Transforming growth factor-beta is a potent inhibitor of extracellular matrix degradation by cultured human mesangial cells.

Accumulation of the glomerular extracellular matrix (ECM) is a pivotal event in the progression from acute glomerular injury to end-stage renal disease. Although enhanced ECM synthesis has been demonstrated to contribute to ECM accumulation, the role of decreased ECM degradation is largely unknown. It was previously shown that glomerular ECM degradation is mediated by a plasminogen activator (PA)/plasmin/matrix metalloproteinase 2 (MMP-2) cascade. However, little information is available regarding the factors that regulate the activity of this degradative cascade in normal or pathologic states. Transforming growth factor-beta1 (TGF-beta1) is shown here to be a potent inhibitor of ECM degradation by cultured human mesangial cells. Using human mesangial cells grown on thin films of 125I-labeled Matrigel, dose-dependent inhibition of ECM degradation in the presence of TGF-beta1 was observed, reaching >90% inhibition with 0.4 ng/ml TGF-beta1. Addition of anti-TGF-beta antibodies (4 microg/ml) in the absence of exogenous TGF-beta increased ECM degradation (1.8+/-0.2-fold versus controls, P<0.05). In contrast, platelet-derived growth factor, at concentrations up to 10 ng/ml, had no effect on ECM degradation. TGF-beta completely blocked the conversion of plasminogen to plasmin and markedly reduced the conversion of latent MMP-2 to active MMP-2. TGF-beta did not significantly alter the levels of tissue PA, total MMP-2, or tissue inhibitor of metalloproteinase-1, but did increase the levels of PA inhibitor- (1.8-fold, P<0.05), the major physiologic inhibitor of PA. These data document that TGF-beta is a potent inhibitor of ECM degradation by cultured human mesangial cells, and they suggest that decreased mesangial matrix degradation, caused by TGF-beta-mediated decreases in the activity of the PA/plasmin/MMP-2 cascade, may contribute to the glomerular matrix accumulation that occurs in progressive renal disease.

Bradykinin stimulates the ERK-->Elk-1-->Fos/AP-1 pathway in mesangial cells.

Among its diverse biological actions, the vasoactive peptide bradykinin (BK) induces the transcription factor AP-1 and proliferation of mesangial cells (S. S. El-Dahr, S. Dipp, I. V. Yosipiv, and W. H. Baricos. Kidney Int. 50: 1850-1855, 1996). In the present study, we examined the role of protein tyrosine phosphorylation and the mitogen-activated protein kinases, ERK1/2,in mediating BK-induced AP-1 and DNA replication in cultured rat mesangial cells. BK (10(-9) to 10(-7) M) stimulated a rapid increase in tyrosine phosphorylation of multiple proteins with an estimated molecular mass of 120-130, 90-95, and 44-42 kDa. Immunoblots using antibodies specific for ERK or tyrosine-phosphorylated ERK revealed a shifting of p42 ERK2 to a higher molecular weight that correlated temporally with an increase in tyrosine-phosphorylated ERK2. Genistein, a specific tyrosine kinase inhibitor, prevented the phosphorylation of ERK2 by BK. In-gel kinase assays indicated that BK-induced tyrosine phosphorylation of ERK2 is accompanied by fourfold activation of its phosphotransferase activity toward the substrate PHAS-I (P < 0.05). Furthermore, BK stimulated a 2.5-fold increase (P < 0.05) in phosphorylation of Elk-1, a transcription factor required for growth factor-induced c-fos transcription. In accord with the stimulation of Elk-1 phosphorylation, BK induced c-fos gene expression and the production of Fos/AP-1 complexes. In addition, thymidine incorporation into DNA increased twofold (P < 0. 05) following BK stimulation. Each of these effects was blocked by tyrosine kinase inhibition with genistein or herbimycin A. Similarly, antisense oligodeoxynucleotide targeting of ERK1/2 mRNA inhibited BK-stimulated DNA synthesis. In contrast, protein kinase C inhibition or depletion had no effect on BK-induced c-fos mRNA, AP-1-DNA binding activity, or DNA synthesis. Collectively, these data demonstrate that BK activates the ERK-->Elk-1-->AP-1 pathway and that BK mitogenic signaling is critically dependent on protein tyrosine phosphorylation.

