Identification and independent regulation of human mesangial cell metalloproteinases

Thrombin Suppresses Matrix Metalloproteinase 2 Activity and Increases Tissue Inhibitor of Metalloproteinase 1 Synthesis in Cultured Human Peritoneal Mesothelial Cells

Objective

Recently, high levels of intraperitoneally generated thrombin were found in the effluent of patients treated with continuous ambulatory peritoneal dialysis (CAPD). The aim of the present study was to investigate in human peritoneal mesothelial cells (HMCs) the effect of thrombin on the activity and synthesis of matrix metalloproteinases (MMPs), which regulate the degradation of basement membrane collagen.

Methods

Cultured HMCs were isolated from omental tissue and used at confluence for the experiments. Conditioned media were obtained by incubating cells with serum-free M199 containing the relevant doses of thrombin. Activity of MMP-2 and MMP-9 were determined by an activity assay system. The antigen levels of MMPs and of the specific tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by ELISA. Northern blot analysis was applied to analyze mRNA expression of MMP-2 and TIMP-1.

Results

Incubation of HMCs with increasing doses of thrombin resulted in a concentration- and time-dependent suppression of MMP-2 activity. No changes in MMP-9 activity were seen. After a 48-hour stimulation period with thrombin (5 U/mL), MMP-2 activity decreased to 53% of that seen in control conditions. Antigen measurements revealed that this decrease was paralleled by a slight reduction in MMP-2 levels, which became significant at a thrombin dose of 5 U/mL [50.65 ± 7.5 ng/105cells (48 hours, 5 U/mL) vs 64.6 ± 10.1 ng/105cells (control)]. Under the same conditions, TIMP-1 levels were considerably increased [3.9 ± 0.46 μg/105cells (48 hours, 5 U/mL) vs 1.2 ± 0.14 μg/105cells (control)]. Hirudin (10 U/mL) completely inhibited the thrombin-induced effects on MMP-2 and TIMP-1 synthesis. These results were also reflected by Northern blot hybridization, where a slight decrease in MMP-2 and an increase in TIMP-1 mRNA expression were observed in response to thrombin.

Conclusions

Our results suggest that high thrombin levels suppress MMP-2 activity through decreased MMP-2 and increased TIMP-1 synthesis. Thus, thrombin may promote the accumulation of basement membrane collagen. In addition to fibrin formation, this mechanism may represent a further contribution by thrombin to peritoneal thickening during CAPD.

Production and Regulation of Matrix Metalloproteinases and Their Inhibitors by Human Peritoneal Mesothelial Cells

Objective

Human peritoneal mesothelial cells (HPMC) are likely to be involved in maintenance of the peritoneal membrane. We determined whether these cells were able to synthesize the matrix degrading enzymes, matrix metalloproteinases (MMPs), likely to be responsible for the breakdown of this membrane, and whether this secretion could be modulated by cytokines involved in the inflammatory response.

Design

MMP activity in conditioned medium of growth-arrested HPMC was measured by zymography. Cultures were incubated in the presence and absence of the cytokines transforming growth factor-beta (TGFβ) and interleukin (IL)-1β in order to determine the effects of these cytokines on this process. The mRNA for these MMPs, together with that of their specific inhibitors, tissue inhibitors of metalloproteinases (TIMPs), was also examined by reverse transcriptase polymerase chain reaction (RT-PCR).

Results

HPMC were shown to constitutively secrete the metalloproteinases MMP-2 and MMP-3 in vitro. In response to the proinflammatory cytokine IL-1β, the protein and mRNA for MMP-9 was induced, while secretion of MMP-2 was unaltered. Similarly, the mRNA for MMP-3 was also increased relative to actin following the addition of IL-1β. TGFβ was shown to slightly induce the secretion of MMP-2 together with the mRNA for TIMP I, TIMP II, and, to a greater extent, TIMP III. Used peritoneal dialysate was also shown to induce MMP-9 secretion, and this effect was blocked by the co-incubation of IL-1 receptor antagonist. The secretion of enzyme activity was shown to be from the apical surface of the cells.

Conclusion

HPMC have the ability to control the accumulation of extracellular matrix by secreting the matrix degrading molecules MMP-2, MMP-3, and MMP-9. In addition, the secretion of these enzymes, together with that of their inhibitors (TIMPs) is regulated by the cytokines IL-1β and TGFβ. This process is likely to be important in both the normal maintenance of the integrity of the peritoneal membrane and in the changes that occur following prolonged peritoneal dialysis.

Mesangial cells are key contributors to the fibrotic damage seen in the lupus nephritis glomerulus

Background

Lupus nephritis (LN) affects up to 80% of juvenile-onset systemic lupus erythematosus patients. Mesangial cells (MCs) comprise a third of the glomerular cells and are key contributors to fibrotic changes within the kidney. This project aims to identify the roles of MCs in an in vitro model of LN.

Methods

Conditionally immortalised MCs were treated with pro-inflammatory cytokines or with patient sera in an in vitro model of LN and assessed for their roles in inflammation and fibrosis.

Results

MCs were shown to produce pro-inflammatory cytokines in response to a model of the inflammatory environment in LN. Further the cells expressed increased levels of mRNA for extracellular matrix (ECM) proteins (COL1A1, COL1A2, COL4A1 and LAMB1), matrix metalloproteinase enzymes (MMP9) and tissue inhibitors of matrix metalloproteinases (TIMP1). Treatment of MCs with serum from patients with active LN was able to induce a similar, albeit milder phenotype. Treatment of MCs with cytokines or patient sera was able to induce secretion of TGF-β1, a known inducer of fibrotic changes. Inhibition of TGF-β1 actions through SB-431542 (an activin A receptor type II-like kinase (ALK5) inhibitor) was able to reduce these responses suggesting that the release of TGF-β1 plays a role in these changes.

Conclusions

MCs contribute to the inflammatory environment in LN by producing cytokines involved in leukocyte recruitment, activation and maturation. Further the cells remodel the ECM via protein deposition and enzymatic degradation. This occurs through the actions of TGF-β1 on its receptor, ALK5. This may represent a potential therapeutic target for treatment of LN-associated fibrosis.

Insulin-like growth factor binding protein 7 and tissue inhibitor of metalloproteinases-2: differential expression and secretion in human kidney tubule cells

We have characterized the expression and secretion of the acute kidney injury (AKI) biomarkers insulin-like growth factor binding protein 7 (IGFBP7) and tissue inhibitor of metalloproteinases-2 (TIMP-2) in human kidney epithelial cells in primary cell culture and tissue. We established cell culture model systems of primary kidney cells of proximal and distal tubule origin and observed that both proteins are indeed expressed and secreted in both tubule cell types in vitro. However, TIMP-2 is both expressed and secreted preferentially by cells of distal tubule origin, while IGFBP7 is equally expressed across tubule cell types yet preferentially secreted by cells of proximal tubule origin. In human kidney tissue, strong staining of IGFBP7 was seen in the luminal brush-border region of a subset of proximal tubule cells, and TIMP-2 stained intracellularly in distal tubules. Additionally, while some tubular colocalization of both biomarkers was identified with the injury markers kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin, both biomarkers could also be seen alone, suggesting the possibility for differential mechanistic and/or temporal profiles of regulation of these early AKI biomarkers from known markers of injury. Last, an in vitro model of ischemia-reperfusion demonstrated enhancement of secretion of both markers early after reperfusion. This work provides a rationale for further investigation of these markers for their potential role in the pathogenesis of acute kidney injury.

