Objectives: To characterize the molecular events underlying cartilage injury in the early phase of mono-iodoacetate-induced osteoarthritis (OA) in rats.
Methods: Experimental osteoarthritis was induced by intra-articular injection of 0.03 mg mono-iodoacetate (MIA) in Wistar rats. Animals were killed 2, 5, 10, 15 and 20 days post-injection. Synovial tissue and standardized biopsies from different areas of knee cartilage were examined. Proteoglycan synthesis (35S incorporation) and gelatinase activities (zymography), semi-quantitative RT-PCR and immunohistochemistry for IL1β, iNOS, COX2 and PPARγ, were performed on these samples.
Results: Changes in proteoglycan synthesis and gelatinase activities were time and site-dependent. Proteoglycan synthesis inhibition was maximal by day 2 while the highest gelatinase activities were observed at day 5. Central part of patella and posterior plateaus and condyles, i.e. the weight-bearing cartilage areas, were the most affected.
IL1β and iNOS transcripts were induced early in cartilage at time of maximal proteoglycan synthesis inhibition, especially in weight-bearing areas. COX-2 was slightly up-regulated whereas PPARγ gene expression remained unchanged. Gene expression profile in synovium paralleled that of cartilage, except for PPARγ which was up-regulated at day 15 and 20.
Immunostaining for IL1β and iNOS showed that proteins were located in diseased cartilage areas at early stage of the experimental OA (day 2). At later time-points (day 20), IL1β and iNOS were expressed in perilesional areas whereas immunostaining became below control level for COX-2 and PPARγ.
Conclusions: Time-dependent degradation of cartilage after injection of low dose of MIA (0.03mg) into rat knee joint can be related to early loss of proteoglycan anabolism, increased gelatinase activities and expression of IL1β and downstream inflammatory genes. Increased susceptibility to MIA in weight-bearing areas of cartilage further indicate that MIA-induced experimental OA is a relevant model to study not only metabolical but also biomechanical aspects of human OA.
