Background/Purpose: Lupus nephritis is most common cause of mortality and morbidity in systemic lupus erythematosus (SLE) patients and 60% of SLE patients develops lupus nephritis. HRES-1/RAB4 genomic locus has been associated with disease manifestations in SLE patients (Arthritis Rheum. 58:532-520). Inhibition of Rab geranylgeranyl transferase prevented nephritis in lupus-prone mice (Ann. Rheum. Dis. 73:1887-1897). To investigate the role of Rab4A in lupus pathogenesis, we developed a mouse model Rab4A-KO^CD4Cre (Rab4A^KO; mice lacking expression of Rab4A in T cells relative to C57Bl/6 wild-type (WT) and floxed Rab4A^Q72L knock-in (Rab4A^Q72L) as a control. Previously we showed that Rab4A^Q72L knock-in prevents ANA production, immunoglobulin and C3 depositions in glomeruli and lymphocytic infiltration in kidneys relative to Rab4A^KO mice. These preliminary results provided rationale for testing our hypothesis that HRES-1/Rab4 plays a crucial role in SLE, including the pathogenesis of lupus nephritis.

Methods: Age and gender matched WT, Rab4A^Q72L and Rab4A^KO female mice were injected with 0.5 mL pristane per 20 g of body weight, intraperitoneally. 14 days post pristane injection, kidneys were fixed in formalin for H&E and PAS staining or snap freeze in OCT for confocal microscopy. To assess the podocyte injury, 8 µm frozen kidney sections were analyzed anti-podocin and anti-CD51 (Integrin αV). Frozen kidney sections were further analyzed using anti-CCR6 and anti-IL17. To study the effect of Rab4A on GLUT1 glucose transporter, Kidney sections were stained with anti-GLUT1. Splenic germinal centers were investigated using 6 µm frozen spleen sections stained with anti-B220, anti-F4/80, anti-CD3 and anti-CD138. Kidney histology was blindly evaluated by an expert pathologist.

Results: Kidney histology revealed accelerated glomerulonephritis (GN) (3-fold; p=7.6×10^-4), glomerulosclerosis (GS) (8-fold; p=0.0106) in Rab4A^KO mice relative to Rab4a^Q72L mice. Further, we found 1.7-fold reduction in podocin and 1.9-fold reduction in CD51 expression in kidneys of Rab4A^KO relative to WT mice (podocin, p=0.0027; CD51, p= 0.0002) or Rab4a^Q72L mice (podocin, p=0.03; CD51, p<0.0001), suggesting podocyte injury in Rab4A^KO animals. In addition, CCR6 and IL-17 expression by kidney-infiltrating lymphocytes was significantly higher in Rab4A^KO as compared to WT and Rab4a^Q72L mice. GLUT1 expression was elevated 4-fold and confined to the kidney medulla of Rab4A^KO mice relative to Rab4a^Q72L (p=0.004) and WT controls (p= 0.0001). Relative to WT controls, splenic germinal centers exhibited 1.3-fold increased size in Rab4A^KO mice (p= 0.0.0452) with 3-fold expansion of T cell zones (p< 0.0001) and 2-fold accumulation of plasma cells (p=0.0197). Interestingly, spleen sections from Rab4a^Q72L mice had smaller splenic germinal centers with fewer CD138⁺ plasma cells in comparison to WT (p=0.0002: p=0.0427) and Rab4A^KO mice (p= 0.0083).

Conclusion: The results suggest that Rab4A protects from nephritis in the pristane-induced model of SLE by limiting the germinal center formation and pro-inflammatory expression of GLUT1 and Integrin αV by renal epithelial cells.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/rab4a-protects-from-lupus-nephritis-by-limiting-germinal-center-formation-and-pro-inflammatory-expression-of-glut1-and-integrin-by-renal-epithelial-cells/