Expression of matrix metalloproteinases 2 and 9 and tissue inhibitors of matrix metalloproteinases 2 and 1 in the glomeruli of human glomerular diseases: the results of studies using immunofluorescence, in situ hybridization, and immunoelectron microscopy

BACKGROUND

It has been reported matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of matrix metalloproteinases (TIMPs), play important roles in the decomposition of the extracellular matrices of the glomerulus during the pathological processes in various glomerular diseases. Although the activity of these enzymes in cases of experimental glomerulonephritis has been described, the expression sites in the glomeruli of human renal diseases have been identified in only a few articles and remain controversial.

METHODS

The expression of the gelatinase group of MMPs (MMP-2 and MMP-9) and their inhibitors (TIMP-2 and TIMP-1) were evaluated in 19 renal biopsies of several types of glomerular diseases by immunofluorescence (IF) labeling. In addition, several samples of immunoglobulin A nephropathy (IgAN) were also investigated by in situ hybridization (ISH) and immunoelectron microscopy (IEM).

RESULTS

The expression of MMP-2 was observed in all the cases examined by IF and ISH. TIMP-2 expression varied from negative to positive among 11 cases of IgAN, but was negative in the cases with lupus nephritis (LN) (n = 3), membranoproliferative glomerulonephritis (MPGN) (n = 2), and post-streptococcal glomerulonephritis (n = 1). However, it was weakly positive in the cases of diabetic nephropathy (DMN) (n = 2). MMP-2 was mainly observed along glomerular capillary loops (GCLs) and Bowman's capsules, whereas TIMP-2 was found in the mesangial area. The expression of MMP-9 in cases of IgAN varied, and was local, not diffuse, if it was present. MMP-9 expression in cases of LN, MPGN, and DMN was diffuse, but the intensity of staining varied. MMP-9 was primarily expressed in the mesangium. TIMP-1 expression was negative in all cases except for those with IgAN. The localization of MMP-2 in patients with IgAN, which was investigated by IEM, was revealed to be mainly on the endothelial cell membranes of GCLs, podocyte membranes, the parietal cell membranes of Bowman's capsules, and some on the membranes of mesangial cells.

CONCLUSION

The study results suggest that the expression levels and patterns of MMPs and TIMPs are generally similar in several types of glomerular diseases, even though each case has a somewhat different distribution and intensity of expression. When these enzymes were present, their main sites were as follows: MMP-2 was found along glomerular basement membrane, TIMP-2 was located in the acellular mesangial area, MMP-9 was seen in the mesangium, and TIMP-1 was hardly detected. MMP-2 expression is clearly demonstrated to exist at the above-described sites by IEM in patients with IgAN.

Effect of angiotensin type 2 receptor over-expression on the rat mesangial cell fibrotic phenotype: effect of gender

BACKGROUND AND AIM

The protective role of angiotensin type 2 receptors (AT2-Rs) is still controversial. As AT2-Rs are minimally expressed in adult tissues the aim of the current study was to over-express AT2-Rs in rat mesangial cells in order to ascertain their potential role in modulating renal scarring.

METHODS

Male and female mesangial cells were transiently transfected with AT2-R or control vector then 'injured' with macrophage-conditioned medium (MCM). Culture supernatants and extracted RNA were analysed for evidence of an anti-fibrotic phenotype.

RESULTS

Supernatant fibronectin levels in female mesangial cells treated with MCM were reduced in AT2-R transfected cells (p < 0.001) compared to controls. AT2-R transfected male cells showed a trend towards lower constitutive fibronectin levels. There was no effect of AT2-R transfection on TGF-β or TNF-α secretion; however, IL-1β levels were reduced in male cells treated with MCM. RT-PCR demonstrated that constitutive kallikrein mRNA levels were suppressed in both male and female AT2-R transfected cells. Bradykinin receptors (BkB2-R and BkB1-R) were unaffected in female cells although the BkB1-R was upregulated in male cells treated with MCM.

CONCLUSION

This data provides a case for AT2 receptors playing a protective role in rat mesangial cells independent of the effects of blood pressure control.

Glomerular matrix metalloproteinases and their regulators in the pathogenesis of lupus nephritis

Lupus nephritis is a major contributor to morbidity and mortality in systemic lupus erythematosus, but little is known about the pathogenic processes that underlie the progressive decay in renal function. A common finding in lupus nephritis is thickening of glomerular basement membranes associated with immune complex deposition. It has been speculated that alterations in the synthesis or degradation of membrane components might contribute to such changes, and thereby to initiation and progression of nephritis through facilitation of immune complex deposition. Matrix metalloproteinases (MMPs) are enzymes that are intimately involved in the turnover of major glomerular basement membrane constituents, including collagen IV and laminins. Alterations in the expression and activity of MMPs have been described in a number of renal diseases, suggesting their relevance to the pathogenesis of various glomerulopathies. The same is true for their natural inhibitors, the tissue inhibitor of metalloproteinase family. Recent data from our group have identified an increase in proteolytic activity within the glomerulus coinciding with the development of proteinuria in the mouse model of systemic lupus erythematosus. (NXB x NZW)F1 Here we review current understanding of MMP/tissue inhibitor of metalloproteinase function within the kidney, and discuss their possible involvement in the development and progression of lupus nephritis.

Perindoprilat modulates the activity of lipoprotein receptor-related protein in human mesangial cells

Low density lipoprotein receptor-related protein (LRP) is a multifunctional endocytic receptor implicated in the modulation of a number of cellular processes, including the turnover of proteases and the degradation of extracellular matrix proteins. As such, it can play a key role in the control of fibrosis. The aim of this investigation was to ascertain whether the anti-fibrotic effects exerted by the angiotensin-converting enzyme inhibitor (ACE-I) perindoprilat on macrophage-conditioned medium (MPCM)-injured human mesangial cells can be modulated by this receptor. Addition of receptor-associated protein to MPCM-injured mesangial cells with and without ACE-I increased the amount of tissue plasminogen activator protein detected in mesangial cell culture supernatants without affecting the protein levels of plasminogen activator inhibitor-1. The ability of ACE-I to reduce fibronectin was diminished in the presence of receptor-associated protein. ACE-I induced an increase in mesangial cell MMP9 mRNA, but reduced the MMP9 enzyme activity detected in mesangial cell supernatants. Mesangial cell lysates from ACE-I-treated cells were able to bind immobilized fibronectin at higher dilutions than cell lysates from untreated cells. Flow cytometry showed that MPCM induced an increase in LRP surface expression in mesangial cells over that in control cells and that this expression was further increased by ACE-I treatment. The increase in LRP expression in response to ACE-I was also observed by Western blotting. Northern blot analysis of RNA extracted from cells following a 24-h exposure to MPCM with and without ACE-I demonstrated that there was no change in LRP mRNA expression upon ACE-I treatment. In conclusion, we show that ACE-I treatment is able to modulate mesangial cell-surface expression of LRP, providing an additional mechanism whereby ACE-Is can mediate anti-fibrotic actions independent of their hemodynamic actions.

