Characterization of a glomerular epithelial cell metalloproteinase as matrix metalloproteinase-9 with enhanced expression in a model of membranous nephropathy

Mechanisms of immune-deposit formation and the mediation of immune renal injury

The passive trapping of preformed immune complexes is responsible for some forms of glomerulonephritis that are associated with mesangial or subendothelial deposits. The biochemical characteristics of circulating antigens play important roles in determining the biologic activity of immune complexes in these cases. Examples of circulating immune complex diseases include the classic acute and chronic serum sickness models in rabbits, and human lupus nephritis. Immune deposits also form "in situ". In situ immune deposit formation may occur at subepithelial, subendothelial, and mesangial sites. In situ immune-complex formation has been most frequently studied in the Heymann nephritis models of membranous nephropathy with subepithelial immune deposits. While the autoantigenic target in Heymann nephritis has been identified as megalin, the pathogenic antigenic target in human membranous nephropathy had been unknown until the recent identification of neutral endopeptidase as one target. It is likely that there is no universal antigen in human membranous nephropathy. Immune complexes can damage glomerular structures by attracting circulating inflammatory cells or activating resident glomerular cells to release vasoactive substances, cytokines, and activators of coagulation. However, the principal mediator of immune complex-mediated glomerular injury is the complement system, especially C5b-9 membrane attack complex formation. C5b-9 inserts in sublytic quantities into the membranes of glomerular cells, where it produces cell activation, converting normal cells into resident inflammatory effector cells that cause injury. Excessive activation of the complement system is normally prevented by a series of circulating and cell-bound complement regulatory proteins. Genetic deficiencies or mutations of these proteins can lead to the spontaneous development of glomerular disease. The identification of specific antigens in human disease may lead to the development of fundamental therapies. Particularly promising future therapeutic approaches include selective immunosuppression and interference in complement activation and C5b-9-mediated cell injury.

Renal redox stress and remodeling in metabolic syndrome, type 2 diabetes mellitus, and diabetic nephropathy: paying homage to the podocyte

Type 2 diabetes mellitus has reached epidemic proportions and diabetic nephropathy is the leading cause of end-stage renal disease. The metabolic syndrome constitutes a milieu conducive to tissue redox stress. This loss of redox homeostasis contributes to renal remodeling and parallels the concurrent increased vascular redox stress associated with the cardiometabolic syndrome. The multiple metabolic toxicities, redox stress and endothelial dysfunction combine to weave the complicated mosaic fabric of diabetic glomerulosclerosis and diabetic nephropathy. A better understanding may provide both the clinician and researcher tools to unravel this complicated disease process. Cellular remodeling of podocyte foot processes in the Ren-2 transgenic rat model of tissue angiotensin II overexpression (TG(mREN-2)27) and the Zucker diabetic fatty model of type 2 diabetes mellitus have been observed in preliminary studies. Importantly, angiotensin II receptor blockers have been shown to abrogate these ultrastructural changes in the foot processes of the podocyte in preliminary studies. An integrated, global risk reduction, approach in therapy addressing the multiple metabolic abnormalities combined with attempts to reach therapeutic goals at an earlier stage could have a profound effect on the development and progressive nature to end-stage renal disease and ultimately renal replacement therapy.

Experimental membranous nephropathy redux

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.

Activation of gelatinases by fibrin is PA/plasmin system-dependent in human glomerular endothelial cells

Evidence suggests that fibrin deposit is related to severity of glomerulonephropathy. Fibrin is considered to play an active role beyond a haemostatic plug or temporary matrix in response to injury. We have reported that fibrin induced specific morphological changes and up-regulated intercellular adhesion molecule-1 expression of glomerular endothelial cells (GECs). Changes of gelatinases activity have been implicated playing a prominent role in glomerular diseases involving matrix turnover. This study examined whether overlying fibrin influences the expression of gelatinase A and B in cultured human GECs and mechanism underlying the activation. No gelatinase activity was detectable in supernatant of cultured GECs; however, physiological concentration of fibrin (0.5-2.0 mg/ml) induced a dramatic expression of activated MMP-2 and MMP-9 at both mRNA and protein level in a dose and time dependent manner. Increased mRNA level of membrane-type 1 matrix metalloproteinases (MT1-MMPs) was also found. Interestingly, we observed that fibrin also induced the expression of tissue type plasminogen activator (tPA), urokinase type plasminogen activator (uPA) and plasminogen activator inhibitor-1 by casein zymographic and reverse zymographic analysis. Fibrin plate assay revealed the net activity was PA predominant. Serine protease inhibitor aprotinin blocked the conversion of pro-gelatinase A and B to their active forms. The results demonstrate that overlying fibrin increased the secretion of gelatinase A and B from GECs. PA/plasmin proteolytic pathways contributed to the activation of gelatinases.

Renal expression of SIBLING proteins and their partner matrix metalloproteinases (MMPs)

BACKGROUND

Three members of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family of proteins have recently been shown to bind and activate specific promatrix metalloproteinases (MMPs) and to overcome the inhibition of tissue inhibitors of MMPs (TIMPs). Although usually associated with mineralized tissues, we have shown that the SIBLINGs and their MMP partners, when known, are coexpressed in salivary gland ductal cells. The present study examined the expression patterns of both the SIBLINGs and their MMP partners in adult kidney.

METHODS

The expression patterns of all five SIBLINGs known to date, and their MMP partners were determined in monkey kidney using immunohistochemistry and in situ hybridization techniques.

RESULTS

Bone sialoprotein (BSP) and its partner, MMP-2, were coexpressed in both the proximal and distal tubules. Osteopontin, as previously shown, was expressed in the distal tubules while its partner MMP-3 was expressed in both the proximal tubule and distal tubles. Dentin matrix protein-1 (DMP1) and MMP-9 were coexpressed throughout the nephron, including both parietal cells of Bowman's capsule and the thin limb of the loop of Henle. Dentin sialophosphoprotein (DSPP) and matrix extracellular phosphoglycoprotein (MEPE) were expressed in the proximal tubule and distal tubule, and proximal tubule, respectively.

CONCLUSION

In contrast to salivary gland in which all SIBLINGs and their MMP partners were coexpressed throughout the length of the ducts, these proteins were differentially expressed within the normal adult nephron. We hypothesize that the cells use the SIBLING/MMP pairs in the normal turnover of cell surface proteins and/or pericellular matrix proteins such as those in basement membranes.

Decreased expression of matrix metalloproteinases and tissue inhibitors of metalloproteinase in the kidneys of hereditary nephrotic (ICGN) mice

Matrix metalloporoteinases (MMPs), which are dominantly regulated by tissue inhibitors of metalloproteinase (TIMPs), play important roles in extracellular matrix (ECM) degradation and are involved in the progression of kidney diseases. In glomeruli and tubulointerstitum of hereditary nephrotic (ICR-derived glomerulonephritis: ICGN) mouse kidneys, hyper-accumulation of ECM components occurred, and MMP activity decreased. In the present study, because lower levels of MMP activity may contribute to the progression of renal fibrosis in ICGN mice, Western blotting analysis and immunohistochemical staining for MMPs and TIMPs were performed to verify the expression levels of these proteins. Levels of MMP-2, MMP-9, MT1-MMP, TIMP-1 and TIMP-2 in the kidneys were decreased in ICGN mice in comparison with normal ICR mice. These results indicate that small amounts and low levels of activity of MMPs cause the progression of renal fibrosis in ICGN mice.

Molecular pathomechanisms of membranous nephropathy: from Heymann nephritis to alloimmunization

Membranous nephropathy (MN), the most common cause of idiopathic nephrotic syndrome in white adults, is characterized by an accumulation of immune deposits on the outer aspect of the glomerular basement membrane. In Heymann nephritis, the rat experimental model for MN, megalin--the target antigen of the nephritogenic antibodies--is expressed on the surface of podocytes, where immune complexes are formed, leading to complement activation and nephrotic-range proteinuria. However, megalin cannot be held responsible for human MN because it has not been found in human podocytes or detected in subepithelial immune deposits in patients with MN. Several potential antigens have been identified in so-called secondary forms of MN, but there is no real proof that these antigens are pathogenic. In a subgroup of infants with antenatal MN, neutral endopeptidase (NEP) has been identified as the first protein target on human podocytes of nephritogenic antibodies. The infants' mothers became immunized during pregnancy against NEP expressed on syncytiotrophoblastic cells because they were NEP deficient as a result of truncating mutations in the MME gene. Severity of neonatal renal disease was determined by the mothers' IgG response that led to the formation of the membrane attack complex of complement in the subepithelial deposits. Alloimmunization against NEP is a novel pathomechanism of MN that might also account for some cases of MN after renal or bone marrow transplantation. Other types of alloimmunization should be investigated in MN but also in other renal and nonrenal diseases, particularly those that affect the pediatric age.

