Bcl-xL expression in vivo in rheumatoid synovium

Shikonin suppresses rheumatoid arthritis by inducing apoptosis and autophagy via modulation of the AMPK/mTOR/ULK-1 signaling pathway

BACKGROUND

The overproliferation of fibroblast-like synoviocytes (FLS) contributes to synovial hyperplasia, a pivotal pathological feature of rheumatoid arthritis (RA). Shikonin (SKN), the active compound from Lithospermum erythrorhizon, exerts anti-RA effects by diverse means. However, further research is needed to confirm SKN's in vitro and in vivo anti-proliferative functions and reveal the underlying specific molecular mechanisms.

PURPOSE

This study revealed SKN's anti-proliferative effects by inducing both apoptosis and autophagic cell death in RA FLS and adjuvant-induced arthritis (AIA) rat synovium, with involvement of regulating the AMPK/mTOR/ULK-1 pathway.

METHODS

SKN's influences on RA FLS were assessed for proliferation, apoptosis, and autophagy with immunofluorescence staining (Ki67, LC3B, P62), EdU incorporation assay, staining assays of Hoechst, Annexin V-FITC/PI, and JC-1, transmission electron microscopy, mCherry-GFP-LC3B puncta assay, and western blot. In AIA rats, SKN's anti-arthritic effects were assessed, and its impacts on synovial proliferation, apoptosis, and autophagy were studied using Ki67 immunohistochemistry, TUNEL, and western blot. The involvement of AMPK/mTOR/ULK-1 pathway was examined via western blot.

RESULTS

SKN suppressed RA FLS proliferation with reduced cell viability and decreased Ki67-positive and EdU-positive cells. SKN promoted RA FLS apoptosis, as evidenced by apoptotic nuclear fragmentation, increased Annexin V-FITC/PI-stained cells, reduced mitochondrial potential, elevated Bax/Bcl-2 ratio, and increased cleaved-caspase 3 and cleaved-PARP protein levels. SKN also enhanced RA FLS autophagy, featuring increased LC3B, reduced P62, autophagosome formation, and activated autophagic flux. Autophagy inhibition by 3-MA attenuated SKN's anti-proliferative roles, implying that SKN-induced autophagy contributes to cell death. In vivo, SKN mitigated the severity of rat AIA while also reducing Ki67 expression, inducing apoptosis, and enhancing autophagy within AIA rat synovium. Mechanistically, SKN modulated the AMPK/mTOR/ULK-1 pathway in RA FLS and AIA rat synovium, as shown by elevated P-AMPK and P-ULK-1 expression and decreased P-mTOR expression. This regulation was supported by the reversal of SKN's in vitro and in vivo effects upon co-administration with the AMPK inhibitor compound C.

CONCLUSION

SKN exerted in vitro and in vivo anti-proliferative properties by inducing apoptosis and autophagic cell death via modulating the AMPK/mTOR/ULK-1 pathway. Our study revealed novel molecular mechanisms underlying SKN's anti-RA effects.

Targeting regulated chondrocyte death in osteoarthritis therapy

In vivo articular cartilage degeneration is an essential hallmark of osteoarthritis (OA), involving chondrocyte senescence, extracellular matrix degradation, chondrocyte death, cartilage loss, and bone erosion. Among them, chondrocyte death is one of the major factors leading to cartilage degeneration. Many studies have reported that various cell death modes, including apoptosis, ferroptosis, and autophagy, play a key role in OA chondrocyte death. Currently, there is insufficient understanding of OA pathogenesis, and there remains a lack of treatment methods to prevent OA and inhibit its progression. Studies suggest that OA prevention and treatment are mainly directed to arrest premature or excessive chondrocyte death. In this review, we a) discuss the forms of death of chondrocytes and the associations between them, b) summarize the critical factors in chondrocyte death, c) discuss the vital role of chondrocyte death in OA, d) and, explore new approaches for targeting the regulation of chondrocyte death in OA treatment.

