Apoptosis in the rheumatic diseases

A Small Step, a Giant Leap: Somatic Hypermutation of a Single Amino Acid Leads to Anti-La Autoreactivity

The anti-La mab 312B, which was established by hybridoma technology from human-La transgenic mice after adoptive transfer of anti-human La T cells, immunoprecipitates both native eukaryotic human and murine La protein. Therefore, it represents a true anti-La autoantibody. During maturation, the anti-La mab 312B acquired somatic hypermutations (SHMs) which resulted in the replacement of four aa in the complementarity determining regions (CDR) and seven aa in the framework regions. The recombinant derivative of the anti-La mab 312B in which all the SHMs were corrected to the germline sequence failed to recognize the La antigen. We therefore wanted to learn which SHM(s) is (are) responsible for anti-La autoreactivity. Humanization of the 312B ab by grafting its CDR regions to a human Ig backbone confirms that the CDR sequences are mainly responsible for anti-La autoreactivity. Finally, we identified that a single amino acid replacement (D > Y) in the germline sequence of the CDR3 region of the heavy chain of the anti-La mab 312B is sufficient for anti-La autoreactivity.

Association between thiazolidinedione use and rheumatoid arthritis risk in patients with type II diabetes, a population-based, case-control study

AIM

A previous study revealed that PPARγ agonists have anti-inflammatory effects in rheumatoid arthritis (RA). Furthermore, some studies have shown that type 2 diabetes mellitus (T2DM) may elicit the development of RA. In this study, we aimed to investigate whether the use of thiazolidinediones (TZDs) is associated with a lower risk of developing RA in patients with T2DM.

METHODS

Based on the Taiwan National Health Insurance Research Database, we conducted a nationwide case-control study. The selected cases were patients with T2DM who were diagnosed with RA between 2000 and 2013. The controls were retrieved at a ratio of 1:4 by propensity score matching. Logistic regression was conducted to evaluate whether TZD use lowers the risk of RA in patients with T2DM. The dose-response effect was examined according to the total TZD dose, within 2 years before the index date (the first diagnosis date of RA), and TZD doses were divided into four groups by cumulative Defined Daily Dose (cDDD): <30, 31-90, 91-365, and >365 cDDDs.

RESULTS

A total of 3605 cases and 14 420 controls were included in this study. After adjusting for age, sex, baseline comorbidities, the results demonstrated that TZD use did not significantly reduce the risk of RA in patients with T2DM (adjusted OR = 0.91, 95% CI 0.81-1.02). In the subgroup analysis by total TZD exposure dose within 2 years, 91-365 cDDDs of TZD had a lower risk of RA development, aOR = 0.87 (95% CI 0.71-1.06) and >365 cDDDs of TZD, aOR = 0.85 (95% CI 0.73-1.01). In the trend test, P was <.05.

CONCLUSIONS

TZD use might reduce the risk of RA in patients with T2DM, but it was non-statistically significant. Further research is necessary to assess this association.

T Cell Mediated Conversion of a Non-Anti-La Reactive B Cell to an Autoreactive Anti-La B Cell by Somatic Hypermutation

Since the first description of nuclear autoantigens in the late 1960s and early 1970s, researchers, including ourselves, have found it difficult to establish monoclonal antibodies (mabs) against nuclear antigens, including the La/SS-B (Sjögrens' syndrome associated antigen B) autoantigen. To date, only a few anti-La mabs have been derived by conventional hybridoma technology; however, those anti-La mabs were not bona fide autoantibodies as they recognize either human La specific, cryptic, or post-translationally modified epitopes which are not accessible on native mouse La protein. Herein, we present a series of novel murine anti-La mabs including truly autoreactive ones. These mabs were elicited from a human La transgenic animal through adoptive transfer of T cells from non-transgenic mice immunized with human La antigen. Detailed epitope and paratope analyses experimentally confirm the hypothesis that somatic hypermutations that occur during T cell dependent maturation can lead to autoreactivity to the nuclear La/SS-B autoantigen.

Validation of galectin-1 as potential diagnostic biomarker of early rheumatoid arthritis

Galectin 1 (Gal1) is a lectin with a wide cellular expression that functions as a negative regulator of the immune system in several animal models of autoimmune diseases. Identification of patients with rheumatoid arthritis (RA) has improved during the last decade, although there is still a need for biomarkers allowing an early diagnosis. In this regard, it has been recently proposed that Gal1 serum levels are increased in patients with RA compared to the general population. However, this topic is controversial in the literature. In this work, we provide additional information about the potential usefulness of Gal1 serum levels as a biomarker for RA diagnosis. We studied Gal1 serum and synovial fluid levels and clinical parameters in samples from 62 patients with early arthritis belonging to the PEARL study. In addition, 24 healthy donors were studied. We found that both patients fulfilling RA criteria and patients with undifferentiated arthritis showed higher Gal1 levels than healthy donors. Similar findings were observed in synovial fluid, which showed even higher levels than serum. However, we did not find correlation between Gal1 levels and disease activity or disability. Therefore, our results suggest that Gal1 could be a diagnostic but not a severity biomarker.

Increased level of B cell differentiation factor in systemic lupus erythematosus patients

Most autoimmune disease are driven by a dysfunction in T and B cells, but B cells are still an interesting area of research, perturbations in their development are implicated in autoimmune diseases. B cell differentiating factor (BCDF) plays a part in the differentiation of B cells. The aim was To assess the levels of BCDF, IgM and IgG in SLE patients and whether they have any peculiarity in the clinical context of SLE. Thirty six patients with SLE and 24 healthy volunteers as control were enrolled in the study. BCDF was measured using Sandwich ELISA, total human IgM and IgG were measured by calorimetric methods. The mean concentrations of BCDF and IgM were significantly higher in patients with SLE as compared with controls (P < 0.001 and P < 0.0001 respectively). No significant difference was observed as regard IgG. We observed positive correlation between BCDF and IgM (r = 0.281, P = 0.03), and between IgG and IgM, duration of the disease (r = 0.468, P = 0.004, r = 0.337, P = 0.008 respectively). Moreover we observed lower IgM level in patients with discoid lesion (P = 0.009) and lower IgG level in those with hematologic manifestations (P = 0.02). ROC analysis revealed area under curve (AUC) 0.861 for BCDF and 0.902 for IgM, they can delineate SLE from controls at a cut-off value of 98.5 pg/ml, and 18 mg/dl IgM respectively.

Conclusion

BCDF and IgM are increased in SLE patients and are promissing diagnostic markers for SLE.

A Potential of sFasL in Preventing Gland Injury in Sjogren's Syndrome

Fas and its ligand FasL, members of tumor necrosis factor receptor superfamily, have been implicated in the process of cell apoptosis. FasL consists of two forms, membrane FasL (mFasL) and soluble FasL (sFasL). sFasL can be produced by mFasL cleaved by matrix metalloproteinases (MMP) and also reveals a role for binding to Fas which is expressed on cell surface. Although Fas/FasL axis has been implicated in a variety of diseases, its role in Sjogren's syndrome still remains ill defined. In this study, we investigated the potential of sFasL in the pathogenesis of Sjogren's syndrome (SS). We found that the serum levels of sFasL in SS patients were significantly lower than healthy subjects. Moreover, serum levels of sFasL in patients with mild disease activity were higher than patients with severe disease activity. There is a positive correlation of the serum level of sFasL with uptake index of parotid gland in our expectation. In addition, liver injury involvement in SS patients showed decreased level of sFasL. Furthermore, we here also observed that the protective cytokine IL-10 expression was positively correlated with sFasL expression. Thus, our results here suggest a potential of sFasL in maintaining gland organ homeostasis.