Hyaluronan induces the selective accumulation of matrix- and cell-associated proteoglycans by mesangial cells

Mesangial cells (MCs) are essential for normal renal function through the synthesis of their own extracellular matrix, which forms the structural support of the renal glomerulus. In many renal diseases this matrix is reorganized in response to a variety of cytokines and growth factors. This study examines proteoglycan and hyaluronan (HA) synthesis by MCs triggered by proinflammatory agents and investigates the effect of an exogenous HA matrix on matrix synthesis by MCs. Metabolic labeling, ion exchange and size exclusion chromatography, Western blotting, and immunocytochemistry were used to identify changes in matrix accumulation. When incubated with interleukin-1, platelet-derived growth factor, or fetal calf serum, MCs initiated rapid HA synthesis associated with the up-regulation of HA synthase-2 and increased the synthesis of versican, perlecan, and decorin/biglycan. HA was both released into the medium and incorporated into extensive pericellular coats. Adding exogenous HA to unstimulated cells that had undetectable pericellular coats of HA selectively reduced perlecan and versican turnover, whereas other proteoglycans were unaffected. These results suggest that high levels of HA in the mesangium in disease is a mechanism controlling the accumulation of specific mesangial matrix components. HA may thus be an attractive target for therapeutic intervention.

TNF-alpha and IL-1 beta-mediated regulation of MMP-9 and TIMP-1 in human glomerular mesangial cells

BACKGROUND

Renal cells such as mesangial cells are known to secrete metalloproteinases that are capable of degrading the constituents of the glomerular basement membrane (GBM). Disruption of the GBM via cytokine-induced alterations in matrixmetalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) may be an important mechanism in the renal disease process. In renal disease, both resident renal cells and infiltrating immune cells are capable of secreting pro-inflammatory cytokines including tumour necrosing factor-alpha (TNFalpha) and interleukin-1 beta (IL-1 beta). In this study, we examine the potential of these cytokines to alter levels of MMPs and TIMPs in human mesangial cells.

METHODS

The T-HMC human mesangial cell line was cultured in RPMI 1640 containing 5% serum. Cells at confluency were serum starved for 24 h prior to exposure to TNF-alpha (0.1-100 ng/ml) or IL-1 beta (0.1-100 ng/ml) or a combination of both for 48 h. Activity of MMP-9 was examined by gelatin zymography and TIMP-1 expression was analysed by Western blotting.

RESULTS

TNF-alpha but not IL-1 beta resulted in a dose-dependent increase in the latent form of MMP-9 and a decrease in TIMP-1 production. Co-treatment with IL-1 beta had no effect on the induction of MMP-9 but increased the inhibition of TIMP-1 in the presence of TNF-alpha. Inhibition of PKC provided evidence of the importance of this pathway in mediating the TNF-alpha-induced suppression of TIMP-1. Activation of the ERK 1/2 MAPK mediated both the upregulation of MMP-9 and the inhibition of TIMP-1 following TNF-alpha treatment. p38 MAPK activation was also found to be involved in the TNF-alpha-stimulated MMP-9.

CONCLUSION

The cytokine TNF-alpha causes different effects on human mesangial MMP-9 and TIMP-1 expression which are mediated through the TNF-RI, and the different signalling pathways of PKC, ERK 1/2 and p38 MAPK. This suggests an important role for pro-inflammatory cytokines in renal disease progression.

Pharmacological enhancement of the kallikrein-kinin system promotes anti-fibrotic responses in human mesangial cells

The aim of the present study was to investigate whether pharmacological enhancement of the renal kallikrein-kinin system using the vasopeptidase inhibitor omapatrilat plays a direct role in modulating the fibrotic responses of human mesangial cells to injury. Treatment with 40 micromol/L omapatrilat was able to reduce macrophage-conditioned medium (MPCM)-induced fibronectin levels without affecting mRNA expression. MPCM injury also suppressed kallikrein and low molecular weight kininogen mRNA. Omapatrilat was able to attenuate this suppression. Bradykinin levels in contrast were increased by MPCM and treatment with omapatrilat further augmented levels. Co-incubation with the bradykinin B2 receptor antagonist HOE 140 attenuated the omapatrilat-induced lowering of fibronectin. Moreover, inhibition of cGMP release had a similar effect. Paradoxically, RT-PCR and Southern blotting demonstrated that bradykinin B2 receptor mRNA levels were down regulated in response to omapatrilat. Western blotting supported this data. Supernatant levels of tissue plasminogen activator (tPA), a product of bradykinin stimulation, were decreased by omapatrilat while cell associated tPA levels were increased. Matrix metalloproteinase-9 (MMP-9) mRNA expression was up regulated by omapatrilat treatment, although no difference in active zymogen levels was observed. In conclusion enhancement of kallikrein-kinin system appears to play a direct role in promoting anti-fibrotic responses in MPCM-injured human mesangial cells.

The aetiology and pathogenesis of chronic allograft nephropathy

Renal transplantation is the ultimate form of renal replacement therapy, and is the treatment of choice for many patients with end-stage renal failure. The advent of calcineurin inhibitor based immunosuppression resulted in the 1-year renal allograft failure rate dropping from around 50% twenty years ago to less than 10% in more recent times. Despite a massive improvement in renal allograft survival in the first year following transplantation 10-year graft survival can be as low as 50%. Chronic allograft nephropathy (CAN) is recognised as the main cause of renal allograft failure following the first year after transplantation. The diagnosis of CAN can only be made histologically. Typically biopsy specimens in grafts with CAN demonstrate an overall fibrotic appearance effecting the vascular endothelium, renal tubules, interstitium, and glomerulus. The risk factors for CAN are divided into alloimmune and alloimmune independent. Alloimmune dependent factors include acute cellular rejection, severity of rejection, subclinical rejection and HLA mismatch. Alloimmune independent factors such as delayed graft function, donor age, Cytomegalovirus infection, donor/recipient co-morbidity and of course calcineurin inhibitor toxicity are important in the development of CAN. The pathogenesis of CAN is complex, multifactorial, and unfortunately incompletely understood. There are a number of pivotal steps in the initiation and propagation of the fibrosis seen in biopsy specimens from kidneys with CAN. Endothelial activation in response to one or more of the aforementioned risk factors stimulates leukocyte activation and recruitment. Recruited leukocytes subsequently infiltrate through the endothelium and induce key effector cells to secrete excessive and abnormal extracellular matrix (ECM). Enhanced deposition of ECM is a histological hallmark of CAN. This paper aims to present a concise yet accurate and up-to-date review of the literature concerning the aetiological factors and pathological processes which are present in the generation of CAN.

The pluripotent cytokine pleiotrophin is induced by wounding in human mesangial cells

Mesangial re-modeling and mesangial cell (MC) migration are features of several glomerular diseases including mesangiocapillary glomerulonephritis. In vitro investigations have recently identified ADAM-15, a multidomain adamalysin, as central to the migration of MC. The current study used array technology to investigate the expression of other genes in migrating cells and identified pleiotrophin (PTN), platelet-derived growth factor alpha polypeptide chain, colony stimulating factor, and four members of the tumor necrosis factor-alpha superfamily as major genes that were upregulated. Transcriptional induction of PTN was confirmed by reverse transcription-polymerase chain reaction and Northern blotting and induction of the protein by Western blotting and immunohistochemical localization. PTN was observed associated with mesangial 'hillocks' in confluent MC cultures. In contrast, in models of migration, migrating cells had the highest expression of cell-associated PTN. PTN protein was less evident, however, in the conditioned medium of MCs. Treatment of MC with heparanase removed PTN from the cells suggesting that its localization was owing to an association with heparan sulfates on the cell surface or in the extracellular matrix. This is the first description of the expression of PTN by human MCs and the data suggest that it is rapidly induced in cells that are triggered to migrate. The result of this induction is currently under investigation.

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

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.

