Alpha8 integrin in glomerular mesangial cells and in experimental glomerulonephritis.
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BACKGROUND: Mesangial cell (MC) proliferation and extracellular matrix accumulation are typical responses of renal glomeruli to injury. Extracellular matrix components are known to affect MC behavior, which is mediated primarily via integrin receptors of the beta1 family. In addition to alpha1, alpha3, alpha5, and alpha6 chains of beta1 integrins, recent studies have shown the alpha8 chain to be expressed in glomeruli and renal vasculature. alpha8beta1 can serve as a receptor for fibronectin, which is abundant in the mesangium. We investigated the glomerular expression pattern of the alpha8 chain in renal tissues of mouse, rat, and humans as well as in cultured MCs. In addition, the regulation of alpha8 expression in MCs was studied in culture and in nephritic rats. METHODS: The expression of alpha8 protein in kidney tissue and cultured MCs was investigated by immunohistochemistry, immunocytochemistry, and Western blotting. The effects of TGF-beta1 on alpha8 mRNA levels in MCs were studied by Northern blot analysis. In addition, time course studies of glomerular abundance and localization of alpha8 were performed in rats with mesangioproliferative anti-Thy1.1 nephritis. RESULTS: In tissue sections of normal human, rat, and mouse kidney, we found strong immunohistochemical staining for alpha8 in the mesangium and in the media of renal arterioles. Double staining for alpha8 and Thy1.1, a surface antigen of rat MCs, showed alpha8 to be specifically expressed in MCs but not in glomerular endothelial and epithelial cells. In anti-Thy1.1 nephritis of rats, the glomerular abundance of alpha8 protein was reduced in the early mesangiolytic phase but was increased greatly with subsequent MC proliferation, peaking at day 6 of disease. At later stages of this reversible form of nephritis, the number of MCs and the extent mesangial alpha8 staining declined to control levels. Cell culture experiments revealed that freshly plated MCs organize alpha8 into focal contacts within one hour after attachment to fibronectin and vitronectin substrata, showing colocalization with focal contact proteins vinculin and talin. Stimulation of MCs with transforming growth factor-beta1 led to increases of alpha8 mRNA and protein levels. CONCLUSIONS: These results show that in human, rat, and mouse glomeruli, alpha8 integrin is strongly and exclusively expressed in MCs. Gene expression of alpha8 is regulated in cultured MCs, and alpha8 protein abundance is regulated in vivo and in MC culture. It is currently unclear what functional properties this integrin receptor protein has with regard to MC anchorage to extracellular matrix and modulation of the MC phenotype in normal and diseased glomeruli. However, in view of its abundance in the mesangium, alpha8beta1 integrin could be an important MC receptor of matrix ligands and may play a role in the embryology, physiology, and pathophysiology of the glomerular capillary tuft. (+info)
Recurrent ANCA-associated small vessel vasculitis after transplantation: A pooled analysis.
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BACKGROUND: Recurrent antineutrophil cytoplasmic antibody (ANCA)-associated small vessel vasculitis (ANCA-SVV) after renal transplantation has been described in case series. However, general information regarding the frequency, character, and predictors of recurrent disease after transplantation is currently lacking. We considered the rate of relapse, whether a positive ANCA at the time of transplantation predicted relapse, and whether cyclosporine A prevented recurrent disease. METHODS: We performed a pooled analysis of published data, added to the experience at the Universities of North Carolina (14 patients) and Lund, Sweden (11 patients). To avoid reporting bias, only case series were included for analysis. Subgroup analysis was performed by disease category (Wegener's granulomatosis, microscopic polyangiitis, or necrotizing crescentic glomerulonephritis) and ANCA staining pattern. RESULTS: ANCA-SVV recurred in 17.3% of all patients (N = 127), in 20% of cyclosporine A-treated patients (N = 85), and in 25.6% of patients with circulating ANCA at the time of transplantation (N = 39). There was no statistically significant difference in the relapse rate between patients treated and those not treated with cyclosporine A (P = 0.45), between those with and without circulating ANCA at the time of transplant (P = 0.75), or between patients with Wegener's granulomatosis and those with microscopic polyangiitis or necrotizing crescentic glomerulonephritis alone (P = 0.62). CONCLUSION: There is a substantial relapse rate in the ANCA-SVV population. Therapy with cyclosporine A does not protect against recurrent ANCA-SVV, and the presence of a positive ANCA at the time of transplantation does not preclude transplantation. These conclusions must be substantiated with a prospective study of renal transplantation in patients with ANCA-SVV so as to optimize their management. (+info)
