Absence of association of asporin polymorphisms and osteoarthritis susceptibility in US Caucasians

Multifaceted Roles of Asporin in Cancer: Current Understanding

The small leucine-rich proteoglycan (SLRP) family consists of 18 members categorized into five distinct classes, the traditional classes I–III, and the non-canonical classes IV–V. Unlike the other class I SLRPs (decorin and biglycan), asporin contains a unique and conserved stretch of aspartate (D) residues in its N terminus, and germline polymorphisms in the D-repeat-length are associated with osteoarthritis and prostate cancer progression. Since the first discovery of asporin in 2001, previous studies have focused mainly on its roles in bone and joint diseases, including osteoarthritis, intervertebral disc degeneration and periodontal ligament mineralization. Recently, asporin gene expression was also reported to be dysregulated in tumor tissues of different types of cancer, and to act as oncogene in pancreatic, colorectal, gastric, and prostate cancers, and some types of breast cancer, though it is also reported to function as a tumor suppressor gene in triple-negative breast cancer. Furthermore, asporin is also positively or negatively correlated with tumor proliferation, migration, invasion, and patient prognosis through its regulation of different signaling pathways, including the TGF-β, EGFR, and CD44 pathways. In this review, we seek to elucidate the signaling pathways and functions regulated by asporin in different types of cancer and to highlight some important issues that require investigation in future research.

Identification of potential biomarkers for differential diagnosis between rheumatoid arthritis and osteoarthritis via integrative genome‑wide gene expression profiling analysis

The present study aimed to identify potential novel biomarkers in synovial tissue obtained from patients with Rheumatoid Arthritis (RA) and Osteoarthritis (OA) for differential diagnosis. The genome-wide expression profiling datasets of synovial tissues from RA and OA cohorts, including GSE55235, GSE55457 and GSE55584 datasets, were retrieved and used to identify differentially expressed genes (DEGs; P<0.05; false discovery rate <0.05 and Fold Change >2) between RA and OA using R software. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses of DEGs were performed to determine molecular and biochemical pathways associated with the identified DEGs, and a protein-protein interaction (PPI) network of the DEGs was constructed using Cytoscape software. Significant modules in the PPI network and candidate driver genes were screened using the Molecular Complex Detection Algorithm. Potential biomarkers were evaluated by receiver operating characteristic and logistic regression analyses. Large numbers of DEGs were detected, including 273, 205 and 179 DEGs in the GSE55235, GSE55457 and GSE55584 datasets, respectively. Among them, 80 DEGs exhibited identical expression trends in all the three datasets, including 49 upregulated and 31 downregulated genes in patients with RA. DEGs in patients suffering from RA compared with patients suffering from OA were predominantly associated with the primary immunodeficiency pathway, including interleukin 7 receptor (IL7R) and signal transducer activator of transcription 1 (STAT1). The sensitivity of IL7R + STAT1 to differentiate RA from OA was 93.94% with a specificity of 80.77%. The results generated from analyses of the GSE36700 dataset were closely associated with results generated from analyses of GSE55235, GSE55457 and GSE55584 datasets, which further verified the reliability of the aforementioned results. The results of the present study suggested that increased expression of IL7R and STAT1 in synovial tissue as well as in the primary immunodeficiency may be associated with RA occurrence. These identified novel biomarkers may be used to predict disease occurrence and clinically differentiate RA from OA.

Association between the aspartic acid D-repeat polymorphisms and osteoarthritis susceptibility: An updated systematic review and meta-analyses

OBJECTIVES

Association between the D-repeat of asporin (ASPN) gene and osteoarthritis (OA) was still inconsistent. We performed this meta-analysis to systematically assess the D-repeat polymorphisms in OA susceptibility.

METHODS

Relevant studies were enrolled by searching databases. Odd ratios (ORs) with 95% confidence intervals (95% CIs) were used for evaluating the association between ASPN gene and OA. Heterogeneity was calculated using the Q statistic, and three different subgroup analyses were performed on ethnicity, gender, and OA positions respectively. False discovery rate (FDR) was applied to regulate the multiple comparisons.

