Background/Purpose: Response Gene to Complement (RGC)-32 is a cell cycle regulator widely expressed in normal tissues, multiple tumors and  a variety of cell lines. RGC-32 is induced by TGF-β in fibroblasts, astrocytes and human renal proximal tubular cells and mediates TGF-β dependent profibrotic pathways.  In immune cells, RGC-32 is upregulated preferentially in murine and human Th17 cells and promotes their differentiation in vitro and in vivo.  Increased expression of IL-17 in kidneys of SLE patients and lupus prone mice is critical for the development of lupus nephritis (LN). We have previously shown that RGC-32 expression is increased in T cells from SLE patients and in tubules and glomerular infiltrating cells in kidney biopsies of patients with LN. To directly assess whether RGC-32 plays a local role in LN downstream of antibody production, we used the nephrotoxic nephritis (NTN)  model of immune complex mediated glomerulonephritis  to compare parameters of disease severity in RGC-32 deficient and sufficient mice.

Methods: NTN was induced in WT and RGC-32-/- mice by immunization with sheep IgG in Complete Freund’s Adjuvant followed by injection of sheep nephrotoxic serum.  Proteinuria, blood urea nitrogen and kidney histopathology were determined to assess kidney function and damage.  Single cell suspension of kidneys and spleens were analyzed by flow cytometry.  Circulating levels and kidney deposition of mouse anti-sheep IgG were quantitated by ELISA and IF, respectively. Splenic B and T cell responses were characterized by flow cytometry. mRNA expression of IL-17A, CXCL1, CXCL5, collagen I, III, IV and FN was determined by RT-PCR.

Results: RGC-32 mRNA was significantly upregulated in the renal cortex and kidney infiltrating cells of WT mice with NTN compared to controls. RGC-32 KO mice displayed attenuated renal damage as shown by decreased proteinuria and glomerular scores and a trend for decreased blood urea nitrogen. RGC-32 deficiency did not interfere with the induction of NTN as mouse anti-sheep IgG titers, percentage of splenic germinal center B cells, plasma cells, effector CD4⁺ T cells, Tregs, IL-17A and IFN-g secreting cells did not differ between RGC-32 KO and WT mice. Furthermore, kidney deposition of autologous antibodies and C3 were comparable between the two groups. IL-17 mRNA expression in renal cortex and the proportion of CD4⁺ IL17A ⁺ cells  isolated from kidneys on day 7 after NTN induction were significantly upregulated in WT but not RGC-32 KO mice. RGC-32 KO mice displayed decreased frequency of infiltrating PMN and downregulation of CXCL1 and CXCL5, suggesting a decrease in IL-17 dependent neutrophil recruitement. Collagen I, III , IV and Fibronectin (FN) were significantly lower in  RGC-32 KO mice by RT- PCR, while trichrome and FN staining showed decreased interstitial, glomerular and periglomerular fibrosis.

Conclusion: These results suggest that RGC-32 contributes to the pathogenesis of immune complex mediated GN by promoting proinflammatory and profibrotic pathways. These data support further efforts to examine the mechanisms by which RGC-32 modulates these pathways and suggest that RGC-32 is a potential novel therapeutic target in the treatment of LN.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/response-gene-to-complement-32-exerts-proinflammatory-and-profibrotic-effects-in-immune-complex-gediated-glomerulonephritis/