Acetazolamide ameliorates the severity of collagen-induced arthritis in rats: Involvement of inducing synovial apoptosis and inhibiting Wnt/β-catenin pathway

We previously revealed that the overexpression of synovial aquaporin 1 (AQP1) aggravated collagen-induced arthritis (CIA) in rats via regulating β-catenin signaling. This study was to demonstrate the therapeutic effect of acetazolamide (AZ, an AQP1 inhibitor) on rat CIA and explored its underlying mechanisms. Paw swelling, arthritis index, pathological assessments, and serum levels of collagen type II (Col II) antibody, IL-1β and TNF-α were measured to evaluate the anti-arthritic effect of AZ on rat CIA. Ki67 immunohistochemistry and TUNEL assay were performed to reveal the anti-proliferative and pro-apoptotic effects of AZ on synovial cells in vivo. The protein levels of apoptosis-related genes and Wnt/β-catenin pathway key members were detected by western blot. We found that AZ treatment on CIA rats could inhibit paw swelling, reduce arthritis index, alleviate the pathologic changes of ankle joint and decrease the serum levels of Col II antibody, TNF-α and IL-1β. AZ could reduce Ki67 expression and increase apoptosis index in CIA synovial tissues by reducing Bcl-2 protein level, increasing Bax and caspase 3 protein levels and normalizing Bcl-2/Bax ratio. Moreover, AZ could reduce the protein levels of Wnt1, β-catenin, p-GSK-3β (Ser9), c-myc, cyclin D1 and MMP9, while increase GSK-3β protein level in CIA synovial tissues. Importantly, these mentioned effects of AZ (60 mg/kg) on CIA rats could be reversed by the combined use of lithium chloride (LiCl), an activator of Wnt/β-catenin pathway. In short, AZ exerted potent anti-arthritic effects on CIA rats by inducing synovial apoptosis and inhibiting Wnt/β-catenin pathway.

Potential role of mitochondria in synoviocytes

Synoviocytes are located in the synovium lining layer, which is composed of macrophage-like synoviocytes (MLS) and fibroblast-like synoviocytes (FLS) with different characteristics. Mitochondria, which exist in most cells, are two membrane-covered organelles. In addition to providing the necessary ATP for synoviocytes, mitochondria are involved in the regulation of redox homeostasis and the integration of synoviocytes death signals. In recent years, mitochondrial dysfunction has been found in rheumatoid arthritis (RA) and osteoarthritis (OA). Interestingly, recent studies have started uncovering that mitochondria that were previously reported to play a role in chondrocytes or immune cells, but not known to have pronounced roles in synoviocytes, can actually play crucial roles in the regulation of the pathological properties of the synoviocytes. The purpose of this review is to summarize our current understanding of the key role of mitochondria in synoviocytes, including mitochondrial dysfunction in synoviocytes can induce and aggravate inflammatory responses and changes in mitochondrial structure and function with the involvement of multiple cytokines, signal pathway, and hypoxic state of synovial tissue alter the response of synoviocytes to apoptotic stimulation. Also, mitochondrial abnormalities in synoviocytes promote the synoviocytes invasion and proliferation.

The inflammatory role of phagocyte apoptotic pathways in rheumatic diseases

Rheumatoid arthritis affects nearly 1% of the world's population and is a debilitating autoimmune condition that can result in joint destruction. During the past decade, inflammatory functions have been described for signalling molecules classically involved in apoptotic and non-apoptotic death pathways, including, but not limited to, Toll-like receptor signalling, inflammasome activation, cytokine production, macrophage polarization and antigen citrullination. In light of these remarkable advances in the understanding of inflammatory mechanisms of the death machinery, this Review provides a snapshot of the available evidence implicating death pathways, especially within the phagocyte populations of the innate immune system, in the perpetuation of rheumatoid arthritis and other rheumatic diseases. Elevated levels of signalling mediators of both extrinsic and intrinsic apoptosis, as well as the autophagy, are observed in the joints of patients with rheumatoid arthritis. Furthermore, risk polymorphisms are present in signalling molecules of the extrinsic apoptotic and autophagy death pathways. Although research into the mechanisms underlying these pathways has made considerable progress, this Review highlights areas where further investigation is particularly needed. This exploration is critical, as new discoveries in this field could lead to the development of novel therapies for rheumatoid arthritis and other rheumatic diseases.

