Arthritis pathogenesis: Development of novel diagnostic and therapeutic approaches

Chondrocytes are the only cell type in cartilage and play a pivotal role in tissue homeostasis and cartilage remodeling in Osteoarthritis (OA). OA-dependent metabolic changes affecting extracelluar matrix composition as well as variations in the response to cytokines and growth factors have been investigated in human chondrocytes. However, the molecular mechanisms causing age-dependent variation of the chondrocyte phenotype are poorly characterized. The proinflammatory mediator nitric oxide (NO) is produced when chondrocytes are exposed to cytokines such as IL-1. NO affects the energy metabolism of cells through interfering with mitochondrial respiration and glycolysis and has been implicated in extracellular matrix synthesis and degradation and chondrocyte death. NO may contribute to the aging process by compromising the energy balance in chondrocytes through the generation of an oxidizing environment and this may in turn affect matrix gene expression. In human chondrocytes NO effects on the expression of extacelluar matrix genes or genes related to matrix structure have not been addressed comprehensively. In this study cultured chondrocytes from a single donor was either be left unstimulated (control) or stimulated with IL-1, L-NMMA or IL-1 L-NMMA for a period of 8 days in order to achieve sufficiently high levels of intracellular NO and stable expression of a subset of genes. Samples were hybridized and analyzed using the GLYCOv2 array. L-NMMA (NG-monomethyl-L-arginine) is a competitive inhibitor NO synthesis.