Thiazolidinediones and inflammation

Thiazolidinediones (TZDs) are selective ligands of peroxisome-proliferator-activated receptor g increasingly used in the treatment of type 2 diabetes. Both in vitro and in vivo studies provide evidence that TZDs have anti-inflammatory properties. TZDs inhibit macrophage activation and decrease inflammatory cytokine expression and release in macrophage and monocyte. In vivo, treatment with TZDs decreases circulating mononuclear cells nuclear NF-kB content while increasing, in the same cells, expression of IkB, an NK-kB inhibitor. Furthermore, TZD treatment results in decreased plasma levels of inflammation and cardiovascular risk markers such as CRP, MMP9, PAI-1 and sCD40 in both obese and type 2 diabetic patients. Finally, TZDs induce synoviocyte apoptosis and reduce secretion of TNFa, IL-6 and IL-8 in synoviocyte from rheumatoid arthritis patients. TZDs might thus be considered for use in clinical trials targeting prevention of atherosclerosis and cardiovascular diseases and in pilot trials exploring the possibility that TZDs might help in the treatment of rheumatic diseases.

Therapeutic effects of hybrid liposomes without drugs for rheumatoid arthritis

Hybrid liposomes (HLs) can be prepared by simply sonicating a mixture of vesicular and micellar molecules in buffer solutions. This study aims to demonstrate inhibitory effects of HLs on the growth of fibroblast-like synoviocytes along with apoptosis and therapeutic effects of HLs in a mouse model with rheumatoid arthritis (RA). HLs composed of 95 mol% L-α-dimyristoylphosphatidylcholine (DMPC) and 5 mol% polyoxyethylene(23)dodecyl ether (C12(EO)23) were prepared by the sonication method. The inhibitory effects of HLs on the growth of human fibroblast-like synoviocytes-RA (HFLS-RA) cells in vitro and their inhibitory mechanism were examined. High inhibitory effects of HLs on the growth of HFLS-RA cells were observed. The induction of apoptosis by HLs was revealed on the basis of flow cytometric analysis. Furthermore, therapeutic effects of HLs in the mouse model with RA were examined in vivo. Our results demonstrate that HLs showed inhibitory effects on the growth of HFLS-RA cells in vitro along with apoptosis and therapeutic effects in mouse models of RA in vivo.

p53 Levels positively correlate with carotid intima-media thickness in patients with subclinical atherosclerosis

BACKGROUND

The level of circulating p53 is related to inflammation in asymptomatic subjects with cardiovascular risk factors. Whether p53 is associated with the severity of atherosclerosis remains to be determined.

HYPOTHESIS

This study examines the relationship of systemic p53 levels with atherosclerotic risk factors and subclinical atherosclerosis.

METHODS

Circulating levels of p53 and markers of inflammation were measured in 356 subjects with cardiovascular risk factors but who were free from clinical cardiovascular disease. Subclinical atherosclerosis was evaluated by both the mean carotid intima-media thickness (IMT) and the presence of atherosclerotic plaques with the use of B-mode ultrasound in all subjects.

RESULTS

p53 levels were positively correlated with age (r = 0.382, P < 0.001), intercellular adhesion molecular-1 (ICAM-1; r = 0.510, P < 0.01), vascular cell adhesion molecular-1 (VCAM-1; r = 0.497, P < 0.01), E-selectin (r = 0.337, P < 0.01), and carotid IMT (r = 0.594, P < 0.01). The association between p53 and IMT remained significant in multiple regression analysis (P < 0.01) when controlling for traditional atherosclerotic risk factors and inflammatory markers.

CONCLUSION

Higher plasma p53 levels were associated with an increase in inflammatory markers, as well as increased carotid IMT. Circulating p53 may be useful in identifying subclinical atherosclerosis in subjects symptomatically free from cardiovascular disease.

Apoptosis in the rheumatoid arthritis synovial membrane: modulation by disease-modifying anti-rheumatic drug treatment

OBJECTIVES

RA is characterized at the synovial tissue level by synovial lining hyperplasia, angiogenesis and mononuclear cell infiltrates. A failure of apoptotic pathways may explain these pathological changes in RA synovial tissue. This study aims to demonstrate the presence of initiators and inhibitors of apoptosis in RA synovial tissue and the effect of treatment with DMARDs on apoptotic pathways in RA.

METHODS

Synovial biopsy specimens were obtained at arthroscopy from 16 RA patients before and at 3- or 6-month intervals after commencing treatment with a DMARD. Apoptosis (by the terminal deoxynucleotidyl transferase mediated dUTP nick end labelling method and polyADP-ribose polymerase staining), proteins regulating apoptosis [Fas, FADD-like IL1b converting enzyme inhibitory protein (FLIP), Bcl-2, Survivin and X-linked inhibitor of apoptosis protein (XIAP)] and the presence of activated caspases (caspases 3 and 8) were detected by immunohistochemistry and quantified using image analysis and semiquantitative techniques.

RESULTS

Fifteen patients responded to treatment, with an ACR response of > or =20%, 13 achieving an ACR response of > or =50% and 3 achieving an ACR remission. There was a significant reduction in SM macrophages and memory T cells, with an increase in fibroblast-like synovial lining cells following DMARD treatment. Apoptosis was not detected in the inflamed synovial tissue of RA patients before starting treatment, despite evidence of caspase activation, but was detectable after successful treatment with DMARDs. Inhibitors of activated caspases (FLIP, Survivin and XIAP) were detected in RA synovial tissue and were down-modulated with successful DMARD treatment.

CONCLUSIONS

Apoptotic pathways are defective in RA synovial tissue from patients with active disease, despite the presence of activated caspases, possibly due to the abundant expression of inhibitors of the caspase pathway in RA synovial tissue. DMARD treatment can modulate apoptosis in the RA SM, which may lead to restoration of the SM architecture towards that of normal synovial tissue.

Elevated expression of caspase-3 inhibitors, survivin and xIAP correlates with low levels of apoptosis in active rheumatoid synovium

INTRODUCTION

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a tumour necrosis factor (TNF) family member capable of inducing apoptosis in many cell types.

METHODS

Using immunohistochemistry, terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling (TUNEL) and real-time PCR we investigated the expression of TRAIL, TRAIL receptors and several key molecules of the intracellular apoptotic pathway in human synovial tissues from various types of arthritis and normal controls. Synovial tissues from patients with active rheumatoid arthritis (RA), inactive RA, osteoarthritis (OA) or spondyloarthritis (SpA) and normal individuals were studied.

RESULTS

Significantly higher levels of TRAIL, TRAIL R1, TRAIL R2 and TRAIL R4 were observed in synovial tissues from patients with active RA compared with normal controls (p < 0.05). TRAIL, TRAIL R1 and TRAIL R4 were expressed by many of the cells expressing CD68 (macrophages). Lower levels of TUNEL but higher levels of cleaved caspase-3 staining were detected in tissue from active RA compared with inactive RA patients (p < 0.05). Higher levels of survivin and x-linked inhibitor of apoptosis protein (xIAP) were expressed in active RA synovial tissues compared with inactive RA observed at both the protein and mRNA levels.