Bradykinin stimulates c-fos expression, AP-1-DNA binding activity and proliferation of rat glomerular mesangial cells.

An important role for bradykinin (BK) in nephrogenesis has been suggested based on impairment of renal growth in developing rats treated with a kinin antagonist. However, direct effects of BK on renal cell mitogenesis have not been reported. In the present study, we examined the mitogenic effects of BK on cultured rat mesangial cells. Transcripts encoding BK-B2 receptors were detected in quiescent and proliferating mesangial cells by reverse transcription-coupled polymerase chain reaction. In quiescent mesangial cell cultures (0.5% FCS for 48 hr), BK (10(-9) to 10 (-7)M) caused a significant increase in DNA synthesis (3H-thymidine incorporation into DNA) and cell number. BK-induced DNA synthesis was preceded by activation of c-fos gene expression and both of these effects were inhibited by Hoe-140, a specific BK-B2 antagonist. Electrophoretic gel mobility shift assays revealed enhanced binding of AP-1 complexes to a consensus AP-1 DNA sequence in BK-stimulated cells. Gel supershift assays confirmed that the AP-1 complexes contained the fos protein. These data document a direct mitogenic effect of BK, acting on B2 receptors, on mesangial cells.

Plasminogen activators augment endothelial cell organization in vitro by two distinct pathways.

Endothelial cell differentiation into capillary structures is a complex process that requires the concerted effects of several extracellular matrix proteases, including plasminogen activators. Here, the role of tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) was evaluated in an in vitro model of endothelial morphogenesis involving organization of human umbilical vein endothelial cells into tubular structures when they are cultured on the basement membrane preparation, Matrigel. Both uPA and tPA were detected in HUVEC cultures on Matrigel, and inhibitors of plasminogen activators or of serine proteases decreased the extent of the tube network formed by the cells. The decrease resulting from serine protease inhibitors was additive to that from matrix metalloproteinase inhibitors which have previously been shown to decrease tube formation in this model, suggesting that the two classes of proteases modulate tube formation by distinct mechanisms. Plasminogen activator inhibitor (PAI)-1 decreased tube formation by 50% when added up to 4.5 h after the initiation of an 18 h assay and caused 25% inhibition when added 9.5 h after culture initiation, indicating that the effects of plasminogen activators are not limited to an early event in the differentiation process. Steady-state expression of mRNA for uPA increased during the first several hours of culture on Matrigel, further supporting a role for PA activity throughout the process of tube formation. These findings suggested that PAs may affect multiple events during tube-forming activity. A fucosylated peptide comprising the amino-terminal domain of uPA that binds to the uPA receptor (uPAR) but lacking proteolytic activity enhanced tube formation. In contrast, a defucosylated form of the same peptide had no effect. Since fucosylation of this fragment has been shown to be essential in other models of cell stimulation by uPA-uPAR interaction, these data support the hypothesis that uPA enhances endothelial morphogenesis both through proteolytic activity and via uPAR occupancy. Plasminogen activators could facilitate angiogenesis in vivo.

Chronic renal disease: do metalloproteinase inhibitors have a demonstrable role in extracellular matrix accumulation?

Recent evidence suggests that decreased degradation of the glomerular extracellular matrix may contribute to the matrix accumulation that occurs in the progression of chronic renal disease. The presence of matrix metalloproteinases in cultured glomerular cells and possibly in glomeruli in vivo combined with the ability of these proteinases to degrade extracellular matrix components suggests that these proteinases may play important roles in glomerular extracellular matrix degradation. Decreased activity of these proteinases mediated by upregulation of their inhibitors could theoretically contribute to matrix accumulation. In the limited number of studies that have addressed this issue directly, there is evidence both to support and refute this hypothesis. It is reasonable to suspect, however, that either increased matrix formation, decreased matrix degradation, or both, might contribute to extracellular matrix accumulation in progressive renal disease, depending on the primary etiology.

ECM degradation by cultured human mesangial cells is mediated by a PA/plasmin/MMP-2 cascade.

