Background: Osteoarthritis (OA) is a degenerative disease characterized by altered homeostasis of joint cartilage and bone, the functionality of which relies on chondrocytes and osteoblasts, that leads to the formation of a defective extracellular matrix (ECM). The ECM plays an essential role in bone biology as it provides the structure of cartilage which serves as a template for bone formation. Collagen X, main component of the ECM, has been described by our group as down-regulated in OA [1]. Our data also points to an important role of the Wnt pathway in OA [1,2]. Furthermore, Wnt proteins have been reported to inhibit chondrogenesis [3], and the Wnt pathway and its modulators have gained attention [4]. Glypicans (GPC1 to GPC6) and NOTUM, among others, have been identified as modulators of this pathway [5,6]. Notably, due to its highly specific inhibition of the Wnt pathway, NOTUM has been proposed as a therapeutic target in conditions with a high activity of the Wnt pathway is involved, such as OA [7].

Objectives: We hypothesize that modulators of the Wnt pathway are involved in the development of OA. The aim of this study is to evaluate the presence of Glypicans and NOTUM in the serum of OA patients and healthy individuals in order to determine whether significant differences exist and could clarify their likely involvement in OA.

Methods: Peripheral blood samples were obtained from OA patients during routine rheumatologist hospital visits. OA diagnosis was established according to the ACR criteria. Samples from healthy individuals were obtained from the local Blood Bank. In both cases, blood samples were centrifugated (2000g, 15 minutes, 10°C) and serum was obtained.

Quantitative ELISA assays for GPC1-6 and NOTUM were carried out using commercial kits (Human GPC1 ELISA Kit, #E-EL-H1710, Elabscience; Human GPC2 ELISA Kit, #E-EL-H1711, Elabscience; Human GPC3 ELISA Kit, #E-EL-H1712, Elabscience; Human GPC4 ELISA Kit, #E-EL-H1713, Elabscience; Human GPC5 ELISA Kit, #ELH-GPC5, RayBiotech; Human GPC6 ELISA Kit, #CSB-EL009708HU, Cusabio; Human Protein NOTUM homolog ELISA Kit, #EK3787, Sab Biotech) and measured in a plate reader (Heales MB-580,Shenzhen Heales Technology Development Co. Ltd.). Protein concentration in serum was calculated using GraphPad Prism 7 software. Differences between samples were analysed with Mann-Withney U test. Significance level set was p<0.05.

Results: Serum from 40 OA patients and 40 healthy donors were included in the study. There were no differences between groups (Table 1).

Conclusion: Our results suggest that low levels of NOTUM may contribute to the development of OA. The lack of this inhibitor promotes the activation of the Wnt pathway, high activity of which has been related with OA.

References: [1]Lamas JR et al. Ann Rheum Dis, 2010. 69(10):1880-5.

[2]Tornero-Esteban P et al. PLoS One, 2015. 10(9): p. e0137170.

[3]Day et al. Dev Cell. 2005. 8(5):739-50.

[4]Monteagudo S and Lories RJ. Nat Rev Rheumatol, 2017. 13(11): p. 670-681.

[6]Li N et al. Trends Cancer. 2018 Nov;4(11):741-754.

[7]De Robertis M et al. Oncotarget, 2015. 6(38): p. 41237-57.

[8]Nusse R. Nature, 2015. 519(7542): p. 163-4.

Disclosure of Interests: Arkaitz Mucientes: None declared, Eva Herranz: None declared, Pia Lois: None declared, Francisco J. Blanco Grant/research support from: Sanofi-Aventis, Lilly, Bristol MS, Amgen, Pfizer, Abbvie, TRB Chemedica International, Glaxo SmithKline, Archigen Biotech Limited, Novartis, Nichi-iko pharmaceutical Co, Genentech, Jannsen Research & Development, UCB Biopharma, Centrexion Theurapeutics, Celgene, Roche, Regeneron Pharmaceuticals Inc, Biohope, Corbus Pharmaceutical, Tedec Meiji Pharma, Kiniksa Pharmaceuticals, Ltd, Gilead Sciences Inc, Consultant of: Lilly, Bristol MS, Pfizer, Lydia Abasolo: None declared, Luis Rodriguez Rodriguez: None declared, José Ramón Lamas: None declared, Benjamin Fernandez: None declared