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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

Chronic kidney disease (CKD) is associated with decreased renal nitric oxide (NO) production and increased plasma levels of methylarginines. The naturally occurring guanidino-methylated arginines N-monomethyl-L-arginine (L-NMMA) and asymmetric dimethyl-L-arginine (ADMA) inhibit NO synthase activity. We hypothesized that ADMA and L-NMMA compromise the integrity of the glomerular filtration barrier via NO depletion. We studied the effect of ADMA on albumin permeability ([P.sub.alb]) in isolated glomeruli and examined whether this effect involves NO- and superoxide ([O.sup.*-.sub.2])-dependent mechanisms. ADMA at concentrations found in circulation of patients with CKD decreased cGMP and increased [P.sub.alb] in a dose-dependent manner. A similar increase in [P.sub.alb] was caused by L-NMMA but at a concentration two orders of magnitude higher than that of ADMA. NO donor DETA-NONOate or cGMP analog abrogated the effect of ADMA on [P.sub.alb] . The SOD mimetic tempol or the NAD(P)H oxidase inhibitor apocynin also prevented the ADMA-induced increase in [P.sub.alb] . The NO-independent soluble guanylyl cyclase (sGC) activator BAY 41-2272, at concentrations that increased glomerular cGMP production, attenuated the ADMA-induced increase in [P.sub.alb] . Furthermore, sGC incapacitation by the heine site-selective inhibitor ODQ increased [P.sub.alb]. We conclude that ADMA compromises the integrity of the filtration barrier by altering the bioavailability of NO and [O.sup.*-.sub.2] and that NO-independent activation of sGC preserves the integrity of this barrier under conditions of NO depletion. NO-independent activation of sGS may be a useful pharmacotherapeutic approach for preservation of glomerular function in CKD thereby reducing the risk for cardiovascular events. chronic kidney disease; cardiorenal disease

Research suggests that glomerular epithelial cells within the kidney react differently to the vasoconstrictor angiotensin II than other renal cell types. Evidence indicates that renal epithelial cells are directly involved with angiontensin I in glomerular filtration barrier control. Experiments designed to compare the effect of angiotensin II on glomerular epithelial cells, proximal tubular epithelial cells and mesangial cells are described.

A chemical circulating in the plasma may be responsible for focal segmental glomerulosclerosis. Focal segmental glomerulosclerosis is a kidney disease characterized by scarring of the glomeruli, which are the part of the kidney that filters blood. Researchers took serum samples from 100 patients with focal segmental glomerulosclerosis and tested them in an assay using rat glomeruli. The permeability of rat glomeruli to the protein albumin was 0.18 when exposed to the patients' serum, compared to 0.06 when exposed to the serum of healthy volunteers. Some serum samples from patients with focal segmental glomerulosclerosis caused the permeability of rat glomeruli to jump to 0.50 or higher. Several patients were treated with plasmapheresis, a procedure in which plasma is replaced. Following plasmapheresis, their plasma lost the ability to increase the permeability of rat glomeruli. This indicates that a chemical in plasma may contribute to focal segmental glomerulosclerosis.

The ultrafiltrate flow over the major processes and cell body generates fluid flow shear stress (FFSS) on podocytes. Hyperfiltration-associated increase in FFSS can lead to podocyte injury and detachment. Previously, we showed that FFSS-induced upregulation of the cyclooxygenase 2 (COX2)-PGE2-prostaglandin E receptor 2 (EP2) axis in podocytes activates Akt-glycogen synthase kinase-3β-β-catenin and MAPK/ERK signaling in response to FFSS. Integrative MultiOmics Pathway Resolution (IMPRes) is a new bioinformatic tool that enables simultaneous time-series analysis of more than two groups to identify pathways and molecular connections. In the present study, we used previously characterized COX2 [prostaglandin- endoperoxide synthase 2 (Ptgs2)], EP2 (Ptger2), and β1- catenin (Ctnnb1) as "seed genes" from an array data set of four groups analyzed over a time course. The 3 seed genes shared 7 pathways and 50 genes of 14 pathways and 89 genes identified by IMPRes. A composite of signaling pathways highlighted the temporal molecular connections during mechanotransduction signaling in FFSS-treated podocytes. We investigated the "proteoglycans in cancer" and "galactose metabolism" pathways predicted by IMPRes. A customdesigned PCR array validated 60.7% of the genes predicted by IMPRes analysis, including genes for the above-named pathways. Further validation using Western blot analysis showed increased expression of phosho-Erbb2, phospho-mammalian target of rapamycin (mTOR), CD44, and hexokinase II (Hk2); decreased total Erbb2, galactose mutarotase (Galm), and β-1,4-galactosyltransferase 1 (B4galt1); and unchanged total mTOR and AKT3. These findings corroborate our previously reported results. This study demonstrates the potential of the IMPRes method to identify novel pathways. Identifying the "proteoglycans in cancer" and "galactose metabolism" pathways has generated a lead to study the significance of FFSSinduced glycocalyx remodeling and possible detachment of podocytes from the glomerular matrix. [ABSTRACT FROM AUTHOR]

