The fibrinolytic pattern of rheumatoid synoviocytes is invasive like neoplastic cells
© The Author(s) 2003
Published: 12 September 2003
In rheumatoid arthritis (RA), the synovial membrane proliferates and invades the underlying tissues. The fibrinolytic cascade is involved both in the genesis and maintenance of synovial inflammation, and is pivotal in cell invasion and proliferation.
To evaluate the fibrinolytic pattern and the proliferative potential of urokinase-plasminogen activator (u-PA) on RA synoviocytes (SY), in order to establish the role of each component of the fibrinolytic cascade in the genesis and progression of the RA synovitis.
Materials and methods
The levels of plasminogen activators and inhibitors, and the u-PA-dependent proliferation were studied in vitro on SY from four controls and four RA patients undergoing joint surgery. SY monolayers were used within the seventh passage in culture: u-PA and plasminogen activator inhibitor-1 (PAI-1) were assayed on supernatants, and urokinase-plasminogen activator receptor (u-PAR) was determined on cell lysates. Levels of u-PA, u-PAR and PAI-1 were assayed by specific ELISA and by RT-PCR of mRNAs. To evaluate the SY proliferative potential, cells were seeded on to multiwell plates with RPMI 1640 supplemented with 10% FCS and were incubated for 48 hours. The FCS concentration was then reduced to 0.1% for an additional 48 hours. SY were then treated with 500 ng/ml u-PA and/or antibodies to anti u-PA (5B4) and anti-u-PAR (R3) for 48 hours, and were counted. Cell invasion was measured with the Boyden chamber.
RA SY showed significantly higher levels of PAI-1 (6.3 μg/million cells ± 1.1 standard deviation [SD] versus 2.9 μg/million cells ± 0.7 SD for controls, P = 0.01), lower levels of u-PA (2.6 ng/million cells ± 1.4 SD versus 10.9 ng/million cells ± 2.1 SD for controls, P = 0.01), and higher u-PAR on their surface (28.5 ng/million cells ± 4.8 SD versus 13 ng/million cells ± 3.0 SD for controls, P < 0.05). Treatment of RA SY with u-PA provided a proliferative effect similar to 10% FCS (P < 0.05), blocked by 5B4 and R3, and different in RA patients with respect to controls (P < 0.05). RA SY are more prone than controls to spontaneous and u-PA-challenged invasion and proliferation, which are counteracted by antagonists of the fibrinolytic system.
RA SY present the typical fibrinolytic pattern of the invasive tumor-like cells. RA SY proliferation is stimulated by u-PA. The fibrinolytic system thus provides the extracellular proteolysis required for the synovial invasion of articular tissues and for the first steps of synovitis. Antagonists of the fibrinolytic system may revert growth and invasion of RA SY. The components of this system may be a future target for new RA therapies.