Bcl-2 overexpression ameliorates immune complex-mediated arthritis by altering FcγRIIb expression and monocyte homeostasis

RA is a chronic autoimmune disease characterized by accumulation of inflammatory cells within synovial joints. RA is associated with a failure of apoptosis of infiltrating leukocytes, thought to be a result of overexpression of prosurvival Bcl-2 proteins. Overexpression of Bcl-2 in hematopoietic cells can result in spontaneous autoimmunity. We therefore hypothesized that increased Bcl-2 in the hematopoietic compartment would reduce apoptosis and thereby, exacerbate inflammatory arthritis. Paradoxically, we found that overexpression of Bcl-2 in mice (vav-bcl-2) markedly reduced pathology in antibody-dependent models of RA (CIA and K/BxN serum transfer arthritis). No such protection was observed in a model of CD4(+) T cell-dependent, B cell-independent arthritis (mBSA/IL-1-induced arthritis). In CIA, vav-bcl-2 Tg mice had lower antibody production to CII, which might explain reduced disease. However, Bcl-2 overexpression also reduced passive K/BxN serum transfer arthritis. Overexpression of Bcl-2 caused a monocytosis, with preferential expansion of Ly6C(lo) monocytes and increased expression of the inhibitory receptor for IgG, FcγRIIb, on leukocytes. Skewing of the myeloid cell population, increases in FcγRIIb, and reduced arthritis were independent of the hypergammaglobulinemia found in vav-bcl-2 Tg mice. These data reveal selective effects of the Bcl-2-regulated apoptotic pathway on monocyte differentiation and the expression of FcRs critical for regulation of antibody/immune complex-mediated disease.

Pro-apoptotic effect of epigallo-catechin-3-gallate on B lymphocytes through regulating BAFF/PI3K/Akt/mTOR signaling in rats with collagen-induced arthritis

To investigate the role of PI3K/Akt/mTOR signaling mediated by B cell-activating factor belonging to the TNF family (BAFF) involved in anti-apoptosis of B lymphocytes in rats with collagen-induced arthritis (CIA) and the regulation of epigallo-catechin-3-gallate (EGCG). Sprague-Dawley rats were immunized to induce CIA. CIA rats were randomly separated into different groups and treated with EGCG (40, 80 mg/kg), Paeoniflorin (100mg/kg) from day 18 to day 38 after immunization. The effects of EGCG on B lymphocytes were evaluated by the levels of BAFF, anti-CII antibody, IgA, IgG and IgM, and the expressions of BAFF receptor, P110δ, p-Akt, mTORC1, Bcl-xL and Bim. B lymphocyte proliferations were analyzed by MTT assay. Apoptosis of B lymphocyte were assayed by flow cytometry. Results showed that, in CIA rats, the levels of BAFF, anti-CII antibody, IgA, IgG and IgM enhanced. BAFF receptor, P110δ, p-AKT, mTORC1 and Bcl-xL were expressed highly, while Bim expression decreased. EGCG (40, 80 mg/kg) and Paeoniflorin decreased the levels of BAFF, anti-CII antibody, IgA, IgG, IgM and the expressions of BAFF receptor, P110δ, p-AKT, mTORC1, Bcl-xL in CIA rats, and increased Bim expression. Further studies showed that EGCG could reduce the expression of P110δ and mTORC1 in vitro. EGCG inhibited B lymphocyte proliferation and induced B lymphocyte apoptosis. In conclusion, BAFF/BAFF receptor might regulate B cell anti-apoptosis through PI3K/Akt/mTOR pathway. EGCG had therapeutic effects on CIA rats, which might be relative to the inhibition effects of EGCG on BAFF and PI3K/Akt/mTOR signaling, and then the apoptosis of B lymphocytes was promoted further.

