The contribution of genes to osteoarthritis

Molecular Mechanisms Linking Osteoarthritis and Alzheimer's Disease: Shared Pathways, Mechanisms and Breakthrough Prospects

Alzheimer's disease (AD) is a progressive neurodegenerative disease mostly affecting the elderly population. It is characterized by cognitive decline that occurs due to impaired neurotransmission and neuronal death. Even though deposition of amyloid beta (Aβ) peptides and aggregation of hyperphosphorylated TAU have been established as major pathological hallmarks of the disease, other factors such as the interaction of genetic and environmental factors are believed to contribute to the development and progression of AD. In general, patients initially present mild forgetfulness and difficulty in forming new memories. As it progresses, there are significant impairments in problem solving, social interaction, speech and overall cognitive function of the affected individual. Osteoarthritis (OA) is the most recurrent form of arthritis and widely acknowledged as a whole-joint disease, distinguished by progressive degeneration and erosion of joint cartilage accompanying synovitis and subchondral bone changes that can prompt peripheral inflammatory responses. Also predominantly affecting the elderly, OA frequently embroils weight-bearing joints such as the knees, spine and hips leading to pains, stiffness and diminished joint mobility, which in turn significantly impacts the patient's standard of life. Both infirmities can co-occur in older adults as a result of independent factors, as multiple health conditions are common in old age. Additionally, risk factors such as genetics, lifestyle changes, age and chronic inflammation may contribute to both conditions in some individuals. Besides localized peripheral low-grade inflammation, it is notable that low-grade systemic inflammation prompted by OA can play a role in AD pathogenesis. Studies have explored relationships between systemic inflammatory-associated diseases like obesity, hypertension, dyslipidemia, diabetes mellitus and AD. Given that AD is the most common form of dementia and shares similar risk factors with OA-both being age-related and low-grade inflammatory-associated diseases, OA may indeed serve as a risk factor for AD. This work aims to review literature on molecular mechanisms linking OA and AD pathologies, and explore potential connections between these conditions alongside future prospects and innovative treatments.

Clinical aspects and outcomes in osteoarthritis

Osteoarthritis (OA) is the most prevalent type of arthritis worldwide, and its incidence significantly increases with age. It commonly affects the knees, hips, spine, big toes, and hands. OA can be identified through clinical examination, symptoms, and imaging methods. Its main symptoms include pain, stiffness, and limitations in joint movement. Examinations may reveal coarse crepitus, bony enlargement, and tenderness at the joint line. In severe cases of OA, rest pain, night pain, and deformity may occur. OA can lead to decreased physical activity, function, and quality of life due to symptoms such as pain and stiffness. To evaluate these impacts, patient-reported outcome measures (PROMs) are necessary. Various generic, disease-specific, and joint-specific PROMs have been developed and used in clinical practice to assess the outcomes of OA.

Contrast-enhanced micro-computed tomography of compartment and time-dependent changes in femoral cartilage and subchondral plate in a murine model of osteoarthritis

A lack of understanding of the mechanisms underlying osteoarthritis (OA) progression limits the development of effective long-term treatments. Quantitatively tracking spatiotemporal patterns of cartilage and bone degeneration is critical for assessment of more appropriately targeted OA therapies. In this study, we use contrast-enhanced micro-computed tomography (μCT) to establish a timeline of subchondral plate (SCP) and cartilage changes in the murine femur after destabilization of the medial meniscus (DMM). We performed DMM or sham surgery in 10-12-week-old male C57Bl/6J mice. Femora were imaged using μCT after 0, 2, 4, or 8 weeks. Cartilage-optimized scans were performed after immersion in contrast agent CA4+. Bone mineral density distribution (BMDD), cartilage attenuation, SCP, and cartilage thickness and volume were measured, including lateral and medial femoral condyle and patellar groove compartments. As early as 2 weeks post-DMM, cartilage thickness significantly increased and cartilage attenuation, SCP volume, and BMDD mean significantly decreased. Trends in cartilage and SCP metrics within each joint compartment reflected those seen in global measurements, and both BMDD and SCP thickness were consistently greater in the lateral and medial condyles than the patellar groove. Sham surgery also resulted in significant changes to SCP and cartilage metrics, highlighting a potential limitation of using surgical models to study tissue morphology or composition changes during OA progression. Contrast-enhanced μCT analysis is an effective tool to monitor changes in morphology and composition of cartilage, and when combined with bone-optimized μCT, can be used to assess the progression of degenerative changes after joint injury.

The Role of Wolves in Regulating a Chronic Non-communicable Disease, Osteoarthritis, in Prey Populations

It is widely accepted that predators disproportionately prey on individuals that are old, weak, diseased or injured. By selectively removing individuals with diseases, predators may play an important role in regulating the overall health of prey populations. However, that idea is seldom tested empirically. Here we assess the extent that wolves (Canis lupus) select adult moose (Alces alces) in Isle Royale National Park on the basis of age-class and osteoarthritis, a chronic, non-communicable disease. We also assess how temporal variation in kill rates (on moose by wolves) were associated with the subsequent incidence of osteoarthritis in the moose population over a 33-year period (1975–2007). Wolves showed strong selection for senescent moose and tended to avoid prime-aged adults. However, the presence of severe osteoarthritis, but not mild or moderate osteoarthritis, appeared to increase the vulnerability of prime-aged moose to predation. There was weak evidence to suggest that senescent moose with osteoarthritis maybe more vulnerable to wolves, compared to senescent moose without the disease. The incidence of osteoarthritis declined following years with higher kill rates–which is plausibly due to the selective removal of individuals with osteoarthritis. Together those results suggest that selective predation plays an important role in regulating the health of prey populations. Additionally, because osteoarthritis is influenced by genetic factors, these results highlight how wolf predation may act as a selective force against genes associated with developing severe osteoarthritis as a prime-aged adult. Our findings highlight one benefits of allowing predators to naturally regulate prey populations. The evidence we present for predation’s influence on the health of prey populations is also relevant for policy-related arguments about refraining from intensively hunting wolf populations.

Osteoarthritis: Prognosis and emerging therapeutic approach for disease management

Osteoarthritis (OA), a disorder of joints, is prevalent in older age. The contemporary cure for OA is aimed to confer symptomatic relief, consisting of temporary pain and swelling relief. In this paper, we discuss various modalities responsible for the onset of OA and associated with its severity. Inhibition of chondrocytes receptors such as DDR2, SDF-1, Asporin, and CXCR4 by specific pharmacological inhibitors attenuates OA, a critical step for finding potential disease modifying drugs. We critically analyzed recent OA studies with an emphasis on intermediate target molecules for OA intervention. We also explored some novel and safe treatments for OA by considering disease prognosis crosstalk with cellular signaling pathways.