The role of ADAM 15 in glomerular mesangial cell migration

Mesangial cells (MC) occupy the core of the renal glomerulus and are surrounded by a mesangial matrix. In certain diseases, MC migrate through this matrix into the pericapillary space. The mechanisms involved, however, are poorly understood. Members of the ADAM (A Disintegrin And Metalloproteinase) family of membrane proteins have the potential to be key modulators of cell-matrix interactions through the activities of their constituent domains. We have studied the possible role of ADAM 15 in human (H) MC migration in vitro. HMC ADAM 15 was expressed at low levels in serum-free medium but was increased during migration. Antibodies to the individual domains of ADAM 15 and the incorporation of antisense ADAM 15, (but not control oligonucleotide) inhibited this migration. Furthermore, inhibition of migration by the broad spectrum metalloproteinase inhibitor BB3103, demonstrated that metalloproteinase activity was essential for migration. ADAM 15, extracted from HMC membranes, was an active metalloproteinase, which degraded both type IV collagen and gelatin prepared from fibrillar collagen. Activity was inhibited by EDTA but not by phenylmethylsulfonyl fluoride. This is the first report of the potential of ADAM 15 for involvement in the restructuring of the mesangial matrix and in the migration of MC in disease.

Effects of mesangium glycation on matrix metalloproteinase activities: possible role in diabetic nephropathy

High glucose concentrations can decrease degradation of mesangium by reducing the activities of matrix metalloproteinases (MMPs). The aim of this study was to investigate the effects of glycation of mesangium matrix on MMP-2, the principal MMP secreted by mesangial cells to degrade type IV collagen. Also examined were membrane type 1 MMP (MT1-MMP), tissue inhibitors of MMPs (TIMP)-1 and -2, and transforming growth factor-beta (TGF-beta), which together regulate MMP-2 activities in an interacting manner. Human fetal mesangial cells were grown on mesangium matrix glycated by incubation in 500 mmol/l ribose, with or without aminoguanidine. The activities and gene expression of the abovementioned enzymes/inhibitors were measured by degradation of radiolabeled mesangium matrix, RT-PCR, and zymography. Glycation of mesangium matrix resulted in a threefold increase in advance glycation end products and reduced by 45% the matrix-degrading activity of MMPs secreted by mesangial cells. Analogous to the direct effects of high glucose concentrations, glycation of matrix increased the gene expression of MMP-2 and TIMP-1 (control 100 +/- 16.9 vs. glycated 197.3 +/- 30.6% and control 100 +/- 5.3 vs. glycated 152.1 +/- 20.1%, respectively; P < 0.05) and decreased MT1-MMP (control 100 +/- 1.17 vs. glycated 54.1 +/- 15.2%; P < 0.05). However, unlike high glucose concentrations, glycation was not associated with decreased activation of MMP-2. Similarly, glycation but not high glucose increased expression of TIMP-2 (control 100 +/- 5.9 vs. glycated 168.2 +/- 31.4%; P < 0.05), and the effects of glycation on degradation can be abolished by anti-TIMP-2 antibody. Glycation of matrix decreased TGF-beta mRNA by 38.2% and total and active TGF-beta by 35.5 and 21.5%, respectively, opposite the effects of high glucose concentrations. Our results indicate that glycation of matrix affects the balance between MMP-2 and its activator and inhibitors, but this phenomenon is not due to TGF-beta. The process of glycation may impart to the mesangium matrix a memory effect that contributes to the long-term toxicity of hyperglycemia.

Molecular mechanisms of renal allograft fibrosis

BACKGROUND

Chronic graft nephropathy (CGN) remains the leading cause of renal allograft loss after the first year following transplantation. Histologically it is characterized by glomerulosclerosis, intimal hyperplasia and interstitial fibrosis. The pathogenesis is unclear, but is likely to involve both immunological and non-immunological factors. Despite improvements in short-term graft survival rates, new immunosuppressive regimens have made no impact on CGN.

METHODS

A review of the current literature on renal transplantation, novel immunosuppression regimens and advances in the molecular pathogenesis of renal allograft fibrosis was performed.

RESULTS AND CONCLUSION

Recent advances in understanding of the underlying molecular mechanisms involved suggest autocrine secretion of cytokines and growth factors, especially transforming growth factor beta, are associated with a change in fibroblast phenotype leading to the deposition of extracellular matrix. Repeated insults trigger upregulation of the tissue inhibitors of matrix metalloproteinases, favouring accumulation of extracellular matrix. To date, no drug has proved effective in inhibiting or reducing allograft fibrosis. The deleterious consequences of chronic immunosuppression on the development of such fibrosis are now recognized; newer immunosuppressive drugs, including rapamycin and mycophenolate mofetil, reduce profibrotic gene expression in both experimental and clinical settings, and offer potential strategies for prolonging allograft survival.

Peripheral blood level alterations of TIMP-1, MMP-2 and MMP-9 in patients with type 1 diabetes

AIM

To determine the plasma levels of enzymes and inhibitors involved in extracellular matrix turnover in patients with Type 1 diabetes with normal renal function.

METHODS

Plasma levels of matrix metalloproteinases 2 and 9 (MMP-2, MMP-9) and tissue inhibitor of metalloproteinase 1 (TIMP-1) were measured in 43 Type 1 diabetic subjects and age- and sex-matched controls.

RESULTS

No significant difference in plasma MMP-2 between diabetic patients and controls was observed. MMP-9 was detected in the plasma of 15 diabetic patients (35%), but undetectable in all control subjects (P < 0.015). Plasma TIMP-1 concentrations were significantly elevated (P < 0.001) in diabetic patients compared to controls. There was no correlation observed between MMP-2, MMP-9 and TIMP-1 and similarly between MMP-2, MMP-9 and TIMP-1 and age, duration of diabetes, blood pressure and glycated haemoglobin (HbA1c).

CONCLUSIONS

This study has demonstrated alterations in several plasma extracellular matrix modulators in the absence of significant vascular disease.

Induction of metalloproteinases by glomerular mesangial cells stimulated by proteins of the extracellular matrix

Human glomerular mesangial cells (HMC) are embedded in the mesangial matrix (MM) and control its turnover through a dynamic equilibrium between synthesis and degradation. Degradation is controlled by matrix metalloproteinases (MMP), whose activity has been causally implicated in the progression of glomerular disease. In other systems, MMP secretion may be directly affected by exposure to specific matrix proteins. The present study, therefore, investigated the effect of different matrix components on the adherence of HMC and on their secretion and activation of the gelatinases MMP2 and MMP9. HMC adhered strongly (quantified using crystal violet staining) to collagen IV and collagen I (P < 0.01, relative to binding to control, bovine serum albumin (BSA)-coated wells) and to a lesser extent to gelatin IV and fibronectin (P < 0.05). Binding to vitronectin and laminin was not statistically different to control wells. After the addition of these matrix proteins (0.1 microg/ml to 100 microg/ml) to growth-arrested HMC for 72 h, zymography of the conditioned medium established that only fibronectin and collagens I and IV dose-dependently increased latent (72 kD) MMP2 secretion and activation. Fibronectin, however, also induced the secretion of MMP9. Membranes from HMC that had been co-cultured with fibronectin for 72 h were prepared to investigate whether the activation of MMP2 in this system was due to the action of membrane-type (MT)-MMP. When incubated with latent MMP2 for times up to 24 h, these membranes activated the enzyme in a time- and dose-dependent manner. The results demonstrate that specific matrix components increased the secretion of MMP2 and MMP9 from HMC. In addition, MT-MMP activity, selectively induced by fibronectin, was implicated in the activation of the secreted proteinases.