We examined the role of the plasminogen activator/plasmin system in extracellular matrix (ECM) degradation by human mesangial cells cultured on thin films of 125I-labeled ECM (Matrigel). ECM degradation (release of 125I into the medium) was dependent on exogenous plasminogen, proportional to the number of mesangial cells and amount of plasminogen added, and coincident with the appearance of plasmin in the medium. ECM degradation was completely blocked (P < 0.001) by two plasmin inhibitors, alpha-2-antiplasmin (40 micrograms/ml) and aprotinin (216 KIU/ml), and partially reduced (-33 +/- 1.8%, P < 0.01) by TIMP-1 (40 micrograms/ml), a specific inhibitor of matrix metalloproteinases. Zymography of medium obtained from cells cultured in the absence of plasminogen revealed the presence of latent matrix metalloproteinase-2 (MMP-2) which was converted to a lower molecular weight, active form in the presence of mesangial cells and plasminogen. Northern analysis of poly A+RNA prepared from cultured human mesangial cells revealed mRNA for tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA), plasminogen activator inhibitor-1 (PAI-1), and uPA receptor (uPAR). The presence of uPA protein in medium obtained from cultured human mesangial cells was demonstrated by Western blotting and ELISA which revealed a large molar excess of PAI-1 (1.2 +/- 0.1 x 10(-9) M) over uPA (1.2 +/- 0.1 x 10(-12) M) and tPA (0.19 +/- 0.04 x 10(-9) M). ECM degradation was reduced by a monoclonal antibody (MAb) against human tPA (-54 +/- 8.6%) or human uPA (-39 +/- 5.2%) compared to cells treated with identical amounts of non-specific monoclonal IgG (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of IgA nephropathy in ethanol consumption: animal model and cell culture studies.

Using the intragastric ethanol infusion model of IgA nephropathy, we investigated the hypothesis that in this model mesangial changes commence prior to the deposition of IgA. We studied the two cellular components of the glomerular mesangium: the mononuclear phagocyte and the contractile mesangial cell. In the in vivo model, we observed a mononuclear phagocyte influx in the mesangium of alcoholic rats before the deposition of IgA. Using molecular techniques on cultured contractile mesangial cells, we demonstrated a threefold increase in interleukin-6 mRNA expression in contractile cells incubated with ethanol. These mesangial changes in the cellular composition, and in the autocrine cytokine system, suggest a direct role for ethanol in the pathogenesis of IgA nephropathy.

Role of plasmin and gelatinase in extracellular matrix degradation by cultured rat mesangial cells.

We have examined the ability of mesangial cells (MCs) to degrade extracellular matrix (ECM) using cultured rat MCs grown on thin films of radiolabeled Matrigel. ECM degradation by cultured MCs was observed only in presence of exogenously added plasminogen and was a function of plasminogen concentration (0-50 mU), cell number (0-50,000 cells), and length of incubation (0-72 h). A high positive correlation (r > 0.93) was observed between ECM degradation and plasmin activity in medium, suggesting an important role for plasmin in ECM degradation by cultured MCs. This suggestion was confirmed by ability of plasmin inhibitors, alpha 2-antiplasmin (40 micrograms/ml) and aprotinin (216 kallikrein inhibition units/ml), to inhibit (> 90%) ECM degradation. Inhibitors of cysteine proteinases [trans-epoxysuccinyl-L-leucylamido(4-guanidino)butane, 10 microM] and aspartic proteinases (pepstatin, 5.0 micrograms/ml) had no effect on ECM degradation. However, in presence of plasminogen, inhibitors of matrix metalloproteinases, TIMP-1 (40 micrograms/ml) and o-phenanthroline (100 microM), inhibited ECM degradation -42 +/- 4% and -43 +/- 3% (SE), respectively (n = 8-10). Thus, in addition to plasmin, a matrix metalloproteinase(s) is also involved in ECM degradation by cultured rat MCs. Zymography of culture medium obtained from MCs grown on radiolabeled Matrigel films in absence of plasminogen revealed only two closely migrating bands of gelatinase activity, relative mol wt of approximately 70,000-72,000. MCs grown in absence of plasminogen failed to degrade ECM despite presence of gelatinase in medium, indicating that, in absence of plasmin, gelatinase is present in an inactive form, either as a latent proenzyme or as a gelatinase-inhibitor complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence suggesting a role for cathepsin L in an experimental model of glomerulonephritis.

