Animal models of studying the pathogenesis of multi-organ tissue damage in lupus.

Moderate-to-severe systemic lupus erythematosus (SLE) is characterized by extensive autoantibody deposition and persistent autoinflammation. As the existing animal models are limited in accurately reproducing the pathological characteristics of human SLE, we introduced a novel animal model simulating multi-organ autoinflammation through intra-organ injections. The model closely mimicked key features of SLE, including IgG deposition, inflammation, and tissue damage. The model could be used to assess the roles of IgG, immune cells, cytokines, and Fc gamma receptor (FcγR) in the pathogenesis of autoinflammation. The results obtained from this model could be confirmed by lupus MRL/lpr mice. The review suggested that the diagnostic criteria should be reconsidered to incorporate IgG deposition in tissues and highlighted the limitations of current T-cell and B-cell-focused treatments. To summarize, the IgG deposition model can be used to investigate the pathogenesis and treatment of multi-organ tissue damage associated with SLE.

Regulatory effects of autoantibody IgG on osteoclastogenesis.

Inflammatory arthritis is common in both systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), and eventually leads to bone homeostasis disorders. However, RA patients generally have severe bone destruction, which is rare in SLE patients. Recent studies have demonstrated that anti-citrullinated protein antibodies are important factors leading to bone destruction in RA. On the other hand, SLE patients present deposition of autoantibodies in the joints, which plays an important role in bone protection. These different phenomena occur because of the effects of the autoantibodies on the monocytes/macrophages during osteoclastogenesis, and the mechanisms underlying these effects differ between SLE and RA patients.

The role of neutrophils in skin damage induced by tissue-deposited lupus IgG.

Skin injury is the second most common clinical manifestation in patients with systemic lupus erythematosus (SLE). Neutrophils are crucial effector cells in the immune system but the significance of neutrophils in the pathogenesis of SLE is not clear. This study is to explore the role of neutrophils in the skin damage of SLE. We used lupus-prone mice and a C57BL/6 mouse model of lupus serum IgG-induced skin inflammation to investigate the role of neutrophils in skin damage of SLE. We found that a few neutrophils infiltrated the inflammatory sites of skin in lupus-prone mice and the lupus-IgG-induced skin damage mouse model. Depletion of neutrophils did not affect the development of skin inflammation caused by lupus IgG, and lupus IgG can induce apoptosis of neutrophils. The apoptosis of neutrophils induced by lupus IgG is related to FcγRIII and Fas/Fas ligand pathways. Our study indicates that neutrophils are not major contributors in the skin damage caused by tissue-deposited lupus IgG but death of neutrophils caused by lupus IgG may provide a resource of a large amount of autoantigens in SLE.

Pathogenesis of Skin Injury of Systemic Lupus Erythematosus.

PURPOSE OF REVIEW: The second most common clinical expression in lupus patients is skin damage that the pathogenesis remains unclear. We discuss the role of pathological factors in the development of skin damage in SLE. RECENT FINDINGS: Skin deposited IgG is a crucial pathologic factor in the development of skin damage in SLE. Macrophages and signaling of TNFα/TNFR1 and IFN/IFNR play an important role in the skin injury of SLE. The intracellular molecules including Syk and calcium/calmodulin 4 and NFAT are involved in the manifestation of skin damage in lupus-prone mice. UV is the most typical environmental factor to trigger skin injury in areas of IgG deposition in SLE. These evidences indicate that skin deposited IgG is a crucial pathological factor to trigger skin lesions in SLE and blockade of IgG signaling may be effective target against skin injury of SLE.

Skin inflammation induced by lupus serum was inhibited in IL-1R deficient mice.

Skin inflammation induced by lupus serum is a useful tool to investigate the pathogenesis of lupus skin injury. IL-1 is a proinflammatory cytokine, and its role in lupus skin lesion is still unclear. We determined the role of IL-1 in lupus skin injury by using gene deficient mice. We found that skin inflammation induced by lupus serum was significantly reduced in IL-1R deficient mice and caspase-1 deficient mice. IL-1R deficiency did not affect the expression of FcγRI (CD64), FcγRII (CD32) and MHC class II (CD74) induced by lupus serum. IL-1R deficiency reduced the lipid raft clustering, and decreased expression of MCP-1 and TNFα in monocytes. Keratinocyte proliferation induced by lupus serum was significantly decreased in TNFα deficient mice. Our findings indicate that IL-1 plays an important role in skin lesions of SLE. This study suggests that IL-1 is a therapeutic target in skin lesions of SLE.

