Osteoarthritis (OA) is a debilitating disease of joints that afflicts horses of all ages and breeds and can result in lameness, suboptimal performance, and decreased quality of life. The pro-inflammatory cytokine interleukin-1 (IL-1) has been associated with the initiation and pathogenesis of joint disease. In part, this occurs by induction of proteases and oxidative pathways that contribute to the degradation of structural components of the articular cartilage extracellular matrix. Elucidating the complex macromolecular and molecular effects of IL-1 on articular tissues may further our understanding of the roles of IL-1 and inflammation in OA pathobiology. Full-length gene sequences encoding three recombinant equine interleukin-1 proteins (EqIL-1a, EqIL-1b, and EqIL-1 receptor antagonist), were previously cloned and expressed in-vitro. The objectives of this dissertation were to 1) establish EqIL-1 induced experimental models of equine OA, and 2) to investigate specific IL-1-induced immuno-inflammatory responses.

Effects of EqIL-1 on articular cartilage explant proteoglycan metabolism and synthesis of a downstream inflammatory product, prostaglandin E2, established culturing conditions and furthered the rationale to use EqIL-1 in the in-vitro modeling of early joint disease. A customized cDNA array was used to profile changes in mRNA levels resulting from EqIL-1 treatments of cultured articular cartilage chondrocytes. EqIL-1a induced elevated mRNA levels corresponding to six genes after 1 hour relative to media control chondrocytes (p<0.05). EqIL-1b increased transcript levels of seven genes after 6 hours (p<0.0004); 102 additional transcripts were elevated > 2-fold over controls. A subset of the array-generated data was verified using optimized reverse transcriptase-PCR amplification. Results of principal component analysis indicate co-regulation of EqIL-1 induced transcript levels to relate to chondrocyte differentiation and cell-cycle processes. Subtractive hybridization-PCR identified 148 differentially expressed cDNAs in synovium resulting from a 6-hour intra-articular EqIL-1b injection.

Combined results demonstrate the potent bioactivity of our equine IL-1 proteins and support the argument for crucial roles of IL-1 in pro-inflammatory processes and cytokine imbalances underlying early OA pathogenesis. These results add to the current knowledge of IL-1 modulated transcription that may precede ECM catabolic processes characteristic of OA. The culture systems, assays, and techniques for gene expression analysis may be useful for future studies attempting to elucidate macromolecular and transcriptional events underlying inflammatory-associated joint disease processes in horses. Reported information may further efforts toward improved diagnostic and preventive strategies and development of anti-IL-1 directed therapies.