Expression of Ser729 phosphorylated PKCepsilon in experimental crescentic glomerulonephritis: an immunohistochemical study.

PKCε, a DAG-dependent, Ca2+- independent kinase attenuates extent of fibrosis following tissue injury, suppresses apoptosis and promotes cell quiescence. In crescentic glomerulonephritis (CGN), glomerular epithelial cells (GEC) contribute to fibro-cellular crescent formation while they also transdifferentiate to a mesenchymal phenotype. The aim of this study was to assess PKCε expression in CGN. Using an antibody against PKC-ε phosphorylated at Ser729, we assessed its localization in rat model of immune-mediated rapidly progressive CGN. In glomeruli of control animals, pPKCε was undetectable. In animals with CGN, pPKCε was expressed exclusively in glomerular epithelial cells (GEC) and in GEC comprising fibrocellular crescents that had acquired a myofibroblast-type phenotype. In non-immune GEC injury induced by puromycin aminonucleoside and resulting in proteinuria of similar magnitude as in CGN, pPKCε expression was absent. There was constitutive pPKCε expression in distal convoluted tubules, collecting ducts and thick segments of Henley's loops in both control and experimental animals. We propose that pPKCε expression occurring in GEC and in fibrocellular crescentic lesions in CGN may facilitate PKCε dependent pathologic processes.

Regulation of human P2X1 promoter activity by beta helix-loop-helix factors in smooth muscle cells.

We isolated and characterized genomic clones of the human P2X1 receptor (hP2X1) gene in an effort to understand its tissue specific expression. The hP2X1 gene contains 12 exons spanning 20 kb, with exon sizes ranging from 59 to 143 bp. A 385 bp upstream fragment promoted hP2X1 gene expression in smooth muscle (A7R5 and primary trachealis) and fibroblast (NIH3T3) cell lines, and mutation of a consensus E box sequence (CACCTG) within this fragment (-340 to -345) did not alter basal promoter activity. However, co-transfected bHLH factors regulated activity of the 385 bp minimal P2X1 promoter in a tissue-specific manner. E12 expression inhibited and ITF2b augmented activity in A7R5 cells, but had no effect in NIH3T3 cells. ITF2a, Myo-D, and Id1 proteins had no effect on either cell line, but co-expression of ITF2a blocked E12 inhibition in A7R5 cells, while ITF2b failed to reverse the inhibition. Northern analysis of A7R5 RNA identified high levels of E12 and ITF2b transcripts, and gel shift assays using A7R5 and NIH3T3 nuclear extracts indicated the formation of a protein-DNA complex with an oligonucleotide corresponding to -330 and -348, which was abolished by base substitutions within the E box motif. Our results identify a critical E box response element in the hP2X1 promoter that binds bHLH factors and demonstrate smooth muscle specific transcriptional regulation by E proteins.

Induction of heme oxygenase 1 in radiation nephropathy: role of angiotensin II.

Datta, P. K., Moulder, J. E., Fish, B. L., Cohen, E. P. and Lianos, E. A. Induction of Heme Oxygenase 1 in Radiation Nephropathy: Role of Angiotensin II. Radiat. Res. 155, 734-739 (2001). In a rat model of radiation-induced nephropathy, we investigated changes in expression of heme oxygenase 1 (Hmox1, also known as HO-1), an enzyme that catalyzes conversion of heme into biliverdin, carbon monoxide and iron. The study explored whether radiation induces Hmox1 expression in the irradiated kidney and whether angiotensin II (AII) mediates Hmox1 expression in glomeruli isolated from irradiated kidneys. To assess the effects of radiation on Hmox1 expression, rats received 20 Gy bilateral renal irradiation and were randomized to groups receiving an AII type 1 (AT(1)) receptor antagonist (L-158,809) or no treatment. Drug treatment began 9 days prior to bilateral renal irradiation and continued for the duration of the study. Estimation of Hmox1 levels in glomerular protein lysates assessed by Western blot analysis revealed a significant increase in Hmox1 protein at 50 and 65 days postirradiation. In animals treated with the AT(1) receptor antagonist, there was no induction of Hmox1, suggesting that AII may be a mediator of Hmox1 induction. To confirm that AII stimulates Hmox1 expression, animals were infused with 200, 400 or 800 ng/kg min(-1) of AII for 18-19 days, and Hmox1 protein levels in glomeruli were assessed. There was a significant induction of Hmox1 in glomeruli of animals infused with 800 ng/kg min(-1) of AII. These studies demonstrate that glomerular Hmox1 expression is elevated in the middle phase of radiation nephropathy and that AII can increase glomerular Hmox1 levels.