Cellular Response to Injury in Membranous Nephropathy

The pathogenesis of membranous nephropathy (MN) involves in situ formation of subepithelial immune deposits that produce glomerular injury by damaging and/or activating podocytes through complement-dependent processes. C5b-9 formation and insertion into podocyte cell membranes causes glomerular injury in MN. C5b-9 in sublytic quantities stimulates podocytes to produce proteases, oxidants, prostanoids, extracellular matrix components, and cytokines including TGF-beta. C5b-9 also causes alterations of the cytoskeleton that lead to abnormal distribution of slit diaphragm protein and detachment of viable podocytes that are shed into Bowman's space. These events result in disruption of the functional integrity of the glomerular basement membrane and the protein filtration barrier of podocytes with subsequent development of massive proteinuria. Complement components in proteinuric urine also induce tubular epithelial cell injury and mediate progressive interstitial disease in MN. Measurements of urinary C5b-9 or podocyte excretion in the urine may be useful in the diagnosis of MN and as measures of disease activity and response to therapy. Recent studies of cell-cycle proteins and DNA damage in podocytes have clarified why podocytes fail to proliferate in response to C5b-9-mediated injury and podocyte loss in MN, resulting in the development of glomerular sclerosis and renal failure. Improved understanding of the role of complement in the pathogenesis of MN and of the cellular response to C5b-9 attack creates several new opportunities for therapeutic intervention that may benefit patients with MN in the future.

Ischemia–reperfusion injury stimulates gelatinase expression and activity in kidney glomeruli

Although ischemia remains the leading cause of acute renal failure in humans, there is little information on the expression and activities of gelatinases of kidney glomeruli during ischemia–reperfusion injury. In this study, we used a unilateral ischemia–reperfusion model to investigate the activity and expression of gelatinases in glomeruli during acute ischemia. Unilateral ischemia was induced in rats by vascular clamping (30 min) followed by reperfusion (60 min) and isolation of glomeruli. The activity and expression of gelatinase proteins were determined by gelatin zymography and Western blotting. Gelatinase mRNA levels were evaluated by reverse transciptase-PCR. Ischemia and reperfusion increased serum creatinine levels, hallmark of acute renal failure. Ischemia induced mRNA and protein MMP-2 expression. There was strong stimulation of MMP-9 mRNA, both forms of dimeric MMP-9, and active mono meric MMP-9. In contrast to TIMP-1 decreasing, TIMP-2 protein and mRNA increased during ischemia. During reperfusion, there was a gradual reversal of the MMP-2 and MMP-9 levels and a strong inhibition of TIMP-1 and TIMP-2 at the protein and mRNA levels. Endocytic receptor LRP was increased during ischemia and returned to normal during reperfusion. Expression of MMP-9 docking receptor CD-44 was increased during reperfusion. Finally, ZO-1, an in vivo MMP-9 substrate, was degraded during ischemia, revealing that MMP-9 upregulated during ischemia was functional. Our data suggest that stimulation of gelatinase activity during ischemia could contribute to glomeruli injury, providing new therapeutic targets for acute renal failure in humans. In contrast, elevated monomeric MMP-9 activity due to TIMP-1 decrease during reperfusion may participate to glomerular recovery.Key words: gelatinases, ischemia-reperfusion, TIMPs, ZO-1, CD-44, LRP, glomeruli.

Co-operative interactions between NFAT (nuclear factor of activated T cells) c1 and the zinc finger transcription factors Sp1/Sp3 and Egr-1 regulate MT1-MMP (membrane type 1 matrix metalloproteinase) transcription by glomerular mesangial cells

The transition of normally quiescent glomerular MCs (mesangial cells) to a highly proliferative phenotype with characteristics of myofibroblasts is a process commonly observed in inflammatory diseases affecting the renal glomerulus, the ultimate result of which is glomerulosclerosis. Generation of proteolytically active MMP (matrix metalloproteinase)-2 by the membrane-associated membrane type 1 (MT1)-MMP is responsible for the transition of mesangial cells to the myofibroblast phenotype [Turck, Pollock, Lee, Marti and Lovett (1996) J. Biol. Chem. 271, 15074-15083]. In the present study, we show that the expression of MT1-MMP within the context of MCs is mediated by three discrete cis -acting elements: a proximal non-canonical Sp1 site that preferentially binds Sp1; an overlapping Sp1/Egr-1-binding site that preferentially binds Egr-1; and a more distal binding site for the NFAT (nuclear factor of activated T cells) that binds the NFAT c1 isoform present in MC nuclear extracts. Transfection with an NFAT c1 expression plasmid, or activation of calcineurin with a calcium ionophore, yielded major increases in NFAT c1 nuclear DNA-binding activity, MT1-MMP transcription and protein synthesis, which were additive with the lower levels of transactivation provided by the proximal Sp1 and the overlapping Sp1/Egr-1 sites. Specific binding of NFAT c1 to the MT1-MMP promoter was confirmed by chromatin immunoprecipitation studies, while MT1-MMP expression was suppressed by treatment with the calcineurin inhibitor, cyclosporin A. These studies are the first demonstration that a specific NFAT isoform enhances transcription of an MMP (MT1-MMP) that plays a major role in the proteolytic events that are a dominant feature of acute glomerular inflammation. Suppression of MT1-MMP by commonly used calcineurin inhibitors may play a role in the development of renal fibrosis following renal transplantation.

Changes in the localization of type I, III and IV collagen mRNAs in the kidneys of hereditary nephritic (ICGN) mice with renal fibrosis

Renal fibrotic change, extreme accumulation of extracellular matrix (ECM) components in glomeruli and tubulointerstitum, is one of the characteristic features of ICR-derived glomerulonephritis (ICGN) mice. Decreased degradation of ECMs by matrixmetalloproteinases was demonstrated in kidneys of ICGN mice. To determine the balance between production and degradation of ECMs in kidneys of ICGN mice, we examined expression of mRNAs of ECMs in those. To demonstrate the localization of type I, III and IV collagen mRNAs in kidney sections of ICGN and control ICR mice, in situ hybridization using digoxigenin-labeled oligonucleotide antisense probes for procollagen-alpha(1) (I), -alpha(1) (III) and -alpha(1) (IV) mRNAs, respectively, was performed. Negative or trace expressions of type I and III collagen mRNAs were observed in the kidneys of control mice, but stronger expressions of those were seen in glomeruli and injured renal tubules of the kidneys of ICGN mice. Moderate expression of type IV collagen mRNA was demonstrated in a part of glomeruli and renal tubules of both control and ICGN mice, and no remarkable difference was seen between them. Severe renal fibrosis, extreme accumulation of interstitial type I and III collagens is caused by increased production and decreased degradation in the kidneys of ICGN mice. Thus, the profiles of metabolism between interstitial and membranous collagens may be different in the kidneys of ICGN mice, and excessive production of interstitial collagens may be the dominant cause of renal disease in them.

Decreased expression of vascular endothelial growth factor in idiopathic membranous glomerulonephritis: relationships to clinical course

BACKGROUND

Membranous glomerulonephritis (MGN) has a variable clinical course, and factors that determine the prognosis are unknown. Our previous study suggested that urinary excretion of vascular endothelial growth factor (VEGF) is decreased in active MGN, but normalizes in remission. In the present study, VEGF protein and messenger RNA (mRNA) expression were investigated in this disease.

METHODS

Twelve patients with clinically active and/or progressive MGN were studied by using urinary assays for VEGF and soluble VEGF receptor-1 (sVEGF-R1), semiquantitative scoring of serial renal biopsy specimens by using immunohistochemical staining for VEGF protein, and in situ hybridization for VEGF mRNA. Results were compared with healthy controls and normal parts of nephrectomized kidneys.

