047 Stretching Magnitude-Dependent Inflammatory Response of Human Tendon Fibroblasts

Abstract

Previous studies have shown that cyclic mechanical stretching exerts anti-inflammatory effects on rabbit chondrocytes. But whether mechanical stretching has similar effects on human tendon fibroblasts are not known. This study therefore aimed to test the hypothesis that cyclic mechanical stretching regulates IL-1β induced COX-2 gene expression in a stretching magnitude-dependent manner. In custom-made silicone dishes, human patellar tendon fibroblasts (HPTFs) were grown on microgrooved culture surfaces, with which the shape and organization of HPTFs in vivo were closely mimicked. To induce inflammatory responses in HPTFs, 10 pM of IL-1β was added to the culture medium. A 4% or 8% cyclic uniaxial stretching was then applied to silicone dishes for 4 hrs using a custom-design stretching apparatus. After the end of stretching, total RNA of stretched and nonstretched tendon fibroblasts was collected, and RT-PCR was performed for measuring COX-2 mRNA expression levels. We found that tendon fibroblasts subjected to 4% stretching decreased COX-2 mRNA expression level by 20%(p = 0.0002; n = 6) compared to that of nonstretched, IL-1β-treated cells. However, cells subjected to 8% stretching showed a 39% increase (p = 0.007, n = 6) in COX-2 mRNA expression. Thus, the results of this study suggest that small stretching (4%) has anti-inflammatory effects on HPTFs in a mildly inflammatory environment such as that induced by 10 pM of IL-1β. In contrast, large stretching (8%) may amplify inflammatory responses of tendon fibroblasts. Therefore, physical therapy with low levels of tendon stretching may be beneficial in reducing mild tendon inflammation. Supported by the Arthritis Investigator Award and NIHAR049921 (JHW)