Abstract
BackgroundRenal podocytes form the main filtration barrier possessing a unique phenotype maintained by proteins including podocalyxin and nephrin, the expression of which is suppressed in pathological conditions. We used an in vitro model of human glomerular epithelial cells (HGEC) to investigate the role of high glucose in dysregulating the podocytic epithelial phenotype and determined the time needed for this change to occur.ResultsIn our in vitro podocyte system changes indicating podocyte dedifferentiation in the prolonged presence of high glucose included loss of podocalyxin, nephrin and CD10/CALLA concomitant with upregulation of mesenchymal vimentin. Our study demonstrates for the first time that podocyte-specific markers undergo changes of expression at different time intervals, since glucose-mediated podocalyxin downregulation is a progressive process that precedes downregulation of nephrin expression. Finally we demonstrate that high glucose permanently impaired WT1 binding to the podocalyxin gene promoter region but did not affect WT1 binding on the nephrin gene promoter region.ConclusionThe presence of high glucose induced a phenotypic conversion of podocytes resembling partial dedifferentiation. Our study demonstrates that dysregulation of the normal podocytic phenotype is an event differentially affecting the expression of function-specific podocytic markers, exhibiting downregulation of the epithelial marker CD10/CALLA and PC first, followed by stably downregulated nephrin. Furthermore, it is herein suggested that WT1 may not be directly involved with upregulation of previously reduced PC and nephrin expression.
Highlights
Renal podocytes form the main filtration barrier possessing a unique phenotype maintained by proteins including podocalyxin and nephrin, the expression of which is suppressed in pathological conditions
Transient culture of human glomerular epithelial cells (HGEC) in high glucose resulted in reversible upregulation of vimentin protein expression Vimentin is a well-known mesenchymal marker and its upregulation is considered a significant marker of dedifferentiation [19] and podocyte injury [22]
Since HGEC permanently grown in 25 mM glucose (HGEC:25 mM) display almost totally suppressed PC levels, compared to HGEC exposed to 5 mM glucose (HGEC:5 mM) [12], we examined whether this change could be attributed to dysregulation of the podocytic phenotype, earmarked by enhanced vimentin expression
Summary
Renal podocytes form the main filtration barrier possessing a unique phenotype maintained by proteins including podocalyxin and nephrin, the expression of which is suppressed in pathological conditions. The loss of podocyte-specific proteins is reminiscent of dedifferentiation, which has been described as epithelial-to-mesenchymal transition (EMT) [3]. Injurious stimuli trigger different responses, ranging from podocytic hypertrophy and detachment to apoptosis [3]. Under these pathological conditions podocytes lose their specialized features and phenotype and may acquire mesenchymal markers [3,5]. This has been shown to be the case in HIV-induced nephropathy and collapsing glomerulopathy [6] as well as TGF-β-induced podocyte injury [7]
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