RESULTS

Urinary VEGF excretion was decreased significantly (P < 0.001 versus controls) in MGN, but there was no difference in sVEGF-R1 excretion compared with healthy subjects. VEGF protein expression was diminished significantly in glomerular podocytes (P = 0.008), as well as in extraglomerular small arteries (P = 0.03) and arterioles (P = 0.008) in MGN. Total kidney VEGF score (the sum of scores of individual kidney compartments) also was decreased in MGN (P < 0.05) and remained low in repeated biopsies. Expression of VEGF mRNA localized predominantly to podocytes in normal kidneys was greatly reduced in MGN.

CONCLUSION

Clinically active MGN is associated with diminished expression of VEGF protein and mRNA, mainly in podocytes, and expression remains depressed in persistently active and/or progressive disease. This is reflected by decreased urinary VEGF excretion. These findings point to potentially reversible podocyte injury and, together with our previous study, suggest that VEGF may have a protective role during the evolution of MGN.

Angiotensin-Converting Enzyme Inhibition but not Angiotensin II Receptor Blockade Regulates Matrix Metalloproteinase Activity in Patients with Glomerulonephritis

ABSTRACT. Equivalent long-term effects on the kidney are attributed to angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II type 1 receptor blockers (ARB). Nevertheless, it is unknown to which degree effects of these compounds on individual inflammatory mediators, including matrix metalloproteinases (MMP), are comparable. On the basis of structural and functional differences, it was hypothesized that ACEI and ARB differentially regulate MMP activity. In a randomized, prospective crossover trial, the effect of an ACEI (fosinopril; 20 mg/d) and of an ARB (irbesartan; 150 mg/d) on MMP activity was evaluated. Ten hypertensive patients with glomerulonephritis and normal or mildly reduced creatinine clearance were studied. MMP activity and tissue inhibitors of metalloproteinase (TIMP) levels were analyzed in serum and urine: without therapy, with ACEI, with ARB, and with both agents combined. Treatment periods continued for 6 wk separated by periods of 4 wk each without therapy. Untreated patients with glomerulonephritis displayed distinctively higher serum levels of MMP-2 but much lower MMP-1/-8/-9 concentrations compared with healthy control subjects. Immunohistology of MMP-2 and MMP-9 in kidney biopsy specimen was accordingly. However, these patients excreted higher amounts of MMP-2 and MMP-9 in urine than healthy control subjects, possibly reflecting ongoing glomerular inflammation. In patients with glomerulonephritis, ACEI significantly reduced overall MMP serum activity to 25%, whereas ARB did not show any effect. Activities of MMP-1/-2/-8/-9 were also significantly inhibited by fosinopril but not by irbesartan. Levels of TIMP-1/-2 remained unaffected. In conclusion, ACEI and ARB differentially regulate MMP activity, which may ultimately have consequences in certain types of MMP-dependent glomerulonephritis. E-mail: hpmarti@bluewin.ch

Doxycycline decreases proteinuria in glomerulonephritis

Treatment options for crescentic glomerulonephritis include the use of steroids, cytotoxic therapy, and, in severe cases, intravenous immunoglobulins and plasmapheresis. Injury and lysis of capillary glomerular basement membrane, which is made up of type IV collagen, laminin, fibronectin, and proteoglycans, by serine proteinases and matrix metalloproteinases (MMPs) likely is an important participant in the pathogenesis of crescentic glomerulonephritis. Tetracycline derivatives inhibit not only the activity of MMPs, but also their production, and have been investigated for the treatment of disorders in which the MMP system becomes amplified, such as degenerative osteoarthritis, periodontitis, cancer, and abdominal aortic aneurysm. We report an interesting case of crescentic glomerulonephritis in a young man who was treated with cyclophosphamide and prednisone. The patient developed steroid-induced acne that was treated with long-term oral doxycycline therapy. During the period the patient was administered doxycycline, proteinuria decreased by 70% and recurred when doxycycline was stopped. To our knowledge, this is the first report of possible benefits of a metalloproteinase inhibitor (doxycycline) in glomerulonephritis in humans. Future studies are urgently required to explore the option of metalloproteinase inhibitors in the treatment of proliferative glomerulonephritis.

Evaluation of genetic variation and association in the matrix metalloproteinase 9 (MMP9) gene in ESRD patients

BACKGROUND

Matrix metalloproteinases are Zn2+- and Ca2+-dependent endopeptidases secreted by many cells. Expression of the matrix metalloproteinase 9 (MMP9) gene is increased in a variety of renal diseases. Several genetic studies have associated MMP9 with end-stage renal disease (ESRD).

METHODS

In this study, 2.2 kb of the promoter region and all 13 exons (3.3 kb) of MMP9 genomic DNA were scanned for polymorphisms. Genetic associations between MMP9 polymorphisms and renal disease were evaluated.

RESULTS

Eleven single-nucleotide polymorphisms (SNPs; 4 promoter, 6 coding region, and 1 3' untranslated region [UTR]) were identified in Caucasians and 19 SNPs (11 promoter, 8 coding region, 1 3' UTR) were identified in African Americans. A previously identified highly polymorphic (CA)n repeat in the promoter region of MMP9 also was evaluated. We found 15 alleles in Caucasians and 14 alleles in African Americans. Allele frequencies, genotypes, and 3-marker haplotypes were compared between patient and control populations. Differences were not observed using single-locus analyses. Two haplotypes that included the (CA)n repeat allele in African-American patients with type 2 diabetic nephropathy (T2DM/ESRD) showed borderline significant differences. Dichotomizing the (CA)n repeat distribution showed that shorter alleles in Caucasian cases were associated with ESRD using an additive disease-predisposing model (P = 0.05). Analysis of the (CA)n repeat in expanded sets of subjects showed strong evidence for an association of shorter alleles with ESRD in Caucasians (P = 0.00012) and suggested a similar trend in African Americans with T2DM/ESRD (P = 0.086) and subjects without T2DM/ESRD (P = 0.047).

CONCLUSION

This comprehensive analysis of MMP9 and renal disease suggests a possible role for the (CA)n repeat in renal disease, consistent with previous reports.

Gelatinase A (MMP-2) is necessary and sufficient for renal tubular cell epithelial-mesenchymal transformation

Progressive renal interstitial fibrosis and tubular atrophy represent the final injury pathway for all commonly encountered forms of renal disease that lead to end-stage renal failure. It has been recently recognized that myofibroblastic cells are the major contributors to the deposition of interstitial collagens. While there are several potential cellular sources of myofibroblasts, attention has focused on the transformation of the organized tubular epithelium to the myofibroblastic phenotype, a process potently driven both in vitro and in vivo by transforming growth factor-beta1 (TGF-beta1). Integrity of the underlying basal lamina provides cellular signals that maintain the epithelial phenotype, and disruption by discrete proteases could potentially initiate the transformation process. We demonstrate that TGF-beta1 coordinately stimulates the synthesis of a specific matrix metalloproteinase, gelatinase A (MMP-2), and its activator protease, MT1-MMP (MMP-14), and that active gelatinase A is absolutely required for epithelial-mesenchymal transformation induced by TGF-beta1. In addition, purified active gelatinase A alone is sufficient to induce epithelial-mesenchymal transformation in the absence of exogenous TGF-beta1. Gelatinase A may also mediate epithelial-mesenchymal transformation in a paracrine manner through the proteolytic generation of active TGF-beta1 peptide. MT1-MMP and gelatinase A were co-localized to sites of active epithelial-mesenchymal transformation and basal lamina disruption in the rat remnant kidney model of progressive renal fibrosis. These studies indicate that a discrete matrix metalloproteinase, gelatinase A, is capable of inducing the complex genetic rearrangements that characterize renal tubular epithelial-mesenchymal transformation.

