Abstract
Osteoarthritis (OA) is a whole joint disease characterized by an important remodeling of the osteochondral junction. It includes cartilage mineralization due to chondrocyte hypertrophic differentiation and bone sclerosis. Here, we investigated whether gremlin-1 (Grem-1) and its BMP partners could be involved in the remodeling events of the osteochondral junction in OA. We found that Grem-1, BMP-2, and BMP-4 immunostaining was detected in chondrocytes from the deep layer of cartilage and in subchondral bone of knee OA patients, and was positively correlated with cartilage damage. ELISA assays showed that bone released more Grem-1 and BMP-4 than cartilage, which released more BMP-2. In vitro experiments evidenced that compression stimulated the expression and the release of Grem-1 and BMP-4 by osteoblasts. Grem-1 was also overexpressed during the prehypertrophic to hypertrophic differentiation of murine articular chondrocytes. Recombinant Grem-1 stimulated Mmp-3 and Mmp-13 expression in murine chondrocytes and osteoblasts, whereas recombinant BMP-4 stimulated the expression of genes associated with angiogenesis (Angptl4 and osteoclastogenesis (Rankl and Ccl2). In conclusion, Grem-1 and BMP-4, whose expression at the osteochondral junction increased with OA progression, may favor the pathological remodeling of the osteochondral junction by inducing a catabolic and tissue remodeling program in hypertrophic chondrocytes and osteoblasts.
Highlights
Osteoarthritis (OA) is the most common musculoskeletal degenerative disease and a major cause of pain and disability in the elderly [1,2,3,4]
Our results suggest that Grem-1 and bone morphogenetic protein (BMP)-4 may act as partners in the remodeling events occurring at the osteochondral junction in OA
We previously showed in a model of progressive hypertrophic differentiation of murine articular chondrocytes that the prehypertrophic to hypertrophic differentiation was associated with an overexpression of both Bmp-2 and Bmp-4 Mrna [42]
Summary
Osteoarthritis (OA) is the most common musculoskeletal degenerative disease and a major cause of pain and disability in the elderly [1,2,3,4]. The remodeling of the osteochondral junction is thought to play a determinant role in OA and is reminiscent of the endochondral ossification process It involves the hypertrophic differentiation of chondrocytes of the deepest layer of the hyaline articular cartilage followed by the mineralization and the vascularization of the cartilage matrix and the replacement of cartilage by bone, leading to sclerosis of the subchondral bone plate [8,9,10]. Compression was proposed to be responsible for the phenotypic changes of osteoblasts in OA subchondral bone leading to sclerosis of the subchondral bone plate [22] In this context, Gremlin-1 (Grem-1) has been identified as a mechanosensitive factor, whose expression is increased in articular cartilage under a tensile mechanical loading or joint injury [25,26,27,28]. Our results suggest that Grem-1 and BMP-4 may act as partners in the remodeling events occurring at the osteochondral junction in OA
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