Fas (CD95)-related apoptosis and rheumatoid arthritis

Pro-apoptotic effect of nonsteroidal anti-inflammatory drugs on synovial fibroblasts

Rheumatoid arthritis (RA) is a systemic inflammatory disease that mainly affects the articular synovial tissues. Although the etiology of RA has not yet been elucidated, physical and biochemical inhibition of synovial hyperplasia, which is the origin of articular destruction, may be an effective treatment for RA. Nonsteroidal anti-inflammatory drugs (NSAIDs) have long been used for the treatment of RA. The mechanism of action of NSAIDs generally involves the inhibition of cyclooxygenase (COX) at sites of inflammation. Thus, NSAIDs were not generally considered to have a so-called anti-rheumatic effect, including inhibition of progressive joint destruction and induction of remission. However, certain conventional NSAIDs and celecoxib, a selective COX-2 inhibitor, have been reported to inhibit synovial hyperplasia by inducing the apoptosis of human synovial fibroblasts. Therefore, it has been suggested that such NSAIDs may not only have an anti-inflammatory effect but also an anti-rheumatic effect. In this review, we summarize findings about the pro-apoptotic effect, in other words, anti-proliferative effect of NSAIDs on synovial fibroblasts from patients with RA.

Soluble Fas ligand inhibits angiogenesis in rheumatoid arthritis

The characteristics of rheumatoid arthritis (RA) pathology include the infiltration of inflammatory leukocytes, the proliferation of synovial cells, and the presence of extensive angiogenesis, referred to as rheumatoid pannus. Fas ligand is critical to the homeostatic regulation of the immune response, but its role in the angiogenic process of RA remains to be defined. In this study, we investigated whether soluble Fas ligand (sFasL) induces synoviocyte apoptosis and regulates angiogenesis of endothelial cells in RA. The levels of sFasL were elevated in the synovial fluids of RA patients when compared to those of osteoarthritis (OA) patients, and they correlated inversely with vascular endothelial growth factor₁₆₅ (VEGF₁₆₅) concentrations. sFasL, ranging from 10 to 100 ng/ml, induced the apoptosis of RA fibroblast-like synoviocytes (FLS) in vitro, and thereby decreased VEGF₁₆₅ production. In addition, sFasL inhibited VEGF₁₆₅-induced migration and chemotaxis of endothelial cells to basal levels in a manner independent of the Fas-mediated cell death. sFasL dose-dependently suppressed the VEGF₁₆₅-stimulated increase in pAkt expression in endothelial cells, which might be associated with its anti-migratory effect on endothelial cells. Moreover, sFasL strongly inhibited neovascularization in the Matrigel plug in vivo. Our data suggest that sFasL shows anti-angiogenic activity within RA joints not only by inducing apoptosis of VEGF₁₆₅-producing cells but also by blocking VEGF₁₆₅-induced migration of endothelial cells, independent of Fas-mediated apoptosis.

Expression of high levels of human proteinase inhibitor 9 blocks both perforin/granzyme and Fas/Fas ligand-mediated cytotoxicity

Proteinase inhibitor 9 (PI-9, SerpinB9) is the only known human intracellular granzyme B inhibitor. Whether expression of PI-9 is sufficient to block cytolysis induced by cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells remains controversial. To evaluate the roles of PI-9, we isolated and tested three lines of stably transfected HeLa cells expressing wild-type PI-9 and one line expressing an inactive mutant PI-9. Expressions of wild-type PI-9, but not the inactive mutant PI-9, inhibited cytolysis induced by human NK92 and NKL natural killer cells. Expression of high levels of PI-9 is therefore sufficient to protect human cells against NK cell-mediated cell death. Using two assays, we show that expressing wild-type PI-9, but not the inactive mutant PI-9, blocks Fas/Fas ligand (Fas/FasL)-mediated apoptosis. PI-9 expression has no effect on etoposide-induced apoptosis. HeLa cells exhibiting substantial resistance to Fas/FasL-mediated apoptosis contain 2- to 3-fold higher PI-9 levels than HCT116 human colon cancer cells and 2- to 3-fold lower PI-9 levels than MCF7/ERHA breast cancer cells, in which PI-9 is strongly induced by estrogens, and by tamoxifen. Expression of increasing levels of PI-9 in target cells may progressively inhibit immune surveillance by blocking NK and CTL-induced cytotoxicity through the perforin/granzyme pathway and then through the Fas/FasL pathway.

Analysis of the thiol status of peripheral blood leukocytes in rheumatoid arthritis patients

Although the exact etiology of rheumatoid arthritis (RA) remains unknown, there is increasing evidence that reactive oxygen species and a pro-oxidant/antioxidant imbalance are an important part of the pathogenesis of joint tissue injury. Flow cytometry was used to evaluate the thiol status [surface-thiols and intracellular glutathione (iGSH)] of leukocytes from RA patients and controls. Levels of surface-thiols and iGSH of leukocytes from RA patients were significantly lower than of leukocytes from controls. CD53, a glycoprotein of the tetraspanin superfamily, which coprecipitates with the GSH recycling enzyme gamma-glutamyl transpeptidase, was elevated significantly on leukocytes from RA patients compared with leukocytes from controls. Surface-thiols and GSH play important roles in redox buffering of cells, providing protection from oxidative stress. The chronic inflammation of RA has been associated with oxidative stress, which is shown to cause a decline in the levels of cellular antioxidant sulfhydryls (R-SH). As antioxidant-protective levels also decline with age, the problem is compounded in older RA patients, who did have fewer R-SH. Chronic stress can also have an effect on telomere lengths, determining cell senescence and longevity. Although telomeres shorten with increasing age, our flow cytometry studies indicate that accelerated shortening in telomere lengths occurs with increasing age of RA patients, suggesting premature cellular aging. The paradox is that lymphocytes from RA patients are believed to resist apoptosis, and we suggest that the elevated expression of CD53, which results from the increased oxidative stress, may protect against apoptosis.

