GDF5 deficiency prevents cardiac rupture following acute myocardial infarction in mice

BACKGROUND

We previously showed that growth differentiation factor 5 (GDF5) limits infarct expansion post-myocardial infarction (MI). We now examine the acute post-MI role of GDF5 in cardiac rupture.

METHODS AND RESULTS

Following permanent ligation of the left anterior descending artery, GDF5 deficiency (i.e., GDF5 knockout mice) reduced the incidence of cardiac rupture (4/24 vs. 17/24; P < .05), and improved survival over 28-d compared to wild-type (WT) mice (79% vs. 25%; P < .0001). Moreover, at 3-d post-MI, GDF5-deficient mice manifest: (a) reduced heart weight/body weight ratio (P < .0001) without differences in infarct size or cardiomyocyte size; (b) increased infarct zone expression of Col1a1 (P < .05) and Col3a1 (P < .01), suggesting increased myocardial fibrosis; and (c) reduced aortic and left ventricular peak systolic pressures (P ≤ .05), suggesting reduced afterload. Despite dysregulated inflammatory markers and reduced circulating monocytes in GDF5-deficient mice at 3-d post-MI, reciprocal bone marrow transplantation (BMT) failed to implicate GDF5 in BM-derived cells, suggesting the involvement of tissue-resident GDF5 expression in cardiac rupture.

CONCLUSIONS

Loss of GDF5 reduces cardiac rupture post-MI with increased myocardial fibrosis and lower afterload, albeit at the cost of chronic adverse remodeling.

HOXA10 promotes Gdf5 expression in articular chondrocytes

Growth differentiation factor 5 (GDF5), a BMP family member, is highly expressed in the surface layer of articular cartilage. The GDF5 gene is a key risk locus for osteoarthritis and Gdf5-deficient mice show abnormal joint development, indicating that GDF5 is essential in joint development and homeostasis. In this study, we aimed to identify transcription factors involved in Gdf5 expression by performing two-step screening. We first performed microarray analyses to find transcription factors specifically and highly expressed in the superficial zone (SFZ) cells of articular cartilage, and isolated 11 transcription factors highly expressed in SFZ cells but not in costal chondrocytes. To further proceed with the identification, we generated Gdf5-HiBiT knock-in (Gdf5-HiBiT KI) mice, by which we can easily and reproducibly monitor Gdf5 expression, using CRISPR/Cas9 genome editing. Among the 11 transcription factors, Hoxa10 clearly upregulated HiBiT activity in the SFZ cells isolated from Gdf5-HiBiT KI mice. Hoxa10 overexpression increased Gdf5 expression while Hoxa10 knockdown decreased it in the SFZ cells. Moreover, ChIP and promoter assays proved the direct regulation of Gdf5 expression by HOXA10. Thus, our results indicate the important role played by HOXA10 in Gdf5 regulation and the usefulness of Gdf5-HiBiT KI mice for monitoring Gdf5 expression.

The association of growth differentiation factor 5 rs143383 gene polymorphism with osteoarthritis: a systematic review and meta-analysis

BACKGROUND

Osteoarthritis (OA) is caused by a complex set of pathophysiological factors. The genetic factors involved in the occurrence and progress of the disease have been widely discussed by scholars. It was found that growth differentiation factor 5 (GDF5) gene polymorphisms may be linked to OA susceptibility, which has been controversial and needs to be further confirmed by an updated meta-analysis.

OBJECTIVES

We examined the association between GDF5 rs143383 single nucleotide polymorphism (SNP) and OA susceptibility.

METHODS

All relevant articles that met the criteria are retrieved and included, and the search deadline is June 2022. The allele frequencies and different genotype frequencies of GDF5 rs143383 loci in each study were extracted and statistically analyzed by R4.1.3 software, and the different genetic models were analyzed based on their odds ratio (OR) and 95% confidence interval (CI).

RESULTS

The meta-analysis explained that GDF5 rs143383 SNP was crucial correlated with OA in all patients with OA of knee, hip and hand. The codominant gene model in the whole crowd (OR = 1.17, 95% CI 1.07-1.27, P < 0.01) enlightened that OA was vitally associated with GDF5 gene polymorphism. At the same time, we did a subgroup analysis based on ethnicity. The codominant gene model (OR = 1.31, 95% CI 1.12-1.53, P < 0.01) in Asian population, the codominant homozygote model (OR = 1.28, 95% CI 1.14-1.43), codominant heterozygote gene model (OR = 1.12, 95% CI 1.01-1.23, P = 0.02), and dominant gene model (OR = 1.19, 95% CI 1.09-1.31, P < 0.01) in Caucasian are analyzed by subgroup analysis. It means that there is a momentous relationship between the GDF5rs143383 gene polymorphism and OA, especially among Caucasians. In addition, we also discussed different types of OA separately and discover that the GDF5rs143383 gene polymorphism was relevant for knee osteoarthritis (KOA) and hand osteoarthritis, and it was more significant in the Caucasian population. But due to the high heterogeneity in hip osteoarthritis, it could not be accurately concluded. Furthermore, we also analyzed the osteoarthritis of different genders and found that the GDF5 rs143383 SNP was associated with both men and women and was still significant in the Caucasian population.

CONCLUSION

We found a close association between osteoarthritis and GDF5rs143383SNP in this study. From the analysis of each group, we got the same conclusion in KOA and hand OA, but which need further verification in hip OA. Considering gender, we found a close relationship between GDF5 rs143383 SNP and OA of the knee, hip and hand, both for men and women. This conclusion is more obvious in Caucasian people.

Influence of Different Evolutive Forces on GDF5 Gene Variability

The GDF5 gene is involved in the development of skeletal elements, synovial joint formation, tendons, ligaments, and cartilage. Several polymorphisms are present within the gene, and two of them, rs143384 and 143383, were reported to be correlated with osteoarticular disease or muscle flexibility. The aim of this research is to verify if the worldwide distribution of the rs143384 polymorphism among human populations was shaped by selective pressure, or if it was the result of random genetic drift events. Ninety-four individuals of both the male and female sexes, 18-28 years old, from Sardinia were analyzed. We observed the following genotype frequencies: 28.72% of AA homozygotes, 13.83% of GG homozygotes, and 57.45% of AG heterozygotes. The allele frequencies were 0.574 for allele A and 0.426 for allele G. The relationships between the populations were verified via Multidimensional Scaling (MDS). Our data show (i) a clear heterogeneity within the African populations; (ii) a strong differentiation between the African populations and the other populations; and that (iii) the Sardinian population is placed within the European cluster. To reveal possible traces of selective pressure, the Population Branch Statistic (PBS) was calculated; both the rs143384 and 143383 SNPs have low PBS values, suggesting that there are no signals of selective pressure in those areas of the gene.

Association Analysis of GDF5 and Contributing Factors in Developmental Dysplasia of the Hip in Infants

BACKGROUND

Developmental dysplasia of the hip (DDH) is a developmental disorder which is reported to be associated with hip instability. When untreated, it can lead to irreversible joint damage. DDH is known to be a multifactorial disease involving genetic, mechanical and environmental factors. The greatest causative potential is attributed to the genetic component. Growth Differentiation Factor 5 (GDF5) is among the most studied genes associated with processes of regeneration and maintenance of joints. The aim of this work was to analyse the association of SNP rs143383 in the GDF5 gene and the occurrence of DDH, along with association with various contributing factors in the Caucasian population.

MATERIAL AND METHODS

A total of 118 samples were analysed for the presence of the mutation. DNA was isolated from all individuals from peripheral blood. SNP rs143383 in the GDF5 gene was genotyped using the TaqMan assay. A standard chi-square test was used to compare allele and genotype distributions in patients and healthy controls.

RESULTS

The association analysis of genotypes of DDH and rs143383 revealed a significant association. Also, the association of GDF5 and selected contributing factors was statistically significant in female gender (p=0.002), family history (p&lt;0.001), count of pregnancy (p=0.009), laterality of hip involvement and initial US examination.

CONCLUSIONS

1. The results indicate an important effect of rs143383 polymorphism in the GDF5 gene on DDH development. 2. However, our results also suggest that rs143383 is not the only contributing factor in the genetic component of DDH.

