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Glomerular capillary filtration barrier characteristics are determined in part by the slit-pore junctions of glomerular podocytes. Protein tyrosine phosphatase receptor-O (PTPro) is a transmembrane protein expressed on the apical surface of podocyte foot processes. Tyrosine phosphorylation of podocyte proteins including nephrin may control the filtration barrier. To determine whether PTPro activity is required to maintain glomerular macromolecular permeability, albumin permeability ([P.sub.alb]) was studied after incubation of glomeruli from normal animals with a series of monoclonal (mAb) and polyclonal antibodies. Reagents included mAbs to rabbit and rat PTPro and polyclonal rabbit immune IgG to rat PTPro. mAb 4C3, specific to the amino acid core of PTPro, decreased its phosphatase activity and increased [P.sub.alb] of rabbit glomeruli in a time-and concentration-dependent manner. In contrast, mAb P8E7 did not diminish phosphatase activity and did not alter [P.sub.alb]. Preincubation of 4C3 with PTPro extracellular domain fusion protein blocked glomerular binding and abolished permeability activity. In parallel experiments, [P.sub.alb] of rat glomeruli was increased by two mAbs (IB4 and 1D1) or by polyclonal anti-rat PTPro. We conclude that PTPro interaction with specific antibodies acutely increases [P.sub.alb]. The identity of the normal ligand for PTPro and of its substrate, as well as the mechanism by which phosphatase activity of this receptor affects the filtration barrier, remain to be determined. glomerulus; podocyte; slit-pore junction; filtration barrier

Background Proteinuria and/or albuminuria are widely used for noninvasive assessment of kidney diseases. However, proteinuria is a nonspecific marker of diverse forms of kidney injury, physiologic processes and filtration of small proteins of monoclonal and other pathologic processes. The opportunity to develop new glomerular disease biomarkers follows the realization that the degree of podocyte depletion determines the degree of glomerulosclerosis, and if persistent, determines the progression to end-stage kidney disease (ESKD). Podocyte cell lineage-specific mRNAs can be recovered in urine pellets of model systems and in humans. In model systems, progressive glomerular disease is associated with decreased nephrin mRNA steady-state levels compared with podocin mRNA. Thus, the urine podocin:nephrin mRNA ratio (PNR) could serve as a useful progression biomarker. The use of podocyte-specific transcript ratios also circumvents many problems inherent to urine assays. Methods To test this hypothesis, the human diphtheria toxin receptor (hDTR) rat model of progression was used to evaluate potentially useful urine mRNA biomarkers. We compared histologic progression parameters (glomerulosclerosis score, interstitial fibrosis score and percent of podocyte depletion) with clinical biomarkers [serum creatinine, systolic blood pressure (BP), 24-h urine volume, 24-h urine protein excretion and the urine protein:creatinine ratio(PCR)] and with the novel urine mRNA biomarkers. Results The PNR correlated with histologic outcome as well or better than routine clinical biomarkers and other urine mRNA biomarkers in the model system with high specificity and sensitivity, and a low coefficient of assay variation. Conclusions We concluded that the PNR, used in combination with proteinuria, will be worth testing for its clinical diagnostic and decision-making utility. [ABSTRACT FROM AUTHOR]

Glomemlar capillary filtration barrier characteristics are determined in part by the slit-pore junctions of glomerular podocytes. Protein tyrosine phosphatase receptor-O (PTPro) is a transmembrane protein expressed on the apical surface of podocyte foot processes. Tyrosine phosphorylation of podocyte proteins including nephrin may control the filtration barrier. To determine whether PTPro activity is required to maintain glomerular macromolecular permeability, albumin permeability (Palb) was studied after incubation of glomeruli from normal animals with a series of monoclonal (mAb) and polyclonal antibodies. Reagents included mAbs to rabbit and rat PTPro and polyclonal rabbit immune IgG to rat PTPro. mAb 4C3, specific to the amino acid core of PTPro, decreased its phosphatase activity and increased Palb of rabbit glomeruli in a time-and concentration-dependent manner. In contrast, mAb P8E7 did not diminish phosphatase activity and did not alter Palb. Preincubation of 4C3 with PTPro extracellular domain fusion protein blocked glomerular binding and abolished permeability activity. In parallel experiments, Palb of rat glomeruli was increased by two mAbs (1B4 and 1D1) or by polyclonal anti-rat PTPro. We conclude that PTPro interaction with specific antibodies acutely increases Palb. The identity of the normal ligand for PTPro and of its substrate, as well as the mechanism by which phosphatase activity of this receptor affects the filtration barrier, remain to be determined. [ABSTRACT FROM AUTHOR]

Glomemlar capillary filtration barrier characteristics are determined in part by the slit-pore junctions of glomerular podocytes. Protein tyrosine phosphatase receptor-O (PTPro) is a transmembrane protein expressed on the apical surface of podocyte foot processes. Tyrosine phosphorylation of podocyte proteins including nephrin may control the filtration barrier. To determine whether PTPro activity is required to maintain glomerular macromolecular permeability, albumin permeability (Palb) was studied after incubation of glomeruli from normal animals with a series of monoclonal (mAb) and polyclonal antibodies. Reagents included mAbs to rabbit and rat PTPro and polyclonal rabbit immune IgG to rat PTPro. mAb 4C3, specific to the amino acid core of PTPro, decreased its phosphatase activity and increased Palb of rabbit glomeruli in a time-and concentration-dependent manner. In contrast, mAb P8E7 did not diminish phosphatase activity and did not alter Palb. Preincubation of 4C3 with PTPro extracellular domain fusion protein blocked glomerular binding and abolished permeability activity. In parallel experiments, Palb of rat glomeruli was increased by two mAbs (1B4 and 1D1) or by polyclonal anti-rat PTPro. We conclude that PTPro interaction with specific antibodies acutely increases Palb. The identity of the normal ligand for PTPro and of its substrate, as well as the mechanism by which phosphatase activity of this receptor affects the filtration barrier, remain to be determined. [ABSTRACT FROM AUTHOR]