Apoptosis as a mechanism of action of tumor necrosis factor antagonists in rheumatoid arthritis

Tumor necrosis factor (TNF) antagonists are drugs developed to block endogenous TNF, an essential proinflammatory molecule with a central role in the pathogenesis of rheumatoid arthritis (RA). Although extensive studies have been performed concerning the mode of action of TNF-blocking agents, there are still many unresolved questions and potential differences between different TNF-blocking drugs. One unresolved issue is to what extent apoptosis is affected by TNF blockade in RA. We provide an overview of studies that have investigated the proapoptotic effect of different anti-TNF drugs in RA, searching for a unified interpretation of somewhat contradictory data.

Evaluation of the Bcl-2 family antagonist ABT-737 in collagen-induced arthritis

Therapeutic manipulation of cellular apoptosis holds great promise for malignant and potentially nonmalignant diseases. A relative resistance to apoptosis in RA synovium is associated with increased expression of prosurvival Bcl-2 family members. In this study, we demonstrate that treatment of DBA/1 mice, prior to the onset of CIA with ABT-737, a BH3 mimetic targeting Bcl-2, Bcl-w, and Bcl-x(L), ameliorated disease development. In contrast, treatment of mice with ABT-737 in established CIA did not alter the course of disease. ABT-737 induced lymphopenia, however pathogenic lymphoid populations in CIA mice were less affected, as shown by relatively normal T and B cell responses to CII. Naïve lymphocytes were highly sensitive to apoptosis after culture with ABT-737, but synovial macrophages and neutrophils were not. Mcl-1 was detected in synovial monocyte/macrophages and neutrophils and strikingly, its expression, rather than Bcl-2 and Bcl-x(L), increased in the affected paws and lymphoid organs of mice with CIA. These observations implicate Mcl-1, which is not targeted by ABT-737, in the survival of inflammatory cells in established CIA and suggest that antagonism of Mcl-1 may be more effective in diseases such as RA.

Bim-Bcl-2 homology 3 mimetic therapy is effective at suppressing inflammatory arthritis through the activation of myeloid cell apoptosis

OBJECTIVE

Rheumatoid arthritis (RA) is a destructive autoimmune disease characterized by an increased inflammation in the joint. Therapies that activate the apoptotic cascade may have potential for use in RA; however, few therapeutic agents fit this category. The purpose of this study was to examine the potential of Bim, an agent that mimics the action of Bcl-2 homology 3 (BH3) domain-only proteins that have shown success in preclinical studies of cancer, in the treatment of autoimmune disease.

METHODS

Synovial tissues from RA and osteoarthritis patients were analyzed for the expression of Bim and CD68 using immunohistochemistry. Macrophages from Bim(-/-) mice were examined for their response to lipopolysaccharide (LPS) using flow cytometry, real-time polymerase chain reaction analysis, enzyme-linked immunosorbent assay, and immunoblotting. Bim(-/-) mice were stimulated with thioglycollate or LPS and examined for macrophage activation and cytokine production. Experimental arthritis was induced using the K/BxN serum-transfer model. A mimetic peptide corresponding to the BH3 domain of Bim (TAT-BH3) was administered as a prophylactic agent and as a therapeutic agent. Edema of the ankles and histopathologic analysis of ankle tissue sections were used to determine the severity of arthritis, its cellular composition, and the degree of apoptosis.

