Aberrantly glycosylated IgA1 induces mesangial cells to produce platelet-activating factor that mediates nephrin loss in cultured podocytes.

The reaction of mesangial cells with aberrantly glycosylated IgA1 has been implicated in the etiology of IgA nephropathy (IgAN). Tumor necrosis factor, which is assumed to mediate the interaction between mesangial cells and podocytes, also induces the expression of platelet-activating factor (PAF). In this study, we determined whether PAF affects the expression of nephrin (an adhesion molecule critical to glomerular permselectivity) and cytoskeletal F-actin organization in podocytes. We treated human mesangial cells with atypically glycosylated IgA1 either prepared in vitro or derived from the sera of patients with IgAN. We then prepared conditioned media from these cells and added them to cultured human podocytes in the presence of PAF receptor antagonists. Podocytes transfected to overexpress acetylhydrolase, the main catabolic enzyme of PAF, served as controls. Downregulation of nephrin expression and F-actin reorganization occurred when podocytes were cultured with mesangial cell-conditioned medium. Preincubation of podocytes with a PAF receptor antagonist prevented the loss and redistribution of nephrin. In control podocytes overexpressing acetylhydrolase, nephrin loss was abrogated. Our results suggest that atypically glycosylated IgA-induced PAF from mesangial cells is a mediator of podocyte changes, which, when more directly tested elsewhere, were found to be associated with proteinuria. Hence, it is possible that these in vitro findings may be relevant to the proteinuria of IgAN.

Upregulation of the immunoproteasome in peripheral blood mononuclear cells of patients with IgA nephropathy.

In order to present an antigen to T-cells, the antigen must first be degraded by proteasomes. Following exposure to interferons, some proteasome subunits (ss1,ss2,ss5) are replaced by others (LMP2, LMP7, MECL-1) that have more optimal catalytic properties for peptide presentation; this more efficient organelle is termed the immuno-proteasome. Here we measured gene expression of various subunits in peripheral mononuclear cells of patients with IgA nephropathy, a disease with features of immune dysregulation. We used quantitative PCR to measure the expression of proteasomal subunit mRNA in mononuclear cells from IgA nephropathy patients, a group of proteinuric control patients with idiopathic nephrotic syndromes, and healthy controls. A significant switch in the expression of trypsin- and chymotrypsin-like proteasome subunits to corresponding immuno-proteasome subunits was found in patients as compared to healthy controls. Further, we found that nuclear translocation of NF-kappaB p50 and p65 was significantly greater in the IgA nephropathy patients, but this did not correlate with the switch to the immuno-proteasome phenotype. Patients with proteinuria greater than 0.5 g/1.73 m(2)/day had a significant switch of the chymotryptic-like beta5 protease to the LMP7 subunit, but this did not occur in patients with idiopathic nephrotic syndrome. The switch to an immuno-proteasome in peripheral blood mononuclear cells of patients with IgA nephropathy suggests an increased efficiency of antigen processing and presentation. This switch appears to be independent of a coincidental activation of the NF-kappaB pathway but is associated with high levels of proteinuria, a well known risk factor for progression of IgA nephropathy.

Effect of glucose degradation products, glucose-containing dialysate and icodextrin on AQP1 and eNOS expression in cultured endothelial cells.

BACKGROUND: Aquaporin-1 (AQP1) and endothelial NO synthase (eNOS) expression on the endothelium of peritoneal vessels modulates ultrafiltration during peritoneal dialysis (PD) by different mechanisms. Protracted eNOS activation may, in the long term, be deleterious for peritoneal functioning. We aimed at examining the effect of peritoneal dialysis solutions (PDSs) and glucose degradation products (GDPs) on the expression of AQP1 and eNOS in cultured endothelial cells. METHODS: An endothelial cell line (t End.1) was incubated for 24 hours with 2 GDPs (2-furaldehyde [Fur] or methylglyoxal [MGly] at concentrations found in traditional PDSs) or with a different PDS (1.36% glucose, 3.86% glucose and 7.5% icodextrin) in Transwell culture devices. AQP1 and eNOS gene expression were detected by reverse transcriptase polymerase chain reaction. RESULTS: Fur and MGly at concentrations reported in traditional PDSs (Fur 0.8 microM; MGly 35 microM) significantly up-regulated eNOS mRNA and tended to down-regulate AQP1 mRNA in cultured endothelial cells. Glucose-based PDS as well as icodextrin PDS significantly up-regulated basal AQP1 and eNOS mRNA. The effect of 3.86% glucose PDS on AQP1 was significantly higher than that of icodextrin. CONCLUSIONS: In cultured endothelial cells, all PDSs triggered both AQP1 and eNOS in a likely feedback mechanism. GDPs stimulated e-NOS expression only, and this effect might favor PD ultrafiltration failure in the long term.