Effects of all-trans-retinoic acid (atRA) on inducible nitric oxide synthase (iNOS) activity and transforming growth factor beta-1 production in experimental anti-GBM antibody-mediated glomerulonephritis.

Sustained high output release of Nitric oxide (NO) as result of activation of inducible nitric oxide synthase (iNOS), and increased production of the antiproliferative/profibrotic cytokine transforming growth factor-beta1 (TGF-beta1) are well documented in glomerulonephritis. Modulation of iNOS activity and of TGF-beta1 production can therefore be viewed as anti-inflammatory strategies. The present study employed all-trans retinoic acid (atRA) which is known to have anti-inflammatory effects and to modulate expression of iNOS and TGF-beta1, in order to explore its effect on iNOS enzyme activity and TGF-beta1 production in anti-GBM antibody induced glomerulonephritis. Glomerulonephritis was induced in Lewis rats by injection of anti-GBM antibody. A group of nephritic rats were given daily administration of atRA for 14-16 days. Extent of proteinuria was assessed by measuring urine protein and creatinine excretion. iNOS enzyme activity was measured by calculating conversion of L[14C]arginine to L-[14C]citrulline in glomerular protein lysates. Levels of TGF-beta1 in glomerular protein lysates were measured by quantitative ELISA. Levels of proliferating nuclear antigen (PCNA), TGF-beta receptor II (TGFbeta-RII), and fibronectin were assessed by Western blot analysis. Glomerular iNOS activity in atRA treated nephritic animals was attenuated in comparison to that in nephritic controls that were not. Glomerular expression of PCNA was also reduced. Levels of TGF-beta1 were increased in glomeruli of atRA treated nephritic animals. In these animals, there was no change in glomerular levels of TGF-beta receptor II (TGFbeta-RII) or fibronectin. and there was no reduction in urine protein excretion. These results suggest that atRA attenuates iNOS activity and proliferation in glomeruli of nephritic animals. The failure of atRA treatment to reduce proteinuria could be due to the increase in TGF-beta1 levels and to inhibition of iNOS-driven NO production.

Heme oxygenase-1 induction attenuates inducible nitric oxide synthase expression and proteinuria in glomerulonephritis.

In glomerulonephritis, there is intraglomerular activation of inducible nitric oxide synthase (iNOS) leading to high output production of nitric oxide (NO). This can result in supraphysiologic amounts of NO and cause oxidative injury. It is unknown whether mechanisms of cellular defense against NO-mediated injury exist. Induction of the heme catabolizing enzyme heme oxygenase-1 (HO-1), which generates biliverdin, carbon monoxide (CO), and iron (Fe), may provide such a mechanism, as CO and Fe are two negative modulators of iNOS activity and expression. This study assessed whether upregulation of HO-1 by a specific inducer, hemin, negatively modulates iNOS expression and activity in anti-glomerular basement membrane antibody-mediated glomerulonephritis. Glomerular HO-1 expression in nephritic animals was upregulated by treatment with hemin (30 micromol/kg body wt). iNOS and HO-1 mRNA expression were assessed by reverse transcription-PCR of glomerular total RNA from nephritic animals or nephritic animals pretreated with hemin. iNOS activity in glomeruli was measured by assessing conversion of [14C] L-arginine to [14C] L-citrulline. HO-1 protein levels in glomeruli were assessed by Western blot analysis. The effect of hemin treatment on monocyte/macrophage infiltration was assessed by enumeration of ED-1-positive cells in nephritic glomeruli. iNOS and HO-1 were coinduced in nephritic glomeruli. Hemin treatment of nephritic animals resulted in upregulation of glomerular HO-1 levels and a two- to threefold reduction in glomerular iNOS mRNA levels. iNOS activity in glomeruli was significantly reduced in hemin-treated nephritic animals in which proteinuria was also attenuated without a change in monocyte/macrophage infiltration. Hemin (100 to 200 microM) also reduced iNOS protein levels and enzyme activity in cultured mesangial cells stimulated with cytokines. These studies demonstrate that in glomerular immune injury, hemin treatment upregulates glomerular HO-1 with an attendant downregulation of iNOS expression, and thus points to regulatory interaction between the two systems. The beneficial effect of hemin treatment on proteinuria could be linked to downregulation of iNOS.

