Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.6.3.1 (NADPH oxidase)
 11,281 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the rat passive Heymann nephritis model of membranous nephropathy, complement C5b-9 induces sublethal glomerular epithelial cell (GEC) injury and proteinuria. C5b-9 activates cytosolic phospholipase A(2) (cPLA(2)), and products of cPLA(2)-mediated phospholipid hydrolysis modulate GEC injury and proteinuria. In the present study, we demonstrate that C5b-9 activates c-Jun N-terminal kinase (JNK) in cultured rat GECs and that JNK activity is increased in glomeruli isolated from proteinuric rats with passive Heymann nephritis, as compared with control rats. Stable overexpression of cPLA(2) in GECs amplified complement-induced release of arachidonic acid (AA) and JNK activity, as compared with neo (control) GECs. Activation of JNK was not affected by indomethacin. Incubation of GECs with complement stimulated production of superoxide, and pretreatment with the antioxidants, N-acetylcysteine, glutathione, and alpha-tocopherol as well as with diphenylene iodonium, an inhibitor of the NADPH oxidase, inhibited complement-induced JNK activation. Conversely, H(2)O(2) activated JNK, whereas exogenously added AA stimulated both superoxide production and JNK activity. Overexpression of a dominant-inhibitory JNK mutant or treatment with diphenylene iodonium exacerbated complement-dependent GEC injury. Thus, activation of cPLA(2) and release of AA facilitate complement-induced JNK activation. AA may activate the NADPH oxidase, leading to production of reactive oxygen species, which in turn mediate the activation of JNK. The functional role of JNK activation is to limit or protect GECs from complement attack.
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PMID:Complement activates the c-Jun N-terminal kinase/stress-activated protein kinase in glomerular epithelial cells. 1219 30

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Active and passive Heymann nephritis (HN) in rats are valuable experimental models because their features so closely resemble human MN. In HN, subepithelial immune deposits form in situ as a result of circulating antibodies. Complement activation leads to assembly of C5b-9 on glomerular epithelial cell (GEC) plasma membranes and is essential for sublethal GEC injury and the onset of proteinuria. This review revisits HN and focuses on areas of substantial progress in recent years. The response of the GEC to sublethal C5b-9 attack is not simply due to disruption of the plasma membrane but is due to the activation of specific signaling pathways. These include activation of protein kinases, phospholipases, cyclooxygenases, transcription factors, growth factors, NADPH oxidase, stress proteins, proteinases, and others. Ultimately, these signals impact on cell metabolic pathways and the structure/function of lipids and key proteins in the cytoskeleton and slit-diaphragm. Some signals affect GEC adversely. Thus C5b-9 induces partial dissolution of the actin cytoskeleton. There is a decline in nephrin expression, reduction in F-actin-bound nephrin, and loss of slit-diaphragm integrity. Other signals, such as endoplasmic reticulum stress, may limit complement-induced injury, or promote recovery. The extent of complement activation and GEC injury is dependent, in part, on complement-regulatory proteins, which act at early or late steps within the complement cascade. Identification of key steps in complement activation, the cellular signaling pathways, and the targets will facilitate therapeutic intervention in reversing GEC injury in human MN.
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PMID:Experimental membranous nephropathy redux. 1615