Role of IL-17 gene polymorphisms in osteoarthritis: A meta-analysis based on observational studies

BACKGROUND

Osteoarthritis (OA) is a chronic complex multifactorial joint disease, and a major degenerative form of arthritis. Existing studies on the association between polymorphisms of the IL-17 gene and the risk of OA in different populations have yielded conflicting findings.

AIM

To investigate the association between polymorphisms of the IL-17 gene and the risk of OA.

METHODS

We conducted a meta-analysis by systematically searching databases, including PubMed, EMBASE, MEDLINE, Cochrane Library, and Google Scholar to evaluate this association by calculating pooled odds ratios with 95% confidence intervals. Moreover, subgroup analyses stratified by ethnicity and OA type were also conducted.

RESULTS

In a total of 6 citations involving 8 studies (2131 cases and 2299 controls), 4 single nucleotide polymorphisms were identified. Of these 4 polymorphisms, 2 (rs2275913, rs763780) were common in five case-control studies. Together, the pooled results revealed that the A allele and genotype AA/GA of the rs2275913 polymorphism, and the C allele and genotype CC of the rs763780 polymorphism in the IL-17 gene increased the risk of OA. Furthermore, stratification analyses by ethnicity and OA type showed that the rs2275913 polymorphism increased the risk of OA among Asians and in knee/hip OA, respectively. In addition, stratification analyses also revealed that the rs763780 polymorphism increased OA risk among both Asians and Caucasians in knee/hip OA.

CONCLUSION

The rs763780 polymorphism of the IL-17F gene increased the risk of OA, whereas the rs2275913 polymorphism of the IL-17A gene increased the risk of OA only among Asians. Due to the limitations of this study, these findings should be validated in future studies.

Genetic estrogen receptor alpha gene PvuII polymorphism in susceptibility to knee osteoarthritis in a Chinese Han population: A southern Jiangsu study

BACKGROUND

Knee osteoarthritis (KOA) is the most prevalent type of arthritis and genetic factors play an important role in KOA pathogenesis. Some studies have reported the association of estrogen receptor alpha (ESRα) gene polymorphism and KOA susceptibility in different populations. This study was designed to verify whether ESRα gene polymorphism (rs2234693) was associated with primary KOA in a Chinese Han population living in the south of Jiangsu.

METHODS

A case-control association study on single nucleotide polymorphism (SNP) rs2234693 was performed, and a total of 1953 subjects (1033 OA cases and 920 controls) were genotyped. Allele and genotype frequencies were compared between KOA cases and control participants.

RESULTS

SNP rs2234693 was significantly associated with KOA in the dominant genetic model (TT + TC vs. CC) in all the subjects (odds ratio (OR) = 1.30; 95% confidence interval (CI) = 1.02-1.66; P = .03), and T allele frequency was also higher compared with allele C (OR = 1.38; 95% CI = 1.06-1.80; P = .02). After stratification by gender, there was no evident difference between the two groups in female and male subjects (P > .05). With a stratification for KOA severity, the combined genotype (TT + TC) (OR = 1.47; 95% CI = 1.12-1.94; P < .01) and T allele (OR = 1.61; 95% CI = 1.19-2.19; P < .01) were evidently associated with mild KOA, but not with severe KOA.

CONCLUSIONS

ESRα gene is of considerable importance in the pathogenesis of early-stage KOA in a Chinese Han population living in southern Jiangsu.

Spa therapy and rehabilitation of musculoskeletal pathologies: a proposal for best practice in Italy

Spa therapy is a heterogeneous collection of treatments and methods based on natural resources. It is often considered as an option in the common therapeutic approach to many musculoskeletal disorders, as well as respiratory, vascular, and dermatological disorders. The objective of this paper is to highlight possible interactions between rehabilitation and spa medicine in the field of musculoskeletal disorders, through an analysis of the scientific literature, in order to give the practitioner the ability to integrate good clinical practice in the field of rehabilitation through practical application involving spa therapies. The literature search was conducted using Medline, PEDro, Cochrane Database, and Google Scholar. Only studies published in English and works concerning the implementation of spa thermal treatment in neuro-musculoskeletal diseases were included. Specifically, the publications analyzed dealt with the treatment of diseases such as arthritis, rheumatic arthritis, ankylosing spondylitis, and low back pain through the use of thermal spa therapies. In conjunction with its widespread use in clinical practice, many studies in the literature suggest the effectiveness of crenobalneotherapy for a number of musculoskeletal disorders, generally those which are chronic and debilitating, finding significant clinical improvement both in terms of pain and functional limitations. Some of the guidelines formulated by national and international bodies on the treatment of specific diseases, such as the Italian Rheumatology Society (SIR) and the Osteoarthritis Research Society International (OARSI) guidelines, recognize the value of thermal medicine as a complement, but not a replacement, for conventional therapy (pharmacological or not).

Association analysis of the common varieties of IL17A and IL17F genes with the risk of knee osteoarthritis

Osteoarthritis is mediated by various types of cytokines, growth factors, and inflammatory factors that the role of the interleukin-17 family in this disease is becoming increasingly apparent. The aim of this study is to determine the association between the common polymorphisms of IL17A (including rs2275913) and IL17F (including rs2397084 and rs763780) genes with the knee osteoarthritis risk which was followed by a bioinformatics approach. In a case-control study, 254 participants consisting of 127 healthy individuals and 127 subjects with knee osteoarthritis referring to Shahid Beheshti Hospital dependents on Kashan University of Medical Sciences (Kashan, Iran) were enrolled. After samples collection, the polymorphisms genotyping was determined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Finally, some bioinformatics tools were used to analyze the molecular effects of the three studied polymorphisms. Data analysis showed a significant association between rs2275913-GA genotype and the decreased risk of knee osteoarthritis (OR = 0.57, 95% CI = 0.33-0.97, P = .040). However, rs763780-AG genotype (OR = 2.29, 95%CI = 1.11-4.69, P = .024) and rs763780-G allele (OR = 2.01, 95% CI = 1.09-3.72, P = .026) were associated with an increased risk of knee osteoarthritis. However, no significant associations were found between the rs2397084 polymorphism and knee osteoarthritis risk. Our structural analysis revealed that the rs2275913 polymorphism could create a new binding site for TFII-I at the promoter region of IL17A. Also, rs2397084 and rs763780 could significantly affect the function and structure of IL17A. Based on our findings, rs2275913 and rs763780 could be considered as protective and risk factors for knee osteoarthritis, respectively. Therefore, these polymorphisms can be considered as biomarkers for the screening of knee osteoarthritis susceptible persons.