Effect of thromboxane A2 inhibition and antagonism on prostaglandin and leukotriene synthesis in glomerular immune injury.

In glomerulonephritis there is co-activation of the arachidonic acid cyclooxygenase pathway toward synthesis of prostaglandins (PG) and thromboxane (Tx) and of lipoxypenase pathways toward synthesis of hydroxyeicosatetraenoic acids (HETEs) and leukotrienes (LTs). Cyclooxygenase inhibition with non-steroidal anti-inflammatory drugs results in enhanced glomerular LT synthesis with potentially adverse effects on the severity of the inflammation. The effect of Tx inhibition or antagonism on LT synthesis is unknown. Because TxA2 is the most abundant eicosanoid synthesized in nephritic glomeruli, and because TxA2 synthase inhibitors and receptor antagonists are now available for the treatment of glomerulonephritis, it becomes important to address this question. In this study we assessed the effect of a TxA2 synthase inhibitor, Dazmegrel, and a TxA2 receptor antagonist, SQ-29 548, on glomerular PGE2, LTB4, and 12-HETE synthesis in a model of mesangial nephritis induced in the rat by the administration of a monoclonal antibody against the Thy 1.1 antigen of rat mesangial cells. Dazmegrel, in doses sufficient to effectively block glomerular TxA2 synthesis, significantly increased 12-HETE and PGE2 synthesis without an effect on the synthesis of LTB4. SQ-29 548 had no effect on glomerular PGE2, LTB4, or 12-HETE production. Because PGE2 preserves kidney function in glomerulonephritis, and because 12-HETE inhibits 5-lipoxygenase, the enhanced PGE2 and 12-HETE production within nephritic glomeruli after TxA2 synthase inhibition may be a superior anti-inflammatory strategy when compared with TxA2 receptor antagonism.

Enhanced expression of the cytoskeleton-associated proteins paxillin and focal adhesion kinase in glomerular immune injury.

In a rat model of glomerular immune injury induced by antibody against the glomerular basement membrane (GBM), we assessed changes in the levels and in the extent of tyrosine phosphorylation of two cytoskeleton-associated proteins, focal adhesion kinase (FAK) and paxillin. Glomeruli were isolated 2, 7, and 14 days after the administration of a rabbit anti-rat GBM antibody that induced proliferative nephritis and proteinuria. FAK and paxillin levels in glomerular protein lysates were assessed by immunoprecipitation followed by Western blot analysis. Changes in the tyrosine phosphorylation of immunoprecipitated paxillin and FAK were assessed by Western blot analysis with antiphosphotyrosine antibodies. Glomerular levels of FAK and paxillin were increased in nephritic glomeruli as compared with non-nephritic controls at all time points. There was a discordant increase in the tyrosine phosphorylation levels of paxillin and FAK; the increase in the tyrosine phosphorylation of FAK was sustained and peaked on day 7 of immune injury, whereas that of paxillin was short-lived and peaked on day 2 of injury. We propose that these changes in FAK and paxillin expression and tyrosine phosphorylation reflect interactions between glomerular cells and accumulating extracellular matrix proteins in the course of immune injury, or they constitute parts of wider signaling events within the nephritic glomerulus that involve the cytoskeleton.

Retinoic acids inhibit inducible nitric oxide synthase expression in mesangial cells.

