The differential expression of MAGI2 in glomerulopathies and its application as a molecular discriminator of podocytopathies.

Background: Podocyte dysfunction is central to various glomerular diseases, necessitating reliable biomarkers for early detection and diagnosis. This study investigates the regulatory mechanisms of membrane-associated guanylate kinase inverted 2 (MAGI2) and its potential as a biomarker for podocytopathies.

Methods: Using fluorescence confocal laser scanning microscopy and super-resolution structured illumination microscopy of immunostained tissue sections of murine, human, and zebrafish tissue we investigated the subcellular location of MAGI2 in the kidney. We assessed the differential regulation of MAGI2 in glomerular disease animal models, and isolated glomerular dedifferentiation using immunostainings and LC-MS/MS tandem mass spectrometry. With CRISPR-Cas9, we generated zebrafish F0 generation mutants lacking either the zebrafish orthologue magi2a or nphs1.

Results: The expression of the gene coding for the scaffolding protein MAGI2 was examined across four species and demonstrated to be conserved within the podocyte filtration slit. In vitro and in vivo studies using isolated glomeruli and mammalian animal models of glomerular disease, including DOCA-salt hypertension, nephrotoxic serum nephritis, and puromycin aminonucleoside nephropathy, demonstrated significant downregulation of MAGI2 in injured podocytes. This downregulation was also conserved in a zebrafish model of focal and segmental glomerulosclerosis (FSGS), and the podocyte-specific MAGI2 ortholog Magi2a was reduced post podocyte injury. CRISPR/Cas9-generated zebrafish mutants for magi2a exhibited marked glomerular filtration barrier defects and downregulation of nephrin, underscoring MAGI2's critical role in podocyte function. Human biopsy analyses revealed differential MAGI2 expression: it was increased in minimal change disease (MCD) patients but significantly decreased in primary, but not secondary FSGS cases. As MAGI2 localization did not change in disease states it is an alternative marker for super-resolution microscopy-based morphometry of the filtration slit, correlating with nephrin-based measurements.

Conclusions: These findings highlight the potential of MAGI2 as a sensitive biomarker for podocyte injury and its diagnostic utility as a molecular discriminator in differentiating between primary FSGS and MCD in kidney biopsies.