Novel NFκB Inhibitor SC75741 Mitigates Chondrocyte Degradation and Prevents Activated Fibroblast Transformation by Modulating miR-21/GDF-5/SOX5 Signaling

Osteoarthritis (OA) is a common articular disease manifested by the destruction of cartilage and compromised chondrogenesis in the aging population, with chronic inflammation of synovium, which drives OA progression. Importantly, the activated synovial fibroblast (AF) within the synovium facilitates OA through modulating key molecules, including regulatory microRNAs (miR's). To understand OA associated pathways, in vitro co-culture system, and in vivo papain-induced OA model were applied for this study. The expression of key inflammatory markers both in tissue and blood plasma were examined by qRT-PCR, western blot, immunohistochemistry, enzyme-linked immunosorbent assay (ELISA) and immunofluorescence assays. Herein, our result demonstrated, AF-activated human chondrocytes (AC) exhibit elevated NFκB, TNF-α, IL-6, and miR-21 expression as compared to healthy chondrocytes (HC). Importantly, AC induced the apoptosis of HC and inhibited the expression of chondrogenesis inducers, SOX5, TGF-β1, and GDF-5. NFκB is a key inflammatory transcription factor elevated in OA. Therefore, SC75741 (an NFκB inhibitor) therapeutic effect was explored. SC75741 inhibits inflammatory profile, protects AC-educated HC from apoptosis, and inhibits miR-21 expression, which results in the induced expression of GDF-5, SOX5, TGF-β1, BMPR2, and COL4A1. Moreover, ectopic miR-21 expression in fibroblast-like activated chondrocytes promoted osteoblast-mediated differentiation of osteoclasts in RW264.7 cells. Interestingly, in vivo study demonstrated SC75741 protective role, in controlling the destruction of the articular joint, through NFκB, TNF-α, IL-6, and miR-21 inhibition, and inducing GDF-5, SOX5, TGF-β1, BMPR2, and COL4A1 expression. Our study demonstrated the role of NFκB/miR-21 axis in OA progression, and SC75741's therapeutic potential as a small-molecule inhibitor of miR-21/NFκB-driven OA progression.

A Novel Volume-Stable Collagen Matrix Induces Changes in the Behavior of Primary Human Oral Fibroblasts, Periodontal Ligament, and Endothelial Cells

The aim of the present study was to investigate the influence of a novel volume-stable collagen matrix (vCM) on early wound healing events including cellular migration and adhesion, protein adsorption and release, and the dynamics of the hemostatic system. For this purpose, we utilized transwell migration and crystal violet adhesion assays, ELISAs for quantification of adsorbed and released from the matrix growth factors, and qRT-PCR for quantification of gene expression in cells grown on the matrix. Our results demonstrated that primary human oral fibroblasts, periodontal ligament, and endothelial cells exhibited increased migration toward vCM compared to control cells that migrated in the absence of the matrix. Cellular adhesive properties on vCM were significantly increased compared to controls. Growth factors TGF-β1, PDGF-BB, FGF-2, and GDF-5 were adsorbed on vCM with great efficiency and continuously delivered in the medium after an initial burst release within hours. We observed statistically significant upregulation of genes encoding the antifibrinolytic thrombomodulin, plasminogen activator inhibitor type 1, thrombospondin 1, and thromboplastin, as well as strong downregulation of genes encoding the profibrinolytic tissue plasminogen activator, urokinase-type plasminogen activator, its receptor, and the matrix metalloproteinase 14 in cells grown on vCM. As a general trend, the stimulatory effect of the vCM on the expression of antifibrinolytic genes was synergistically enhanced by TGF-β1, PDGF-BB, or FGF-2, whereas the strong inhibitory effect of the vCM on the expression of profibrinolytic genes was reversed by PDGF-BB, FGF-2, or GDF-5. Taken together, our data strongly support the effect of the novel vCM on fibrin clot stabilization and coagulation/fibrinolysis equilibrium, thus facilitating progression to the next stages of the soft tissue healing process.

GDF5 mutation case report and a systematic review of molecular and clinical spectrum: Expanding current knowledge on genotype-phenotype correlations

INTRODUCTION

Brachydactyly is a bone development abnormality presenting with variable phenotypes and different transmission patterns. Mutations in GDF5 (Growth and Differentiation Factor 5, MIM *601146) account for a significant amount of cases. Here, we report on a three-generation family, where the proband and the grandfather have an isolated brachydactyly with features of both type A1 (MIM #112500) and type C (MIM #113100), while the mother shows only subtle hand phenotype signs.

MATERIALS AND METHODS

Whole Exome Sequencing (WES) was performed on the two affected individuals. An in-depth analysis of GDF5 genotype-phenotype correlations was performed through literature reviewing and retrieving information from several databases to elucidate GDF5-related molecular pathogenic mechanisms.

RESULTS

WES analysis disclosed a pathogenic variant in GDF5 (NM_000557.5:c.157dup; NP_000548.2:p.Leu53Profs*41; rs778834209), segregating with the phenotype. The frameshift variant was previously associated with Brachydactyly type C (MIM #113100), in heterozygosity, and with the severe Grebe type chondrodysplasia (MIM #200700), in homozygosity. In-depth analysis of literature and databases allowed to retrieve GDF5 mutations and correlations to phenotypes. We disclosed the association of 49 GDF5 pathogenic mutations with eight phenotypes, with both autosomal dominant and recessive transmission patterns. Clinical presentations ranged from severe defects of limb morphogenesis to mild redundant ossification. We suggest that such clinical gradient can be linked to a continuum of GDF5-activity variation, with loss of GDF5 activity underlying bone development defects, and gain of function causing disorders with excessive bone formation.

CONCLUSIONS

Our analysis of GDF5 pathogenicity mechanisms furtherly supports that mutation and zygosity backgrounds resulting in the same level of GDF5 activity may lead to similar phenotypes. This information can aid in interpreting the potential pathogenic effect of new variants and in supporting an appropriate genetic counseling.

Growth differentiation factor 5 in cartilage and osteoarthritis: A possible therapeutic candidate

Growth differentiation factor 5 (GDF-5) is essential for cartilage development and homeostasis. The expression and function of GDF-5 are highly associated with the pathogenesis of osteoarthritis (OA). OA, characterized by progressive degeneration of joint, particularly in cartilage, causes severe social burden. However, there is no effective approach to reverse the progression of this disease. Over the past decades, extensive studies have demonstrated the protective effects of GDF-5 against cartilage degeneration and defects. Here, we summarize the current literature describing the role of GDF-5 in development of cartilage and joints, and the association between the GDF-5 gene polymorphisms and OA susceptibility. We also shed light on the protective effects of GDF-5 against OA in terms of direct GDF-5 supplementation and modulation of the GDF-5-related signalling. Finally, we discuss the current limitations in the application of GDF-5 for the clinical treatment of OA. This review provides a comprehensive insight into the role of GDF-5 in cartilage and emphasizes GDF-5 as a potential therapeutic candidate in OA.

Genome-wide meta-analysis of muscle weakness identifies 15 susceptibility loci in older men and women

Low muscle strength is an important heritable indicator of poor health linked to morbidity and mortality in older people. In a genome-wide association study meta-analysis of 256,523 Europeans aged 60 years and over from 22 cohorts we identify 15 loci associated with muscle weakness (European Working Group on Sarcopenia in Older People definition: n = 48,596 cases, 18.9% of total), including 12 loci not implicated in previous analyses of continuous measures of grip strength. Loci include genes reportedly involved in autoimmune disease (HLA-DQA1 p = 4 × 10-17), arthritis (GDF5 p = 4 × 10-13), cell cycle control and cancer protection, regulation of transcription, and others involved in the development and maintenance of the musculoskeletal system. Using Mendelian randomization we report possible overlapping causal pathways, including diabetes susceptibility, haematological parameters, and the immune system. We conclude that muscle weakness in older adults has distinct mechanisms from continuous strength, including several pathways considered to be hallmarks of ageing.

GDF-5 promotes epidermal stem cells proliferation via Foxg1-cyclin D1 signaling

OBJECTIVE

Epidermal stem cells (EpSCs) can self-renew, which are responsible for the long-term maintenance of the skin, and it also plays a critical role in wound re-epithelization, but the mechanism underlying EpSCs proliferation is unclear. GDF-5, also known as BMP-14, is a member of the BMP family and can be used as a self-renewal supporter. Here, we studied the effects of GDF-5 on mouse EpSCs proliferation mechanism in wound healing.

METHODS

Firstly, the effects of GDF-5 on EpSCs proliferation was tested by using CCK8 reagent and PCNA expression was analyzed by Western blotting. Secondly, we screened genes that promote EpSCs proliferation in the FOX and cyclin family by qPCR, and then the protein expression level of the selected genes was further analyzed by Western blotting. Thirdly, siRNA plasmids and pAdEasy adenovirus were transfected or infected, respectively, into mouse EpSCs to detect the effect of target genes on GDF-5-induced cell proliferation. Furthermore, we injected GDF-5 to a deep partial thickness burn mouse model for finding out whether EpSCs proliferation can be detected by immunohistochemical. Finally, the relevant target genes were analyzed by qPCR, immunoblotting, and dual-luciferase reporter gene detection.

RESULTS

We discovered that 100 ng/ml recombinant mouse GDF-5 was the optimal concentration for promoting mouse EpSCs proliferation. Through preliminary screened by qPCR, we found that Foxg1 and cyclin D1 could be the downstream molecules of GDF-5, and the results were confirmed by Western blotting. And the effect of GDF-5 on mouse EpSCs proliferation was adjusted by Foxg1/cyclin D1 in vitro and in vivo. Besides, GDF-5-induced transcription of cyclin D1 was regulated by Foxg1-mediated cyclin D1 promoter activity.