BACKGROUND: Nitric oxide (NO) release as a result of cytokine-mediated activation of inducible nitric oxide synthase (iNOS) in mesangial cells can be sustained and lead to oxidative injury in various forms of glomerular inflammation. Inhibition of iNOS expression and/or activity could therefore be an effective anti-inflammatory strategy. The present study was undertaken to explore whether retinoids, which are known to have anti-inflammatory and immuno-modulatory actions, can attenuate cytokine-stimulated iNOS expression and enzyme activity in murine mesangial cells. METHODS: Expression of iNOS was evaluated by NO production (nitrite analysis), protein (Western blot analysis) and mRNA (RT-PCR analysis) levels in mesangial cells stimulated by a combination of lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) in the presence and absence of all-trans-retinoic acid (ATRA) or its active metabolite, 13-cis-retinoic acid (13-cis-RA). Changes in iNOS enzyme activity were assessed by calculating conversion of L-[14C]arginine to L-[14C]citrulline. The levels of transcription factors nuclear factor-kappaB (NF-kappaB) and activated protein-1 (AP-1) in nuclear extracts prepared from mesangial cells stimulated by a combination of LPS and IFN-gamma in the presence and absence of ATRA was assessed by immunoblot analysis. The effect of both retinoids on transforming growth factor-beta1 (TGF-beta1) levels was also assessed by a quantitative enzyme immunoassay method. RESULTS: The combination of LPS/IFN-gamma stimulated NO production, induced iNOS expression (mRNA and protein) and increased iNOS enzyme activity. ATRA and 13-cis-RA dose-dependently attenuated NO production. This effect was most pronounced at ATRA concentration of 10 microM. At this concentration, ATRA attenuated iNOS expression (mRNA and protein levels) and enzyme activity. ATRA also reduced nuclear levels of both subunits (p50 and p65) of NF-kappaB. TGF-beta1 levels in mesangial cells stimulated with LPS/IFN-gamma in presence of ATRA or 13-cis-RA were also reduced indicating that TGF-beta1 did not mediate the suppressive effect of retinoids on iNOS. CONCLUSIONS: Our studies demonstrate that the retinoids ATRA and 13-cis-RA attenuate iNOS expression and activity in cytokine-stimulated murine mesangial cells. These retinoids may emerge as naturally occurring compounds for treatment of inflammatory glomerular diseases.

Nitric oxide induces heme oxygenase-1 gene expression in mesangial cells.

BACKGROUND: Nitric oxide (NO) release as a result of activation of inducible NO synthase (iNOS) can be sustained and reach cytotoxic concentrations. It is unknown whether cells possess intrinsic systems to attenuate NO-mediated cytotoxicity. One potential system is the heme oxygenase-1 (HO-1) enzyme because it catabolizes heme and therefore may limit synthesis or availability of iNOS. These studies were undertaken to explore whether NO derived from NO donors or from activation of iNOS induces HO-1 in mesangial cells. METHODS: The expression of the HO-1 gene was evaluated at the mRNA (Northern blot analysis) and protein (Western blot analysis) levels in mesangial cells treated with two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetyl-DL-penicillamine (SNAP), or was stimulated by the combination of lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) to induce iNOS in the presence and absence of NOS inhibitor NG-Monomethyl-L-arginine (L-NMMA). RESULTS: HO-1 was constitutively expressed in mesangial cells. Both SNP and SNAP induced HO-1 mRNA in a dose-dependent manner. The increase in mRNA was associated with an increase in HO-1 protein in SNP-treated cells. The combination of the LPS/IFN-gamma mixture induced iNOS expression and NO production in murine mesangial cells, as assessed by Western blot analysis and measurement of nitrite levels. HO-1 expression was also increased in response to LPS/IFN-gamma. L-NMMA dose dependently attenuated HO-1 mRNA and protein levels. In contrast, iNOS expression was dose dependently enhanced. CONCLUSIONS: Our studies demonstrate that both exogenously or iNOS-derived NO enhance HO-1 expression in mesangial cells and point to regulatory interactions between the iNOS and HO pathways. HO-1 activation may defend against NO-mediated toxicity.

Glucocorticoid effect on human mesangial cell cytoskeletal proteins.

In human mesangial cells (HMCs), we assessed the effect of dexamethasone on the expression and levels of tyrosine phosphorylation of two cytoskeleton-associated proteins: focal adhesion kinase (FAK) and paxillin. Dexamethasone, 10(-7) mol/L, increased levels of tyrosine phosphorylation of both proteins within 15 to 30 minutes without a change in protein levels. The exposure of HMCs to cytochalasin B, a disrupter of the cytoskeleton assembly, reduced basal tyrosine phosphorylation of both proteins. This effect was reversed by dexamethasone. These observations support a stabilizing effect of dexamethasone on the mesangial cell cytoskeleton. This may constitute a cytoprotective mechanism in the context of the anti-inflammatory action of the steroids in various glomerulopathies.

