Genome-wide association scan identifies a prostaglandin-endoperoxide synthase 2 variant involved in risk of knee osteoarthritis

Osteoarthritis year in review 2023: Biology

Great progress continues to be made in our understanding of the multiple facets of osteoarthritis (OA) biology. Here, we review the major advances in this field and progress towards therapy development over the past year, highlighting a selection of relevant published literature from a PubMed search covering the year from the end of April 2022 to the end of April 2023. The selected articles have been arranged in themes. These include 1) molecular regulation of articular cartilage and implications for OA, 2) mechanisms of subchondral bone remodelling, 3) role of synovium and inflammation, 4) role of age-related changes including cartilage matrix stiffening, cellular senescence, mitochondrial dysfunction, metabolic dysfunction, and impaired autophagy, and 5) peripheral mechanisms of OA pain. Progress in the understanding of the cellular and molecular mechanisms responsible for the multiple aspects of OA biology is unravelling novel therapeutic targets for disease modification.

Gene Expression in Glenoid Articular Cartilage Varies Across Acute Instability, Chronic Instability, and Osteoarthritis

BACKGROUND

Shoulder instability is a common pathology associated with an elevated risk of osteoarthritis (OA). Little is known about gene expression in the cartilage of the glenohumeral joint after dislocation events, particularly as it relates to the risk of posttraumatic OA. This study tested the hypothesis that gene expression in glenoid cartilage varies among acute instability (<3 dislocations), chronic instability (≥3 dislocations), and OA.

METHODS

Articular cartilage was collected from the anteroinferior glenoid of consenting patients undergoing shoulder stabilization surgery (n = 17) or total shoulder arthroplasty (n = 16). Digital quantitative polymerase chain reaction was used to assess the relative expression of 57 genes (36 genes from OA risk allele studies, 21 genes from differential expression studies), comparing (1) OA versus instability (acute and chronic combined), (2) acute versus chronic instability, (3) OA versus acute instability, and (4) OA versus chronic instability.

RESULTS

The expression of 11 genes from OA risk allele studies and 9 genes from differential expression studies was significantly different between cartilage from patients with instability and those with OA. Pro-inflammatory genes from differential expression studies and genes from OA risk allele studies were more highly expressed in cartilage in the OA group compared with the instability group, which expressed higher levels of extracellular matrix and pro-anabolic genes. The expression of 14 genes from OA risk allele studies and 4 genes from differential expression studies, including pro-inflammatory genes, anti-anabolic genes, and multiple genes from OA risk allele studies, was higher in the acute instability group compared with the chronic instability group. Cartilage in the OA group displayed higher expression of CCL3, CHST11, GPR22, PRKAR2B, and PTGS2 than cartilage in the group with acute or chronic instability. Whereas cartilage in both the acute and chronic instability groups had higher expression of collagen genes, cartilage in the OA group had expression of a subset of genes from OA risk allele studies or from differential expression studies that was lower than in the acute group and higher than in the chronic group.

CONCLUSIONS

Glenoid cartilage has an inflammatory and catabolic phenotype in shoulders with OA but an anabolic phenotype in shoulders with instability. Cartilage from shoulders with acute instability displayed greater (cellular) metabolic activity compared with shoulders with chronic instability.

CLINICAL RELEVANCE

This exploratory study identified genes of interest, such as CCL3, CHST11, GPR22, PRKAR2B, and PTGS2, that have elevated expression in osteoarthritic glenoid cartilage. These findings provide new biological insight into the relationship between shoulder instability and OA, which could lead to strategies to predict and potentially modify patients' risk of degenerative arthritis due to shoulder instability.

Hypoxia and Wnt signaling inversely regulate expression of chondroprotective molecule ANP32A in articular cartilage

OBJECTIVES

ANP32A is a key protector of cartilage health, via preventing oxidative stress and Wnt hyper-activation. We aimed to unravel how ANP32A is regulated in cartilage.

METHODS

A bioinformatics pipeline was applied to identify regulators of ANP32A. Pathways of interest were targeted to study their impact on ANP32A in in vitro cultures of the human chondrocyte C28/I2 cell-line and primary human articular chondrocytes (hACs) from up to five different donors, using Wnt-activator CHIR99021, hypoxia-mimetic IOX2 and a hypoxia chamber. ANP32A was evaluated using real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot. In vivo, the effect of hypoxia was examined by immunohistochemistry in mice injected intra-articularly with IOX2 after destabilization of the medial meniscus. Effects of Wnt hyper-activation were investigated using Frzb-knockout mice and wild-type mice treated intra-articularly with CHIR99021. Wnt inhibition effects were assessed upon intra-articular injection of XAV939.

RESULTS

The hypoxia and Wnt signaling pathways were identified as networks controlling ANP32A expression. In vitro and in vivo experiments demonstrated increases in ANP32A upon hypoxic conditions (1.3-fold in hypoxia in C28/I2 cells with 95% confidence interval (CI) [1.11-1.54] and 1.90-fold in hACs [95% CI: 1.56-2] and 1.67-fold in ANP32A protein levels after DMM surgery with IOX2 injections [95% CI: 1.33-2.08]). Wnt hyper-activation decreased ANP32A in chondrocytes in vitro (1.23-fold decrease [95% CI: 1.02-1.49]) and in mice (1.45-fold decrease after CHIR99021 injection [95% CI: 1.22-1.72] and 1.41-fold decrease in Frzb-knockout mice [95% CI: 1.00-1.96]). Hypoxia and Wnt modulated ataxia-telangiectasia mutated serine/threonine kinase (ATM), an ANP32A target gene, in hACs (1.89-fold increase [95% CI: 1.38-2.60] and 1.41-fold decrease [95% CI: 1.02-1.96]).

CONCLUSIONS

Maintaining hypoxia and limiting Wnt activation sustain ANP32A and protect against osteoarthritis.

Novel genetic loci associated with osteoarthritis in multi-ancestry analyses in the Million Veteran Program and UK Biobank

Osteoarthritis is a common progressive joint disease. As no effective medical interventions are available, osteoarthritis often progresses to the end stage, in which only surgical options such as total joint replacement are available. A more thorough understanding of genetic influences of osteoarthritis is essential to develop targeted personalized approaches to treatment, ideally long before the end stage is reached. To date, there have been no large multiancestry genetic studies of osteoarthritis. Here, we leveraged the unique resources of 484,374 participants in the Million Veteran Program and UK Biobank to address this gap. Analyses included participants of European, African, Asian and Hispanic descent. We discovered osteoarthritis-associated genetic variation at 10 loci and replicated findings from previous osteoarthritis studies. We also present evidence that some osteoarthritis-associated regions are robust to population ancestry. Drug repurposing analyses revealed enrichment of targets of several medication classes and provide potential insight into the etiology of beneficial effects of antiepileptics on osteoarthritis pain.