We have utilized specific, irreversible inhibitors of cysteine proteinases to examine the role of renal cathepsin B and cathepsin L in the proteinuria which occurs in an experimental model of human glomerular disease. Administration of trans-epoxysuccinyl-L-leucylamido-(3-methyl)butane (Ep475) a specific, irreversible inhibitor of cysteine proteinases, including cathepsins B and L, significantly reduced proteinuria in rats with experimentally induced, neutrophil-independent, anti-GBM antibody disease (controls: 10 +/- 1 mg/24 h, N = 8; anti-GBM antibody disease: 203 +/- 30 mg/24 h, N = 8; anti-GBM antibody disease + Ep475: 112 +/- 13 mg/24 h, mean +/- SEM, N = 6, P less than 0.05). There was a marked reduction in the activity of both cathepsin B and cathepsin L in renal cortices obtained from Ep475-treated rats compared to either saline-treated controls or rats treated with anti-GBM IgG only. Administration of Z-Phe-Tyr(O-t-butyl)CHN2, a specific, irreversible cysteine proteinase inhibitor with a high degree of selectivity toward cathepsin L, also caused a reduction in anti-GBM antibody-induced proteinuria (90 +/- 18 mg/24 h, N = 6, P less than 0.05). This reduction in proteinuria was accompanied by a marked decrease (-84%) in the specific activity of renal cortical cathepsin L in Z-Phe-Tyr(O-t-butyl)CHN2-treated rats. However, cathepsin B activity was unchanged. There was no significant change in the renal anti-GBM antibody uptake, plasma urea nitrogen, or plasma creatinine values in the Z-Phe-Tyr(O-t-butyl)CHN2-treated rats compared to rats treated with anti-GBM IgG only or saline-treated controls. These data document the ability of cysteine proteinase inhibitors to decrease the proteinuria which occurs in a neutrophil-independent model of human anti-GBM antibody disease and suggest an important role for cathepsin L in the pathophysiology of the proteinuria which occurs in this model.

Glomerular basement membrane degradation by endogenous cysteine proteinases in isolated rat glomeruli.

Recent in vitro and in vivo studies suggest that cysteine proteinases may play an important role in degradation of the glomerular basement membrane (GBM) by renal glomeruli. However, little information is available concerning the cysteine proteinases present in glomeruli, the distribution of cysteine proteinases in other areas of the kidney, or the potential role of endogenous glomerular cysteine proteinases in GBM degradation. Using well characterized fluorogenic substrates, we have documented the presence of the cysteine proteinases, cathepsins B, H, and L, in glomeruli (0.45 +/- 0.06, 0.39 +/- 0.05, and 0.66 +/- 0.14 mU/mg protein, mean +/- SEM, N = 8) and other fractions prepared from normal rat kidney. The presence of cysteine proteinases in glomeruli was verified by fluorescence microscopy. For each proteinase, the activity was: proportional to the amount of tissue protein and time of incubation; dependent on the presence of exogenously added dithiothreitol; and completely inhibited by the specific cysteine proteinase inhibitor, E-64. The pH optimum for cathepsin B (substrate: Z-Arg-Arg-HNMec) and L (substrate: Z-Phe-Arg-HNMec in the presence of Z-Phe-Phe-CHN2) was approximately pH 6.0 for both glomeruli and renal cortex; while that for cathepsin H (substrate: Arg-HNMec) was approximately 6.5. Incubation of sonicated glomeruli with 3H-GBM under conditions optimal for cysteine proteinase activity (pH 4.5, 1 mM EDTA, and 1 mM dithiothreitol, 37 degrees C) resulted in significant GBM degradation as measured by the release of non-sedimentable (10,000 x g, 10 min) radioactivity or hydroxyproline.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of cathepsin B and L in anti-glomerular basement membrane nephritis in rats.