CONCLUSION

This paper showed that GDF-5 promotes mouse EpSCs proliferation via Foxg1-cyclin D1 signal pathway. It is suggested that GDF-5 may be a new approach to make EpSCs proliferation which can be used in wound healing.

Evolutionary Selection and Constraint on Human Knee Chondrocyte Regulation Impacts Osteoarthritis Risk

During human evolution, the knee adapted to the biomechanical demands of bipedalism by altering chondrocyte developmental programs. This adaptive process was likely not without deleterious consequences to health. Today, osteoarthritis occurs in 250 million people, with risk variants enriched in non-coding sequences near chondrocyte genes, loci that likely became optimized during knee evolution. We explore this relationship by epigenetically profiling joint chondrocytes, revealing ancient selection and recent constraint and drift on knee regulatory elements, which also overlap osteoarthritis variants that contribute to disease heritability by tending to modify constrained functional sequence. We propose a model whereby genetic violations to regulatory constraint, tolerated during knee development, lead to adult pathology. In support, we discover a causal enhancer variant (rs6060369) present in billions of people at a risk locus (GDF5-UQCC1), showing how it impacts mouse knee-shape and osteoarthritis. Overall, our methods link an evolutionarily novel aspect of human anatomy to its pathogenesis.

Regulation of Gdf5 expression in joint remodelling, repair and osteoarthritis

Growth and Differentiation Factor 5 (GDF5) is a key risk locus for osteoarthritis (OA). However, little is known regarding regulation of Gdf5 expression following joint tissue damage. Here, we employed Gdf5-LacZ reporter mouse lines to assess the spatiotemporal activity of Gdf5 regulatory sequences in experimental OA following destabilisation of the medial meniscus (DMM) and after acute cartilage injury and repair. Gdf5 expression was upregulated in articular cartilage post-DMM, and was increased in human OA cartilage as determined by immunohistochemistry and microarray analysis. Gdf5 expression was also upregulated during cartilage repair in mice and was switched on in injured synovium in prospective areas of cartilage formation, where it inversely correlated with expression of the transcriptional co-factor Yes-associated protein (Yap). Indeed, overexpression of Yap suppressed Gdf5 expression in chondroprogenitors in vitro. Gdf5 expression in both mouse injury models required regulatory sequence downstream of Gdf5 coding exons. Our findings suggest that Gdf5 upregulation in articular cartilage and synovium is a generic response to knee injury that is dependent on downstream regulatory sequence and in progenitors is associated with chondrogenic specification. We propose a role for Gdf5 in tissue remodelling and repair after injury, which may partly underpin its association with OA risk.

Whole-genome resequencing analysis of 20 Micro-pigs

BACKGROUND

Miniature pigs have been increasingly used as mammalian model animals for biomedical research because of their similarity to human beings in terms of their metabolic features and proportional organ sizes. However, despite their importance, there is a severe lack of genome-wide studies on miniature pigs.

OBJECTIVE

In this study, we performed whole-genome sequencing analysis of 20 Micro-pigs obtained from Medi Kinetics to elucidate their genomic characteristics.

RESULTS

Approximately 595 gigabase pairs (Gb) of sequence reads were generated to be mapped to the swine reference genome assembly (Sus scrofa 10.2); on average, the sequence reads covered 99.15% of the reference genome at an average of 9.6-fold coverage. We detected a total of 19,518,548 SNPs, of which 8.7% were found to be novel. With further annotation of all of the SNPs, we retrieved 144,507 nonsynonymous SNPs (nsSNPs); of these, 5968 were found in all 20 individuals used in this study. SIFT prediction for these SNPs identified that 812 nsSNPs in 402 genes were deleterious. Among these 402 genes, we identified some genes that could potentially affect traits of interest in Micro-pigs, such as RHEB and FRAS1. Furthermore, we performed runs of homozygosity analysis to locate potential selection signatures in the genome, detecting several loci that might be involved in phenotypic characteristics in Micro-pigs, such as MSTN, GDF5, and GDF11.

CONCLUSION

In this study, we identified numerous nsSNPs that could be used as candidate genetic markers with involvement in traits of interest. Furthermore, we detected putative selection footprints that might be associated with recent selection applied to miniature pigs.

Mechanisms of synovial joint and articular cartilage development

Articular cartilage is formed at the end of epiphyses in the synovial joint cavity and permanently contributes to the smooth movement of synovial joints. Most skeletal elements develop from transient cartilage by a biological process known as endochondral ossification. Accumulating evidence indicates that articular and growth plate cartilage are derived from different cell sources and that different molecules and signaling pathways regulate these two kinds of cartilage. As the first sign of joint development, the interzone emerges at the presumptive joint site within a pre-cartilage tissue. After that, joint cavitation occurs in the center of the interzone, and the cells in the interzone and its surroundings gradually form articular cartilage and the synovial joint. During joint development, the interzone cells continuously migrate out to the epiphyseal cartilage and the surrounding cells influx into the joint region. These complicated phenomena are regulated by various molecules and signaling pathways, including GDF5, Wnt, IHH, PTHrP, BMP, TGF-β, and FGF. Here, we summarize current literature and discuss the molecular mechanisms underlying joint formation and articular development.

Genome-wide association study of knee pain identifies associations with GDF5 and COL27A1 in UK Biobank

Knee pain is one of the most common musculoskeletal complaints that brings people to medical attention. Approximately 50% of individuals over the age of 50 report an experience of knee pain within the past 12 months. We sought to identify the genetic variants associated with knee pain in 171,516 subjects from the UK Biobank cohort and seek supporting evidence in cohorts from 23andMe, the Osteoarthritis Initiative, and the Johnston County Osteoarthritis Project. We identified two loci that reached genome-wide significance in the UK Biobank: rs143384, located in GDF5 (P = 1.32 × 10-12), a gene previously implicated in osteoarthritis; and rs2808772, located near COL27A1 (P = 1.49 × 10-8). These findings were supported in cohorts with self-reported osteoarthritis/radiographic knee osteoarthritis without pain information. In this report on genome-wide association of knee pain, we identified two loci in or near GDF5 and COL27A1 that are associated with knee pain.

GWAS of bone size yields twelve loci that also affect height, BMD, osteoarthritis or fractures

Bone area is one measure of bone size that is easily derived from dual-energy X-ray absorptiometry (DXA) scans. In a GWA study of DXA bone area of the hip and lumbar spine (N ≥ 28,954), we find thirteen independent association signals at twelve loci that replicate in samples of European and East Asian descent (N = 13,608 - 21,277). Eight DXA area loci associate with osteoarthritis, including rs143384 in GDF5 and a missense variant in COL11A1 (rs3753841). The strongest DXA area association is with rs11614913[T] in the microRNA MIR196A2 gene that associates with lumbar spine area (P = 2.3 × 10-42, β = -0.090) and confers risk of hip fracture (P = 1.0 × 10-8, OR = 1.11). We demonstrate that the risk allele is less efficient in repressing miR-196a-5p target genes. We also show that the DXA area measure contributes to the risk of hip fracture independent of bone density.

Genetic Influence in Developmental Dysplasia of the Hip in Saudi Arabian Children Due to GDF5 Polymorphism

Developmental dysplasia of the hip (DDH) is quite common among Saudi Arabian babies. With an objective to assess the presence of SNP rs143383 and the alleles in the GDF5 gene among patients with DDH, parents, and unaffected siblings, we undertook this case-controlled study. We collected and analyzed for a functional single nucleotide polymorphism (SNP) in the 5'-untranslated region of the GDF5 gene (rs143383), 473 blood samples, (100 patients, 200 parents, 73 siblings and 100 healthy controls. We determined the association between the patients' genotype and their fathers', mothers' and siblings' genotype through Chi-square analysis. The majority of those screened possessed the TC genotype, and 61.8% of patients and their fathers had the TT genotype. There was no association between patients' and fathers' genotype, P value < 0.332, 95% CI (0.328-0.346), and between patients' and mothers', P < 0.006, 95% CI (0.004-0.007). When considering DDH patients' and the control group's genotypes, the odds ratios of TT versus other combined (0.641 > 1) and CC versus other combined (0.474 < 1) revealed that the TT genotype has higher risk of developing DDH compared with the CC genotype. The 95 percent confidence interval of TT versus other combined and CC versus other combined is 0.932-2.891 and 0.208-1.078, respectively. For patients' and fathers' genotypes, the odds ratios of TT versus other combined (1.275 > 1) and CC versus other combined (0.815 < 1) indicate that the TT genotype has higher risk of exhibiting DDH compared to the CC genotype. For patients' and siblings' genotypes, the odds ratios of TT versus other combined (1.669) and CC versus other combined (1.048) specify that the TT genotype possesses higher risk of developing DDH compared with the CC genotype. Our study shows that there exists a relationship between GDF5 (SNP rs143383) and DDH in our population. Second, we found for the first time that the genotype TT and the T allele were overly expressed in the patients and the fathers. More studies on the confirmation of this genetic marker for DDH are called for.