ANP32A represses Wnt signaling across tissues thereby protecting against osteoarthritis and heart disease

OBJECTIVES

To investigate how ANP32A, previously linked to the antioxidant response, regulates Wnt signaling as unraveled by transcriptome analysis of Anp32a-deficient mouse articular cartilage, and its implications for osteoarthritis (OA) and diseases beyond the joint.

METHODS

Anp32a knockdown chondrogenic ATDC5 cells were cultured in micromasses. Wnt target genes, differentiation markers and matrix deposition were quantified. Wnt target genes were determined in articular cartilage from Anp32a-deficient mice and primary human articular chondrocytes upon ANP32A silencing, using qPCR, luciferase assays and immunohistochemistry. Co-immunoprecipitation, immunofluorescence and chromatin-immunoprecipitation quantitative PCR probed the molecular mechanism via which ANP32A regulates Wnt signaling. Anp32a-deficient mice were subjected to the destabilization of the medial meniscus (DMM) OA model and treated with a Wnt inhibitor and an antioxidant. Severity of OA was assessed by cartilage damage and osteophyte formation. Human Protein Atlas data analysis identified additional organs where ANP32A may regulate Wnt signaling. Wnt target genes were determined in heart and hippocampus from Anp32a-deficient mice, and cardiac hypertrophy and fibrosis quantified.

RESULTS

Anp32a loss triggered Wnt signaling hyper-activation in articular cartilage. Mechanistically, ANP32A inhibited target gene expression via histone acetylation masking. Wnt antagonist treatment reduced OA severity in Anp32a-deficient mice by preventing osteophyte formation but not cartilage degradation, contrasting with antioxidant treatment. Dual therapy ameliorated more OA features than individual treatments. Anp32a-deficient mice also showed Wnt hyper-activation in the heart, potentially explaining the cardiac hypertrophy phenotype found.

CONCLUSIONS

ANP32A is a novel translationally relevant repressor of Wnt signaling impacting osteoarthritis and cardiac disease.

Rare variant association study of veteran twin whole-genomes links severe depression with a nonsynonymous change in the neuronal gene BHLHE22

OBJECTIVES

Major Depressive Disorder (MDD) is a complex neuropsychiatric disease with known genetic associations, but without known links to rare variation in the human genome. Here we aim to identify rare genetic variants associated with MDD using deep whole-genome sequencing data in an independent population.

METHODS

We report the sequencing of 1,688 whole genomes in a large sample of male-male Veteran twins. Depression status was classified based on a structured diagnostic interview according to DSM-III-R diagnostic criteria. Searching only rare variants in genomic regions from recent GWAS on MDD, we used the optimised sequence kernel association test and Fisher's Exact test to fine map loci associated with severe depression.

RESULTS

Our analysis identified one gene associated with severe depression, basic helix loop helix e22 (P_Adjusted = 0.03) via SKAT-O test between unrelated severely depressed cases compared to unrelated non-depressed controls. The same gene BHLHE22 had a non-silent variant rs13279074 (P_Adjusted = 0.032) based on a single variant Fisher's Exact test between unrelated severely depressed cases compared to unrelated non-depressed controls.

CONCLUSION

The gene BHLHE22 shows compelling genetic evidence of directly impacting the severe depression phenotype. Together these results advance understanding of the genetic contribution to major depressive disorder in a new cohort and link a rare variant to severe forms of the disorder.

Single-Cell RNA-Seq Reveals Transcriptomic Heterogeneity and Post-Traumatic Osteoarthritis-Associated Early Molecular Changes in Mouse Articular Chondrocytes

Articular cartilage is a connective tissue lining the surfaces of synovial joints. When the cartilage severely wears down, it leads to osteoarthritis (OA), a debilitating disease that affects millions of people globally. The articular cartilage is composed of a dense extracellular matrix (ECM) with a sparse distribution of chondrocytes with varying morphology and potentially different functions. Elucidating the molecular and functional profiles of various chondrocyte subtypes and understanding the interplay between these chondrocyte subtypes and other cell types in the joint will greatly expand our understanding of joint biology and OA pathology. Although recent advances in high-throughput OMICS technologies have enabled molecular-level characterization of tissues and organs at an unprecedented resolution, thorough molecular profiling of articular chondrocytes has not yet been undertaken, which may be in part due to the technical difficulties in isolating chondrocytes from dense cartilage ECM. In this study, we profiled articular cartilage from healthy and injured mouse knee joints at a single-cell resolution and identified nine chondrocyte subtypes with distinct molecular profiles and injury-induced early molecular changes in these chondrocytes. We also compared mouse chondrocyte subpopulations to human chondrocytes and evaluated the extent of molecular similarity between mice and humans. This work expands our view of chondrocyte heterogeneity and rapid molecular changes in chondrocyte populations in response to joint trauma and highlights potential mechanisms that trigger cartilage degeneration.

An across-breed validation study of 46 genetic markers in canine hip dysplasia

Background

Canine hip dysplasia (CHD) is a common disease, with a complex genetic background. Dogs with severe CHD sometimes also suffer from osteoarthritis (OA), an inflammatory, often painful and incurable condition. Previous studies have reported breed-specific genetic loci associated with different hip dysplasia and OA phenotypes. However, the independent replication of the known associations within or across breeds has been difficult due to variable phenotype measures, inadequate sample sizes and the existence of population specific variants.

Results

We execute a validation study of 46 genetic markers in a cohort of nearly 1600 dogs from ten different breeds. We categorize the dogs into cases and controls according to the hip scoring system defined by the Fédération Cynologique Internationale (FCI). We validate 21 different loci associated on fourteen chromosomes. Twenty of these associated with CHD in specific breeds, whereas one locus is unique to the across-breed study. We show that genes involved in the neddylation pathway are enriched among the genes in the validated loci. Neddylation contributes to many cellular functions including inflammation.

