Molecular monitoring of equine joint homeostasis

Diseases affecting synovial joints are a major cause of chronic disability both in humans and in companion animal species, most notably dogs and horses. As progressive deterioration of the articular cartilage is the hallmark of degenerative joint disease or osteoarthritis, research efforts traditionally tended to focus primarily on cartilage pathology. However, in recent years it has become clear that synovial joints should be considered intricate organs in their own right, with each of the constituent tissues (cartilage, bone, and synovial membrane) interacting with each other both in health and disease. Moreover, with the advent of modern molecular biology techniques, the importance of synovial inflammation in disease development and progression has become increasingly recognized. These realizations have spurred the need for tools that allow a more comprehensive, integral study of synovial joint homeostasis. This review provides a brief overview of synovial joint biology and the concept of joint homeostasis, followed by a discussion of methods that may be used to study joint homeostasis (varying from in vitro tissue culture to in vivo imaging) including specific advantages and limitations of each approach. It then zooms in on one such approach, synovial fluid biomarker analysis, as a promising avenue in synovial joint research, highlighting some results from equine studies performed in the author's own laboratory that illustrate how such studies may help shed light on in vivo joint homeostasis and therapeutic modulation thereof. The review concludes with some future perspectives and promising developments in the field.