Comparison of mouse and human ankles and establishment of mouse ankle osteoarthritis models by surgically-induced instability

OBJECTIVE

Prevalence of ankle osteoarthritis (OA) is lower than that of knee OA, however, the molecular mechanisms underlying the difference remain unrevealed. In the present study, we developed mouse ankle OA models for use as tools to investigate pathophysiology of ankle OA and molecular characteristics of ankle cartilage.

DESIGN

We anatomically and histologically examined ankle and knee joints of C57BL/6 mice, and compared them with human samples. We examined joints of 8-week-old and 25-month-old mice. For experimental models, we developed three different ankle OA models: a medial model, a lateral model, and a bilateral model, by resection of respective structures. OA severity was evaluated 8 weeks after the surgery by safranin O staining, and cartilage degradation in the medial model was sequentially examined.

RESULTS

Anatomical and histological features of human and mouse ankle joints were comparable. Additionally, the mouse ankle joint was more resistant to cartilage degeneration with aging than the mouse knee joint. In the medial model, the tibiotalar joint was markedly affected while the subtalar joint was less degenerated. In the lateral model, the subtalar joint was mainly affected while the tibiotalar joint was less altered. In the bilateral model, both joints were markedly degenerated. In the time course of the medial model, TdT-mediated dUTP nick end labeling (TUNEL) staining and Adamts5 expression were enhanced at early and middle stages, while Mmp13 expression was gradually increased during the OA development.

CONCLUSION

Since human and mouse ankles are comparable, the present models will contribute to ankle OA pathophysiology and general cartilage research in future.

Identification of Hic-5 as a novel regulatory factor for integrin αIIbβ3 activation and platelet aggregation in mice

BACKGROUND

Integrin αIIbβ3 plays key roles in platelet aggregation and subsequent thrombus formation. Hydrogen peroxide-inducible clone-5 (Hic-5), a member of the paxillin family, serves as a focal adhesion adaptor protein associated with αIIbβ3 at its cytoplasmic strand.

OBJECTIVES

Hic-5 function in αIIbβ3 activation and subsequent platelet aggregation remains unknown. To address this question, platelets from Hic-5(-/-) mice were analyzed.

METHODS AND RESULTS

Hic-5(-/-) mice displayed a significant hemostatic defect and resistance to thromboembolism, which were explained in part by weaker thrombin-induced aggregation in Hic-5(-/-) platelets. Mechanistically, Hic-5(-/-) platelets showed limited activation of αIIbβ3 upon thrombin treatment. Morphological alteration in Hic-5(-/-) platelets after thrombin stimulation on fibrinogen plates was also limited. As a direct consequence, the quantity of actin co-immunoprecipitating with the activated αIIbβ3 was smaller in Hic-5(-/-) platelets than in wild-type platelets.

CONCLUSION

We identified Hic-5 as a novel and specific regulatory factor for thrombin-induced αIIbβ3 activation and subsequent platelet aggregation in mice.