Background/Purpose:

B cell depletion therapies have been efficacious in several glomerulopathies. The contributions of B cells to proteinuria and foot process effacement remain unknown. The development of a murine model of B-cell induced proteinuria would enhance our understanding of immune-based glomerular diseases.

Methods:

The B cell model antigen model hen egg lysozyme (HEL) was biotinylated and complexed to avidin. Following intravenous (IV) injection in mice, purified naïve HEL-specific B cells were adoptively transferred and proteinuria assessed using PAGE. Kidneys were processed for immunofluorescence (IF), H&E and PAS staining, and scanning electron microscopy (SEM). Cultured podocyte membrane ruffling was assessed with DIC videomicroscopy.

Results:

HEL embedded within the glomerular basement membrane (GBM) following IV injection. Proteinuria occurred after the transfer of HEL-specific B cells and was associated with foot process effacement. No antibody or complement deposition was observed in the GBM. 2-photon microscopy of live mice demonstrated that HEL-specific B cells arrested trafficking within glomeruli in the presence of HEL.

The rapid kinetics of proteinuria induction suggested cytokines secreted by activated intraglomerular B cells may be responsible. We hypothesize that activation of the small Rho GTPase Rac is important in podocyte injury by virtue of its ability to regulate the actin cytoskeleton. Using murine cultured podocytes, we measured membrane ruffling in the presence of cytokines as a surrogate for Rac activation. IL-4 significantly increased cultured podocyte membrane ruffling and induced foot process retractions on ex vivo fragments of renal cortex. Hydrodynamic DNA immunization of wild-type 129 mice with plasmid encoding IL-4 lead to proteinuria.

Conclusion:

We have developed a novel model of B cell-induced proteinuria with foot process effacement. Furthermore, these data demonstrate that cytokines can induce alterations in foot process morphology, leading to proteinuria. This has important implications in therapies preserving podocyte function in glomerular disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-novel-murine-model-of-b-cell-mediated-proteinuria-suggests-cytokines-mediate-podocyte-injury/