Proteinuria is an independent risk factor for the progression of kidney injury, cardiovascular morbidity, and overall mortality. In this thesis, the pathways leading to proteinuria are explored by... Show moreProteinuria is an independent risk factor for the progression of kidney injury, cardiovascular morbidity, and overall mortality. In this thesis, the pathways leading to proteinuria are explored by revisiting elements previously considered essential, investigating known pathways, and identifying new players in the field of proteinuria. First, a zebrafish embryo model for developing new therapeutic options for the rare but devastating disease of nephropathic cystinosis is presented. The studies presented in thesis also investigate loss of heparan sulphate glycosaminoglycans in a zebrafish embryo model and in multiple osteochondroma patients. These studies show that loss of heparan sulphate glycosaminoglycans does not always lead to proteinuria. Next, dynamin is described as a promising potential therapeutic target for treating proteinuria. The final study introduces transmembrane protein 14A as an essential factor in maintaining glomerular filtration barrier function. Overall, these studies contribute to elucidating the pathways to proteinuria in the hope to keep advancing the field towards targeted treatment of proteinuria for the benefit of our patients. Show less
Garsen, M.; Buijsers, B.; Sol, M.; Gockeln, L.; Sonneveld, R.; Kuppevelt, T.H. van; ... ; Vlag, J. van der 2023
Background Proteinuria is associated with many glomerular diseases and a risk factor for the progression to renal failure. We previously showed that heparanase (HPSE) is essential for the... Show moreBackground Proteinuria is associated with many glomerular diseases and a risk factor for the progression to renal failure. We previously showed that heparanase (HPSE) is essential for the development of proteinuria, whereas peroxisome proliferator-activated receptor y (PPARy) agonists can ameliorate proteinuria. Since a recent study showed that PPARy regulates HPSE expression in liver cancer cells, we hypothesized that PPARy agonists exert their reno-protective effect by inhibiting glomerular HPSE expression.Methods Regulation of HPSE by PPARy was assessed in the adriamycin nephropathy rat model, and cultured glomerular endothelial cells and podocytes. Analyses included immunofluorescence staining, real-time PCR, heparanase activity assay and transendothelial albumin passage assay. Direct binding of PPARy to the HPSE promoter was evaluated by the luciferase reporter assay and chromatin immunoprecipitation assay. Furthermore, HPSE activity was assessed in 38 type 2 diabetes mellitus (T2DM) patients before and after 16/24 weeks treatment with the PPARy agonist pioglitazone.Findings Adriamycin-exposed rats developed proteinuria, an increased cortical HPSE and decreased heparan sulfate (HS) expression, which was ameliorated by treatment with pioglitazone. In line, the PPARy antagonist GW9662 increased cortical HPSE and decreased HS expression, accompanied with proteinuria in healthy rats, as previously shown. In vitro, GW9662 induced HPSE expression in both endothelial cells and podocytes, and increased trans -endothelial albumin passage in a HPSE-dependent manner. Pioglitazone normalized HPSE expression in adriamycin-injured human endothelial cells and mouse podocytes, and adriamycin-induced transendothelial albumin passage was reduced as well. Importantly, we demonstrated a regulatory effect of PPARy on HPSE promoter activity and direct PPARy binding to the HPSE promoter region. Plasma HPSE activity of T2DM patients treated with pioglitazone for 16/24 weeks was related to their hemoglobin A1c and showed a moderate, near significant correlation with plasma creatinine levels.Interpretation PPARy-mediated regulation of HPSE expression appears an additional mechanism explaining the anti-proteinuric and renoprotective effects of thiazolidinediones in clinical practice.Copyright (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Show less
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
In this study, the effect of heterozygous germline mutations in the heparan sulfate (HS) glycosaminoglycan chain co-polymerases EXT1 and EXT2 on glomerular barrier function and the endothelial... Show moreIn this study, the effect of heterozygous germline mutations in the heparan sulfate (HS) glycosaminoglycan chain co-polymerases EXT1 and EXT2 on glomerular barrier function and the endothelial glycocalyx in humans is investigated. Heparan sulfate (HS) glycosaminoglycans are deemed essential to the glomerular filtration barrier, including the glomerular endothelial glycocalyx. Animal studies have shown that loss of HS results in a thinner glycocalyx. Also, decreased glomerular HS expression is observed in various proteinuric renal diseases in humans. A case report of a patient with an EXT1 mutation indicated that this could result in a specific renal phenotype. This patient suffered from multiple osteochondromas, an autosomal dominant disease caused by mono-allelic germline mutations in the EXT1 or EXT2 gene. These studies imply that HS is indeed essential to the glomerular filtration barrier. However, loss of HS did not lead to proteinuria in various animal models. We demonstrate that multiple osteochondroma patients do not have more microalbuminuria or altered glycocalyx properties compared to age-matched controls (n = 19). A search for all Dutch patients registered with both osteochondroma and kidney biopsy (n = 39) showed that an EXT1 or EXT2 mutation does not necessarily lead to specific glomerular morphological phenotypic changes. In conclusion, this study shows that a heterozygous mutation in the HS backbone elongating enzymes EXT1 and EXT2 in humans does not result in (micro)albuminuria, a specific renal phenotype or changes to the endothelial glycocalyx, adding to the growing knowledge on the role of EXT1 and EXT2 genes in pathophysiology. Show less