VEGF(165), the most abundant isoform in man, is an angiogenic cytokine that also regulates vascular permeability. Its function in the renal glomerulus, where it is expressed in visceral epithelial and mesangial cells, is unknown. To assess the role of VEGF(165) in glomerular disease, we administered a novel antagonist - a high-affinity, nuclease-resistant RNA aptamer coupled to 40-kDa polyethylene glycol (PEG) - to normal rats and to rats with mesangioproliferative nephritis, passive Heymann nephritis (PHN), or puromycin aminonucleoside nephrosis (PAN). In normal rats, antagonism of VEGF(165) for 21 days failed to induce glomerular pathology or proteinuria. In rats with mesangioproliferative nephritis, the VEGF(165) aptamer (but not a sequence-scrambled control RNA or PEG alone) led to a reduction of glomerular endothelial regeneration and an increase in endothelial cell death, provoking an 8-fold increase in the frequency of glomerular microaneurysms by day 6. In contrast, early leukocyte influx and the proliferation, activation, and matrix accumulation of mesangial cells were not affected in these rats. In rats with PHN or PAN, administration of the VEGF(165) aptamer did not influence the course of proteinuria using various dosages and administration routes. These data identify VEGF(165) as a factor of central importance for endothelial cell survival and repair in glomerular disease, and point to a potentially novel way to influence the course of glomerular diseases characterized by endothelial cell damage, such as various glomerulonephritides, thrombotic microangiopathies, or renal transplant rejection. (+info)
Renal protective effects of blocking the intrarenal renin-angiotensin system.
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It has been well demonstrated that angiotensin-converting enzyme inhibitors (ACEIs) can retard the progression of renal failure and kidney sclerosis in patients and animal models with glomerular diseases. The aim of this study was to observe the influences of ACEI on intrarenal Ang II and TGFbeta1 local formation and their relation to renal protective effects. Experimental glomerulosclerosis with nephrotic syndrome was induced in unilateral nephrectomized rats with repeated injections of adriamycin. Rats were randomly divided into three groups: 1) a sham-operated control group (n=8); 2) an NS group treated with ACEI (benazepril 4 mg/kg/d) (n=10), and 3) an NS group not treated (n=10). After 8 wk, serum, urine and renal tissue were collected for study. ACE activity and Ang II concentration in renal tissue were measured by colorimetry and radioimmunoassay, respectively. Immunohistochemistry staining was employed for transforming growth factor-beta1 (TGFbeta1) and extracellular matrix (ECM) examination. TGFbeta1 mRNA was assessed by in situ hybridization. Compared with those of non-treated nephropathy rats, ACE activity (13.39+/-5.02 vs. 49.13+/-12.92 U/ml, p< 0.01) and Ang II (402.61+/-80.22 vs. 751.63+/-137.45 pg/mg/pr p < 0.01) in renal tissue were significantly inhibited in the rats treated with ACEI. At the same time, proteinuria was significantly reduced (155.06+/-103.56 vs. 421.11+/-148.45 mg/24 h, p < 0.01) and renal function improved (Scr 76.3+/-33.1 vs. 107.1+/-71.0, p < 0.05), concomitant with a reduction in the glomerular sclerosis index (30.6+/-19.5 vs. 120.3+/-61.9, p < 0.01) and a reduction in ECM accumulation such as Col IV, III, LN and FN (29.2+/-9.8 vs. 76.8+/-12.4; 29.5+/-12.4 vs. 85.9+/-11.5; 26.0+/-5.1 vs. 69.6+/-1.73; 32.4+/-12.4 vs. 70.5+/-13.5; p< 0.01 in all cases). In the ACEI treated group, these histologic benefits coincided with a reduced expression of TGFbeta1 in both tubular cells and sclerosed glomeruli in protein as well as mRNA level. These findings provide further evidence that ACEI (benazepril) can prevent the progression of renal damage in both the function and morphologic changes which associated with a down-regulation of intrarenal Ang II level through the relative inhibition of renal ACE activity. The blocking of the intrarenal renin angiotensin system (RAS) might contribute to the inhibition of TGFbeta1 local formation and the TGFbeta1-mediated ECM accumulation that are related to the renal protective effects of ACEI. (+info)
Immunopathology of ANCA-associated vasculitis.