Impact of broad regulatory regions on Gdf5 expression and function in knee development and susceptibility to osteoarthritis

OBJECTIVES

Given the role of growth and differentiation factor 5 (GDF5) in knee development and osteoarthritis risk, we sought to characterise knee defects resulting from Gdf5 loss of function and how its regulatory regions control knee formation and morphology.

METHODS

The brachypodism (bp) mouse line, which harbours an inactivating mutation in Gdf5, was used to survey how Gdf5 loss of function impacts knee morphology, while two transgenic Gdf5 reporter bacterial artificial chromosome mouse lines were used to assess the spatiotemporal activity and function of Gdf5 regulatory sequences in the context of clinically relevant knee anatomical features.

RESULTS

Knees from homozygous bp mice (bp/bp) exhibit underdeveloped femoral condyles and tibial plateaus, no cruciate ligaments, and poorly developed menisci. Secondary ossification is also delayed in the distal femur and proximal tibia. bp/bp mice have significantly narrower femoral condyles, femoral notches and tibial plateaus, and curvier medial femoral condyles, shallower trochlea, steeper lateral tibial slopes and smaller tibial spines. Regulatory sequences upstream from Gdf5 were weakly active in the prenatal knee, while downstream regulatory sequences were active throughout life. Importantly, downstream but not upstream Gdf5 regulatory sequences fully restored all the key morphological features disrupted in the bp/bp mice.

CONCLUSIONS

Knee morphology is profoundly affected by Gdf5 absence, and downstream regulatory sequences mediate its effects by controlling Gdf5 expression in knee tissues. This downstream region contains numerous enhancers harbouring human variants that span the osteoarthritis association interval. We posit that subtle alterations to morphology driven by changes in downstream regulatory sequence underlie this locus' role in osteoarthritis risk.

Association of BMP-14 rs143383 ploymorphism with its susceptibility to osteoarthritis: A meta-analysis and systematic review according to PRISMA guideline

BACKGROUND

Osteoarthritis (OA) is a complex disease which can be caused by both environmental and genetic factors. A functional locus rs143383 of bone morphogenetic protein-14 (BMP-14) has been pointed out to be associated with OA etiology, but conflicting conclusions have been reached. To provide a more comprehensive conclusion about this issue, we performed this meta-analysis.

METHODS

Relevant studies were searched from electronic databases including PubMed, Chinese National Knowledge Infrastructure, Embase, and Wanfang. The strength of correlations was examined with pooled odds ratios (ORs) and 95% confidence intervals (95% CIs). Subgroup analyses stratified by ethnicity and source of control were carried out. All statistical analyses were performed with STATA software (version 12.0).

RESULTS

Overall, BMP-14 rs143383 polymorphism was negatively correlated with the susceptibility to knee OA and hand OA under genetic contrasts of CC versus TT, CC + TC versus TT, CC versus TT + TC, C versus T, TC versus TT (OR = 0.71, 95% CI = 0.65-0.79; OR = 0.81, 95% CI = 0.73-0.89; OR = 0.79, 95% CI = 0.71-0.86; OR = 0.85, 95% CI = 0.81-0.90; OR = 0.84, 95% CI = 0.75-0.93), and TC versus TT, CC versus TT + TC, C versus T (OR = 0.76, 95% CI = 0.65-0.89; OR = 0.79, 95% CI = 0.68-0.92; OR = 0.90, 95% CI = 0.85-0.95), respectively; similar results were observed in subgroups after stratification analyses. Additionally, the polymorphism also reduced hip OA risk in Asian group after stratified analysis by ethnicity.

CONCLUSION

BMP-14 rs143383 polymorphism may be a protective factor against OA occurrence.

Polymorphisms in the Growth Differentiation Factor 5 (GDF 5) Gene in Knee Osteoarthritis

OBJECTIVE

To identify the frequency of the rs143383 SNPin the GDF5 gene, which is located in the 5'-untranslated region of Turkish population with knee osteoarthritis (OA).

STUDY DESIGN

Acase-control study.

PLACE AND DURATION OF STUDY

Orthopedics and Traumatology Department, Bozok University Medical Faculty, Yozgat, Turkey, from 2012 to 2014.

METHODOLOGY

Patients diagnosed with OA(n=94) and patients who did not have joint complaints (n=279) were enrolled in this study. Patients diagnosed with osteoarthritis according to the 1986 American College of Rheumatology osteoarthritis criteria and Kellgren and Lawrence scores were investigated, based on age, gender, and X-ray findings. Blood samples were taken for the identification of GDF5 (rs143383) SNPs by PCR/RFLP, according to a standard protocol.

RESULTS

This study included 373 patients. The OAgroup (25.2%; n=94) was characterized by specific genotypes: TT (39.4%; n=37); heterozygotes (TC; 45.7%; n=43); and homozygotes (CC; 14.9%; n=14). The control group (74.8%; n=279) was comprised of TT(26.5%; n=74), TC (54.8%; n=153), and CC (18.6%; n=52) genotypes. An analysis of rs143383 SNP of the GDF5 gene polymorphism revealed that the rs143383 TTgenotype had a higher risk for OA(crude OR=1.798, 95% CI=1.010-2.941, p=0.021).

CONCLUSION

This study demonstrated that there is a correlation of +104T/C polymorphism in the 5'-UTR of GDF5 with knee OAin a Turkish population.

A consistent and potentially exploitable response during chondrogenesis of mesenchymal stem cells from osteoarthritis patients to the protein encoded by the susceptibility gene GDF5

Osteoarthritis (OA) is a common joint disease characterised by the focal loss of the protective cartilage layer at the ends of the bones. It is painful, disabling, multifactorial and polygenic. The growth differentiation factor 5 gene GDF5 was one of the first reported OA susceptibility signals that showed consistent association to OA, with the transcript single nucleotide polymorphism (SNP) rs143383 demonstrating association in Asians and Europeans. The functional effect of the signal is reduced expression of the gene. The GDF5 protein is an extracellular matrix signalling molecule that is active during chondrogenesis and in mature chondrocytes. Due to the functional impact of the susceptibility, we previously assessed the effect of supplementing chondrocytes from OA patients with exogenous GDF5. Their response was highly discordant, precluding the application of GDF5 as a simple means of attenuating the genetic deficit. Since GDF5 is also active during development, we have now assessed the effect of exogenous GDF5 on bone marrow derived mesenchymal stem cells (MSCs) that are undergoing chondrogenesis during cartilage disc formation. MSCs from healthy donors and OA patients were studied and the effect of GDF5 was assessed by measuring the wet mass of the discs, by histological staining, and by monitoring the change in expression of anabolic, catabolic and hypertrophic protein-coding genes. The MSCs expressed the three principal GDF5 receptor genes and responded in a significantly anabolic manner (increase in wet mass, p = 0.0022; Bonferroni corrected p = 0.018) to a variant form of GDF5 that targets the most abundantly expressed receptor, BMPR-IA. GDF5 elicited significant (p < 0.05) changes in the expression of anabolic, catabolic and hypertrophic genes with several consistent effects in healthy donors and in OA patients. Our data implies that, unlike OA chondrocytes, OA MSCs do respond in a predictable, anabolic manner to GDF5, which could therefore provide a route to modulate the genetic deficit mediated by the rs143383 association signal.

Heads, Shoulders, Elbows, Knees, and Toes: Modular Gdf5 Enhancers Control Different Joints in the Vertebrate Skeleton

Synovial joints are crucial for support and locomotion in vertebrates, and are the frequent site of serious skeletal defects and degenerative diseases in humans. Growth and differentiation factor 5 (Gdf5) is one of the earliest markers of joint formation, is required for normal joint development in both mice and humans, and has been genetically linked to risk of common osteoarthritis in Eurasian populations. Here, we systematically survey the mouse Gdf5 gene for regulatory elements controlling expression in synovial joints. We identify separate regions of the locus that control expression in axial tissues, in proximal versus distal joints in the limbs, and in remarkably specific sub-sets of composite joints like the elbow. Predicted transcription factor binding sites within Gdf5 regulatory enhancers are required for expression in particular joints. The multiple enhancers that control Gdf5 expression in different joints are distributed over a hundred kilobases of DNA, including regions both upstream and downstream of Gdf5 coding exons. Functional rescue tests in mice confirm that the large flanking regions are required to restore normal joint formation and patterning. Orthologs of these enhancers are located throughout the large genomic region previously associated with common osteoarthritis risk in humans. The large array of modular enhancers for Gdf5 provide a new foundation for studying the spatial specificity of joint patterning in vertebrates, as well as new candidates for regulatory regions that may also influence osteoarthritis risk in human populations.