The features of skin inflammation induced by lupus serum.

We recently developed a model of lupus serum-induced skin inflammation, which was used to study the pathogenesis of skin injury in systemic lupus erythematosus (SLE). We further characterized the features of lupus serum-induced skin inflammation. This skin inflammation was evident within 3h and lasted for at least two weeks. The skin inflammation was characterized by an influx of monocytic, CD11b+cells and by a scarcity of T and B lymphocytes. Depletion of IgG from the serum abrogated the skin inflammatory response. The skin inflammation was related to lupus patients' skin history but not to SLE disease activity and type of autoantibody. The expression of TNFR1, NF-kB and MCP-1 was increased locally in skin lesions. The TLR9 ligand and lupus serum act synergistically to trigger skin inflammation. These findings suggest that this novel model is valuable for the study of the pathogenesis and therapy of skin injury in SLE.

T cell CD3ζ deficiency enables multiorgan tissue inflammation.

Although a population of T cells with CD3ζ chain deficiency has been found in patients with systemic lupus erythematosus, rheumatoid arthritis, cancer, and infectious disease, the role of CD3ζ chain in the disease pathogenesis remains unknown. To understand the contribution of CD3ζ deficiency to the expression of organ injury, we have performed the following studies. We used CD3ζ-deficient mice to investigate the role of CD3ζ in the pathogenesis of organ tissue inflammation. We found that the CD3ζ(-/-) mice can spontaneously develop significant organ inflammation that can be accelerated following the administration of polyinosinic:polycytidylic acid or allogeneic cells (graft versus host). T cells from CD3ζ(-/-) mice display increased expression of the adhesion molecules CD44 and CCR2 and produce increased amounts of IFN-γ blockade, which mitigates tissue inflammation. Our results demonstrate that CD3ζ deficiency bestows T cells with the ability to infiltrate various tissues and instigate inflammation. Decreased CD3ζ expression noted in T cells from various diseases contributes independently to tissue inflammation and organ damage. Approaches to restore CD3ζ expression of the surface of T cells should be expected to mitigate tissue inflammation.

Immunoglobulin G inhibits glucocorticoid-induced osteoporosis through occupation of FcγRI.

Glucocorticoid-induced osteoporosis (GIOP) is a severe and common complication of long-term usage of glucocorticoids (GCs) and lacks of efficient therapy. Here, we investigated the mechanism of anti-inflammation effect and osteoclastogenesis side effect of GCs and immunoglobulin G (IgG) treatment against GIOP. GCs inhibited SLE IgG-induced inflammation, while IgG inhibited GCs-induced osteoclastogenesis. FcγRI and glucocorticoid receptor (GR) were found directly interacted with each other. GCs and IgG could reduce the expression of FcγRI on macrophages. The deficiency of FcγRI affected osteoclastogenesis by GCs and systemic lupus erythematosus (SLE) IgG-induced inflammation. Also, IgG efficiently reduced GIOP in mice. These data showed that GCs could induce osteoporosis and inhibit IgG-induced inflammation through FcγRI while IgG efficiently suppressed osteoporosis induced by GCs through FcγRI. Hence, our findings may help in developing a feasible therapeutic strategy against osteoporosis, such as GIOP.

Lupus serum IgG induces skin inflammation through the TNFR1 signaling pathway.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by high autoantibody levels and multiorgan tissue damage, including kidney and skin. Cutaneous manifestations are frequent in patients with SLE, yet the etiology and pathogenesis of skin injury in SLE remains unclear. We reasoned that lupus serum containing high levels of autoreactive Ig contributes to skin injury. In this article, we report that serum from SLE patients and lupus-prone mice induces skin inflammation following intradermal injection into normal mice. Lupus serum depleted of IgG failed to cause skin inflammation. Monocytes, but not lymphocytes, were found to be crucial in the development of lupus serum-induced skin inflammation, and lupus serum IgG induced monocyte differentiation into dendritic cells (DCs). TNF-alpha and TNFR1, but not TNFR2, were required for the development of lupus serum-induced skin inflammation. TNFR1, not TNFR2, represented the main molecule expressed in the skin lesions caused by injected lupus serum. Our studies demonstrated that lupus serum IgG causes skin injury by involving the TNFR1 signaling pathway and monocyte differentiation to DCs. Accordingly, disruption of the TNFR1-mediated signaling pathway and blockade of DC generation may prove to be of therapeutic value in patients with cutaneous lupus erythematosus.

Amelioration of inflammatory arthritis by targeting the pre-ligand assembly domain of tumor necrosis factor receptors.