Conclusions

Our study successfully replicates many loci and highlights the complex genetic architecture of CHD. Further characterisation of the associated loci could reveal CHD-relevant genes and pathways for improved understanding of the disease pathogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07375-x.

Inhibition of cyclooxygenase-2 activity in subchondral bone modifies a subtype of osteoarthritis

Osteoarthritis (OA) causes the destruction of joints. Its pathogenesis is still under investigation, and there is no effective disease-modifying therapy. Here, we report that elevated cyclooxygenase-2 (COX-2) expression in the osteocytes of subchondral bone causes both spontaneous OA and rheumatoid arthritis (RA). The knockout of COX-2 in osteocytes or treatment with a COX-2 inhibitor effectively rescues the structure of subchondral bone and attenuates cartilage degeneration in spontaneous OA (STR/Ort) mice and tumor necrosis factor-α transgenic RA mice. Thus, elevated COX-2 expression in subchondral bone induces both OA-associated and RA-associated joint cartilage degeneration. The inhibition of COX-2 expression can potentially modify joint destruction in patients with arthritis.

A hyperactivating proinflammatory RIPK2 allele associated with early-onset osteoarthritis

Osteoarthritis (OA) is a common debilitating disease characterized by abnormal remodeling of the cartilage and bone of the articular joint. Ameliorating therapeutics are lacking due to limited understanding of the molecular pathways affecting disease initiation and progression. Notably, although a link between inflammation and overt OA is well established, the role of inflammation as a driver of disease occurrence is highly disputed. We analyzed a family with dominant inheritance of early-onset OA and found that affected individuals harbored a rare variant allele encoding a significant amino acid change (p.Asn104Asp) in the kinase domain of receptor interacting protein kinase 2 (RIPK2), which transduces signals from activated bacterial peptidoglycan sensors through the NF-κB pathway to generate a proinflammatory immune response. Functional analyses of RIPK2 activity in zebrafish embryos indicated that the variant RIPK2104Asp protein is hyperactive in its signaling capacity, with augmented ability to activate the innate immune response and the NF-κB pathway and to promote upregulation of OA-associated genes. Further we show a second allele of RIPK2 linked to an inflammatory disease associated with arthritis also has enhanced activity stimulating the NF-κB pathway. Our studies reveal for the first time the inflammatory response can function as a gatekeeper risk factor for OA.

Human C-reactive protein aggravates osteoarthritis development in mice on a high-fat diet

OBJECTIVE

C-reactive protein (CRP) levels can be elevated in osteoarthritis (OA) patients. In addition to indicating systemic inflammation, it is suggested that CRP itself can play a role in OA development. Obesity and metabolic syndrome are important risk factors for OA and also induce elevated CRP levels. Here we evaluated in a human CRP (hCRP)-transgenic mouse model whether CRP itself contributes to the development of 'metabolic' OA.

DESIGN

Metabolic OA was induced by feeding 12-week-old hCRP-transgenic males (hCRP-tg, n = 30) and wild-type littermates (n = 15) a 45 kcal% high-fat diet (HFD) for 38 weeks. Cartilage degradation, osteophytes and synovitis were graded on Safranin O-stained histological knee joint sections. Inflammatory status was assessed by plasma lipid profiling, flow cytometric analyses of blood immune cell populations and immunohistochemical staining of synovial macrophage subsets.

RESULTS

Male hCRP-tg mice showed aggravated OA severity and increased osteophytosis compared with their wild-type littermates. Both classical and non-classical monocytes showed increased expression of CCR2 and CD86 in hCRP-tg males. HFD-induced effects were evident for nearly all lipids measured and indicated a similar low-grade systemic inflammation for both genotypes. Synovitis scores and synovial macrophage subsets were similar in the two groups.

CONCLUSIONS

Human CRP expression in a background of HFD-induced metabolic dysfunction resulted in the aggravation of OA through increased cartilage degeneration and osteophytosis. Increased recruitment of classical and non-classical monocytes might be a mechanism of action through which CRP is involved in aggravating this process. These findings suggest interventions selectively directed against CRP activity could ameliorate metabolic OA development.

ANP32A regulates ATM expression and prevents oxidative stress in cartilage, brain, and bone

Osteoarthritis is the most common joint disorder with increasing global prevalence due to aging of the population. Current therapy is limited to symptom relief, yet there is no cure. Its multifactorial etiology includes oxidative stress and overproduction of reactive oxygen species, but the regulation of these processes in the joint is insufficiently understood. We report that ANP32A protects the cartilage against oxidative stress, preventing osteoarthritis development and disease progression. ANP32A is down-regulated in human and mouse osteoarthritic cartilage. Microarray profiling revealed that ANP32A protects the joint by promoting the expression of ATM, a key regulator of the cellular oxidative defense. Antioxidant treatment reduced the severity of osteoarthritis, osteopenia, and cerebellar ataxia features in Anp32a-deficient mice, revealing that the ANP32A/ATM axis discovered in cartilage is also present in brain and bone. Our findings indicate that modulating ANP32A signaling could help manage oxidative stress in cartilage, brain, and bone with therapeutic implications for osteoarthritis, neurological disease, and osteoporosis.

A case-control study and meta-analysis reveal the association between COX-2 G-765C polymorphism and primary end-stage hip and knee osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a popular arthrosis featured as pain, limited joint activity, and deformity. Cyclooxygenase-2 (COX-2) has been reported to be up-regulated in arthritic tissues and is integral to the progression of osteoarthritis (OA). Previous studies showed the COX-2 promoter G-765C polymorphism could influence COX-2 expression. However, the relationship between the variant and OA risk is contrasting.

METHODS

We conducted a case-control study with 196 primary end-stage hip and knee OA cases and 196 controls in a Chinese Han population. Subsequently, we integrated this case-control study in a meta-analysis to acquire greater statistical power. The results from our case-control study using MassARRAY genotyping technology and binary logistic regression statistical methods.

RESULTS

The variant carriers in the Chinese Han population had a lower primary end-stage hip and knee OA susceptibility (C vs G: OR = 0.350, 95%CI: 0.154-0.797, P = .012; GC vs GG: adjusted OR = 0.282, 95%CI: 0.118-0.676, P = .005). Stratification studies indicated that a higher GC frequency in women decreased not only knee OA susceptibility but also unilateral knee OA risk. The meta-analysis showed that the variant exhibited a significantly decreased OA risk through comparisons involving allelic, homozygous, heterozygous, and dominant models.

