis shows the complex nature of this disease. At the moment, the genetic mechanisms of this pathology are not known, however, which seems clear is that levels of expression of several genes are altered, and that the inheritance will become a substantial factor in future considerations of diagnosis and treatment of the osteoarthitis.

Gene expression profiling of chondrocytes from a porcine impact injury model

OBJECTIVE

To identify differentially expressed genes between axially impacted and control articular cartilage taken from porcine patellae maintained in organ culture for 14 days.

METHODS

Porcine patellae were impacted perpendicular to the articular surface to create an impact injury. Intact patellae (control and impacted) were maintained in culture for 14 days. Total RNA was then extracted from the articular cartilage beneath the impaction and used to prepare two Serial Analysis of Gene Expression (SAGE) libraries. Approximately 42,500 SAGE long tags were sequenced from the libraries. The expression of select genes was confirmed by quantitative real-time PCR analysis.

RESULTS

Thirty-nine SAGE tags were significantly differentially expressed in the impacted and control libraries, representing 30 different annotated pig genes. These genes represented gene products associated with matrix molecules, iron and phosphate transport, protein biosynthesis, skeletal development, cell proliferation, lipid metabolism and the inflammatory response. Twenty-three of the 30 genes were down-regulated in the impacted library and five were up-regulated in the impacted library. Quantitative real-time PCR follow-up of four genes supported the results found with SAGE.

CONCLUSION

We have identified 30 putative genes differentially expressed in a porcine impact injury model and validated these findings for four of these genes using real-time PCR. Results using this impact injury model have contributed further evidence that damaged chondrocytes may de-differentiate into fibroblast-like cells and proliferate in an attempt to repair themselves. Additional work is underway to study these genes in further detail at earlier time points to provide a more complete story about the fate of chondrocytes in articular cartilage following an injury.

Normalization and gene p-value estimation: issues in microarray data processing

Introduction

Numerous methods exist for basic processing, e.g. normalization, of microarray gene expression data. These methods have an important effect on the final analysis outcome. Therefore, it is crucial to select methods appropriate for a given dataset in order to assure the validity and reliability of expression data analysis.

Furthermore, biological interpretation requires expression values for genes, which are often represented by several spots or probe sets on a microarray. How to best integrate spot/probe set values into gene values has so far been a somewhat neglected problem.

Results

We present a case study comparing different between-array normalization methods with respect to the identification of differentially expressed genes. Our results show that it is feasible and necessary to use prior knowledge on gene expression measurements to select an adequate normalization method for the given data. Furthermore, we provide evidence that combining spot/probe set p-values into gene p-values for detecting differentially expressed genes has advantages compared to combining expression values for spots/probe sets into gene expression values. The comparison of different methods suggests to use Stouffer’s method for this purpose.

The study has been conducted on gene expression experiments investigating human joint cartilage samples of Osteoarthritis related groups: a cDNA microarray (83 samples, four groups) and an Affymetrix (26 samples, two groups) data set.

Conclusion

The apparently straight forward steps of gene expression data analysis, e.g. between-array normalization and detection of differentially regulated genes, can be accomplished by numerous different methods. We analyzed multiple methods and the possible effects and thereby demonstrate the importance of the single decisions taken during data processing. We give guidelines for evaluating normalization outcomes. An overview of these effects via appropriate measures and plots compared to prior knowledge is essential for the biological interpretation of gene expression measurements.

