ATP modulates load‐inducible IL‐1β, COX 2, and MMP‐3 gene expression in human tendon cells

Abstract

Tendon cells receive mechanical signals from the load bearing matrices. The response to mechanical stimulation is crucial for tendon function. However, overloading tendon cells may deteriorate extracellular matrix integrity by activating intrinsic factors such as matrix metalloproteinases (MMPs) that trigger matrix destruction. We hypothesized that mechanical loading might induce interleukin-1beta (IL-1beta) in tendon cells, which can induce MMPs, and that extracellular ATP might inhibit the load-inducible gene expression. Human tendon cells isolated from flexor digitorum profundus tendons (FDPs) of four patients were made quiescent and treated with ATP (10 or 100 microM) for 5 min, then stretched equibiaxially (1 Hz, 3.5% elongation) for 2 h followed by an 18-h-rest period. Stretching induced IL-1beta, cyclooxygenase 2 (COX 2), and MMP-3 genes but not MMP-1. ATP reduced the load-inducible gene expression but had no effect alone. A medium change caused tendon cells to secrete ATP into the medium, as did exogenous UTP. The data demonstrate that mechanical loading induces ATP release in tendon cells and stimulates expression of IL-1beta, COX 2, and MMP-3. Load-induced endogenous IL-1beta may trigger matrix remodeling or a more destructive pathway(s) involving IL-1beta, COX 2, and MMP-3. Concomitant autocrine and paracrine release of ATP may serve as a negative feedback mechanism to limit activation of such an injurious pathway. Attenuation or failure of this negative feedback mechanism may result in the progression to tendinosis.

Mechanoregulation of gene expression in fibroblasts

“…The results suggest that mechanical load and inflammatory cytokine together can initiate matrix destruction. Similar experiments in human tendon cells with a different loading protocol (3.5% biaxial stretching at 1 Hz for 2 h) showed induction of IL-1β, COX-2, and MMP-3 genes (Tsuzaki et al, 2003a). This result suggests that load-induced IL-1β may trigger matrix remodeling/destruction via COX-2 and MMP-3 expression.…”

“…In contrast to the anabolic effects of TGF-β1 on mechanical load-induced collagen production, inflammatory cytokines such as IL-1β can significantly upregulate matrix degrading enzymes, MMPs, in the presence of mechanical loading (Archambault et al, 2002a;Tsuzaki et al, 2003a). IL-1β alone has been shown to induce mRNA expression of MMP-1, -3, and -13 in tendon cells (Archambault et al, 2002a,b;Tsuzaki et al, 2003b).…”

Expression profiling of metalloproteinases and tissue inhibitors of metalloproteinases in normal and degenerate human achilles tendon

“…Since metalloproteinase expression in tendon cells is known to be modulated by mechanical loading (31)(32)(33)(34), it is possible, given the absence of inflammation in most specimens, that at least some of the changes in gene expression described herein are induced by an altered mechanical environment. Remodeling of the tendon matrix may be induced by increased levels of strain and shear or compressive forces acting on the tissue.…”

Coordinate Regulation of IL-1β and MMP-13 in Rat Tendons Following Subrupture Fatigue Damage

“…Clinical histopathologic findings demonstrate altered expression of several collagenases in tendinopathy [16,27,32,33], while animal exercise and overuse have produced both inflammatory and degenerative changes in tendons [5,9,29,34,38]. Similarly, mechanical overloading of tendon explants [13,15] and tendon cells [2,4,8,26,36,41,45,46] in vitro led to increases in both collagenase and inflammatory mediators, in conjunction with a loss of mechanical integrity. MMP-13 (collagenase-3), which has been implicated in osteoarthritis, rheumatoid One or more of the authors (HBS, MBS, ELF) has received funding from the National Institutes of Health.…”