Joints, such as the hip and knee, are crucial for support and locomotion in animals, and are the frequent sites of serious human diseases such as arthritis. The Growth and differentiation factor 5 (Gdf5) gene is required for normal joint formation, and has been linked to risk of common arthritis in Eurasians. Here, we surveyed the mouse gene for the regulatory information that controls Gdf5's expression pattern in stripes at sites of joint formation. The gene does not have a single regulatory sequence that drives expression in all joints. Instead, Gdf5 has multiple different control sequences that show striking specificity for joints in the head, vertebral column, shoulder, elbow, wrist, hip, knee, and digits. Rescue experiments show that multiple control sequences are required to restore normal joint formation in Gdf5 mutants. The joint control sequences originally found in mice are also present in humans, where they are marked as active regions during fetal development and post-natal life, and map to a large region associated with arthritis risk in human populations. Regulatory variants in the human GDF5 control sequences can now be studied for their potential role in altering joint development or disease risk at particular locations in the skeleton.

Characterization of an acromesomelic dysplasia, Grebe type case: novel mutation affecting the recognition motif at the processing site of GDF5

Acromesomelic dysplasia, Grebe type is a very rare skeletal dysplasia characterized by severe dwarfism with marked micromelia and deformation of the upper and lower limbs, with a proximodistal gradient of severity. CDMP1 gene mutations have been associated with Grebe syndrome, Hunter-Thompson syndrome, Du Pan syndrome and brachydactyly type C. The proband is a 4-year-old boy, born of consanguineous Pakistani parents. Radiographic imaging revealed features typical of Grebe syndrome: severe shortening of the forearms with an acromesomelic pattern following a proximodistal gradient, with distal parts more severely affected than medial parts; hypoplastic hands, with the phalangeal zone more affected than the metacarpal zone; and severe hypoplastic tibial/femoral zones in both limbs. After molecular analyses, the p.Arg377Trp variant in a homozygous pattern was identified in the CDMP1 gene in the affected child. In silico and structural analyses predicted the p.Arg377Trp amino acid change to be pathogenic. Of the 34 mutations described in the CDMP1 gene, four different missense mutations have been associated with Grebe syndrome. The CDMP1 gene encodes growth differentiation factor 5 (GDF5), which plays a role in regulation of limb patterning, joint formation and distal bone growth. Homozygous mutations in the mature domain of GDF5 result in severe limb malformations such as the Grebe type or the Hunter-Thompson type of acromesomelic chondrodysplasia. The p.Arg377Trp mutation is located within the recognition motif at the processing site of GDF5 where the sequence RRKRR changes to WRKRR. The genotype-phenotype correlation allowed not only confirmation of the clinical diagnosis but also appropriate genetic counselling to be offered to this family.

MiR-132-3p Regulates the Osteogenic Differentiation of Thoracic Ligamentum Flavum Cells by Inhibiting Multiple Osteogenesis-Related Genes

Ossification of the ligamentum flavum (OLF) is a disorder of heterotopic ossification of spinal ligaments and is the main cause of thoracic spinal canal stenosis. Previous studies suggested that miR-132-3p negatively regulates osteoblast differentiation. However, whether miR-132-3p is involved in the process of OLF has not been investigated. In this study, we investigated the effect of miR-132-3p and its target genes forkhead box O1 (FOXO1), growth differentiation factor 5 (GDF5) and SRY-box 6 (SOX6) on the osteogenic differentiation of ligamentum flavum (LF) cells. We demonstrated that miR-132-3p was down-regulated during the osteogenic differentiation of LF cells and negatively regulated the osteoblast differentiation. Further, miR-132-3p targeted FOXO1, GDF5 and SOX6 and down-regulated the protein expression of these genes. Meanwhile, FOXO1, GDF5 and SOX6 were up-regulated after osteogenic differentiation and the down-regulation of endogenous FOXO1, GDF5 or SOX6 suppressed the osteogenic differentiation of LF cells. In addition, we also found FOXO1, GDF5 and SOX6 expression in the ossification front of OLF samples. Overall, these results suggest that miR-132-3p inhibits the osteogenic differentiation of LF cells by targeting FOXO1, GDF5 and SOX6.

Improved bone defect healing by a superagonistic GDF5 variant derived from a patient with multiple synostoses syndrome

Multiple synostoses syndrome 2 (SYNS2) is a rare genetic disease characterized by multiple fusions of the joints of the extremities, like phalangeal joints, carpal and tarsal joints or the knee and elbows. SYNS2 is caused by point mutations in the Growth and Differentiation Factor 5 (GDF5), which plays an essential role during skeletal development and regeneration. We selected one of the SYNS2-causing GDF5 mutations, p.N445T, which is known to destabilize the interaction with the Bone Morphogenetic Protein (BMP) antagonist NOGGIN (NOG), in order to generate the superagonistic GDF5 variant GDF5(N445T). In this study, we tested its capacity to support regeneration in a rat critical-sized defect model in vivo. MicroCT and histological analyses indicate that GDF5(N445T)-treated defects show faster and more efficient healing compared to GDF5 wild type (GDF5(wt))-treated defects. Microarray-based gene expression and quantitative PCR analyses from callus tissue point to a specific acceleration of the early phases of bone healing, comprising the inflammation and chondrogenesis phase. These results support the concept that disease-deduced growth factor variants are promising lead structures for novel therapeutics with improved clinical activities.

Growth without growth hormone: can growth and differentiation factor 5 be the mediator?

Growth without growth hormone (GH) is often observed in the setup of obesity; however, the missing link between adipocytes and linear growth was until now not identified. 3T3L1 cells were induced to differentiate into adipocytes and their conditioned medium (CM) (adipocytes CM, CMA) was added to metatarsals bone culture and compared to CM derived from undifferentiated cells. CMA significantly increased metatarsals bone elongation. Adipogenic differentiation increased the expression of growth and differentiation factor (GDF)-5, also found to be secreted into the CMA. GDF-5 significantly increased metatarsal length in culture; treatment of the CMA with anti-GDF-5 antibody significantly reduced the stimulatory effect on bone length. The presence of GDF-5 receptor (bone morphogenetic protein receptor; BMPR1) in metatarsal bone was confirmed by immunohistochemistry. Animal studies in rodents subjected to food restriction followed by re-feeding showed an increase in GDF-5 serum levels concomitant with nutritional induced catch up growth. These results show that adipocytes may stimulate bone growth and suggest an additional explanation to the growth without GH phenomenon.

Gene expression analysis suggests bone development-related genes GDF5 and DIO2 are involved in the development of Kashin-Beck disease in children rather than adults

OBJECTIVE

To investigate the differences in gene expression between children and adults with Kashin-Beck disease (KBD).

METHODS

12 children with KBD and 12 healthy children were selected and divided into 4 KBD vs. control pairs matched according to age and gender, with each pair having 3 KBD children and 3 healthy children. Additionally, 15 adults with KBD and 15 healthy adults were selected and divided into 5 KBD vs. control pairs matched according to age and gender, with each pair having 3 KBD adults and 3 healthy adults. Total RNA was isolated from peripheral blood mononuclear cells (PBMCs) respectively. A total of 367 target genes were selected based on previous genome-wide gene expression profile analysis. Expression levels of the 367 genes were evaluated by customized oligonucleotide microarray and the differentially expressed genes were identified. Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) was conducted to validate the microarray data.

RESULTS

A total of 95 (25.9%) genes in KBD children and 158 (43.1%) genes in KBD adults were found to exhibit more than two-fold change in gene expression level relative to healthy controls. By comparing differentially expressed genes identified in KBD children to those of KBD adults, 42 genes were found to be differentially expressed only in KBD children. And 105 genes were found to be differentially expressed only in KBD adults. Further, 16 differentially expressed genes common to both KBD children and adults were found to be asynchronously expressed in KBD children compared to KBD adults.

CONCLUSION

Significant differences in gene expression pattern were identified between KBD children and KBD adults, indicating different molecular mechanisms underlying cartilage lesions of KBD children and KBD adults. In addition, bone development-related genes GDF5 (expression ratio = 2.14±0.02) and DIO2 (expression ratio = 0.11±0.05) may contribute to the development of KBD in children rather than in adults.

Impact of estrogen-related receptor α on the biological characteristics of rat mandibular condylar chondrocytes

It is well‑known that estrogen-related receptor α (ERRα) affects numerous metabolic pathways and biological functions in the body, although the function of ERRα in the mandibular condylar chondrocytes (MCCs) of the temporomandibular joint remains unclear. The aim of the present study was to investigate the effect of ERRα on the biological characteristics of MCCs in female rats. Immunofluorescent staining was used to observe the expression level and distribution of ERRα in MCCs and tissues. Quantitative polymerase chain reaction (qPCR) was performed to detect the impact of estrogen intervention on the biological characteristics of female rat MCCs and ERRα expression levels. Liposome transfection and XCT‑790 were used to overexpress and inhibit ERRα expression, respectively, and then qPCR was performed to detect changes in the biological characteristics of MCCs. ERRα expression was detected in the nucleus and cytoplasm of rat MCCs. 17‑β estradiol (E2) (10‑8 M) increased the mRNA and protein expression levels of ERRα, Sox9, GDF‑5 and aromatase during in vitro MCC cultivation. In addition, E2 affected MCC proliferation through the regulation of ERRα expression levels. Overexpression of ERRα positively regulated the mRNA and protein expression levels of Sox9 and GDF‑5, but did not exhibit a significant effect on the mRNA and protein expression levels of aromatase and Col2a1. In conclusion, ERRα exhibited an important regulatory role in the proliferation and differentiation of female Sprague‑Dawley rat MCCs in vitro through regulating Sox9 and GDF-5.