DNA Methylation in Osteoarthritis: Current Status and Therapeutic Implications

Background:

Primary Osteoarthritis (OA) is a multifactorial disease in which genetic factors are strongly associated with its development; however, recently it has been observed that epigenetic modifications are also involved in the pathogenesis of OA. DNA methylation is related to gene silencing, and several studies have investigated its role in the loci of different pathways or molecules associated to OA.

Objective:

This review is focused on the current status of DNA methylation studies related to OA pathogenesis.

Method:

A review of the literature was conducted on searching in PUBMED for original papers on DNA methylation in OA.

Conclusion:

The DNA methylation research of loci related to OA pathogenesis has shown a correlation between methylation and gene repression; however, there are some exceptions to this rule. Recently, the development of genome-wide methylation and genome-wide hydroxymethylation profiles has demonstrated that several genes previously associated with OA can have changes in their methylation status, favoring the development of the disease, and these have even shown the role of other epigenetic markers.

Transcriptome comparison of meniscus from patients with and without osteoarthritis

OBJECTIVE

To assess the impact of osteoarthritis (OA) on the meniscus by comparing transcripts and biological processes in the meniscus between patients with and without OA.

DESIGN

RNA microarrays were used to identify transcripts differentially expressed (DE) in meniscus obtained from 12 OA and 12 non-OA patients. The non-OA specimens were obtained at the time of arthroscopic partial meniscectomy. Real-time PCR was performed on selected transcripts. Biological processes and gene-networking was examined computationally. Transcriptome signatures were mapped with 37 OA-related transcripts to evaluate how meniscus gene expression relates to that of OA cartilage.

RESULTS

We identified 168 transcripts significantly DE between OA (75 elevated, 93 repressed) and non-OA samples (≥1.5-fold). Among these, CSN1S1, COL10A1, WIF1, and SPARCL1 were the most prominent transcripts elevated in OA meniscus, POSTN and VEGFA were most highly repressed in OA meniscus. Transcripts elevated in OA meniscus represented response to external stimuli, cell migration and cell localization while those repressed in OA meniscus represented histone deacetylase activity (related to epigenetics) and skeletal development. Numerous long non-coding RNAs (lncRNAs) were DE between the two groups. When segregated by OA-related transcripts, two distinct clustering patterns appeared: OA meniscus appeared to be more inflammatory while non-OA meniscus exhibited a "repair" phenotype.

CONCLUSIONS

Numerous transcripts with potential relevance to the pathogenesis of OA are DE in OA and non-OA meniscus. These data suggest an involvement of epigenetically regulated histone deacetylation in meniscus tears as well as expression of lncRNAs. Patient clustering based on transcripts related to OA in articular cartilage confirmed distinct phenotypes between injured (non-OA) and OA meniscus.

The role of thermal balneotherapy in the treatment of obese patient with knee osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis clinically characterized by joint pain, functional limitation, and reduced quality of life. Several studies have shown a clear link between obesity and higher risk of knee OA. According to the multifactorial OA pathogenesis, the management of this condition requires a multidisciplinary approach. The objective of this study is to evaluate hydrokinesitherapy effects in thermal setting in obese patients with knee OA. Fifty-three patients were assessed for eligibility, of which 33 refused the treatment, while 10 patients dropped out after the enrollment for personal reasons or inability to adhere to the program. Ten patients (8 females, 2 males, mean age of 59.4 years) with obesity (range BMI 30-45 kg/m2) and knee OA (II-III grade of Kellgren-Lawrence scale) treated with hydrokinetic therapy in thermal water (two sessions per week for 8 consecutive weeks) completed the study. Primary outcome measure was pain (VAS). Secondary outcomes were clinical knee evaluation (range of motion-ROM, lower-limb muscle strength), WOMAC, and Lequesne Algofunctional Index. Patellar tendon and peri-articular soft tissue ultrasound evaluation and gait analysis at baseline (T0), at the end of treatment (T1), and at 6 months of follow-up (T2) were performed. Significant decrease on VAS pain during walking on a flat surface and going up/down stairs was reached from baseline at T1 (p = 0.0039; p = 0.0098) and was maintained at T2 (p = 0.00954) exclusively for VAS pain during walking on a flat surface. WOMAC score showed a significant reduction between T0 and T1 (p = 0.0137) and between T0 and T2 (p = 0.006438), as ROM evaluations. Kinematic path assessment did not show significant results in individual gait steps, except for the space-time variables of the average speed and the values of ground reaction force (GRF) obtained with force platforms. Hydrokinesitherapy in thermal environment in obese patients with knee OA may determine pain relief, joint function improvement, and walking speed increase until 6 months of follow-up.

Night work as a risk factor for future cause-specific disability pension: A prospective twin cohort study in Sweden

The objectives of the study were to investigate the associations between night work and disability pension (DP) due to all causes, cardiovascular (CVD), mental, and other diagnoses, adjusting for familial confounding. The material of the study included comprehensive survey data on 27 165 Swedish twins born in 1935-1958 that were linked with DP data for the survey period (1998-2003) to 2013. Night work was assessed as years of working nights at least every now and then, and categorized into not at all, 1-10 years and over 10 years. For statistical analyses, Cox proportional hazards regressions were used to calculate hazard ratios (HRs) with 95% confidence intervals (CIs). The results of the study indicated that over 10 years duration of night work had an age- and sex-adjusted HR of 1.48 (95% CI 1.11-1.98) for DP due to CVD and 1-10 years of night work an HR of 1.28 (95% CI 1.06-1.55) for DP due to mental diagnoses, but attenuated when covariates were adjusted for. Both 1-10 years (HR 1.27, 95% CI 1.17-1.39) and >10 years of night work (HR 1.20, 95% CI 1.08-1.34) were associated with DP due to all causes and other diagnoses. These risks remained after adjusting for covariates. To conclude, even modest exposure in terms of duration of night work is a risk factor for all-cause DP, but also for DP due to mental and other diagnoses. The risk of DP due to CVD seems to be associated with longer (>10 years) periods of night work. All the associations between night work and DP seem to be influenced by various covariates.

Expression of Genes and Their Polymorphism Influences the Risk of Knee Osteoarthritis

Introduction

Genetic factors including the level of expression of the fingerprint of genes involved in the development of bones and cartilage such as GDF-5 or ESR-α or CALM-1 are known to be strong determinants of the osteoarthritis (OA) in Caucasian and Oriental populations. Because of high prevalence of OA in Indian population and availability of limited genetic data, we determined whether similar genetic factors are involved in Indians as well.

Methods

A case control study was carried out involving 500 patients of knee OA and equal number of healthy controls. Genotyping analyses in whole blood, mRNA, and protein expressions in peripheral blood lymphocytes (PBLs) were performed using established protocols.

