No abstract

Diabetic kidney disease (DKD) is the single most common cause of albuminuria and end-stage kidney disease in the UnitedStates. We found increased expression of Wnt/␤-catenin (Ctnnb1) pathway transcripts and proteins in glomeruli and podocytes of patients and mouse models of DKD. Mice with podocyte-specific expression of stabilized Ctnnb1 exhibited basement membrane abnormalities, albuminuria, and increased susceptibility to glomerular injury. Mice with podocyte-specific deletion of Ctnnb1 or podocyte-specific expression of the canonical Wnt inhibitor Dickkopf-related protein 1 (Dkk1) also showed increased susceptibility to DKD. Podocytes with stabilized Ctnnb1 were less motile and less adhesive to different matrices. Deletion of Ctnnb1 in cultured podocytes increased the expression of podocyte differentiation markers and enhanced cell motility; however, these cells were more susceptible to apoptosis. These results indicate that Wnt/Ctnnb1 signaling in podocytes plays a critical role in integrating cell adhesion, motility, cell death, and differentiation. Balanced Ctnnb1 expression is critical for glomerular filtration barrier maintenance. Diabetic kidney disease (DKD)2 is one of the most devastating complications of diabetes and the single most common cause of albuminuria, chronic kidney disease, and end-stage renal disease (ESRD) in the Western world (1). DKD causes filtration unit dysfunction leading to the development of albuminuria, which is the most abundant protein component of the blood. The glomerular filtration barrier consists of three layers as follows: glomerular endothelial cells, the glomerular basement membrane (GBM), and the glomerular epithelial cell (or podocyte) layer (2-4). Decreased glomerular podocyte density is shown to be the strongest predictor for end-stage renal disease development in patients with diabetes (5). Hyperglycemia via the generation of reactive oxygen species induces podocyte apoptosis and loss, which has been well documented in many different mouse DKD models (6, 7). As podocytes are terminally differentiated cells, they are unable to proliferate; therefore, apoptosis or detachment can lead to podocyte deficiency, which in turn will lead to glomerulosclerosis development (8, 9). Early administration of drugs that prevent podocyte apoptosis has been shown to ameliorate DKD in rodent models; however, this may not be a clinically translatable strategy (6, 10). Another early lesion in diabetes is the thickening of the basement membrane. The role and mechanism of GBM thickening are not fully understood. It is speculated that GBM thickening could cause alterations in integrin expression, which could interfere with podocyte adhesiveness. Genetic deletion of podocyte-specific integrins, Itgb1 and Itga3, causes albuminuria and glomerulosclerosis; however, the contribution of podocyte adhesion to DKD development has not been demonstrated (11,12). Understanding the mechanism of podocyte differentiation, adhesion and cell death could be highly relevant for the development of targets f...

Recent studies indicate that the Notch signaling pathway plays an important role in diabetic kidney disease (DKD) and focal segmental glomerulosclerosis (FSGS) development, but the specificity and the clinical significance of Notch activation have not been studied in a broader set of diseases. Here we analyzed the degree of expression and localization of Notch ligands (Jagged1 and Delta1) and Notch receptors (Notch1 and Notch2) in healthy human kidneys and in biopsy samples obtained from patients with minimal change disease, membranous nephropathy, lupus nephritis ISN/RPS classes III/IV/V, hypertensive nephrosclerosis, crescentic glomerulonephritis, tubulointerstitial fibrosis, IgA nephropathy, DKD and FSGS. We found that cleaved Notch1, Notch2 and Jagged1 are expressed on podocytes in proteinuric nephropathies and their level of expression correlates with the amount of proteinuria (across all disease groups). The degree of glomerulosclerosis correlated with podocyte expression of cleaved Notch1, while the severity of tubulointerstitial fibrosis and the estimated glomerular filtration rate correlated with expression of cleavedNotch1 in the tubulointerstitium. In summary, here we show that the expression of Notch pathway proteins correlates with proteinuria and kidney dysfunction in a wide range of acquired renal diseases. Our results raise the possibility that Notch pathway activation is a common mechanism in the development of albuminuria, glomerulosclerosis and kidney dysfunction.

No abstract

Hemoglobin (Hb) serves as the main oxygen transporter in erythrocytes, but it is also expressed in nonhematopoietic organs, where it serves an unknown function. In this study, microarray and proteomic analyses demonstrated Hb expression in the kidney. Rat kidneys were perfused extensively with saline, and glomeruli were isolated by several techniques (sieving, manual dissection, and laser capturemicrodissection). Reverse transcriptase-PCR revealed glomerular ␣-and ␤-globin expression, and immunoblotting demonstrated expression of the protein. In situ hybridization studies showed expression of the globin subunits in the mesangium, and immunostaining confirmed this localization of Hb. Furthermore, globin mRNA expression was detected in primary cultures of rat mesangial cells but not in cultured glomerular endothelial or epithelial cells. For investigation of Hb function in mesangial cells, the SV40-MES13 murine mesangial cell line was transfected with a vector expressing ␣-and ␤-globins; this overexpression reduced production of hydrogen peroxide-induced intracellular radical oxygen species and enhanced cell viability against oxidative stress. In summary, Hb is expressed by rat mesangial cells, and its potential functions may include antioxidative defense.