We have examined the potential role of the cysteine proteinases, cathepsin B and L, in renal tubular protein degradation and increased permeability of the glomerular basement membrane (GBM) which occurs in a neutrophil- and complement-independent model of anti-GBM antibody disease. The specific activity of cathepsin L, but not cathepsin B, was significantly increased (157%, p greater than 0.01) in cortical homogenates (85-90% tubules) prepared from anti-GBM-treated rats compared to saline-treated controls. Using highly purified cathepsin B and L, we documented the ability of these proteinases to degrade albumin in vitro (Km 5.92 and 0.22 microM for B and L, respectively). In two separate studies, treatment of rats with trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane, (E-64), a specific and irreversible inhibitor of cysteine proteinases, significantly reduced proteinuria (-45 and -41%, p less than 0.01) in the 24-hour period following injection of the anti-GBM IgG. Taken together, these data suggest an important role for cysteine proteinases in the increased tubular protein degradation which occurs in response to increased filtered protein loads and in the increased GBM permeability (proteinuria) characteristic of glomerular disease.

Degradation of glomerular basement membrane by purified mammalian metalloproteinases.

Neutral metalloproteinases degrade components of the extracellular matrix, including collagen types I-V, fibronectin, laminin and proteoglycan. However, their ability to degrade intact glomerular basement membrane (GBM) has not previously been investigated. Incubation of [3H]GBM (50,000 c.p.m.; pH 7.5; 24 h at 37 degrees C) with purified gelatinase or stromelysin (2 units) resulted in significant GBM degradation: gelatinase, 46 +/- 2.2; stromelysin, 59 +/- 5.8 (means +/- S.E.M.; percentage release of non-sedimentable radioactivity; n = 4). In contrast, 2 units of collagenase released only 5.6 +/- 0.52% (n = 3) of the [3H]GBM radioactivity compared with 2.0 +/- 0.15% (n = 7) released from [3H]GBM incubated alone. Sephadex G-200 gel chromatography of supernatants obtained from incubations of [3H]GBM with either gelatinase or stromelysin confirmed the ability of these enzymes to degrade GBM and revealed both high-(800,000) and relatively low-(less than 20,000) Mr degradation products for both enzymes. GBM degradation by gelatinase and stromelysin was dose-dependent (range 0.02-2.0 units), near maximal between pH 6.0 and 8.6, and was completely inhibited (greater than 95%) by 2 mM-o-phenanthroline. Collagenase (2 units) did not enhance the degradation of GBM by either gelatinase (0.02 or 0.2 unit) or stromelysin (0.02 or 0.2 unit). Our results indicate that metalloproteinase-mediated GBM degradation by neutrophils and glomeruli may be attributable to gelatinase (neutrophils) and/or stromelysin (glomeruli) and suggest an important role for these proteinases in glomerular pathophysiology.

The cysteine proteinase inhibitor, E-64, reduces proteinuria in an experimental model of glomerulonephritis.

Proteinuria is a major manifestation of glomerular disease (glomerulonephritis, GN). We examined the effect of trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E-64), a specific and irreversible cysteine proteinase inhibitor, on urinary protein excretion in a complement- and neutrophil-independent model of antiglomerular basement membrane (GBM) antibody disease. A single injection of rabbit antirat-GBM IgG produced a marked increase in urinary protein excretion 24hr after injection. In two separate studies using different pools of antiGBM IgG, administration of E-64 (5mg every 6h starting 2hr prior to induction of GN) reduced proteinuria (-45 +/- 7%, and -41 +/- 14%, Mean +/- SEM, n = 6; P less than 0.001) in the 24 hour period following induction of the disease. This reduction in urinary protein excretion was accompanied by a marked decrease in the specific activity of the cysteine proteinases cathepsins B and L in glomeruli (B: -97%; L: -84%) and renal cortex (B: -87%; L: -75%) isolated from the same E-64-treated rats compared to same saline-treated controls. These data, combined with the specificity of E-64 for cysteine proteinases, suggest a potential role for cysteine proteinases in the increased GBM permeability and proteinuria in this experimental model of glomerular disease.

Human kidney cathepsins B and L. Characterization and potential role in degradation of glomerular basement membrane.