Tumor necrosis factor (TNF)-alpha has an important role in the pathogenesis of autoimmune and inflammatory diseases such as rheumatoid and septic arthritis. The biological effects of TNF-alpha are mediated by binding to TNF receptors TNFR1 (also known as P60) or TNFR2 (also known as P80). The pre-ligand assembly domain (PLAD) is a portion of the extracellular region of TNFRs that mediates receptor-chain association essential for signaling. We found that soluble versions of PLAD, especially those derived from P60, block the biochemical effects of TNF-alpha in vitro and potently inhibit arthritis in animal models. Thus, targeting the PLAD may have clinical value in the treatment of human arthritis and other disorders involving receptors of the TNFR superfamily.

The role of organ-deposited IgG in the pathogenesis of multi-organ and tissue damage in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE), often known simply as lupus, is a severe chronic autoimmune disease that is characterized by multi-organ and tissue damage and high levels of autoantibodies in serum. We have recently investigated, using animal models, the role of organ-deposited IgG autoantibodies in the pathogenesis of organ and tissue damage in SLE. We found that intra-organ injection of serum from mice with lupus (i.e., lupus mice) into healthy mice triggered inflammation in tissue and organs but that serum from other healthy mice did not, and that the severity of inflammation was related to the dose of serum injected. Immunohistochemistry showed that a large number of IgG molecules are deposited at the site of organ and tissue damage in lupus mice, and that IgG is a major contributor to the development of tissue inflammation triggered by serum from lupus mice or patients. The development of tissue inflammation induced by IgG in serum from lupus mice requires the presence of monocytes/macrophages, but not of lymphocytes or neutrophils; tumor necrosis factor (TNF)/tumor necrosis factor receptor 1 (TNFR1) and interleukin 1 (IL-1) also play essential roles in the development of tissue inflammation triggered by IgG. In addition, it has been found that TNFR1 inhibitors can suppress skin injury in lupus mice and that spleen tyrosine kinase (Syk) inhibitors, which can block the signaling transduction of IgG/Fc gamma receptors (FcγRs), can prevent and treat skin injury and kidney damage in lupus mice. We have also observed that lupus IgG might protect against bone erosion. Based on these results, we conclude that IgG plays a crucial role in the development of organ and tissue damage in SLE and in protecting bone erosion and arthritis, and we suggest that the IgG/FcγR signaling pathway is an important therapeutic target in SLE.

ANGPTL4 Regulates Psoriasis via Modulating Hyperproliferation and Inflammation of Keratinocytes.

Background: Psoriasis is characterized by keratinocyte proliferation and massive inflammatory leukocytes infiltration, affecting 0.14%-1.99% of the world's population. Our aim was to identify novel potential therapeutic strategies for psoriasis. Methods: Weighted gene co-expression network analysis (WGCNA) was performed to identify gene modules that were closely related to psoriasis based on the GSE30999 dataset, which contained expression data from 85 patients with moderate-to-severe psoriasis. Then, angiopoietin-like 4 (ANGPTL4), one of the most related hub genes, was selected for in vitro and in vivo functional assays. In our experiments, imiquimod (IMQ)-induced psoriasiform dermatitis in mice and human keratinocytes (HaCaT) cells were used to study the potential roles and mechanisms of ANGPTL4 in psoriasis. Results: WGCNA analysis revealed the turquoise module was most correlated with psoriasis, and ANGPTL4 is one of the most related hub genes that significantly upregulated in psoriasis lesions compared with non-lesional skin. Consistent with the bioinformatic analysis, the expression of ANGPTL4 was significantly upregulated in IMQ-induced psoriasiform skin of mice. Exogenous recombinant ANGPLT4 protein treatment could promote the proliferation and induce the expression of inflammatory cytokines in HaCaTs, whereas silencing of ANGPTL4 effectively inhibited these effects. Then we demonstrated that recombinant ANGPTL4 protein exacerbated psoriasiform inflammation and epidermal hyperproliferation in vivo. Mechanismly, extracellular signal-regulated kinase 1/2 (ERK1/2) and signal transducer and activator of transcription 3 (STAT3) pathways were involved in ANGPTL4-mediated regulation of proliferation and inflammation. Conclusion: We found ANGPTL4 was significantly increased in IMQ-induced psoriasiform skin of mice. ANGPTL4 could promote keratinocyte proliferation and inflammatory response via ERK1/2 and STAT3 dependent signaling pathways in psoriasis.

Amelioration of Lupus Serum-Induced Skin Inflammation in CD64-Deficient Mice.