Amplification of IL-1 beta-induced matrix metalloproteinase-9 expression by superoxide in rat glomerular mesangial cells is mediated by increased activities of NF-kappa B and activating protein-1 and involves activation of the mitogen-activated protein kinase pathways

The modulation of cell signaling by free radicals is important for the pathogenesis of inflammatory diseases. Recently, we have shown that NO reduces IL-1beta-induced matrix metalloproteinase (MMP-9) expression in glomerular mesangial cells (MC). Here we report that exogenously administrated superoxide, generated by the hypoxanthine/xanthine oxidase system (HXXO) or by the redox cycler 2, 3-dimethoxy-1,4-naphtoquinone, caused a marked amplification of IL-1beta-primed, steady state, MMP-9 mRNA level and an increase in gelatinolytic activity in the conditioned medium. Superoxide generators alone were ineffective. Cytokine-induced steady state mRNA levels of TIMP-1, an endogenous inhibitor of MMP-9, were affected similarly by HXXO. Transient transfection of rat mesangial cells with 0.6 kb of the 5'-flanking region of the rat MMP-9 gene proved a transcriptional regulation of MMP-9 expression by superoxide. HXXO augmented the IL-1beta-triggered nuclear translocation of p65 and c-Jun and, in parallel, increased DNA binding activities of NF-kappaB and AP-1. Mutation of either response element completely prevented MMP-9 promoter activation by IL-1beta. Moreover, specific inhibitors of the classical extracellular signal-regulated kinase (ERK) pathway and p38 mitogen-activated protein kinase (MAPK) cascade, partially reversed the HXXO-mediated effects on MMP-9 mRNA levels, thus demonstrating involvement of ERKs and p38 MAPKs in MMP-9 expression. Furthermore, IL-1beta-triggered phosphorylation of all three MAPKs, including p38-MAPK, c-Jun N-terminal kinase, and ERK, was substantially enhanced by superoxide. Our data identify superoxide as a costimulatory factor amplifying cytokine-induced MMP-9 expression by interfering with the signaling cascades leading to the activation of AP-1 and NF-kappaB.

Platelet release of trimolecular complex components MT1-MMP/TIMP2/MMP2: involvement in MMP2 activation and platelet aggregation

Matrix metalloproteinase 2 (MMP2) has been reported to be secreted by collagen-stimulated platelets, and active MMP2 has been shown to play a role in platelet aggregation. It has been demonstrated that MMP2 activation is dependent on the complex (membrane type 1 [MT1]-MMP/tissue inhibitor of MMP2 [TIMP2]) receptor and MMP2. We have investigated human platelets as a possible source of MT1-MMP, and we have studied its role in MMP2 activation and in platelet aggregation. Gelatin zymograms showed the existence of MMP2 at proforms (68 kd) and activated-enzyme forms (62-59 kd) in supernatants of resting and activated platelets, respectively. No gelatinolytic activity was associated with the platelet pellet after aggregation, suggesting a total release of MMP2 during cell activation. By Western blot analysis in nonreduced conditions, MT1-MMP was found on resting platelet membranes in 2 forms–the inactive 45-kd form and an apparent 89-kd form, which totally disappeared under reduced conditions. After platelet degranulation, only the 45-kd form was detected. Reverse transcription–polymerase chain reaction experiments showed the expression in platelets of messenger RNA encoding for MMP2, MT1-MMP, and TIMP2. Flow cytometry analysis showed that MT1-MMP, MMP2, and TIMP2 expressions were enhanced at the activated platelet surface. MMP inhibitors, recombinant TIMP2, and synthetic BB94 inhibited collagen-induced platelet aggregation in a concentration-dependent manner, indicating the role of activated MT1-MMP in the modulation of platelet function. In conclusion, our results demonstrate the expression of the trimolecular complex components (MT1-MMP/TIMP2/MMP2) by blood platelets as well as the ability of MMP inhibitors to modulate the aggregating response.

Differential effects of cyclosporin and tacrolimus on the expression of fibrosis-associated genes in isolated glomeruli from renal transplants

BACKGROUND

Chronic allograft nephropathy is characterized by an excessive accumulation of extracellular matrix proteins leading to glomerular and interstitial fibrosis. The aim of this study was to determine the effects of two different immunosuppressive agents (cyclosporin and tacrolimus) on the expression of the genes controlling extracellular matrix deposition in renal transplant glomeruli.

METHODS

Fifty-one renal transplant recipients were randomized to receive immunosuppression with either microemulsion cyclosporin or tacrolimus. Isolated glomeruli were plucked from protocol transplant biopsies performed 1 week, 3 months and 6 months after transplantation. Expression of the genes for collagen IValpha2, collagen III, matrix metalloproteinase 2, tissue inhibitor of metalloproteinases (TIMP) 1 and TIMP-2, tenascin and transforming growth factor (TGF) beta1 was studied by quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

The expression of messenger RNA (mRNA) for collagen III and TIMP-1 was significantly higher in patients receiving cyclosporin therapy than in those having tacrolimus (P < 0.01); this finding was accounted for by differences in the biopsy material at 1 week. A significant difference in collagen III, TIMP-1 and TIMP-2 mRNA expression was also detected between patients depending on the source of renal donor (cadaveric or living). There were no significant differences in the level of glomerular TGF-beta1.

CONCLUSION

The data provide new in vivo evidence that tacrolimus may exert a less fibrogenic influence on transplant glomeruli than cyclosporin.

Platelet release of trimolecular complex components MT1-MMP/TIMP2/MMP2: involvement in MMP2 activation and platelet aggregation

Matrix metalloproteinase 2 (MMP2) has been reported to be secreted by collagen-stimulated platelets, and active MMP2 has been shown to play a role in platelet aggregation. It has been demonstrated that MMP2 activation is dependent on the complex (membrane type 1 [MT1]-MMP/tissue inhibitor of MMP2 [TIMP2]) receptor and MMP2. We have investigated human platelets as a possible source of MT1-MMP, and we have studied its role in MMP2 activation and in platelet aggregation. Gelatin zymograms showed the existence of MMP2 at proforms (68 kd) and activated-enzyme forms (62-59 kd) in supernatants of resting and activated platelets, respectively. No gelatinolytic activity was associated with the platelet pellet after aggregation, suggesting a total release of MMP2 during cell activation. By Western blot analysis in nonreduced conditions, MT1-MMP was found on resting platelet membranes in 2 forms–the inactive 45-kd form and an apparent 89-kd form, which totally disappeared under reduced conditions. After platelet degranulation, only the 45-kd form was detected. Reverse transcription–polymerase chain reaction experiments showed the expression in platelets of messenger RNA encoding for MMP2, MT1-MMP, and TIMP2. Flow cytometry analysis showed that MT1-MMP, MMP2, and TIMP2 expressions were enhanced at the activated platelet surface. MMP inhibitors, recombinant TIMP2, and synthetic BB94 inhibited collagen-induced platelet aggregation in a concentration-dependent manner, indicating the role of activated MT1-MMP in the modulation of platelet function. In conclusion, our results demonstrate the expression of the trimolecular complex components (MT1-MMP/TIMP2/MMP2) by blood platelets as well as the ability of MMP inhibitors to modulate the aggregating response.

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.

