Human cartilage glycoprotein 39 (HC gp-39) mRNA expression in adult and fetal chondrocytes, osteoblasts and osteocytes by in-situ hybridization

Objective: To examine the expression pattern of human cartilage glycoprotei n 39 (HC gp-39) mRNA in human cartilage and bone. Design: In-situ hybridization analysis was used to examine the expression p attern of human cartilage glycoprotein 39 (HC gp-39) mRNA in adult human os teoarthritic articular cartilage from various stages of disease, as well as in human osteophytic tissue and in human fetal bone. Results: In cartilage from patients with mild osteoarthritic cartilage dege neration, HG gp-39 was expressed at moderate to high levels only in chondro cytes of the superficial zone. In advanced OA cartilage, cloning chondrocyt es of the superficial zone expressed high levels of HC gp-39 and chondrocyt es of the mid- and deep zones were also positive. HC gp-39 was undetectable in the chondrocytes of normal articular cartilage. In osteophytic tissue, the expression of HC gp-39 mRNA was intense in flattened, end-stage osteobl asts and in primary osteocytes in both endochondral and intramembranous bon e formation. Proliferating osteoblasts expressed low to moderate levels. No tably, mature osteocytes were negative for HC gp-39 expression. Chondrocyte s in the secondary ossification center of developing fetal cartilage demons trated high expression while growth plate and mineralized cartilage chondro cytes had lower expression. Osteoblasts at sites of endochondral and intram embranous bone formation were positive for expression of HC gp-39. Conclusions: The stage-specific expression of HC gp-39 in fetal development and adult remodelling bone and cartilage provides evidence for a specific functional or structural role for HC gp-39 in bone and cartilage tissue. HC gp-39 is expressed in diseased human osteoarthritic cartilage and osteophy te, but not in non-diseased tissue, and its distribution within the tissue changes as disease progresses. OA is characterized not only by cartilage de generation, but by increased subchondral bone formation and osteophytosis. The results from this study indicate that the increased HC gp-39 expression in OA serum and synovial fluid may reflect not only cartilage degeneration but increased osteogenesis. (C) 2000 OsteoArthritis Research Society Inter national.