Nerve growth factor (
NGF) is a
neurotrophin with many functions. In humans, it is involved in
inflammation, nerve growth, apoptosis and
pain signalling. Increased concentrations of
NGF in synovial fluid has been shown in humans and dogs with
osteoarthritis. Despite
osteoarthritis being a common problem in horses, no studies have previously been published on
NGF in the equine joint. The aim of this study was to quantify
NGF in equine synovial fluid from healthy joints, acutely inflamed septic joints and joints with structural changes associated with
osteoarthritis. A secondary aim was to identify the localisation of
NGF and its two receptors, TrkA and p75NTR, in healthy and osteoarthritic articular cartilage.
NGF concentrations in synovial fluid from osteoarthritic joints (n = 27), septic joints (n = 9) and healthy joints (n = 16) were determined by ELISA. In addition, articular cartilage from osteoarthritic and healthy joints was examined for
NGF, TrkA and p75NTR using immunohistochemistry staining.
NGF was present in equine synovial fluid and articular cartilage. Compared to synovial fluid from healthy joints,
NGF concentration was higher in synovial fluid from joints with structural osteoarthritic changes (P = 0.032) or acute septic
inflammation (P = 0.006). In articular cartilage with severe osteoarthritic changes, there was more abundant positive immunohistochemistry staining for
NGF and its receptors than in normal articular cartilage. Further studies should focus on identifying precursor forms of
NGF, and on receptor expression and downstream signalling of TrkA and P75NTR in health and disease.