CONCLUSION

Our findings suggest that the COX-2 G-765C polymorphism exerts a protective effect against primary end-stage knee osteoarthritis in a female Chinese Han population.

Association between EN1 rs4144782 and susceptibility of knee osteoarthritis: A case-control study

Osteoarthritis (OA) is a complex disease that affects the whole joint, resulting from the combined influence of biomechanical factors and genetic factors. The heritable component for primary OA accounts for about 60% of variation in population liability to the disease. So far, genome-wide association studies (GWAS) and candidate gene studies have established many OA-related loci. However, these findings account for only a rather small fraction of the genetic component. To further reveal the genetic architecture of OA, we conducted this case-control study to explore the association of locus EN1 rs4144782 and knee OA susceptibility in a Chinese population. EN1 rs4144782 was significantly associated with increased risk of knee OA (OR=1.26; 95% CI: 1.05-1.50, P value=0.012). In dominant model, compared with carriers of GG genotype, those with AG or AA genotype have an 1.44-fold increased risk of OA (OR: 1.44; 95% CI: 1.10-1.88; P value=0.008). Subgroup analyses didn't change the results materially. This should be the first association study of EN1 locus on risk of OA, and our finding suggested that the EN1 rs4144782 might contribute to the susceptibility of knee OA.

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.

The genetics behind osteoarthritis: Asian focus

Osteoarthritis (OA), a degenerative joint disease, is the most common form of arthritis in the elderly. Problems arising from the condition are not only health, physical, and psychological, but also economical and social. OA is a complex disease causes by environmental factors (obesity, female gender, advancing age) and genetics. A strong genetic contribution to primary OA has been observed in several studies. Asian population is undoubtedly genetically different from European, whom most studies have been performed. This review systematically compares results of molecules involved with OA from studies performed on Asian and Caucasian populations. The clear differences between Asian and Caucasian populations may be from the sex- and ethnic-specific nature of the disease, as well as from the inclusion criteria of the studies. Global collaboration is highly significant in understanding genetic underlying OA. Knowledge gained from genetic study is important to the development of prevention and therapeutic intervention, and to identify individuals at risk of developing severe or progressive OA.

Phenome-Wide Association Study to Explore Relationships between Immune System Related Genetic Loci and Complex Traits and Diseases

We performed a Phenome-Wide Association Study (PheWAS) to identify interrelationships between the immune system genetic architecture and a wide array of phenotypes from two de-identified electronic health record (EHR) biorepositories. We selected variants within genes encoding critical factors in the immune system and variants with known associations with autoimmunity. To define case/control status for EHR diagnoses, we used International Classification of Diseases, Ninth Revision (ICD-9) diagnosis codes from 3,024 Geisinger Clinic MyCode^® subjects (470 diagnoses) and 2,899 Vanderbilt University Medical Center BioVU biorepository subjects (380 diagnoses). A pooled-analysis was also carried out for the replicating results of the two data sets. We identified new associations with potential biological relevance including SNPs in tumor necrosis factor (TNF) and ankyrin-related genes associated with acute and chronic sinusitis and acute respiratory tract infection. The two most significant associations identified were for the C6orf10 SNP rs6910071 and “rheumatoid arthritis” (ICD-9 code category 714) (p_METAL = 2.58 x 10⁻⁹) and the ATN1 SNP rs2239167 and “diabetes mellitus, type 2” (ICD-9 code category 250) (p_METAL = 6.39 x 10⁻⁹). This study highlights the utility of using PheWAS in conjunction with EHRs to discover new genotypic-phenotypic associations for immune-system related genetic loci.

Del1 Knockout Mice Developed More Severe Osteoarthritis Associated with Increased Susceptibility of Chondrocytes to Apoptosis

OBJECTIVE

We identified significant expression of the matricellular protein, DEL1, in hypertrophic and mature cartilage during development. We hypothesized that this tissue-specific expression indicated a biological role for DEL1 in cartilage biology.

METHODS

Del1 KO and WT mice had cartilage thickness evaluated by histomorphometry. Additional mice underwent medial meniscectomy to induce osteoarthritis, and were assayed at 1 week for apoptosis by TUNEL staining and at 8 weeks for histology and OA scoring. In vitro proliferation and apoptosis assays were performed on primary chondrocytes.

RESULTS

Deletion of the Del1 gene led to decreased amounts of cartilage in the ears and knee joints in mice with otherwise normal skeletal morphology. Destabilization of the knee led to more severe OA compared to controls. In vitro, DEL1 blocked apoptosis in chondrocytes.

CONCLUSION

Osteoarthritis is among the most prevalent diseases worldwide and increasing in incidence as our population ages. Initiation begins with an injury resulting in the release of inflammatory mediators. Excessive production of inflammatory mediators results in apoptosis of chondrocytes. Because of the limited ability of chondrocytes to regenerate, articular cartilage deteriorates leading to the clinical symptoms including severe pain and decreased mobility. No treatments effectively block the progression of OA. We propose that direct modulation of chondrocyte apoptosis is a key variable in the etiology of OA, and therapies aimed at preventing this important step represent a new class of regenerative medicine targets.

The association between DVWA polymorphisms and osteoarthritis susceptibility: a genetic meta-analysis

It has been reported that the double von Willebrandfactor domain A (DVWA) gene polymorphisms may be associated with osteoarthritis (OA) risk. However, some studies yielded conflicting results. Therefore, we conducted a comprehensive meta-analysis to identify the association of DVWA gene polymorphisms and the susceptibility to OA. We conducted a systematic search in PubMed, Embase (Ovid), China National Knowledge Internet (CNKI) and Wangfang databases up to May 15, 2015. Odds ratio (OR) and 95% confidence interval (CI) were used to pool the effect size. Statistical analyses were performed with STATA 11.0 software. In total, 11 studies from five articles with 13,579 subjectswere included in this meta-analysis. The overall results indicated that there was a significant association between DVWA rs7639618 polymorphism and OA susceptibility observed in dominant and co-dominant models. In the subgroup analysis, we found that DVWA gene rs7639618 and rs11718863 polymorphism was associated with OA risk in Asians (GG+GA vs. AA: OR=1.34, P<0.001; G vs. A: OR=1.29, P=0.019). Furthermore, for rs7639618, the dominant (GG+GA) and heterozygote (GA) may strongly increase the knee OA susceptibility (GG+GA vs. AA: OR=1.27, P<0.001), especially in Asians. In addition, as for rs11718863, a trend of increased knee OA risk was found in Asians (TT+TA vs. AA: OR=1.54, P<0.001). In conclusion, the meta-analysis results suggested that DVWArs7639618 and rs11718863 polymorphisms may increase the risk of knee OA susceptibility in Asians, but not in Caucasians. However, no significant association between SNP rs7639618 and rs11718863 and hip OA risk was identified.

