Molecular Mechanisms of Childhood Idiopathic Nephrotic Syndrome

Abstract

Idiopathic nephrotic syndrome (iNS), a podocytopathy, is the most common glomerulopathyin children, characterized by significant proteinuria, hypoalbuminemia, and edema, and is managed with steroid therapy. Despite the prevalence of iNS, it remains poorly understood, withno definitive etiology, and no reliable biomarkers for predicting relapse, remission, or long-term outcome. This thesis investigated the role of podocyte-derived extracellular vesicles (EVs), particularly large EVs (LEVs), as biomarkers of iNS disease activity, and as indicators of fundamental biological processes in the podocyte. I used integrated and novel approaches to further the molecular understanding of iNS, including in vitro models of podocyte stress, an in vivo rat nephrosis model, and urinary specimens from children with iNS. I identified that in vitro, podocytes respond to puromycin aminonucleoside (PAN)-induced injury by increasing vesiculation, and further that PAN induces a mitochondrial bioenergetic stress linked with packaging of LEVs with mitochondrial DNA (mtDNA). Prednisolone, the gold-standard immunomodulatory agent used in pediatric iNS, was shown to attenuate these PAN-induced impacts in vitro. Lastly, proteomic profiling of LEVs from podocytes, as well as those derived from urinary specimens from children, revealed hundreds of proteins specific to disease relapse, as well as PAN-induced podocyte stress. These novel observations suggest that LEVs reflect dynamic podocyte states which might reflect disease conditions in humans. This work provides the impetus for future studies directed at further understanding the LEV mtDNA and proteomic cargo which will offer further insights into iNS pathophysiology.