[Epidemiology of bone and joint disease - the present and future - . Genetic epidemiology on osteoarthritis]

Although a large number of studies have been made to identify genetic loci associated with osteoarthritis (OA), there are only a few that have been reported to be associated with OA in many regions and countries. One of the reasons for the lack of success may be small effect sizes. A sufficiently large sample size is required for the genetic epidemiology on OA to elucidate genetic influence regarding the occurrence and progression.

Identification of duplication downstream of BMP2 in a Chinese family with brachydactyly type A2 (BDA2)

Brachydactyly type A2 (BDA2, MIM 112600) is characterized by the deviation and shortening of the middle phalange of the index finger and the second toe. Using genome-wide linkage analysis in a Chinese BDA2 family, we mapped the maximum candidate interval of BDA2 to a ∼1.5 Mb region between D20S194 and D20S115 within chromosome 20p12.3 and found that the pairwise logarithm of the odds score was highest for marker D20S156 (Zmax = 6.09 at θ = 0). Based on functional and positional perspectives, the bone morphogenetic protein 2 (BMP2) gene was identified as the causal gene for BDA2 in this region, even though no point mutation was detected in BMP2. Through further investigation, we identified a 4,671 bp (Chr20: 6,809,218-6,813,888) genomic duplication downstream of BMP2. This duplication was located within the linked region, co-segregated with the BDA2 phenotype in this family, and was not found in the unaffected family members and the unrelated control individuals. Compared with the previously reported duplications, the duplication in this family has a different breakpoint flanked by the microhomologous sequence GATCA and a slightly different length. Some other microhomologous nucleotides were also found in the duplicated region. In summary, our findings support the conclusions that BMP2 is the causing gene for BDA2, that the genomic location corresponding to the duplication region is prone to structural changes associated with malformation of the digits, and that this tendency is probably caused by the abundance of microhomologous sequences in the region.

[Preliminary study on transgenic cell sheet with cartilage-derived morphogenetic protein]

OBJECTIVE

To construct a transgenic cell sheet of cartilage-derived morphogenetic protein 1 (CDMP1) by adenovirus vector in vitro and to identify its biological activity.

METHODS

The bone mesenchymal stem cells (BMSCs) were isolated from bone marrow of 1-month-old rabbit, and cultured in vitro. The 3rd-6th generation of BMSCs were used for experiment. The experiment was divided into 3 groups: BMSCs transfected by adenovirus (Ad)-cytomegalovirus (CMV)-human CDMP1 (hCDMP1)-internal ribosome entry site (IRES)-enhanced green fluorescent protein (EGFP) in group A, BMSCs transfected by Ad-CMV-EGFP in group B, and untransfected BMSCs in group C. The expression of green fluorescence was observed in 3 groups under fluorescent inverted microscope. MTT assay was used to detect the proliferation of the cells. The cell sheet was obtained by means of temperature-responsive culture dish for 14 days. The morphological and HE staining observations of the cell sheet were carried out. RT-PCR and Western blot were used to detect the expressions of hCDMP1 and collagen type II at gene and protein levels, while alcian blue staining was used to detect the expression of glycosaminoglycans (GAG).

RESULTS

Bright green fluorescence was observed in transfected cells at 72 hours under fluorescent inverted microscope, and the transfection efficiency was up to 90%. MTT assay showed approximate S-shaped growth curves in 3 groups, showing no significant difference in the absorbance (A) value among 3 groups within 9 days (P > 0.05). The three-dimensional cell sheets were successfully harvested in vitro. The RT-PCR and Western blot showed that there were positive expressions of hCDMPl and collagen type II in group A and negative expression in other 2 groups. HE staining and alcian blue staining showed that there were rich fibrous tissues, mass extracellular matrix, and dark blue metachromatic granules in group A, but there was less fibrous tissues and no specific blue metachromatic granules in other 2 groups; and the positive expression area was significantly lower and gray scale of GAG was significantly higher in group A than that in groups B and C (P < 0.05).

CONCLUSION

A transgenic cell sheet of exogenous recombinant hCDMP1 by adenovirus vector can express collagen type II and GAG, so it has chondrogenic capacity. This technology that overcomes limitations in traditional tissue engineering, such as low cell-attachment efficiency and inflammatory reaction, may be a new tissue engineering approach for hard tissue reconstruction and is hopeful to build a large density of tissue engineered cartilage.

Human chondrocytes respond discordantly to the protein encoded by the osteoarthritis susceptibility gene GDF5

A genetic deficit mediated by SNP rs143383 that leads to reduced expression of GDF5 is strongly associated with large-joint osteoarthritis. We speculated that this deficit could be attenuated by the application of exogenous GDF5 protein and as a first step we have assessed what effect such application has on primary osteoarthritis chondrocyte gene expression. Chondrocytes harvested from cartilage of osteoarthritic patients who had undergone joint replacement were cultured with wildtype recombinant mouse and human GDF5 protein. We also studied variants of GDF5, one that has a higher affinity for the receptor BMPR-IA and one that is insensitive to the GDF5 antagonist noggin. As a positive control, chondrocytes were treated with TGF-β1. Chondrocytes were cultured in monolayer and micromass and the expression of genes coding for catabolic and anabolic proteins of cartilage were measured by quantitative PCR. The expression of the GDF5 receptor genes and the presence of their protein products was confirmed and the ability of GDF5 signal to translocate to the nucleus was demonstrated by the activation of a luciferase reporter construct. The capacity of GDF5 to elicit an intracellular signal in chondrocytes was demonstrated by the phosphorylation of intracellular Smads. Chondrocytes cultured with TGF-β1 demonstrated a consistent down regulation of MMP1, MMP13 and a consistent upregulation of TIMP1 and COL2A1 with both culture techniques. In contrast, chondrocytes cultured with wildtype GDF5, or its variants, did not show any consistent response, irrespective of the culture technique used. Our results show that osteoarthritis chondrocytes do not respond in a predictable manner to culture with exogenous GDF5. This may be a cause or a consequence of the osteoarthritis disease process and will need to be surmounted if treatment with exogenous GDF5 is to be advanced as a potential means to overcome the genetic deficit conferring osteoarthritis susceptibility at this gene.

Growth differentiation factor-5 promotes brown adipogenesis in systemic energy expenditure

Although growth differentiation factor-5 (GDF5) has been implicated in skeletal development and joint morphogenesis in mammals, little is known about its functionality in adipogenesis and energy homeostasis. Here, we show a critical role of GDF5 in regulating brown adipogenesis for systemic energy expenditure in mice. GDF5 expression was preferentially upregulated in brown adipose tissues from inborn and acquired obesity mice. Transgenic overexpression of GDF5 in adipose tissues led to a lean phenotype and reduced susceptibility to diet-induced obesity through increased systemic energy expenditure. Overexpression of GDF5 facilitated the development of brown fat-like cells, called brite or beige cells, along with the expression of uncoupling protein-1 in inguinal subcutaneous white adipose tissue. In mutant mice harboring the dominant-negative GDF5, marked impairment in energy expenditure and thermogenesis was seen under obesogenic conditions. Recombinant GDF5 promoted brown adipogenesis through the mothers against decapentaplegic homolog (Smad) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) pathways after activation of bone morphogenetic protein receptor (BMPR). These results suggest that brown adipogenesis and energy homeostasis are both positively regulated by the GDF5/BMPR/Smad/PGC-1α signaling pathway in adipose tissues. Modulation of these pathways might be an effective therapeutic strategy for obesity and type 2 diabetes.

A GDF5 point mutation strikes twice--causing BDA1 and SYNS2

Growth and Differentiation Factor 5 (GDF5) is a secreted growth factor that belongs to the Bone Morphogenetic Protein (BMP) family and plays a pivotal role during limb development. GDF5 is a susceptibility gene for osteoarthritis (OA) and mutations in GDF5 are associated with a wide variety of skeletal malformations ranging from complex syndromes such as acromesomelic chondrodysplasias to isolated forms of brachydactylies or multiple synostoses syndrome 2 (SYNS2). Here, we report on a family with an autosomal dominant inherited combination of SYNS2 and additional brachydactyly type A1 (BDA1) caused by a single point mutation in GDF5 (p.W414R). Functional studies, including chondrogenesis assays with primary mesenchymal cells, luciferase reporter gene assays and Surface Plasmon Resonance analysis, of the GDF5^W414R variant in comparison to other GDF5 mutations associated with isolated BDA1 (p.R399C) or SYNS2 (p.E491K) revealed a dual pathomechanism characterized by a gain- and loss-of-function at the same time. On the one hand insensitivity to the main GDF5 antagonist NOGGIN (NOG) leads to a GDF5 gain of function and subsequent SYNS2 phenotype. Whereas on the other hand, a reduced signaling activity, specifically via the BMP receptor type IA (BMPR1A), is likely responsible for the BDA1 phenotype. These results demonstrate that one mutation in the overlapping interface of antagonist and receptor binding site in GDF5 can lead to a GDF5 variant with pathophysiological relevance for both, BDA1 and SYNS2 development. Consequently, our study assembles another part of the molecular puzzle of how loss and gain of function mutations in GDF5 affect bone development in hands and feet resulting in specific types of brachydactyly and SYNS2. These novel insights into the biology of GDF5 might also provide further clues on the pathophysiology of OA.