CONCLUSIONS

This study indicates that the induction of apoptosis in active RA synovial tissues is inhibited despite stimulation of the intracellular pathway(s) that lead to apoptosis. This inhibition of apoptosis was observed downstream of caspase-3 and may involve the caspase-3 inhibitors, survivin and xIAP.

Edaravone inhibits collagen-induced arthritis possibly through suppression of nuclear factor-kappa B

OBJECTIVE

Rheumatoid arthritis (RA) is a chronic autoimmune disease which is induced by proinflammatory cytokines or oxidative stress. The activation of nuclear factor-kappa B (NF-kappaB) that contributed to imbalance between apoptosis and proliferation of rheumatoid synovial cells (SC). Edaravone, clinically available free radical scavenger in Japan, is confirmed to be beneficial in the acute stage of stroke. We aimed to investigate the suppressive effect of edaravone on collagen-induced arthritis (CIA) mice and on the activated molecules in SC stimulated by interleukin-1beta (IL-1beta).

METHODS

Edaravone was administrated intravenously at a dose of 3mg/kg of body weight to CIA mice. The progression of CIA was evaluated by the macroscopic arthritis scoring system of paws. Interleukin-6 (IL-6) and matrix metalloproteinase-3 (MMP-3) concentrations in culture medium of human SC were measured by enzyme linked immunosorbent assays. Caspase-3/7 activity and nuclear factor-kappa B (NF-kappaB) protein level of cultured human SC were estimated by fluorometric assay and Western blot analysis, respectively.

RESULTS

Edaravone significantly decreased macroscopic arthritis score in CIA mice. Acceleration of IL-6 and MMP-3 productions and attenuation of caspase-3/7 activity in IL-1beta-stimulated SC were abated by edaravone. Activated NF-kappaB in IL-1beta-stimulated SC was suppressed by edaravone.

CONCLUSION

Edaravone, antioxidants available for clinical use, appears to have therapeutic effect on RA. We suggest that the inhibitory effect of edaravone on RA might be exerted, at least in part, through suppression of activated NF-kappaB. Therefore, we expect therapeutical use of edaravone as an anti-rheumatic agent.

Pathophysiology of Sjögren's syndrome

The term Sjögren's syndrome refers to keratoconjunctivitis sicca and xerostomia due to lymphocytic infiltrates of lachrymal and salivary glands. The current used criteria for diagnosis of primary Sjögren's syndrome is the American-European consensus. Primary Sjögren's syndrome is an autoimmune disorder characterized by lymphocytic infiltrates and destruction of the salivary and lachrymal glands and systemic production of autoantibodies to the ribonucleoprotein particles SS-A/Ro and SS-B/La. The infiltrating cells (T- and B-cells, dendritic cells) interfere with glandular function at several points: destruction of glandular elements by cell-mediated mechanisms; secretion of cytokines that activate pathways bearing the signature of type 1 and 2 interferons; production of autoantibodies that interfere with muscarinic receptors; and secretion of metalloproteinases (MMPs) that interfere with the interaction of the glandular cell with its extracellular matrix, which is necessary for efficient glandular function. As the process progresses, the mucosal surfaces become sites of chronic inflammation and the start of a vicious circle. Despite extensive study of the underlying cause of Sjögren's syndrome, the pathogenesis remains obscure. In broad terms, pathogenesis is multifactorial; environmental factors are thought to trigger inflammation in individuals with a genetic predisposition to the disorder.

Increased Bcl-2/p53 ratio in human osteoarthritic cartilage: a possible role in regulation of chondrocyte metabolism

OBJECTIVE

To determine whether Bcl-2, p53, and Fas/CD95 help to control cartilage metabolism.

METHODS

Six normal and 14 osteoarthritic (OA) cartilage samples were examined, and two zones from each sample showing the least (Min) and most (Max) anatomical damage were selected. Chondrocytes were isolated by sequential enzymatic digestion and freshly processed. Bcl-2, p53, and Fas/CD95 expression was evaluated by immunofluorescence and FACS analysis; the cell cycle was analysed using propidium iodide, and chondrocyte proliferation assessed by [(3)H]thymidine incorporation.

RESULTS

Intracellular levels of Bcl-2 were significantly higher in Max (27.5%) than in Min (21%, p<0.01) OA or normal chondrocytes (18.5%, p<0.01). Intracellular p53 expression was significantly decreased in Max (25.5%) compared with Min (37%, p<0.01) OA or normal cartilage (41.5%, p<0.05). Fas/CD95 receptor expression on surface chondrocytes did not significantly differ between OA and normal cartilage. Cell cycle analysis showed that the proportion of activated chondrocytes in the S phase was significantly higher in Max (69%) than in Min (49%) OA or normal cartilage (43%). The prevalence of proliferating chondrocytes progressively increased according to the degree of OA damage (mean (SEM) Min 1247 (260), Max 2423 (460), p<0.05). Chondrocyte [(3)H]thymidine uptake correlated positively with Bcl-2 (r(s) = 0.62, p = 0.009) and correlated inversely with p53 levels (r(s) = -0.55, p = 0.02).

CONCLUSIONS

Bcl-2 and p53 play a part in apoptosis, but also help to regulate chondrocyte growth and differentiation. Whereas Bcl-2 promotes cell survival, p53 can arrest cell cycle. The data confirm that chondrocyte activity is enhanced in OA and suggest that the increased Bcl-2/p53 ratio sustains the metabolic boost of chondrocytes.

Increased CD8+ T cell apoptosis in scleroderma is associated with low levels of NF-kappa B

Our objectives were (1) to compare lymphocyte subpopulation apoptosis rates in SSc patients versus healthy controls and (2) to compare Bcl-2 and NF-kappa B expression in cultured CD8 lymphocytes of SSc patients versus controls. Peripheral blood samples were obtained from 27 SSc patients meeting the American College of Rheumatology criteria for SSc and 28 healthy individuals. Mononuclear cells were isolated by Ficoll-Hypaque density gradient separation and cultured for 48 hr. For determination of apoptosis within specific cell populations, samples were labeled with PE-conjugated monoclonal antibody to CD8, CD4, and a FITC-conjugated monoclonal antibody to Annexin V. Flow cytometry was carried out with a FACS operating with Cellquest software. CD8+ lymphocytes were positively selected with magnetic microbeads conjugated to antihuman CD8. CD8 T cells were separated, then incubated with activation for 48 hr, and NF-kappa B and Bcl-2 analysis was carried out using Western immunoblotting. The CD4:CD8 ratio was increased in SSc compared to controls (2.6 +/- 1.13 vs.1.87 +/- 0.76; P = 0.018). The spontaneous apoptosis rate of SSc CD8 lymphocytes was increased compared to that of controls of (21.9 +/- 13.7 vs. 13.3 +/- 9.9; P = 0.019). No difference was found in the rate of CD4 apoptosis of SSc patients versus controls (9.8 +/- 5.2 vs. 7.18 +/- 4.89%; P = ns). The expression of NF-kappa B in SSc CD8 lymphocytes was decreased compared with that of CD8 lymphocytes from healthy controls (144 +/- 13 vs. 188 +/- 11; P = 0.018). Whereas expression of Bcl-2 was similar in activated CD8+ T cells of SSc patients and healthy controls, CD8+ T cell apoptosis rate was found to be in reverse correlation with expression of NF-kappa B in these cells ( r = - 0.53, P = 0.029). The increased CD4:CD8 ratio in SSC may result from increased CD8+ T cell apoptosis. Increased SSc CD8 T cell apoptosis is associated with low levels of NF-kappa B.

