Aberrant glycosylation of IgG in children with active lupus nephritis alters podocyte metabolism and causes podocyte injury

Background Podocytes are integral to the maintenance of the glomerular filtration barrier. Their injury results in proteinuria and disease progression in lupus nephritis (LN). Aberrant IgG glycosylation drives podocyte injury in LN and leads to cytoskeletal rearrangement, motility changes and decreased nephrin production. Based on these findings, we hypothesized that IgG glycosylation patterns differentiate SLE with and without LN and that this aberrant glycosylation reprograms podocyte metabolism. Methods IgG was isolated from forty pediatric SLE and from 7 healthy control samples. N‐glycan analysis was performed utilizing mass spectrometry. IgG deglycosylation was performed through enzymatic treatment by PNGase‐F for functional studies in podocytes. Untargeted metabolomics was performed in cultured podocytes after exposure to healthy, LN derived or deglycosylated LN IgG and analyzed by MSEA. Digital droplet PCR was utilized to evaluate urine cells and podocytes in culture for pyruvate kinase expression. Results The glycosylation pattern of IgG from children with LN was different from that in children with SLE without kidney involvement. Successful treatment led to normalization of IgG glycosylation. Cultured podocytes treated with LN‐derived IgG had a lower rate of glycolysis compared to podocytes incubated with deglycosylated LN‐IgG or IgG from healthy volunteers. Untargeted metabolomics of podocytes revealed glycolysis as the most enriched pathway in LN and identified 5 key metabolites (pyruvic acid, phosphoenolpyruvic acid, 2‐phosoglycerate, 3 phosphoglycerate, fructose 1,6 bisphosphate) whose levels significantly differed between podocytes exposed to LN‐derived IgG (LN‐IgG) compared and healthy and deglycosylated LN‐IgG. This analysis also revealed clustering around a rate limiting step of glycolysis catalyzed by PKM. Urine analyses revealed elevated pyruvic acid and greater expression of pyruvate kinase in podocytes shed in urine in patients with LN compared to levels in patients with SLE without kidney involvement.. Podocytes in culture had elevated PKM levels when exposed to LN‐IgG compared to IgG from patients with non‐renal SLE and LN in remission. Conclusions Aberrant IgG glycosylation develops in children with LN and adversely alters podocyte metabolism, rendering these cells vulnerable to injury. Successful treatment reverses IgG glycosylation to patterns comparable to those in non‐renal SLE patients. These data lay a strong foundation for larger translational studies evaluating the potential of IgG glycosylation as a predictive and pharmacodynamic biomarker for LN. This work also supports a need for development of approaches to control the aberrant glycosylation of self‐targeting IgG in LN patients as a mechanism to minimize podocytopathy.