ARTHRITIS & RHEUMATISM Vol. 58, No. 2, February 2008, pp 442–455 DOI 10.1002/art.23159 © 2008, American College of Rheumatology Phenotypic Characterization of Osteoblasts From the Sclerotic Zones of Osteoarthritic Subchondral Bone Christelle Sanchez, 1 Michelle A. Deberg, 1 Akeila Bellahcne `e, 1 Vincent Castronovo, 1 Philippe Msika, 2 J. P. Delcour, 3 J. M. Crielaard, 1 and Yves E. Henrotin 1 Objective. To determine the phenotype of osteo- blasts from the sclerotic zones of human osteoarthritic (OA) subchondral bone. Methods. Human osteoblasts were isolated from sclerotic or nonsclerotic areas of subchondral bone and cultured for 14 days in monolayer. The expression of 14 genes was investigated by real-time reverse transcription– polymerase chain reaction. The activities of alkaline phosphatase (AP) and transglutaminases (TGases) were quantified by enzymatic assays. C-terminal type I procollagen propeptide (CPI), interleukin-1 (IL-1), IL-6, IL-8, transforming growth factor 1 (TGF1), osteocalcin (OC), and osteopontin (OPN) were assayed in the culture medium by immunoassay. Results. Gene expression levels of matrix metal- loproteinase 13, COL1A1 and COL1A2, OPN, tissue- nonspecific AP, OC, vascular endothelial growth factor, ANKH, TGase 2, factor XIIIA, and dentin matrix pro- tein 1 were significantly up-regulated in sclerotic osteo- blasts compared with nonsclerotic osteoblasts. In con- trast, parathyroid hormone receptor gene expression was depressed in sclerotic osteoblasts, but bone sialo- protein levels were unchanged. The activities of AP and TGases were increased in sclerotic osteoblasts, while matrix mineralization, revealed by alizarin red staining, was decreased. In parallel, protein synthesis of CPI, OC, OPN, IL-6, IL-8, and TGF1 was significantly higher in sclerotic osteoblasts than in nonsclerotic osteoblasts, while IL-1 production was similar in both groups. Conclusion. These findings contribute to a better understanding of the mechanisms involved in subchon- dral bone sclerosis and identify osteoblasts with an altered phenotype as a potential target for future OA therapies. Osteoarthritis (OA) is a common leading cause of disability in the elderly that is characterized by cartilage degradation, synovium and tendon inflamma- tion, muscle weakness, osteophyte formation, and sub- chondral bone plate thickening (1). Although it is not yet clear whether it precedes (2–4) or occurs subsequently to cartilage damage (5–7), subchondral bone remodeling is an important feature in the pathophysiology of OA and is characterized by osteoid substance accumulation, decreased mineralization, and increased amounts of type I homotrimer (8). It is speculated that subchondral bone remodeling is linked to cartilage degradation, not only by modifying the mechanical properties of the subchondral bone (9) but also by releasing factors that may influence cartilage metabolism (10,11). Thus, the understanding of the mechanisms leading to bone scle- rosis is of the utmost importance in the treatment of OA. Indeed, previous studies have demonstrated that some osteoblasts are phenotypically different and may produce increased levels of alkaline phosphatase (AP), osteocalcin (OC), transforming growth factor 1 (TGF1), insulin-like growth factor 1 (IGF-1), and urokinase plasminogen activator, while levels of IGF binding proteins 3, 4, and 5 are lower and plasminogen activator inhibitor 1 and interleukin-1 (IL-1) levels remain unchanged (12–15). Because it is a potent stim- ulator of bone matrix formation by osteoblasts, the local Supported by the Belgian National Foundation for Scientific Research, and Laboratoires Expanscience. Dr. Sanchez is a Postdoc- toral Researcher from the Belgian National Foundation for Scientific Research. Dr. Bellahce `ne is a Research Associate from the Belgian National Foundation for Scientific Research. 1 Christelle Sanchez, PhD, Michelle A. Deberg, PhD, Akeila Bellahce `ne, PhD, Vincent Castronovo, MD, PhD, J. M. Crielaard, MD, PhD, Yves E. Henrotin, PhD: University of Lie `ge, Sart-Tilman, Lie `ge, Belgium; 2 Philippe Msika, PhD: Laboratoires Expanscience, Epernon, France; 3 J. P. Delcour, MD: Centre Hospitalier du Bois de l’Abbaye, Seraing, Belgium. Address correspondence and reprint requests to Yves E. Henrotin, PhD, Bone and Cartilage Research Unit, Institute of Pathology, CHU Bat B23, B-4000 Lie `ge, Belgium. E-mail: yhenrotin@ ulg.ac.be. Submitted for publication February 16, 2007; accepted in revised form October 26, 2007. 442