Osteoprotegerin (OPG) acts as an endogenous decoy receptor in tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis of fibroblast-like synovial cells

We examined the role of osteoprotegerin (OPG) on tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in rheumatoid fibroblast-like synovial cells (FLS). OPG protein concentrations in synovial fluid from patients with rheumatoid arthritis (RA) correlated with those of interleukin (IL)-1beta or IL-6. A similar correlation was present between IL-1beta and IL-6 concentrations. Rheumatoid FLS in vitro expressed both death domain-containing receptors [death receptor 4 (DR4) and DR5] and decoy receptors [decoy receptor 1 (DcR1) and DcR2]. DR4 expression on FLS was weak compared with the expression of DR5, DcR1 and DcR2. Recombinant TRAIL (rTRAIL) rapidly induced apoptosis of FLS. DR5 as well as DR4 were functional with regard to TRAIL-mediated apoptosis induction in FLS; however, DR5 appeared be more efficient than DR4. In addition to soluble DR5 (sDR5) and sDR4, OPG administration significantly inhibited TRAIL-induced apoptogenic activity. OPG was identified in the culture supernatants of FLS, and its concentration increased significantly by the addition of IL-1beta in a time-dependent manner. Neither IL-6 nor tumour necrosis factor (TNF)-alpha increased the production of OPG from FLS. TRAIL-induced apoptogenic activity towards FLS was reduced when rTRAIL was added without exchanging the culture media, and this was particularly noticeable in the IL-1beta-stimulated FLS culture; however, the sensitivity of FLS to TRAIL-induced apoptosis itself was not changed by IL-1beta. Interestingly, neutralization of endogenous OPG by adding anti-OPG monoclonal antibody (MoAb) to FLS culture restored TRAIL-mediated apoptosis. Our data demonstrate that OPG is an endogenous decoy receptor for TRAIL-induced apoptosis of FLS. In addition, IL-1beta seems to promote the growth of rheumatoid synovial tissues through stimulation of OPG production, which interferes with TRAIL death signals in a competitive manner.

Nitric oxide acts on the mitochondria and protects human endothelial cells from apoptosis

Proliferation of small blood vessels in synovial tissues is one of the pathologic features of rheumatoid arthritis. In this study we tested the hypothesis that nitric oxide (NO) protects endothelial cells (ECs) against apoptogenic agents in vitro. Human umbilical-vein endothelial cells (HUVECs) were cultured with and without NO donor S -nitro- N -acetylpenicillamine (SNAP) and further incubated in the presence or absence of Z-leucine-leucine-leucine-aldehyde (LLL-CHO), etoposide, or C2-ceramide. After cultivation, apoptosis of HUVECs was quantified on the basis of disruption of mitochondrial transmembrane potential (DeltaPsim), activation of caspases, and the presence of hypodiploid DNA-positive cells. Treatment of HUVECs with LLL-CHO, etoposide, or C2-ceramide induced DeltaPsim, activation of caspase-3, caspase-8, and caspase-9 and the appearance of hypodiploid DNA-positive cells. NO production in HUVECs was clearly increased by SNAP. Apoptotic cell death in HUVECs induced by LLL-CHO, etoposide, and C2-ceramide was significantly suppressed by SNAP treatment. HUVECs in vitro expressed Bcl-2, Bcl-xL, and Bax; however, expression was not changed by SNAP treatment in the presence or absence of LLL-CHO, etoposide, or C2-ceramide. Although the molecule(s) responsible for the protective effects of NO remains to be identified, our data imply that NO protects HUVECs against mitochondrial perturbation caused by apoptogenic agents. These results suggest that NO promotes endothelial-cell proliferation and angiogenesis in the synovial tissues of patients with rheumatoid arthritis and that NO may be a therapeutic target for rheumatoid arthritis.

Possible role of apoptosis in the pathogenesis of bleomycin-induced scleroderma

To elucidate the role of apoptosis in cutaneous sclerosis, we examined the induction of apoptosis and expression of Fas, Fas ligand, as well as caspase-3 in a murine model of bleomycin-induced scleroderma. Dermal sclerosis was induced by local injections of bleomycin (1 mg per mL) in C3H/HeJ mice. Induction of apoptosis was examined by TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling) assay and DNA gel electrophoresis. TUNEL positivity was prominently detected on keratinocytes and infiltrating mononuclear cells, but not endothelial cells and fibroblasts, in the lesional skin. DNA fragmentation revealed laddering at 3 to 4 wk following bleomycin treatment. Immunohistochemistry showed increased expression of Fas in infiltrating mononuclear cells at early phases following bleomycin exposure, whereas constitutive expression in fibroblasts. Fas ligand expression was increased in mononuclear cells as well as fibroblasts in the sclerotic skin. Results of reverse transcription-polymerase chain reaction analysis revealed that expression of Fas ligand mRNA was upregulated and reached a maximum at 3 wk, whereas Fas mRNA was continuously detected. mRNA expression as well as activity of caspase-3 was also enhanced at 3 wk. Administration of neutralizing anti-Fas ligand antibody together with local bleomycin treatment reduced the development of dermal sclerosis, associated with the reduction of TUNEL-positive mononuclear cells and also with the blockade of apoptosis. Caspase-3 activity in the lesional skin was also significantly reduced after anti-Fas ligand treatment. These findings suggest that excessive apoptosis, which is mediated by Fas/Fas ligand pathway and caspase-3 activation, is involved in the pathogenesis of bleomycin-induced scleroderma, possibly by playing an inflammatory role.

Akt is an endogenous inhibitor toward tumor necrosis factor-related apoptosis inducing ligand-mediated apoptosis in rheumatoid synovial cells

Akt is known to be activated in the rheumatoid synovial tissues. We examined here functional role of Akt during tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-mediated apoptosis in rheumatoid synovial cells. Rheumatoid synovial cells in vitro were rapidly committed to apoptosis in response to TRAIL in mitochondria-dependent manner whereas Akt and extracellular signal-regulated kinase (ERK) were also phosphorylated. TRAIL-mediated apoptosis in synovial cells was significantly increased through inactivation of Akt by LY294002, however, that process was not so changed by adding ERK inhibitor, PD98059. Platelet-derived growth factor (PDGF) clearly phosphorylated both Akt and ERK in synovial cells, and PDGF pretreatment markedly suppressed TRAIL-mediated synovial cell apoptosis. The use of not PD98059 but LY294002 abrogated PDGF-mediated inhibitory effect toward TRAIL-induced apoptosis in synovial cells. The above protective effect of Akt was confirmed by the use of short interfering RNA (siRNA)-directed inhibition of Akt. Our data suggest that Akt is an endogenous inhibitor during TRAIL-mediated synovial cell apoptotic pathway, which may explain that synovial cells in situ of the rheumatoid synovial tissues are resistant toward apoptotic cell death in spite of death receptor expression.