Differential expression of MMP-2/MMP-9 and potential benefit of an MMP inhibitor in experimental acute kidney allograft rejection

Acute cellular allograft rejection is characterized by leukocyte invasion and tissue destruction, associated with qualitative and quantitative alterations in the extracellular matrix (ECM) compartment. Metabolism of ECM proteins is mainly regulated by matrix metalloproteinases (MMP), that are zinc depended endoproteinases. MMP, especially basement membrane degrading MMP-2 and MMP-9, also facilitate tissue invasion of leukocytes. In addition, MMP-2 exerts a direct pro-inflammatory effect upon glomerular mesangial cells. Therefore, the investigation of the role of MMP in transplant rejection may lead to novel approaches in the therapy of rejection processes. To our knowledge, this is the first study of acute allograft rejection, formally addressing expression and activity of MMP, including the effect of a MMP inhibiting agent. For our studies, we used the orthotopic kidney allograft model in the stringent Dark Agouti-to-Lewis rat strain combination. Animals were divided into four groups: group A, healthy untreated Lewis rats (n=3); group B, sham operated Lewis rats (n=3); group C, transplanted Lewis rats treated with vehicle solution only (n=12); group D, transplanted Lewis rats treated with MMP inhibitor BB-94 (n=12). Respective animals were treated once daily intraperitonealy with BB-94 (30 mg/kg) or vehicle solution only. Treatment lasted from the third preoperative day until the end of the experiment, the time of severe rejection at day +7. Acute kidney allograft rejection led to alterations in the expression and activity of MMP. Overall MMP activity slightly increased despite severe destruction of kidney histology. The MMP inhibitor BB-94 successfully inhibited MMP activity to a high extent. MMP expression did not show uniform findings, since acute rejection led to differential expression of MMP-2 and MMP-9. During the rejection process, MMP-9 showed a small but significant increase, whereas MMP-2 production decreased substantially. Interestingly, BB-94 was able to keep proteinuria at a low level in transplanted animals. In conclusion, MMP-especially MMP-9-appear to represent new mediators involved in acute kidney transplant rejection.

Matrix metalloproteinase-9 and tissue inhibitor of metalloproteinases-1 in acute pyelonephritis and renal scarring

The aim of the present study was to elucidate the role of matrix metalloproteinase-9 (MMP-9), and its main inhibitor tissue inhibitor of metalloproteinases-1 (TIMP-1), in acute pyelonephritis and the process of renal scarring. Urine samples from 40 children with acute pyelonephritis, 16 children at 6-wk follow-up and 15 children with nonrenal fever were analyzed using ELISA. MMP-9 and TIMP-1 levels were compared with the outcome of pyelonephritis as measured by renal static scintigraphy. A mouse model of acute ascending pyelonephritis was used to localize the sites of production and the kinetics of MMP-9 and TIMP-1 using immunohistochemistry and ELISA. Human renal epithelial A498 cells, primary mesangial cells and monocytic THP-1 cells were stimulated by Escherichia coli. MMP-9 and TIMP-1 mRNA was analyzed by reverse transcription-PCR (RT-PCR) and protein production by ELISA. We demonstrate a significant increase of MMP-9 and TIMP-1 in the urine of children with acute pyelonephritis. Both proteins were produced mainly by leukocytes, and TIMP-1 also by resident kidney cells. Cells reacted differently after stimulation by bacteria. In mesangial cells and monocytes a decreased constitutive TIMP-1 production was found, which was in contrast to epithelial cells. Out of 40 children with pyelonephritis, 23 had higher urinary TIMP-1 than MMP-9 levels. These children had significantly more severe changes in both acute and follow-up scintigraphy scans indicating higher degree of acute tissue damage and renal scarring. Thus, our findings suggest an association between TIMP-1 and the process of renal scarring.

Macrophage metalloelastase as a major factor for glomerular injury in anti-glomerular basement membrane nephritis

Rat anti-glomerular basement membrane (GBM) nephritis is a model of crescentic glomerulonephritis induced by injection of anti-GBM antiserum. To elucidate the mechanism of glomerular injury, we analyzed the gene expression patterns in the kidneys of anti-GBM nephritis rats using DNA arrays, and found that macrophage metalloelastase/matrix metalloproteinase (MMP)-12 was one of the highly expressed genes in the kidneys on days 3 and 7 after the injection of anti-GBM antiserum. Enhancement of MMP-12 mRNA expression was confirmed by Northern blot analysis, and in situ hybridization revealed that MMP-12 mRNA was expressed in ED-1-positive macrophages and multinuclear giant cells in the glomeruli with crescent. Moreover, these cells were positive with anti-rat rMMP-12 Ab on the section of the kidneys of anti-GBM nephritis rats on day 7. To clarify the role of MMP-12, we conducted a neutralization experiment using anti-rat rMMP-12 Ab, which had an ability to inhibit rMMP-12 activity of degrading natural substrate such as bovine elastin or human fibronectin in vitro. Anti-rat rMMP-12 Ab or control Ig was injected in each of six rats on days 0, 2, 4, and 6 after the injection of anti-GBM antiserum. Consequently, crescent formation and macrophage infiltration in the glomeruli were significantly reduced in the rats treated with anti-rat rMMP-12 Ab, and the amount of urine protein was also decreased. These results disclosed that MMP-12 played an important role in glomerular injury in a crescentic glomerulonephritis model, and inhibition of MMP-12 may lead to a new therapeutic strategy for this disease.

DNA damage is a novel response to sublytic complement C5b-9-induced injury in podocytes

In response to Ab-complement-mediated injury, podocytes can undergo lysis, apoptosis, or, when exposed to sublytic (<5% lysis) amounts of C5b-9, become activated. Following the insertion of sublytic quantities of C5b-9, there is an increase in signaling pathways and growth factor synthesis and release of proteases, oxidants, and other molecules. Despite an increase in DNA synthesis, however, sublytic C5b-9 is associated with a delay in G(2)/M phase progression in podocytes. Here we induced sublytic C5b-9 injury in vitro by exposing cultured rat podocytes or differentiated postmitotic mouse podocytes to Ab and a complement source; we also studied the passive Heymann nephritis model of experimental membranous nephropathy in rats. A major finding was that sublytic C5b-9-induced injury caused an increase in DNA damage in podocytes both in vitro and in vivo. This was associated with an increase in protein levels for p53, the CDK inhibitor p21, growth-arrest DNA damage-45 (GADD45), and the checkpoint kinases-1 and -2. Sublytic C5b-9 increased extracellular signal-regulated kinase-1 and -2 (ERK-1 and -2), and inhibiting ERK-1 and -2 reduced the increase in p21 and GADD45 and augmented the DNA damage response to sublytic C5b-9-induced injury. These results show that sublytic C5b-9 induces DNA damage in vitro and in vivo and may explain why podocyte proliferation is limited following immune-mediated injury.

Cell biology of the glomerular podocyte

Glomerular podocytes are highly specialized cells with a complex cytoarchitecture. Their most prominent features are interdigitated foot processes with filtration slits in between. These are bridged by the slit diaphragm, which plays a major role in establishing the selective permeability of the glomerular filtration barrier. Injury to podocytes leads to proteinuria, a hallmark of most glomerular diseases. New technical approaches have led to a considerable increase in our understanding of podocyte biology including protein inventory, composition and arrangement of the cytoskeleton, receptor equipment, and signaling pathways involved in the control of ultrafiltration. Moreover, disturbances of podocyte architecture resulting in the retraction of foot processes and proteinuria appear to be a common theme in the progression of acquired glomerular disease. In hereditary nephrotic syndromes identified over the last 2 years, all mutated gene products were localized in podocytes. This review integrates our recent physiological and molecular understanding of the role of podocytes during the maintenance and failure of the glomerular filtration barrier.

Expression of hepatocyte growth factor mRNA in rat liver cirrhosis induced by N-nitrosodimethylamine as evidenced by in situ RT-PCR

Hepatocyte growth factor (HGF) is a potent inducer of hepatocyte proliferation and is expressed during liver failure. In this study we used the in situ reverse transcriptase-polymerase chain reaction (RT-PCR) method to detect HGF mRNA expression in normal rat livers and cirrhotic rat livers induced by treatment with N-nitrosodimethylamine (DMN). In normal control livers, in situ RT-PCR detected HGF mRNA expression in Ito cells and Kupffer cells, both of which showed rounded morphologies. However, in the cirrhotic livers induced by DMN, HGF mRNA-positive cells were spindle-shaped and surrounded the hepatocytes located around the sinusoids. These cells appeared to be sinusoidal endothelial cells as well as Ito and Kupffer cells. Because it has been suggested that HGF expression is related to transforming growth factor-beta (TGF-beta) levels that may play an essential role in disease progression in cirrhotic livers, TGF-beta mRNA expression in normal and cirrhotic livers was also compared using in situ RT-PCR. Our results confirmed that expression of TGF-beta mRNA co-localized with HGF mRNA expression in the cirrhotic liver.

Selective modulation of the secretion of proteinases and their inhibitors by growth factors in cultured differentiated podocytes

Selective modulation of the secretion of proteinases and their inhibitors by growth factors in cultured differentiated podocytes.

