FRI0294 Injured podocytes express complement factor h and process immune complex deposition in glomerular subendothelial area

Background Glomerular Immune complex (IC) deposition causes glomerulonephritis in lupus nephritis. The reaction of intrinsic glomerular cells differs according to the area of IC deposition. Subepithelial IC deposits cause functional and structural changes on podocytes (glomerular visceral epithelial cells) through complement pathway activation as is well known in membranous glomerulonephritis. In this setting, podocytes can induce some complement factors including complement factor H (CFH) which serves not only to regulate the alternative pathway but also to process subepithelial IC deposition.1 However, whether podocyte processing of IC deposition is limited to only the subendothelial area is obscure. Objectives To clarify the role of podocytes in IC deposition in the glomerular subendothelial area. Methods NEP25 mice genetically expressing human CD25 in podocytes were used. Intravenous immunotoxin for human CD25 (LMB2) provokes podocyte-specific injury (NEP25/LMB2). By shortening the period of LMB2 exposure to NEP25 mice, we mitigated the podocyte injury. We administered intraperitoneally IgG3-producing hybridoma clones, 2B11.3, which were previously established from an unmanipulated MRL/lpr mouse, to NEP25 mice (NEP25/hybridoma). Furthermore, we also injected short-term LMB2 to NEP25/hybridoma mice (NEP25/hybridoma/LMB2). We investigated IC deposits by immunofluorescence and electronic microscopic study. We measured complement regulatory factor mRNA expression including CFH, complement factor I (CFI), decay-accelerating factor (DAF), complement receptor 1-related gene/protein y (Crry), C3a receptor (C3aR) and C5a receptor (C5aR) of isolated glomeruli of each mouse by quantitative real time-PCR. In an in vitro study, we assessed CFH mRNA expression of immortalised mouse podocytes injured by puromycin. Results First, NEP25/LMB2 mice showed glomerular tuft collapse with epithelial cell hyperplasia, suggesting podocyte loss by light microscopy study as reported previously. mRNA expression of all complement regulatory factors but C5aR was decreased in NEP25/LMB2 mice as compared with NEP25 mice. This result suggests that podocytes produce these complement regulatory factors. On the other hand, when the podocyte injury was mitigated, CFH and C3aR mRNA expression increased, and CFI, DAF and Crry mRNA expression decreased as compared with NEP25 mice. Second, we detected IC deposition only in the glomerular subendothelial area without endocapillary proliferative lesion in NEP25/hybridoma mice. They showed increase of C3aR mRNA expression, and decrease of CFI and DAF mRNA expression as compared with controls. Notably, subendothelial IC deposition did not alter CFH mRNA expression. Third, NEP25/hybridoma/LMB2 (milder podocyte injury) showed decrease of IC deposits in glomeruli and increase of only CFH mRNA expression (1.7-fold) as compared to NEP25/hybridoma mice, while there was no significant change in mRNA expression of other complement regulatory factors. Finally, puromycin-induced mild podocyte injury promoted CFH mRNA expression in cultured podocytes as compared to controls. Conclusions Mildly injured podocytes induce CFH expression, and serve to process IC deposition in the glomerular subendothelial area. Reference [1] J Am Soc Nephrol2007;18:1157–66. Disclosure of Interest None declared