Paracrine signaling between podocytes and glomerular endothelial cells through vascular endothelial growth factor A (VEGFA) maintains a functional glomerular filtration barrier. Heparan sulfate proteoglycans (HSPGs), located on the cell surface or in the extracellular matrix, bind signaling molecules such as VEGFA and affect their local concentrations, but whether modulation of these moieties promotes normal crosstalk between podocytes and endothelial cells is unknown. Here, we found that the transcription factor Wilms' Tumor 1 (WT1) modulates VEGFA and FGF2 signaling by increasing the expression of the 6-O-endosulfatases Sulf1 and Sulf2, which remodel the heparan sulfate 6-O-sulfation pattern in the extracellular matrix. Mice deficient in both Sulf1 and Sulf2 developed age-dependent proteinuria as a result of ultrastructural abnormalities in podocytes and endothelial cells, a phenotype similar to that observed in children with WT1 mutations and in Wt1 ϩ/Ϫ mice. These kidney defects associated with a decreased distribution of VEGFA in the glomerular basement membrane and on endothelial cells. Collectively, these data suggest that WT1-dependent sulfatase expression plays a critical role in maintaining the glomerular filtration barrier by modulating the bioavailability of growth factors, thereby promoting normal crosstalk between podocytes and endothelial cells.

Individuals with Denys-Drash syndrome (DDS) develop diffuse mesangial sclerosis, ultimately leading to renal failure. The disease is caused by mutations that affect the zinc finger structure of the Wilms' tumor protein (WT1), but the mechanisms whereby these mutations result in glomerulosclerosis remain largely obscure. How WT1 regulates genes is likely to be complex, because it has multiple splice forms, binds both DNA and RNA, and associates with spliceosomes. Herein is described that in DDS podocytes, the ratio of both WT1 ؉KTS isoforms C to D differs considerably from that of normal child and adult control podocytes and more closely resembles fetal profiles. Aside from the delay in podocyte maturation, DDS glomeruli show swollen endothelial cells, reminiscent of endotheliosis, together with incompletely fused capillary basement membranes; a dramatic decrease in collagen ␣4(IV) and laminin ␤2 chains; and the presence of immature or activated mesangial cells that express ␣-smooth muscle actin. Because appropriate vascular endothelial growth factor A (VEGF-A) expression is known to be essential for the development and maintenance of glomerular architecture and function, this article addresses the question of whether VEGF-A expression is deregulated in DDS. The data presented here show that DDS podocytes express high levels of the proangiogenic isoform VEGF165, but completely lack the inhibitory isoform VEGF165b. The VEGF165/VEGF165b ratio in DDS resembles that of fetal S-shaped bodies, rather than that of normal child or adult control subjects. The alteration in VEGF-A expression presented here may provide a mechanistic insight into the pathogenesis of DDS.

Context/ObjectiveEpidemiological studies have demonstrated that women have a significantly better prognosis in chronic renal diseases compared to men. This suggests critical influences of gender hormones on glomerular structure and function. We examined potential direct protective effects of estradiol on podocytes.MethodsExpression of estrogen receptor alpha (ERα) was examined in podocytes in vitro and in vivo. Receptor localization was shown using Western blot of separated nuclear and cytoplasmatic protein fractions. Podocytes were treated with Puromycin aminonucleoside (PAN, apoptosis induction), estradiol, or both in combination. Apoptotic cells were detected with Hoechst nuclear staining and Annexin-FITC flow cytometry. To visualize mitochondrial membrane potential depolarization as an indicator for apoptosis, cells were stained with tetramethyl rhodamine methylester (TMRM). Estradiol-induced phosphorylation of ERK1/2 and p38 MAPK was examined by Western blot. Glomeruli of ERα knock-out mice and wild-type controls were analysed by histomorphometry and immunohistochemistry.ResultsERα was consistently expressed in human and murine podocytes. Estradiol stimulated ERα protein expression, reduced PAN-induced apoptosis in vitro by 26.5±24.6% or 56.6±5.9% (flow cytometry or Hoechst-staining, respectively; both p<0.05), and restored PAN-induced mitochondrial membrane potential depolarization. Estradiol enhanced ERK1/2 phosphorylation. In ERα knockout mice, podocyte number was reduced compared to controls (female/male: 80/86 vs. 132/135 podocytes per glomerulus, p<0.05). Podocyte volume was enhanced in ERα knockout mice (female/male: 429/371 µm3 vs. 264/223 µm3 in controls, p<0.05). Tgfβ1 and collagen type IV expression were increased in knockout mice, indicating glomerular damage.ConclusionsPodocytes express ERα, whose activation leads to a significant protection against experimentally induced apoptosis. Possible underlying mechanisms include stabilization of mitochondrial membrane potential and activation of MAPK signalling. Characteristic morphological changes indicating glomerulopathy in ERα knock-out mice support the in vivo relevance of the ERα for podocyte viability and function. Thus, our findings provide a novel model for the protective influence of female gender on chronic glomerular diseases.