The Study On HMGB1 And Its Receptor RAGE In The Pathogenesis Of Systemic Lupus Erythematosus

Background:Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of diverse types of autoantibodies in blood of patients that target tissues within their own body. Several system and organs can be affected through the immune complex pathway. SLE is usually diagnosed in women in their childbearing years. Compared with the male peers, the ratio is 7:1 to 10:1. The prevalence of SLE varies about 10-100/105 in the world,70/105 in China and 1:1000 in Chinese women.Up to now, the precise pathogenesis of SLE has not been fully understood. It has been documented that multifactorial interaction among various genetic, sex hormone and environmental factors may lead to disregulation in immune system and, ultimately the development of SLE. Immunological dysfunction almost covers the whole immune system in SLE, so it has been regarded as the prototype of autoimmune diseases. It has been observed that dysregulation of cytokine expression is very common in SLE, which is usually related to the breakage of immunological tolerance against native nuclear components. For instance, interferon-alpha (IFN-a) has been reported at a high level in the serum of SLE patients and high serum IFN-a activity is considered as a heritable risk factor for SLE. In patients with chronic infections and malignant diseases, an SLE-like syndrome can be induced during long-term IFN-a treatment, indicating that IFN-a plays an important role in the pathogenesis of SLE. Furthermore, as a strong inflammatory mediator, tumor necrosis factor (TNF) contributes to the pathogenesis of certain autoimmune diseases. In the serum of active SLE patients, TNF-a is markedly increased, which is associated with clinical disease activity. On the other hand, TNF can check the autoimmunity of immune regulation. TNF blockage not only suppresses the inflammatory manifestations of SLE, but also induces or increases autoantibodies to chromatin and to phospholipids. Of particular interesting is the finding that the level of high mobility group protein 1 (HMGB1), a novel alarmin, is increased in the sera of patients with SLE.HMGB1 is a ubiquitously expressed evolutionary conserved chromosomal protein. Its gene is located on human chromosome 13q12-13 and encodes a protein of 215 amino acids with a molecular weight of 25KD. It consists of two positively charged DNA binding domains (HMG box A and B) and a negatively charged C-terminal domain. The N-terminus contains heparin-binding motifs whereas the B-box confers proinflammatory activity to the protein and is involved in binding to the receptor for advanced glycation end products. The A-box functions as specific antagonist to inhibit the proinflammatory activity of HMGB1. Inside the cell, HMGB1 binds to DNA and modulates a variety of processes, including transcription. Outside the cell, HMGB1 can serve as an alarmin to mediate disease manifestations in animal models of sepsis and arthritis. Studies have shown that in these disease models, blocking HMGB1 significantly attenuate disease. In systemic sclerosis, HMGB1 is elevated in serum, which is associated with the disease severity and immunological abnormalities. Previous studies have demonstrated that extracellular HMGB1 is increased in the dermis and epidermis of skin lesions of patients with cutaneous lupus erythematosus and in the minor salivary glands of patients with Sjogren's Syndrome.It has been demonstrated that HMGB1 is secreted by both plasmacytoid DCs and myeloid DCs after stimulation with CpG oligodeoxynucleotide, and regulates the production of IFN-a through an autocrine pathway. Moreover, HMGB1 induces the production of TNF-a and IL-6 in monocytes. We hypothesize that HMGB1 may also contribute to autoimmune disorders including SLE, which is characterized by high-level IFN-a. So far, the precise role of HMGB1 in SLE has not been fully understood. The interaction and regulation between IFN-a, TNF-a and HMGB1 in SLE is still elusive. No investigation on the simultaneous changes on plasma HMGB1, as well as IFN-a and TNF-a has been conducted in SLE.Objectives:To investigate plasma level of HMGB1, IFN-a and TNF-a, as well as the possible association with autoantibodies production, clinical features, and laboratory parameters in SLE, so to determine the potential role of HMGB1 in the pathogenesis of SLE and interaction with IFN-a and TNF-a as well as the possibility of HMGB1 as an efficient therapeutic target.Methods:A total of 37 patients and 39 sex- and age- matched normal individuals were enrolled in the present study. All patients fulfilled the American College of Rheumatology classification criteria for the diagnosis of SLE. The demographic, clinical, and laboratory data were recorded at the time of blood collection (sex, age, disease duration, rash, arthritis, lupus