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.

Background and objectives Rituximab is used with variable success in difficult FSGS. Because B cell depletion significantly affects T cell function, we characterized T cell subsets in patients with FSGS to determine if an immunologic signature predictive of favorable response to rituximab could be identified.Design, setting, participants, & measurements Twenty-two consecutive patients with FSGS (median age =14.4 years old; range =6.2-25.0 years old) and age of onset of nephrotic syndrome 1-18 years old receiving rituximab for clinical indications between October of 2009 and February of 2014 were studied. Indications for rituximab were lack of sustained remission despite calcineurin inhibitors (CNIs) and mycophenolate in steroid-resistant patients and lack of steroid-sparing effect with cyclophosphamide and CNI or CNI toxicity in steroid-dependent patients. Exclusion criteria were infantile onset, known genetic mutations, and secondary causes. Rituximab (375 mg/m 2 ) was given fortnightly up to a maximum of four doses. Immunologic subset monitoring was performed at baseline and regular intervals until relapse. Median follow-up duration postrituximab was 26.7 months (range =6.5-66.5 months). Baseline immunologic subsets were examined for association with rituximab response defined as resolution of proteinuria with discontinuation of prednisolone and CNI 3 months postrituximab.Results Twelve patients (54.5%) responded to rituximab. Mitogen-stimulated CD154 + CD4 + CD3 + subset before rituximab was significantly lower in FSGS responders compared with nonresponders (54.9%628.1% versus 78.9%616.4%; P=0.03). IFN-g + CD3 + and IL-2 + CD3 + were similarly decreased in responders compared with nonresponders (0.6%60.8% versus 7.5%66.1%; P=0.003 and 0.2%60.5% versus 4.0%64.7%; P,0.01, respectively). Recovery of all three activation subsets occurred 6 months postrituximab treatment (CD154 + CD4 + CD3 + , 74.8%617.2%; IFN-g + CD3 + , 7.1%67.7%; and IL-2 + CD3 + , 7.9%610.9%; P,0.01). Receiver-operating characteristic analysis using optimal cutoff values showed that activated CD154 + CD4 + CD3 + ,83.3% (area under the curve [AUC], 0.81; 95% confidence interval [95% CI], 0.61 to 1.00), IFN-g + CD3 + ,2.5% (AUC, 0.90; 95% CI, 0.75 to 1.00), and IL-2 + CD3 + ,0.3% (AUC, 0.78; 95% CI, 0.57 to 0.98) were good predictors of rituximab response.Conclusions We have identified prognostic markers that define a subset of patients with FSGS bearing an immunologic signature representing hyporesponsiveness to T cell stimulation and therefore, who respond better to rituximab.

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