Gelatinase A is a glomerular mesangial cell growth and differentiation factor

Renal dysfunction and intragraft proMMP9 activity in renal transplant recipients with interstitial fibrosis and tubular atrophy

Chronic renal allograft injury is reflected by interstitial fibrosis and tubular atrophy (IF/TA) and by the accumulation of extracellular matrix (ECM). Metalloproteinases (MMPs) are renal physiologic regulators of ECM degradation. Changes in MMPs expression or activity may disturb ECM turnover leading to glomerular scarring and worsening renal function. Our goal was to investigate intragraft MMP2 and MMP9 activities and their correlation with renal dysfunction. Plasma MMP2 and MMP9 activities were analyzed as noninvasive markers of renal allograft deterioration. Transplanted patients were biopsied and histopathologically characterized as IF/TA+ or IF/TA-. Renal function was evaluated by serum creatinine, glomerular filtration rate (GFR) estimated by Modification of Diet in Renal Disease equation and urinary protein/creatinine ratio. Kidney and plasma MMP2 and MMP9 activities were analyzed by zymography. A significant renal dysfunction was observed in IF/TA+ patients. Intragraft proMMP9 showed a significant higher activity in IF/TA+ than in IF/TA- samples and was inversely correlated with the GFR. Intragraft proMMP2 activity tended to increase in IF/TA+ samples, although no statistic significance was reached. Circulating proMMP2 and proMMP9 activities did not show significant differences between groups. Our data provide evidence that correlates intragraft proMMP9 activity with the fibrotic changes and renal dysfunction observed in IF/TA.

Soluble biglycan as a biomarker of inflammatory renal diseases

Chronic renal inflammation is often associated with a progressive accumulation of various extracellular matrix constituents, including several members of the small leucine-rich proteoglycan (SLRP) gene family. It is becoming increasingly evident that the matrix-unbound SLRPs strongly regulate the progression of inflammation and fibrosis. Soluble SLRPs are generated either via partial proteolytic processing of collagenous matrices or by de novo synthesis evoked by stress or injury. Liberated SLRPs can then bind to and activate Toll-like receptors, thus modulating downstream inflammatory signaling. Preclinical animal models and human studies have recently identified soluble biglycan as a key initiator and regulator of various inflammatory renal diseases. Biglycan, generated by activated macrophages, can enter the circulation and its elevated levels in plasma and renal parenchyma correlate with unfavorable renal function and outcome. In this review, we will focus on the critical role of soluble biglycan in inflammatory signaling in various renal disorders. Moreover, we will provide new data implicating proinflammatory effects of soluble decorin in unilateral ureteral obstruction. Finally, we will critically evaluate the potential application of soluble biglycan vis-à-vis other SLRPs (decorin, lumican and fibromodulin) as a promising target and novel biomarker of inflammatory renal diseases.

Deficient degradation of homotrimeric type I collagen, α1(I)3 glomerulopathy in oim mice

Col1a2-deficient (oim) mice synthesize homotrimeric type I collagen due to nonfunctional proα2(I) collagen chains. Our previous studies revealed a postnatal, progressive type I collagen glomerulopathy in this mouse model, but the mechanism of the sclerotic collagen accumulation within the renal mesangium remains unclear. The recent demonstration of the resistance of homotrimeric type I collagen to cleavage by matrix metalloproteinases (MMPs), led us to investigate the role of MMP-resistance in the glomerulosclerosis of Col1a2-deficient mice. We measured the pre- and post-translational expression of type I collagen and MMPs in glomeruli from heterozygous and homozygous animals. Both the heterotrimeric and homotrimeric isotypes of type I collagen were equally present in whole kidneys of heterozygous mice by immunohistochemistry and biochemical analysis, but the sclerotic glomerular collagen was at least 95-98% homotrimeric, suggesting homotrimeric type I collagen is the pathogenic isotype of type I collagen in glomerular disease. Although steady-state MMP and Col1a1 mRNA levels increased with the disease progression, we found these changes to be a secondary response to the deficient clearance of MMP-resistant homotrimers. Increased renal MMP expression was not sufficient to prevent homotrimeric type I collagen accumulation.

