HMGB2 is associated with pressure loading in chondrocytes of temporomandibular joint: In vitro and in vivo study

Abstract

High mobility group protein B2 (HMGB2) is an important protein attributed to tissue function and homeostasis in osteoarthritis (OA), however, its roles in the temporomandibular joint with mechanical pressure are unclear. This study investigated the expression patterns of HMGB2 in chondrocytes of TMJ on OA-related cellular and animal models. The transcriptional level and protein expression of HMGB2 as well as Col- II, MMP-13 and β-catenin were examined in primary cultured chondrocytes from TMJs with hydrostatic pressures (HP). The immunohistochemistry of HMGB2, Col- II, MMP13 and β-catenin in rabbits with surgical anterior disc displacement (ADD) were analyzed. The results indicated that HP decreased the mRNA expression of HMGB2, MMP-13, and β-catenin. HMGB2 knockdown attenuated the sensitivity of chondrocytes response to pressure loading. Immunohistochemical results showed that the rabbits with ADD exhibited thinner condylar cartilage with disordered cell arrangement. The distribution of HMGB2 was chiefly in the fibrous layer and the proliferative layer of the condylar cartilage. In rabbit cartilage with ADD, the expression of HMGB2 and β-catenin were elevated at 1 week followed by sustained decrease at 2 and 4 weeks. Our findings suggested that HMGB2 is necessary for TMJ chondrocytes to sense pressure loading, which plays an important role in the pathogenesis of chondrogenesis and TMJOA following mechanical loading.