Xylosyltransferase-I Regulates Glycosaminoglycan Synthesis during the Pathogenic Process of Human Osteoarthritis Narayanan Venkatesan, Lydia Barre´ , Mustapha Bourhim, Jacques Magdalou, Didier Mainard, Patrick Netter, Sylvie Fournel-Gigleux, Mohamed Ouzzine* UMR 7561 CNRS-Universite´ Nancy 1, Faculte´ de Me´decine, Vandœuvre-le`s-Nancy, France Abstract Loss of glycosaminoglycan (GAG) chains of proteoglycans (PGs) is an early event of osteoarthritis (OA) resulting in cartilage degradation that has been previously demonstrated in both huma and experimental OA models. However, the mechanism of GAG loss and the role of xylosyltransferase-I (XT-I) that initiates GAG biosynthesis onto PG molecules in the pathogenic process of human OA are unknown. In this study, we have characterized XT-I expression and activity together with GAG synthesis in human OA cartilage obtained from different regions of the same joint, defined as ‘‘normal’’, ‘‘late-stage’’ or adjacent to ‘‘late-stage’’. The results showed that GAG synthesis and content increased in cartilage from areas flanking OA lesions compared to cartilage from macroscopically ‘‘normal’’ unaffected regions, while decreased in ‘‘late-stage’’ OA cartilage lesions. This increase in anabolic state was associated with a marked upregulation of XT-I expression and activity in cartilage ‘‘next to lesion’’ while a decrease in the ‘‘late-stage’’ OA cartilage. Importantly, XT-I inhibition by shRNA or forced- expression with a pCMV-XT-I construct correlated with the modulation of GAG anabolism in human cartilage explants. The observation that XT-I gene expression was down-regulated by IL-1b and up-regulated by TGF-b1 indicates that these cytokines may play a role in regulating GAG content in human OA. Noteworthy, expression of IL-1b receptor (IL-1R1) was down-regulated whereas that of TGF-b1 was up-regulated in early OA cartilage. Theses observations may account for upregulation of XT-I and sustained GAG synthesis prior to the development of cartilage lesions during the pathogenic process of OA. Citation: Venkatesan N, Barre´ L, Bourhim M, Magdalou J, Mainard D, et al. (2012) Xylosyltransferase-I Regulates Glycosaminoglycan Synthesis during the Pathogenic Process of Human Osteoarthritis. PLoS ONE 7(3): e34020. doi:10.1371/journal.pone.0034020 Editor: Joy Marilyn Burchell, King’s College London, United Kingdom Received November 28, 2011; Accepted February 20, 2012; Published March 30, 2012 Copyright: 2012 Venkatesan et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Fondation pour la Recherche Me´dicale (DVO20081013491, Vieillissement Oste´oarticulaire) and the Agence Nationale de la Recherche (ANR-BLAN-0163- 01, GlycoCart). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: ouzzine@medecine.uhp-nancy.fr Introduction Osteoarthritis (OA) is a chronic, progressive, degenerative disorder of joint characterized by breakdown of articular cartilage leading to functional failure of the joint. OA is characterized by progressive loss of extracellular matrix (ECM) proteins, causing mechanical disruption of the articular cartilage surface, together with subchondral bone sclerosis and osteophyte formation [1]. One of the earliest changes in OA development is the loss of matrix proteoglycans (PGs) [2], and studies have monitored loss of aggrecan, the predominant cartilage PG, which provides cartilage the characteristic mechanical properties of compressibility and resilience [3]. Evidence from studies in vitro and in vivo indicates that interleukin-1b (IL-1b) and tumor necrosis factor-a (TNF-a) are the predominant cytokines involved in the initiation and progression of articular cartilage destruction [4,5]. IL-1b, besides its catabolic activity, inhibits PG synthesis in cartilage, a process observed in early stages of OA [4–6]. Notably, loss of PG anabolism not only participates in alteration of the mechanical properties of cartilage but may also impair the chondrocyte metabolism and ability to repair the damage. Indeed, PGs control diverse cellular and biological activities, including cell prolifera- tion, migration and differentiation. Numerous studies suggest that most of the biological activity of PGs is mediated by their glycosaminoglycan (GAG) chains. In this context, GAG chains play important roles in growth factor signaling, cellular differen- tiation, morphogenesis, and pathophysiology [7,8]. Therefore, alteration in the capacity of OA chondrocytes to restore the integrity of the cartilage matrix may be due to dysfunction of the regulatory pathway leading to formation of glycosaminoglycan chains. In contrast to catabolism of OA cartilage, the synthesis side of OA has not received much attention. This is important because the repair potential of cartilage is gaining more attention as target for OA treatment. The initial event in response to injury by chondrocytes is an attempt to repair the damaged matrix by up- regulation of matrix synthesis including PGs. Proteomics studies have demonstrated elevated anabolism in OA cartilage associated with enhanced gene expression and biosynthesis of COL2A1 [9]. However, studies in animal models [10] and analysis of cartilage samples from OA patients [11,12] indicated that this differential expression may depend upon the zone of cartilage analyzed in conjunction with the stage of OA progression. In a previous study [13] we showed that during the early phases of cartilage repair, PLoS ONE | www.plosone.org 1 March 2012 | Volume 7 | Issue 3 | e34020