Doxycycline: a pilot study to reduce diabetic proteinuria

BACKGROUND

Activity of matrix metalloproteinases (MMPs), the enzymes primarily responsible for the deposition of extracellular matrix proteins, contributes to the pathogenesis of diabetic proteinuria. We evaluated the effect of doxycycline, a potent nonselective MMPs inhibitor, on reduction of proteinuria in diabetic patients.

MATERIAL AND METHODS

In a self-control clinical trial, 35 patients with overt diabetic nephropathy (proteinuria >300 mg/24 h) received oral doxycycline 100 mg/day for 2 months. Twenty-four-hour urine volume, Cr and protein excretion were measured at baseline, after 1 and 2 months of treatment, and after 4 months of its discontinuation. Treatment-related side effects were closely monitored and documented.

RESULTS

Mean (+/-SD) 24-hour urine protein was 888 +/- 419 mg at baseline, 884 +/- 368 mg after 1 month, and 643 +/- 386 mg after the 2 months of doxycycline treatment. There was statistically significant reduction in proteinuria at 2 months of treatment vs. at the baseline (p < 0.001). Mean 24-hour urine protein excretion increased to 1,021 +/- 422 mg 4 months after doxycycline was discontinued. The changes in serum sodium, potassium, BUN and Cr concentrations, and blood pressure measurements during the 2 months of treatment and follow-up period were not statistically significant.

CONCLUSION

Proteinuria in patients with diabetic nephropathy can be reduced with low dose doxycycline therapy over a 2-month period of drug administration. Further studies are necessary to determine the long-term effect, the optimal dose, and the optimal duration of this potentially novel therapy.

Relationships between circulating matrix metalloproteinase-2 and -9 and renal function in patients with chronic kidney disease

BACKGROUND

It has been proven that extracellular matrix turnover is involved in the pathogenesis of various renal fibrosis diseases. Matrix metalloproteinase-2 and -9 (MMP-2 and -9) are the extracellular matrix degrading enzymes that are believed to play important roles in renal diseases. However, the relationship of circulating levels of MMP-2, -9 and serum creatinine in the patients of chronic kidney disease (CKD) has not yet been investigated.

METHODS

Gelatin zymography and ELISA were employed to measure MMP-2 and MMP-9 activities in the plasma samples of 60 CKD patients and 40 control subjects.

RESULTS

Serum creatinine concentrations and MMP-2 activities were significantly higher (p<0.001) while MMP-9 activity and creatinine clearance (CCr) were significantly lower (p<0.05 and p<0.001, respectively) in CKD patients, as compared with those of control subjects. In addition, serum creatinine concentrations correlated with MMP-2 activity (R=0.288, p<0.05) and inversely correlated with that of MMP-9 (R=0.344, p<0.01).

CONCLUSIONS

This study demonstrated a correlation between MMP-2, -9 and serum creatinine in CKD patients to suggest that MMP-2 and MMP-9 might contribute in the pathogenesis of CKD.

Fibrillin-1 regulates mesangial cell attachment, spreading, migration and proliferation

The microfibrillar protein fibrillin-1 is present in many organs, including the vasculature, eye, and dermis, and is thought to convey structural anchorage and elastic strength. Fibrillin-1 is also a component of the mesangial matrix. To assess the functional relevance of fibrillin-1 for cell-matrix interactions in the glomerulus, we studied the attachment, spreading, migration and proliferation of mesangial cells on fibrillin-1 and the regulation of fibrillin-1 in experimental anti-Thy1.1 nephritis displaying mesangial cell migration and proliferation in vivo. During the acute phase of experimental Thy1.1 nephritis, glomerular fibrillin-1 messenger ribonucleic acid expression and protein immunoreactivity were significantly induced as compared to controls. In a hexosaminidase-based adhesion assay, mesangial cells showed concentration-dependent attachment to fibrillin-1, similar to what was observed for fibronectin. The cell attachment was Arg-Gly-Asp dependent. Further, fibrillin-1 significantly promoted spreading and focal contact formation detected by immunostaining for vinculin. Mesangial cell migration, assessed by a transmigration assay, and proliferation, measured by a 5-bromo-2'-deoxy-uridine incorporation assay, were augmented by fibrillin-1. In diabetic mice underexpressing fibrillin-1, glomerular cell proliferation, determined by counting proliferating cell nuclear antigen-positive cells in renal sections, was significantly lower than in diabetic control mice. We conclude that fibrillin-1 promotes mesangial cell attachment, spreading, migration, and proliferation. We speculate that fibrillin-1 may thus contribute to mesangial hypercellularity during glomerular disease.