Results

Our results showed a significantly decreased level of mRNA and protein expressions for GDF-5, ESR-α, and CALM-1 genes in PBLs of OA cases when compared to healthy controls. The frequency of variant genotypes of these genes was also increased significantly in cases of OA compared to controls.

Conclusion

Our results demonstrated that the decrease in expression of GDF-5, ESR-α, and CALM-1 in PBLs and association of polymorphism in these genes may be important in predicting the severity and thereby the progression of OA in Indian population.

Dmp1 Null Mice Develop a Unique Osteoarthritis-like Phenotype

Patients with hypophosphatemia rickets (including DMP1 mutations) develop severe osteoarthritis (OA), although the mechanism is largely unknown. In this study, we first identified the expression of DMP1 in hypertrophic chondrocytes using immunohistochemistry (IHC) and X-gal analysis of Dmp1-knockout-lacZ-knockin heterozygous mice. Next, we characterized the OA-like phenotype in Dmp1 null mice from 7-week-old to one-year-old using multiple techniques, including X-ray, micro-CT, H&E staining, Goldner staining, scanning electronic microscopy, IHC assays, etc. We found a classical OA-like phenotype in Dmp1 null mice such as articular cartilage degradation, osteophyte formation, and subchondral osteosclerosis. These Dmp1 null mice also developed unique pathological changes, including a biphasic change in their articular cartilage from the initial expansion of hypertrophic chondrocytes at the age of 1-month to a quick diminished articular cartilage layer at the age of 3-months. Further, these null mice displayed severe enlarged knees and poorly formed bone with an expanded osteoid area. To address whether DMP1 plays a direct role in the articular cartilage, we deleted Dmp1 specifically in hypertrophic chondrocytes by crossing the Dmp1-loxP mice with Col X Cre mice. Interestingly, these conditional knockout mice didn't display notable defects in either the articular cartilage or the growth plate. Because of the hypophosphatemia remained in the entire life span of the Dmp1 null mice, we also investigated whether a high phosphate diet would improve the OA-like phenotype. A 8-week treatment of a high phosphate diet significantly rescued the OA-like defect in Dmp1 null mice, supporting the critical role of phosphate homeostasis in maintaining the healthy joint morphology and function. Taken together, this study demonstrates a unique OA-like phenotype in Dmp1 null mice, but a lack of the direct impact of DMP1 on chondrogenesis. Instead, the regulation of phosphate homeostasis by DMP1 via the axis of “FGF23-renal phosphorus reabsorption” is vital for maintaining a healthy joint.

Matrilin-3 Role in Cartilage Development and Osteoarthritis

The extracellular matrix (ECM) of cartilage performs essential functions in differentiation and chondroprogenitor cell maintenance during development and regeneration. Here, we discuss the vital role of matrilin-3, an ECM protein involved in cartilage development and potential osteoarthritis pathomechanisms. As an adaptor protein, matrilin-3 binds to collagen IX to form a filamentous network around cells. Matrilin-3 is an essential component during cartilage development and ossification. In addition, it interacts directly or indirectly with transforming growth factor β (TGF-β), and bone morphogenetic protein 2 (BMP2) eventually regulates chondrocyte proliferation and hypertrophic differentiation. Interestingly, matrilin-3 increases interleukin receptor antagonists (IL-Ra) in chondrocytes, suggesting its role in the suppression of IL-1β-mediated inflammatory action. Matrilin-3 downregulates the expression of matrix-degrading enzymes, such as a disintegrin metalloproteinase with thrombospondin motifs 4 (ADAMTS4) and ADAMTS5, matrix metalloproteinase 13 (MMP13), and collagen X, a hypertrophy marker during development and inflammatory conditions. Matrilin-3 essentially enhances collagen II and aggrecan expression, which are required to maintain the tensile strength and elasticity of cartilage, respectively. Interestingly, despite these attributes, matrilin-3 induces osteoarthritis-associated markers in chondrocytes in a concentration-dependent manner. Existing data provide insights into the critical role of matrilin-3 in inflammation, matrix degradation, and matrix formation in cartilage development and osteoarthritis.

Targeted re-sequencing of linkage region on 2q21 identifies a novel functional variant for hip and knee osteoarthritis

OBJECTIVE

The aim of the study was to identify genetic variants predisposing to primary hip and knee osteoarthritis (OA) in a sample of Finnish families.

METHODS

Genome wide analysis was performed using 15 independent families (279 individuals) originating from Central Finland identified as having multiple individuals with primary hip and/or knee OA. Targeted re-sequencing was performed for three samples from one 33-member, four-generation family contributing most significantly to the LOD score. In addition, exome sequencing was performed in three family members from the same family.

RESULTS

Genome wide linkage analysis identified a susceptibility locus on chromosome 2q21 with a multipoint LOD score of 3.91. Targeted re-sequencing and subsequent linkage analysis revealed a susceptibility insertion variant rs11446594. It locates in a predicted strong enhancer element region with maximum LOD score 3.42 under dominant model of inheritance. Insertion creates a recognition sequence for ELF3 and HMGA1 transcription factors. Their DNA-binding affinity is highly increased in the presence of A-allele compared to wild type null allele.

CONCLUSION

A potentially novel functional OA susceptibility variant was identified by targeted re-sequencing. This variant locates in a predicted regulatory site and creates a recognition sequence for ELF3 and HMGA1 transcription factors that are predicted to play a significant role in articular cartilage homeostasis.

Wnts talking with the TGF-β superfamily: WISPers about modulation of osteoarthritis

The Wnt signalling pathway is gaining increasing attention in the field of joint pathologies, attributable to its role in the development and homeostasis of the tissues found in the joint, including bone and cartilage. Imbalance in this pathway has been implicated in the development and progression of OA, and interference with the pathway might therefore depict an effective treatment strategy. Though offering multiple opportunities, it is yet to be decided which starting point will bring forth the most promising results. The complexity of the pathway and its interaction with other pathways (such as the TGF-β signalling pathway, which also has a central role in the maintenance of joint homeostasis) means that acting directly on proteins in this signalling cascade entails a high risk of undesired side effects. Therefore, interference with Wnt-induced proteins, such as WISP1, might be an overall more effective and safer therapeutic approach to inhibit the pathological events that take place during OA.

Genome-wide DNA methylation study of hip and knee cartilage reveals embryonic organ and skeletal system morphogenesis as major pathways involved in osteoarthritis

Background

Evidence suggests that epigenetics plays a role in osteoarthrits (OA). The aim of the study was to describethe genome wide DNA methylation changes in hip and knee OA and identify novel genes and pathwaysinvolved in OA by comparing the DNA methylome of the hip and knee osteoarthritic cartilage tissues withthose of OA-free individuals.

