Idiopathic focal segmental glomerulosclerosis plasmas increase lipid droplet formation and perilipin-2 expression in human podocytes

Background: Many patients with idiopathic focal segmental glomerulosclerosis (FSGS) develop recurrence of proteinuria after kidney transplantation. Several circulating permeability factors (CPFs) responsible for recurrence have been suggested, but there is no consensus about the identity of CPFs in FSGS. We aimed to find proteins involved in the mechanism of action of the CPF(s) and/or potential biomarkers for the presence of CPF(s). Methods: Cultured human podocytes were exposed to plasma from patients with FSGS with presumed CPF(s), or from (disease) controls. Podocyte proteomes were analyzed by mass spectrometry and differentially expressed proteins were validated using flow cytometry, RT-PCR, and immunofluorescence. Changes in podocyte granularity were examined using flow cytometry, electron microscopy imaging and BODIPY staining. Results: Perilipin-2 protein expression was increased in podocytes exposed to presumed CPF-containing plasmas, which was related to disease state and capacity of plasma to induce granularity in podocytes. Elevated perilipin-2 levels were confirmed at protein and mRNA level. The granules observed in podocytes actually are lipid droplets. Importantly, increased perilipin-2 staining was also detected in glomeruli of the FSGS patients whose active disease plasmas induced lipid droplets in podocytes. Conclusions: Our study demonstrates that presumably CPF-containing plasma from FSGS patients alter podocyte lipid metabolism and increase perilipin-2 protein and lipid droplet accumulation. Future research should address the mechanism underlying CPF-induced alterations in podocyte lipid metabolism in the context of the pathogenesis of (recurrent) FSGS, which ultimately may result in novel leads for treatment.