Inactive matrix metalloproteinase 2 is a normal constituent of human glomerular basement membrane. An immuno-electron microscopic study

Remodelling of the extracellular matrix requires tight control not only of matrix synthesis, but also of matrix degradation. Control of matrix degradation is achieved mainly through the matrix metalloproteinase (MMP) enzymes. In the glomerulus, MMP-2 and MMP-9 are believed to be particularly important, as they have activity against type IV collagen. This study has demonstrated by immuno-electron microscopy that most of the immunoreactivity for MMP-2 in the normal glomerulus is located within the glomerular basement membranes and mesangial matrix. mRNA for MMP-2 is also detectable in normal glomeruli, but the other main gelatinase, MMP-9, could not be localized by immuno-electron microscopy. In the normal glomerulus, it seemed likely that MMP-2 is present in an inactive form. To confirm this, in situ zymography was carried out using frozen sections of normal kidney. Baseline activity of normal kidney was relatively weak, but this was dramatically increased by chemical activation of metalloproteinases. The results imply that MMP-2, in an inactive form, is a normal constituent of the extracellular matrix and glomerular basement membranes. Activation would presumably render the matrix 'self-degrading'; membrane-bound MMPs (MT-MMPs) seem particularly likely to be involved in leukocyte penetration of basement membranes in inflammation.

YB-1 regulation of the human and rat gelatinase A genes via similar enhancer elements

Experimental and clinical studies strongly suggest that gelatinase A plays a central role in the evolution of glomerular injury and sclerosis. The sequences of the 5' flanking regions of the human and rat gelatinase A genes do not share similarities with other members of the matrix metalloproteinase gene family and are regulated in a distinctive manner. The human and rat gelatinase A genes include regions of significant homology (r2 human; RE-1 rat), which have been shown to act as potent cis-activators of transcription. The rat RE-1 sequence interacts specifically with the developmentally regulated transcription factors AP2 and YB-1, resulting in a synergistic activation of gelatinase A transcription. Although the human r2 sequence specifically interacts with AP2 (Mol Cell Biol 10: 6524-6532, 1990), there is no clear evidence for the presence of a canonical YB-1 binding site (Y-box) within this sequence. This study demonstrates, despite the absence of a canonical Y-box sequence in the r2 element, that YB-1 and AP2 specifically interact with r2, yielding synergistic transactivation of the human gelatinase A gene. It is concluded that the r2 element is the conserved functional analog of the RE-1 element, and that interactions of AP2 and YB-1 govern human gelatinase A gene expression.

Thrombin stimulates synthesis of type IV collagen and tissue inhibitor of metalloproteinases-1 by cultured human mesangial cells

Glomerular accumulation of extracellular matrix (ECM) is the common pathologic feature following glomerular injury, and the alteration in the synthesis and degradation of ECM may be involved in the glomerular accumulation of ECM. Glomerular fibrin formation occurs in various forms of human and experimental glomerulonephritis, and it may play an important role in progressive glomerular injury. Thrombin, a multifunctional serine proteinase that is generated at the site of vascular injury, has central functions in hemostasis and it also shows various biologic effects. In this study, it is hypothesized that thrombin may alter the production and the degradation of type IV collagen, which is an important component of ECM in the glomeruli. Human mesangial cells (HMC) were cultured, and the levels of type IV collagen, tissue inhibitor of metalloproteinase-1 (TIMP-1), and matrix metalloproteinase-2 (MMP-2) in the culture supernatants were measured by enzyme immunoassay using specific antibodies. MMP-2 activity was also evaluated by zymography using polyacrylamide/ sodium dodecyl sulfate gel-containing gelatin. Thrombin increased the production of type IV collagen and TIMP-1 in a dose-and time-dependent manner, but it did not increase MMP-2. Thrombin also stimulated the gene expressions of the type IV collagen and TIMP-1 in HMC in a dose- and time-dependent manner. Thrombin treated with diisopropylfluorophosphate, a serine proteinase inhibitor, did not show any of these effects. Hirudin, a natural thrombin inhibitor, and anti-transforming growth factor-beta-neutralizing antibody inhibited the stimulating effect of thrombin. These findings suggest that thrombin may contribute to the excessive accumulation of ECM and progression of glomerulosclerosis through an increase of type IV collagen production and a decreased matrix degradation presumably via a transforming growth factor-beta-dependent mechanism.

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.

Pentosan polysulfate decreases proliferation and net extracellular matrix production in mouse mesangial cells

Glomerulosclerosis is characterized by extracellular matrix accumulation and is often associated with mesangial cell proliferation. Heparin-like molecules have been shown to decrease glomerulosclerosis in vivo, although their cellular site and mechanism of action is still unclear. In this study, a line of glomerular mesangial cells derived from normal mice was used to determine whether pentosan polysulfate (PPS) inhibited proliferation and altered extracellular matrix turnover. Cells treated with PPS showed a decrease in cell number beginning 24 h after treatment, which was maintained for 5 d. For matrix accumulation and degradation studies, cells were treated for 5 d and collagen types I and IV protein were measured by enzyme-linked immunosorbent assay as well as matrix metalloproteinases (MMP) measured by zymography. Collagen types 1 and type IV were significantly decreased in the media (P < 0.0001) and cell layer (P < 0.005) after treatment with PPS but not after treatment with heparin. By zymography, MMP-2 was significantly increased after treatment with PPS (P < 0.001) and heparin (P < 0.05). PPS and heparin also decreased MMP-9 (P < 0.001) after treatment. Reverse zymography showed the presence of tissue inhibitors of metalloproteinases (TIMP)-1 and -2 in control mesangial cells. Treatment with PPS and heparin increased TIMP-1. In addition, TIMP-3 was found in the medium of treated but not control cells. In conclusion, PPS alters extracellular matrix turnover through the induction of MMP-2 and alterations in the TIMP profile and may be useful in decreasing progressive glomerulosclerosis.

Soluble latent membrane-type 1 matrix metalloprotease secreted by human mesangial cells is activated by urokinase

BACKGROUND

Matrix metalloprotease 2 (MMP2) is secreted in a latent inactive form (pro-MMP2) that is activated on the cell surface by a membrane-type 1 MMP (MT1-MMP) in the presence of the tissue inhibitor of MMP (TIMP2). In spite of evidence for the synthesis of MT1-MMP shown by immunoblotting, immunocytochemistry and RT-PCR, and of TIMP2, MMP2 was found exclusively in a latent form in human mesangial cells (HMC) serum-free culture medium.

METHODS AND RESULTS

On purified membranes of HMC, MT1-MMP was found in a 63 kD latent form and as a faint band of 55 kD. The 55 kD band was also present in the ultracentrifuged conditioned medium and likely represented MT1-MMP cleaved from its transmembrane domain, since Northern blot analysis showed only one transcription product. The addition of urokinase plasminogen activator (uPA, 100 nM) to HMC membranes induced the activation of pro-MMP2 via the activation of latent membrane-associated MT1-MMP as reflected by the cleavage of the 63 and 55 kD forms. In addition, when the conditioned medium was successively incubated with uPA and alpha 2-macroglobulin and analyzed by immunoblotting, MT1-MMP decreased, indicating that the soluble MT1-MMP was in a latent form and was activated by uPA.

CONCLUSION

Our results provide the first evidence, to our knowledge, of the existence of a soluble latent form of MT1-MMP secreted by primary human cells in culture, confirming that MT1-MMP is an ectoenzyme, and show that uPA can regulate MT1-MMP activity in a soluble phase.