Regulation of type II collagen expression by histone deacetylase in articular chondrocytes

Histone deacetylase (HDAC) regulates various cellular processes by modulating gene expression. Here, we investigated the role of HDAC in the expression of type II collagen, a marker of differentiated chondrocytes. We found that HDAC activity in primary articular chondrocytes decreases during dedifferentiation induced by serial monolayer culture and that the activity recovered during redifferentiation induced by three-dimensional culture in a cell pellet. Inhibition of HDAC with trichostatin A or PXD101 was sufficient to block type II collagen expression in primary culture chondrocytes. HDAC inhibition also blocked the redifferentiation of dedifferentiated chondrocytes by suppressing the synthesis and accumulation of type II collagen. HDAC inhibition promoted the expression of Wnt-5a, which is known to inhibit type II collagen expression, and knockdown of Wnt-5a blocked the ability of HDAC inhibitors to suppress type II collagen expression. In addition, the induction of Wnt-5a expression by HDAC inhibitors was associated with acetylation of the Wnt-5a promoter. Taken together, our results suggest that HDAC promotes type II collagen expression by suppressing the transcription of Wnt-5a.

Increased expression of chitinase 3-like protein 1 secondary to joint immobility

Previous studies have established mechanical stimulation of joints is necessary to maintain the structure and function of the articular cartilage. Immobilization of the rat knee joint induces cartilage degeneration and reduces the joint range of motion, two of the clinical parameters used to define a joint contracture. We hypothesized chondrocytes from articular cartilage increase their expression of the chitinase 3-like protein 1 (CHI3L1) gene in response to joint immobility. We selected the CHI3L1 gene on the basis of its identification as a differentially expressed gene in the articular cartilage obtained from immobilized rat knee joints. Expression of CHI3L1 mRNA was increased after 2 and 4 weeks of immobility. A time-course study revealed that CHI3L1 immuno-reactivity was increased at 2 and 4 weeks and return to basal levels at all later time points. CHI3L1 gene adds to the list of differentially expressed genes defining the response of cartilage to joint immobility. Our data confirm a protective role for CHI3L1 in the initial phase of degeneration induced by immobility.

Genetic influences on joint contractures secondary to immobilization

The primary research question of this study queries whether, beyond environmental conditions, genetic factors affect the development of joint contractures. We hypothesized that intrinsic genetic factors influence the severity of joint contractures developing secondary to joint immobilization. Forty rats from four inbred rat strains had one leg immobilized in knee flexion for 4 weeks. The contracture was measured mechanically as the lack of range of motion to a standardized torque. Using the contralateral leg as a control, the average severity of the contracture could be calculated and compared between strains. All immobilized legs presented knee contractures after 4 weeks of immobilization. Two strains (Dark Agouti and Fisher 344) showed a larger mean knee contracture than those of the two other rat strains (Augustus Copenhagen Irish and Brown Norway). Environmental factors, such as immobility, are usually identified as a cause of a joint contracture. These results demonstrate that, in addition to mechanical factors in the environment of a joint, intrinsic genetic factors participate in the process leading to joint contracture. This demonstration has important consequences for directing future research and may lead to interventions to help patients at risk of developing joint contractures.

Establishment of a Reliable Method for Direct Proteome Characterization of Human Articular Cartilage

Articular cartilage consists mainly of extracellular matrix, mostly made of collagens and proteoglycans. These macromolecules have so far impaired the detailed two-dimensional electrophoresis-based proteomic analysis of articular cartilage. Here we describe a method for selective protein extraction from cartilage, which excludes proteoglycans and collagen species, thus allowing direct profiling of the protein content of cartilage by two-dimensional electrophoresis. Consistent electrophoretic patterns of more than 600 protein states were reproducibly obtained after silver staining from 500 mg of human articular cartilage from joints with diverse pathologies. The extraction yield increased when the method was applied to a chondrosarcoma sample, consistent with selective extraction of cellular components. Nearly 200 of the most intensely stained protein spots were analyzed by MALDI-TOF mass spectrometry after trypsin digestion. They represented 127 different proteins with diverse functions. Our method provides a rapid, efficient, and pertinent alternative to previously proposed approaches for proteomic characterization of cartilage phenotypes. It will be useful for detecting protein expression patterns that relate pathophysiological processes of cartilaginous tissues such as osteoarthritis and chondrosarcoma.