The inhibition of myeloperoxidase by ceruloplasmin can be reversed by anti-myeloperoxidase antibodies.

BACKGROUND: The purpose of this study was to characterize the recently reported inhibition of myeloperoxidase (MPO) by ceruloplasmin and to determine whether this may be disturbed in the presence of anti-MPO antibodies. METHODS: Specificity of the binding between ceruloplasmin and MPO was confirmed by Western blotting and enzyme-linked immunosorbent assay (ELISA), and the enzymatic activity of MPO was measured in the presence of ceruloplasmin, affinity-purified anti-MPO antibodies, or both. The affinity of the binding between MPO and ceruloplasmin and MPO and the anti-MPO antibodies was measured using a biosensor, with the results confirmed by chaotrope ELISA. RESULTS: Affinity-purified anti-MPO antibodies from patients with microscopic polyangiitis and florid renal vasculitis inhibited the binding between ceruloplasmin and MPO to a maximum of 72.9 +/- 12.8%, whereas those from patients with Wegener's granulomatosis and only minimal renal involvement inhibited the binding to a maximum of only 36.8 +/- 10.9% (P < 0. 001), with comparable reversal of the ceruloplasmin-mediated inhibition of MPO activity. Measurement of the affinity of the interactions demonstrated that binding between MPO and the anti-MPO antibodies is stronger than that between MPO and ceruloplasmin (1.61 x 107 to 1.33 x 108 vs. 7.46 x 106 m-1), indicating that binding to the autoantibody would be favored in vivo. CONCLUSIONS: This study confirms a role for ceruloplasmin as a physiological inhibitor of MPO, and demonstrates how the inhibition may be disrupted in the presence of anti-MPO antibodies. Because a majority (16 of 21) of the antibodies did not themselves inhibit MPO activity, their interference with the inhibition mediated by ceruloplasmin may be brought about by steric hindrance consequent upon the binding of the antibody to a dominant epitope at or near the active site.

Changes in glomerular thromboxane A2 receptor expression and ligand binding following immune injury.

BACKGROUND: Thromboxane (Tx) A2 is a potent vasoconstrictor eicosanoid that attains high levels within nephritic glomeruli and mediates a drop in glomerular filtration rate (GFR). In the course of nephritis, however, GFR recovers despite high intraglomerular TxA2 levels. We hypothesized that this recovery indicates a reduced responsiveness of the glomerular vasculature to TxA2, and explored whether changes in TxA2 receptor protein expression and receptor-ligand binding are underlying mechanisms. METHODS: Glomerulonephritis was induced in male Sprague-Dawley rats using an antibody raised in rabbits against rat particulate glomerular basement membrane (GBM). Changes in Tx receptor levels were assessed in protein lysates of glomeruli on days 3 and 7 after a single intravenous injection of the anti-GBM antibody. Ligand-binding studies were performed at the same time points using isolated glomeruli and the TxA2 receptor ligand [3H]-SQ-29,548. GFR was measured as the clearance of endogenous creatinine. RESULTS: There was a marked increase in Tx receptor protein in the lysates of nephritic glomeruli on days 3 and 7. In contrast, binding sites (Bmax) of [3H]-SQ-29,548 decreased, indicating that the excess receptor became either inaccessible to its ligand (sequestered) or desensitized. Daily administration of the Tx synthase inhibitor Furegrelate starting prior to injection of anti-GBM antibody prevented the decrease in [3H]-SQ-29,548 binding. Furegrelate treatment starting in an established stage of nephritis had no effect. In these animals, GFR was lower than nephritic controls not treated with Furegrelate. CONCLUSIONS: These observations indicate that in the course of glomerulonephritis, there is a marked increase in glomerular Tx receptor expression. The enhanced intraglomerular TxA2 synthesis causes either a sequestration or desensitization of its receptor. As a result, access of unbound TxA2 to efferent arterioles may become facilitated, and constriction of these arterioles may preserve GFR.

TGF-beta 1 production in radiation nephropathy: role of angiotensin II.

