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Proteinuria is a hallmark of many glomerular diseases and an independent risk factor for the progression of renal failure. Proteinuria results from damage to the glomerular filtration barrier (GFB), which plays a critical role in size- and charge-selective filtration. The GFB consists of three layers, which is the fenestrated endothelium that is covered by the glycocalyx, the podocytes and the intervening glomerular basement membrane. Defects in one of the three layers in the GFB can lead to the development of proteinuria. Heparan sulphate (HS) is a negatively charged polysaccharide that is abundantly expressed in all layers of the GFB. HS expression in the GFB is reduced in the majority of patients with proteinuria, which is associated with an increased glomerular expression of the HS-degrading enzyme heparanase. The primary role of HS in the development of proteinuria has been challenged after the establishment of several genetically engineered mouse models with an altered HS expression that did not display development of overt proteinuria. However, in a recent study, we showed that heparanase is essential for the development of proteinuria in diabetic nephropathy, which suggests that loss of HS contributes to the development of proteinuria. Recent studies also further highlight the importance of the glomerular endothelial glycocalyx in charge-selective filtration and the development of proteinuria. This review aims to summarize our current knowledge on the role of in particular HS and heparanase in the development of proteinuria. [ABSTRACT FROM PUBLISHER]

Background A reduced heparan sulphate (HS) expression in the glomerular basement membrane of patients with overt diabetic nephropathy is associated with an increased glomerular heparanase expression. We investigated the possible association of urinary heparanase activity with the development of proteinuria in patients with Type 1 diabetes (T1D), Type 2 diabetes (T2D), or membranous glomerulopathy (MGP) as non-diabetic disease controls. Methods Heparanase activity, albumin, HS and creatinine were measured in the urine of patients with T1D (n = 58) or T2D (n = 31), in patients with MGP (n = 52) and in healthy controls (n = 10). Heparanase messenger RNA (mRNA) expression in leukocytes was determined in a subgroup of patients with T1D (n = 19). Results Urinary heparanase activity was increased in patients with T1D and T2D, which was more prominent in patients with macroalbuminuria, whereas no activity could be detected in healthy controls. Albuminuria levels were associated with increased urinary heparanase activity in diabetic patients (r = 0.20; P < 0.05) but not in patients with MGP (r = 0.11; P = 0.43). A lower urinary heparanase activity was observed in diabetic patients treated with inhibitors of the renin–angiotensin–aldosterone system (RAAS), when compared to diabetic patients treated with other anti-hypertensives. Additionally, urinary heparanase activity was associated with age in T1D and MGP. In MGP, heparanase activity and β2-microglobulin excretion correlated. In patients with T1D, no differences in heparanase mRNA expression in leukocytes could be observed. Conclusions Urinary heparanase activity is increased in diabetic patients with proteinuria. However, whether increased heparanase activity is a cause or consequence of proteinuria requires additional research. [ABSTRACT FROM PUBLISHER]