Extracellular matrix and the kidney

Particulate kidney extracellular matrix: bioactivity and proteomic analysis of a novel scaffold from porcine origin

Decellularized matrices are attractive substrates, being able to retain growth factors and proteins present in the native tissue. Several biomaterials can be produced by processing these matrices. However, new substrates capable of being injected that reverse local kidney injuries are currently scarce. Herein, we hypothesized that the decellularized particulate kidney porcine ECM (pKECM) could support renal progenitor cell cultures for posterior implantation. Briefly, kidneys are cut into pieces, decellularized by immersion on detergent solutions, lyophilized and reduced into particles. Then, ECM particles are analyzed for nuclear material remaining by DNA quantification and histological examination, molecular conformation by FITR and structural morphology by SEM. Protein extraction is also optimized for posterior identification and quantification by mass spectrometry. The results obtained confirm the collagenous structure and composition of the ECM, the effective removal of nucleic material and the preservation of ECM proteins with great similarity to human kidneys. Human renal progenitor cells (hRPCs) are seeded in different ratios with pKECM, on 3D suspensions. The conducted assays for cell viability, proliferation and distribution over 7 days of culture suggest that these matrices as biocompatible and bioactive substrates for hRPCs. Also, by analyzing CD133 expression, an optimal ratio for specific phenotypic expression is revealed, demonstrating the potential of these substrates to modulate cellular behavior. The initial hypothesis of developing and characterizing a particulate ECM biomaterial as a consistent substrate for 3D cultures is successfully validated. The findings in this manuscript suggest these particles as valuable tools for regenerative nephrology by minimizing surgeries and locally reversing small injuries which can lead to chronic renal disfunction.

Bioprinting of 3D Convoluted Renal Proximal Tubules on Perfusable Chips

Three-dimensional models of kidney tissue that recapitulate human responses are needed for drug screening, disease modeling, and, ultimately, kidney organ engineering. Here, we report a bioprinting method for creating 3D human renal proximal tubules in vitro that are fully embedded within an extracellular matrix and housed in perfusable tissue chips, allowing them to be maintained for greater than two months. Their convoluted tubular architecture is circumscribed by proximal tubule epithelial cells and actively perfused through the open lumen. These engineered 3D proximal tubules on chip exhibit significantly enhanced epithelial morphology and functional properties relative to the same cells grown on 2D controls with or without perfusion. Upon introducing the nephrotoxin, Cyclosporine A, the epithelial barrier is disrupted in a dose-dependent manner. Our bioprinting method provides a new route for programmably fabricating advanced human kidney tissue models on demand.

High collagen I gene expression as an independent predictor of adverse renal outcomes in lupus nephritis patients with preserved renal function

CONTEXT

The deposition of extracellular matrix is a major pathogenic mechanism leading to fibrosis and progressive decline in renal function in patients with lupus nephritis (LN). Currently, available clinicopathologic features cannot predict renal outcome consistently.

OBJECTIVE

To test that the expression of renal fibrogenic genes correlates with renal fibrosis at the time of biopsy and is predictive of renal outcomes.

DESIGN

Renal gene expression levels of transforming growth factor β-1 (TGFB1), and collagen I (COL1) were studied by real-time multiplex quantitative polymerase chain reaction in a prospective cohort of patients with LN (n = 39). Extracellular matrix index (ECMI) and collagen I/III matrix index were measured from Picro-Sirius Red-stained slides under normal and polarized light, respectively.

RESULTS

After follow-up (median, 43.9 months), renal failure (50% reduction in glomerular filtration rate [GFR] or dialysis) had developed in 13 subjects. The expression levels of renal fibrogenic genes were increased as compared to controls without LN. COL1 correlated with collagen I/III matrix index at baseline. Both high expression of TGFB1 or COL1 tended to predict renal failure by univariate analysis. By multivariate analysis, high ECMI and low GFR were predictive of renal failure. In patients with baseline GFR of 60 mL/min/1.73 m(2) or greater, high renal COL1 expression was an independent (hazard ratio = 4.4, P = .04) predictor of renal failure.

CONCLUSIONS

High renal COL1 expression is a strong predictor of adverse renal outcome in patients with LN and preserved baseline GFR. These findings support larger prospective studies to confirm the benefits of COL1 in identifying patients at high risk of progression to renal disease.

Cytokine mediated tissue fibrosis

Acute inflammation is a recognised part of normal wound healing. However, when inflammation fails to resolve and a chronic inflammatory response is established this process can become dysregulated resulting in pathological wound repair, accumulation of permanent fibrotic scar tissue at the site of injury and the failure to return the tissue to normal function. Fibrosis can affect any organ including the lung, skin, heart, kidney and liver and it is estimated that 45% of deaths in the western world can now be attributed to diseases where fibrosis plays a major aetiological role. In this review we examine the evidence that cytokines play a vital role in the acute and chronic inflammatory responses that drive fibrosis in injured tissues. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Connective tissue growth factor gene expression and decline in renal function in lupus nephritis