Methods

Cartilage samples were collected from hip or knee joint replacement patients either due to primary OA or hip fractures as controls. DNA was extracted from the collected cartilage and assayed by Illumina Infinium HumanMethylation450 BeadChip array, which allows for the analysis of >480,000 CpG sites. Student T-test was conducted for each CpG site and those sites with at least 10 % methylation difference and a p value <0.0005 were defined as differentially methylated regions (DMRs) for OA. A sub-analysis was also done for hip and knee OA separately. DAVID v6.7 was used for the functional annotation clustering of the DMR genes. Clustering analysis was done using multiple dimensional scaling and hierarchical clustering methods.

Results

The study included 5 patients with hip OA, 6 patients with knee OA and 7 hip cartilage samples from OA-free individuals. The comparisons of hip, knee and combined hip/knee OA patients with controls resulted in 26, 72, and 103 DMRs, respectively. The comparison between hip and knee OA revealed 67 DMRs. The overall number of the sites after considering the overlaps was 239, among which 151 sites were annotated to 145 genes. One-fifth of these genes were reported in previous studies. The functional annotation clustering of the identified genes revealed clusters significantly enriched in skeletal system morphogenesis and development. The analysis revealed significant difference among OA and OA-free cartilage, but less different between hip OA and knee OA.

Conclusions

We found that a number of CpG sites and genes across the genome were differentially methylated in OA patients, a remarkable portion of which seem to be involved in potential etiologic mechanisms of OA. Genes involved in skeletal developmental pathways and embryonic organ morphogenesis may be a potential area for further OA studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-015-0745-5) contains supplementary material, which is available to authorized users.

Investigation of association between hip osteoarthritis susceptibility loci and radiographic proximal femur shape

OBJECTIVE

To test whether previously reported hip morphology or osteoarthritis (OA) susceptibility loci are associated with proximal femur shape as represented by statistical shape model (SSM) modes and as univariate or multivariate quantitative traits.

METHODS

We used pelvic radiographs and genotype data from 929 subjects with unilateral hip OA who had been recruited previously for the Arthritis Research UK Osteoarthritis Genetics Consortium genome-wide association study. We built 3 SSMs capturing the shape variation of the OA-unaffected proximal femur in the entire mixed-sex cohort and for male/female-stratified cohorts. We selected 41 candidate single-nucleotide polymorphisms (SNPs) previously reported as being associated with hip morphology (for replication analysis) or OA (for discovery analysis) and for which genotype data were available. We performed 2 types of analysis for genotype-phenotype associations between these SNPs and the modes of the SSMs: 1) a univariate analysis using individual SSM modes and 2) a multivariate analysis using combinations of SSM modes.

RESULTS

The univariate analysis identified association between rs4836732 (within the ASTN2 gene) and mode 5 of the female SSM (P = 0.0016) and between rs6976 (within the GLT8D1 gene) and mode 7 of the mixed-sex SSM (P = 0.0003). The multivariate analysis identified association between rs5009270 (near the IFRD1 gene) and a combination of modes 3, 4, and 9 of the mixed-sex SSM (P = 0.0004). Evidence of associations remained significant following adjustment for multiple testing. All 3 SNPs had previously been associated with hip OA.

CONCLUSION

These de novo findings suggest that rs4836732, rs6976, and rs5009270 may contribute to hip OA susceptibility by altering proximal femur shape.

Association of rs9340799 polymorphism in estrogen receptor alpha gene with the risk of osteoarthritis: evidence based on 8,792 subjects

Osteoarthritis (OA) is one of the most common skeletal disease, which seriously affects the quality of life of patients, particularly in the middle-aged and elderly individuals. We aimed to explore whether rs9340799 [estrogen receptor alpha (ER-α) XbaI A/G] polymorphism was associated with OA using a meta-analysis. A literature search for eligible studies published before March 28, 2014 was conducted in the PubMed, Web of Science, Embase, Cochrane database, Current Controlled Trials, Clinicaltrials.gov, Chinese Clinical Trial Registry, CBMdisc, CNKI, Google Scholar and Baidu Library. The association between the rs9340799 polymorphism and OA risk was assessed by odds ratios (ORs) together with their 95 % confidence intervals (CIs). A total of 663 articles were found. After article review and quality assessment, 10 articles involving 2,924 OA cases and 5,868 controls were included in the final meta-analysis. The combined evidence suggested that rs9340799 polymorphism contributed significantly to an increased risk of OA (for G allele vs. A allele: OR = 1.21, 95 % CI 1.03-1.43, p = 0.02; for G/G vs. A/A: OR = 1.30, 95 % CI 1.07-1.57, p = 0.009). In the subgroup analyses, significant associations were found between the rs9340799 polymorphism and the OA risk in the European group, Asian group, and knee osteoarthritis group, respectively. These results suggested that the rs9340799 polymorphism might be associated with the risk of OA. However, the results should be interpreted with caution because of the publication bias.

Practical approach to hip pain

Hip pain is a common complaint among patients presenting to outpatient clinics. Stratifying patients based on age, acuity, and location of pain (extra-articular vs intra-articular) can help to aid in appropriate imaging and timely referral to an orthopedic surgeon. A thorough history and an organized physical examination combined with radiographs are usually sufficient to diagnose most hip complaints. If the diagnosis remains uncertain, magnetic resonance imaging, usually with intra-articular gadolinium, is the imaging modality of choice in diagnosing both intra-articular and extra-articular pathologies.

The Association between a History of Parental Addictions and Arthritis in Adulthood: Findings from a Representative Community Survey

Aims. To examine the relationship between a history of parental addictions and the cumulative lifetime incidence of arthritis while controlling for age, sex, race, and four clusters of risk factors: (1) other adverse childhood experiences, (2) adult health behaviors (i.e., smoking, obesity, inactivity, and alcohol consumption), (3) adult socioeconomic status and (4) mental health. Materials and Methods. Secondary analysis of 13,036 Manitoba and Saskatchewan respondents of the population-based 2005 Canadian Community Health Survey. Sequential logistic regression analyses were conducted. Findings. After controlling for demographic characteristics, including age, gender, and race, respondents who reported a history of parental addictions had significantly higher odds of arthritis in comparison to individuals without (OR=1.58; 95% CI 1.38–1.80). Adjustment for socioeconomic status, adult health behaviors, and mental health conditions had little impact on the parental addictions and arthritis relationship. The association between parental addictions and arthritis was substantially reduced when adverse childhood experiences (OR=1.33; 95% CI 1.15–1.53) and all four groups of risk factors collectively (OR=1.30; 95% CI = 1.12–1.51) were included in the analyses; however, the relationship remained statistically significant. Conclusions. A robust association was found between parental addictions and cumulative lifetime incidence of arthritis. This link remained even when controlling for four groups of potential risk factors.