RESULTS

Twelve qualified articles involving 5190 OA patients and 5167 healthy controls were included. With D13 polymorphism, Caucasian male patients have low OA susceptibility (P = .008, PFDR = .024, OR [95% CI] = 0.83 [0.73-0.95]). As to D14 polymorphism, all male patients (P = .0004, PFDR = .001, OR [95% CI] = 1.38 [1.15-1.64]), Asian male patients (P = .01, PFDR = .01, OR [95% CI] = 1.72 [1.11-2.66]), and Caucasian male patients (P = .005, PFDR = .001, OR [95% CI] = 1.32 [1.09-1.60]) have high OA susceptibility. In the pooled-population of KOA with D14 polymorphism, overall male patients (P = .03, PFDR = .045, OR [95% CI] = 1.35 [1.02-1.78]) and Asian male patients (P = .01, PFDR = .03, OR [95% CI] = 1.72 [1.11-2.66]) have high OA risk. With D16 polymorphism, Latin America patients may have high OA risk (P = .04, PFDR = .15, OR [95% CI] = 1.43 [1.02-2.01]).

CONCLUSION

Our results suggest that D-repeat of ASPN gene is mainly associated with male patients. The D13 polymorphism plays a protective role for OA in Caucasians male individuals while D14 plays a risk factor for KOA in male patients.

Genetic polymorphism in the asporin gene is not a key risk factor for osteoarthritis: Evidence based on an updated cumulative meta-analysis

To provide an evidence-based medical basis for the treatment of osteoarthritis, a meta-analysis was performed to assess the association between asporin (ASPN) gene polymorphism and susceptibility to osteoarthritis (OA). The current study searched the literature from January 1st, 1915 through February 1st, 2017 using the Cochrane Library, PubMed, the Excerpta Medica database (EMBASE) and three main Chinese databases (VIP, CNKI and Wan Fang). Cohort and case-control studies that explored the association between different types of ASPN alleles and OA susceptibility were evaluated. The K/L grading system, clinical and radiological diagnoses were used for OA diagnosis. A random-effects model was used in a pooled analysis to adjust for heterogeneity of the included studies, and the differences between treatment groups were reported as odds ratio (OR), 95% confidence intervals (CIs) and P-values. Begg's funnel plots and Egger's tests were used to assess publication bias in the present meta-analysis. Following document retrieval and screening, a total of 10 studies were deemed eligible, including 4,842 patients and 3,661 healthy subjects. Results of the multivariate meta-regression analysis revealed that the study sample size was a source of heterogeneity between studies. The D17 allele was a risk factor for the development of OA (OR=1.33, 95% CI: 1.02–1.73, P<0.05). The other alleles were not considered as risk factors for development of OA (P>0.05). The results of the meta-analysis verified that ASPN polymorphisms were not significantly relevant to an increased OA risk. However, the mechanisms contributing to the association between ASPN polymorphisms and OA risk still require further study.

Association of aspartic acid repeat polymorphism in the asporin gene with osteoarthritis of knee, hip, and hand: A PRISMA-compliant meta-analysis

OBJECTIVE

Several human studies have been conducted to explore the association between aspirin (ASPN) D-repeat polymorphisms and OA susceptibility, but these provide inconsistent results. Our primary aim is to examine whether D-repeat polymorphisms are related to OA risk.

METHODS

We conducted a meta-analysis to investigate the association between ASPN D-repeat polymorphisms and OA. Electronic database was searched, including PubMed, Embase, CNKI, Ovid, and the reference lists of relevant articles published from the inception to January 24, 2018. The included studies were assessed in the following allele model: D14 allele versus others combined, D13 allele versus others combined, D15 allele versus others combined, and D14 allele versus D13 allele. Female population was also analyzed separately.

RESULTS

Eleven articles (12 comparisons) with 4975 patients of knee, hip, and/or hand OA and 3754 controls were considered in this meta-analysis. For the D13 allele, OR and 95% CI in combined population indicated an borderline association (odds ratio [OR] = 0.94, confidence interval [CI]: 0.89-0.99, P = .027). No significant association between OA and the D14 allele and D15 allele in all pooled studies were observed.

CONCLUSION

Our result based on previously published studies demonstrated that the ASPN D13 allele was a protective factor for OA of knee, hip, and hand. For D14 and D15 allele, our present meta-analysis did not demonstrate statistically significant association. Further studies with larger sample size would be required.

Functional polymorphisms in asporin and CILP together with joint loading predispose to hand osteoarthritis

Background

Osteoarthritis (OA) is the most common degenerative joint disease afflicting people in the Western world and has a strong genetic influence. The aim of this study was to examine the association of two known functional polymorphisms in the TGF-β inhibiting genes, asporin (ASPN) and cartilage intermediate layer protein (CILP), with hand OA and potential gene-occupational hand loading interaction.

