Understanding osteoarthritis in cats – from whole-body to molecular changes

Osteoarthritis is a chronic and painful joint disorder causing permanent joint dysfunction. Osteoarthritis is common in both mammals and humans. In fact, osteoarthritis is one of the most important musculoskeletal diseases in humans, affecting hundreds of millions of people globally and causing considerable individual suffering and socioeconomic burden to the society. Due to disability, increased comorbidities and mortality in people affected by osteoarthritis, there are calls for osteoarthritis to be designated as a serious disease. Osteoarthritis was for many years considered a disease related to “wear and tear”; however, inflammation is now recognized to be important in disease development. In people, different subtypes, such as post-traumatic, age-related and metabolic osteoarthritis are being defined. The latter, metabolic osteoarthritis, is associated with obesity and metabolic syndrome.

Osteoarthritis is also common in cats, and just like in people osteoarthritis is more common in older individuals. Although there are known predisposing factors for osteoarthritis in cats, such as trauma and inherited disease, in the majority of cases an underlying cause is not identified at the time of diagnosis. Furthermore, little is known about the actual mechanisms that are involved in disease development in cats. At the time of diagnosis joint changes are often well developed and a cure is not expected.

The joint is a complex structure being composed of several different tissues. A central feature of osteoarthritis is the loss of articular cartilage. However, changes also occur in other joint tissues, including bone, joint capsule, ligament and menisci. Osteoarthritis is therefore regarded a “whole joint organ disease”. In which order these changes develop has not been fully clarified, neither in people nor in cats. Both disturbances in the local joint milieu, related to changes within the joint tissues, as well as influences from substances circulating systemically in the blood and the body composition could potentially affect the development of the disease. Influence from systemic factors and body composition may be particularly important in metabolic osteoarthritis. Obesity is considered a low-grade inflammatory state, and substances produced in the fat tissue may negatively affect the joint. Considering high numbers of overweight and obese individuals in today´s society, further insights into associations between obesity and osteoarthritis are relevant and may increase our understanding of osteoarthritis development.

Being a pathologist I am intrigued to understand why and how osteoarthritis develops. My research in cats embraces a whole-body approach, using computed tomography (CT) as a tool to evaluate osteoarthritis in the entire cat, as well as evaluation of amounts of body fat, lean tissue and total bone mass. CT-findings are coupled to blood analyses to be able to identify substances that may be important in disease development and to find potential diagnostic biomarkers of osteoarthritis. My specialist competence lies in pattern recognition, based on gross tissue changes and light microscopic structural and cellular alterations. By defining pathologic changes in joint tissues, and by combining these with results from gene expression analyses, immunohistochemistry, CT evaluation and blood analyses, my aim is to define and explore potential subtypes of osteoarthritis in the cat. If such subtypes can be identified, tailored treatment may be constructed and cat welfare improved.

In addition, my research visions include to investigate associations between osteoarthritis and other important age-related diseases in cats, such as diabetes mellitus and chronic kidney disease. In these investigations, laboratory studies using cell cultures would be used. Further, I am interested in investigating if cats share similar features to humans in regard to associations between osteoarthritis and other disease and to evaluate the cat as a suitable animal model for human osteoarthritis.