nephritis, cytopenia, serositis, history of drug therapy, blood urea nitrogen level, serum creatinine, proteinuria, and blood routine examination). In addition, immunologic parameters including serum C3, C4, immunoglobulins, CRP, and autoantibodies including antinuclear antibodies (ANA), anti-Sm, anti-dsDNA, and anti-nucleosome antibodies (AnuA) were also analyzed. Plasma HMGB1, TNF-a, and IFN-a were determined with ELISA. The possible associations of these cytokines with disease activities, clinical features, serum levels of autoantibodies as well as certain laboratory parameters were also explored.Results:1.The plasma levels of HMGB1, TNF-a, and IFN-a were increased in SLE patients compared with those of HC (P<0.05). Moreover, the levels of HMGB1 and TNF-a in the active SLE patients were elevated compared with those in inactive patients and HC.2. Plasma levels of TNF-a and IFN-a were significantly increased in nephritis-positive SLE compared with those of HC, while the levels of TNF-a and IFN-a in nephritis-negative patients were not significantly different compared to that of nephritis-positive SLE patients and HC. Plasma level of HMGB1 in nephritis-negative patients was significantly higher than that in HC, whereas the levels of HMGB1 in nephritis-positive SLE patients versus nephritis-negative patients and HC were not significantly different.3. Plasma levels of HMGB1 in SLE patients positive for autoantibodies (anti-dsDNA, anti-Sm, AnuA) were not significantly different from those of their negative counterparts and HC.4. Plasma HMGB1 was positively correlated with peripheral neutrophils, and plasma TNF-a was positively correlated with anti-Sm, ESR and CRP, while plasma IFN-a was inversely correlated with the age and platelet level in SLE patients.Conclusions:1. Plasma HMGB1 was associated with disease activity in SLE, which was similar to TNF-a.2. IFN-a and TNF-a may be related to nephritis in SLE.3. High level of plasma IFN-a may be associated with thrombocytopenia in SLE.4. IFN-a may play different roles in the developing SLE and chronic SLE.5. No significant association was found between plasma HMGB1 and autoantibodies production in SLE. Background:Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of diverse types of autoantibodies in blood of patients that target tissues within their own body. Several system and organs can be affected through the immune complex pathway. A wide range of molecules are involved in SLE, therefore, the pathogenesis of the disease is complex and still unclear. It has been documented that multifactorial interaction among various genetic, sex hormone and environmental factors may lead to disregulation in immune system, and, ultimately the development of SLE.It has been demonstrated that increased apoptosis and decreased clearance of apoptotic material may underlie the pathogenesis of SLE. Release of pro-inflammatory mediators and autoantigens including HMGB1 also occurs in late apoptosis. HMGB1 may contribute to the pathogenesis of chronic inflammatory and autoimmune diseases due to its pro-inflammatory and immunostimulatory properties. Recent studies showed that increased serum levels of HMGB1 was associated with lupus disease activity, and HMGB1 may act as a proinflammatory mediator in anti-DNA antibody-induced kidney damage in SLE.HMGB1 binds to cell surface receptors including receptor for advanced glycation end products (RAGE), toll like receptor 2 (TLR2) and TLR4. RAGE was the first identified receptor for HMGB1, it is a transmembrane protein and a member of the immunoglobulin superfamily. RAGE-ligand binding results in phosphorylation of various protein kinases including MAPKs, Rac/Cdc42 and Jak/STATs, and subsequently activates NF-?B pathway. In addition to HMGB1,ligands for RAGE also includes AGE, S100/calgranulin family, amyloid-(3 and Mac-1. Researches indicated that HMGB 1-RAGE participated in the production of IFN-a, which play central role in the pathogenesis of SLE. Moreover, TNF-a and IL-6, which are implicated in association with disease activity or involvement of some organs in SLE, can be induced by extracellular HMGB1. It has been documented that RAGE seemed to involve in all responses that depend on HMGB1. All these imply that HMGB 1-RAGE pathway may participate in the pathogenesis of SLE.Soluble RAGE (sRAGE), a truncated form of the receptor, is composed of only the extracellular ligand-binding domain lacking the cytosolic and transmembrane domains. sRAGE is produced either by alternative splicing of RAGE mRNA or by carboxyterminal truncation of RAGE through metalloproteinase. sRAGE has the same ligand-binding specificity as RAGE and may function as a 'decoy' by binding pro-inflammatory ligands including HMGB 1 and preventing them from accessing cell surface RAGE. Zong et al. demonstrated that RAGE forms homodimers at the plasma membrane