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disorder characterized by high autoantibodies levels and multiorgan tissue damage. The current study investigated the role of CD64 in SLE patients and animal models. According to a flow cytometry study, SLE patients showed an increase in CD64 expression in circulating monocytes. There was a correlation between CD64 and SLEDAI, blood urea nitrogen levels, and anti-Sm antibodies. In skin lesions of lupus MRL/lpr mice, there was high IgG deposition and CD64 expression. In vitro, cytokines IL-10 and IFN-γ upregulated CD64 expression in monocytes/macrophages that was inhibited by glucocorticoids. In CD64-deficient mice, skin inflammation induced by lupus serum was reduced. Furthermore, activation of spleen tyrosine kinase (Syk), Akt, and extracellular signal-regulated kinase (Erk) was inhibited in CD64-deficient monocytes. The results suggest that CD64 could be a biomarker for observing SLE progression, as well as a mechanistic checkpoint in lupus pathogenesis.

Targeted tumor necrosis factor receptor I preligand assembly domain improves skin lesions in MRL/lpr mice.

OBJECTIVE: Skin disease is the second most common manifestation in patients with systemic lupus erythematosus (SLE). Tumor necrosis factor receptor (TNFR) preligand assembly domain (PLAD) has been found to block the effect of TNFalpha, and TNFRI PLAD (p60 PLAD) inhibits inflammatory arthritis. This study was undertaken to investigate whether TNFR PLAD limits inflammatory skin injury in a mouse model of SLE. METHODS: Female MRL/lpr mice received p60 PLAD (100 microg/mouse intraperitoneally), p80 PLAD (100 microg/mouse intraperitoneally), or phosphate buffered saline (100 microl/mouse intraperitoneally) 3 times a week for 26 weeks, starting at age 6 weeks. RESULTS: Immunohistochemistry studies demonstrated that TNFRI but not TNFRII was dominantly expressed in skin lesions in MRL/lpr mice. We found that TNFRI PLAD (p60 PLAD) but not TNFRII PLAD (p80 PLAD) protein significantly inhibited skin injury in the MRL/lpr mouse model of lupus. NF-kappaB, monocyte chemotactic protein 1, and inducible nitric oxide synthase expression in skin lesions were significantly inhibited by p60 PLAD. Lupus serum-induced monocyte differentiation into dendritic cells was reduced by p60 PLAD, but p60 PLAD did not reduce IgG deposition in the skin or improve the progression of kidney damage in MRL/lpr mice. CONCLUSION: Our results indicate that TNFRI is involved in the expression of skin injury in MRL/lpr mice with lupus and that p60 PLAD or similar biologics may be of clinical value if applied locally.

Suppression of skin and kidney disease by inhibition of spleen tyrosine kinase in lupus-prone mice.

OBJECTIVE: Spleen tyrosine kinase (Syk) is involved in membrane-mediated signaling in various cells, including immune cells. It is overexpressed in T cells from patients with systemic lupus erythematosus (SLE), and its inhibition has been shown to improve T cell function as well as to improve disease manifestations in (NZB x NZW)F(1) lupus-prone mice and in patients with rheumatoid arthritis. While clinical trials examining Syk inhibition in patients with SLE are being considered, the aim of our experiments was to determine whether the therapeutic effects of Syk inhibition extend to other strains of lupus-prone mice and whether they result in improvement in skin disease and modification of established disease. METHODS: Female MRL/lpr or BAK/BAX mice were studied. Starting either at age 4 weeks (before disease) or at age 16 weeks (after established disease) and continuing for up to 16 weeks, mice were fed chow containing the Syk inhibitor R788 or control chow. RESULTS: We found that inhibition of Syk in MRL/lpr and BAK/BAX mice prevented the development of skin disease and significantly reduced established skin disease. Similarly, Syk inhibition reduced the size of the spleen and lymph nodes, suppressed the development of renal disease, and suppressed established renal disease. Discontinuation of treatment resulted in extended suppression of skin disease for at least 8 weeks and suppression of renal disease for 4 weeks. CONCLUSION: Syk inhibition suppresses the development of lupus skin and kidney disease in lupus-prone mice, suppresses established disease in lupus-prone mice, and may represent a valuable treatment for patients with SLE.

The role of bacterial DNA containing CpG motifs in diseases.