Results

Statistically significant interaction of the CILP rs2073711 T and ASPN D15 alleles with hand OA was observed (OR = 2.48, 95% CI 1.27–4.85, p = 0.008) in a Finnish hand OA cohort of 543 women (aged 45–63). When stratified by variation in working tasks, low variation of working tasks increased the risk further (OR = 3.00, 95% CI 1.35–6.66, p = 0.007). Based on the analysis of ASPN and CILP protein-coding regions, functional studies were performed with one observed variant, rs41278695 in the ASPN gene. Analyses showed that bone morphogenetic protein 2 (BMP2) mediated expression of aggrecan (Agc1) and type II collagen (Col2a1) was significantly suppressed (p = 0.011 and p = 0.023, respectively) in a murine chondrocytic cell line (ATDC5) with cells stably expressing ASPN rs41278695.

Conclusions

The carriage of either ASPN D15 or CILP rs2073711 TT is associated with increased risk of symmetrical hand OA, particularly in individuals with low variation in work tasks. ASPN rs41278695 SNP had an effect on Agc1 and Col2a1 gene expression when induced with BMP-2 suggesting an effect on the cartilage extracellular matrix composition.

An updated meta-analysis of the asporin gene D-repeat in knee osteoarthritis: effects of gender and ethnicity

Background

Knee osteoarthritis (KOA) is the most prevalent form of knee joint disease and characterized by the progressive degeneration of articular cartilage. Although pathology of KOA remains unknown, genetic factors are considered to be the major cause. Asporin is a group of biologically active components of extracellular matrix (ECM) in articular cartilage, and asporin gene (ASPN) D-repeat polymorphism was reported to be associated with KOA. Thus, our meta-analysis is aimed at investigation of the association between asporin D-repeat polymorphism and susceptibility of KOA.

Methods

We gathered data from MEDLINE, Embase, OVID, and ScienceDirect to search relevant published epidemiological studies through April 2017. Compared with previous studies, our meta-analysis is the first study to investigate the association of ASPN D15, D16, and D17 alleles and KOA susceptibility by ethnic- and sex-stratified subgroup analysis.

Results

We found no significant association between D15 allele and susceptibility to KOA (OR = 1.05, 95% CI 0.95–1.17) in overall population. The same results were observed in the analysis of D16 (OR = 1.01, 95% CI 0.80–1.28) and D17 alleles (OR = 1.28, 95% CI 0.91–1.80). The ethnic- and sex-subgroup analyses did not alter the ORs. However, significant association was detected in the sensitivity analysis of D17 in overall population (OR = 1.05, 95% CI 0.95–1.17) and Asian population (OR = 1.78, 95% CI 1.02–3.11, P < 0.05).

Conclusion

Our results indicated that D-repeat polymorphism of ASPN may not play a major role in susceptibility of KOA in ethnic- and sex-specific analysis. Because of the limitations of the present meta-analysis, firm conclusions could not be drawn based on the current evidence, and further studies are required to detect genuine role of ASPN.

Association between aspartic acid repeat polymorphism of the asporin gene and risk of knee osteoarthritis: A systematic review and meta-analysis

OBJECTIVE

Studies have assessed the association between aspartic acid (D)-repeat polymorphism in the gene encoding Asporin (ASPN) and knee osteoarthritis (KOA) risk, but the results were inconclusive and contradictory. Therefore, we performed a meta-analysis to investigate the association between ASPN gene D-repeat polymorphism and KOA risk.

METHODS

Eligible studies were identified by searching several electronic databases for relevant reports published before September 2016. The pooled odds ratios (ORs) for the association between ASPN polymorphism and KOA and their corresponding 95% confidence intervals (CIs) were estimated using the random- or fixed-effect model.

RESULTS

A total of eleven case-control studies in ten publications with 4610 KOA cases and 3621 controls were included for the ASPN D-repeat polymorphism. Overall, no significant association was detected for D14 allele carrier (D14 vs. D13: OR = 1.10, 95% CI = 0.90-1.36, p = 0.32). Meta-analysis of D14 vs. other alleles and D13 vs. other alleles showed the same pattern of KOA association as the D14 vs. D13 (OR = 1.30, 95% CI = 1.00-1.70, p = 0.06; OR = 0.93, 95% CI = 0.82-1.06, p = 0.33, respectively). Also, in the stratified analysis by ethnicity, no significant association of this polymorphism with risk of KOA was found in the European and Asians populations (OR = 1.05, 95% CI = 0.91-1.21, p = 0.49; OR = 0.98, 95% CI = 0.78-1.23, p = 0.88, respectively).

