Objective: The TGF-β pathway plays a central role in joint development with polymorphism in TGF-β 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 invitro 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.

Allelic expression, Aneurysm, Genetics, Osteoarthritis, SMAD3, Susceptibility
dx.doi.org/10.1016/j.joca.2014.02.931, hdl.handle.net/1765/62101
Osteoarthritis and Cartilage
This work was funded by the European Commission 7th Framework Programme; grant id fp7/305815 - Novel Diagnostics and Biomarkers for Early Identification of Chronic Inflammatory Joint Diseases (D-BOARD)
Department of Clinical Genetics

Raine, K., Reynard, L.N, van de Laar, I.M.B.H, Bertoli Avella, A.M, & Loughlin, J. (2014). Identification and analysis of a SMAD3 cis-acting eQTL operating in primary osteoarthritis and in the aneurysms and osteoarthritis syndrome. Osteoarthritis and Cartilage, 22(5), 698–705. doi:10.1016/j.joca.2014.02.931