Association of matrilin-3 polymorphisms with spinal disc degeneration and osteoarthritis of the first carpometacarpal joint of the hand

BACKGROUND

Seven polymorphisms in the matrilin-3(MATN3) gene were previously tested for genetic association with hand osteoarthritis in an Icelandic cohort. One of the variants, involving a conserved amino acid substitution (T303M; SNP5), was related to idiopathic hand osteoarthritis.

OBJECTIVES

To investigate SNP5 and two other promising polymorphisms (rs2242190; SNP3, rs8176070; SNP6) for association with radiographic and symptomatic hand osteoarthritis phenotypes, as well as other heritable phenotypes.

METHODS

Polymorphisms were examined in two distinct cohorts of subjects: a population based sample from the Rotterdam study (n = 809), and affected siblings from the genetics, osteoarthrosis and progression (GARP) study (n = 382).

RESULTS

The originally described association of T303M with the hand osteoarthritis phenotype was not observed in the populations studied. In the Rotterdam sample, however, carrying the T allele of T303M conferred an odds ratio of 2.9 (95% confidence interval (CI), 1.2 to 7.3; p = 0.02) for spinal disc degeneration. In the GARP study, carriers of the A allele of SNP6 had an odds ratio of 2.0 (95% CI, 1.3 to 3.1, p = 0.004) for osteoarthritis of the first carpometacarpal joint (CMC1) as compared with the Rotterdam sample as a control group. Subsequent haplotype analysis showed that a common haplotype, containing the risk allele of SNP6, conferred a significant risk in sibling pairs with CMC1 osteoarthritis (odds ratio = 1.7 (95% CI, 1.1 to 2.7, p = 0.02)).

CONCLUSIONS

These associations suggest that the MATN3 region also determines susceptibility to spinal disc degeneration and CMC1 osteoarthritis.

Upregulation of apoptotic and matrix-related gene expression during fresh osteochondral allograft storage

We identified changes in proapoptotic and extracellular matrix-related gene expression with prolonged storage of fresh osteochondral allografts using gene array analysis to better understand the process of graft degradation during storage. Six human distal femurs were obtained according to standard organ harvesting protocol and stored in serum-free allograft media. Each was examined at baseline (within 72 hours postmortem), 21 days (average time of implantation), and 35 days (maximum time to implantation) for proapoptotic and extracellular matrix-related gene expression using two 100-gene microarrays, cell viability using confocal microscopy, and proteoglycan synthesis via SO4 incorporation. We found numerous genes showing upregulation associated with increased storage time, including CD30, CD30 ligand, Fas, Fas ligand, tumor necrosis factor-alpha, and several caspases. Cell viability and proteoglycan synthesis also were significantly decreased with increased storage. Loss of chondrocytes via apoptosis is likely a key determinant of osteochondral allograft viability during storage, whereas extracellular matrix degeneration may occur at a later stage. These findings provide targets for future media modulation. Improved graft viability and the potential for lengthened storage periods through improved storage conditions may improve clinical outcomes and availability of fresh osteochondral allografts.

Association between the abnormal expression of matrix-degrading enzymes by human osteoarthritic chondrocytes and demethylation of specific CpG sites in the promoter regions

OBJECTIVE

To investigate whether the abnormal expression of matrix metalloproteinases (MMPs) 3, 9, and 13 and ADAMTS-4 by human osteoarthritic (OA) chondrocytes is associated with epigenetic "unsilencing."

METHODS

Cartilage was obtained from the femoral heads of 16 patients with OA and 10 control patients with femoral neck fracture. Chondrocytes with abnormal enzyme expression were immunolocalized. DNA was extracted, and the methylation status of the promoter regions of MMPs 3, 9, and 13 and ADAMTS-4 was analyzed with methylation-sensitive restriction enzymes, followed by polymerase chain reaction amplification.