CONCLUSIONS

The present meta-analysis suggests that the ASPN D-repeat polymorphism is not associated with an increased KOA risk. However, future large studies with gene-gene and gene-environment interactions are needed to validate these findings.

LEVEL OF EVIDENCE

Level III diagnostic study.

Glycoprotein asporin as a novel player in tumour microenvironment and cancer progression

BACKGROUND

Small leucine rich proteoglycans (SLRPs), major non-collagen components of the extracellular matrix (ECM), have multiple biological roles with diverse effects. Asporin, a member of the SLRPs class I, competes with other molecules in binding to collagen and affects its mineralization. Its role in cancer is only now being elucidated.

METHODS

The PubMed online database was used to search relevant reviews and original articles. Furthermore, altered asporin expression was analysed in publicly available genome-wide expression data at the Gene Expression Omnibus database.

RESULTS

Polymorphisms in the N-terminal polyaspartate domain, which binds calcium, are associated with osteoarthritis and prostate cancer. Asporin also promotes the progression of scirrhous gastric cancer where it is required for coordinated invasion by cancer associated fibroblasts and cancer cells. Besides the enhanced expression of asporin observed in multiple cancer types, such as breast, prostate, gastric, pancreas and colon cancer, tumour suppressive effects of asporin were described in triple-negative breast cancer. We also discuss a number of factors modulating asporin expression in different cell types relevant for alterations toing the tumour microenvironment.

CONCLUSION

The apparent contradicting tumour promoting and suppressive effects of asporin require further investigation. Deciphering the role of asporin and other SLRPs in tumour-stroma interactions is needed for a better understanding of cancer progression and potentially also for novel tumour microenvironment based therapies.

Germline Variants in Asporin Vary by Race, Modulate the Tumor Microenvironment, and Are Differentially Associated with Metastatic Prostate Cancer

PURPOSE

Prostate cancers incite tremendous morbidity upon metastatic growth. We previously identified Asporin (ASPN) as a potential mediator of metastatic progression found within the tumor microenvironment. ASPN contains an aspartic acid (D)-repeat domain and germline polymorphisms in D-repeat-length have been associated with degenerative diseases. Associations of germline ASPN D polymorphisms with risk of prostate cancer progression to metastatic disease have not been assessed.

EXPERIMENTAL DESIGN

Germline ASPN D-repeat-length was retrospectively analyzed in 1,600 men who underwent radical prostatectomy for clinically localized prostate cancer and in 548 noncancer controls. Multivariable Cox proportional hazards models were used to test the associations of ASPN variations with risk of subsequent oncologic outcomes, including metastasis. Orthotopic xenografts were used to establish allele- and stroma-specific roles for ASPN D variants in metastatic prostate cancer.

RESULTS

Variation at the ASPN D locus was differentially associated with poorer oncologic outcomes. ASPN D14 [HR, 1.72; 95% confidence interval (CI), 1.05-2.81, P = 0.032] and heterozygosity for ASPN D13/14 (HR, 1.86; 95% CI, 1.03-3.35, P = 0.040) were significantly associated with metastatic recurrence, while homozygosity for the ASPN D13 variant was significantly associated with a reduced risk of metastatic recurrence (HR, 0.44; 95% CI, 0.21-0.94, P = 0.035) in multivariable analyses. Orthotopic xenografts established biologic roles for ASPN D14 and ASPN D13 variants in metastatic prostate cancer progression that were consistent with patient-based data.

CONCLUSIONS

We observed associations between ASPN D variants and oncologic outcomes, including metastasis. Our data suggest that ASPN expressed in the tumor microenvironment is a heritable modulator of metastatic progression.

Asporin and osteoarthritis

OBJECTIVE

To provide an overview of the literature describing the role of asporin, a small leucine-rich proteoglycan (SLRP), in osteoarthritis (OA).

METHOD

A literature search was performed and reviewed using the narrative approach.