Recently, we and others have found that hyperfiltration- associated increase in biomechanical forces, namely, tensile stress and fluid flow shear stress (FFSS), can directly and distinctly alter podocyte structure and function. The ultrafiltrate flow over the major processes and cell body generates FFSS to podocytes. Our previous work suggests that the cyclooxygenase-2 (COX-2)- PGE2-PGE2 receptor 2 (EP2) axis plays an important role in mechanoperception of FFSS in podocytes. To address mechanotransduction of the perceived stimulus through EP2, cultured podocytes were exposed to FFSS (2 dyn/cm2) for 2 h. Total RNA from cells at the end of FFSS treatment, 2-h post-FFSS, and 24-h post-FFSS was used for whole exon array analysis. Differentially regulated genes (P < 0.01) were analyzed using bioinformatics tools Enrichr and Ingenuity Pathway Analysis to predict pathways/molecules. Candidate pathways were validated using Western blot analysis and then further confirmed to be resulting from a direct effect of PGE2 on podocytes. Results show that FFSS-induced mechanotransduction as well as exogenous PGE2 activate the Akt-GSK3β-β-catenin (Ser552) and MAPK/ERK but not the cAMP-PKA signal transduction cascades. These pathways are reportedly associated with FFSS-induced and EP2-mediated signaling in other epithelial cells as well. The current regimen for treating hyperfiltration-mediated injury largely depends on targeting the renin-angiotensin-aldosterone system. The present study identifies specific transduction mechanisms and provides novel information on the direct effect of FFSS on podocytes. These results suggest that targeting EP2- mediated signaling pathways holds therapeutic significance for delaying progression of chronic kidney disease secondary to hyperfiltration. [ABSTRACT FROM AUTHOR]

Nephrogenic systemic fibrosis (NSF) is a devastating condition associated with gadolinium (Gd3+)-based contrast agents (GBCAs) in patients with kidney disease. The release of toxic Gd3+ from GBCAs likely plays a major role in NSF pathophysiology. The cause and etiology of Gd3+ release from GBCAs is unknown. Increased Acidic Serine Aspartate Rich MEPE-associated peptides (ASARM peptides) induce bone mineralization abnormalities and contribute to renal phosphate-handling defects in inherited hypophosphatemic rickets and tumor-induced osteomalacia. The proteolytic cleavage of related bone matrix proteins with ASARM motifs results in release of ASARM peptide into bone and circulation. ASARM peptides are acidic, reactive, phosphorylated inhibitors of mineralization that bind Ca2+ and hydroxyapatite. Since the ionic radius of Gd3+ is close to that of Ca2+, we hypothesized that ASARM peptides increase the risk of NSF by inducing release of Gd3+ from GBCAs. Here, we show 1) ASARM peptides bind and induce release of Gd3+ from GBCAs in vitro and in vivo; 2) A bioengineered peptide (SPR4) stabilizes the Gd3+-GBCA complex by specifically binding to ASARM peptide in vitro and in vivo; and 3) SPR4 peptide infusion prevents GBCA-induced NSF-like pathology in a murine model with increased ASARM peptide (Hyp mouse). We conclude ASARM peptides may play a role in NSF and SPR4 peptide is a candidate adjuvant for preventing or reducing risk of disease. [ABSTRACT FROM AUTHOR]