Low-intensity pulsed ultrasound promotes aggrecan expression via ZNT-9 in temporomandibular joint chondrocytes.

Temporomandibular joint osteoarthritis (TMJ-OA) is one of the most common joint diseases. It causes severe pain and poor quality of life. One key feature of TMJ-OA is degeneration of the chondrocyte extracellular matrix (ECM). Low-intensity pulsed ultrasound (LIPUS) can promote the synthesis of ECM in cartilage. However, the exact mechanism is still unclear. We aimed to explore the mechanism by which LIPUS promotes the expression of aggrecan in chondrocytes. In vivo, TMJ-OA rats established by unilateral occlusal trauma were treated with LIPUS. In our RNA sequencing data, we found that ADAMTS-8 was downregulated by LIPUS. In vitro, chondrocytes were treated with IL-1β and LIPUS. Among Zn exporters, ZNT-9 was specifically upregulated by LIPUS. Activation of ZNT-9 by LIPUS downregulated ECM-degrading enzymes (MMP-3, ADAMTS-5 and ADAMTS-8) and metal regulatory transcription factor-1 (MTF-1) and upregulated aggrecan in chondrocytes. Furthermore, ZNT-9 knockdown caused upregulation of MMP-3, ADAMTS-5, ADAMTS-8 and MTF-1, with concomitant downregulation of aggrecan. The opposite results were obtained after ZNT-9 overexpression. Our experiments demonstrate that LIPUS protects chondrocytes by increasing the expression of aggrecan through ZNT-9.