RESULTS

The expression of Bim was reduced in RA synovial tissue as compared with controls, particularly in macrophages. Bim(-/-) macrophages displayed elevated expression of markers of inflammation and secreted more interleukin-1beta following stimulation with LPS or thioglycollate. TAT-BH3 ameliorated arthritis development, reduced the number of myeloid cells in the joint, and enhanced apoptosis without inducing cytotoxicity.

CONCLUSION

These data demonstrate that BH3 mimetic therapy may have significant potential for the treatment of RA.

Aberrant reactive oxygen and nitrogen species generation in rheumatoid arthritis (RA): causes and consequences for immune function, cell survival, and therapeutic intervention

The infiltration and persistence of hematopoietic immune cells within the rheumatoid arthritis (RA) joint results in elevated levels of pro-inflammatory cytokines, increased reactive oxygen (ROS) and -nitrogen (RNS) species generation, that feeds a continuous self-perpetuating cycle of inflammation and destruction. Meanwhile, the controlled production of ROS is required for signaling within the normal physiological reaction to perceived "foreign matter" and for effective apoptosis. This review focuses on the signaling pathways responsible for the induction of the normal immune response and the contribution of ROS to this process. Evidence for defects in the ability of immune cells in RA to regulate the generation of ROS and the consequence for their immune function and for RA progression is considered. As the hypercellularity of the rheumatoid joint and the associated persistence of hematopoietic cells within the rheumatoid joint are symptomatic of unresponsiveness to apoptotic stimuli, the role of apoptotic signaling proteins (specifically Bcl-2 family members and the tumor suppressor p53) as regulators of ROS generation and apoptosis are considered, evaluating evidence for their aberrant expression and function in RA. We postulate that ROS generation is required for effective therapeutic intervention.

BH3-only proteins in rheumatoid arthritis: potential targets for therapeutic intervention

Rheumatoid arthritis (RA) is a debilitating disease, resulting in the destruction of bone and cartilage, and in the permanent disfigurement of joints. Although the precise cause of RA is currently unresolved, it has become clear that the damaging effects are a result of the toxic milieu caused by an influx of inflammatory cells and the resulting heightened proinflammatory state within the joint. As the amount of literature suggesting that this preponderance of cells is a result of decreased local apoptosis in the joint continues to increase, in this review, we describe how Bcl-2 family pro-apoptotic BH3-only proteins, particularly Bim and Bid, could act to protect against the development of the disease. We also suggest a role for BH3-mimetic drugs as potential therapeutics in the treatment of RA.

Telomerase transduced osteoarthritis fibroblast-like synoviocytes display a distinct gene expression profile

OBJECTIVE

To examine the differential gene expression in telomerase transduced osteoarthritis fibroblast-like synoviocytes (hTERT-OA 13A FLS) and telomerase transduced rheumatoid arthritis FLS (hTERT-RA 516 FLS) and test the hypothesis that longterm culture of hTERT-OA 13A FLS display a disease-specific gene expression profile.

METHODS

Gene expression in passage 8 hTERT-OA 13A FLS and passage 8 hTERT-RA 516 FLS were compared using microarray assays. Differential expression of selected genes was further examined by reverse transcription-polymerase chain reaction (RT-PCR). After continuous expansion in culture for an additional 4 months, gene expression in the longterm cultures of hTERT-OA 13A FLS and hTERT-RA 516 FLS was again examined with microarray and real-time RT-PCR.

RESULTS

hTERT-OA 13A FLS displayed a distinct gene expression profile. While hTERT-RA 516 FLS expressedADAMTS1, ADAMTS3, ADAMTS5, and several carboxypeptidases, hTERT-OA 13A FLS expressed matrix metalloproteinase (MMP)1, MMP3, and several cathepsins at higher levels. Numerous genes classified in the immune response, lipid transport/catabolism, and phosphate transport biological processes were also expressed at higher levels in hTERT-OA 13A FLS. In contrast, numerous genes classified in the positive regulation of cell proliferation, anti-apoptosis, and angiogenesis biological processes were expressed at higher levels in hTERT-RA 516 FLS. Further, of the recently proposed 21 candidate synovial biomarkers of OA, 12 (57%) were detected in our study.