BACKGROUND

Podocyte damage is considered to be an important factor in the development of glomerulosclerosis. Morphological studies on experimental models of progressive glomerular disease have identified the detachment of podocytes from the glomerular basement membrane (GBM) as a critical step in the development and progression of glomerulosclerosis. Degradation of the GBM by proteinases also might be a potential mechanism of the detachment because the process impairs the connection between podocytes and the GBM. The present study examined the effects of basic fibroblast growth factor (bFGF), transforming growth factor-beta1 (TGF-beta1) and platelet-derived growth factor (PDGF) on the secretion of proteinases [cathepsin L and matrix metalloproteinases (MMPs)] and their inhibitors [cystatin C and tissue inhibitor of metalloproteinase-2 (TIMP-2)] from differentiated podocytes in culture.

METHODS

Expression of mRNAs for receptors of growth factors (bFGF, PDGF, TGF-beta1), the proteinases and their inhibitors in differentiated podocytes were shown by RT-PCR. The secretion of cathepsin L, cystatin C and TIMP-2 from differentiated podocytes were shown by immunoblot analysis. The activities of MMPs-2 and -9 from differentiated podocytes were shown by gelatin zymography.

RESULTS

Expression of mRNAs for receptors of the growth factors, the proteinases and their inhibitors were confirmed. bFGF increased the secretion of cathepsin L (5.04-fold at 20 ng/mL), but did not alter the secretion of its extracellular inhibitor, cystatin C. In contrast, TGF-beta1 increased the activities of MMPs-2 and -9 (3.23-fold at 10 ng/mL and 25.3-fold at 10 ng/mL, respectively) from differentiated podocytes, but did not enhance the secretion of its inhibitor, TIMP-2. In addition, bFGF enhanced the secretion of TIMP-2 (2.75-fold at 20 ng/mL) and TGF-beta1 enhanced the secretion of cystatin C (2.32-fold at 20 ng/mL). These results demonstrate the imbalance of the secretion of proteinases and their inhibitors after incubation of such growth factors. Of particular interest was the observation of differences in regulation of proteinases and their extracellular inhibitors in response to bFGF and TGF-beta1. PDGF only slightly increased the secretion of cathepsin L (2.54-fold at 20 ng/mL) but exerted no effect on the secretion of cystatin C, MMPs, and TIMP-2 from differentiated podocytes.

CONCLUSION

These results indicate, to our knowledge for the first time, that in differentiated podocytes, both cathepsin L and its inhibitor are independently regulated by different growth factors. It appears that increases in proteolytic activities may induce degradation of the glomerular basement membrane (GBM), which plays an important role in the progression of glomerulosclerosis.

Regulation of adhesive interaction between podocytes and glomerular basement membrane

Glomerular filtration depends on well-orchestrated cell-cell and cell-matrix contacts of glomerular podocytes. Over the last years critical constituents of these contacts have been identified via molecular approaches. Podocyte cell-matrix interactions have been shown to be mediated in part by alpha(3)beta(1)-integrin heterodimers. Disturbances of integrin matrix interaction lead to detachment of podocytes in vitro, corresponding to the critical event of foot process retraction and glomerular basement membrane (GBM) denudation in vivo. Further, dystroglycan-mediated matrix attachment appears to play a critical role for podocyte foot process architecture. Downstream signaling events are currently elucidated concentrating mainly on integrin-dependent cascades and their consequences for podocyte adhesion and proliferation. An activation of the integrin-linked kinase in podocyte damage in vivo and in vitro makes this molecule a particularly interesting candidate for integrin-mediated inside-out and outside-in signaling in podocytes. Podocyte cell-cell interaction has been characterized in a few studies in vitro, indicating the slit diaphragm to be a modified adherens junction. The structural link between the cell-matrix and cell-cell contacts is maintained by the actin cytoskeleton, which may also enable cross-talk between these two cell contact sites. Examining podocyte function in tissue culture, animal models and human expression studies should allow further detailed dissection of the molecular pathways responsible for maintenance and failure of the glomerular filtration barrier.

Activity of matrix metalloproteinase-9 is elevated in sera of patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the increased production of autoantibodies and by systemic clinical manifestations and damage to multiple organs. The aim of the present study was to analyse matrix metalloproteinase (MMP)-9 activity in sera of patients with active and inactive SLE in order to evaluate its role in the pathogenesis and course of the disease, as well as its diagnostic value. We measured activity levels of MMP-9 and MMP-2, using both gel zymography and activity assay kits, in sera of 40 SLE patients and of 25 healthy controls. We found that MMP-9 activity, but not MMP-2 activity, is significantly elevated in the sera of SLE patients compared with sera samples of healthy controls. High activity levels of MMP-9 were determined in sera of 68% of the SLE patients. Elevated levels of MMP-9 were correlated with the presence of discoid rash, Raynaud phenomenon, pneumonitis, mucosal ulcers and anti-phospholipid antibodies. Changes in activity levels of MMP-9, but not of MMP-2, were observed in sera of the same patient at different periods of the disease course. High levels of MMP-9 did not correlate with disease activity index (SLEDAI, BILAG) in female patients, but correlated with SLE activity in the group of male patients. The results of the present study suggest that MMP-9 plays a role in the pathogenesis of SLE.

Matrix metalloproteinase 9 protects mice from anti-glomerular basement membrane nephritis through its fibrinolytic activity

Matrix metalloproteinase (MMP)9/gelatinase B is increased in various nephropathies. To investigate its role, we used a genetic approach. Adult MMP9-deficient (MMP9(-/)-) mice showed normal renal histology and function at 3 mo. We investigated the susceptibility of 3-mo-old mice to the accelerated model of anti-glomerular basement membrane nephritis, in which fibrin is an important mediator of glomerular injury and renal impairment. Unexpectedly, nephritis was more severe in MMP9(-/)- than in control mice, as attested by levels of serum creatinine and albuminuria, and the extent of crescents and fibrin deposits. Circulating or deposited immunoglobulin G, interleukin (IL)-1beta, or IL-10 were the same in MMP9(-/-) and MMP9(+/+) mice. However, we found that fibrin is a critical substrate for MMP9, and in its absence fibrin accumulated in the glomeruli. These data indicate that MMP9 is required for a novel protective effect on the development of fibrin-induced glomerular lesions.

Activation of nuclear factor-kappa B by podocytes in the autologous phase of passive Heymann nephritis

BACKGROUND

The present study examined whether activation of nuclear factor-kappa B (NF-kappa B) occurs within podocytes in passive Heymann nephritis (PHN) and contributes to the pathogenesis of proteinuria.

METHODS

Electrophoretic mobility shift assays (EMSAs) were used to detect NF-kappa B activation, and supershift assays were used to determine the subunits involved. Localization of the activated NF-kappa B subunit p50 was performed by immunohistochemistry. Expression of the NF-kappa B-dependent genes interleukin-1 beta (IL-1 beta) and matrix metalloproteinase-9 (MMP-9) were determined by reverse transcription-polymerase chain reaction and, for IL-1 beta, immunohistochemistry. To inhibit activation of NF-kappa B in vivo, pyrrolidone dithiocarbamate (PDTC) was administered for 10 days following induction of PHN.

RESULTS

Glomerular nuclear extracts from rats with PHN showed increased NF-kappa B binding activity in comparison to normal rats. The major Rel/NF-kappa B proteins in these activated complexes were p65 and p50. Immunohistochemistry showed that nuclear translocation of p50 occurred predominantly within podocytes. IL-1 beta mRNA was increased in the PHN rats, and increased IL-1 beta protein was localized predominantly to podocytes by immunohistochemistry. To investigate whether activation of NF-kappa B is involved in the pathogenesis of proteinuria, PDTC was administered to rats with PHN. Electrophoretic mobility shift assays of glomerular nuclear extracts showed a significant reduction in NF-kappa B binding activity in the PDTC-treated rats with a striking reduction in MMP-9 mRNA. Compared with control rats, there was a significant reduction in albuminuria at days 15 (P < 0.001) and 20 (P < 0.001) when PHN was induced with a suboptimal dose of anti-Fx1A antiserum. There was no detectable difference in the systemic immune response to sheep Ig in the treated rats.

CONCLUSIONS

These data show that NF-kappa B is activated within podocytes in PHN and suggest that it contributes to autologous phase proteinuria. The critical genes regulated by NF-kappa B in the podocyte have not yet been determined, but may include MMP-9.