Cathepsins B and L were purified from human kidney. SDS/polyacrylamide-gel electrophoresis demonstrated that cathepsins B and L, Mr 27000-30000, consist of disulphide-linked dimers, subunit Mr values 22000-25000 and 5000-7000. The pH optimum for the hydrolysis of methylcoumarylamide (-NHMec) substrates (see below) is approx. 6.0 for each enzyme. Km and kcat. are 252 microM and 364s-1 and 2.2 microM and 25.8 s-1 for the hydrolysis of Z-Phe-Arg-NHMec (where Z- represents benzyloxycarbonyl-) by cathepsins B and L respectively, and 184 microM and 158 s-1 for the hydrolysis of Z-Arg-Arg-NHMec by cathepsin B. A 10 min preincubation of cathepsin B (40 degrees C) or cathepsin L (30 degrees C) with E-64 (2.5 microM) results in complete inhibition. Under identical conditions Z-Phe-Phe-CHN2 (0.56 microM) completely inhibits cathepsin L but has little effect on cathepsin B. Incubation of glomerular basement membrane (GBM) with purified human kidney cathepsin L resulted in dose-dependent (10-40 nM) GBM degradation. In contrast, little degradation of GBM (less than 4.0%) was observed with cathepsin B. The pH optimum for GBM degradation by cathepsin L was 3.5. Cathepsin L was significantly more active in degrading GBM than was pancreatic elastase, trypsin or bacterial collagenase. These data suggest that cathepsin L may participate in the lysosomal degradation of GBM associated with normal GBM turnover in vivo.

The role of aspartic and cysteine proteinases in albumin degradation by rat kidney cortical lysosomes.

We have investigated the degradation of 125I-labeled bovine serum albumin by lysates of rat kidney cortical lysosomes. Maximal degradation of albumin occurred at pH 3.5-4.2, with approximately 70% of the maximal rate occurring at pH 5.0. Degradation was proportional to lysosomal protein concentration (range 100-600 micrograms) and time of incubation (1-5 h). Dithioerythritol (2 mM) stimulated albumin degradation 5- to 10-fold. Albumin degradation was not inhibited by phenylmethanesulfonyl fluoride (1 mM) or EDTA (5 mM), indicating that neither serine nor metalloproteinases are involved to a significant extent. Pepstatin (5 micrograms/ml), an inhibitor of aspartic proteinases, inhibited albumin degradation by approximately 50%. Leupeptin (10 microM) and N-ethylmaleimide (10 mM), inhibitors of cysteine proteinases, decreased albumin degradation by 34 and 65%, respectively. Combinations of aspartic and cysteine proteinase inhibitors produced nearly complete inhibition of albumin degradation. Taken together, these data indicate that aspartic and cysteine proteinases are primarily responsible for albumin degradation by renal cortical lysosomes under these conditions. In keeping with the above data, we have measured high activities of the cysteine proteinases, cathepsins B, H, and L, in cortical tubules, the major site of renal protein degradation. Using the peptidyl 7-amino-4-methylcoumarin (NHMec) substrates (Z-Arg-Arg-NHMec, for cathepsin B; Arg-NHMec for cathepsin H; and Z-Phe-Phe-CHN2-inhibitable hydrolysis of Z-Phe-Arg-NHMec corrected for inhibition of cathepsin B activity for cathepsin L) values obtained were (means +/- SE, mU/mg protein, 1 mU = production of 1 nM product/min, n = 6): cathepsin B, 2.1 +/- 0.34; cathepsin H, 1.35 +/- 0.19; cathepsin L, 14.49 +/- 1.26. In comparison, the activities of cathepsins B, H, and L in liver were: 0.56 +/- 0.03, 0.28 +/- 0.04, and 1.27 +/- 0.16, respectively.

Degradation of human glomerular basement membrane by stimulated neutrophils. Activation of a metalloproteinase(s) by reactive oxygen metabolites.