RESULTS

As a class I SLRP member, asporin, is distinct from other SLRPs. Accumulating evidence demonstrates the involvement of asporin in OA pathogenesis. Many human studies have been conducted to explore the association between the D-repeat polymorphisms and OA susceptibility, but these yield inconsistent results. Possible mechanisms for the involvement of asporin in OA pathology include its influence on TGF-β (transforming growth factor-β) signaling pathways and collagen mineralization. To date, no studies were found to use an asporin-deficient animal model that would help to understand disease mechanisms. Many issues must be addressed to clarify the link between asporin and OA to provide a novel therapeutic strategy for OA, perhaps through controlling and modifying the TGF-β-ECM system.

CONCLUSIONS

Studies examined demonstrate the involvement of asporin in OA pathogenesis, and possible mechanisms by which asporin may be involved in this process have been proposed. However, large-scale interracial studies should be conducted to investigate the association between asporin and OA, and further investigations are needed to obtain a better understanding of the disease mechanism, develop novel therapeutic strategies, and explore new approaches for diagnosis of OA.

Association between aspartic acid repeat polymorphism of the asporin gene and susceptibility to knee osteoarthritis: a genetic meta-analysis

OBJECTIVE

Knee osteoarthritis (KOA) is a common disease that is characterized by the degeneration of joint cartilage in the knee. Genetic factors have been implicated in KOA. Recently, several genetic studies have suggested that susceptibility to KOA is affected by the number of aspartic acid (D) residues in the amino-terminal of the asporin protein, but evidence remains conflicting. Therefore, the objective of the present meta-analysis was to investigate whether or not the D-repeat polymorphism is associated with susceptibility to KOA.

METHODS

A systematic search of all relevant studies published through Dec 2012 was conducted using the MEDLINE, EMBASE, OVID, and ScienceDirect. Allelic counts were evaluated for the D14 and D13 alleles respectively. The included studies were only assessed in the analysis of the following allele model: D14 allele vs others alleles combined, D13 allele vs others alleles combined, and D14 allele vs D13 allele.

RESULTS

Seven studies (eight comparisons) with 5515 total participants (2334 KOA patients and 3181 controls), which involved four Caucasian and four Asian populations, were eligible for inclusion. Meta-analysis was conducted for genotype D14 vs others combined, D13 vs others combined, and D14 vs D13. In the stratification based on ethnicity, studies were divided into Caucasian and Asian populations. We did not detect positive association between KOA and the D14 allele in Asian populations (OR = 1.527, 95% CI: 0.879-2.653) and in Caucasian populations (OR = 1.053, 95% CI: 0.905-1.225). There was also no positive association between susceptibility to KOA and D13 allele in Asian populations (OR = 0.950, 95% CI: 0.732-1.233) and in Caucasian populations (OR = 0.866, 95% CI: 0.723-1.037).

CONCLUSION

The present results suggest that the D-repeat of asporin gene (ASPN) may not be a major susceptibility locus in the Caucasian and Asian populations with KOA. Because of the limitations of the present meta-analysis, accurate conclusions could not be drawn based on the current evidence, and further studies with large sample size are required.

The D-repeat polymorphism in the ASPN gene and primary knee osteoarthritis in a Mexican mestizo population: a case-control study

BACKGROUND

A genetic association between osteoarthritis (OA) and a polymorphism in the aspartic acid (D) repeat of the asporin (ASPN) gene has been reported in Japanese, Han Chinese, Greek and UK Caucasian populations of patients having knee and hip OA. Such an association has not been previously described among the Mexican mestizo population. The aim of this study was to analyze the association of the ASPN gene D-repeat polymorphism in a Mexican mestizo population with primary knee OA as well as in healthy controls.

MATERIALS AND METHODS

A case-control study was conducted on a Mexican mestizo population of northern Mexico. The repeat polymorphism was genotyped in 440 subjects (218 cases and 222 healthy controls). Primary knee OA was diagnosed according to American College of Rheumatology and Kellgren-Lawrence criteria, and allelic association was examined adjusting for other risk variables.

RESULTS

After adjusting for some covariates, menopause and the D16 allele showed a trend toward being risk factors for knee OA in a Mexican mestizo population. Also, the D12 allele could be considered as a protective factor.

CONCLUSIONS

These findings suggest that polymorphisms within the ASPN gene could influence knee OA susceptibility, but these associations must be confirmed by independent studies in larger samples and different ethnic groups to support the role of the D-repeat polymorphism in the ASPN gene as risk or protection factors for knee OA in a Mexican population.

