Focal segmental glomerulosclerosis (FSGS) is a heterogeneous renal histopathological entity that affects the glomerulus. It is characterized by podocyte injury, proteinuria and scarring of the... Show moreFocal segmental glomerulosclerosis (FSGS) is a heterogeneous renal histopathological entity that affects the glomerulus. It is characterized by podocyte injury, proteinuria and scarring of the glomerular tuft. In this thesis we investigated various mechanisms that are implicated in the development of FSGS. Firstly, we studied biopsy samples of patients with minimal change disease, a related glomerulopathy with minimal glomerular injury and better prognosis. We showed that loss of nephrin could serve as a biomarker for renal function loss and the progression to FSGS in this patient group. We also investigated renal biopsy material of patients with FSGS to determine the role of complement activation and endothelial-podocyte interaction in the pathogenesis of FSGS. We show that complement activation via the classical pathway and endothelial injury, especially via endothelin-1 signaling, are associated with the development of FSGS in humans. This thesis also describes the study of the genomic architecture of the Munich Wistar Frömter rat model for FSGS, which led to the prioritization of TMEM63c and PTGR2 in the development of podocyte injury and proteinuria in this model. The identification of these mechanisms in the development of FSGS, increases our understanding of the pathophysiology of FSGS and can guide future studies into new, highly needed therapeutic strategies. Show less
Lest, N.A. van de; Bakker, A.E.; Dijkstra, K.L.; Zandbergen, M.; Heemskerk, S.A.C.; Wolterbeek, R.; ... ; Scharpfenecker, M. 2021
Introduction: The podocyte is thought to be the mainly affected cell type in focal segmental glomerulosclerosis (FSGS). However, recent studies have also indicated a role for glomerular endothelial... Show moreIntroduction: The podocyte is thought to be the mainly affected cell type in focal segmental glomerulosclerosis (FSGS). However, recent studies have also indicated a role for glomerular endothelial cells and podocyte-endothelial crosstalk in FSGS development. An experimental model for podocyte injury showed that increased endothelin-1 (ET-1) signaling between podocytes and endothelial cells induces endothelial oxidative stress and subsequent podocyte loss. In the current study, we investigated endothelial endothelin receptor A (ETAR) expression in patients with FSGS and its association with podocyte injury and glomerular oxidative stress.Methods: We selected 39 biopsy samples of patients with FSGS and 8 healthy control subjects, and stained them for ETAR, nephrin and 8-oxo-guanine, a DNA lesion caused by oxidative damage. Glomeruli with ETAR-positive endothelium and with nephrin loss were scored, and the 8-oxo-guanine-positive glomerular area was measured.Results: The mean percentage of glomeruli with ETAR-positive endothelial cells in patients with FSGS was higher compared to that in healthy control subjects (52% vs. 7%; P < 0.001). The presence of glomerular ETAR-positive endothelium was strongly associated with nephrin loss both on the biopsy level (rho = 0.47; P < 0.01), as on the level of individual glomeruli (odds ratio = 2.0; P < 0.001). Moreover, glomeruli with ETAR-positive endothelium showed more 8-oxo-guanine-positive staining (1.9% vs. 2.4%; P = 0.037). Finally, 8-oxo-guanine positivity in glomeruli was associated with increased levels of proteinuria.Conclusion: Taking together our findings, we show that ETAR is increased in glomerular endothelial cells of patients with FSGS and associated with podocyte damage and glomerular oxidative stress. These findings support the hypothesis that ET-1 signaling in glomerular endothelial cells contributes to disease development in patients with FSGS. Show less
Lest, N.A. van de; Zandbergen, M.; Wolterbeek, R.; Kreutz, R.; Trouw, L.A.; Dorresteijn, E.M.; ... ; Chua, J.S. 2019
Unraveling the genetic susceptibility of complex diseases such as chronic kidney disease remains challenging. Here, we used inbred rat models of kidney damage associated with elevated blood... Show moreUnraveling the genetic susceptibility of complex diseases such as chronic kidney disease remains challenging. Here, we used inbred rat models of kidney damage associated with elevated blood pressure for the comprehensive analysis of a major albuminuria susceptibility locus detected in these models. We characterized its genomic architecture by congenic substitution mapping, targeted next-generation sequencing, and compartment-specific RNA sequencing analysis in isolated glomeruli. This led to prioritization of transmembrane protein Tmem63c as a novel potential target. Tmem63c is differentially expressed in glomeruli of allele-specific rat models during onset of albuminuria. Patients with focal segmental glomerulosclerosis exhibited specific TMEM63C loss in podocytes. Functional analysis in zebrafish revealed a role for tmem63c in mediating the glomerular filtration barrier function. Our data demonstrate that integrative analysis of the genomic architecture of a complex trait locus is a powerful tool for identification of new targets such as Tmem63c for further translational investigation. Show less
