Assessment of some tools for the characterization of the human osteoarthritic cartilage proteome

Since the proteome of osteoarthritic articular cartilage has been poorly investigated as yet, we adapted proteomic technologies to the study of the proteins secreted or released by fresh human osteoarthritic cartilage in culture. Fresh cartilage explants were obtained from three donors undergoing surgery for knee joint replacement. The explants were dissected out, minced, and incubated in serum-free culture medium. After 48 h, proteins in the medium were identified by two-dimensional or off-gel electrophoresis coupled to tandem mass spectrometry, or by using an antibody-based protein microarray designed to detect angiogenic factors, growth factors, chemokines, and cytokines. We identified a series of 43 proteins. Some of these proteins were already described as secretion products of chondrocytes, such as YKL-39 or osteoprotegerin, while several other were known proteins but have never been reported previously in cartilage, such as the serum amyloid P-component, the vitamin D binding protein, the pigment epithelium derived factor, the pulmonary and activation-regulated chemokine, lyl-1, thrombopoietin, fibrinogen, angiogenin, gelsolin, and osteoglycin/mimecan. While this study enabled the identification of novel proteins secreted or released by human osteoarthritic cartilage, the goal of the present work was essentially to describe the technical approach necessary for a systematic study of osteoarthritic cartilages from a large population of donors, in order to be able to select the good markers and/or targets for this poorly explored disease.