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.

Mesangial cell expression of proto-oncogene Ets-1 during progression of mesangioproliferative glomerulonephritis

BACKGROUND

Ets-1 is a transactivator of matrix-associated genes and key factor in neoangiogenesis. The expression of Ets-1 mRNA and protein was analyzed in healthy rat kidney and in a model for mesangioproliferative disease without and with inhibition of platelet-derived growth factor-B (PDGF-B) activity.

METHODS

Immunohistochemistry was performed using a specific noncrossreacting anti-Ets-1 antibody and included a counterstain with alpha-smooth muscle actin (alpha-SMA). Nuclear proteins from isolated glomeruli were analyzed by Western blotting. Changes in Ets-1 mRNA levels were detected by in situ hybridization and Northern blotting. PDGF-B antagonism was performed in nephritic rats by specific aptamers.

RESULTS

The distribution of Ets-1-positive cells in healthy rats was heterogenous with exclusively nuclear staining of glomerular, tubular, and vascular cells. Profound changes were detected in the anti-Thy 1.1 glomerulonephritis. Nuclear Ets-1 staining was intense in mesangial cells, whereas podocyte and endothelial cell staining was unchanged. The strongest signal was seen on days 2 to 7. By Western blotting of glomerular proteins a single 52 kD band was detected in healthy rats, which was increased 4.5-fold after disease induction. At the same time a 54 kD band appeared that most likely represents phosphorylated Ets-1. Ets-1 transcripts were detected in mesangial cells that include exon IV but lack exon VII. A concordant 6.4-fold up-regulation of mRNA was detected in glomeruli. Specific PDGF-B antagonism by aptamer treatment from days 3 to 7 after disease induction led to reduced Ets-1 expression on day 7, correlating with decreased mesangial cell numbers.

CONCLUSION

A temporal increase of mesangial cell Ets-1 expression correlates with mesangial cell activation in mesangioproliferative glomerulonephritis. PDGF-B may partially contribute to the increased expression.

Mechanism of matrix accumulation and glomerulosclerosis in spontaneously hypertensive rats

BACKGROUND

Renal interstitial fibrosis and thickening of the glomerular basement membrane are associated with hypertension. However, the mechanism of matrix accumulation is unclear. Spontaneously hypertensive rats (SHR) develop hypertension at between 2 and 6 weeks of age.

METHODS

To test the hypothesis that increased matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP) contribute to the pathomechanisms of hypertensive nephropathy, the cortex and medulla of male SHR at 2 and 6 weeks were analyzed for MMP-2, MMP-7, and MMP-9 by gelatin and elastin gel zymography. The levels of TIMP-4 were measured by western blot analysis. The bands in blots were scanned and normalized with actin. To localize MMP-2 and TIMP-4 in situ, immuno-labeling was performed. To determine proteinuresis, urinary protein was measured by Bio-Rad dye binding assay. The mean arterial pressure (mmHg) was measured in Inactin-anesthetized rats by a PE-50 catheter in the femoral artery. Age-sex matched normotensive Wistar rats (NWR) were used as controls and grouped: (1). SHR, 2 weeks; (2). SHR, 6 weeks; (3). NWR, 2 weeks; and (4). NWR, 6 weeks (n = 6 in each group).

RESULTS

Levels of cortex MMP-2 and MMP-9 were increased in 6 week SHR as compared with NWR. In the medulla, MMP-9 and MMP-7 were increased, but there was no change in MMP-2. The levels of cortex TIMP-4 tended to increase but insignificantly. In contrast, there were significant increases in the levels of TIMP-4 in the medulla of 6 week SHR as compared with 2 week SHR or NWR. In addition, there were substantial elastinolytic activity in the cortex of 6 week SHR. The in situ labeling suggested no TIMP-4 in the glomeruli. There was substantial TIMP-4 in the epithelial layer of tubules. The levels of fibrotic collagen were significantly higher in both the glomeruli and tubular interstitium. Urinary protein excretion was increased significantly in 6 week SHR when compared with other groups. The mean arterial pressure was 1.6-fold higher in 6 week SHR than in controls.