and dimerisation is an important step in RAGE signaling. sRAGE can also bind RAGE and inhibits RAGE dimerisation and subsequent activation of NF-?B pathways. Therefore, decreased sRAGE levels may indicate activation of RAGE signaling and enhanced inflammation.In recent years, the role of sRAGE in chronic inflammatory diseases has received increasing attention. Decreased serum level of sRAGE was demonstrated in primary SS, MS, KD and atherosclerosis and the resulted activation of HMGB 1-RAGE pathway, at least in part, contribute to the inflammatory state of related diseases. Moreover, administration of sRAGE was used as the therapeutic treatment in a number of experimental animal models and modulation of sRAGE levels by different treatments has been reported in few studies.Only one report published recently investigated the role of sRAGE in the pathogenesis of SLE. It showed that serum levels of sRAGE were increased in patients with SLE, and active SLE patients had even higher sRAGE levels compared to those in inactive patients. However, the main limitation of the study is the low case number (n=10). Further investigation with a larger cohort of SLE patients should be valuable to determine the potential role of sRAGE in the pathogenesis of SLE.Objectives:The present study was undertaken to investigate the characteristics of plasma sRAGE as well as the possible association with autoantibodies production, clinical features, and laboratory parameters in SLE, so to determine the potential role of sRAGE in the pathogenesis of SLE. Meanwhile the effect of different treatment on plasma sRAGE was also explored.Methods:A total of 105 patients and 43 sex- and age- matched normal individuals were enrolled in the present study. All patients fulfilled the American College of Rheumatology classification criteria for the diagnosis of SLE. The demographic, clinical, and laboratory data (sex, age, disease duration, clinical characteristics including rash, arthritis, vasculitis, myositis, serositis, and renal, hematology disorders, history of drug therapy, blood urea nitrogen level, serum creatinine, proteinuria, and blood routine examination) were recorded at the time of blood collection. Meanwhile, immunological parameters including serum C3, C4, immunoglobulins, CRP and autoantibodies (ANA, anti-dsDNA, AnuA, anti-Sm) levels were also analyzed. Plasma sRAGE were determined with ELISA. The possible associations of sRAGE with disease activities, clinical features, autoantibodies, and certain laboratory parameters were also explored. Meanwhile the effect of different treatment on plasma sRAGE was also investigated.Results:1. Plasma levels of sRAGE in SLE patients were significantly lower than those in HC (P=0.003). There was no significant difference between the level of sRAGE in active SLE patients and that in inactive SLE patients (P=0.303).2. SLE patients with rash or serositis had higher levels of plasma sRAGE than their negative counterparts (P=0.039 and P=0.02, respectively). SLE patients with nephritis, arthritis, vasculitis or hematological disorders had comparable sRAGE levels in comparison to their negative counterparts.3. Untreated and treated SLE patients had comparable sRAGE levels. No significant difference of plasma sRAGE was observed in patients receiving monotherapy of corticosteroids, therapy of corticosteroids combined with antimalarials or therapy of corticosteroid combined with immunosuppressors. Plasma sRAGE in patients receiving short period treatment (<1 month) showed an immediate decrease compared to the untreated patients (P=0.023). In contrast, the levels of plasma sRAGE in patients receiving long period treatment (>1 month) were significantly increased compared to those with short period treatment (P=0.000) and comparable to those in HC (P=0.305).4. sRAGE levels were negatively correlated with the leukocyte count, absolute values of lymphocytes, neutrophils and monocytes in peripheral blood of SLE patients (P<0.05 for all).5. There was no significant difference between the sRAGE levels in autoantibody-positive patients and those in autoantibody-negative patients.6. Plasma sRAGE was not correlated with age, age at disease onset and duration of disease in SLE patients.Conclusions:1. The significant decreased levels of sRAGE in SLE patients may be associated with enhanced inflammation in SLE, support the essential role of RAGE in SLE clinical pathology.2. Long period anti-lupus treatment counteracts the decreased sRAGE levels in SLE patients.3. Plasma sRAGE was associated with certain clinical characteristics in SLE patients.4. The level of plasma sRAGE was not associated with autoantibodies production in SLE patients.5. Plasma sRAGE was not correlated with disease activity in SLE patients.6. Plasma sRAGE was not related to age, age at disease onset and duration of disease in SLE patients.