STR/ort Mice, a Model for Spontaneous Osteoarthritis, Exhibit Elevated Levels of Both Local and Systemic Inflammatory Markers

Osteoarthritis is a common joint disease that currently lacks disease-modifying treatments. Development of therapeutic agents for osteoarthritis requires better understanding of the disease and cost-effective in vivo models that mimic the human disease. Here, we analyzed the joints of STR/ort mice, a model for spontaneous osteoarthritis, for levels of inflammatory and oxidative stress markers and measured serum cytokines to characterize the local and systemic inflammatory status of these mice. Markers of low-grade inflammatory and oxidative stress—RAGE, AGE, S100A4, and HMGB1—were evaluated through immunohistochemistry. Of these, AGE and HMGB1 levels were elevated strongly in hyperplastic synovium, cartilage, meniscus, and ligaments in the joints of STR/ort mice compared with CBA mice, an osteoarthritis-resistant mouse strain. These increases (particularly in the synovium, meniscus, and ligaments) correlated with increased histopathologic changes in the cartilage. Serum analysis showed higher concentrations of several cytokines including IL1β, IL12p70, MIP1β, and IL5 in STR/ort mice, and these changes correlated with worsened joint morphology. These results indicate that STR/ort mice exhibited local and systemic proinflammatory conditions, both of which are present in human osteoarthritis. Therefore, the STR/ort mouse model appears to be a clinically relevant and cost-effective small animal model for testing osteoarthritis therapeutics.