Mutations can be generally classified in loss- or gain-of-function mutations depending on their specific pathomechanism. Here we report on a GDF5 mutation, p.W414R, which is associated with brachydactyly type A1 (BDA1) and Multiple Synostoses Syndrome 2 (SYNS2). Interestingly, whereas shortening of phalangeal elements (brachydactyly) is thought to be caused by a loss of function, bony fusions of joints (synostoses) are due to a gain of function mechanism. Therefore, the question arises as to how p.W414R in GDF5 leads to this combination of phenotypes. In our functional studies, we included two reported GDF5 mutations, which are associated with isolated forms of SYNS2 (GDF5^E491K) or BDA1 (GDF5^R399C), respectively. We demonstrate that an impaired interaction between the extracellular antagonist NOGGIN (NOG) and GDF5 is likely to cause a joint fusion phenotype such as SYNS2. In contrast, GDF5 mutations associated with BDA1 rather exhibit an altered signaling activity through BMPR1A. Consequently, the GDF5^W414R mutation negatively affects both interactions in parallel, which causes the combined phenotype of SYNS2 and BDA1.

Genetics of disc-related disorders: current findings and lessons from other complex diseases

Disc-related disorders are highly genetic conditions with heritability estimates of up to 75 % and yet, few genomic locations have been moderately associated with the disorders. Candidate gene studies have shown possible disease associations on loci and genes of 1p21.1 (COL11A1), 6q27 (THBS2), 9q22.31 (ASPN), 10p12.31 (SKT), 20q11.2 (GDF5) and 20q13.12 (MMP9). More recently, in 2012, the first genome-wide association study revealed variants on loci and genes of 3p26.2, 6p21.32 (HLA region) and 6q26 (PARK2) that associate with disc-related disorders. In many other complex diseases, large meta-analyses of hundreds of thousands of study subjects and loci have revealed remarkable pathways. As methodology is evolving rapidly, we have already stepped into the era of routinely sequencing all bases in all human exons and we are approaching the era of sequencing the entire genome of study subjects with common diseases. The past decade has taught us that the common variants seen throughout populations seem to have low effects in many common diseases, explain relatively little of the overall heritability of the diseases and demand thousands of study subjects to identify associations. It seems that familial rare variants play an important role in many common diseases leading us back to valuing studies with large families and isolated populations. Moreover, careful characterization of environmental conditions are needed to explore and determine gene-environment interactions as genes that increase disease risk in one context may not do so under another context.

The identification of trans-acting factors that regulate the expression of GDF5 via the osteoarthritis susceptibility SNP rs143383

rs143383 is a C to T transition SNP located in the 5′untranslated region (5′UTR) of the growth differentiation factor 5 gene GDF5. The T allele of the SNP is associated with increased risk of osteoarthritis (OA) in Europeans and in Asians. This susceptibility is mediated by the T allele producing less GDF5 transcript relative to the C allele, a phenomenon known as differential allelic expression (DAE). The aim of this study was to identify trans-acting factors that bind to rs143383 and which regulate this GDF5 DAE. Protein binding to the gene was investigated by two experimental approaches: 1) competition and supershift electrophoretic mobility shift assays (EMSAs) and 2) an oligonucleotide pull down assay followed by quantitative mass spectrometry. Binding was then confirmed in vivo by chromatin immunoprecipitation (ChIP), and the functional effects of candidate proteins investigated by RNA interference (RNAi) and over expression. Using these approaches the trans-acting factors Sp1, Sp3, P15, and DEAF-1 were identified as interacting with the GDF5 5′UTR. Knockdown and over expression of the factors demonstrated that Sp1, Sp3, and DEAF-1 are repressors of GDF5 expression. Depletion of DEAF-1 modulated the DAE of GDF5 and this differential allelic effect was confirmed following over expression, with the rs143383 T allele being repressed to a significantly greater extent than the rs143383 C allele. In combination, Sp1 and DEAF-1 had the greatest repressive activity. In conclusion, we have identified four trans-acting factors that are binding to GDF5, three of which are modulating GDF5 expression via the OA susceptibility locus rs143383.

GDF5 is an important growth factor that plays a vital role in the development and repair of articulating joints. rs143383 is a polymorphism within the regulatory region of the GDF5 gene and has two allelic forms, C and T. Genetic studies have demonstrated that the T allele is associated with an increased risk of osteoarthritis in a range of ethnic populations whilst previous functional studies revealed that this allele mediates its effect by producing less GDF5 transcript than the C allele. In this study, we sought to identify transcription factors that are binding to rs143383 and that are responsible for mediating this differential level of expression. Using two different approaches we have identified four factors and our functional studies have revealed that three of these factors repress GDF5 expression and that DEAF-1 modulates the differential expression of the two rs143383 alleles. The factors that we have identified could serve as novel therapeutic targets, with their depletion restoring the expression levels of GDF5 in patients with the osteoarthritis susceptibility T allele. The relevance of our results extends beyond osteoarthritis, since the T allele of rs143383 is also a risk factor for a number of other musculoskeletal diseases.

Association study of candidate genes for the progression of hand osteoarthritis

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

GDF5 regulates TGFß-dependent angiogenesis in breast carcinoma MCF-7 cells: in vitro and in vivo control by anti-TGFß peptides

BACKGROUND

TGFß overproduction in cancer cells is one of the main characteristics of late tumor progression being implicated in metastasis, tumor growth, angiogenesis and immune response. We investigated the therapeutic efficacy of anti-TGFß peptides in the control of angiogenesis elicited by conditional over-expression of TGFß.

METHODS

We have inserted in human MCF7 mammary-cancer cells a mutated TGFß gene in a tetracycline-repressible vector to obtain conditional expression of mature TGFß upon transient transfection, evaluated the signaling pathways involved in TGFß-dependent endothelial cells activation and the efficacy of anti-TGFß peptides in the control of MCF7-TGFß-dependent angiogenesis.

RESULTS

TGFß over-expression induced in MCF7 several markers of the epithelial-to-mesenchymal transition. Conditioned-medium of TGFß-transfected MCF7 stimulated angiogenesis in vivo and in vitro by subsequent activation of SMAD2/3 and SMAD1/5 signaling in endothelial cells, as well as SMAD4 nuclear translocation, resulting in over-expression of the pro-angiogenic growth and differentiation factor-5 (GDF5). Inhibition or silencing of GDF5 in TGFß-stimulated EC resulted in impairment of GDF5 expression and of TGFß-dependent urokinase-plasminogen activator receptor (uPAR) overproduction, leading to angiogenesis impairment. Two different TGFß antagonist peptides inhibited all the angiogenesis-related properties elicited in EC by exogenous and conditionally-expressed TGFß in vivo and in vitro, including SMAD1/5 phosphorylation, SMAD4 nuclear translocation, GDF5 and uPAR overexpression. Antagonist peptides and anti-GDF5 antibodies efficiently inhibited in vitro and in vivo angiogenesis.

CONCLUSIONS

TGFß produced by breast cancer cells induces in endothelial cells expression of GDF5, which in turn stimulates angiogenesis both in vitro and in vivo. Angiogenesis activation is rapid and the involved mechanism is totally opposed to the old and controversial dogma about the AKL5/ALK1 balance. The GDF-dependent pro-angiogenic effects of TGFß are controlled by anti-TGFß peptides and anti-GDF5 antibodies, providing a basis to develop targeted clinical studies.

Genetic contribution to radiographic severity in osteoarthritis of the knee

OBJECTIVE

Knee osteoarthritis (OA) has a significant genetic component. The authors have assessed the role of three variants reported to influence risk of knee OA with p<5×10-8 in determining patellofemoral and tibiofemoral Kellgren Lawrence (K/L) grade in knee OA cases.

METHODS

3474 knee OA cases with sky-line and weight-bearing antero-posterior x-rays of the knee were selected based on the presentation of K/L grade ≥2 at either the tibiofemoral or patellofemoral compartments for one or both knees. Patients belonging to three UK cohorts, were genotyped for rs143383, rs4730250 and rs11842874 mapping to the GDF5, COG5 and MCF2L genes, respectively. The association between tibiofemoral K/L grade and patellofemoral K/L grade was assessed after adjusting for age, gender and body mass index.

RESULTS

No significant association was found between the rs4730250 and radiographic severity. The rs11842874 mapping to MCF2L was found to be nominally significantly associated with patellofemoral K/L grade as a quantitative trait (p=0.027) but not as a binary trait. The GDF5 single nucleotide polymorphism rs143383 was associated with tibiofemoral K/L grade (β=0.05 (95% CI 0.02 to 0.08) p=0.0011).