Do matrix metalloproteinases MMP-2 and MMP-9 (gelatinases) play a role in renal development, physiology and glomerular diseases?

Metalloproteinases MMP-2 and MMP-9 (also called gelatinases) are involved in cell invasion and in embryonic development and organogenesis. A growing number of reports suggest that MMP-2 and MMP-9 play some role in renal development, renal tubule physiology and glomerular pathophysiology. This editorial will focus on recent controversial data, especially those obtained from studies on MMP-9-deficient mice, which shed new light on the functions of gelatinases in normal and diseased kidneys.

Renal expression of the Ets-1 proto-oncogene during progression of rat crescentic glomerulonephritis

The ets-1 proto-oncogene is a member of the transcriptional factor family and was identified by homology to the v-ets oncogene. It was recently demonstrated that Ets-1 protein interacts with the promoter region of the genes coding for proteinases, including matrix metalloproteinase-1 (MMP-1), MMP-3, and urokinase-type plasminogen activator, suggesting that it may play an important role in the regulation of MMP expression. The role of the ets-1 proto-oncogene in advanced glomerular diseases, where extracellular matrix accumulation is observed, remains undefined. In this study, the expression of ets-1 mRNA and protein during the progression of rat crescentic glomerulonephritis was examined using immunohistochemical analysis, reverse transcription-PCR, and in situ hybridization. Passive accelerated anti-glomerular basement membrane-induced nephritis was induced in rats by intravenous injection of nephrotoxic serum. Rats were euthanized on day 7, 14, 21, 28, or 42. Immunohistochemical analysis demonstrated significant upregulation of Ets-1 protein expression in glomeruli and the interstitium in anti-glomerular basement membrane-induced nephritis. The numbers of Ets-1-positive cells were increased 8.8-fold on day 21 in glomeruli (1.2+/-0.1 cells/glomerular cross-section, P<0.001) and sixfold on day 28 in the interstitium (21+/-1.3 cells/mm(2), P<0.001), compared with control samples. Ets-1 protein was predominantly localized in glomerular epithelial cells, endothelial cells, and interstitial cells. A small number of vascular endothelial cells, macrophages, and T cells also expressed Ets-1 protein. MMP-3 deposition was upregulated and positive cells in the interstitium often coexpressed Ets-1, whereas only a few glomerular cells were positive for both MMP-3 and Ets-1 protein. The expression of ets-1 mRNA was also markedly increased in diseased kidneys. The distribution of ets-1 mRNA was similar to that of the protein. These results indicate that overexpression of the ets-1 proto-oncogene by phenotypically altered renal cells might be associated with the pathogenesis of rat crescentic glomerulonephritis.

Abnormal expression of glomerular basement membrane laminins in membranous glomerulonephritis

BACKGROUND

Proteinuria associated with glomerular diseases is secondary to alterations of the charge-selective and/or size-selective properties of the glomerular basement membrane (GBM), but molecular alterations that are responsible for these functional changes are still poorly understood. Analysis of mice harbouring a null mutation in the gene encoding the beta 2 chain of laminin has suggested that the presence of abnormal laminin chains within the GBM can be responsible for proteinuria.

METHODS

We have investigated whether abnormal laminin ss chains could be detected by immunohistochemistry within the GBM of patients with proteinuria and minimal change disease (five patients), focal and segmental glomerulosclerosis (five patients), or primary membranous glomerulonephritis (10 patients). Three patients with mesangiocapillary glomerulonephritis and three patients with IgA nephropathy were also studied as controls.

RESULTS

We showed that the GBM of all 10 patients with membranous glomerulonephritis, but not of patients with other glomerulopathies, contained laminin beta 1, which is normally expressed only during metanephros development. The re-expression of the beta 1 chain of laminin was not associated with that of the embryonic alpha 1 chain of type IV collagen, or with the loss of expression of vimentin and synaptopodin, two markers of differentiated podocytes.

CONCLUSIONS

The presence of new laminin isoforms within the GBM of patients with membranous glomerulonephritis could play a role in the occurrence of proteinuria, by modifying either the sieving properties of the GBM or the interactions between podocytes and the GBM.

Urinary excretion of podocytes in patients with diabetic nephropathy

BACKGROUND

Detection of podocytes in the urinary sediments of children with glomerulonephritis has been shown to indicate severe injury to the podocytes. The aim of the present study was to determine whether podocytes are present in the urine sediments of adult patients with diabetes with and without nephropathy and whether trandolapril is effective for podocyte injury.

METHODS

Fifty diabetic patients (10 with normoalbuminuria, 15 with microalbuminuria, 15 with macroalbuminuria and 10 with chronic renal failure) and 10 healthy controls were studied. Urinary podocytes were examined by immunofluorescence using monoclonal antibodies against podocalyxin, which is present on the surface of podocytes. In addition, we studied plasma metalloproteinase (MMP)-9 concentrations in all patients.

RESULTS

Urinary podocytes were absent in healthy controls, diabetic patients with normoalbuminuria and diabetic patients with chronic renal failure. Podocytes were detected in the urine of eight diabetic patients with microalbuminuria (53%) and of 12 patients with macroalbuminuria (80%). The number of podocytes in the urine of patients with macroalbuminuria was significantly greater than in patients with microalbuminuria (P:<0.01). However, there was no relationship between urinary albumin excretion and urinary podocytes. In addition, plasma MMP-9 concentrations were significantly correlated with the number of urinary podocytes (P:<0.01). Twelve diabetic patients with macroalbuminuria and eight patients with microalbuminuria who had urinary podocytes were treated with the angiotensin-converting enzyme inhibitor trandolapril. Urinary albumin excretion, the number of podocytes and plasma MMP-9 concentrations were reduced by the trandolapril treatment.

CONCLUSIONS

Podocytes in the urine may be a useful marker of disease activity in diabetic nephropathy. Trandolapril may be effective for podocyte injury.

Gelatinase B (MMP-9) is not essential in the normal kidney and does not influence progression of renal disease in a mouse model of Alport syndrome

Matrix metalloproteinases are matrix degrading enzymes implicated in many biological processes, including development and inflammation. Gelatinase B (gelB; also known as MMP-9) is expressed in the kidney and is hypothesized to be involved in basement membrane remodeling and in preventing pathogenic accumulation of extracellular matrix in the kidney. Inhibition of gelB activity in metanephric organ culture disrupts branching morphogenesis of the ureteric bud, suggesting that gelB plays a role in kidney development in vivo. We studied kidneys of gelB-deficient mice to search for developmental, histological, molecular, ultrastructural, and functional defects. Surprisingly, no differences between gelB-/- and control kidneys were detected, and renal function was normal in gelB mutants. In addition, gelB-/- embryonic kidneys developed normally in organ culture. Gelatinase B-deficient mice were bred with Col4a3-/- mice, a model for Alport syndrome, to determine whether gelB influences the progression of glomerulonephritis. This is an important question, as it has been hypothesized that proteases are involved in damaging Alport glomerular basement membrane. However, the presence or absence of gelB did not affect the rate of progression of renal disease. Thus, gelB does not have a discernible role in the normal kidney and gelB is not involved in the progression of glomerulonephritis in a mouse model of Alport syndrome.

Participation of macrophages in glomerular sclerosis through the expression and activation of matrix metalloproteinases

In order to investigate the role of macrophages in glomeruli in the progression of glomerular sclerosis, methyl-cellulose (MC) was administered intraperitoneally to Wistar rats, in addition to intravenous injection of anti-thy1-1 antibody. In this group of rats (Thy-1 + MC group), many macrophages infiltrated in the lytic mesangium accompanied by rupture of capillary loops at an early stage and stayed with abundant deposition of mesangial matrices until day 35, whereas the proliferative lesions following mesangiolysis almost vanished in the rats treated with anti-thy1-1 antibody alone (Thy-1 group). In immunostaining, matrix metalloproteinase (MMP)-9 was expressed along regenerating capillaries of the Thy-1 group and in extracapillary lesions of the Thy-1 + MC group after day 7. In gelatin zymography, the gelatinolytic band for MMP-9 was expressed much more strongly in the Thy-1 + MC group than in the Thy-1 group at day 3, but it was expressed a little more strongly in the Thy-1 group than in the Thy-1 + MC group at day 7. The bands for an active form of MMP-2 were more strongly expressed in the Thy-1 + MC group than in the Thy-1 group throughout the experimental period. These results suggest that persistent accumulation of macrophages in mesangium induces glomerular sclerosis through expression and activation of MMP.