Association study of candidate genes for the progression of hand osteoarthritis

OBJECTIVE

Although a few consistent osteoarthritis (OA) susceptibility genes have been identified, little is known on OA progression. Since OA progression is clinically the most relevant phenotype, we investigate the association between asporin (ASPN), bone morphogenetic protein 5 (BMP5) and growth differentiation factor 5 (GDF5) polymorphisms and progression of hand OA.

METHODS

Single-nucleotide polymorphisms (SNPs) ASPN rs13301537, BMP5 rs373444 and GDF5 rs143383 were genotyped in 251 hand OA patients from the Genetics osteoARthritis and Progression (GARP) study and 725 controls. In a case-control comparison we assessed the association between these SNPs and radiographic progression of hand OA over 6 years, which was based on change in osteophytes or joint space narrowing (JSN), above the smallest detectable change. SNPs with suggestive evidence for association were further analysed for their effect on progression over 2 years, and for the mean change in osteophytes and JSN.

RESULTS

The minor allele of ASPN SNP rs13301537 was associated with hand OA progression over 6 years (odds ratio (OR) (95% CI) 1.49 (1.06-2.07); P = 0.020). The mean change in osteophytes and JSN was higher in carriers of the minor allele compared to homozygous carriers of the common allele with mean difference of 0.73 (95% CI - 0.07-1.56; P = 0.073) and 0.82 (95% CI 0.12-1.52; P = 0.022), respectively. An association with similar effect size was found between ASPN SNP rs13301537 and 2-year progression, and the mean change in osteophytes and JSN was significantly higher in homozygotes.

CONCLUSION

ASPN is associated with hand OA progression. This gives insight in the pathogenesis of hand OA progression and identified a potential target for therapeutic approaches.

Etiology of osteoarthritis: genetics and synovial joint development

Osteoarthritis (OA) has a considerable hereditary component and is considered to be a polygenic disease. Data derived from genetic analyses and genome-wide screening of individuals with this disease have revealed a surprising trend: genes associated with OA tend to be related to the process of synovial joint development. Mutations in these genes might directly cause OA. In addition, they could also determine the age at which OA becomes apparent, the joint sites involved, the severity of the disease and how rapidly it progresses. In this Review, I propose that genetic mutations associated with OA can be placed on a continuum. Early-onset OA is caused by mutations in matrix molecules often associated with chondrodysplasias, whereas less destructive structural abnormalities or mutations confer increased susceptibility to injury or malalignment that can result in middle-age onset. Finally, mutations in molecules that regulate subtle aspects of joint development and structure lead to late-onset OA. In this Review, I discuss the genetics of OA in general, but focus on the potential effect of genetic mutations associated with OA on joint structure, the role of joint structure in the development of OA--using hip abnormalities as a model--and how understanding the etiology of the disease could influence treatment.

The relationship between fibrogenic TGFβ1 signaling in the joint and cartilage degradation in post-injury osteoarthritis

OBJECTIVE

To review the literature on modulation of chondrocyte activities in the osteoarthritic joint, and to discuss these changes in relation to established hard and soft tissue repair paradigms, with an emphasis on transforming growth factor beta (TGFβ1)-mediated signaling which can promote either a chondrogenic or fibrogenic phenotype.

METHODS

Papers addressing the close relationship between repair in general, and the specific post-injury response of joint tissues are summarized. Different interpretations of the role of TGFβ1 in the emergence of an "osteoarthritic" chondrocyte are compared and the phenotypic plasticity of "reparative" progenitor cells is examined. Lastly, emerging data on a central role for A-Disintegrin-And-Metalloproteinase-with-Thrombospondin-like-Sequences-5 (ADAMTS5) activity in modulating TGFβ1 signaling through activin receptor-like kinase 1 (ALK1) and activin receptor-like kinase 5 (ALK5) pathways is discussed.

RESULTS

The review illustrates how a transition from ALK5-mediated fibrogenic signaling to ALK1-mediated chondrogenic signaling in joint cells represents the critical transition from a non-reparative to a reparative cell phenotype. Data from cell and in vivo studies illustrates the mechanism by which ablation of ADAMTS5 activity allows the transition to reparative chondrogenesis. Multiple large gene expression studies of normal and osteoarthritis (OA) human cartilages (CAs) also support an important role for TGFβ1-mediated pro-fibrogenic activities during disease progression.