CONCLUSIONS

Our data indicate that within individuals affected by radiographic knee OA, OAGDF5 has a modest but significant effect on radiographic severity after adjustment for the major risk factors.

Positive selection on the osteoarthritis-risk and decreased-height associated variants at the GDF5 gene in East Asians

GDF5 is a member of the bone morphogenetic protein (BMP) gene family, and plays an important role in the development of the skeletal system. Variants of the gene are associated with osteoarthritis and height in some human populations. Here, we resequenced the gene in individuals from four geographically separated human populations, and found that the evolution of the promoter region deviated from neutral expectations, with the sequence evolution driven by positive selection in the East Asian population, especially the haplotypes carrying the derived alleles of 5' UTR SNPs rs143384 and rs143383. The derived alleles of rs143384 and rs143383, which are associated with a risk of osteoarthritis and decreased height, have high frequencies in non-Africans and show strong extended haplotype homozygosity and high population differentiation in East Asian. It is concluded that positive selection has driven the rapid evolution of the two osteoarthritis osteoarthritis-risk and decreased height associated variants of the human GDF5 gene, and supports the suggestion that the reduction in body size during the terminal Pleistocene and Holocene period might have been an adaptive process influenced by genetic factors.

Delayed fracture healing in growth differentiation factor 5-deficient mice: a pilot study

BACKGROUND

Growth differentiation factor-5 (GDF-5) is a key regulator of skeletogenesis and bone repair and induces bone formation in spinal fusions and nonunion applications by enhancing chondrocytic and osteocytic differentiation and stimulating angiogenesis. Elucidating the contribution of GDF-5 to fracture repair may support its clinical application in complex fractures.

QUESTIONS/PURPOSE

We therefore asked whether the absence of GDF-5 during fracture repair impaired bone healing as assessed radiographically, histologically, and mechanically.

METHODS

In this pilot study, we performed tibial osteotomies on 10-week-old male mice, stabilized by intramedullary and extramedullary nailing. Healing was assessed radiographically and histologically on Days 1 (n = 1 wild-type; n = 5 bp [brachopodism]), 5 (n = 3 wild-type; n = 3 bp), 10 (n = 6 wild-type; n = 3 bp), 14 (n = 6 wild-type; n = 6 bp), 21 (n = 6 wild-type; n = 6 bp), 28 (n = 7 wild-type; n = 6 bp), and 56 (n = 6 wild-type; n = 6 bp) after fracture. After 10 (n = 7 wild-type; n = 7 bp contralateral and n = 3 bp fractured tibiae), 14 (n = 6 wild-type; n = 6 bp), 21 (n = 6 wild-type; n = 6 bp), 28 (n = 6 wild-type; n = 3 bp), and 56 (n = 8 wild-type; n = 6 bp) days, the callus cross-sectional area was calculated. We characterized the mechanical integrity of the healing fracture by yield stress and Young's modulus at 28 (n = 6 wild-type; n = 3 bp) and 56 (n = 8 wild-type; n = 6 bp) days postfracture.

RESULTS

The absence of GDF-5 impaired cartilaginous matrix deposition in the callus and reduced callus cross-sectional area. After 56 days, the repaired bp fracture was mechanically comparable to that of controls.

CONCLUSIONS

Although GDF-5 deficiency did not compromise long-term fracture healing, a delay in cartilage formation and remodeling supports roles for GDF-5 in the early phase of bone repair.

CLINICAL RELEVANCE

Local delivery of GDF-5 to clinically difficult fractures may simulate cartilage formation in the callus and support subsequent remodeling.

Expression of the osteoarthritis-associated gene GDF5 is modulated epigenetically by DNA methylation

GDF5 is involved in synovial joint development, maintenance and repair, and the rs143383 C/T single nucleotide polymorphism (SNP) located in the 5'UTR of GDF5 is associated, at the genome-wide significance level, with osteoarthritis susceptibility, and with other musculoskeletal phenotypes including height, congenital hip dysplasia and Achilles tendinopathy. There is a significant reduction in the expression of the disease-associated T allele relative to the C allele in synovial joint tissues, an effect influenced by a second SNP (rs143384, C/T) also within the 5'UTR. The differential allelic expression (DAE) imbalance of the C and T alleles of rs143383 varies intra- and inter-individually, suggesting that DAE may be modulated epigenetically. The C alleles of both SNPs form CpG dinucleotides that are potentially amenable to regulation by methylation. Here, we have examined whether DNA methylation regulates GDF5 expression and the allelic imbalance caused by rs143383. We observed methylation of the GDF5 promoter and 5'UTR in cell lines and joint tissues, with demethylation correlating with increased GDF5 expression. The CpG sites created by the C alleles at rs143383 and rs143384 were variably methylated, and treatment of a heterozygous cell line with a demethylating agent further increased the allelic expression imbalance between the C and T alleles. This demonstrates that the genetic effect of the rs143383 SNP on GDF5 expression is modulated epigenetically by DNA methylation. The variability in DAE of rs143383 is therefore partly accounted for by differences in DNA methylation that could influence the penetrance of this allele in susceptibility to common musculoskeletal diseases.

Functional effects of susceptibility genes in osteoarthritis

Osteoarthritis is the most common chronic musculoskeletal disorder. Although osteoarthritis is a multifactorial disease, it is known to have a significant genetic contribution. Identified genes so far, contributing to the prevalence and progression of the disease, belong to signaling pathways such as the bone morphogenetic protein and the wingless-type signaling families. These pathways are important during development and appear to be reactivated in postnatal joint homeostasis and repair. Among the most consistently associated genes, so far, are GDF5 and FRZB, which were both originally identified from a chondrogenic extract of articular cartilage. We focus on the functional aspects of these susceptibility genes and summarize recent evidence, obtained in specific animal models, for their possible roles in osteoarthritis. These data support the view that all tissues within the joint may contribute to osteoarthritis and that pathways important in skeletal development are also involved in the disease processes thereby presenting attractive therapeutic targets.

[Recent advance in the genomic study for osteoarthritis]

Osteoarthritis (OA) is a polygenic disease. Genetic factors are involved in its onset and progression. Identification of its genetic factor, i.e., the susceptibility genes for OA is rapidly in progress by using genomic approaches including genome-wide association study. Recent advance in the study of OA susceptibility genes is reviewed.

Osteoarthritis susceptibility genes influence the association between hip morphology and osteoarthritis

OBJECTIVE

The identified osteoarthritis (OA) susceptibility genes are mainly active in skeletal development and could thus affect joint geometry. Because nonoptimal joint geometry is a risk factor for the development of OA, we investigated if and how the path that leads from nonoptimal joint geometry to OA of the hip is influenced by these genes.

METHODS

The shape of the hips of subjects in the Genetics, Osteoarthritis and Progression Study, consisting of sibling pairs with symptomatic OA at multiple joint locations, was quantified by applying a statistical shape model to radiographs. Shape aspects (modes) were correlated to OA characteristics. We then tested for the association of shape modes with OA susceptibility single-nucleotide polymorphisms (SNPs) of GDF5, FRZB, and DIO2.

RESULTS

Four of 23 shape modes (mode 1, mode 17, mode 18, and mode 21) were strongly associated with OA characteristics. We observed a significant interaction between carrier status of DIO2 rs12885300 and hip OA characteristics for mode 1 (P = 0.005). This indicates that this specific aspect of hip shape correlates with OA characteristics only in carriers of the susceptibility allele.

CONCLUSION

Our results suggest that it is more likely that the rs12885300 SNP of DIO2 increases the vulnerability of cartilage to nonoptimal bone shapes rather than directly influencing the formation of these shapes.

Purification, crystallization and preliminary data analysis of the ligand-receptor complex of the growth and differentiation factor 5 variant R57A (GDF5R57A) and BMP receptor IA (BRIA)

The binary ligand-receptor complex of human growth and differentiation factor 5 (GDF5) bound to its type I receptor BMP receptor IA (BRIA) was prepared and crystallized. By utilizing the GDF5 variant R57A, which exhibits a high affinity in the subnanomolar range for BRIA, the binary complex of GDF5R57A bound to the extracellular domain of BRIA could be produced and purified. Crystals of this complex belonged to a monoclinic space group: either I2, with unit-cell parameters a = 63.81, b = 62.85, c = 124.99 Å, β = 95.9°, or C2, with unit-cell parameters a = 132.17, b = 62.78, c = 63.53 Å, β = 112.8°.

Osteoarthritis year 2010 in review: genetics

At the 2010 Osteoarthritis Research Society International (OARSI) congress in Brussels I was asked to present on "Genetics" in the "Year in Review" session. This gave me an opportunity to reflect on the talk that I gave on the same topic at the 2007 OARSI congress in Ft Lauderdale, Florida. My 2007 talk was very upbeat and ended with the hostage to fortune statement "The next few years will provide tremendous clarity in our genetic understanding of osteoarthritis".