Celecoxib can suppress expression of genes associated with PGE2 pathway in chondrocytes under inflammatory conditions

This study aimed to investigate the effect of a selective cyclooxygenase-2 (COX-2) inhibitor (celecoxib) on the expression of arachidonate-associated inflammatory genes in cultured human normal chondrocytes. Normal chondrocytes were obtained from the cartilage of three different amputated patients without osteoarthritis (OA). Affymetrix Human microarray was used to assess the alterations in gene expression in three groups of cells: untreated cells (negative control group), cells treated with interleukin-1β (IL-1β) (positive control group), and cells treated with IL-1β and celecoxib. The patterns of up-regulation and down-regulation of gene expression were further validated by real-time PCR. A total of 1091 up-regulated genes and 1252 down-regulated genes were identified in the positive control group compared with the negative control group. Among them, PTGS2, ADAMTS5, PTGER2, mPTGES and PTGER4 are known to be involved in chondrocyte inflammation, while VEGFA, BCL2, TRAF1, CYR61, BMP6, DAPK1, DUSP7, IL1RN, MMP13 and TNFSF10 were reported being associated with cytokine and chemokine signaling. 189 up-regulated genes and 177 down-regulated genes were identified in the positive control group compared with intervention group. PTGS1, PTGS2, ADAMTS5, PTGER2, mPTGES and PTGER4 were among the genes down-regulated upon the treatment with celecoxib. Our results demonstrated that the OA chondrocytes are the site of active eicosanoid production. IL-1β can activate inflammation in chondrocytes and trigger the production of various proteins involved in cyclooxygenase pathway. The expression of genes corresponding to these proteins can be down-regulated by celecoxib. The findings indicate that the therapy with prostaglandin E2 (PGE2)-blocking agents may decrease the PGE2 production not only by direct inhibition of COX-2 activity, but also by down-regulating the expression of genes encoding for COX-2, microsomal prostaglandin-endoperoxide synthase 1 (mPGES-1) and prostaglandin E receptors 4 (EP4) in the articular chondrocytes.

Kinetics of gene expression and bone remodelling in the clinical phase of collagen-induced arthritis

Introduction

Pathological bone changes differ considerably between inflammatory arthritic diseases and most studies have focused on bone erosion. Collagen-induced arthritis (CIA) is a model for rheumatoid arthritis, which, in addition to bone erosion, demonstrates bone formation at the time of clinical manifestations. The objective of this study was to use this model to characterise the histological and molecular changes in bone remodelling, and relate these to the clinical disease development.

Methods

A histological and gene expression profiling time-course study on bone remodelling in CIA was linked to onset of clinical symptoms. Global gene expression was studied with a gene chip array system.

Results

The main histopathological changes in bone structure and inflammation occurred during the first two weeks following the onset of clinical symptoms in the joint. Hereafter, the inflammation declined and remodelling of formed bone dominated.

Global gene expression profiling showed simultaneous upregulation of genes related to bone changes and inflammation in week 0 to 2 after onset of clinical disease. Furthermore, we observed time-dependent expression of genes involved in early and late osteoblast differentiation and function, which mirrored the histopathological bone changes. The differentially expressed genes belong to the bone morphogenetic pathway (BMP) and, in addition, include the osteoblast markers integrin-binding sialoprotein (Ibsp), bone gamma-carboxyglutamate protein (Bglap1), and secreted phosphoprotein 1 (Spp1). Pregnancy-associated protein A (Pappa) and periostin (Postn), differentially expressed in the early disease phase, are proposed to participate in bone formation, and we suggest that they play a role in early bone formation in the CIA model. Comparison to human genome-wide association studies (GWAS) revealed differential expression of several genes associated with human arthritis.

Conclusions

In the CIA model, bone formation in the joint starts shortly after onset of clinical symptoms, which results in bony fusion within one to two weeks. This makes it a candidate model for investigating the relationship between inflammation and bone formation in inflammatory arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0531-7) contains supplementary material, which is available to authorized users.

Improved prediction of knee osteoarthritis progression by genetic polymorphisms: the Arthrotest Study

OBJECTIVE

The aim of this study was to develop a genetic prognostic tool to predict radiographic progression towards severe disease in primary knee OA (KOA) patients.

METHODS

This investigation was a cross-sectional, retrospective, multicentric association study in 595 Spanish KOA patients. Caucasian patients aged ≥40 years at the time of diagnosis of primary KOA of Kellgren-Lawrence grade 2 or 3 were included. Patients who progressed to Kellgren-Lawrence score 4 or who were referred for total knee replacement within 8 years after diagnosis were classified as progressors to severe disease. Clinical variables of the initial stages of the disease (gender, BMI, age at diagnosis, OA in the contralateral knee, and OA in other joints) were registered as potential predictors. Single nucleotide polymorphisms and clinical variables with an association of P < 0.05 were included in the multivariate analysis using forward logistic regression.

RESULTS

A total of 23 single nucleotide polymorphisms and the time of primary KOA diagnosis were significantly associated with KOA severe progression in the exploratory cohort (n = 220; P < 0.05). The predictive accuracy of the clinical variables was limited: area under the curve (AUC) = 0.66. When genetic variables were added to the clinical model (full model), the prediction of KOA progression was significantly improved (AUC = 0.82). Combining only genetic variables (rs2073508, rs10845493, rs2206593, rs10519263, rs874692, rs7342880, rs780094 and rs12009), a predictive model with good accuracy was also obtained (AUC = 0.78). The predictive ability for KOA progression of the full model was confirmed on the replication cohort (two-sample Z-test; n = 62; P = 0.190).

CONCLUSION

An accurate prognostic tool to predict primary KOA progression has been developed based on genetic and clinical information from OA patients.

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.

Assessment of osteoarthritis candidate genes in a meta-analysis of nine genome-wide association studies

Objective

To assess candidate genes for association with osteoarthritis (OA) and identify promising genetic factors and, secondarily, to assess the candidate gene approach in OA.