Association of single nucleotide polymorphisms in estrogen receptor alpha gene with susceptibility to knee osteoarthritis: a case-control study in a Chinese Han population

Osteoarthritis (OA) is the most prevalent form of arthritis and its multifactorial nature has been increasingly recognized. Genetic factors play an important role in OA etiology and estrogen receptor alpha (ESR1) gene polymorphisms may be involved. This study tried to explore whether the ESR1 gene single nucleotide polymorphisms (SNPs) were associated with primary knee OA in the Chinese Han population. Two SNPs, rs2234693 and rs9340799, were genotyped in 469 cases and 522 controls. Rs2234693 was associated with knee OA in the dominant genetic model (TT + TC versus CC) (P = 0.025) and a higher T allele frequency existed (P = 0.047) among females. The combined genotype (TT + TC) (P = 0.025) and T allele (P = 0.016) were related with mild knee OA only. For rs9340799, A allele was associated with knee OA in all subjects (P = 0.031) and females (P = 0.046). Statistical differences were detected in the dominant genetic model (AA + AG versus GG) among females (P = 0.030). The combined genotype (AA + AG) (P = 0.036) and A allele (P = 0.039) were merely correlated with mild knee OA. ESR1 gene is considerably associated with knee OA etiology in the Chinese Han population.

The genetic contribution to severe post-traumatic osteoarthritis

Objective

to compare the combined role of genetic variants loci associated with risk of knee or hip osteoarthritis (OA) in post-traumatic (PT) and non-traumatic (NT) cases of clinically severe OA leading to total joint replacement.

Methods

A total of 1590 controls, 2168 total knee replacement (TKR) cases (33.2% PT) and 1567 total hip replacement (THR) cases (8.7% PT) from 2 UK cohorts were genotyped for 12 variants previously reported to be reproducibly associated with risk of knee or hip OA. A genetic risk score was generated and the association with PT and NT TKR and THR was assessed adjusting for covariates.

Results

For THR, each additional genetic risk variant conferred lower risk among PT cases (OR=1.07, 95% CI 0.96 to 1.19; p=0.24) than NT cases (OR 1.11, 95% CI 1.06 to 1.17; p=1.55×10⁻⁵). In contrast, for TKR, each risk variant conferred slightly higher risk among PT cases (OR 1.12, 95% CI 1.07 to 1.19; p=1.82×10⁻⁵) than among NT cases (OR 1.08, 95% CI 1.03 to 1.1; p=0.00063).

Conclusions

Based on the variants reported to date PT TKR cases have at least as high a genetic contribution as NT cases.

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.

Epidemiology of osteoarthritis and associated comorbidities

Osteoarthritis (OA) is the most common cause of walking-related disability among older adults in the United States, and the prevalence and incidence of OA are increasing rapidly. Systemic and local risk factors for knee OA have been identified, and obesity and joint injury appear to be the strongest risk factors that are both modifiable and have the potential for substantial impact on a population level. The risk factors for functional decline and disability in persons with symptomatic OA have been examined in relatively few studies. The course of functional decline in persons with symptomatic OA on a population level is generally one of stable to slowly deteriorating function, but on an individual level, many patients maintain function or improve during the first 3 years of follow-up. Obesity stands out as one of few modifiable risk factors of OA that also is a potentially modifiable predictor of functional decline. Physical activity also appears to have a substantial protective impact on future OA-related disability. Further epidemiologic studies and randomized controlled trials are needed to prioritize prevention through targeting these modifiable risk factors for OA and related disability.

No evidence of an association between mitochondrial DNA variants and osteoarthritis in 7393 cases and 5122 controls

Objectives

Osteoarthritis (OA) has a complex aetiology with a strong genetic component. Genome-wide association studies implicate several nuclear genes in the aetiology, but a major component of the heritability has yet to be defined at the molecular level. Initial studies implicate maternally inherited variants of mitochondrial DNA (mtDNA) in subgroups of patients with OA based on gender and specific joint involvement, but these findings have not been replicated.

Methods

The authors studied 138 maternally inherited mtDNA variants genotyped in a two cohort genetic association study across a total of 7393 OA cases from the arcOGEN consortium and 5122 controls genotyped in the Wellcome Trust Case Control consortium 2 study.

Results

Following data quality control we examined 48 mtDNA variants that were common in cohort 1 and cohort 2, and found no association with OA. None of the phenotypic subgroups previously associated with mtDNA haplogroups were associated in this study.

Conclusions

We were not able to replicate previously published findings in the largest mtDNA association study to date. The evidence linking OA to mtDNA is not compelling at present.

Abundant pleiotropy in human complex diseases and traits

We present a systematic review of pleiotropy among SNPs and genes reported to show genome-wide association with common complex diseases and traits. We find abundant evidence of pleiotropy; 233 (16.9%) genes and 77 (4.6%) SNPs show pleiotropic effects. SNP pleiotropic status was associated with gene location (p = 0.024; pleiotropic SNPs more often exonic [14.5% versus 4.9% for nonpleiotropic, trait-associated SNPs] and less often intergenic [15.8% versus 23.6%]), "predicted transcript consequence" (p = 0.001; pleiotropic SNPs more often predicted to be structurally deleterious [5% versus 0.4%] but not more often in regulatory sequences), and certain disease classes. We develop a method to calculate the likelihood that pleiotropic links between traits occurred more often than expected and demonstrate that this approach can identify etiological links that are already known (such as between fetal hemoglobin and malaria risk) and those that are not yet established (e.g., between plasma campesterol levels and gallstones risk; and between immunoglobulin A and juvenile idiopathic arthritis). Examples of pleiotropy will accumulate over time, but it is already clear that pleiotropy is a common property of genes and SNPs associated with disease traits, and this will have implications for identification of molecular targets for drug development, future genetic risk-profiling, and classification of diseases.

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.

