Abstract
Glomerular protein handling mechanisms have received much attention in studies of nephrotic syndrome. Histopathological findings in renal biopsies from severely proteinuric patients support the likelihood of protein endocytosis by podocytes. ClC-5 is involved in the endocytosis of albumin in the proximal tubule.AimTo investigate whether ClC-5 is expressed in the glomerular compartment and whether it has a role in proteinuric nephropathies. ClC-5 expression was studied using Real-time PCR in manually- and laser-microdissected biopsies from patients with type 2 diabetes (n 37) and IgA nephropathy (n 10); in biopsies of membranous glomerulopathy (MG) (n 14) immunohistochemistry for ClC-5 (with morphometric analysis) and for WT1 was done. Controls: cortical tissue (n 23) obtained from unaffected parts of tumor-related nephrectomy specimens.ResultsClC-5 was expressed at glomerular level in all biopsies. Glomerular ClC-5 levels were significantly higher in diabetic nephropaty and MG at both mRNA and protein level (p<0.002; p<0.01). ClC-5 and WT1 double-staining analysis in MG showed that ClC-5 was localized in the podocytes. ClC-5 ultrastructural immunolocalization was demonstrated in podocytes foot processes. Our study is the first to demonstrate that ClC-5 is expressed in human podocytes. The ClC-5 overexpression found in biopsies of proteinuric patients suggests that proteinuria may play a part in its expression and that podocytes are likely to have a key role in albumin handling in proteinuric states.
Highlights
Glomerular protein handling mechanisms have received much attention in studies on nephrotic syndrome that proteinuria has been recognized as an independent risk factor for both renal failure and cardiovascular disease
The ClC-5 overexpression found in biopsies of proteinuric patients suggests that proteinuria may play a part in its expression and that podocytes are likely to have a key role in albumin handling in proteinuric states
The aim of our study was to investigate whether ClC-5, as part of the macromolecular complex involved in albumin re-uptake, is expressed in the glomerular compartment, and whether it has a role in proteinuric nephropathies
Summary
Glomerular protein handling mechanisms have received much attention in studies on nephrotic syndrome that proteinuria has been recognized as an independent risk factor for both renal failure and cardiovascular disease. ClC-5, belongs to the highly conserved ClC family of chloride channels and chloride/proton exchangers, and is part of the molecular complex involved at proximal tubular level in the endocytotic re-uptake of low-molecular-weight (LMW) proteins and of albumin too. This mechanism needs a very active receptormediated pathway, as Hryciw et al neatly explained [3]. The endosomal H+/Cl2 exchanger ClC-5 has been located in the kidney using immunoabsorbed ClC-5-specific polyclonal antibodies raised against a synthetic peptide corresponding to the ClC-5 extracellular domain It has been found in the proximal tubules, the thick ascending limb and the intercalated cells of the collecting ducts, but never in human glomeruli [4]
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