Methods

A total of 199 candidate genes for association with OA were identified using Human Genome Epidemiology (HuGE) Navigator. All of their single-nucleotide polymorphisms (SNPs) with an allele frequency of >5% were assessed by fixed-effects meta-analysis of 9 genome-wide association studies (GWAS) that included 5,636 patients with knee OA and 16,972 control subjects and 4,349 patients with hip OA and 17,836 control subjects of European ancestry. An additional 5,921 individuals were genotyped for significantly associated SNPs in the meta-analysis. After correction for the number of independent tests, P values less than 1.58 × 10⁻⁵ were considered significant.

Results

SNPs at only 2 of the 199 candidate genes (COL11A1 and VEGF) were associated with OA in the meta-analysis. Two SNPs in COL11A1 showed association with hip OA in the combined analysis: rs4907986 (P = 1.29 × 10⁻⁵, odds ratio [OR] 1.12, 95% confidence interval [95% CI] 1.06−1.17) and rs1241164 (P = 1.47 × 10⁻⁵, OR 0.82, 95% CI 0.74−0.89). The sex-stratified analysis also showed association of COL11A1 SNP rs4908291 in women (P = 1.29 × 10⁻⁵, OR 0.87, 95% CI 0.82−0.92); this SNP showed linkage disequilibrium with rs4907986. A single SNP of VEGF, rs833058, showed association with hip OA in men (P = 1.35 × 10⁻⁵, OR 0.85, 95% CI 0.79−0.91). After additional samples were genotyped, association at one of the COL11A1 signals was reinforced, whereas association at VEGF was slightly weakened.

Conclusion

Two candidate genes, COL11A1 and VEGF, were significantly associated with OA in this focused meta-analysis. The remaining candidate genes were not associated.

Tibiofemoral subchondral surface ratio (SSR) is a predictor of osteoarthritis symptoms and radiographic progression: data from the Osteoarthritis Initiative (OAI)

OBJECTIVE

Symptomatic knee osteoarthritis (OA) is poorly correlated with radiographic severity, but subchondral bone measures may be useful for risk assessment as bone shape is grossly unaffected at early radiographic stages. We sought to determine whether compartment-specific size mismatch in the naturally asymmetric tibiofemoral joint, measured as tibiofemoral subchondral surface ratio (SSR): (1) predicts incident symptoms, (2) predicts incident or progressive OA, (3) is reproducible and time invariant.

DESIGN

OA Initiative participants with baseline MRIs and up to 48-month follow-up (n = 1,338) were analyzed. Logistic regression was used to determine the association between SSR and incident symptoms, incident OA, and progression of OA after adjusting for demographic, radiologic, injury-related, and lifestyle-related factors. Reproducibility was assessed as % coefficient of variation (CV) on repeat MRI studies at baseline and 24 months.

RESULTS

Increased medial SSR is protective against incident symptoms at 48 months (per 0.1 increase: OR 0.48 CI 0.30, 0.75; P = 0.001). Increased lateral SSR values are protective against lateral OA incidence (OR 0.23 CI 0.06, 0.77; P = 0.016) or progression (OR 0.66 CI 0.43, 0.99; P = 0.049) at 24 months. Both medial and lateral SSR are stable over time (medial: mean change 0.001 SD 0.016; lateral: mean change 0.000 SD 0.017) and are highly reproducible (3.0% CV medial SSR; 2.7% CV lateral SSR).

CONCLUSIONS

A larger medial SSR is protective against developing OA-related symptoms. A larger lateral SSR is protective against lateral OA incidence or progression. Finally, lateral and medial SSR are stable over time and are highly reproducible across MRI studies.

Genetic influences on hand osteoarthritis in Finnish women--a replication study of candidate genes

Objectives

Our aims were to replicate some previously reported associations of single nucleotide polymorphisms (SNPs) in five genes (A2BP1, COG5, GDF5, HFE, ESR1) with hand osteoarthritis (OA), and to examine whether genes (BCAP29, DIO2, DUS4L, DVWA, HLA, PTGS2, PARD3B, TGFB1 and TRIB1) associated with OA at other joint sites were associated with hand OA among Finnish women.

Design

We examined the bilateral hand radiographs of 542 occupationally active Finnish female dentists and teachers aged 45 to 63 and classified them according to the presence of OA by using reference images. Data regarding finger joint pain and other risk factors were collected using a questionnaire. We defined two hand OA phenotypes: radiographic OA in at least three joints (ROA) and symptomatic DIP OA. The genotypes were determined by PCR-based methods. In statistical analysis, we used SNPStats software, the chi-square test and logistic regression.

Results

Of the SNPs, rs716508 in A2BP1 was associated with ROA (OR = 0.7, 95% CI 0.5–0.9) and rs1800470 in TGFB1 with symptomatic DIP OA (1.8, 1.2–2.9). We found an interaction between ESR1 (rs9340799) and occupation: teachers with the minor allele were at an increased risk of symptomatic DIP OA (2.8, 1.3–6.5). We saw no association among the dentists. We also found that the carriage of the COG5 rs3757713 C allele increased the risk of ROA only among women with the BCAP29 rs10953541 CC genotype (2.6; 1.1–6.1). There was also a suggestive interaction between the HFE rs179945 and the ESR1 rs9340799, and the carriage of the minor allele of either of these SNPs was associated with an increased risk of symptomatic DIP OA (2.1, 1.3–2.5).

Conclusions

Our results support the earlier findings of A2BP1 and TBGF1 being OA susceptibility genes and provide evidence of a possible gene-gene interaction in the genetic influence on hand OA predisposition.

Transcriptomics of wild-type mice and mice lacking ADAMTS-5 activity identifies genes involved in osteoarthritis initiation and cartilage destruction

OBJECTIVE

To identify changes in gene expression in mice with osteoarthritis (OA) in order to explore the mechanisms of the disease.

METHODS

Gene expression profiling was performed in cartilage from mice with surgically induced OA. We used wild-type (WT) mice and Adamts5Δcat mice, in which ADAMTS-5 activity is lacking and aggrecan loss and cartilage erosion are inhibited, to distinguish gene expression changes that are independent of ADAMTS-5 activity and cartilage breakdown. Mechanical instability was introduced into the knee joints of 10-week-old male mice via surgical destabilization of the medial meniscus (DMM). Cartilage from the developing lesion in the destabilized medial meniscus and corresponding regions in sham-operated joints was harvested by microdissection at 1, 2, and 6 weeks postsurgery, and RNA was extracted, amplified, and hybridized to whole-genome microarrays.