CONCLUSION

These results suggest that increased MMP-2 and MMP-9 activity contributes to glomerular injury and hypertensive remodeling. The increased levels of TIMP-4 in the medulla may inhibit the collagenolytic activity of MMP but is unable to inhibit the elastinolytic activity. An important role of MMP-2, MMP-9, and TIMP-4 in hypertensive remodeling of the cortex and medulla in the SHR is demonstrated.

Matrix metalloproteinases and tissue inhibitors of metalloproteinases: structure, function, and biochemistry

Matrix metalloproteinases (MMPs), also designated matrixins, hydrolyze components of the extracellular matrix. These proteinases play a central role in many biological processes, such as embryogenesis, normal tissue remodeling, wound healing, and angiogenesis, and in diseases such as atheroma, arthritis, cancer, and tissue ulceration. Currently 23 MMP genes have been identified in humans, and most are multidomain proteins. This review describes the members of the matrixin family and discusses substrate specificity, domain structure and function, the activation of proMMPs, the regulation of matrixin activity by tissue inhibitors of metalloproteinases, and their pathophysiological implication.

Involvement of HB-EGF and EGF receptor transactivation in TGF-beta-mediated fibronectin expression in mesangial cells

BACKGROUND

Gq-coupled receptors are known to transactivate epidermal growth factor receptor (EGFR) via the Ca2+ and PKC pathways to phosphorylate extracellular signal-regulated kinase (ERK).

METHODS

We studied the involvement of EGFR in transforming growth factor-beta (TGF-beta)-mediated fibronectin (FN) expression using glomerular mesangial cells.

RESULTS

TGF-beta up-regulated FN mRNA accumulation in a time- and dose-dependent manner, which was completely inhibited by phosphatidylcholine-phospholipase C (PC-PLC) inhibitor and PKC inhibitors (calphostin-C and staurosporin). The EGFR inhibitor AG1478 completely abolished TGF-beta-mediated FN expression. ERK inactivation by PD98059, and p38MAPK inhibitor SB203580 also showed significant inhibitory effects. Addition of neutralizing anti-heparin-binding EGF-like growth factor (HB-EGF) antibody, pretreatment with heparin and the metalloproteinase (MMP) inhibitor batimastat blocked FN expression. In mesangial cells stably transfected with a chimera containing HB-EGF and alkaline phosphatase (ALP) genes, ALP activity in incubation medium was rapidly increased by TGF-beta (2.1-fold at 0.5 min) and reached a 3.7-fold increase at two minutes, which was abolished by calphostin-C or batimastat. TGF-beta phosphorylated EGFR, ERK and p38MAPK in a PKC- and MMP-dependent manner. Smad2 phosphorylation by TGF-beta was not affected by AG1478, and HB-EGF did not activate Smad2. FN mRNA stability was not affected by TGF-beta. Cycloheximde did not interfere with TGF-beta-mediated FN expression.

CONCLUSIONS

The present study demonstrated that HB-EGF processed and released via PC-PLC-PKC signaling is an intermediate molecule for TGF-beta-mediated EGFR transactivation, and subsequent activation of ERK and p38MAPK is involved in FN expression via transcriptional regulation without requiring new protein synthesis.

Combinatorial interactions of p53, activating protein-2, and YB-1 with a single enhancer element regulate gelatinase A expression in neoplastic cells

Gelatinase A, also denoted matrix metalloproteinase 2, plays multiple critical roles in the neoplastic process, including facilitation of neoangiogenesis and formation of distal metastases. The transcriptional regulation of the gelatinase A gene is under the control of strong, evolutionarily conserved cis-acting enhancer elements, designated the r2 (human) or RE-1 (rat), that harbor contiguous binding motifs for the transcription factors activating protein-2 (AP2), p53, and YB-1. Using recombinant transcription factors, complex patterns of RE-1 binding were observed by electrophoretic mobility shift assay. Increased complex formation was detected with the AP2/YB-1 and AP2/p53 combinations, while YB-1 competed with p53 for binding. The combination of AP2, p53, and YB-1 yielded novel ternary complexes, particularly when binding to single-stranded RE-1 probes. Transient transfection of hepatocellular carcinoma cell lines with a series of gelatinase A luciferase reporter constructs were in accordance with the binding patterns determined by electrophoretic mobility shift assay. Combined AP2 and p53 increased gelatinase A luciferase reporter activity significantly, and the inclusion of YB-1 yielded further increase in both reporter activity and secreted levels of gelatinase A protein. YB-1 and p53 expression are increased following multiple genotoxic stresses, including irradiation, and the synergistic interactions of these induced transcription factors with the widely expressed AP2 protein provide a probable pathophysiologic mechanism for the enhanced tumor cell synthesis of gelatinase A induced by radiation.