RESULTS

Very few chondrocytes from control cartilage expressed the degrading enzymes, whereas all clonal chondrocytes from late-stage OA cartilage were immunopositive. The overall percentage of non-methylated sites was increased in OA patients (48.6%) compared with controls (20.1%): 20% versus 4% for MMP-13, 81% versus 47% for MMP-9, 57% versus 30% for MMP-3, and 48% versus 0% for ADAMTS-4. Not all CpG sites were equally susceptible to loss of methylation. Some sites were uniformly methylated, whereas in others, methylation was generally absent. For each enzyme, there was 1 specific CpG site where the demethylation in OA patients was significantly higher than that in controls: at -110 for MMP-13, -36 for MMP-9, -635 for MMP-3, and -753 for ADAMTS-4.

CONCLUSION

This study provides the first evidence that altered synthesis of cartilage-degrading enzymes by late-stage OA chondrocytes may have resulted from epigenetic changes in the methylation status of CpG sites in the promoter regions of these enzymes. These changes, which are clonally transmitted to daughter cells, may contribute to the development of OA.

Chondrocyte cluster formation in agarose cultures as a functional assay to identify genes expressed in osteoarthritis

Understanding altered gene expression in osteoarthritic cartilage can lead to new targets for drug intervention. We established a functional assay based on chondrocyte cluster formation, a phenotype associated with osteoarthritis (OA), to screen an OA cartilage gene library. Previous reports have demonstrated that normal chondrocytes grown in suspension culture maintain their chondrocytic phenotype, however, certain growth factors such as basic fibroblast growth factor (bFGF) will induce the cells to proliferate in tight clusters similar to those seen in osteoarthritic cartilage. In this study we validate that overexpression of bFGF by retrovirally transduced normal chondrocytes would similarly induce the proliferation of tight cell clusters. We then used this approach as a basis to set up a functional screen where an entire OA cartilage cDNA library was tranduced into normal chondrocytes to search for other genes that would also induce cluster formation. Seven potential genes were isolated from the OA gene library, including BPOZ, IL-17 receptor C, NADH ubiquinone oxidoreductase, COMP, Soluble carrier 16 (MCT 3), C1r, and bFGF itself. None of the identified genes were upregulated by bFGF, however, all of them upregulated the expression of bFGF suggesting a common pathway. Although cluster formation is not considered to be destructive in OA cartilage, it is consistent with the disease and could yield answers to the altered phenotype. Further studies are needed to elucidate how these genes are linked to the disease state.

Targeted disruption of Mig-6 in the mouse genome leads to early onset degenerative joint disease

Degenerative joint disease, also known as osteoarthritis, is the most common joint disorder in human beings. The molecular mechanism underlying this disease is not fully understood. Here, we report that disruption of mitogen-inducible gene 6 (Mig-6) in mice by homologous recombination leads to early onset degenerative joint disease, which is revealed by simultaneous enlargement and deformity of multiple joints, degradation of articular cartilage, and the development of bony outgrowths or osteophyte formation within joint space. The osteophyte formation appears to be derived from proliferation of mesenchymal progenitor cells followed by differentiation into chondrocytes. Absence of the Rag2 gene does not rescue the joint phenotype, excluding a role for the acquired immune system in the development of this disease. Our results provide insight into the mechanism of osteoarthritis by showing that loss of Mig-6 leads to early onset of this disease, implying that this gene or its pathway is important in normal joint maintenance. Because of the striking similarity of osteoarthritis in humans and mice, the Mig-6 mutant mouse should provide a useful animal model for studying the mechanism of this disease and for testing drugs or therapies for treating osteoarthritis.

Association of the frizzled-related protein gene with symptomatic osteoarthritis at multiple sites

OBJECTIVE

To confirm the association of 2 variants of the Frizzled-related protein gene (FRZB) with osteoarthritis (OA) of the hip, and to investigate whether these variants also associate with other heritable generalized OA phenotypes.