Oxygen free radicals and systemic autoimmunity

Reactive oxygen species generated during various metabolic and biochemical reactions have multifarious effects that include oxidative damage to DNA leading to various human degenerative and autoimmune diseases. The highly reactive hydroxy radical (*OH) can interact with chromatin and result in a wide range of sugar and base-derived products, DNA-protein cross-links and strand breaks. Studies from our laboratory have demonstrated that after modification the DNA becomes highly immunogenic and the induced antibodies exhibit variable antigen-binding characteristics. Systemic lupus erythematosus, a prototype autoimmune disease, is characterized by the presence of autoantibodies to multiple nuclear antigens. The detection of 8-hydroxyguanosine in the immune complex derived DNA of systemic lupus erythematosus patients reinforces the evidence that reactive oxygen species may be involved in its pathogenesis. Increased apoptosis and decreased clearance of apoptotic cells as observed in systemic lupus erythematosus (SLE) might well be a contributory factor in systemic autoimmunity. Clinically, titres of autoantibodies are closely related to the degree of renal inflammation. Anti-DNA antibodies may combine with circulating antigen and contribute to the deposition of immune complexes in renal glomeruli.

B cell diversity and longevity in systemic autoimmunity

Despite much investigation, the nature of the primary disturbances that culminate in the production of pathogenic autoantibodies remains imprecise. However, major advances in the understanding of the genetics, the cellular and the molecular basis of pathogenic autoreactivity have been achieved in recent years. Not only B cells play a paramount role in systemic autoimmunity, but their role is not limited to secretion of autoantibodies. Under certain experimental conditions, B cells can activate memory T cells, and can process and present self-antigens to naive T cells, implying the existence of an antibody-independent mechanism for tissue injury in systemic autoimmune diseases, such as lupus. In both the mouse and the human disease, B cells secreting autoantibodies exhibit features which suggest that they are selected by specific autoantigens. Factors, such as BAFF, that support differentiation of selected B cells into mature long-lived B cells may be critical in generating deleterious autoimmune responses, at least in experimental animals. During these selection processes, the amount of signals received by the B cells are fine-tuned for optimal transmission, and kinases and phosphatases control most activities. Since a tight regulation of signaling pathways is required to prevent overt autoimmunity, faulty cell signaling may cause or exacerbate disorders of the immune system. Several observations showing altered expression of signaling molecules in T and B lymphocytes from patients with human lupus suggest that the subversion of immune receptor signaling could account for the hyperproduction of autoantibodies.

Matrix metalloproteinase 9, apoptosis, and vascular morphology in early arthritis

OBJECTIVE

To examine matrix metalloproteinase 9 (MMP-9) in the synovial fluid (SF) and synovial membrane (SM) in relation to vascular endothelial cell (EC) apoptosis, vascular endothelial growth factor (VEGF), and SM vascular pattern.

METHODS

Thirty-four patients underwent needle arthroscopy of the knee joint; 12 had early rheumatoid arthritis (RA), 12 had early psoriatic arthritis (PsA), and 10 had osteoarthritis (OA). The early RA and early PsA patients were matched for disease activity. SF levels of MMP-9 and VEGF were measured by an enzyme-linked immunosorbent assay, and EC apoptosis was measured by TUNEL assay. MMP-9 expression was examined in SM by immunohistochemistry. Synovial tissue explants were stimulated with VEGF, and MMP-9 levels were measured in the supernatants. The synovial vascular pattern was recorded.

RESULTS

SF MMP-9 levels were significantly higher in early PsA patients than in early RA patients; OA patients had minimal levels. MMP-9 levels correlated with blood vessel morphology and SF VEGF levels. MMP-9 expression was greater in early PsA SM than in early RA SM, but the difference was not significant. In contrast however, EC apoptosis was greater in early RA SM than in early PsA SM. MMP-9 levels increased 2-fold and 9-fold, respectively, in SM explant culture supernatants on day 7 in response to stimulation with 25 ng/ml and 50 ng/ml of VEGF.

CONCLUSION

SF MMP-9 levels correlate with the pattern of SM neovascularization and SF VEGF levels in early inflammatory arthritis, and VEGF increases MMP-9 production by SM. Endothelial cell apoptosis, however, appears to be more prevalent in early RA. This combination of factors may explain the pattern of differential angiogenesis in these arthritides.

Importance of NF-kappaB in rheumatoid synovial tissues: in situ NF-kappaB expression and in vitro study using cultured synovial cells

OBJECTIVES

To examine whether inhibition of NF-kappaB induces apoptosis of human synovial cells stimulated by tumour necrosis factor alpha (TNFalpha), interleukin 1beta (IL1beta), and anti-Fas monoclonal antibody (mAb).

METHODS

The expression of proliferating cell nuclear antigen (PCNA), NF-kappaB, and the presence of apoptotic synovial cells were determined in synovial tissues. Apoptosis of cultured synovial cells was induced by inhibition of NF-kappaB nuclear translocation by Z-Leu-Leu-Leu-aldehyde (LLL-CHO). The activation of caspase-3 and expression of XIAP and cIAP2 in synovial cells in LLL-CHO induced apoptosis was also examined.

RESULTS

Abundant PCNA+ synovial cells were found in rheumatoid arthritis (RA) synovial tissue, though a few apoptotic synovial cells were also detected in the RA synovial tissues. Nuclear NF-kappaB was expressed in RA synovial cells. Electrophoretic mobility shift assay showed that treatment of cells with TNFalpha or IL1beta significantly stimulated nuclear NF-kappaB activity. A small number of apoptotic synovial cells expressing intracellular active caspase-3 were found after treatment of cells with LLL-CHO. Although treatment of RA synovial cells with TNFalpha or IL1beta alone did not induce apoptosis, apoptosis induced by LLL-CHO and caspase-3 activation were clearly enhanced in TNFalpha or IL1beta stimulated synovial cells compared with unstimulated synovial cells. Furthermore, induction of apoptosis of synovial cells with caspase-3 activation by anti-Fas mAb was clearly increased by LLL-CHO. The expression of cIAP2 and XIAP in synovial cells may not directly influence the sensitivity of synovial cells to apoptosis induced by LLL-CHO.

CONCLUSION

The results suggest that NF-kappaB inhibition may be a potentially important therapeutic approach for RA by correcting the imbalance between apoptosis and proliferation of synovial cells in RA synovial tissue.

Western and Chinese antirheumatic drug-induced T cell apoptotic DNA damage uses different caspase cascades and is independent of Fas/Fas ligand interaction

Spontaneous or therapeutic induction of T cell apoptosis plays a critical role in establishing transplantation tolerance and maintaining remission of autoimmune diseases. We investigated the mechanisms of apoptosis induced by Chinese and Western antirheumatic drugs (ARDs) in human T cells. We found that hydroxychloroquine, Tripterygium wilfordii hook F, and tetrandrine (Tet), but not methotrexate, at therapeutic concentrations can cause T cell death. In addition, Tet selectively killed T cells, especially activated T cells. Although ARD-induced cytotoxicity was mediated through apoptotic mechanisms, Fas/Fas ligand interaction was not required. We further demonstrated that the processes of phosphatidylserine externalization and DNA damage along the ARD-induced T cell apoptotic pathway could operate independently, and that selective inhibition of DNA damage by caspase inhibitors did not prevent T cells from undergoing cell death. Moreover, we found that Tet- and Tripterygium wilfordii hook F-induced T cell DNA damage required caspase-3 activity, and hydroxychloroquine-induced T cell DNA damage was mediated through a caspase-3- and caspase-8-independent, but Z-Asp-Glu-Val-Asp-fluomethyl ketone-sensitive, signaling pathway. Finally, the observation that ARD-induced activation of caspase-3 in both Fas-sensitive and Fas-resistant Jurkat T cells indicates that Fas/Fas ligand interaction plays no role in ARD-induced T cell apoptosis. Our observations provide new information about the complex apoptotic mechanisms of ARDs, and have implications for combining Western and Chinese ARDs that have different immunomodulatory mechanisms in the therapy of autoimmune diseases and transplantation rejection.

