Load Down-Regulates TNF-Alpha Induced Cartilage Degradation in Part Through NF-KB and P38 Pathways

Pro-inflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor (TNF), can induce cartilage degradation after acute injury or in inflammatory diseases [1,2,3,7]. The degradative events are coordinated through the elevation and activation of two classes of enzymes, namely matrix metalloproteinases (MMPs) and aggrecanases (ADAMTS-4 and −5) [1,6]. Prior studies suggested that pro-inflammatory responses induced by IL-1β can be inhibited by tensile load [2] and more recently by cyclic compression [8]. It is, however, not clear whether load affects other cytokines, such as TNF-α. TNF-α is known to bind its receptor (TNFR1) to cause a cascade that ends with degradation of an inhibitor, IκBα, and release of the transcription factor NF-κB [3]. The actions of TNF-α are also known to be affected by at least three NF-κB independent pathways including the p38, ERK, and JNK pathways [4]. The objective of this study was to determine whether cyclic compression could affect TNF-α induced cartilage degradation and to determine the roles of p38, ERK, and JNK pathways in TNF-induced cartilage degradation. We hypothesized that cyclic loading would inhibit the degradative effects caused by TNF-α.