METHODS

An association analysis of 2 variants (R200W and R324G) of FRZB was performed in a random sample of 1,369 subjects (ages 55-70 years) from a population-based cohort (the Rotterdam Study) scored for radiographic characteristics of OA in the hip, hand, spine, and knee and in a patient population of Caucasian probands (ages 40-70 years) and their siblings selected for the presence of primary symptomatic OA at multiple sites.

RESULTS

The allele frequency of the 2 variants was not significantly different between subjects with hip radiographic OA (ROA) and controls. The frequency of the G allele of the R324G variant was significantly increased in subjects with generalized ROA from the Rotterdam Study (0.10) and in subjects from the Genetics, osteoARthritis and Progression study (0.11) compared with that in controls from the Rotterdam Study (0.08). Carriers of this G allele had increased susceptibility for generalized ROA (odds ratio [OR] 1.4, 95% confidence interval [95% CI] 0.9-1.9, P = 0.10) or familial symptomatic OA at multiple sites (OR 1.6, 95% CI 1.1-2.3, P = 0.02).

CONCLUSION

Our results confirm that the R324G variant of the FRZB gene is involved in OA and indicate a role of this variant in several generalized OA phenotypes. A more extended OA phenotype may indeed be expected from genetic variation in an essential pathway of skeletal development such as Wnt signaling.

Familial inheritance of osteoarthritis: documented family subsets

Identifying susceptibility genes for a common complex disease is complicated by heterogeneity at several levels including allelic, locus, clinical, and population. The latter two can be alleviated by focusing on particular subsets of families that have well-defined disease. For osteoarthritis it was commonly thought that a generalized disease approach was the wisest ascertainment because this would target a systemic disease that had to have a major genetic component. However, this intuitive idea has not yet provided the breakthroughs many expected and it has become apparent that a joint-specific and gender-specific approach may be more fruitful. Large collections of osteoarthritis cohorts have been assembled either as part of prospective studies or more directly. Some of these collections have targeted specific joints, others have not. The latter are, however, amenable to stratification. Many collectors included the acquisition of DNA as a core study aim. A variety of osteoarthritis subsets are therefore available for genetic analysis. Open accessibility is another matter. Although many collections were funded partly or wholly by public or charitable organizations, they can be jealously guarded or have arcane access rights. Open access, with necessary safeguards, is something the osteoarthritis research community should strive for if progress toward susceptibility gene identification is to be swift.

Estrogen receptor-alpha gene haplotype is associated with primary knee osteoarthritis in Korean population

Estrogen and estrogen receptors (ERs) are known to play important roles in the pathophysiology of osteoarthritis (OA). To investigate ER-alpha gene polymorphisms for its associations with primary knee OA, we conducted a case-control association study in patients with primary knee OA (n = 151) and healthy individuals (n = 397) in the Korean population. Haplotyping analysis was used to determine the relationship between three polymorphisms in the ER-alpha gene (intron 1 T/C, intron 1 A/G and exon 8 G/A) and primary knee OA. Genotypes of the ER-alpha gene polymorphism were determined by PCR followed by restriction enzyme digestion (PvuII for intron 1 T/C, XbaI for intron 1 A/G, and BtgI for exon 8 G/A polymorphism). There was no significant difference between primary knee OA patients and healthy control individuals in the distribution of any of the genotypes evaluated. However, we found that the allele frequency for the exon 8 G/A BtgI polymorphism (codon 594) was significantly different between primary knee OA patients and control individuals (odds ratio = 1.38, 95% confidence interval = 1.01-1.88; P = 0.044). In haplotype frequency estimation analysis, there was a significant difference between primary knee OA patients and control individuals (degrees of freedom = 7, chi2 = 21.48; P = 0.003). Although the number OA patients studied is small, the present study shows that ER-alpha gene haplotype may be associated with primary knee OA, and genetic variations in the ER-alpha gene may be involved in OA.