Fas/FasL mediated apoptosis of thyrocytes in Graves' disease

We examined in the present study the possible involvement of Fas and its ligand (FasL) in the process of Graves' disease. Immunohistochemical analysis showed that few normal thyrocytes expressed Fas but many thyrocytes in Graves' disease expressed this molecule. The percentage of FasL-positive thyrocytes in Graves' thyroids was, however, less than in normal thyroids. Several apoptotic thyrocytes and infiltrating mononuclear cells (MNCs) were detected scattered throughout Graves' thyroid tissues and abundant proliferating cell nuclear antigen (PCNA)-positive thyrocytes were present. Apoptotic cells, as well as PCNA-positive cells, were scarcely detectable in normal thyroid glands, however. In vitro treatment of thyrocytes by IL-1beta a cytokine found to be expressed in Graves' thyroid glands, increased Fas but reduced FasL expression. IL-1beta-stimulated thyrocytes became sensitive to apoptosis by anti-Fas IgM monoclonal antibody (mAb). Activated T cells, which strongly expressed FasL, showed cytotoxic activity toward IL-1beta-stimulated thyrocytes but not toward unstimulated thyrocytes. This cytotoxic activity involved the Fas/FasL pathway. Importantly, unstimulated thyrocytes could kill activated, but not resting, T cells. IL-1beta-stimulated thyrocytes, with down-regulated FasL expression, could not efficiently kill activated T cells. The cytotoxic activity of unstimulated thyrocytes toward activated T cells was inhibited by anti-FasL mAb. Interestingly, unstimulated thyrocytes induced apoptosis in IL-1beta-stimulated thyrocytes but not in unstimulated thyrocytes. These interactions were also blocked by anti-FasL mAb. Our results suggest that the apoptotic cell death of both thyrocytes and infiltrating MNCs found in Graves' thyroid glands is regulated by IL-1beta through Fas/FasL interactions.

Understanding the pathogenesis of autoimmune hepatitis

OBJECTIVES

The aim of this study was to review the pathogenic mechanisms of autoimmune hepatitis, identify gaps in knowledge, and focus future investigative efforts.

METHODS

The study was based on a review of all relevant articles on the mechanisms of autoimmunity in autoimmune liver disease from 1980 to 2000, extraction of pertinent concepts from the medical literature; and integration of evolving paradigms of pathogenesis with personal experiences and investigations.

RESULTS

Autoimmune hepatitis is a consequence of autoantigen exposure, genetic predisposition, and defective immunoregulatory mechanisms. Autoantigen is optimally presented by class II molecules of the major histocompatibility complex that have lysine residues at position DRbeta71 of the antigen-binding groove. Cytokines and non-disease-specific autoimmune promoters modulate immune reactivity. Cell-mediated and antibody-dependent mechanisms contribute to hepatocyte injury.

CONCLUSIONS

Multiple disturbances in the homeostatic mechanisms that preserve self-tolerance are likely in autoimmune hepatitis. Future investigations must focus on individual determinants of autoantigen presentation, immunocyte activation, and liver cell destruction. Findings can then be integrated into a comprehensive knowledge base that may be applicable to other autoimmune diseases.

Apoptosis as a target for gene therapy in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by chronic inflammation of the synovial joints resulting from hyperplasia of synovial fibroblasts and infiltration of lymphocytes, macrophages and plasma cells, all of which manifest signs of activation. All these cells proliferate abnormally, invade bone and cartilage, produce an elevated amount of pro-inflammatory cytokines, metalloproteinases and trigger osteoclast formation and activation. Some of the pathophysiological consequences of the disease may be explained by the inadequate apoptosis, which may promote the survival of autoreactive T cells, macrophages or synovial fibroblasts. Although RA does not result from single genetic mutations, elucidation of the molecular mechanisms implicated in joint destruction has revealed novel targets for gene therapy. Gene transfer strategies include inhibition of pro-inflammatory cytokines, blockade of cartilage-degrading metalloproteinases, inhibition of synovial cell activation and manipulation of the Th1-Th2 cytokine balance. Recent findings have iluminated the idea that induction of apoptosis in the rheumatoid joint can be also used to gain therapeutic advantage in the disease. In the present review we will discuss different strategies used for gene transfer in RA and chronic inflammation. Particularly, we will high-light the importance of programmed cell death as a novel target for gene therapy using endogenous biological mediators, such as galectin-1, a beta-galactoside-binding protein that induces apoptosis of activated T cells and immature thymocytes.

Lupus susceptibility genes on human chromosome 1

During the past five years, there has been an intense interest in studying candidate susceptibility genes for systemic lupus erythematosus (SLE). Many such studies have been focused on candidates located on chromosome 1, demonstrating association of certain genetic variants with SLE. Some of the tested candidate genes were chosen because they encode molecules with relevant immunological functions that may play a role in the pathogenesis of SLE. More recently, the identification of genomic segments linked to SLE has suggested novel positional candidate genes. Thus far, there is considerable evidence supporting that multiple genes on this chromosome contribute to the development and expression of SLE. This review highlights the genetic loci located on chromosome 1 that have recently been associated with SLE. These include loci encoding the tumor necrosis factor receptor 2 (TNFR2), complement component C1q, Fcgamma receptors, T cell receptor zeta chain, interleukin-10 (IL-10), poly (ADP-ribose) polymerase (PARP), and HRES-1.

Selective inhibitors of apoptotic caspases: implications for novel therapeutic strategies

Caspases are essential for apoptosis. A crucial question regarding the role(s) of these proteases is whether the selective inhibition of an effector caspase will prevent cell death. We have identified potent, selective non-peptide inhibitors of the effector caspases 3 and 7. Apoptosis can be inhibited and cell functionality maintained using an inhibitor selective for caspases 3 and 7. This has important therapeutic implications and the potential to generate novel anti-apoptotic strategies in diseases that involve dysregulated apoptosis.

Molecular aberrations in human systemic lupus erythematosus

Systemic lupus erythematosus is an autoimmune disorder that predominantly affects women during the childbearing years. Clinically, major organ systems are affected, including the skin, kidneys and nervous system. Genetic, hormonal, environmental and immunoregulatory factors contribute to the highly variable expression of the disease. Impaired cellular and humoral immune responses reflect disordered biochemical and molecular functions that might be determined genetically. Enhanced understanding of these molecular abnormalities should enable development of new, effective therapeutic agents in the near future.

Intercellular adhesion molecule 1 underlies the functional heterogeneity of synovial cells in patients with rheumatoid arthritis: involvement of cell cycle machinery

OBJECTIVE

To investigate whether synovial cells from rheumatoid arthritis (RA) synovium can be divided into 2 functionally different subpopulations: active or proliferative cells and apoptotic cells.

