Lubricin and surfacing of articular joints

Abstract

Purpose of review: Understanding lubrication of articular cartilage, provided by synovial fluid, requires knowledge of tribology, cartilage mechanics, biochemistry, and now genetic factors. These advances have implications in the engineering of articular cartilage and in revisiting the importance of lubrication in chondroprotection as it relates to preventing osteoarthritis. Recent findings: Lubricin and superficial zone protein (SZP) share a common primary structure and are expressed by synovial fibroblasts and chondrocytes, respectively. SZP is also secreted by chondrocytes in vitro, cultured on molecular scaffolds in efforts to engineer articular cartilage. The concentration of expressed SZP is suitable to enable boundary lubrication and offers an important biophysical marker in tissue engineering efforts. Researchers have also reported that lubricin levels are diminished in patients with traumatic synovitis. These same patients show collagen type II degeneration, leading one to wonder whether lubricin/SZP is easily degraded during inflammatory events such as early osteoarthritis, thereby contributing to long-term catabolic consequences. Summary: The identification of lubricin and SZP as articular lubricants secreted by synovium and articular cartilage will herald a new venue of investigation into chondroprotection.