We examined the role of reactive oxygen metabolites in the degradation of human glomerular basement membrane (GBM) by stimulated human neutrophils. Neutrophils stimulated with phorbol myristate acetate (PMA) caused a significant degradation of GBM over 3 h resulting in 11.4 +/- 0.9% (SEM), n = 11 release of hydroxyproline compared with 0.3 +/- 0.09%, n = 11 release by unstimulated neutrophils. Superoxide dismutase, a scavenger of superoxide, did not inhibit the GBM degradation, whereas catalase, a scavenger of hydrogen peroxide, caused a marked inhibition (-60 +/- 7%, n = 4, P less than 0.001) of hydroxyproline release. Neither alpha-1 proteinase inhibitor, an inhibitor of elastase, nor soya bean trypsin inhibitor, an inhibitor of cathepsin G, caused any significant inhibition of GBM degradation. GBM degradation by cell-free supernatants obtained from stimulated neutrophils was markedly impaired in the presence of metal chelators EDTA (-72 +/- 7, n = 6, P less than 0.001) and 1,10,phenanthroline (-85 +/- 5%, n = 3, P less than 0.001). Considering these results, we postulated that reactive oxygen metabolites generated by the stimulated neutrophils activate a latent GBM degrading metalloproteinase(s). GBM degradation by supernatants obtained from incubations with catalase, azide, an inhibitor of myeloperoxidase, and methionine and taurine, scavengers of hypochlorous acid, was markedly reduced. Our data thus indicate that degradation of the GBM by PMA-stimulated neutrophils is due to activation of a latent metalloproteinase by hypochlorous acid or a similar oxidant generated by the myeloperoxidase-hydrogen peroxide-halide system.

Degradation of glomerular basement membrane by a neutral metalloproteinase(s) present in glomeruli isolated from normal rat kidney.

Incubation of glomerular homogenates (200 micrograms protein) with glomerular basement membrane (GBM, 30-35 micrograms hydroxyproline) at pH 7.5 for 36 h at 37 degrees C resulted in significant GBM degradation as measured by hydroxyproline release (40 +/- 6%, n = 17). GBM degradation increased with increasing incubation time (12-48 h) and glomerular protein concentration (50-250 micrograms). GBM degradation was not significantly decreased by inhibitors of serine or cysteine proteinases or the inhibitor of bacterial metalloproteinases, phosphoramidon. In contrast GBM degradation by glomerular homogenates was markedly inhibited by the metal chelators 10mM EDTA (-95 +/- 3%, n = 7) and 2mM 1,10-phenanthroline (-96 +/- 2%, n = 4). Preincubation of glomerular homogenates with trypsin (followed by soya bean trypsin inhibitor) markedly stimulated GBM degradation (+103 +/- 20%, n = 11). These results document the presence of a GBM-degrading, neutral metalloproteinase(s) in glomeruli suggesting an important role for this enzyme in glomerular pathophysiology.

Renal neuraminidase. Characterization in normal rat kidney and measurement in experimentally induced nephrotic syndrome.

Several lines of evidence suggest that increased neuraminidase activity may be responsible for the loss of glomerular N-acetylneuraminic acid (AcNeu) observed in various glomerular diseases. However, virtually no information is available on the activity of neuraminidase in glomeruli or the potential role of this enzyme in glomerular pathophysiology. Utilizing 2'-(4-methylumbelliferyl)-alpha-D-N-acetylneuraminic acid (4MU-AcNeu) as substrate, we defined optimal assay conditions and characterized neuraminidase activity in glomeruli and, for comparison, in other renal fractions and liver. Neuraminidase activity in glomeruli, cortex and tubules was maximal at pH 4.4. The Km for 4MU-AcNeu was estimated to be 195 microM for glomeruli and 226 microM for cortex. Glomerular neuraminidase was inhibited by AcNeu (90% at 25 mM) and high concentrations of Triton X-100 (26% at 0.5%), but unaffected by CaCl2, EDTA or N-ethylmaleimide (each 1 mM). Neuraminidase activity (nmol/h per mg of protein; mean +/- S.E.M.) in normal rat kidney was: cortex, 14.47 +/- 0.76; medulla, 7.85 +/- 0.64; papilla, 2.64 +/- 0.11; tubules, 13.79 +/- 0.70; glomeruli, 5.57 +/- 0.28. In comparison, neuraminidase activity in rat liver was 2.58 +/- 0.14. Puromycin aminonucleoside (PAN)-induced nephrotic syndrome is a model of glomerular disease in which the loss of glomerular AcNeu is well documented. In two separate studies, we observed no change in the specific activity of neuraminidase in either glomeruli or cortex isolated from rats treated with PAN (15 mg/100 g, intraperitoneally) and killed at either the onset or the peak of proteinuria. Results were similar whether neuraminidase activity was expressed per mg of protein or per microgram of DNA.