CONCLUSION

The findings indicate that OA FLS may not be a passive bystander in OA and that telomerase transduced OA FLS offer an alternative tool for the study of synovial disease markers and for the identification of new therapeutic targets for OA therapy.

Monocytes are essential for inhibition of synovial T-cell glucocorticoid-mediated apoptosis in rheumatoid arthritis

Introduction

Rheumatoid arthritis (RA) is characterized by synovial inflammation with local accumulation of mononuclear cells such as macrophages and lymphocytes. We previously demonstrated that intra-articular glucocorticoids decrease the synovial tissue (ST) T-cell population and therefore aimed to investigate whether this is mediated through modulation of apoptosis.

Methods

Apoptosis and cell phenotype were evaluated by immunohistochemistry and dual-immunofluorescence in synovial biopsy sections from 12 RA patients before and after a mean of 11 days of an intra-articular triamcinolone knee injection. In vitro, RA synovial fluid (SF)-derived T cells were evaluated for Annexin V expression by multicolor flow cytometry after 24-hour exposure to dexamethasone, methylprednisolone, or triamcinolone. We also tested induction of apoptosis by dexamethasone on psoriatic arthritis SF-derived T cells using the same method.

Results

Intra-articular glucocorticoids reduced ST T cells but not macrophage number. ST apoptosis levels were unchanged following treatment, virtually absent from lymphoid aggregates, and minimal in CD3⁺ cells both before and after treatment. RA SF T cells were resistant to glucocorticoid-induced apoptosis when cultured in the presence of monocytes but were rendered sensitive to all three tested compounds upon SF isolation. Furthermore, transwell coculture of monocytes and T cells demonstrated that soluble factor(s) and not cellular contact are essential for T-cell resistance to glucocorticoid-mediated apoptosis. This feature is RA-specific as far as dexamethasone-induced apoptosis in nonisolated SF T cells obtained from psoriatic arthritis patients is concerned.

Conclusions

We demonstrate that monocytes rescue synovial T cells from glucocorticoid-induced apoptosis, a feature that is specific for RA. To overcome this, we propose the use of monocyte-targeted therapies rather than T-cell apoptosis-inducing therapies.

The role of resident synovial cells in destructive arthritis

Infiltration by inflammatory cells, thickening of the lining layer, and destructive invasion into cartilage and bone are pathognomic features of the synovium in rheumatoid arthritis (RA). However, the most common cell types at the sites of invasion are resident cells of the joint, in particular synovial fibroblasts. These cells differ from healthy synovial fibroblasts in their morphology, their expression of proto-oncogenes and antiapoptotic molecules, and in their lack of certain tumor suppressor genes. Through their production of proinflammatory cytokines and chemokines mediated by signaling via Toll-like receptors, they are not only effector cells but also active parts of the innate immune system attracting inflammatory immune cells to the synovium. Most importantly, by producing matrix-degrading molecules they contribute strongly to the destructive mechanisms operative in RA.

Matrix metalloproteinase-3 production by gut IgG plasma cells in chronic inflammatory bowel disease

BACKGROUND

In both ulcerative colitis (UC) and Crohn's disease (CD) there is a marked increase in mucosal IgG plasma cells (PC), although their precise role is not well established. In this study we isolated gut PCs from patients with IBD and normal controls and analyzed cytokine production, matrix metalloproteinase (MMP)-3 and tissue inhibitor of metalloproteinase (TIMP)-1 production, and PC longevity ex vivo.

METHODS

Lamina propria mononuclear cells (LPMCs) were isolated from patients with CD (n = 19), UC (n = 27), and normal controls (n = 42). PCs were further selected by immunomagnetic isolation using CD138 microbeads. Cytokine, MMP-3, and TIMP-1 expression was investigated by Taqman polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), Western blotting, and confocal microscopy. PC lifespan in vitro was studied by ELISpot analysis.