Transcription factor Ets-1 regulates gelatinase a gene expression in mesangial cells

Ets transcription factors are involved in cell growth and angiogenesis. Ets-1 targets include members of the matrix metalloproteinase superfamily. In inflammatory glomerular diseases, the patterns and regulation of Ets expression have not been fully characterized. In the present study, nuclear binding activities to the consensus Ets-1/PEA3 motif were detected in mesangial cells (MC), and the Ets-1 protein was positively identified by Western blotting, reverse transcription PCR (RT-PCR), and DNA-binding studies. The 5' flanking regions of the human and rat gelatinase A genes contain clusters of potential Ets-1 binding motifs, one of which is evolutionarily conserved. Using a series of 5' deletion reporter constructs of the rat gelatinase A gene and an Ets-1 expression plasmid, a concentration-dependent threefold trans-activation of gene expression mapped to the conserved Ets-1 binding motif at -1004/-1053 bps, designated responsive element-2 (RE-2). The RE-2 was operative within the context of the homologous gelatinase A promoter but not with a heterologous simian virus 40 promoter. Specific Ets-1 binding to this sequence was demonstrated by DNA-binding studies. Transient expression of an Ets-1 expression plasmid increased gelatinase A protein expression. Our findings identify an additional matrix metalloproteinase family member, gelatinase A, as an Ets-1 responsive gene in MC that may play a role in the high level expression of this enzyme in inflammatory glomerular diseases.

The role of matrix metalloproteinases in the activation of mesangial cells

Mesangial cells play a prominent role in renal inflammatory disorders, especially in IgA nephropathy. This disease represents the most common form of glomerulonephritis that eventually leads to progressive kidney failure requiring renal replacement therapy. In kidney transplants, IgA nephropathy displays a high recurrence rate in the order of 50%. Increased cell proliferation rates and extracellular matrix (ECM) accumulation are crucial targets in the therapy of glomerulonephritis, including IgA nephropathy. The active role of matrix metalloproteinases (MMP) in the regulation of these two features is rapidly emerging. We studied a model of a specific type of mesangial cell-mediated glomerular inflammation, such as experimental mesangial proliferative glomerulonephritis and cultured proliferating mesangial cells. In addition, these tools allowed us to evaluate a new therapeutic strategy based on MMP inhibition. Inhibition of MMP activity and synthesis by antisense technology and by a synthetic inhibitor in vitro, successfully reverted the inflammatory mesangial cell phenotype to the physiologically existing resting state. In vivo, a hydramate-based MMP inhibitor attenuated excess mesangial cell proliferation and ECM accumulation in anti-Thy1.1 nephritis. The anti-proliferative effect was achieved by the induction of cell cycle arrest followed by apoptosis, mediated by the induction of p53, p21 and bax, but not by the Fas/FasL pathway. In conclusion, MMP inhibitors provide a new approach to the therapy of inflammation probably even beyond the field of renal disorders.

Angiotensin II signaling and HB-EGF shedding via metalloproteinase in glomerular mesangial cells

BACKGROUND

Angiotensin II (Ang II) has been implicated in the development of glomerulosclerosis by stimulating fibronectin (FN) synthesis. The processing and release of heparin binding-endothelin growth factor (HB-EGF) are activated by protein kinase C (PKC) and Ca2+ signaling. We studied the roles of HB-EGF and endothelial growth factor (EGF) receptor (EGFR) in Ang II-induced FN expression using mesangial cells.

METHODS

Mesangial cells were prepared from mouse kidneys by the explant method and cells were used at passages 4 and 5.