RESULTS

Several previously identified OA-related genes, including Ptgs2, Crlf1, and Inhba, and novel genes, such as Phdla2 and Il11, were up-regulated in both WT mice and Adamts5Δcat mice, indicating that they are independent of ADAMTS-5 activity. The altered expression of other genes, including Col10a1, the sentinel marker of cartilage hypertrophy, and Wnt/β-catenin pathway genes, required ADAMTS-5 activity. Cell death pathway genes were dysregulated, and Tp53, Foxo4, and Xbp1 endoplasmic reticulum-stress transcriptional networks were activated. Analysis of degradome genes identified up-regulation of many proteases, including Mmp3, Capn2, and the novel cartilage proteases Prss46 and Klk8. Comparison with other studies identified 16 genes also dysregulated in rat and human OA as priorities for study.

CONCLUSION

We have identified, for the first time, several genes that have an ADAMTS-5-independent role in OA, identifying them as possible OA initiation candidates. This work provides new insights into the sequence of gene dysregulation and the molecular basis of cartilage destruction in OA.

New horizons in osteoarthritis

Osteoarthritis (OA) is the most common type of arthritis worldwide and rapidly increasing with ageing populations. It is a major source of pain and disability for individuals and economic burden for health economies. Modern imaging, in particular magnetic resonance imaging (MRI), has helped us to understand that OA is a dynamic remodelling process involving all the structures within the joint. Inflammation is common in OA, with a high prevalence of synovitis seen on imaging, and this has been associated with joint pain. MRI detected changes within the subchondral bone are also common and associated with pain and structural progression. Targeting individual pathologies may offer potential new therapeutic options for OA; this is particularly important given the current treatments are often limited by side effects or lack of efficacy. New approaches to understanding the pathology and pain pathways in OA offer hope of novel analgesic options, for example, monoclonal antibodies against nerve growth factor and centrally acting drugs such as duloxetine, tapentadol and bradykinin receptor antagonists have all recently undergone trials in OA. While treatment for OA has until now relied on symptom management, for the first time, recent trials suggest that structure modification may be possible by treating the subchondral bone.

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.

Genetic factors in OA pathogenesis

Osteoarthritis (OA) is known to have an important genetic component and human genetic studies can help unravel the molecular mechanisms responsible for joint damage and nociception involved in OA. Genetic studies in humans have identified molecules involved in signaling cascades that are important for the pathology of the joint components such as the bone morphogenetic protein growth differentiation factor 5 (GDF5). Genomewide association scans (GWAS) in Asians have uncovered a likely role for structural extracellular matrix components (DVWA), and for molecules involved in immune response (HLA class II DQB1 and BTNL2) but these genes are not associated in Caucasian patients. In Caucasians a ~300 kilobase region in chromosome 7q22 containing several genes has been found to be reproducibly associated with OA. A recent European GWAS taking advantage of imputation techniques has uncovered a variant in the MCF2L gene as significantly associated with large joint OA. MCF2L is involved in neurotrophin mediated regulation of cell motility in the peripheral nervous system, and thus potentially implicated in nociception in OA. As the number of OA cases with genomewide genotyping increases it is expected that many more reproducible variants implicated in OA will be reported. This article is part of a Special Issue entitled "Osteoarthritis".

Genetic risk load and age at symptom onset of knee osteoarthritis

To test whether a higher genetic risk load for knee osteoarthritis (OA) is associated with an earlier age at symptom onset. Six polymorphisms in GDF5, PTGS2, 7q22 locus, DVWA, DIO3, and ASPN that have been associated with knee OA were analyzed in 255 patients that had undergone total knee replacement (TKR) because of primary OA and in 457 healthy controls. We looked for association between the number of risk alleles in each patient and his age at symptom onset with linear regression and t-tests between the upper and lower quartiles. There was not even a weak trend in the direction of a younger age at symptom onset in the patients carrying more risk alleles. Patients in the upper quartile of age at symptom onset (67.0 ± 2.8 years) carried the same number of OA risk alleles (5.4 ± 1.4 vs. 5.3 ± 1.0) than patients in the lower quartile (44.6 ± 5.5 years). We did not find any evidence in support of the hypothesis of an earlier knee OA symptom onset associated with higher genetic risk load as determined by the six loci. This result suggests that old age and genetic risk act as independent factors in the pathogenesis of OA. It also indicates that designing OA genetic studies with patients selected for early symptom onset will not provide any substantial power gain.

An Association Study of Interleukin 18 Receptor Genes (IL18R1 and IL18RAP) in Lumbar Disc Degeneration

Objectives:

To examine association of candidate genetic variants in structural, inflammatory, matrix modifying, vitamin D receptor genes and variants associated with osteoarthritis, with surgical candidates and surgical patients with lumbar disc degeneration (LDD), in light of their previously reported susceptibility for LDD.

Methods:

Genotyping of 146 Norwegian LDD patients and 188 Norwegian controls was performed for 20 single-nucleotide polymorphisms (SNPs) from collagen, aggrecan, interleukin, VDR, MMP3 and COX2 genes and 7 SNPs from osteoarthritic genes.

Results:

The neighboring genes IL18R1 and IL18RAP polymorphisms (rs2287037 and rs1420100), showed a statistically non-significant risk for developing LDD (OR 1.36 [95 % CI 0.99 – 1.87]; p=0.06 and OR 1.33 [95 % CI 0.98-1.81]; p=0.07). Homozygosity of these risk alleles was associated with LDD (p=0.023 and p=0.027). The non-risk alleles at these SNPs were situated on a haplotype negatively associated with LDD (p=0.008). Carriage of at least one non-risk allele at both loci also reduces the risk of developing LDD (OR 0.51 [95 % CI 0.33-0.80]; p=0.003).

Conclusion:

Our findings support the polygenic nature of LDD and suggest that variation in interleukin 18 receptor genes could affect the risk of severe LDD and associated low back pain.

