SAT-368 Galactose-deficient IgA1 containing immune complexes deposit in mesangium via endothelial cell injuries

Abstract

IgA nephropathy (IgAN) is the most common primary glomerulonephritis, and causes end-stage renal disease in 20–40% of patients within 20 years after onset of this disease. IgAN is defined by the presence of dominant or co-dominant mesangial IgA1 immune deposits, accompanied by C3 deposits, and deposition of IgA1 includes galactose-deficient IgA1 (Gd-IgA1). Serum levels of Gd-IgA1 and Gd-IgA1-containing immune complexes (IC) with Gd-IgA1-specific autoantibodies are elevated in patients with IgAN. However, the pathogenic role of Gd-IgA1-containing IC and mesangial immune deposits are still unclear. The endothelial surface glycocalyx modulates vascular function. Furthermore, loss of the glomerular endothelial glycocalyx links albuminuric kidney disease. Therefore, we examined that Gd-IgA1-containg ICs deposit in mesangium through glomerular endothelial cell disorder. Gd-IgA1 and recombinant anti-glycan IgG were used to form IC (Gd-IgA1-IgG IC) to inject i.v into nude mice. After various time intervals, mice were sacrificed and kidney was harvested to determine mesangial deposition and kidney injuries. Samples of urine were collected to determine urinary protein and hematuria. Furthermore, human renal glomerular endothelial cells (HRGEC) were co-cultured with Gd-IgA1 alone or Gd-IgA1-IgG IC for 72 h to assess the potential capacity of these IC to activate endothelial cells. Transcript levels of TNF-α, TGF-β, IL-6, ICAM1 and E-selectin in HRGEC were measured by Real-time PCR. Also, to investigate that Gd-IgA1-IgG IC stimulation increases permeability of glomerular microvascular resulted in renal injuries, the renal microvascular endothelial glycocalyx removal was estimated by real-time glycocalyx imaging. Gd-IgA1 alone or Gd-IgA1-IgG IC were injected into nude mice. The glycocalyx were observed for 45 min and after that mice were sacrificed to confirm glomerular deposition. Gd-IgA1 and anti-glycan IgG formed IC that deposited with murine C3 in the mesangium and in small amounts in the subendothelial area of the glomerular capillaries, and induced proteinuria and hematuria. Electron microscopic examination showed that injection of Gd-IgA1-IgG IC induced podocyte and endothelial injuries. Stimulation with Gd-IgA1-IgG IC upregulated transcript levels of TNF-α, IL-6, ICAM1 and E-selectin in HRGEC (P<0.01). Real-time glycocalyx imaging showed that Gd-IgA1-IgG IC removed renal microvascular glycocalyx immediately after injection. Furthermore, after stimulation with Gd-IgA1-IgG IC, IgA and C3 were deposited in mesangium, and proteinuria and hematuria were induced. Gd-IgA1-containg IC might bind to glomerular endothelial cells and induce release of pathogenic cytokines and chemokines. Furthermore, stimulation of Gd-IgA1-containg IC involved in endothelial dysfunction with complementary activation resulted in renal injuries.