RESULTS

Ang II stimulated FN mRNA levels dose-dependently with a maximal increase (3.4-fold) after 12 hours of incubation. This action was completely inhibited by PKC inhibitors and slightly blocked by Ca2+ chelating agents. FN mRNA accumulation by Ang II was abolished by tyrosine kinase inhibitors, a specific inhibitor for EGFR (AG1478) and extracellular signal-regulated kinase (ERK) inactivation. Addition of neutralizing anti-HB-EGF antibody, as well as pretreatment with heparin or the metalloproteinase inhibitor batimastat abolished induction of FN expression by Ang II. In mesangial cells stably transfected with a chimeric construct containing HB-EGF and alkaline phosphatase (ALP) genes, ALP activity in incubation medium was rapidly increased by Ang II (1.7-fold at 0.5 min) and reached a 4.1-fold increase at two minutes. Ang II phosphorylated EGFR (maximal at 2 min) and ERK (maximal at 8 min) in a PKC- and metalloproteinase-dependent manner. Ang II stimulated the expression and release of transforming growth factor-beta (TGF-beta) via EGFR-mediated signaling, and the released TGF-beta also contributed to Ang II-mediated FN expression via EGFR transactivation.

CONCLUSIONS

Ang II-mediated FN expression was regulated by autocrine effects of HB-EGF and TGF-beta, suggesting a novel paradigm for cross-talk between Ang II and growth factor receptor signaling pathways.

t-PA promotes glomerular plasmin generation and matrix degradation in experimental glomerulonephritis

BACKGROUND

In addition to its well-known role in degrading fibrin, recent evidence suggests that plasmin degrades matrix proteins and activates prometalloproteinases. Plasmin is generated from plasminogen by tissue plasminogen activator (t-PA). We hypothesized that t-PA treatment increases plasmin generation in nephritic glomeruli and degrades pathological matrix leading to a therapeutic reduction in matrix accumulation.

METHODS

Anti-Thy-1 nephritis was induced by injection of OX-7 antibody. Rats were given twice daily intravenous injections of saline (disease control group) or human recombinant t-PA (rt-PA; 1 mg/kg body weight) on days 3 through 5. Proteinuria, glomerular matrix protein staining, and glomerular mRNA levels for transforming growth factor-beta 1 (TGF-beta 1), fibronectin, and plasminogen activator inhibitor type 1 (PAI-1) were evaluated at day 6. Localization of rt-PA, plasmin generation by glomeruli in vitro, and glomerular production and content of active TGF-beta1 were also investigated.

RESULTS

Compared with disease control animals, proteinuria and staining score for periodic acid-Schiff (2.75 +/- 0.17 vs. 1.41 +/- 0.09), fibronectin-EDA+ (19 +/- 2 vs. 14 +/- 1), laminin (35 +/- 2 vs. 25 +/- 2), type I collagen (33 +/- 1 vs. 21 +/- 3), and type IV collagen (27 +/- 2 vs. 23 +/- 1) were significantly reduced in treated rats (P < 0.01). Glomerular TGF-beta 1, fibronectin, and PAI-1 mRNA levels were unchanged. rt-PA colocalized with fibrin along glomerular capillary walls and in the mesangium. Nephritic glomeruli in vitro had decreased plasmin activity, which was elevated by an in vivo presacrifice injection of rt-PA. Glomerular production and content of active TGF-beta 1 were unchanged by the rt-PA injection.

CONCLUSIONS

: These results show that injected rt-PA binds to fibrin in nephritic glomeruli, thus increasing plasmin generation and promoting pathological matrix degradation without activating latent TGF-beta. Agents that increase plasmin generation, such as t-PA, may have potential as antifibrotic therapies.

Circulating levels of matrix metalloproteinases MMP-3 and MMP-2 in renal transplant recipients with chronic transplant nephropathy

BACKGROUND

Chronic transplant nephropathy remains the major cause of graft loss after the first year post transplant, with the exception of death with functioning graft. The histological hallmark of chronic kidney rejection is progressive fibrosis in which extracellular matrix turnover plays an important role. This turnover is regulated by several systems of connective tissue proteases, the matrix metalloproteinases family being one of them. Every metalloproteinase exerts a different function over extracellular matrix proteins and can contribute to the pathogenesis of several diseases, such as rheumatoid arthritis and glomerulonephritis. The role of metalloproteinases in the pathogenesis of chronic transplant nephropathy and in kidney transplantation has not yet been addressed.

