Abstract
Osteoarthritis (OA) is characterized by progressive loss of articular cartilage accompanied by the new bone formation and, often, a synovial proliferation that culminates in pain, loss of joint function, and disability. However, the cellular and molecular mechanisms of OA progression and the relative contributions of cartilage, bone, and synovium remain unclear. We recently found that the extracellular matrix (ECM) protein periostin (Postn, or osteoblast-specific factor, OSF-2) is expressed at high levels in human OA cartilage. Multiple groups have also reported elevated expression of Postn in several rodent models of OA. We have previously reported that in vitro Postn promotes collagen and proteoglycan degradation in human chondrocytes through AKT/β-catenin signaling and downstream activation of MMP-13 and ADAMTS4 expression. Here we show that Postn induces collagen and proteoglycan degradation in cartilage by signaling through discoidin domain receptor-1 (DDR1), a receptor tyrosine kinase. The genetic deficiency or pharmacological inhibition of DDR1 in mouse chondrocytes blocks Postn-induced MMP-13 expression. These data show that Postn is signaling though DDR1 is mechanistically involved in OA pathophysiology. Specific inhibitors of DDR1 may provide therapeutic opportunities to treat OA.
Highlights
Osteoarthritis (OA) affects more than 20% of the population over age 60 and is a significant cause of disability for millions of people
To investigate whether Postn binds to discoidin domain receptor-1 (DDR1) in chondrocytes, we performed co-immunoprecipitation experiments with anti-Postn and DDR1 antibodies using primary OA chondrocytes
We examined the effect of DDR1 inhibition on Postn induction of MMP-13 expression
Summary
Osteoarthritis (OA) affects more than 20% of the population over age 60 and is a significant cause of disability for millions of people. The precise cellular mechanisms that drive OA progression are not fully understood; it is clear that events in all three compartments– cartilage, bone, and synovium–play important roles in the initiation and progression of OA. The analysis of the molecular mechanisms underlying dysregulation of cartilage homeostasis and alteration of subchondral bone in OA can provide important insights, and lead to novel strategies for disease-modifying treatments and joint repair. Periostin (Postn), a TGFβ-inducible, ECM protein, known as Osteoblast-Specific Factor 2 (OSF2), is expressed in multiple joint compartments (cartilage, subchondral bone, meniscus, ligaments, and osteophytes) [1,2,3,4,5].
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