Health-related risk factors for disability pensions due to musculoskeletal diagnoses: A 30-year Finnish twin cohort study

Aims: There is a need to better understand work incapacity due to musculoskeletal disorders (MSD) and the factors that contribute to being granted disability pension (DP) with such disorders. A twin cohort study would serve a powerful tool responding to this knowledge gap by providing information on factors affecting DP when controlling for family background. The purpose was to investigate the incidence of and risk factors for DP due to any MSD ( n = 1,819) and specifically due to osteoarthritis (OA, n = 677) in a twin cohort of 24,043 people over a 30-year follow-up. Methods: Data on twin pairs from a mailed questionnaire during the baseline year of 1975 were followed up with register data regarding DP, emigration, old-age pension, and death. For statistical analysis, univariate and multivariate Cox proportional hazard ratios were estimated. Results: Baseline musculoskeletal pain, frequency of use of analgesics, body mass index, and chronic diseases, as well as education and social class were significant risk factors for DP due to MSD at follow-up in both sexes. These factors were also the significant predictors of DP due to OA in men. In women, DP due to OA was best predicted by baseline musculoskeletal pain and lower social class. Conclusions: The risk of DP due to MSD and OA seemed to be influenced by comorbidities, educational level and social class. Analyses of twin pairs discordant for DP confirmed the results. Accumulated health problems and chronic conditions during the life course may lead to permanent work incapacity.

Hip osteoarthritis susceptibility is associated with IL1B -511(G>A) and IL1 RN (VNTR) genotypic polymorphisms in Croatian Caucasian population

Among the predisposing factors to osteoarthritis (OA), a frequent destructive joint disease, is the complex genetic heritage including the interleukin-1 family members like the IL1β (IL1B) and the IL1 receptor antagonist (IL1RN) genes. The aim of this study was to investigate allelic and genotypic frequencies of the IL1B gene single nucleotide polymorphism (SNP) at -511(G>A) and the variable number tandem repeat (VNTR) in the IL1RN gene in a Croatian Caucasian population of hip OA (HOA) cases and healthy controls. A total of 259 HOA patients with total hip replacement (THR) and 518 healthy blood donors as controls were genotyped for IL1B gene SNP -511(G>A) and the VNTR in the IL1RN gene associated with HOA. The genotype G/A (1/2) at IL1B was significantly associated with the protection of the HOA (p < 0.036, OR = 0.72, 95% CI = 0.52-0.99). The genotype G/G (1/1) had only a trend towards the susceptibility (p = 0.053, OR = 1.35, 95% CI = 0.98-1.86) to disease. None of the haplotypes IL1B -511(G>A) and IL1RN (VNTR) were found associated with the HOA. The haplotype 1-2 at these loci had only a trend to susceptibility (p = 0.065). Haplotype 1-3 had a significant male bias in diseased. Furthermore, genotype comprising 2-1/2-2 haplotypes was found significantly associated with predisposition to HOA (p = 0.027, OR = 2.23, 95% CI = 1.03-4.88), whereas genotype 1-1/2-2 with protection to disease (p = 0.028, OR = 0.65, 95% CI = 0.43-0.97). Our findings suggest that HOA in Croatian population might have a different genetic risk regarding the IL1 locus than has been reported for other Caucasian populations previously.

Microarray Analysis of the Infrapatellar Fat Pad in Knee Osteoarthritis: Relationship with Joint Inflammation

Objective.

To examine differences in genes involved in fat metabolism, energy homeostasis, adipogenesis, and inflammation between endstage and early-stage knee osteoarthritis (OA) infrapatellar fat pads (IFP).

Methods.

Twenty-nine endstage and 5 early-stage primary OA IFP were harvested at knee surgery. Total RNA was extracted, labeled, and hybridized to whole-genome expression arrays. Unsupervised analysis of all samples using principal components analysis or 2-way hierarchical clustering showed groupings based on tissue source and disease. Statistical testing identified sets of genes that displayed differences between the 2 fat types. Western blot analysis was performed for protein expression of an identified gene of interest.

Results.

The 29 IFP demonstrated an elevation in the expression of adipokines such as adiponectin and leptin. A statistically significant increased expression was seen for genes of adipogenesis, such as peroxisome proliferator-activated receptor-γ (PPAR-γ), diacylglycerol acyltransferase 2 (DGAT2), cluster of differentiation (CD36), and thyroid hormone responsive spot (THRSP) in the severe OA fat pads as compared to the controls. A subset of 5 patients in the endstage OA group were consistently similar in gene expression to early OA tissue. Protein expression of PPAR-γ2 was 5.4-fold and PPAR-γ1 was 1.4-fold greater in endstage versus early OA tissue.

Conclusion.

Endstage OA fat pads demonstrated a significant upregulation of genes for fat metabolism and energy homeostasis and a mixed result for inflammatory cytokines.

Analysis of estrogen receptor alpha gene haplotype in Mexican mestizo patients with primary osteoarthritis of the knee

The aim of this work was to test the association between estrogen receptor α gene (ERα) polymorphism and primary osteoarthritis (OA) of the knee in Mexican mestizo patients. A case-control study was conducted. Cases were patients >40 years of age, with a body mass index (BMI) ≤ 27 and radiologic score for OA of the knee of ≥2 according to Kellgren-Lawrence scale, and controls were subjects >40 years age with a radiologic score <2. Two restriction fragment length polymorphisms, PvuII (T/C; rs2234693), and XbaI (A/G; rs9340799), of the ERα were analyzed. Allelic haplotypes were constructed and non-conditional logistic regression was developed to evaluate risk magnitude through odds ratios (ORs) and 95% Confidence intervals (95% CI). Three different allelic haplotypes were identified: TA; CG, and CA. Unadjusted analysis of the haplotypes did not show significant associations; nonetheless, when data were adjusted for gender, age, and BMI, a significant decrease risk was observed for CG haplotype (OR [95% CI]) = 0.5 (0.3-0.9)] (P = 0.04). These results suggest that ERα gene CG haplotype could be associated with a reduced risk of primary knee OA in Mexican mestizo population.

Roles of inflammatory and anabolic cytokines in cartilage metabolism: signals and multiple effectors converge upon MMP-13 regulation in osteoarthritis

Human cartilage is a complex tissue of matrix proteins that vary in amount and orientation from superficial to deep layers and from loaded to unloaded zones. A major challenge to efforts to repair cartilage by stem cell-based and other tissue engineering strategies is the inability of the resident chondrocytes to lay down new matrix with the same structural and resilient properties that it had upon its original formation. This is particularly true of the collagen network, which is susceptible to cleavage once proteoglycans are depleted. Thus, a thorough understanding of the similarities and particularly the marked differences in mechanisms of cartilage remodeling during development, osteoarthritis, and aging may lead to more effective strategies for preventing cartilage damage and promoting repair. To identify and characterize effectors or regulators of cartilage remodeling in these processes, we are using culture models of primary human and mouse chondrocytes and cell lines and mouse genetic models to manipulate gene expression programs leading to matrix remodeling and subsequent chondrocyte hypertrophic differentiation, pivotal processes which both go astray in OA disease. Matrix metalloproteinases (MMP)-13, the major type II collagen-degrading collagenase, is regulated by stress-, inflammation-, and differentiation-induced signals that not only contribute to irreversible joint damage (progression) in OA, but importantly, also to the initiation/onset phase, wherein chondrocytes in articular cartilage leave their natural growth- and differentiation-arrested state. Our work points to common mediators of these processes in human OA cartilage and in early through late stages of OA in surgical and genetic mouse models.