Cocaine and the kidney: a synthesis of pathophysiologic and clinical perspectives

Cocaine abuse has reached epidemic proportions in the United States, and several forms of renal disease have been associated with this widespread use. The hemodynamic actions of cocaine, as well as its effects on matrix synthesis, glomerular inflammation, and glomerulosclerosis, may contribute to renal injury. Cocaine abuse has been associated with various forms of acute renal failure and acid-base and/or electrolyte disorders and may also have a role in the progression of chronic renal failure to end-stage renal disease. In utero exposure to cocaine has been associated with urogenital tract anomalies. Medical management of a hypertensive emergency caused by acute cocaine toxicity requires a multisystem approach, with close monitoring of cardiac, neurological, and renal functions.

Identification, cellular distribution and potential function of the metalloprotease-disintegrin MDC9 in the kidney

The complex interactions of glomerular and tubular epithelial cells with the basal laminae play a critical role in renal function. Disruption of these interactions has been widely implicated in glomerular diseases and acute renal failure. MDC are a large family of membrane-bound proteins containing metalloprotease, disintegrin (integrin interaction sites), and cysteine-rich domains. Little information is available concerning the presence of MDC in the kidney or their role in renal pathophysiology. Using degenerate PCR primers for the conserved metalloprotease and disintegrin domains of this protein family, cDNA templates from tubules, whole glomeruli, and glomerular epithelial cells (GEC) yielded a single, 195-bp product, which on sequence analysis corresponded to a region in the disintegrin domain of MDC9. Northern analysis of poly(A)+ RNA from tubules, whole glomeruli, and GEC revealed a 3.9-kb transcript, identical to that of mouse MDC9. Using antibodies generated against a 21-amino acid peptide present in the metalloprotease domain of MDC9, Western analysis of concanavalin A-enriched glomerular microsomal extracts demonstrated both processed (76 kD) and unprocessed (116 kD) forms of MDC9, which upon reduction changed to the corresponding 84- and 124-kD forms. Histochemical studies revealed a basolateral localization of intrinsic MDC9 protein in renal cortical tubule cells and glomerular visceral epithelial cells, which colocalized with the beta1 integrin chain. Expression of green fluorescence protein MDC9 chimeric constructs in GEC or polarized Madin-Darby canine kidney epithelial cells revealed a similar punctate basolateral surface localization. Transient overexpression of the soluble disintegrin domain-green fluorescence protein chimera in GEC led to dramatic changes in cellular morphology with rounding and detachment from cell monolayers. These studies document the presence of MDC9 in renal epithelial cells and suggest an important role for MDC9 in renal epithelial cellular interactions with the basal lamina and adjoining cells.

Complement C5b-9 induces receptor tyrosine kinase transactivation in glomerular epithelial cells

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.

Changes in collagenases and TGF-beta precede structural alterations in a model of chronic renal fibrosis

BACKGROUND

To study the role of collagenases and transforming growth factor-beta (TGF-beta) in the genesis of interstitial fibrosis, we used the model of bromoethylamine (BEA)-induced papillary necrosis, which is known to lead over a period of 1 to 12 months to interstitial fibrosis and renal insufficiency.

METHODS

Rats were injected with BEA, and urine and kidney tissue (cortex and medulla) were collected after 1, 2, 3, 7, and 30 days. One kidney was perfused and fixed for morphological studies and immunostained for collagen type I, III, and IV. The other kidney was used to prepare cortex and medulla extracts for gelatinases (by fluorometric and zymographic techniques), tissue inhibitors of metalloproteinase-1 (TIMP-1), and TIMP-2 (by enzyme-linked immunosorbent assay, ELISA) and TGF-beta1 (by ELISA).

RESULTS

Albuminuria and interstitial fibrosis were present in BEA rats by day 7, which continued until day 30. Immunocytochemical staining for collagen types showed that collagen III and IV increased in the interstitium by day 30, but collagen I remained unchanged. Gelatinase activity in the medulla decreased by 57% compared with control by day 2 and remained low until day 30. In the cortex, gelatinase activity remained unchanged between 0 and 7 days after BEA but decreased by 72% by day 30. TIMP-1 and TIMP-2 were decreased by 80% compared with day 0 in both the medulla (by day 1) and cortex (by day 2) and remained low up to day 30. TGF-beta1 immunoreactivity increased progressively until day 2 in the medulla (16-fold higher than control) and day 3 in the cortex (8-fold higher than control) and returned to control level by day 3 in the medulla and by day 30 in the cortex. Two days after BEA injection, the mRNA for TGF-beta1 was increased eightfold in the cortex and 12-fold in the medulla, and it remained high for up to 30 days.

CONCLUSIONS

The fibrosis that follows papillary necrosis is associated with both high TGF-beta1 expression and depressed gelatinolytic activity.

Evidence that actin disassembly is a requirement for matrix metalloproteinase secretion by sinusoidal endothelial cells during cold preservation in the rat

Cold preservation induces the secretion of matrix metalloproteinases (MMPs) by hepatic sinusoidal endothelial cells (SECs). These enzymes are important mediators of cold preservation injury. The purpose of this study was to determine if low temperature caused actin disassembly in SECs and whether actin disassembly was required for secretion of MMPs under these conditions. To establish the basis of interpreting the effect of low temperature, isolated SECs were exposed to cytochalasin B with or without pretreatment with phalloidin. Cytochalasin B produced actin disassembly and resulted in the secretion of MMPs. Both were retarded by phalloidin pretreatment. Low temperature (4 degrees C) also induced actin disassembly and MMP secretion and pretreatment with phalloidin again retarded actin disassembly and MMP secretion. Cycloheximide had no effect on these results. Actin disassembly began with 30 minutes of exposure of isolated SECs to cold and reached a final state at 8 hours, at which time no actin stress fibers were visible, and the normally fusiform SECs were fully rounded. Increased MMP activity in the supernatant was also present at 30 minutes and continued to rise sharply in the first hour; thereafter the rate of rise diminished. The study shows that secretion of MMPs during cold preservation is dependent on the induction of actin disassembly by low temperature. The rapid appearance of increased MMP activity after exposure to cold and the studies using cycloheximide indicate that the MMPs originate from preformed MMPs rather than newly synthesized MMPs.

The concept of glomerular self-defense

The balance between local offense factors and defense machinery determines the fate of tissue injury: progression or resolution. In glomerular research, the most interest has been on the offensive side, for example, the roles of leukocytes, platelets, complement, cytokines, eicosanoids, and oxygen radical intermediates. There has been little focus on the defensive side, which is responsible for the attenuation and resolution of disease. The aim of this review is to address possible mechanisms of local defense that may be exerted during glomerular injury. Cytokine inhibitors, proteinase inhibitors, complement regulatory proteins, anti-inflammatory cytokines, anti-inflammatory eicosanoids, antithrombotic molecules, and extracellular matrix proteins can participate in the extracellular and/or cell surface defense. Heat shock proteins, antioxidants, protein phosphatases, and cyclin kinase inhibitors may contribute to the intracellular defense. This article outlines how the glomerulus, when faced with injurious cells or exposed to pathogenic mediators, defends itself via the intrinsic machinery that is brought into play in resident glomerular cells.

Induction of albuminuria in mice: synergistic effect of two monoclonal antibodies directed to different domains of aminopeptidase A

BACKGROUND

Aminopeptidase A is an enzyme that is present on podocytes and is involved in the degradation of angiotensin II. In previous studies in mice, we administered single monoclonal antibodies directed against aminopeptidase A. We observed that only monoclonal antibodies that inhibited aminopeptidase A enzyme activity caused albuminuria.

METHODS

In this study, the effects of the combined injections of two monoclonal anti-aminopeptidase A antibodies (mAbs) were studied, using a combination of anti-aminopeptidase A mAbs that were directed against two different domains involved in the aminopeptidase A enzyme activity (ASD-3 or ASD-37) and an anti-aminopeptidase A mAb not related to the enzyme active site (ASD-41).