CONCLUSIONS

We conclude that progressive articular CA damage in post-injury OA results primarily from biomechanical, cell biologic and mediator changes that promote a fibroblastic phenotype in joint cells. Since ADAMTS5 and TGFβ1 appear to control this process, agents which interfere with their activities may not only enhance endogenous CA repair in vivo, but also improve the properties of tissue-engineered CA for implantation.

Age-dependent alteration of TGF-β signalling in osteoarthritis

Osteoarthritis (OA) is a disease of articular cartilage, with aging as the main risk factor. In OA, changes in chondrocytes lead to the autolytic destruction of cartilage. Transforming growth factor-β has recently been demonstrated to signal not only via activin receptor-like kinase 5 (ALK5)-induced Smad2/3 phosphorylation, but also via ALK1-induced Smad1/5/8 phosphorylation in articular cartilage. In aging cartilage and experimental OA, the ratio ALK1/ALK5 has been found to be increased, and the expression of ALK1 is correlated with matrix metalloproteinase-13 expression. The age-dependent shift towards Smad1/5/8 signalling might trigger the differentiation of articular chondrocytes with an autolytic phenotype.

Association of the D repeat polymorphism in the ASPN gene with developmental dysplasia of the hip: a case-control study in Han Chinese

Introduction

Developmental dysplasia of the hip (DDH) is a common skeletal disease, which is characterized by abnormal seating of the femoral head in the acetabulum. Genetic factors play a considerable role in the etiology of DDH. Asporin (ASPN) is an ECM protein which can bind to TGF-β1 and sequentially inhibit TGF-β/Smad signaling. A functional aspartic acid (D) repeat polymorphism of ASPN was first described as an osteoarthritis-associated polymorphism. As TGF-β is well known as an important regulator in the development of skeletal components, ASPN may also be involved in the etiology of DDH. Our objective is to evaluate whether the D repeat polymorphism of ASPN is associated with DDH in Han Chinese.

Methods

The D repeat polymorphism was genotyped in 370 DDH patients and 445 control subjects, and the allelic association of the D repeat was examined.

Results

From D11 to D18, eight alleles were identified. D13 allele is the most common allele both in control and DDH groups, the frequencies are 67.3% and 58.1% respectively. In the DDH group, a significantly higher frequency of the D14 allele and significantly lower frequency of D13 was observed. The association of D14 and D13 was found in both females and males after stratification by gender. There was no significant difference in any other alleles we examined.

Conclusions

Our results show an obvious association between the D repeat polymorphism of ASPN and DDH. It indicates that ASPN is an important regulator in the etiology of DDH.

Genetic epidemiology of hip and knee osteoarthritis

Osteoarthritis (OA) is the most common cause of arthritis and represents an enormous healthcare burden in industrialized societies. Current therapeutic approaches for OA are limited and are insufficient to prevent the initiation and progression of the disease. Genetic studies of patients with OA can help to unravel the molecular mechanisms responsible for specific disease manifestations, including joint damage, nociception and chronic pain. Indeed, these studies have identified molecules, such as growth/differentiation factor 5, involved in signaling cascades that are important for the pathology of joint components. Genome-wide association studies have uncovered a likely role in OA for the genes encoding structural extracellular matrix components (such as DVWA) and molecules involved in prostaglandin metabolism (such as DQB1 and BTNL2). A ∼300 kilobase region in chromosome 7q22 is also associated with OA susceptibility. Finally, the identification of individuals at a high risk of OA and of total joint arthroplasty failure might be facilitated by the use of combinations of genetic markers, allowing for the application of preventive and disease-management strategies.

Developments in the scientific understanding of osteoarthritis

Osteoarthritis is often a progressive and disabling disease, which occurs in the setting of a variety of risk factors--such as advancing age, obesity, and trauma--that conspire to incite a cascade of pathophysiologic events within joint tissues. An important emerging theme in osteoarthritis is a broadening of focus from a disease of cartilage to one of the 'whole joint'. The synovium, bone, and cartilage are each involved in pathologic processes that lead to progressive joint degeneration. Additional themes that have emerged over the past decade are novel mechanisms of cartilage degradation and repair, the relationship between biomechanics and biochemical pathways, the importance of inflammation, and the role played by genetics. In this review we summarize current scientific understanding of osteoarthritis and examine the pathobiologic mechanisms that contribute to progressive disease.