Meta-analysis of genome-wide association studies confirms a susceptibility locus for knee osteoarthritis on chromosome 7q22

OBJECTIVES

Osteoarthritis (OA) is the most prevalent form of arthritis and accounts for substantial morbidity and disability, particularly in older people. It is characterised by changes in joint structure, including degeneration of the articular cartilage, and its aetiology is multifactorial with a strong postulated genetic component.

METHODS

A meta-analysis was performed of four genome-wide association (GWA) studies of 2371 cases of knee OA and 35 909 controls in Caucasian populations. Replication of the top hits was attempted with data from 10 additional replication datasets.

RESULTS

With a cumulative sample size of 6709 cases and 44 439 controls, one genome-wide significant locus was identified on chromosome 7q22 for knee OA (rs4730250, p=9.2 × 10⁻⁹), thereby confirming its role as a susceptibility locus for OA.

CONCLUSION

The associated signal is located within a large (500 kb) linkage disequilibrium block that contains six genes: PRKAR2B (protein kinase, cAMP-dependent, regulatory, type II, β), HPB1 (HMG-box transcription factor 1), COG5 (component of oligomeric golgi complex 5), GPR22 (G protein-coupled receptor 22), DUS4L (dihydrouridine synthase 4-like) and BCAP29 (B cell receptor-associated protein 29). Gene expression analyses of the (six) genes in primary cells derived from different joint tissues confirmed expression of all the genes in the joint environment.

Dietary garlic and hip osteoarthritis: evidence of a protective effect and putative mechanism of action

BACKGROUND

Patterns of food intake and prevalent osteoarthritis of the hand, hip, and knee were studied using the twin design to limit the effect of confounding factors. Compounds found in associated food groups were further studied in vitro.

METHODS

Cross-sectional study conducted in a large population-based volunteer cohort of twins. Food intake was evaluated using the Food Frequency Questionnaire; OA was determined using plain radiographs. Analyses were adjusted for age, BMI and physical activity. Subsequent in vitro studies examined the effects of allium-derived compounds on the expression of matrix-degrading proteases in SW1353 chondrosarcoma cells.

RESULTS

Data were available, depending on phenotype, for 654-1082 of 1086 female twins (median age 58.9 years; range 46-77). Trends in dietary analysis revealed a specific pattern of dietary intake, that high in fruit and vegetables, showed an inverse association with hip OA (p = 0.022). Consumption of 'non-citrus fruit' (p = 0.015) and 'alliums' (p = 0.029) had the strongest protective effect. Alliums contain diallyl disulphide which was shown to abrogate cytokine-induced matrix metalloproteinase expression.

CONCLUSIONS

Studies of diet are notorious for their confounding by lifestyle effects. While taking account of BMI, the data show an independent effect of a diet high in fruit and vegetables, suggesting it to be protective against radiographic hip OA. Furthermore, diallyl disulphide, a compound found in garlic and other alliums, represses the expression of matrix-degrading proteases in chondrocyte-like cells, providing a potential mechanism of action.

The bone-cartilage unit in osteoarthritis

Osteoarthritis (OA) refers to a group of mechanically-induced joint disorders to which both genetic and acquired factors contribute. Current pathophysiological concepts focus on OA as a disease of the whole joint. Within these models, the functional unit formed by the articular cartilage and the subchondral bone seems to be of particular interest. Cartilage and bone receive and dissipate the stress associated with movement and loading, and are therefore continuously challenged biomechanically. Recent data support the view that cartilage and bone can communicate over the calcified tissue barrier; vessels reach out from bone into the cartilage zone, patches of uncalcified cartilage are in contact with bone, and microcracks and fissures further facilitate transfer of molecules. Several molecular signaling pathways such as bone morphogenetic proteins and Wnts are hypothesized to have a role in OA and can activate cellular and molecular processes in both cartilage and bone cells. In addition, intracellular activation of different kinase cascades seems to be involved in the molecular crosstalk between cartilage and bone cells. Further research is required to integrate these different elements into a comprehensive approach that will increase our understanding of the disease processes in OA, and that could lead to the development of specific therapeutics or treatment strategies.

Role of extracellular membrane vesicles in the pathogenesis of various diseases, including cancer, renal diseases, atherosclerosis, and arthritis

Extracellular membrane vesicles (MVs) 30-1000 nm in diameter and of varying cellular origins are increasingly recognized for their participation in a range of processes, including the pathogenesis of various diseases, such as: (1) atherosclerosis, (2) thromboembolism, (3) osteoarthritis (OA), (4) chronic renal disease and pulmonary hypertension, (5) tissue invasion and metastasis by cancer cells, (6) gastric ulcers and bacterial infections, and (7) periodontitis. MVs are derived from many different cell types and intracellular mechanisms, and perform different metabolic functions or roles, depending on the cell of origin.The presence of a metabolically active, outer membrane is a distinguishing feature of all MVs, regardless of their cell type of origin and irrespective of terminologies applied to them such as exosomes, microparticles, or matrix vesicles. The MV membrane provides one of the few protected and controlled internal microenvironments outside cells in which specific metabolic objectives of the host cell may be pursued vigorously at a distance from the host cell. MVs are also involved in various forms of normal and abnormal intercellular communication. Evidence is emerging that circulating MVs are good predictors of the severity of several diseases. In addition, recently, the role of MVs in inducing immunity against cancer cells and bacterial infections has become a topic of interest to researchers in the area of therapeutics. The main objective of this review is to list and briefly describe the increasingly well-defined roles of MVs in selected diseases in which they seem to have a significant role in pathogenesis.

Articular cartilage and subchondral bone in the pathogenesis of osteoarthritis

The articular surface plays an essential role in load transfer across the joint, and conditions that produce increased load transfer or altered patterns of load distribution accelerate the development of osteoarthritis (OA). Current knowledge segregates the risk factors into two fundamental mechanisms related to the adverse effects of "abnormal" loading on normal cartilage or "normal" loading on abnormal cartilage. Although chondrocytes can modulate their functional state in response to loading, their capacity to repair and modify the surrounding extracellular matrix is limited in comparison to skeletal cells in bone. This differential adaptive capacity underlies the more rapid appearance of detectable skeletal changes, especially after acute injuries that alter joint mechanics. The imbalance in the adaptation of the cartilage and bone disrupts the physiological relationship between these tissues and further contributes to OA pathology. This review focuses on the specific articular cartilage and skeletal features of OA and the putative mechanisms involved in their pathogenesis.