Oxidation of the mesangial matrix metalloproteinase-2 impairs gelatinolytic activity

Glomerulosclerosis is characterized by an accumulation of mesangial extracellular matrix. Oxygen radicals are strongly implicated in glomerular injury but it is unclear by what mechanism they could modulate matrix turnover dynamics. We evaluated whether oxidation of the 72 kD mesangial matrix metalloproteinase-2 (MMP-2), the major mesangial matrix-degrading enzyme, could alter its gelatinolytic activity. Oxidation of the MMP-2 using a FeCl3/ascorbate system resulted in impaired ability to degrade [3H]gelatin compared to control. Samples were also subjected to SDS-PAGE gelatin substrate zymography. At the 72 kD position a significant impairment of gelatinolytic activity of oxidized samples was observed, a decrease attenuated by coincubation of samples with the FeCl3/ascorbate system plus the radical spin trap N-tert-butyl-alpha-phenylnitrone suggesting specificity of oxidative changes in the decrease in enzymatic activity. These data represent the first report demonstrating that oxidation of the MMP-2 diminishes its activity and suggest a previously undescribed mechanism by which oxygen radicals may contribute to altered turnover of extracellular matrix.

Exposure of human renal proximal tubular cells to glucose leads to accumulation of type IV collagen and fibronectin by decreased degradation

Thickening and reduplication of the tubular basement membrane has been reported as an early event in diabetic nephropathy. In the current study we examined the effects of elevated D-glucose concentrations on human proximal tubular (HPTC) type IV collagen and fibronectin turnover. Incubation of confluent growth arrested HPTC with 25 mM D-glucose led to accumulation of both type IV collagen and fibronectin. This effect was maximal at 48 hours and represented a sevenfold increase for fibronectin (N = 4, P = 0.04), and a threefold increase for type IV collagen (N = 3, P = 0.03) over cells exposed to 5 mM D-glucose controls. This increase was not dependent on new gene transcription for either protein. Tissue inhibitor of metalloproteinases (TIMP 1 + TIMP 2) were induced following addition of 25 mM D-glucose, but not when cells were exposed to 5 mM D-glucose. Twenty-four hours after the addition of 25 mM D-glucose there was an eightfold increase in TIMP 1 (P = 0.009, N = 4), and a tenfold increase in TIMP 2 levels (P = 0.003, N = 4), over the control values for both inhibitors. The increase in both TIMP 1 and TIMP 2 in response to 25 mM D-glucose was abrogated in a dose dependent manner by the aldose reductase inhibitor sorbinil. Gelatin-substrate gel zymography showed increased activity of gelatinase A, but not of gelatinase B in response to the addition of 25 mM D-glucose to HPTC. The induction of gelatinase A was accompanied by increased gelatinase A mRNA expression, which was inhibited both by protein kinase C (PKC) depletion using PMA pre-treatment, and by the addition of a PKC inhibitor. These data demonstrate that the glucose-induced accumulation of type IV collagen and fibronectin is unrelated to increased gene transcription, but may involve alterations in the degradative pathway of these basement membrane constituents. Furthermore, the data demonstrate that glucose may simultaneously activate two intracellular pathways (the polyol pathway and a PKC dependent activation pathway), which are involved in mediating separate, complementary effects on cell function.

Identification of promoter activity and differential expression of transcripts encoding the murine stromelysin-1 gene in renal cells

Stromelysin-1, matrix metalloproteinase-3 (MMP-3), is an important endopeptidase selectively expressed by somatic cells in organ tissues. The renal tubulointerstitium, for example, comprises tubular epithelium and interstitial fibroblasts forming the principal mass of the kidney. We observed that mRNA encoding stromelysin-1 is detectable in murine renal fibroblasts, but not in proximal tubular epithelium. Transcripts measured by RNase protection assay in renal fibroblasts increase following exposure to phorbol ester, and thereafter, activated stromelysin-1 protein can be detected in culture media by Western blotting. A 6.4 Kb genomic clone containing the putative stromelysin-1 promoter was isolated and a relevant 2.1 Kb PstI restriction fragment including 2.1 Kb of the immediate 5'-flanking region was sequenced on both strands. Two transcriptional start sites were identified by primer extension; the major start site corresponded to a previously established position in the rat promoter, and a second undescribed minor transcriptional start site was located 16 bp upstream of the primary site. A HiNF-A chromatin-activating element at -106 bp was found in the early promoter region of pR336 and an active AP-1 site at -72 bp with an Ets/PEA-3 motif at -203 bp was suggested by transient transfection of luciferase minigenes into renal fibroblasts responsive to phorbol ester. This Ets element was identical to a site in the early promoter of the fibroblast-specific gene FSP1. A baseline enhancement in activity of pR336 in fibroblasts was further observed with the addition of 5' flanking sequence out to -1980 bp. This additional region of flanking sequence contains two modular regions: one of multiple PEA-3 elements between -684 bp and -1955 bp and a second region between -1929 bp and -1980 bps containing a second AP-1 site at -1929 bp, a MBF-1/ MEP-1 metal binding site, and a PPAR peroxisome proliferator element at -1950 bp. Our findings implicate a gene structure with expected activity in a mesenchymal phenotype. The PKC-dependent regulation of the stromelysin-1 gene supports the notion that it may be modulated during inflammation or tissue remodeling.

Role of glomerular mechanical strain in the pathogenesis of diabetic nephropathy

Glomerular rigidity limits the glomerular expansion and mesangial cell (MC) stretch induced by variations in intracapillary pressure. In tissue culture, MC stretch stimulates synthesis of extracellular matrix components (ECM). Therefore, altered glomerular rigidity in diabetes may influence ECM accumulation by modulating the glomerular distention and MC stretch associated with glomerular hypertension. An ambient of high glucose concentration per se also enhances MC formation of ECM, possibly altering the cellular response to mechanical stretch. In this study, compliance was measured in isolated perfused glomeruli from streptozotocin-injected rats at four days (4d-D), five weeks (5w-D) and six months (6m-D) after induction of diabetes. In addition, collagen metabolism induced by stretch was investigated in MC cultured in 8 and 35 mM glucose concentrations. Glomerular compliance was normal in 5w-D rats and moderately increased in 4d-D (16%) and 6m-D animals (14%). As compared to static cultures. MC stretch increased total collagen synthesis (8 mM, 50%; 35 mM, 27%) and catabolism. However, while the fraction of newly formed collagen being catabolized increased in 8 mM-stretched cultures, in 35 mM-stretched it was unchanged. This resulted in marked increase in the net collagen accumulated in the incubation medium (4 vs. 24%) and cell layer 5 vs. 15%) only in the latter. In diabetes, the largely unaltered glomerular stiffness renders hypertension-induced MC stretch unopposed. More importantly, the accumulation of ECM caused by any degree of mechanical strain is greatly aggravated in a milieu of high glucose concentration.

