Steroid-Resistant Idiopathic Nephrotic Syndrome Reveals a Distinct Maladaptive Molecular State

Idiopathic nephrotic syndrome (iNS) is clinically classified by treatment response; however, the molecular basis of multidrug resistance remains poorly defined. We hypothesized that multidrug-resistant disease represents a distinct biological state rather than a more severe form of active disease.

Serum proteomic profiling using liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed in 165 pediatric and young adult patients with iNS, stratified as steroid-dependent nephrotic syndrome (SDNS), multidrug-dependent nephrotic syndrome (MDNS), or multidrug-resistant nephrotic syndrome (MRNS), and compared with healthy donors. Differential expression, pathway enrichment, and multivariate modeling were used to identify discriminative proteins. Selected biomarkers were validated using enzyme-linked immunosorbent assay (ELISA) and independently replicated in a separate validation cohort. Functional effects of patient-derived sera were assessed in cultured human podocytes and peripheral blood mononuclear cells (PBMCs).

Of 810 quantified proteins, 322 differed significantly across clinical groups. A 35-protein signature discriminated MRNS from MDNS and SDNS phenotypes. Integrated analyses identified dystroglycan 1 (DAG1), CD44 antigen (CD44), and RISC-loading complex subunit (TARBP2) as principal contributors to phenotype separation. ELISA confirmed increased DAG1 in MRNS, preserved TARBP2 in remission, and increased CD44 in active disease. Sera from patients with MRNS induced coordinated alterations in cytoskeletal organization, proteostasis, autophagy, and survival signaling in podocytes. An inverse distribution of endoplasmic reticulum (ER) chaperone BIP (GRP78) and phosphorylated AKT (pAKT) was observed in both serum-treated podocytes and patient PBMCs.

MRNS is associated with a distinct proteomic and functional profile characterized by coordinated stress-response dysregulation, supporting biologically informed disease stratification.