Abnormal IgG Sugar Coating Hijacks Kidney Cell Energy in Pediatric Lupus

Lupus nephritis (LN) affects up to 80% of children with systemic lupus erythematosus (SLE) and is the leading cause of morbidity in pediatric SLE. Unlike adults, children experience a more aggressive disease course, making early detection and mechanistic understanding critical. Podocytes—the highly specialized epithelial cells forming the glomerular filtration barrier—are primary targets of autoimmune injury in LN, and their loss (podocytopenia) leads to irreversible kidney damage and proteinuria.

This study investigated whether the glycosylation pattern of circulating IgG differs between pediatric LN and non-renal SLE, and whether aberrant IgG glycosylation reprograms podocyte metabolism. IgG was isolated from 40 pediatric SLE patients (with and without active LN, and in remission) and 7 healthy controls. N-glycan analysis was performed using high-resolution mass spectrometry. Functional studies used an immortalized human podocyte cell line exposed to LN-derived IgG (LN-IgG), deglycosylated LN-IgG (treated with PNGase F enzyme), or healthy control IgG. Untargeted metabolomics identified pathway-level changes, and digital droplet PCR assessed pyruvate kinase M (PKM) expression in cultured podocytes and urinary shed podocytes from patients.

N-glycan profiling revealed that IgG from children with active LN carried a glycome meaningfully different from that of non-renal SLE patients and healthy controls. Specifically, glycan compositions associated with pro-inflammatory, podocyte-injurious properties were enriched in LN. Notably, successful immunosuppressive treatment reversed IgG glycosylation toward patterns seen in non-renal SLE, suggesting glycosylation tracks disease activity. Intracellular calcium measurements in podocytes showed increased calcium influx following LN-IgG exposure, consistent with upstream activation of the CaMK4 signaling axis previously linked to podocyte cytoskeletal injury.

Metabolomic profiling identified glycolysis as the most significantly altered pathway in podocytes exposed to LN-IgG. Five key glycolytic metabolites—pyruvic acid, phosphoenolpyruvic acid, 2-phosphoglycerate, 3-phosphoglycerate, and fructose 1,6-bisphosphate—were significantly dysregulated compared to podocytes exposed to healthy IgG or deglycosylated LN-IgG. The changes clustered around the rate-limiting step catalyzed by pyruvate kinase M (PKM). Podocytes exposed to LN-IgG showed elevated PKM protein levels, and urine from LN patients contained higher pyruvic acid concentrations and greater PKM expression in shed podocytes compared to non-renal SLE patients. Critically, deglycosylation of LN-IgG abolished these metabolic effects, confirming that the glycan moieties—not the antibody protein backbone—are responsible for the metabolic reprogramming.

These findings carry important implications. IgG glycosylation patterns could serve as early, pharmacodynamic blood biomarkers for LN—potentially preceding conventional markers like creatinine or GFR changes. PKM and urinary pyruvic acid emerge as candidate non-invasive urine biomarkers. Therapeutically, strategies aimed at correcting aberrant IgG glycosylation (e.g., glycoengineering approaches, metabolic interventions targeting PKM) represent a novel mechanistic avenue to protect podocytes and reduce LN progression. The study lays groundwork for larger translational studies and future interventional trials.