#4744 MODELIZATION OF THE GUT-RENAL AXIS OF IGA NEPHROPATHY BY DEVELOPING (A1KI+/+ PIGR−/−) GENOTYPE IN MICE
Authors: Majorel Jade , Bon Grégoire , Jullien Perrine , Paul Stéphane , Druilhe Anne , Cogne Michel , Maillard Nicolas 
Published: June 2023

Abstract

Background and Aims
IgA nephropathy is the most frequent primary glomerulonephritis worldwide, responsible for end stage renal disease within 20 years after diagnosis. The origin of the nephritogenic IgA1 in plasma remains poorly understood, but elements accumulate to suspect a mucosal origin after abnormal immune regulation. Herein, we propose a mouse model of IgA nephropathy, based on the modification of mucosal IgA synthesis and transport which drives an excess of polymeric forms of IgA1 in plasma. This model is based on (i) the presence of an IgA1 repertoire produced by mucosal plasma cells (Α1KI+/+ mice) and (ii) the absence of mucosal transcytosis of IgA allowed by the knockout of PIGR (PIGR−/−). This study aimed at describing the phenotype of such a mouse model which is supposed to circulate increased polymeric IgA1 derouted from a mucosal origin, which is a key feature of the human IgAN. The present study is aimed at describing the phenotype of this model (Α1KI+/+ PIGR−/−) through a mucosa-plasma-kidney axis, in comparison to wild type controls (WT), and Α1KI+/+ PIGR+/+.

Method
Tissue fragments were used for immunofluorescence. Antibodies anti-IgA humain (Igah) FITC, antibodies anti-IgA mice (IgAm) HRP, antibodies goat anti-IgG alexa fluor and antibodies goat anti mice C3 FITC are used. To determine the concentration of murine IgA in the mice studied, ELISA tests were performed with anti- IgAm antibodies not conjugated or conjugated with HRP. The determination of IgAh in mice, anti-IgAh rabbit antibodies and antibody IgAh AP were used. Electrophoresis was performed in non-reducing conditions on polyacrylamide gel, transferred to a blot and revealed using anti-mouse IgA or anti- human IgA.

Results
At mucosal level, the observation of ileal slices of (Α1KI+/+ PIGR−/−) mice, revealed that both IgA1h and IgAm were strongly localized in the subepithelial chorion of villi and lamina propria, much more than in WT and the Α1KI+/+ PIGR−/− conditions (figure 1). In serum, human IgA concentration was higher in sera issued from (Α1KI+/+ PIGR−/−) mice than serum from A1KI+/+PIGR+/+ and WT mice (figure 2A). The difference was even more striking for murine IgA with a 2log10 gap (figure 2B). The western blot revealed a marked accumulation of circulating polymeric forms of human IgA1 and murine IgA, mostly dimeric and trimeric (figure 2C). In kidney, immunofluorescence shows the presence of human IgA1, C3 and IgG deposit in renal glomeruli in (Α1KI+/+ PIGR−/−) mice (figure 3), with less IgA and C3 in A1KI+/+PIGR+/+ and no deposit in glomeruli of WT mice. It is noticeable that IgG can codeposit with human IgG in both Α1KI+/+ conditions.

Conclusion
This double genetically altered mouse model of IgA nephropathy (Α1KI+/+ PIGR−/−) display the mucosal-kidney axis of the human disease, by derouting polymeric IgA1 from a mucosal origin. Those IgA1 accumulate at a subepithelial stage, increase in serum with marked proportion of polymeric forms and deposit in kidney as pIgA1-IgG-C3 immune complexes. So this new murine model of IgA nephropathy could be helpful to investigate some potential therapeutic targets and increases the conviction of the role of mucosa to drive the pathogeny of the disease.