Increased susceptibility of osteoarthritis tenocytes to FasL-induced apoptosis is associated with elevated expression of Fas receptor but no alterations in the expression of Sentrin-1/SUMO-1
© The Author(s) 2003
Received: 14 January 2003
Published: 24 February 2003
Background and objective
Alterations in periarticular tendons have been described in osteoarthritis (OA), but the specific properties of OA tenocytes and particularly the regulation of apoptosis in these cells remain poorly understood. Therefore, we analyzed the expression of Fas and sentrin-1/SUMO-1, a small ubiquitin-like modulator of Fas signaling, in tenocytes of patients with knee OA and studied the susceptibility of these cells to FasL-induced apoptosis.
Tenocyte cultures were established from tendon specimens of the quadriceps femoris muscle of OA patients and characterized by FACS analysis with antibodies against fibroblast markers (AS02, 5B5) and monocyte markers (CD45, CD68). Expression levels of Fas and sentrin-1/SUMO-1 were determined by quantitative real-time PCR (TaqMan, Applied Biosystems). Levels of soluble Fas (sFas), and soluble TNF receptor I (sTNFRI) were measured by ELISA. To induce apoptosis, tenocytes were stimulated with 100 ng/ml rhFasL for 16 hours. Apoptosis was determined through the detection of cytoplas-matic mononucleosomes and oligonucleosomes (Cell Death ELISA, Roche). The effects of TNF-α were studied by stimulation with 1, 10 or 100 ng/ml TNF-α alone or 24 hours prior to the induction of apoptosis. Tenocytes from non-OA patients were used as controls.
FACS analysis confirmed the fibroblast-like nature of tenocytes and excluded the presence of monocyte-derived cells in the cultures. Quantitative PCR showed significantly higher levels of Fas mRNA in OA tenocytes in comparison with healthy controls. As demonstrated by ELISA, tenocytes from OA patients produced lower levels of apoptosis-inhibiting sFas. No differences were seen in the expression of sentrin-1/SUMO-1 and sTNFRI. After stimulation with rhFasL, tenocytes from OA patients exhibited higher rates of apoptosis than control cells. TNF-α prevented FasL-induced apoptosis in OA tenocytes but had no effects in normal tenocytes.
The data suggest an association between knee OA and higher susceptibility of periarticular tenocytes to FasL-induced apoptosis. Increased expression of Fas receptor and lower levels of sFas may provide the basis for these alterations that in turn may promote the rupture of tendons. The antiapoptotic effects of TNF-α in OA tenocytes but not in normal cells most likely reflect regenerative attempts. They should be considered when anti-TNF-α strategies are discussed for the treatment of OA.