Therapeutic strategies targeting rage improves renal outcome in lupus nephritis

Abstract Background and Aims Lupus nephritis (LN) occurs in up to 60% of patients with systemic lupus erythematosus (SLE). Despite of current development of immunosuppressant agents, LN still impairs the survival and quality of life in SLE patients. Receptor for advanced glycation endproducts (RAGE) is a multi-ligand receptor that belongs to the immunoglobulin superfamily, which is strongly associated with innate immune system. In the present study, we examined whether RAGE is involved in the development of LN. Further, we explored the therapeutic impact of DNA-aptamer directed against RAGE on lupus-related kidney injury. Method [Protocol 1] RAGE expression in kidneys and urinary RAGE excretion (uRAGE) were determined at 8, 12, 16, 18, 20-week-old by real-time PCR and ELISA, respectively in MRL/lpr, SLE-prone mice. [Protocol 2] LN was induced by peritoneally injecting pristane in wild type and RAGE globally knockout mice. [Protocol 3] MRL/lpr mice were subcutaneously administrated with DNA-aptamer raised against RAGE (RAGE-apt) or Control-aptamer (Ctrl-apt) for 10weeks. Results [Protocol 1] uRAGE, but not urinary protein excretion, was increased in 8-week-old MRL/lpr mice when compared to that of the control of MRL/MPJ mice. uRAGE is positively correlated with urinary NAG, a tubular injury marker, suggesting that uRAGE can predict the onset and the progression of LN. Immunofluorescence staining demonstrated that RAGE was upregulated in distal tubules but not in glomerulus in early stage, meanwhile RAGE started to be extensively expressed in nephron at late stage of LN. Not only tubules, but RAGE was also found in infiltrated macrophages in glomerulus. In proximal tubules (PTC), RAGE was co-localized with cathepsine D, a lysosomal aspartyl protease, and Rab7, a marker of late endocytosis, suggesting that PTC RAGE is involved in endosome-related protein degradation. [Protocol 2] Pristane-induced the increase in systolic blood pressure was reduced with improvement of renal dysfunction in RAGE knockouts. RAGE knockouts also showed less fibrosis with the decrease in macrophage infiltration when compared to wild type mice in pristane-induced lupus nephritis. [Protocol 3] Similar to RAGE knockouts, administration of RAGE-apt reduced systolic blood pressure and attenuated the renal dysfunction. RAGE-apt also ameliorated mesangial expansion, crescent formation, and macrophage infiltration into glomerulus in MRL/lpr mice. The level of pro-inflammatory cytokines gene expression including IL-6, TNF-a, and MCP-1 was reduced by RAGE-apt, but not Ctrl-apt, in MRL/lpr mice. Conclusion RAGE could be involved in the pathogenesis of LN, and RAGE-DNA aptamer might be one of the promising therapeutic strategies for preventing the development of LN.