PURPOSE: Angiotensin II receptor antagonists are effective in the prophylaxis of radiation nephropathy. Studies were designed to determine whether TGF-beta 1, a fibrogenic cytokine, plays a role in mediating the protective effect of AII antagonism. These studies explored the time-course of glomerular TGF-beta 1 production in the irradiated kidney, and whether AII mediates TGF-beta 1 production in glomeruli isolated from irradiated rats. MATERIALS AND METHODS: Rats received 20 Gy of bilateral renal irradiation in five fractions and were randomized to receive an AII type 1 receptor antagonist (L-158,809) at 20mg/l in their drinking water, or no treatment. Drug therapy began 9 days prior to irradiation and continued for the duration of the study. RESULTS: Analysis of renal function showed a significant increase in urinary proteinuria and blood urea nitrogen by 37 days and 63 days after irradiation, respectively. Estimation of glomerular TGF-beta1 levels by quantitative sandwich enzyme immunoassay technique revealed a significant increase in latent but not active TGF-beta 1 levels at 50 days and 63 days after irradiation. In animals treated with the AT1 receptor antagonist, there was a complete elimination in the rise of TGF-beta 1. CONCLUSIONS: These studies demonstrate that glomerular TGF-beta 1 production is elevated in the course of radiation nephropathy, and that AII mediates this induction of TGF-beta 1.

Different activation of mitogen-activated protein kinases in experimental proliferative glomerulonephritis.

Mitogen-activated protein (MAP) kinases are critical for cell signaling goals such as cellular proliferation and induction of apoptosis. We examined whether MAP kinases, as a point of convergence for multiple extracellular stimuli, are activated in proliferative glomerulonephritis (GN) in vivo. Accelerated crescentic anti-glomerular basement membrane (GBM) GN was induced in rats preimmunized with rabbit IgG by administration of rabbit anti-rat GBM serum. Whole cortical tissue and isolated glomeruli were then subjected to kinase activity assays and Western blot analysis. Cortical activity of the archetypal MAP kinase, extracellular signal-regulated kinase (ERK), was increased significantly one, three, and seven days after induction of GN. In contrast, activation of MAP kinases with antiproliferative actions, stress-activated protein kinase, and p38 MAP kinase was detectable only in the early stages of proliferative GN (days one and three), implying that different MAP kinases serve distinct roles in the pathogenesis of GN.

Enhanced expression of the cytoskeletal-associated protein, paxillin, in experimental nephrotic syndrome.

BACKGROUND: In the model of aminonucleoside of Puromycin (PAN)-induced nephrotic syndrome we assessed changes in glomerular expression of three proteins that regulate cell adhesion to extracellular matrix: paxillin, focal adhesion kinase (FAK), and Rho. METHODS: Following a single intravenous injection of PAN in Sprague-Dawley rats, proteinuria ensued and glomeruli were isolated at three stages: prior to onset of proteinuria (days 1 and 2), and when proteinuria peaked (day 9), subsided (day 29) or resolved (day 35). Glomerular protein lysates were analyzed by Western blot for expression of paxillin, FAK, and Rho. RESULTS: There was a progressive increase in glomerular paxillin level that peaked concomitantly with heavy proteinuria (day 9). Paxillin remained increased during the recovery phase of PAN-induced injury and when proteinuria resolved. Expression of FAK and Rho remained unchanged at all time points. To explore whether the increase in paxillin expression following administration of PAN was due to a direct effect on glomerular epithelial cells (GEC), cultured rat GECs were incubated with PAN for 3, 6, and 24 hours, and expression of paxillin was assessed in GEC lysates by Western blot analysis. No change in paxillin levels was observed. CONCLUSIONS: In PAN-induced nephrotic syndrome there is a preferential increase in paxillin expression that cannot be accouted for by an effect of PAN on GEC paxillin synthesis. We propose that the enhanced paxillin synthesis in the course of PAN-induced GEC injury reflects perturbations in contact between GEC and the GBM and may play a role in regulating adherence of GEC to the GBM.

Regulatory interactions between inducible nitric oxide synthase and eicosanoids in glomerular immune injury.