Expression of TNF-alpha and related signaling molecules in the peripheral blood mononuclear cells of rheumatoid arthritis patients

We examined the role of tumor necrosis factor (TNF-alpha) and its related signaling intermediates leading to apoptosis/proliferation in the peripheral blood mononuclear cells (PBMCs) of RA patients. The constitutive expression of mRNA for TNF-alpha receptors (TNFR-I and TNFR-II) and the adapter molecules, such as the TNF receptor-associated death domain protein (TRADD), Fas-associated death domain protein (FADD), receptor interacting protein (RIP), and TNF receptor-associated factor 2 (TRAF-2) were analyzed by reverse transcriptase-PCR (RT-PCR) in PBMCs from control and RA cases. PBMCs of RA patients showed a significant increase in TNF-alpha and TNFR-I expression as compared with that from control subjects along with significantly increased constitutive expression of TRADD, RIP, and TRAF-2 mRNA. There was a decrease in expression of FADD in RA patients, but the difference was not significant as compared to controls. These data suggested enhanced signaling by the TNFR-I-TRADD-RIP-TRAF-2 pathway and suppressed signaling by the TNFR-I-TRADD-FADD pathway in PBMCs of RA patients. However, the regulatory mechanisms for TNF-alpha induced signaling may not be explained only by these pathways.

Immunization with autologous T cells enhances in vivo anti-tumor immune responses accompanied by up-regulation of GADD45β

Immunization with inactivated autoreactive T cells may induce idiotype anti-idiotypic reactions to deplete autoreactive T cells, which are involved in autoimmune diseases. However, it is unknown whether attenuated activated healthy autologous T-cell immunization could increase anti-tumor immune responses. To this end, C57Bl/6 mice were immunized with attenuated activated autologous T cells. The splenocytes from immunized mice showed a higher proliferative ability than that from naive mice. The special phenotype analysis showed that there were more CD8+ T cells and CD62L+ T cells in immunized mice after 24 h of culture with 10% fetal calf serum complete medium in vitro (P<0.01). These results demonstrated that this immunization may activate T cells in vivo. Furthermore, the splenocytes from immunized mice revealed resistance to activation-induced cell death (AICD) in vitro. To further study the relative genes that are responsible for the higher proliferation and resistance to AICD, the expression of Fas/Fas ligand (FasL) and GADD45b was measured by real-time PCR. The results indicated that GADD45beta transcription was higher in the splenocytes from immunized mice than that in the naive mice. In addition, the Fas expression showed a parallel higher, but FasL did not change obviously. To investigate the biologic functions induced by immunization in vivo, a tumor model was established by EL-4 tumor cell inoculation in C57/Bl mice. Mice receiving autologous T-cell immunization had significantly inhibited tumor growth in vivo (P<0.01). This study implicated that immunization with attenuated activated autologous T cells enhances anti-tumor immune responses that participate in tumor growth inhibition.

Increased arthritis susceptibility in cartilage proteoglycan–specific T cell receptor–transgenic mice

OBJECTIVE

To better understand the role of antigen (arthritogenic epitope)-specific T cells in the development of autoimmune arthritis.

METHODS

A transgenic (Tg) mouse expressing the T cell receptor (TCR) Valpha1.1 and V(beta)4 chains specific for a dominant arthritogenic epitope (designated 5/4E8) of human cartilage proteoglycan (HuPG) aggrecan was generated. This TCR-Tg mouse strain was backcrossed into the PG-induced arthritis (PGIA)-susceptible BALB/c strain and tested for arthritis incidence and severity.

RESULTS

CD4+ TCR-Tg T cells carried functionally active TCR specific for a dominant arthritogenic epitope of HuPG (5/4E8). T cells of naive TCR-Tg mice were in an activated stage, since the in vitro response to HuPG or to peptide stimulation induced interferon-gamma and interleukin-4 production. TCR-Tg mice uniformly, without exception, developed severe and progressive polyarthritis, even without adjuvant. Inflamed joints showed extensive cartilage degradation and bone erosions, similar to that seen in the arthritic joints of wild-type BALB/c mice with PGIA. Spleen cells from both naive and HuPG-immunized arthritic TCR-Tg mice could adoptively transfer arthritis when injected into syngeneic BALB/c.SCID recipient mice.

CONCLUSION

TCR-Tg BALB/c mice display increased arthritis susceptibility and develop aggravated disease upon in vivo antigen stimulation. This model using TCR-Tg mice is a novel and valuable research tool for studying mechanisms of antigen (arthritogenic epitope)-driven regulation of arthritis and understanding how T cells recognize autoantigen in the joints. This type of mouse could also be used to develop new immunomodulatory strategies in T cell-mediated autoimmune diseases.