Pathological findings and immunohistochemical evaluation of MMP-2 and TIMPs in equine fetlock affected by degenerative joint disease

Background: MMP-2 and MMP-9 are proteolytic enzymes involved in the remodeling of extracellular matrix and regulated in their function by a family of proteins called TIMPs. MMP-2 and MMP-9 and TIMPs are secreted in joints by both synovial cells and chondrocytes, and are implicated in osteoarthritis onset and progression. The aim of this study was to investigate the localization of MMP-2 and TIMPs expression and their relationship in the synovial membrane of equine fetlock (metacarpo-phalangeal joint), which is the joint most frequently affected by osteoarthritis due to his high weight-bearing impact and shearing forces. Method: This study analyzed the immunohistochemical expression of MMP-2 and tissue inhibitors of MMP (TIMPs) in synovial membrane sections from 40 equine metacarpo-phalangeal joints affected by osteoarthritis in order to better assess their role in the pathogenesis of joint-structure alterations. Immunohistochemical study was performed using the Avidin-Biotin-Peroxidase complex method, and the percentage of labeled cells was assessed semi-quantitatively. Data obtained were statistically revised through the Spearman's rank correlation coefficient. Results: MMP-2 and TIMPs were expressed by type-B synoviocytes and endothelial cells. MMP-2 expression was not significantly associated to the macroscopic findings while a linear correlation between MMP-2 and TIMPs expression was observed. Conclusion: These data suggest that in degenerative joint disease the synovial expression of TIMPs may contribute to the regulation of MMP-2 expression in order to reach a new dynamic balance and that MMP-2 plays an important pro-homeostatic role in physiological and pathological equine synovial membrane