METHODS

Expression of cell surface and cytoplasmic molecules on synovial cells was assessed by immunohistochemistry, flow cytometry, or Western blotting. Cells were categorized as intercellular adhesion molecule 1 (ICAM-1) positive or negative based on positive and negative selection of antibody-coated beads. Cell cycle and apoptosis were assessed using propidium iodide staining, TUNEL method, and DNA fragmentation.

RESULTS

Expression of ICAM-1 and Fas was noted mainly in the synovial lining to sublining layer in vivo, and synovial cells could be clearly distinguished as ICAM-1 positive or negative. The expression of Fas was higher on ICAM-1-positive cells than on ICAM-1-negative cells in vitro. The functional and phenotypic heterogeneity between ICAM-1-positive and -negative cells was further emphasized by cell cycle machinery. The majority of ICAM-1-positive cells were arrested at the G0/G1 phase, whereas many of the ICAM-1-negative cells were at the S to G2/M proliferating phase. In ICAM-1-positive cells, p53 and p21 expression was up-regulated and cyclin-dependent protein kinase 6 activity was inhibited. Most ICAM-1-positive cells were apoptotic (as evidenced by TUNEL positivity and DNA fragmentation). ICAM-1-positive cells were induced not only by interleukin-1beta, but also by Fas crosslinking.

CONCLUSION

ICAM-1-positive synovial cells represent growth arrest and subsequent apoptosis, whereas ICAM-1-negative cells are proliferative. Such differences in regulation of the cell cycle based on ICAM-1 status are important determinants of the lifespan, proliferation, and growth arrest of RA synoviocytes.

Characterization of recombinant human autoantibody fragments directed toward the autoantigenic U1-70K protein

The U1-70K protein is specifically bound to stemloop I of the U1 small nuclear RNA contained in the U1 small nuclear ribonucleoprotein complex (U1 snRNP), which is involved in the splicing of pre-mRNA. All components of the U1 snRNP complex, including the U1-70K protein, are important autoantigens in patients with systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD). Here we describe for the first time the selection and characterization of recombinant human anti-U1-70K single chain autoantibody fragments (anti-hU1-70K scFv) from autoimmune patient-derived phage display antibody libraries. All scFv specifically recognize parts of the hU1-70K protein and its apoptotic 40-kDa cleavage product. In Western blotting assays a number of scFv preferentially recognize the 40-kDa apoptotic cleavage fragment of the U1-70K protein, suggesting a possible involvement of this apoptotic cleavage product in the autoimmune response of patients. The germline gene usage of these recombinant autoantibodies was also determined. Using several U1-70K deletion and point mutants of both human (h) and Drosophila melanogaster (Dm) origin, it was established that the U1-70K epitope that is recognized by the anti-hU1-70K scFv is located within the RNA binding domain.

15-deoxy-delta(12,14)-PGJ(2) induces synoviocyte apoptosis and suppresses adjuvant-induced arthritis in rats

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily and have a dominant regulatory role in adipocyte and monocyte differentiation. PPAR-gamma agonists are also negative regulators of macrophage activation and have modulatory effects on tumorigenesis. In this study we demonstrate that synovial tissue localized expression of PPAR-gamma in patients with rheumatoid arthritis (RA). We detected markedly enhanced expression of PPAR-gamma in macrophages, as well as modestly enhanced expression in the synovial lining layer, fibroblasts, and endothelial cells. Activation of the PPAR-gamma by 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) and the synthetic PPAR-gamma ligand (troglitazone) induced RA synoviocyte apoptosis in vitro. Moreover, intraperitoneal administration of these PPAR-gamma ligands ameliorated adjuvant-induced arthritis with suppression of pannus formation and mononuclear cell infiltration in female Lewis rats. Anti-inflammatory effects of 15d-PGJ(2) were more potent than troglitazone. These findings suggest that PPAR-gamma may be an important immunoinflammatory mediator and its ligands, especially 15d-PGJ(2), may be useful in the treatment of RA.

Caspase-dependent cleavage of nucleic acids

Autoimmune diseases are frequently characterized by the presence of autoantibodies directed against nucleic acid-protein complexes present in the nucleus of the cell. The mechanisms by which these autoantigenic molecules escape immunological tolerance are largely unknown, although a number of recent observations suggest that modified self-proteins generated during apoptosis may play an important role in the development of autoimmunity. It has been hypothesized that the recognition of these modified self-proteins by the immune system may promote autoantibody production. While apoptosis is specifically characterized by posttranslational modification of proteins, recent findings also show that nucleic acids are modified. This review summarizes the specific cleavages of some of these key nucleic acids, i.e. chromosomal DNA, ribosomal RNA and small structural RNAs (U1 snRNA, Y RNA), in apoptotic cells.

Potent and selective nonpeptide inhibitors of caspases 3 and 7 inhibit apoptosis and maintain cell functionality

Caspases have been strongly implicated to play an essential role in apoptosis. A critical question regarding the role(s) of these proteases is whether selective inhibition of an effector caspase(s) will prevent cell death. We have identified potent and selective non-peptide inhibitors of the effector caspases 3 and 7. The inhibition of apoptosis and maintenance of cell functionality with a caspase 3/7-selective inhibitor is demonstrated for the first time, and suggests that targeting these two caspases alone is sufficient for blocking apoptosis. Furthermore, an x-ray co-crystal structure of the complex between recombinant human caspase 3 and an isatin sulfonamide inhibitor has been solved to 2.8-A resolution. In contrast to previously reported peptide-based caspase inhibitors, the isatin sulfonamides derive their selectivity for caspases 3 and 7 by interacting primarily with the S(2) subsite, and do not bind in the caspase primary aspartic acid binding pocket (S(1)). These inhibitors blocked apoptosis in murine bone marrow neutrophils and human chondrocytes. Furthermore, in camptothecin-induced chondrocyte apoptosis, cell functionality as measured by type II collagen promoter activity is maintained, an activity considered essential for cartilage homeostasis. These data suggest that inhibiting chondrocyte cell death with a caspase 3/7-selective inhibitor may provide a novel therapeutic approach for the prevention and treatment of osteoarthritis, or other disease states characterized by excessive apoptosis.

Inhibition of caspase-3-like activity prevents apoptosis while retaining functionality of human chondrocytes in vitro

Apoptosis was induced in a human chondrocyte cell line, T/C 28a4, by treatment with various stimuli, including camptothecin, tumor necrosis factor-alpha, staurosporine, okadaic acid, and reduced serum conditions. All stimuli induced a cytosolic DEVDase activity, coincident with apoptosis. Caspase activities in the lysates were characterized and quantitated with peptide cleavage profiles. To confirm that the results were not related to the immortalized nature of the cell line, primary human chondrocytes also were shown to undergo apoptosis under similar conditions, which resulted in increased cytosolic DEVDase activity. There was little or no caspase-1 (interleukin-1beta-converting enzyme) or caspase-8-like activity in the apoptotic cells. In all cases, the irreversible nonselective caspase inhibitor, Z-VAD-FMK, and the caspase-3-selective inhibitor, Ac-DMQD-CHO, inhibited DEVDase activity and apoptosis, whereas the caspase-1-selective inhibitor, Ac-YVAD-CHO, had no effect. Human chondrocytes were stably and transiently transfected with a type-II collagen gene (COL2A1) regulatory sequence driving a luciferase reporter as a specific marker of chondrocyte gene expression. Treatment of the cells with camptothecin or tumor necrosis factor-alpha plus cycloheximide significantly inhibited COL2A1 transcriptional activity. Significantly, cotreatment with Z-VAD-FMK or Ac-DMQD-CHO maintained COL2A1-reporter gene activity, indicating that the prevention of apoptosis by caspase-3 inhibition was sufficient to maintain cell functionality as assessed by the retention of type-II collagen promoter activity.

