Synovial lining macrophages mediate osteophyte formation during experimental osteoarthritis

Collagenolytic protease expression in cranial cruciate ligament and stifle synovial fluid in dogs with cranial cruciate ligament rupture

OBJECTIVE

To determine expression of collagenolytic genes and collagen degradation in stifle tissues of dogs with ruptured cranial cruciate ligament (CCL).

ANIMALS

Six dogs with CCL rupture and 11 dogs with intact CCL.

PROCEDURES

Gene expression in CCL tissue and synovial fluid cells was studied using reverse transcriptase-polymerase chain reaction (RT-PCR). Collagen degradation was studied using CCL explant cultures and a synovial fluid bioassay.

RESULTS

Expression of matrix metalloproteases (MMP) was not found in young Beagles with intact CCL; however, increased expression of MMP-3 was found in CCL tissue from older hounds with intact CCL, when compared with young Beagles. In dogs with ruptured CCL, expression of MMP-2 and -9 was increased in stifle tissues, when compared with dogs with intact CCL. Similar to MMP-9, expression of tartrate-resistant acid phosphatase (TRAP) and cathepsin S was only found in stifle tissues from dogs with ruptured CCL; in contrast, expression of cathepsin K was found in all ruptured and intact CCL. Collagen degradation was increased in ruptured CCL, when compared with intact CCL.

CONCLUSION

Rupture of the CCL is associated with up-regulation of expression of MMP-2 and -9 (gelatinase A and B), TRAP, and cathepsin S, and increased degradation of collagen.

CLINICAL RELEVANCE

These findings suggest that MMP-2, -9, cathepsin S, and TRAP may be important mediators of progressive joint destruction in dogs with CCL rupture. These genes are markers for macrophages and dendritic cells. MMP and cathepsin S pathways may offer novel targets for anti-inflammatory medical therapy aimed at ameliorating joint degradation associated with inflammatory arthritis.

Bone Morphogenetic Protein signaling in joint homeostasis and disease

Despite advances in therapies that target inflammation and tissue destruction in chronic arthritis, stimulation of tissue repair and restoration of joint function, the ultimate goal of treatment, is far from achieved. We introduce a new paradigm that may help to improve our understanding and management of chronic arthritis. The presence or absence of tissue responses distinguishes destructive arthritis, steady-state arthritis and remodeling arthritis. Increasing evidence suggests that reactivation of embryonic molecular pathways is an important mechanism to stimulate postnatal tissue repair. Bone Morphogenetic Proteins (BMPs) have critical roles in skeletal development and joint morphogenesis, but also in postnatal joint homeostasis and joint tissue remodeling. Therefore, modulation of BMP signaling may be an attractive therapeutic target in chronic arthritis to restore homeostasis and function of synovial joints.

Localization of Cathepsin K and Tartrate-Resistant Acid Phosphatase in Synovium and Cranial Cruciate Ligament in Dogs with Cruciate Disease

OBJECTIVE

To localize cathepsin K and tartrate-resistant acid phosphatase (TRAP) in synovium and cranial cruciate ligament (CCL) of dogs with cruciate disease.

ANIMALS

Dogs (n=15) with cruciate disease and ruptured CCL, and 12 dogs with intact CCL.

METHODS

Synovium and CCL were examined histologically and cells containing cathepsin K or TRAP were identified immunohistochemically and histochemically, respectively.

RESULTS

Increased cellular localization of cathepsin K and TRAP was detected in synovium and ruptured CCL in dogs with cruciate disease, when compared with tissues from dogs with intact CCL. Inflammation of synovium with TRAP+ macrophage-like cells was seen in 73% of dogs with CCL disease, but was not seen in dogs with intact CCL. The presence of cathepsin K and TRAP protein in synovium and CCL tissues was significantly correlated in dogs with CCL rupture.

CONCLUSION

Inflammation of the epiligament of ruptured CCL with cathepsin K+ and TRAP+ macrophage-like cells forms part of a similar, more generalized chronic inflammatory change within the periarticular tissues of the stifle of a large proportion of dogs with CCL rupture.

CLINICAL RELEVANCE

Production of matrix-degrading enzymes by the synovium may induce progressive pathologic rupture of the CCL. Therefore, these collagenolytic pathways may offer a novel target for medical therapy of joint inflammation in canine patients with cruciate disease.