cytochalasin-b and Nephrotic-Syndrome

Scanning and transmission electron microscopy were used to evaluate free surface microprojections on the kidney glomerular epithelium in response to various experimental situations. Normally glomerular epithelial podocytes exhibit a rather sparse population of finger-like or bleb-like projections. Some investigations, however, have suggested that microvillous projections may increase in number during the differentiation of podocytes and in the aging kidney. With the onset of puromycin aminonucleoside induced nephrotic syndrome, podocyte microprojections become very knob-like and irregular in their shapes. In response to the in vitro environment, the number of podocyte microprojections increases dramatically. Neuraminidase removal of the sialic acid component of the glomerular glycocalyx and exposure to either cytochalasin B (25 microgram/ml) or cytochalasin D (2 microgram/ml), prevent the in vitro formation of podocyte microprojections. In vitro incubation in compounds which depolymerize cytoplasmic microtubules (e.g. vinblastine sulfate 10(-5); colchicine 10(-5) M), however, result in the formation of unusually long glomerular epithelial microprojections. Investigations utilizing the cationic ligand polycationized ferritin (PCF) have shown that podocyte microprojections are the most anionic sites on the free surfaces of these cells. During prolonged incubation of PCF treated glomeruli, the tips of podocyte microprojections are the last sites to shed the anionically bound PCF. It is suggested that the highly anionic sialic acid components of the glomerular free surface glycocalyx may play principal roles in the formation, maintenance and shapes of glomerular podocyte microprojections.

Topics: Animals; Cell Membrane; Cytochalasin B; Cytochalasin D; Cytochalasins; Epithelium; Ferritins; Kidney Glomerulus; Microscopy, Electron, Scanning; Microtubules; Microvilli; Nephrotic Syndrome; Neuraminidase; Polymers; Rats

We studied the distribution of nephrin in renal biopsies from 17 patients with diabetes and nephrotic syndrome (7 type 1 and 10 type 2 diabetes), 6 patients with diabetes and microalbuminuria (1 type 1 and 5 type 2 diabetes), and 10 normal subjects. Nephrin expression was semiquantitatively evaluated by measuring immunofluorescence intensity by digital image analysis. We found an extensive reduction of nephrin staining in both type 1 (67 +/- 9%; P < 0.001) and type 2 (65 +/- 10%; P < 0.001) diabetic patients with diabetes and nephrotic syndrome when compared with control subjects. The pattern of staining shifted from punctate/linear distribution to granular. In patients with microalbuminuria, the staining pattern of nephrin also showed granular distribution and reduction intensity of 69% in the patient with type 1 diabetes and of 62 +/- 4% (P < 0.001) in the patients with type 2 diabetes. In vitro studies on human cultured podocytes demonstrated that glycated albumin and angiotensin II reduced nephrin expression. Glycated albumin inhibited nephrin synthesis through the engagement of receptor for advanced glycation end products, whereas angiotensin II acted on cytoskeleton redistribution, inducing the shedding of nephrin. This study indicates that the alteration in nephrin expression is an early event in proteinuric patients with diabetes and suggests that glycated albumin and angiotensin II contribute to nephrin downregulation.

Topics: Adult; Aged; Albuminuria; Angiotensin II; Biopsy; Blotting, Western; Cells, Cultured; Cytochalasin B; Cytoskeleton; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Diabetic Nephropathies; Female; Fluorescent Antibody Technique, Indirect; Gene Expression; Glycated Serum Albumin; Glycation End Products, Advanced; Humans; Kidney; Male; Membrane Proteins; Microscopy, Fluorescence; Middle Aged; Nephrotic Syndrome; Proteins; Receptor for Advanced Glycation End Products; Receptors, Immunologic; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Serum Albumin; Tissue Distribution