LIPUS attenuates knee joint capsule fibrosis and athrogenic contracture through the TGF-β1/Smad signaling pathway

As one of main causes of athrogenic contracture, joint capsule fibrosis which is described as a condition with excessive deposition of collagen components and extracellular matrix (ECM) in joint capsule, is a response to long-time immobilization. The purpose of this study was to explore the effect and the underlying mechanism of low-intensity pulsed ultrasound (LIPUS) in treating knee joint capsule fibrosis. A rabbit model of knee joint capsule fibrosis induced by 6w-immobilization was employed in this study. The degree of knee joint capsule fibrosis was assessed by measurement of arthrogenic contracture and Masson-staining. Furthermore, malondialdehyde (MDA) and superoxide dismutase (SOD) were measured to assess the level of reactive oxygen species (ROS). Apart from these, the activation of TGF-{beta}1/Smad signaling pathway was determined through western blot analysis contained TGF-{beta}1, Smad2, p-Smad2, Smad3, p-Smad3 and Smad4, and immunohistochemical staining for p-Smad2/3 positive cells. After 6 wk-immobilization, the degree of arthrogenic contracture and the collagen density were increased. Moreover, the activity of MDA was upregulated and the content of SOD was downregulated. Correspondingly, the TGF-{beta}1/Smad signaling pathway was significantly activated. After 2 wk-LIPUS treatment, the degree of arthrogenic contracture and the collagen density were lower than 2 wk-remobilizaiton. Relatively, the activity of MDA was decresed and the content of SOD was increased compared with 2 wk-remobilizaiton. Importantly,the TGF-{beta}1/Smad signaling pathway was significantly inhibited compared with 2 wk-remobilizaiton. Our findings thus conclude that high level ROS and hyperactive TGF-{beta}1/Smad signaling pathway might be one of the causes of knee joint capsule fibrosis induced by immobilization and LIPUS attenuated the severity of immobilization-induced knee joint capsule fibrosis through inhibition of the production of ROS and the activation of TGF-{beta}1/Smad signaling pathway. Our findings might provide a theoretical basis for knee joint capsule fibrosis after immobilization and provide the potential therapeutic target.