The immune response to apoptotic cells

Programmed cell death (PCD) can be divided into two distinct but linked sequential processes, killing of the cells and removal of the dead cells, which may be a neighboring cell or a professional phagocyte. Following internalization of the apoptotic cell, the phagocyte typically triggers neither the development of a pro-inflammatory response nor the production of autoantibodies directed against apoptotic self antigens. Since apoptotic cells are characterized by translocation of autoantigens such as nucleosomes to the surface of the cell, we tested the hypothesis that excess or abnormally processed apoptotic cells can generate autoantibodies. We have found that syngeneic apoptotic load can induce transient hypergammaglobulinemia, anti-DNA, anticardiolipin, and glomerular depositions in normal mice. Furthermore, we also found that one of the important mechanisms of uptake of apoptotic cells involves opsonization by the complement system, suggesting that deficient states could lead to aberrant handling of apoptotic cells. Therefore, conditions in which apoptotic cells become immunogenic may explain antigen selection in inflammatory and autoimmune conditions, such as in systemic lupus erythematosus (SLE).

Apoptosis in human autoimmune diseases

The description of apoptosis or programmed cell death nearly thirty years ago did not initially stimulate a great deal of interest. However, the ways cells die is clearly an essential part of biological homeostasis and well worth of study in its own right as the enormous literature on the subject in the past 15 years confirms. In the past decade new avenues of apoptosis research have opened up as the relationship between this form of cell death and autoimmune disease has come under increasing scrutiny. Although most research to date has been in animal study models, there are a variety of studies which have begun to explore links between apoptosis and a wider range of human autoimmune conditions. In this review we analyse briefly the background to what is known about apoptosis and focus on the increasing likelihood that abnormalities in apoptosis are contributory factors in the development of human autoimmunity.

Accelerated development of IgG autoantibodies and autoimmune disease in the absence of secreted IgM

Individuals with systemic lupus erythematosus and rheumatoid arthritis are characterized by the presence of high levels of circulating IgM and IgG autoantibodies. Although IgG autoantibodies often are pathogenic, the role of IgM autoantibodies in autoimmune disease is not clear. Using mice that are unable to secrete IgM but are able to express surface IgM and IgD and to secrete other classes of immunoglobulins, we examined the effect of the absence of secreted IgM in the development of IgG autoantibodies and autoimmune disease in lupus-prone lymphoproliferative (lpr) mice. Compared with regular lpr mice, lpr mice that lack secreted IgM developed elevated levels of IgG autoantibodies to double-stranded DNA and histones and had more abundant deposits of immune complexes in the glomeruli; they also suffered more severe glomerulonephritis and succumbed to the disease at an earlier age. Similarly, the absence of secreted IgM also resulted in an accelerated development of IgG autoantibodies in normal mice. These findings suggest that secreted IgM, including IgM autoantibodies produced naturally or as part of an autoimmune response, may lessen the severity of autoimmune pathology associated with IgG autoantibodies.

Structure and function of Fas/Fas ligand

Fas is a member of the TNF receptor family, that contain 2-6 cysteine-rich domains (CRDs) in their extracellular regions, a single transmembrane domain and variably sized intracytoplasmic domains. Fas belongs to a subgroup of family members that have a "death domain" near the carboxy-terminal region of the molecule. This domain binds to adaptor molecules that transmit a death signal to the cell. Signal transduction is complex and involves caspases, ceramides and stress pathways. Fas ligand is biologically active as a homotrimer. Receptor binding has been localized to the C-terminus and a self-association motif to the N-terminus of the ligand extracellular domain. Expression of ligand in a functionally active form is highly regulated at the transcriptional level as well as by cleavage by metalloproteinases. Since Fas/Fas ligand delete activated cells in the peripheral immune system, defects in this pathway predispose to autoimmune disorders.

The fate of U1 snRNP during anti-Fas induced apoptosis: specific cleavage of the U1 snRNA molecule

During apoptosis, the U1-70K protein, a component of the spliceosomal U1 snRNP complex, is specifically cleaved by the enzyme caspase-3, converting it into a C-terminally truncated 40-kDa fragment. In this study, we show that the 40-kDa U1-70K fragment is still associated with the complete U1 snRNP complex, and that no obvious modifications occur with the U1 snRNP associated proteins U1A, U1C and Sm-B/B'. Furthermore, it is described for the first time that the U1 snRNA molecule, which is the backbone of the U1 snRNP complex, is modified during apoptosis by the specific removal of the first 5 - 6 nucleotides including the 2,2, 7-trimethylguanosine (TMG) cap. The observations that U1 snRNA cleavage is very specific (no such modifications were detected for the other U snRNAs tested) and that U1 snRNA cleavage is markedly inhibited in the presence of caspase inhibitors, indicate that an apoptotically activated ribonuclease is responsible for the specific modification of U1 snRNA during apoptosis.

Nature and nurture in systemic lupus erythematosus

Nowhere across the spectrum of rheumatic and dermatological disease is the interaction of nature and nurture more relevant than in the connective tissue diseases such as SLE. While genetic and environmental factors are clearly involved in both the triggering of the disease and its expression, the interaction is complex with different combinations of factors contributing in different patients. For example, while genetic factors contribute substantially to susceptibility to lupus, this does not follow a simple Mendelian pattern of inheritance and mathematical models suggest that there may be varying contribution from at least four genes with differing inheritances. A variety of candidate genes and environmental factors have been highlighted in SLE but to dissect out the complexity of how these might interact requires the study of patient groups with a better defined clinical and serological phenotype. For example, studies of patients with subacute cutaneous lupus (SCLE) have shown associations with various genes in the MHC region (including HLA, complement and TNF) and suggest that the biological effect of inheriting an extended MHC region may be greater than its individual parts. One can now speculate on how interaction with an environmental factor such as UV light explains pathogenesis.

Spontaneous and induced apoptosis in systemic lupus erythematosus: multiple assays fail to reveal consistent abnormalities

The immunologic basis of systemic lupus erythematosus (SLE) is multifactorial and still elusive. Recent advances in the field of apoptosis have suggested new paradigms for the development of lupus autoimmunity. In the present studies we examined the possibility that individual populations of T and B cells are abnormally resistant to apoptosis or that they stand out in over- or underexpressing Fas. Fas was generally overexpressed in cells freshly isolated from SLE patients but the apoptotic response to FasL was normal. We did not find increased spontaneous ongoing apoptosis in SLE lymphocytes. Normal cleavage of PARP similarly implied that the final biochemical pathway of apoptosis is relatively intact in SLE. Finally we placed special emphasis on the response of SLE patient cells to UV irradiation, especially cells from photosensitive patients, and found no difference in Fas expression. In conclusion our results indicate that SLE patients do not suffer from a major apoptotic abnormality. The results also raise questions concerning the dynamic expression of Fas and the significance of ongoing apoptosis as a risk for autoimmune disease.