Regulation of extracellular matrix by mechanical stress in rat glomerular mesangial cells

Increases in intraglomerular pressure are known to predispose to the development of glomerular sclerosis, which is characterized by accumulation of extracellular matrix within the glomerulus. Glomerular mesangial cells are exposed to pulsatile capillary pressures and are a potential target for mechanical stress. In the present studies, we subjected cultured rat mesangial cells to continuous cycles of stretching and relaxation (stretch/relaxation) and examined alterations in extracellular matrix gene expression. After 48 h of stretch/relaxation, immunofluorescent localization of matrix accumulation indicated increases in types I, III, and IV collagens, fibronectin, and laminin, with the greatest increases seen at the periphery of the culture dish, at the point of the greatest deformation. Northern blot analysis of total RNA revealed time-dependent induction of alpha1(I) collagen, alpha1(III) collagen, alpha1(IV) collagen, fibronectin, and laminin by stretch/relaxation, with maximal increases occurring between 12 and 24 h. Transient transfection of reporter gene constructs of the 5' flanking region of alpha1(I) collagen gene indicated that stimulation of gene transcription was involved in the increased expression of matrix mRNA. Gelatinolytic activity in conditioned media was decreased at 24 and 48 h of stretch/relaxation, in association with a significant decrease in levels of mRNA for matrix metalloproteinase-2 (68-72 kD type IV collagenase) occurring within 6 h of stretch/relaxation. In contrast, expression of tissue inhibitor of metalloproteinase-2 was increased within 12 h of stretch/relaxation. Stretch/relaxation increased immunoreactive TGF-beta at 48 but not 12 h. TGF-beta1 mRNA levels remained unchanged during the initial 12 h of stretch/relaxation, but were significantly elevated at 48 h, and no differences in TGF-beta bioactivity could be detected in conditioned media for up to 12 h of stretch/relaxation. These findings demonstrate that in glomerular mesangial cells, repeated cycles of stretching and relaxation lead to matrix accumulation by stimulating production of extracellular matrix and decreasing activity of degradative enzymes. The observed induction of TGF-beta1 suggests a role in matrix accumulation occurring in response to continued mechanical deformation.

Effect of matrix glycation on expression of type IV collagen, MMP-2, MMP-9 and TIMP-1 by human mesangial cells

Human mesangial cells grown in either 5 or 25 mM glucose were cultured on type IV collagen which had been previously control-incubated or in vitro glycated. Northern blot analysis revealed that after 3-7 days in culture mesangial cells on glycated type IV collagen expressed approximately 25-200% more alpha 1 (IV), approximately 20-50% less matrix metalloproteinase 2 (MMP-2), and 65-75% more tissue inhibitor of metalloproteinase 1 (TIMP-1). Decreased immunoreactivity (approximately 30-40%) and collagenolytic activity (approximately 10-40%) corresponding to MMP-2 was also detected in media conditioned during the third day of culture on glycated type IV collagen. These effects on cell function were related to the extent of type IV collagen modification and were similar for cells cultured in 5 or 25mM glucose. Elevated glucose (25 vrs 5 mM) increased expression of alpha 1 (IV) mRNA (approximately 40-70%) and in conjunction with matrix glycation resulted in detectable levels of MMP-9 message by northern blot although collagenolytic activity corresponding to MMP-9 was not detectable by zymography. We conclude that glucose and matrix glycation may each alter mesangial cell function, perhaps leading to an imbalance in mesangial matrix synthesis and degradation which could contribute to mesangial expansion characteristic of diabetic renal disease.

Matrix metalloproteinase 2 (gelatinase A) regulates glomerular mesangial cell proliferation and differentiation

A biologic role for the 72-kDa gelatinase A (matrix metalloproteinase 2; MMP-2), beyond simple extracellular matrix turnover, was evaluated in glomerular mesangial cells. To determine the significance of MMP-2 secretion for the acquisition of the inflammatory phenotype, we reduced the constitutive secretion of MMP-2 by cultured mesangial cells with antisense RNA expressed by an episomally replicating vector or with specific anti-MMP-2 ribozymes expressed by a retroviral transducing vector. The phenotype of the transfected, or retrovirally infected, cells was profoundly altered from the activated state and closely approximated that of quiescent cells in vivo. The prominent differences included a change in the synthesis and organization of the extracellular matrix, loss of activation markers, and a virtually total exit from the cell cycle. Reconstitution with exogenous active, but not latent MMP-2, induced a rapid return to the inflammatory phenotype in vitro. This effect was specific to MMP-2, because the closely related MMP-9 did not reproduce these changes. Furthermore, this pro-inflammatory effect of MMP-2 is dependent upon the active form of the enzyme, which can be produced by an autocatalytic activation process on the mesangial cell plasma membrane. It is concluded that MMP-2 acts directly upon mesangial cells to permit the development of an inflammatory phenotype. Specific inhibition of MMP-2 activity in vivo may represent an alternate means of ameliorating complex inflammatory processes by affecting the phenotype of the synthesizing cells, per se.

Pexicrine effects of basement membrane components on paracrine signaling by renal tubular cells

Paracrine interactions between tubular epithelium and interstitial cells have been assumed to be mediated largely by soluble cytokines. While the role of extracellular matrix (ECM) and matrix metalloproteinases (MMPs) in modifying cell function is widely appreciated, the role of the renal tubular basement membrane in modulation of tubulointerstitial function has not been studied. To establish whether those components of the ECM which support tubular epithelial cells also influence cell function (that is, a pexicrine effect), we studied their effects on paracrine signaling between epithelium and fibroblasts. Primary cultures of rat renal proximal tubular epithelial cells (PTE) were cultured on laminin (LN), collagen types-IV and -I (COL-IV, COL-I) and fibronectin (FN). PTE attained confluence more rapidly when grown on LN = COL-IV > COL-I = FN = plastic. On all substrates PTE produced the MMPS, gelatinase-A and -B and collagenase with an apparent increase in gelatinase-A and -B production when cultured on LN. MMPs were found to be secreted both apically and basally with basal secretion predominating, except on LN where secretion was primarily from the apical surface. Cultures of rat renal cortical interstitial fibroblasts were established and characterized. Cortical fibroblasts (CF) were found to secrete gelatinase-A and collagenase. Conditioned medium (CM) from PTE cultured on COL-IV stimulated proliferation of CF but proliferation was unaltered by CM from PTE grown on other substrates. By contrast, co-culture of PTE on LN with CF suppressed collagenase and gelatinase activity in both cell types, indicating a bi-directional, paracrine modulation of MMP production. Thus in the tubulointerstitium, the BM components LN and COL-IV not only fulfill a structural role but act as signaling molecules with differential effects which modify the function of the tubular epithelium and its paracrine interaction with adjacent fibroblasts. The initiation of interstitial fibrosis induced by injury to the tubular basement membrane may reside in the perturbation of this interaction.

Tubular gelatinase A (MMP-2) and its tissue inhibitors in polycystic kidney disease in the Han:SPRD rat

Thickening of the tubular basement membrane is one of the hallmarks of the polycystic kidney disease (PKD). The present study was conducted to investigate the potential role of the matrix metalloproteinase-2 (MMP-2) and its specific tissue inhibitors (TIMP-1 and TIMP-2) in the accumulation of matrix components in PKD. As a model of PKD, two-month-old heterozygous Han:SPRD rats, which are at an early stage of cystogenesis, were used. MMP-2, but not MMP-9 (gelatinase B) nor MMP-3 (stromelysin) could be detected in proximal tubules of the normal rat kidney. The presence of the inhibitors TIMP-1 and TIMP-2 was confirmed on the mRNA level. In tubules from PKD rats MMP-2 activity was lower (31 +/- 8 vs. 58 +/- 7 U/prep., N = 9, P < 0.05), mRNA of MMP-2 was reduced 4.2 +/- 0.6-fold (N = 4, P < 0.05) and enzyme protein was depressed 3.8 +/- 0.8-fold (N = 4, P < 0.05). By contrast, TIMP-1 mRNA was 9.0 +/- 1.1-fold and TIMP-2 mRNA 3.8 +/- 0.7-fold (N = 4, P < 0.05) elevated over controls. Cyst fluid from homozygous rats contained MMP-2 protein and activity. These findings indicate that tubular MMP-2 activity is reduced in PKD, due to down-regulation of MMP-2, up-regulation of TIMP-1 and TIMP-2, and luminal secretion of the enzyme. It is conceivable that these alterations relate to the enhanced matrix accumulation observed in the evolution of PKD.