Glomerular Podocyte-specific Protein-of Nephrin In The Pathogenesis Of Minimal Change Nephrotic

The glomerulus is a specialized filtration unit of the kidney, its capillary wall is highly permeable to water ,small solute molecules, and irons, but it serves as a molecular sieve capable of excluding most plasma proteins from urine. It is well established that the glomerular capillary wall consists of three layers: glomerular endothelial cells, the glomerular basement membrane (GBM), and the podocytes (glomerular epitheliar cells). The podocytes form a tight web on the GBM, with interdigitating foot processes derived from different podocytes. The gap between foot processes, referred to as the slit pore, is bridged by a thin membrance called the slit diaphragm.During the past decades, the researches on glomerular endothelial and glomerular basement membrane were more thorough and extensive, but the precise function and the molecular structure of the slit diaphragm have not been fully elucidated. Nephrin is the first identified protein molecule, which is specifically located on the slit diaphragm. It was reported that congenital nephritic syndrome of the Finnish type (CNF) was caused by the mutation in the NPHS1 gene. The mutation of NPHS1 gene induced nephrin disappeared from the slit diaphragm, destroyed the integrality of the glomerular capillary wall, and then leaded the occurrence of proteinuria, which suggesting an important role of nephrin in the development of proteinuria.In order to understand the role of nephrin in the pathophysiological mechaisms of proterinuria, two-part study is carried out.Part one: podocyte injury in rat model of minimal change nephrologyObjective: To investigate the podocyte injury in rat model of puromycin aminonucleoside (PAN) nephrosis.Methods: Thirty rats were divided into four experimental groups (n=24 total) and a control group (n=6). Rats in the experimental groups received a single intravenous injection of puromycin aminonucleoside (PAN), and were sacrificed at 1, 3, 10 and 20 days post-injection. Histopathology changes of podocytes were assessed by light microscopy and transmission electron microscopy. Podocytes were counted in glomeruli using disector/fractionator method.Results: ① The urine protein excretion was gradually elevated and reached its peak during the first 10 days after the injection, while showed a trend of decrease afterward ; ② Following the injection of PAN, injury in the rat podocytes is manifested by the loss of podocyte, foot process fusion, epithelial vacuoles formation; ③ the significant decrease in podocytes per glomerulus occurring by 10 days after injection.Conclusion: The massive proteinuria in puromycin aminonucleoside nephrosis may be primarily due to a glomerular podocyte lesion.Part two: nephrin expression in rat model of minimal change nephrologyObjective: To observe the expression of nephrin mRNA and protein in a rat model of puromycin aminonucleoside (PAN) nephrosis, and to investigate its possible role in the development of proteinuria.Methods: Puromycin aminonucleoside nephrosis was induced by single intraperitoneal injection of puromycin aminonucleoside (PAN). Renal tissues were studied at 1, 3, 10 and 20 days after PAN injection by means of RT-PCR, immunohistochemistry, Western blotting.Results: The expressions of nephrin mRNA and protein were significantly down-regulated with the progression of proteinuria, and recovered with the normalization of the urine protein excretion.