RESULTS

An injection of the combinations ASD-3/37 (total 4 mg, 1:1 ratio) and ASD-37/41 (total 4 mg, 1:1 ratio) in doses that do not cause albuminuria when given alone (4 mg) induced massive albuminuria at day 1 after injection. The combination ASD-3/41 had no effect. This albuminuria was not dependent on systemic immune mediators of inflammation and could not merely be related to a blockade of aminopeptidase A enzyme activity. However, a correlation was observed between the induction of albuminuria and the aggregation of the mAbs injected and aminopeptidase A on the podocytes. An injection of the combinations ASD-3/37 or ASD-37/41 did not cause an increase in systemic blood pressure. The treatment with a combination of enalapril and losartan lowered blood pressure (53 +/- 10 vs. 90 +/- 3 mm Hg in untreated mice) and reduced the acute albuminuria by 55% (11,145 +/- 864 vs. 24,517 +/- 2448 micrograms albumin/18 hr in untreated mice). However, similar effects were observed using triple therapy. Therefore, the reduction of albuminuria by the combined treatment of enalapril/losartan seems to be the consequence of the reduction in the systemic blood pressure. These findings argue against a specific role for angiotensin II in this model.

CONCLUSIONS

The combined injection of two mAbs directed against different domains of aminopeptidase A induces a massive albuminuria in mice, which is not merely dependent on angiotensin II. We hypothesize that the direct binding of mAbs to at least two pathogenic domains on aminopeptidase A triggers the podocyte to release mediators that are involved in the observed albuminuria.

Matrix metalloproteinase 2 (MMP2) and MMP9 are produced by kidney collecting duct principal cells but are differentially regulated by SV40 large-T, arginine vasopressin, and epidermal growth factor

We analyzed the expression and regulation of matrix metalloproteinase 2 (MMP2) and MMP9 gelatinases in a rabbit kidney collecting duct principal cell line (RC.SVtsA58) (Prié, D., Ronco, P. M., Baudouin, B., Géniteau-Legendre, M., Antoine, M., Piedagnel, R., Estrade, S., Lelongt, B., Verroust, P. J., Cassingéna, R., and Vandewalle, A. (1991) J. Cell Biol. 113, 951-962) infected with the temperature-sensitive (ts) SV40 strain tsA58. At the permissive temperature (33 degreesC), cells produced only MMP2. Shifting cells to a nonpermissive temperature (39.5 degreesC) induced a marked increase in total gelatinolytic activity due to an increase of MMP2 and an induction of MMP9 synthesis. This effect was attributed to large-T inactivation at 39.5 degreesC because it was abolished by re-infecting the cells with wild-type SV40 strain LP. Run-on experiments showed that negative regulation of MMP2 and MMP9 by large-T was transcriptional and posttranscriptional, respectively. MMP2 and MMP9 were also produced by primary cultures of collecting duct cells. In rabbit kidney, both MMP2 and MMP9 were almost exclusively expressed in collecting duct cells, where an unexpected apical localization was observed. Arginine vasopressin and epidermal growth factor, which exert opposite hydroosmotic effects in the collecting duct, also exhibited contrasted effects on MMP9 synthesis. Epidermal growth factor increased but arginine vasopressin suppressed MMP9 at a posttranscriptional level, whereas MMP2 was not affected. These results suggest a specific physiological role of MMP2 and MMP9 in principal cells of renal collecting duct.

Progression of glomerular diseases: is the podocyte the culprit?

The stereotyped development of the glomerular lesions in many animal models and human forms of progressive renal disease suggests that there are common mechanisms of disease progression. We propose the outline of such a mechanism based on following aspects: (1) The glomerulus is a complex structure, the stability of which depends on the cooperative function of the basement membrane, mesangial cells and podocytes, counteracting the distending forces originating from the high glomerular hydrostatic pressures. Failure of this system leads to quite uniform architectural lesions. (2) There is strong evidence that the podocyte is incapable of regenerative replication post-natally; when podocytes are lost for any reason they cannot be replaced by new cells. Loss of podocytes may therefore lead to areas of "bare" GBM. which represent potential starting points for irreversible glomerular injury. (3) Attachment of parietal epithelial cells to bare GBM invariably occurs when bare GBM coexists with architectural lesions, leading to the formation of a tuft adhesion to Bowman's capsule, the first "committed" lesion progressing to segmental sclerosis. (4) Within an adhesion the tuft merges with the interstitium, allowing filtration from perfused capillaries inside the adhesion towards the interstitium. The relevance of such filtration is as yet unclear but may play a considerable role in progression to global sclerosis and interstitial fibrosis.

Complement activates phospholipases and protein kinases in glomerular epithelial cells

BACKGROUND

In rat membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which in some models is partially mediated by eicosanoids. In cultured rat GEC, sublytic C5b-9 injures plasma membranes and releases arachidonic acid (AA) and eicosanoids, due to activation of cytosolic phospholipase A2 (cPLA2). In this study, we address the role of protein kinases in cPLA2 activation.

METHODS

GEC were stably transfected with cDNAs of wild-type (wt) cPLA2, and serine505-->alanine mutant (cPLA2-SA505), which lacks the mitogen-activated protein kinase (MAPK) phosphorylation site.

RESULTS

Complement stimulated protein kinase C (PKC) activity in GEC, and activated p42 (but not p38) MAPK. Overexpression of either cPLA2-wt or cPLA2-SA505 markedly amplified the release of [3H]AA by C5b-9. Depletion of PKC blocked the complement-dependent activation of cPLA2-wt or cPLA2-SA505, but inhibition of the p42 MAPK pathway had no effect. Epidermal growth factor was a strong activator of p42 MAPK, but stimulated PKC activity weakly. Unlike complement, activation of cPLA2-wt by epidermal growth factor was dependent on PKC, and was augmented significantly by p42 MAPK. Stable overexpression of phospholipase C-gamma 1 in GEC amplified C5b-9-induced production of [3H]inositol phosphates and [3H]diacylglycerol, an endogenous activator of PKC, and complement stimulated tyrosine phosphorylation of phospholipase C-gamma 1.

CONCLUSIONS

C5b-9 induces activation of cPLA2 that is dependent on the diacylglycerol-PKC pathway. The role of p42 MAPK in cPLA2 activation becomes redundant in the presence of relatively potent PKC activation.

Glomerular mesangial cell-specific transactivation of matrix metalloproteinase 2 transcription is mediated by YB-1

Mesangial cell (MC) activation plays a pivotal role in the development of the end stage sclerotic lesion characteristic of most forms of chronic glomerular disease. We have previously demonstrated that MC activation is directly linked to high level expression of the matrix metalloproteinase-2 (MMP-2) enzyme (Turck, J., Pollock, A. S., Lee, L., Marti, H.-P., and Lovett, D. H. (1996) J. Biol. Chem. 25, 15074-15083), the transcription of which is regulated in a tissue-specific fashion. Recent studies (Harendza, S., Pollock, A., Mertens, P. R., and Lovett, D. H. (1995) J. Biol. Chem. 270, 18786-18796) delineated a strong cis-acting enhancer element, designated MMP-2 RE1, within the 5'-flanking region of the rat MMP-2 gene. Gel shift, DNA footprint, and transcriptional analyses mapped the enhancer element to a unique 40-base pair (bp) sequence located at -1322 to -1282 bp relative to the translational start site. Bromodeoxyuridine-substituted UV cross-linking of the 40-bp enhancer element with MC nuclear extracts yielded a single protein of 52 kDa, while Southwestern blot analysis with MMP-2 RE1 demonstrated three hybridizing nuclear proteins of 52, 62, and 86 kDa size. Screening of a human MC cDNA expression library with MMP-2 RE1 exclusively yielded clones with the identical sequence of the transcription factor YB-1. Western blot and supershift gel analysis of MC nuclear extracts with an anti-YB-1 antibody confirmed the presence of YB-1 within the shifted complex. Examination of the MMP-2 RE1 sequence revealed an incomplete Y-box sequence (CTGCTGGGCAAG), which specifically interacted with recombinant YB-1 on DMS protection footprinting analysis. YB-1 protein preferentially bound the single-stranded components of the 40-bp MMP-2 RE1 and, with increasing concentrations, formed multimeric complexes. Co-transfection of YB-1 in MC increased the enhancer activity within the context of the native MMP-2 promoter, while transfection of non-MMP-2-synthesizing glomerular epithelial cells with YB-1 led to transcriptional suppression. This study indicates that YB-1 is a major, cell type-specific transactivator of MMP-2 transcription by glomerular mesangial cells.