Expression Of High Mobility Group Box 1 In Murine Lupus Nephritis

Background and objectiveSystemic lupus erythematosus is a generalized autoimmune disease affecting multiple end-organs including the kidneys, and glomerulonephritis is a leading cause of death and disability in lupus. Many different factors contribute to the pathogenesis of lupus nephritis, and cytokine is one of the most important factors. Many cytokines may be involved in lupus nephritis, and the balance between proinflammatory cytokines and anti-inflammatory cytokines plays an important role in the immune response. High mobility group box chromosomal protein 1(HMGB-1), an intranuclear architerctural protein is well known for its nuclear functions. Recently, it has been identified as a potent proinflammatory cytokine. HMGB-1 could control the activation and chemotaxis of inflammatory cells, and it stimulates proinflammatory cytokine synthesis in inflammatory cells. Also, it is an endogenous immune adjuvant and endogenous signal for dendritic cell maturation and Th1 polarization, which can promote an effective inflammatory immune response. Many studies have showed that HMGB-1 was involved in autoimmune diseases, and it is a new therapy target for arthritis. The objective of this study was to determine the role of the novel proinflammatory cytokine HMGB-1 in lupus nephritis.Materials and MethodsKidney tissues and serum samples were obtained from MRL/lpr mice and age-matched C57BL/6J(control) mice at ages 6 weeks, 12 weeks and 20 weeks.The following were carried out:1. Anti-dsDNA antibodies levels in serum were determined by enzyme linked immunosorbent Assay (ELISA).2. Renal morphologic features were examined by light microscopy, electron microscopy, and immunohistologic analyses.3. The mRNA expression of HMGB-1, monocyte chemoattractant protein-1 (MCP-1) and interleukin-1 beta (IL-1beta) were investigated by RT-PCR.4. Immunofluorescence assay was employed to examine the localization of HMGB-1 in kidneys.Results1. MRL/lpr mice demonstrated characteristic alterations of serum immune parameters, with progressive increases in the levels of anti-dsDNA antibodies with age, compared with age-matched C57BL/6J(control) mice. The levels of anti-dsDNA antibodies in MRL/lpr mice were significantly higher than what in C57BL/6J mice at ages 12 weeks and 20 weeks2. Conventional histological staining of kidneys showed minimal abnormalities in MRL/lpr mice at ages 6 weeks. MRL/lpr mice demonstrate progressive development of renal damage, which is noticeable at ages 12 weeks and reaches significance at ages 20 weeks. The observed lesions included the presence of enlarged hypercellular glomeruli, with increased numbers of both resident cells and infiltrating leukocytes. A parallel increase in mesangial matrix was also noted. Prominent interstitial mononuclear cell infiltrating was also observed, with predominantly perivascular localization in the cortex and medulla of the kidneys. Crescents were identified in the later phases. In contrast, no histopathologic abnormalities can beobserved in C57BL/6J mice.3. Higher expression of HMGB-1 mRNA (0.853± 0.110) was found in MRL/Ipr mice than what in C57BL/6J mice(0.731 ±0.103). Expression of HMGB-1 was positively correlated with that of MCP-1 mRNA (P < 0.05).4. Strong expression of HMGB-1 protein was found mainly located in glomeruli of MRL/lpr mice, especially in the enlarged hypercelluar glomeruli, whereas weak and negative expression was found in glomeruli of C57BL/6J mice. HMGB-1 was mainly located in the cytoplasm and extracellular presence of secreted HMGB-1 was found.5. Lower expression of IL-1beta mRNA was detected in MRL/lpr mice than that of C57BL/6J mice over 12 weeks old.ConclusionTo our knowledge, this is the first report on the expression of HMGB-1 in murine lupus nephritis. The results of the present study demonstrate that the higher expression of HMGB-1 may contribute to the pathogenesis of lupus nephritis. It is suggested that higher expression of HMGB-1 could enhance the production of many inflammatory mediators such as MCP-1, et al, leading to the inflammatory and proliferation damages of glomeruli, through interacting with its receptors receptor for advanced glycation end products(RAGE).