Background Acidosis-induced kidney injury is mediated by the intrarenal renin-angiotensin system, for which urinary renin is a potential marker. Therefore, we hypothesized that sodium bicarbonate... Show moreBackground Acidosis-induced kidney injury is mediated by the intrarenal renin-angiotensin system, for which urinary renin is a potential marker. Therefore, we hypothesized that sodium bicarbonate supplementation reduces urinary renin excretion in patients with chronic kidney disease (CKD) and metabolic acidosis.Methods Patients with CKD stage G4 and plasma bicarbonate 15-24 mmol/l were randomized to receive sodium bicarbonate (3 x 1000 mg/day, similar to 0.5 mEq/kg), sodium chloride (2 x 1,00 mg/day), or no treatment for 4 weeks (n = 15/arm). The effects on urinary renin excretion (primary outcome), other plasma and urine parameters of the renin-angiotensin system, endothelin-1, and proteinuria were analyzed.Results Forty-five patients were included (62 +/- 15 years, eGFR 21 +/- 5 ml/min/1.73m(2), plasma bicarbonate 21.7 +/- 3.3 mmol/l). Sodium bicarbonate supplementation increased plasma bicarbonate (20.8 to 23.8 mmol/l) and reduced urinary ammonium excretion (15 to 8 mmol/day, both P < 0.05). Furthermore, a trend towards lower plasma aldosterone (291 to 204 ng/L, P = 0.07) and potassium (5.1 to 4.8 mmol/l, P = 0.06) was observed in patients receiving sodium bicarbonate. Sodium bicarbonate did not significantly change the urinary excretion of renin, angiotensinogen, aldosterone, endothelin-1, albumin, or alpha 1-microglobulin. Sodium chloride supplementation reduced plasma renin (166 to 122 ng/L), and increased the urinary excretions of angiotensinogen, albumin, and alpha 1-microglobulin (all P < 0.05).Conclusions Despite correction of acidosis and reduction in urinary ammonium excretion, sodium bicarbonate supplementation did not improve urinary markers of the renin-angiotensin system, endothelin-1, or proteinuria. Possible explanations include bicarbonate dose, short treatment time, or the inability of urinary renin to reflect intrarenal renin-angiotensin system activity. Show less
Goeij, M.C.M. de; Liem, M.; Jager, D.J. de; Voormolen, N.; Sijpkens, Y.W.J.; Rotmans, J.I.; ... ; PREPARE-1 Study Grp 2012
The clinical course of renal diseases depends on the type of renal disorder, genetic factors, environmental influences, and the severity of renal fibrosis. Proteinuria is the abnormal amount of... Show moreThe clinical course of renal diseases depends on the type of renal disorder, genetic factors, environmental influences, and the severity of renal fibrosis. Proteinuria is the abnormal amount of proteins present in the urine. Proteinuria is an independent risk factor for development of renal insufficiency, in which glomerulosclerosis can be seen in biopsies. Experimental models described in this thesis show that different genetic factors are linked to proteinuria and glomerulosclerosis. Furthermore, bone marrow and kidney transplantations between proteinuria-prone and proteinuria-resistant rats, revealed that both renal and bone marrow-derived cells contribute to development of proteinuria or convey resistance to its development. The mechanism of development of segmental glomerulosclerosis is not completely known. We investigated glomerular morphology in hyperfiltration-mediated proteinuria before glomerulosclerosis was present. Segmental glomerulosclerosis started with segmental podocyte damage with loss of podoplanin protein. Focal and segmental glomerulosclerosis is a human renal disease with a wide range of glomerular morphology, a large range of clinical presentations, progression rates, and chances of developing recurrent FGSG after transplantation. A new histological classification was proposed in 2004 in hopes of separating new disease subentities. We found that in most cases FSGS recurred as the same variant, supporting the new classification. The results in this thesis may increase the insights in the development of proteinuria and glomerulosclerosis, hoping to result in earlier recognition of renal disease, better definition of patients and separation of distinct disease entities. This may lead to better and more disease-specific treatment options. Show less
__Bones can break, muscles can atrophy, glands can loaf, even the brain can go to sleep, without immediately endangering our survival, but when the kidneys fail to manufacture the proper kind of... Show more__Bones can break, muscles can atrophy, glands can loaf, even the brain can go to sleep, without immediately endangering our survival, but when the kidneys fail to manufacture the proper kind of blood neither bone, muscle, gland nor brain can carry on__. This quote from Homer Smith's book 'From Fish to Philosopher' indicates the importance of the kidney for the maintenance of the harmonious composition of body fluids __ a function the kidney performs in a way that joins efficacy with elegance. Some of these processes are lined out in this thesis. The first chapter gives an introduction to kidney development, anatomy, and function, as well as a description of malfunction of the kidney, focusing on the development of proteinuria and failure of kidney transplants. The subsequent chapters describe studies that have been performed to investigate the biological mechanism that underly the development of proteinuria and long-term renal transplant failure. Show less