Bacterial DNA containing unmethylated CpG motifs can activate immune cells to release proinflammatory cytokines. Here, the role of bacterial DNA containing CpG motifs in diseases with a focus on arthritis is discussed. Our studies demonstrate that the intraarticular injection of bacterial DNA and oligodeoxynucleotides containing CpG motifs (CpG ODN) induced arthritis. The induction of arthritis involves the role of macrophages over other cells such as neutrophils, NK cells, and lymphocytes. TNF-α and TNFRI play an important role in the development of arthritis. NF-κB also plays a critical regulatory role in arthritis. Systemic anti-inflammatory treatment, along with antibiotic therapy, has beneficial effects on the course and the outcome of bacterial arthritis. Thus, future treatment strategies for bacterial arthritis should include attempts to minimizing bacterial growth while blocking the proinflammatory effects of the bacterial DNA. Significant therapeutic efficiency has also been shown by CpG ODN-mediated Th1 immune activation in mouse models of cancer, infectious disease, and allergy/asthma.

Fc Gamma Receptors as Regulators of Bone Destruction in Inflammatory Arthritis.

Bone erosion is one of the primary features of inflammatory arthritis and is caused by excessive differentiation and activation of osteoclasts. Fc gamma receptors (FcγRs) have been implicated in osteoclastogenesis. Our recent studies demonstrate that joint-deposited lupus IgG inhibited RANKL-induced osteoclastogenesis. FcγRI is required for RANKL-induced osteoclastogenesis and lupus IgG-induced signaling transduction. We reviewed the results of studies that analyzed the association between FcγRs and bone erosion in inflammatory arthritis. The analysis revealed the dual roles of FcγRs in bone destruction in inflammatory arthritis. Thus, IgG/FcγR signaling molecules may serve as potential therapeutic targets against bone erosion.

Cholera toxin B accelerates disease progression in lupus-prone mice by promoting lipid raft aggregation.

Infectious agents, including bacteria and viruses, are thought to provide triggers for the development or exacerbation of autoimmune diseases such as systemic lupus erythematosus in the genetically predisposed individual. Molecular mimicry and engagement of TLRs have been assigned limited roles that link infection to autoimmunity, but additional mechanisms are suspected to be involved. In this study we show that T cells from lupus-prone mice display aggregated lipid rafts that harbor signaling, costimulatory, inflammatory, adhesion, and TLR molecules. The percentage of T cells with clustered lipid rafts increases with age and peaks before the development of lupus pathology. We show that cholera toxin B, a component of Vibrio cholerae, promotes autoantibody production and glomerulonephritis in lupus-prone mice by enhancing lipid raft aggregation in T cells. In contrast, disruption of lipid raft aggregation results in delay of disease pathology. Our results demonstrate that lipid rafts contribute significantly to the pathogenesis of lupus and provide a novel mechanism whereby aggregated lipid rafts represent a potential link between infection and autoimmunity.

Lupus IgG deposition causes arthritis but inhibits bone destruction through competitive occupation of FcγRI and reduced RANKL signalling.

OBJECTIVES: Bone destruction is a remarkable feature of inflammatory arthritis. It remains unknown why arthritis associated with the systemic autoimmune/inflammatory condition systemic lupus erythematosus (SLE) does not result in erosion and destruction. We aimed to determine the role of autoantibody in the pathogenesis of non-erosive arthritis in SLE. METHODS: We analysed medical record of SLE patients, investigated whether autoantibody induces arthritis lacking bone destruction in animal models and determined whether SLE autoantibody inhibits osteoclastogenesis induced by RANKL in vitro experiments. RESULTS: We found that arthritis lacking bone erosions is common in SLE patients and lupus-prone mice. Intraarticular injection of lupus serum or IgG induces immune complex deposition and arthritis, but does not result in bone destruction. Deposition of IgG, monocytes/macrophages and TNF-α is all required for the development of arthritis. Lupus serum or IgG inhibits RANKL-induced differentiation of monocytes into osteoclast in a dose-dependent manner. FcγR acts as co-receptors for RANKL and is involved in osteoclastogenesis. Deficiency of FcγRII or FcγRIII does not affect osteoclastogenesis in the presence of SLE IgG. However, lupus IgG competes for FcγRI binding with RANKL, thereby reducing osteoclastogenesis. CONCLUSION: Observations from this study demonstrate that IgG from SLE patients can induce arthritis and inhibits RANKL-induced osteoclastogenesis through competitive occupation of FcγRI on monocytes/macrophages. This study improves the understanding of the pathophysiology of SLE-associated arthritis and offers a protective mechanism (FcγRI inhibition) that may be targeted in other forms of autoimmune/inflammatory arthritis, such as RA, to prevent or limit bone erosion and inflammatory bone loss.