Proteomic analysis of human articular cartilage: Identification of differentially expressed proteins in knee osteoarthritis

Abstract Objectives The mechanisms underlying the development of age related osteoarthritis (OA) remain unclear. To better understand the pathogenesis of OA and the molecular basis of progressive destruction of articular cartilage in OA, we compared the proteome of OA cartilage with that of normal cartilage. Methods After removal of proteoglycans and collagens, proteins extracted from either normal or OA knee joint cartilage were separated by two-dimensional gel electrophoresis (2-DE). The differentially expressed proteins in OA cartilage were chosen to be further identified by linear ion trap-Fourier transform ion cyclotron resonance mass spectrometry (LTQ-FT/MS). Results A total of 1436 ± 49 or 1472 ± 7 protein spots were resolved by 2-DE of normal or OA cartilage extractions, respectively. Sixteen spots from OA cartilage samples were found to have statistically significant changes in the amount of protein compared with normal samples. Of 16 spots, the identities of 14 proteins were unambiguously determined by LTQ-FT/MS. These OA associated proteins fell into five groups, including glycolysis and energy production (ADH, ADK, ENOA, KPYM and FR), signaling (ANNX-I, PEBP and TUB), Redox (PRDX3 and SODM), and cartilage matrix (COLL-I and COLL-VI). Interestingly, two novel RING (Really Interesting New Gene) domain-containing proteins, RF, Zn-RF, were identified, suggesting novel pathways of cartilage protein regulation. Conclusions This study shows that 2-DE followed by LTQ-FT/MS can be successfully used to characterize the proteome of cartilage without in vitro culturing which could obfuscate physiological differences. The definition of unique OA-associated proteins described here provides significant mechanistic insights into OA by corroborating previously suggested mechanisms and by defining unique players with roles yet to be defined in disease pathogenesis.