Identification and analysis of a SMAD3 cis-acting eQTL operating in primary osteoarthritis and in the aneurysms and osteoarthritis syndrome.

OBJECTIVE: The TGF-ß pathway plays a central role in joint development with polymorphism in TGF-ß pathway genes implicated in osteoarthritis susceptibility. One association is to rs12901499, within intron 1 of SMAD3. Since rs12901499 is not in linkage disequilibrium with a non-synonymous polymorphism, it is likely the association is operating by influencing expression of SMAD3. DESIGN: Using tissues from the joints of primary osteoarthritis patients who had undergone joint replacement we measured the overall expression of SMAD3 by quantitative real-time PCR. We also measured allelic expression of SMAD3 using these tissues and vascular smooth muscle cells from patients with aneurysms and osteoarthritis syndrome, a rare condition featuring early-onset osteoarthritis. We tested the functional effect of SNPs in vitro using luciferase assays and assessed association with osteoarthritis using a large osteoarthritis case-control dataset. RESULTS: We observed that genotype at rs12901499 did not correlate with overall SMAD3 expression or allelic expression. However, genotype at a 3'UTR SNP, rs8031440, did correlate with SMAD3 expression in cartilage (P = 0.005) which was supported by allelic expression data showing that the G allele correlated with decreased SMAD3 expression in joint tissues and vascular smooth muscle cells. This G allele was underrepresented in osteoarthritis cases vs controls (P = 0.027, odds ratio = 0.921). rs8031440 is in perfect linkage disequilibrium with five other SMAD3 3'UTR SNPs and our luciferase analysis identified rs3743342 and rs12595334 as being functional. CONCLUSION: SMAD3 is subject to cis-acting regulatory polymorphism in the tissues of relevance to both primary osteoarthritis and the aneurysms-osteoarthritis syndrome.

Gene expression analysis reveals HBP1 as a key target for the osteoarthritis susceptibility locus that maps to chromosome 7q22.

OBJECTIVES: An osteoarthritis (OA) susceptibility locus has been mapped to chromosome 7q22, to a region of high-linkage disequilibrium encompassing six genes: PRKAR2B, HBP1, COG5, GPR22, DUS4L and BCAP29. The authors assessed whether these genes were subject to cis-acting regulatory polymorphisms that are active in joint tissues and which could contribute to the association signal. METHODS: Using joint tissues from 156 patients with OA, and control cartilage from 25 patients who had neck of the femur fractures, the authors measured the overall gene expression by quantitative PCR and the allelic expression of the genes, using an assay that can distinguish mRNA output from each allele of a transcript single nucleotide polymorphism. RESULTS: Five of the genes were expressed in joint tissues, the exception being GPR22, which the authors could not detect. In OA cartilage compared with control cartilage, significantly reduced expression levels were observed for these five genes. Carriers of the OA-associated alleles showed a significant reduction in expression of HBP1 in cartilage (p=0.0002) and synovium (p=0.02), and of DUS4L in fat pad (p=0.04). HBP1 and DUS4L also demonstrated allelic expression imbalance across a range of different joint tissues, with carriers of the associated allele showing an HBP1 allelic expression imbalance profile that was significantly different from non-carriers (p=0.008). CONCLUSION: Cis-acting regulatory polymorphisms acting on HBP1 contribute to the OA association signal at chromosome 7q22. HBP1 codes for a transcription factor and studies by the authors have enabled them to prioritise this gene for further investigation.

Common variations in estrogen-related genes are associated with severe large-joint osteoarthritis: a multicenter genetic and functional study.

OBJECTIVE: Several lines of evidence suggest that estrogens influence the development of osteoarthritis (OA). The aim of this study was to explore the association of two common polymorphisms within the aromatase (CYP19A1) and estrogen receptor (ER) alpha (ESR1) genes with severe OA of the lower limbs. METHODS: The rs1062033 (CYP19A1) and rs2234693 (ESR1) single nucleotide polymorphisms were genotyped in 5528 individuals (3147 patients with severe hip or knee OA, and 2381 controls) from four centres in Spain and the United Kingdom. Gene expression was measured in femoral bone samples from a group of patients. RESULTS: In the global analysis, both polymorphisms were associated with OA, but there was a significant sex interaction. The GG genotype at rs1062033 was associated with an increased risk of knee OA in women [odds ratio (OR) 1.23; P=0.04]. The CC genotype at rs2234693 tended to be associated with reduced OA risk in women (OR 0.76, P=0.028, for knee OA; OR=0.84, P=0.076 for hip OA), but with increased risk of hip OA in men (OR 1.28; P=0.029). Women with unfavourable genotypes at both loci had an OR of 1.61 for knee OA (P=0.006). The rs1062033 genotype associated with higher OA risk was also associated with reduced expression of the aromatase gene in bone. CONCLUSIONS: Common genetic variations of the aromatase and ER genes are associated with the risk of severe OA of the large joints of the lower limb in a sex-specific manner. These results are consistent with the hypothesis that estrogen activity may influence the development of large-joint OA.