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During the past few years remarkable progress has been achieved in the understanding of the pathogenic mechanisms leading to vascular inflammation and injury in ANCA-associated vasulitides (AAV): Wegener's granulomatosis (WG), microscopic polyangiitis (MPA) and Churg Strauss syndrome (CSS). In this paper we review the immunopathology of these diseases by describing the role of autoantibodies (ANCA), dysregulation and abnormalities at the cellular level, genetic background and environmental factors that predispose to autoimmune response. (+info)
Induced nitric oxide (NO) synthesis in heterologous nephrotoxic nephritis; effects of selective inhibition in neutrophil-dependent glomerulonephritis.
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Increased NO synthesis, due to inducible NO synthase (iNOS) activity, is found in macrophage-associated glomerulonephritis. Little is known about NO in neutrophil-dependent immune complex inflammation, and its role remains controversial. We therefore studied early phase heterologous nephrotoxic nephritis (HNTN) induced in rats by nephrotoxic globulin and the effects of selective iNOS inhibition of this model. At 2 h of the model iNOS mRNA was induced and nitrite (NO-2) was generated in glomeruli incubated ex vivo (5.2 +/- 1.0 nmol/2000 glomeruli per 24 h). There were 14.7 +/- 2.2 polymorphonuclear neutrophils (PMN)/glomerulus (normal controls 0.1 +/- 0.1). At 8 h urinary protein was 69 +/- 15.3 (normal controls 0. 6 +/- 0.2 mg/24 h). Peritoneal PMN expressed iNOS and produced significant NO-2 (basal 11.2 +/- 0.3 nmol/106 cells per 24 h). Selective iNOS inhibition with L-N6-(1-iminoethyl)-lysine (L-NIL) in vitro inhibited nephritic glomerular and PMN NO-2 synthesis. In HNTN L-NIL in vivo significantly suppressed elevated plasma NO-2/NO-3 levels (representative experiment: 17 +/- 2 microM, untreated 40 +/- 4 microM, P = < 0.01, normal control 18 +/- 2 microM). This inhibition did not affect leucocyte infiltration into glomeruli or induce thrombosis. There was no consistent effect on proteinuria. This is the first demonstration of glomerular iNOS induction and high output NO production in the acute phase of PMN-dependent acute immune complex glomerulonephritis. Selective iNOS inhibition does not affect the primary mechanism of injury (leucocyte infiltration) in this model. (+info)
The tenascin-C knockout revisited.
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In the past seven years, two groups have independently produced tenascin-C-knockout mice. These mice are born alive and, originally, were described as showing no abnormalities. More recent studies, many involving pathological intervention, have shown that tenascin-C-knockout mice have several defects. The mice exhibit abnormal behaviour, as well as abnormalities in brain chemistry. They also show defects in structure and repair of neuromuscular junctions, in the ability to recover from snake-venom-induced glomerulonephritis and in chemically induced dermatitis. Healing of skin wounds is morphologically normal, but the mice exhibit defects in healing after suture injury of corneas. In both skin and corneal wounds, fibronectin expression is abnormally low in tenascin-C-knockout mice. Finally, in vitro studies indicate that haemopoietic activity is defective in bone marrow from these mice. When examined together, these studies provide evidence for precise functions for tenascin-C, as well as an explanation for why the sequence of tenascin-C is so highly phylogenetically conserved. (+info)
In the passive Heymann nephritis (PHN) model of membranous nephropathy, C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which is partially mediated via production of eicosanoids. Using rat GEC in culture, we demonstrated that sublytic C5b-9 induced tyrosine phosphorylation of the epidermal growth factor receptor (EGF-R), Neu, fibroblast growth factor receptor-2, and hepatocyte growth factor receptor. In addition, C5b-9 stimulated increases in tyrosine(204) phosphorylation of extracellular signal-regulated kinase-2 (ERK2), as well as free [(3)H]arachidonic acid (AA) and prostaglandin E(2) (PGE(2)). Phosphorylated EGF-R bound the adaptor protein, Grb2, and the EGF-R-selective tyrphostin, AG1478, blocked the C5b-9-induced ERK2 phosphorylation, [(3)H]AA release, and PGE(2) production by 45 to 65%, supporting a functional role for EGF-R kinase in mediating the activation of these pathways. Glomeruli isolated from rats with PHN demonstrated increases in ERK2 tyrosine(204) phosphorylation and PGE(2) production, as compared with glomeruli from control rats, and these increases were partially inhibited with AG1478. Thus, C5b-9 induces transactivation of receptor tyrosine kinases, in association with ERK2 activation, AA release, and PGE(2) production in cultured GEC and glomerulonephritis in vivo. Transactivated tyrosine kinases may serve as scaffolds for assembly and/or activation of proteins, which then lead to activation of the ERK2 cascade and AA metabolism. (+info)