METHODS

We measured the serum levels of proMMP-1, proMMP-2 and proMMP-3 by ELISA in 40 patients with chronic transplant nephropathy, 30 with acute rejection, 30 with stable graft function for a time equivalent to chronic transplant nephropathy, 30 with stable graft function for a time equivalent to acute rejection, and 30 healthy age-paired blood donors.

RESULTS

Serum proMMP-2 and proMMP-3 were significantly higher in patients with chronic transplant nephropathy than in patients with acute rejection, stable graft function and healthy donors. The most striking finding was the significant positive correlation observed between serum levels of proMMP-3 and serum creatinine, and between circulating levels of proMMP-2 and proteinuria. Serum concentration of proMMP-1 was increased in patients with acute rejection compared with those with stable graft function and healthy donors.

CONCLUSIONS

Serum proMMP-2 and proMMP-3 reflect the changes of glomerular and interstitial extracellular matrix in chronic transplant nephropathy, suggesting that they could play a role in the pathogenesis of this condition. Acute rejection is associated with increased levels of proMMP-1, which could be a reflection of the stimulation induced by a number of inflammatory cytokines produced in such a process.

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.

Paracrine stimulation of human renal fibroblasts by proximal tubule cells

Paracrine stimulation of human renal fibroblasts by proximal tubule cells.

BACKGROUND

Interstitial fibrosis strongly predicts the degree and progression of renal failure in human renal disorders. Since active fibrosis tends to initially occur in a peritubular distribution, the possibility that human proximal tubule cells (PTC) relay fibrogenic signals to neighboring cortical fibroblasts was examined in vitro.

METHODS

Cell proliferation (cell counts and thymidine incorporation), total collagen synthesis (proline incorporation), matrix metalloproteinase (MMP) activity (gelatin zymography), and autocrine secretion of insulin-like growth factor-I (IGF-I) were measured in primary cultures of human cortical fibroblasts cocultured with PTC or exposed to PTC-conditioned media (PTCCM).

RESULTS

Cell numbers and thymidine incorporation rates were increased in cortical fibroblasts cocultured with PTC (136.4+/-7.3% and 119.3+/-8.2% of control values, respectively, P < 0.05) or incubated in PTC-CM (114.0+/-5.9%, P < 0.05 and 146.7+/-13.3%, P < 0.05, respectively). PTC-CM stimulated cortical fibroblast collagen synthesis (13.5+/-1.0% vs. 10.8+/-0.7%, respectively, N = 24, P < 0.05) and MMP-2 and MMP-9 secretion. Cortical fibroblast secretion of IGF-I binding protein-3 (IGFBP-3), which in turn modulates the autocrine and paracrine actions of IGF-I, was enhanced in the presence of PTC-CM compared with control (1162.2+/-94.2 vs. 969.1+/-58.9 ng/mg protein/day, P < 0.05), but no change was observed in cortical fibroblast secretion of IGFBP-2 (260.9+/-38.8 vs. 290.9+/-36.6 ng/mg protein/day, P = NS) or IGF-I (56.7+/-6.6 vs. 57.0+/-6.8 ng/mg protein/day, P = NS). Human PTC secreted transforming growth factor-beta1 (TGF-beta1) and the AB heterodimer of platelet-derived growth factor (PDGF-AB) in a time-dependent fashion and the augmentation of cortical fibroblasts mitogenesis, collagen synthesis and IGFBP-3 secretion induced by PTC-CM was replicated by exogenous TGF-beta1 and PDGF. Furthermore, the stimulatory effects of PTC on cortical fibroblasts were potentiated in transiently acidified PTC-CM (which activated latent TGF-beta1), and were abrogated by neutralizing antibodies specifically directed against TGF-beta1 and PDGF-AB. Cortical fibroblasts in turn released a soluble factor(s) into cortical fibroblast-conditioned media that reciprocally stimulated PDGF-AB production by PTC (4.79+/-1.55 vs. 0.78+/-.06 ng/mg protein/day, P < 0.05).

CONCLUSIONS

PTC modulate the biological behavior of neighboring cortical fibroblasts in the human kidney through paracrine mechanisms, which include the production and release of PDGF-AB and TGF-beta1. Renal insults that result in proximal tubule injury may perturb this paracrine interaction, thereby culminating in excessive fibroblast proliferation and interstitial fibrosis.

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.