In a rat model of glomerular immune injury induced by administration of anti-glomerular basement membrane antibody and resembling human rapidly progressive glomerulonephritis, we explored whether activation of inducible nitric oxide synthase (iNOS) regulates synthesis of eicosanoids originating from cyclooxygenation or lipoxygenation of arachidonic acid. At early stages (24 hr) of injury, inhibition of iNOS using the selective inhibitor L-N6-(1-iminoethyl) lysine (L-NIL) at doses sufficient to reduce urinary excretion of nitrate/nitrite, reduced glomerular synthesis of the prostaglandins PGE2 and PGI2, but had no effect on that of thromboxane A2 (TxA2). The syntheses of 5-hydroxyeicosatetraenoic acid (HETE), 15-HETE and leukotriene B4 (LTB4) were also reduced. That of 12-HETE remained unchanged. We also explored the effect of arachidonate cyclooxygenation and lipoxygenation eicosanoids on iNOS expression. Administration of the cyclooxygenase (COX) inhibitor, indomethacin, at doses sufficient to inhibit glomerular prostaglandin synthesis, increased iNOS mRNA levels in glomeruli. Administration of the 5-lipoxygenase (5-LO) inhibitor, MK-0591, at doses sufficient to inhibit glomerular LTB4 synthesis also increased iNOS mRNA. The effect of 5-LO inhibition on iNOS expression was more pronounced than that of COX inhibition. In nephritic animals given the iNOS inhibitor, L-NIL, or indomethacin proteinuria worsened. In those given the 5-lipoxygenase inhibitor there was no change in urine protein excretion. These observations point to regulatory interactions between the arachidonic acid and the L-arginine: NO pathways in glomerulonephritis. These interactions are of importance in considering antiinflammatory strategies based on inhibition of iNOS or of specific eicosanoids.

Changes in inducible nitric oxide synthase expression in experimental glomerulonephritis.

We assessed changes in transcriptional activation of the inducible isoform of nitric oxide synthase (iNOS) in a model of macrophage-dependent proliferative glomerulonephritis in the rat resembling human forms of rapidly progressive nephritis. By the use of a cDNA probe derived from rat glomerular RNA and an RNase protection assay, iNOS expression was assessed at early and late stages of the disease and was correlated with the extent of macrophage infiltration. Prominent iNOS expression occurred in isolated glomeruli 24 hr after onset of immune injury when marked glomerular infiltration by macrophages also occurred. Treatment of animals with immune injury with the arachidonic acid cyclooxygenase inhibitor, indomethacin, potentiated iNOS expression. iNOS expression was short-lived; it was markedly reduced on Day 2 of injury and undetectable on Days 4 and 10, despite sustained infiltration of glomeruli by macrophages. These observations suggest that in glomerular immune injury the enhanced expression of iNOS is not sustainable possibly due to downregulatory factors generated in the course of injury.

Activation of extracellular signal-regulated kinase in proliferative glomerulonephritis in rats.

Multiple extracellular mitogens are involved in the pathogenesis of proliferative forms of glomerulonephritis (GN). In vitro studies demonstrate the pivotal role of extracellular signal-regulated kinase (ERK) in the regulation of cellular proliferation in response to extracellular mitogens. In this study, we examined whether this kinase, as a convergence point of mitogenic stimuli, is activated in proliferative GN in vivo. Two different proliferative forms of anti-glomerular basal membrane (GBM) GN in rats were induced and whole cortical tissue as well as isolated glomeruli examined using kinase activity assays and Western blot analysis. Administration of rabbit anti-rat GBM serum to rats, preimmunized with rabbit IgG, induced an accelerated crescentic anti-GBM GN. A significant increase in cortical, and more dramatically glomerular ERK activity was detected at 1, 3, and 7 d after induction of GN. Immunization of Wistar-Kyoto rats with bovine GBM also induced a crescentic anti-GBM GN with an increase of renal cortical ERK activity after 4, 6, and 8 wk. ERK is phosphorylated and activated by the MAP kinase/ERK kinase (MEK). We detected a significant increase in the expression of glomerular MEK in the accelerated form of anti-GBM GN, providing a possible mechanism of long-term activation of ERK in this disease model. In contrast to ERK, activation of stress-activated protein kinase was only detectable at early stages of proliferative GN, indicating these related kinases to serve distinct roles in the pathogenesis of GN. Our observations point to ERK as a putative mediator of the proliferative response to immune injury in GN and suggest that upregulation of MEK is involved in the long-term regulation of ERK in vivo.