Expression Profile Of Cullin-5 In Glomeruli From Patients With Proteinuria And Cultured Mouse Podocytes

Background:Proteinuria is not only the common clinical manifestations of glomerular disease, but also the important risk factor of chronic renal failure, hypertension and cardiovascular disease. For a long time, people lack of understanding about the mechanisms of the proteinuria in various glomerular diseases, thus there is short of truly effective treatment clinically. Many molecules have been found to be expressed in the glomerular slit diaphragm since 1998 when nephrin was first identified, such as Podocin, CD2AP, etc. These molecules may play an important role to maintain the glomerular development, filtration membrane integrity, cell signal transduction and to prevent leakage from the proteinuria.Cullin-5 (Cul-5), a member of the cullin gene family of scaffold proteins of E3 ubiquitin-ligase complexes, is known to play multiple roles in proteolysis and cell cycle regulation, and it may inhibit cellular growth and tumorigenesis. Our research team found recently that Cullin-5 gene Knock-down can lead to the emergence of proteinuria, edema and renal glomerular changes in the structure through the zebrafish RNAi in animal model, which indicated that Cullin-5 may have a very important role in maintaining zebra physical integrity of the glomerular filtration membrane and maintaining normal glomerular filtration barrier function. But so far, there were no study about Cullin-5 expression in the kidney and its role in maintaining the glomerular structure and function of glomerular filtration membrane integrity in human and mouse.Objective:To analyze the possible role of Cullin-5 in pathogenesis of proteinuria in glomerular disease by detecting the expression profile of Cullin-5 in normal human kidney tissues and biopsy samples from patients with proteinuria.Methods:Indirect immunofluorescence was used to determine the expression profile of Cullin-5 in kidney samples from 8 cases of normal slices (control group),16 cases of isolated hematuria,47 cases of mild & moderate proteinuria, and 28 cases of nephrotic-range proteinuria (totally 91 cases). Cullin-5 expression in cultured mouse podocyte cell line was also analyzed in present study.Results:(1) Compared with results form control group, there are 8 cases with positive Cullin-5 staining in isolated hematuria group (8/8 vs 7/1,χ2= 3.200, P= 0.074); 31 cases with positive Cullin-5 staining in proteinuria group (31/44 vs 7/1, x2= 6.207, P= 0.013).(2) Among the proteinuria patients, compared with results from control group, there are 26 cases with positive Cullin-5 staining in mild or moderate proteinuria group (26/21 vs 7/1, x2= 2.95, P= 0.086) and 5 cases with positive Cullin-5 staining in nephrotic-range proteinuria group (5/23 vs 7/1, x2= 13.58, P＜0.001). Compared the group with mild & moderate proteinuria, there are significant difference in positive case in nephrotic-range proteinuria group (5/23 vs 26/21,χ2= 10.155, P=0.001).(3) There are significant expression of Cullin-5 in cultured mouse podocyte in proliferation and dividing phase.Conclusions:The expression of Cullin-5 in renal tissue from patients with nephrotic-range proteinuria was significantly lower than the results from patients with mild & moderate proteinuria, patients with isolated hematuria and control group. The results imply the role of cullin-5 in the pathogenesis of proteinuria in glomerular disease.