Translational animal models using veterinary patients - An example of canine osteoarthritis (OA)

Background and purpose The use of laboratory animals in pain research has powerfully contributed to our detailed understanding of the physiological mechanisms of pain. Animal models also represent an essential tool to screen and select novel drug molecules with potentially analgesic properties. Despite of the inevitable input of laboratory animal trials, recent studies have shown that animal pain models have repeatedly failed to predict clinical analgesic efficacy and adverse side effects of potential drug molecules in human pain patients. This paper provides a review of the laboratory animal models of OA, which have been developed to test efficacy of novel analgesics. The paper also presents spontaneous OA in canine veterinary patients, and methods to observe chronic pain in nonverbal dogs. Methods PubMed data base was searched as a reference list to locate most relevant articles. A number of 118 articles including 4 reviews were located. Web pages of 4 establishments and 2 private organizations were also accessed. Results The clinical expression and pathogenesis of naturally occurring OA in dogs is considered an analogous disease that occurs in humans, including pain and lameness. OA may occur in any joint in dogs as well as in humans. Primary idiopathic OA in dogs is rare, but certain breeds may be predisposed to it. For the most part, canine OA is considered secondary to acquired or congenital musculoskeletal disorders. Concomitant factors, such as aging and obesity, likely accelerate progression. However, mechanical factors appear to predominate in the etiopathogenesis of canine spontaneous OA. Both subjective (validated questionnaire) and objective (gait analysis) tools are available to measure OA related pain in dogs. Information on the prevalence of canine OA is limited, but rough surveys suggest that 11 million dogs in the United States and 5 million in Europe could suffer from OA. Ethical considerations concerning the use of privately owned dogs can be resolved by a careful experimental design. Conclusion Canine spontaneous OA could serve as a translational animal model that would more closely mimick clinical OA related pain conditions in humans. Privately owned dogs would make a solution to fix the gap between animal pain models and clinical trials when testing potential analgesic drug molecules. Close interdisciplinary cooperation would guarantee that both scientific and ethical intentions would be achieved. Implications The predictability of translational pain research would improve by using privately owned dogs as chronic pain models when testing novel analgesics.

Osteoarthritis of the knee and hip. Part I: aetiology and pathogenesis as a basis for pharmacotherapy

OBJECTIVES

Osteoarthritis (OA) of the knee and hip is among the most frequent and debilitating arthritic conditions. Aside from surgical intervention in severe cases, conventional treatment involves relieving painful symptoms with non-steroidal anti-inflammatory drugs (NSAIDs), narcotic and non-narcotic (weak) analgesics and physical therapy. To obtain insight into the extent of pathological changes in hip and knee OA we reviewed current literature on the pathogenesis of this state as a basis for current pharmacotherapy options.

KEY FINDINGS

Key features of the pathological joint changes in OA include: cartilage destruction by pro-inflammatory cytokines, matrix metalloproteinases and prostaglandins, which promote a catabolic environment; subchondral bone remodelling and resorption; hypertrophic differentiation of chondrocytes; neovascularisation of synovial tissue; and focal calcification of joint cartilage. Despite the central involvement of hyaline cartilage in OA pathogenesis, the source of pain likely stems from the richly innervated synovium, subchondral bone and periosteum components of the joint. Tissue damage during joint degeneration generates nociceptive stimuli. The presence of inflammatory mediators, including bradykinin, prostaglandins and leukotrienes, lowers the threshold of the Aδ and C pain fibres, resulting in a heightened response to painful stimuli.

SUMMARY

It is our opinion that it is important to base and centre the management of OA patients on the severity of patient-important outcomes, rather than purely an assessment of damage to the joint. The joint damage, as interpreted from radiographs, is not necessarily representative of the symptoms experienced. The management of OA primarily comprises pharmacological therapy, surgical interventions and various non-pharmacological interventions.

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.

Combined effect of cytokine gene polymorphisms on end-stage knee osteoarthritis from Chinese Han population

The mechanism of osteoarthritis (OA) is not well understood. Cytokines have been implicated in the episode, and there is increasing evidence that the host's cytokine response is genetically determined. We determined the predictive value of IL-634G./C, ICAM-1 469 K/E and IL-10-1082A/G, -819T/C and -592A/C gene polymorphisms on knee OA. The study included 1007 patients with end-stage knee OA and 910 healthy controls. Genomic DNA was prepared from peripheral blood leukocytes. Genotypes and allele frequencies were determined using restriction fragment length polymorphism analysis of polymerase chain reaction products. No significant difference in the IL-10 promoter allele or haplotype frequencies between end-stage knee OA and controls was found. Patients with end-stage knee OA showed a significantly higher prevalence of IL-6-634G/ICAM-1 469E carrier than that in controls (P = 0.017). Results indicate that IL-6-634G/ICAM-1 469E carrier could be associated with increased susceptibility to end-stage knee OA.

Association of vitamin D status with knee pain and radiographic knee osteoarthritis

OBJECTIVE

The objective of the present study was to explore the association of serum vitamin D concentration and polymorphism in the vitamin D receptor (VDR), with knee pain and radiographic knee osteoarthritis (OA) among men and women in a large population-based UK cohort study.

METHODS

Seven hundred and eighty-seven participants in the Hertfordshire Cohort Study (399 men, 388 women; mean age 65.6±2.7 years) underwent a questionnaire on knee pain and radiographic knee examination. This study examined the association of Fok1, Cdx2 and Apa1 polymorphism in the gene for the VDR and serum 25(OH)D concentration with knee pain and radiographic knee OA by a generalized estimating equations population averaged logistic regression analysis in the Hertfordshire Cohort Study.

RESULTS

There were no associations of Fok1, Cdx2 and Apa1 polymorphisms of the VDR with knee OA except for Aa for Apa1 compared with AA [Odds ratio (OR) 0.59, 95% confidence interval (CI) 0.36-0.95, P=0.031]. While, ff for Fok1 (OR 1.60, 95% CI 1.07-2.39, P=0.022) and AA for Cdx2 polymorphism (OR 2.21, 95% CI 1.07-4.56, P=0.032) was significantly associated with higher prevalence of knee pain compared with FF for Fok1 and GG for Cdx2, respectively. None of these are statistically significant after adjusting for the three polymorphisms tested. 25(OH)D level was not significantly associated with radiographic knee OA, while, low tertile of 25(OH)D level tended to be associated with knee pain compared with high tertile of 25(OH)D level.

CONCLUSION

The present cross-sectional study using a large-scale population from the Hertfordshire Cohort study indicated that vitamin D may be associated with pain rather than radiographic change, but the evidence for an association between vitamin D genetic variation and pain in knee OA is very weak in the present study. Further replication of our results will be required to elucidate the association of vitamin D and knee OA.

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.