In the rat passive Heymann nephritis (PHN) model of membranous nephropathy, complement C5b-9 activates protein kinases in glomerular epithelial cells (GEC), and induces sublethal GEC injury and proteinuria. Complement induces production of reactive oxygen species (ROS) via the NAPDH oxidase, and stimulates phosphorylation of c-Jun N-terminal kinase (JNK) and p38 kinase in a ROS-dependent manner. In the present study, we demonstrate that apoptosis signal-regulating kinase 1 (ASK1) was activated in glomeruli of rats with PHN, and that incubation of GEC in culture with antibody and sublytic C5b-9 stimulated ASK1 activity. The latter was, in part, mediated via the NADPH oxidase and ROS. Sublytic complement induced JNK and p38 phosphorylation, which was amplified in GEC that stably overexpress ASK1, as compared with Neo (control) GEC. Complement-induced lysis was enhanced in GEC that overexpress ASK1, as compared with Neo, and was attenuated in GEC that overexpress a dominant negative ASK1 mutant. Inhibition of p38, but not JNK, attenuated complement lysis in GEC that overexpress ASK1, but not in Neo GEC. In Neo GEC, generation of ROS restricted complement-mediated GEC injury but the protective effect of ROS was lost when ASK1 was overexpressed. We propose that the level of ASK1 expression determines the functional effect of p38 activation, i.e. when ASK1 is overexpressed, p38 activation is amplified, and C5b-9 assembly leads to GEC injury via ASK1 and p38. The present study thus defines a novel role for ASK1 as a mediator of C5b-9-dependent cell injury.
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PMID:Role of apoptosis signal-regulating kinase 1 in complement-mediated glomerular epithelial cell injury. 1817 52

Membranous nephropathy is a major cause of nephrotic syndrome in adults where podocyte injuries were found to mediate the development of proteinuria. Triptolide, a major active component of Tripterygium wilfordii Hook F, has potent immunosuppressive, anti-inflammatory and antiproteinuric effects. To study its antiproteinuric properties, we established an experimental rat model of passive Heymann nephritis and a C5b-9 injury model of podocytes in vitro. Treatment or pretreatment with triptolide markedly reduced established proteinuria as well as the titer of circulating rat anti-rabbit IgG antibodies in these nephritic rats, accompanied by a reduction in glomerular C5b-9 deposits. Expression of desmin, a marker of podocyte injury, diminished after triptolide treatment, whereas quantitative analysis of mean foot process width showed that effacement of foot processes was substantially reversed. In in vitro studies we found that triptolide deactivated NADPH oxidase, suppressed reactive oxygen species generation and p38 mitogen-activated protein kinase, and restored RhoA signaling activity. Triptolide did not interfere with the formation of C5b-9 on the membrane of podocytes. Thus, triptolide reduces established heavy proteinuria and podocyte injuries in rats with passive Heymann nephritis, and protects podocytes from C5b-9-mediated injury.
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PMID:Triptolide reduces proteinuria in experimental membranous nephropathy and protects against C5b-9-induced podocyte injury in vitro. 2037 80

The understanding of cellular and molecular mechanisms involved in the pathogenesis of membranous nephropathy (MN) has come from studies carried out in the Heymann nephritis model of MN in the rat, which closely resembles the clinical and pathologic features of the human disease. MN involves the in situ formation of subepithelial immune deposits as a result of circulating antibodies binding to podocyte antigens. Complement activation leads to assembly of C5b-9 on podocyte plasma membranes, and results in sublethal podocyte injury and proteinuria. The podocyte responds to sublethal C5b-9 attack by activating protein kinases, phospholipases, cyclooxygenases, transcription factors, growth factors, NADPH oxidase, stress pathways, proteinases, etc. These signals impact on cell metabolic pathways, the structure/function of lipids and key proteins in the cytoskeleton and slit diaphragm, and on the turnover of extracellular matrix components. Some effects of C5b-9, including dissolution of the actin cytoskeleton, loss of nephrin expression, reduction in F-actin-bound nephrin and loss of slit diaphragm integrity, affect podocytes adversely. Other effects of complement, such as endoplasmic reticulum stress, may limit injury or promote recovery. A number of studies have confirmed the relevance of several experimental insights to the pathogenesis of human MN, including the presence of autoantibodies directed to podocyte antigens in human MN. Increased understanding of nephritogenic antigens, complement activation, and the cellular signaling pathways and targets of C5b-9 will facilitate the design of new approaches to therapy of this important glomerular disease.
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PMID:Membranous nephropathy. 2125 14