Kidney Week

Abstract: FR-PO847

Na+-K+-ATPase Enables Pathological B Cell Survival and Leads to Glomerular Basement Membrane (GBM) Thickening in Lupus Nephritis

Session Information

• Glomerular Diseases: Inflammation and Immunology
  October 25, 2024 | Location: Exhibit Hall, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Glomerular Diseases

• 1401 Glomerular Diseases: Mechanisms, including Podocyte Biology

Authors

• Ishaq, Tayyaba, Yale University School of Medicine, New Haven, Connecticut, United States

Tayyaba Ishaq, MS

• Chernova, Irene, Yale University School of Medicine, New Haven, Connecticut, United States

Irene Chernova, MD, PhD

Background

The kidney in lupus nephritis (LN) is characterized by a significant immune cell infiltrate and glomerular pathology. How lymphocytes lead to the characteristic damage of glomerular structures in LN is poorly understood. We recently published that intrarenal B lymphocytes upregulate Na⁺-K⁺-ATPase (NKA) in LN and that pharmacologic or genetic blockade of NKA results in fewer intrarenal B cells and reduced albuminuria, dependent on the genotype of the immune cell and not the host. As changes in kidney B cells were the only notable difference between control and NKA-inhibited mice, we hypothesize that kidney B cells affect glomerular basement membrane (GBM) structure and that mice with fewer kidney B cells would have preserved GBM and improved albuminuria.

Methods

We compared lupus-prone MRL^lpr and MRL^lpr.Fxyd2^-/- mice—which lack a gamma NKA subunit and have fewer intrarenal B cells—to define glomerular pathology. Podocyte and GBM pathology were investigated using immunofluorescence (IF), electron microscopy (EM) and real-time PCR.

Results

We found that MRL^lpr mice have proteinuria and thickened GBM on EM as compared to non-lupus B6 mice (277nm and 162nm, respectively, p<0.0001). Both proteinuria and GBM thickness were significantly improved in MRL^lpr.Fxyd2^-/- mice as compared to MRL^lpr controls (200nm and 277nm, respectively, p<0.0001). We found immune complex deposits in both genotypes, with no notable differences on EM. IF showed homogeneously thickened collagen IV staining in MRL^lpr as compared to MRL^lpr.Fxyd2^-/- mice (p<0.0001) while whole-kidney gene expression studies confirmed that the increased expression of glomerular collagen IV genes in MRL^lpr was reduced in the MRL^lpr.Fxyd2^-/- mice. We are currently investigating collagen IV expression in contributing cell types (i.e. podocytes and endothelial cells) as well as looking at metalloproteinases to see if collagen breakdown is affected. Additionally, we are characterizing lupus kidney cytokine profiles to test the hypothesis that B cell-derived cytokines are promoting abnormal collagen deposition in LN.

Conclusion

We show that lupus-prone MRL^lpr mice have a significantly thickened GBM when compared to non-lupus and MRL^lpr.Fxyd2^-/- animals, likely due to abnormal collagen IV deposition. We are currently investigating whether these findings are due to differences in intrarenal B cell numbers and cytokine levels.

Funding

• NIDDK Support