RESULTS

PCs from both controls and IBD patients contained high levels of transcripts for TGFbeta, whereas they did not contain significant transcripts for IL-4, IL-5, IL-10, IFNgamma, TNF, or IL-12p40. PCs from patients with CD and UC expressed significantly higher levels of MMP-3 protein and transcripts than controls (P < 0.0001). The vast majority of MMP-3-expressing PCs were IgG+ve. In culture, IgA PCs from both IBD patients and controls persisted for only a few days, but IgG PCs from IBD patients persisted for at least 3 weeks.

CONCLUSIONS

We have demonstrated that IgG PCs from patients with IBD express large amounts of MMP-3 and that they appear to be long-lived. These results identify a new pathway by which IgG PCs may damage the gut.

Pro-apoptotic Bid is required for the resolution of the effector phase of inflammatory arthritis

Rheumatoid arthritis is an autoimmune disease characterized by hyperplasia of the synovial lining and destruction of cartilage and bone. Recent studies have suggested that a lack of apoptosis contributes to the hyperplasia of the synovial lining and to the failure in eliminating autoreactive cells. Mice lacking Fas or Bim, two pro-apoptotic proteins that mediate the extrinsic and intrinsic death cascades, respectively, develop enhanced K/BxN serum transfer-induced arthritis. Since the pro-apoptotic protein Bid functions as an intermediate between the extrinsic and intrinsic apoptotic pathways, we examined the role that it plays in inflammatory arthritis. Mice deficient in Bid (Bid-/-) show a delay in the resolution of K/BxN serum transfer-induced arthritis. Bid-/- mice display increased inflammation, bone destruction, and pannus formation compared to wild-type mice. Furthermore, Bid-/- mice have elevated levels of CXC chemokine and IL-1β in serum, which are associated with more inflammatory cells throughout the arthritic joint. In addition, there are fewer apoptotic cells in the synovium of Bid-/- compared to Wt mice. These data suggest that extrinsic and intrinsic apoptotic pathways cooperate through Bid to limit development of inflammatory arthritis.

Bim deficiency leads to exacerbation and prolongation of joint inflammation in experimental arthritis

OBJECTIVE

: Rheumatoid arthritis (RA) is characterized by hyperplasia of the synovial lining, inflammation, and destruction of cartilage and bone. Since there are only a few detectable cells undergoing apoptosis in the joint, it is possible that a defect in apoptosis may contribute to synovial hyperplasia. This study sought to identify and characterize the direct role of apoptotic regulators in a mouse model of inflammatory arthritis.

METHODS

Using a serum transfer model, experimental arthritis was induced in mice lacking the proapoptotic Bcl-2 family genes Bak (Bak-/-), Bax (Bax-/-), or Bim (Bim-/-), as compared with wild-type (WT) control mice. Physical examination for edema of the ankles and histopathologic analysis of ankle sections were used to determine the severity of arthritis. The serum and ankles were examined for production of chemokines and cytokines using enzyme-linked immunosorbent or Luminex-based assays.

RESULTS

Bim-/- mice displayed increased severity and prolongation of arthritis. In contrast, Bak-/- and Bax-/- mice showed no difference in the severity of arthritis as compared with WT mice. In addition, Bim-/- mice had elevated levels of proinflammatory chemokines and cytokines, decreased joint and serum production of antiinflammatory cytokines, fewer TUNEL-positive cells, and reduced levels of active caspase 3 as compared with WT mice.

CONCLUSION

These studies are the first to demonstrate a role for the proapoptotic Bcl-2 protein Bim in the effector phase of RA. The findings indicate that Bim potentially functions to repress the effector phase of arthritis by regulating the milieu of the joint and serum, and by inducing apoptosis.