Glycated adducts induce mesothelial cell transdifferentiation: role of glucose and icodextrin dialysis solutions.

BACKGROUND: In peritoneal dialysis (PD), the peritoneum is exposed to intermediate Amadori adducts (AmAs) and advanced (AGE) glycated products of proteins. The aim of this study was to test the capacity of AmAs created in different PD solutions (PDSs) to elicit a fibroblast-like transdifferentiation of human peritoneal mesothelial cells (HPMCs) in culture. METHODS: HPMCs were incubated for 12 hours with AmA obtained by human serum albumin (HSA) incubated for 6 days with commercial 3.86% glucose (Glu), 1.36% Glu and 7.5% icodextrin (Ico) PDS. Mesenchymal (vimentin), epithelial (cadherin) and myofibroblastic (Type I collagen and alpha smooth muscle cell actin [ASMA]) markers were evaluated (RT-PCR, immunostaining and Western blot), as well as TGF-b3 synthesis (ELISA and Western blot). RESULTS: Ico-PDS was less active than 3.86% and 1.36% Glu-PDS in glycating albumin (p<0.001). AmA-HSA-Glu 3.86% and 1.36% induced a significantly higher increase in vimentin and Type I collagen mRNA expression than AmA-HSA-Ico (p<0.0001). By contrast, AmA-HSA-Glu 3.86% and 1.36% induced a reduction in cadherin mRNA expression which was significantly different from AmA- HSA-Ico (p<0.0001). RT-PCR data were confirmed by immunostaining and Western blot analysis. AmA-HSA-Glu 3.86% and 1.36% induced a significantly higher increase in ASMA mRNA expression than AmA-HSA-Ico (p<0.0001). AmA-HSA-Glu 3.86% and 1.36% stimulated ASMA and TGF-b3 synthesis which were significantly higher than AmA-HSA-Ico (p<0.001 and p<0.01, respectively). CONCLUSIONS: Our data suggest that Glu-PDS, but not Ico-PDS, can turn on the fibroblastic-like transdifferentiation in HPMCs, and this mechanism may result in peritoneal sclerosis.

Antibodies to cerebellar nerve fibres in two patients with paraneoplastic cerebellar ataxia.

The aim of this study was to characterize two new atypical anti-neuronal antibodies using an immunohistochemical method on rat cerebellum and Western blot techniques with primate cerebellar tissue and with recombinant neuronal proteins. Atypical sera from two patients with paraneoplastic neurological syndromes associated with different tumours were detected. Case number 1 presented cerebellar degeneration and Merkel cell carcinoma and case number 2 paraneoplastic brainstem encephalitis and malignant fibrous histiocytoma. By immunohistochemistry, the two new atypical antibodies showed a similar fibrillar positivity in the molecular and granular layers and around the Purkinje cells. The dot blot with recombinant neuronal proteins (HuD, NOVA-1, CDR62/Yo, Amphiphysin) was negative, whereas the Western blot with neuronal antigens of primate cerebellum identified two different proteins with molecular weights (64 kD in case number 1, and 70 kD in case number 2). In conclusion, the two new antibody reactivities against nerve fibres should be integrated into the diagnostic paraneoplastic neurological syndromes guidelines.

Detection of paraneoplastic anti-neuronal-specific antibodies: comparison of different immunohistochemical techniques.

Different immunohistochemical techniques have been employed to identify the anti-neuronal antibodies in patients with paraneoplastic neurological syndromes. The finding of anti-neuronal-specific autoantibodies in serum or cerebrospinal fluid well correlates with particular types of tumors, thus leading, in many cases, to an early cancer identification. In this work, we have compared three immunohistochemical methods (immunofluorescence, indirect immunoperoxidase and avidin-biotin immunoperoxidase) on frozen and paraffin-embedded sections of rat cerebellum in order to set up a reliable and simple technique for the diagnosis of these syndromes. Our study demonstrates that the best result was obtained by using frozen sections of rat cerebellum and the avidin-biotin immunoperoxidase method that also allowed the identification of anti-GAD antibodies not detected in paraffin-embedded tissues.