In lupus nephritis (LN), kidney inflammation may be followed by fibrosis and progressive decline in function. Transforming growth factor (TGF)-β is a notable mediator of fibrosis, but it has other beneficial roles, thus indicating a need for alternate therapeutic targets for inhibition of fibrosis. Connective tissue growth factor (CTGF) acts as a downstream mediator of TGF-β in promoting fibrosis, without mediating the immunosuppressive effects of TGF-β. Animal studies show that CTGF may have important roles in renal fibrosis, but data are limited in human subjects. The present study tested the hypothesis that renal CTGF mRNA expression is related to TGF-β1 and collagen I expression and is predictive of renal function deterioration in patients with LN (n=39). Gene expression was measured using multiplex real-time quantitative RT-PCR and renal function was estimated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) glomerular filtration rate (GFR) equation. Decline in GFR was assessed by regression of GFR at biopsy to 1 year following biopsy. CTGF mRNA expression was significantly correlated with TGF-β1 and collagen I. GFR at biopsy was 89.2±39.2 ml/ min. Renal CTGF mRNA expression correlated inversely with baseline GFR. Renal CTGF mRNA was significantly higher in patients with moderate to severe CKD compared to those in the milder CKD group (low GFR 4.92±4.34 vs. high GFR 1.52±1.94, p<0.005). CTGF mRNA was also higher in patients with subsequent decline in GFR [GFR decline (5.19±4.46) vs. no GFR decline (1.79±1.97); P<0.01]. In conclusion, renal expression of CTGF was positively related to TGF-β1 and collagen I in patients with LN. Furthermore, high CTGF mRNA expression was associated with poor GFR at baseline and subsequent deterioration of kidney function. CTGF expression in the kidney may serve as an early marker for renal disease progression and could be evaluated as a target for therapeutic intervention to prevent renal failure in LN.

Direct contribution of epithelium to organ fibrosis: epithelial-mesenchymal transition

Fibrosis of epithelial parenchymal organs and end-stage organ failure represent the final common pathway of many chronic diseases and are a major determinant of morbidity and mortality worldwide. Fibrosis is a complex response initiated to protect the host from an injurious event; nevertheless, it leads to serious organ damage when it becomes independent from the initiating stimulus. It involves massive deposition of matrix by an expanded pool of fibrogenic cells, disruption of the normal tissue architecture, and parenchymal destruction. Fibroblasts, the effector cells of matrix production, when engaged in fibrogenesis, display the highly activated phenotype characteristic of myofibroblasts. These cells are present in a large number in sites with ongoing inflammation, reparative reaction, and fibrosis, but their origin has not yet been definitely elucidated. Although proliferation of preexisting stromal fibroblasts and, probably, recruitment of bone marrow-derived fibrogenic cells may account for a portion of them, emerging evidence seems to indicate that an important number of matrix-producing fibroblasts/myofibroblasts arises through a mechanism of epithelial-mesenchymal transition. Through this process, epithelial cells would lose intercellular cohesion and would translocate from the epithelial compartment into the interstitium where, gaining a full mesenchymal phenotype, they could participate in the synthesis of the fibrotic matrix. Epithelial-mesenchymal transition is induced by the integrated actions of many stimuli including transforming growth factor-beta and matrix-generated signals that are also known to be implicated in inflammation, repair responses, and fibrosis. The consequences of epithelial-mesenchymal transition in chronic fibrosing diseases could be two-fold as follows: on one hand, by supplementing new mesenchymal cells, it might feed the expanding pool of interstitial fibroblasts/myofibroblasts responsible for the matrix accumulation; on the other hand, it could cause loss of epithelial cells, thus, contributing to the parenchyma destruction seen in advanced fibrosis. Markers of epithelium undergoing epithelial-mesenchymal transition include loss of E-cadherin and cytokeratin; de novo expression of fibroblast-specific protein 1/S100A4, vimentin, and alpha-smooth muscle actin; basement membrane component loss; and production of interstitial-type matrix molecules such as fibronectin and type I/III collagen. Evidence of epithelial-mesenchymal transition has been reported in the kidney, lung, liver, eye, and serosal membranes suggesting that epithelial-mesenchymal transition could be involved in the pathogenesis of fibrotic disorders in these organs. Thus, because of its fibrogenic potential, the detection of epithelial-mesenchymal transition in biopsy specimens could be useful diagnostically and represent a new biomarker of progression in chronic fibrosing diseases.

Urinary levels of matrix metalloproteinases and their tissue inhibitors in nephrotic children

The aim of this study was to determine the effects of cyclosporine A (CyA) on urinary levels of matrix metalloproteinase 2 and 9 (MMP2, MMP9) and their tissue inhibitors 1 and 2 (TIMP1, TIMP2) in steroid-dependent nephrotic syndrome (SDNS). The study group (1) consisted of 18 children SDNS aged 3.5-17.0 years treated with CyA. All NS children were examined three times: (A) at proteinuria relapse, before CyA treatment, (B) after 6 months, and (C) after 12 months of CyA administration. The control group (2) consisted of 18 healthy children. Serum CyA level was assessed by immunofluorescence. Enzyme-linked immunosorbent assay kits for total human MMP2 and 9 and TIMP1 and 2 were obtained from R&D Systems. Compared with healthy controls, urinary MMP9/Cr in NS children before CyA was on the same level and increased during CyA treatment, and urinary TIMP1/Cr was twice as high and increased significantly during CyA treatment. MMP9/TIMP1 in NS children treated with CyA increased, but the difference was not statistically significant. Urinary MMP2/Cr was similar, and urinary TIMP2/Cr was significantly higher in children treated with CyA (p < 0.01). The MMP2/TIMP2 ratio in NS children treated with CyA was significantly lower in comparison with healthy controls (p < 0.01). A negative correlation was noted between urinary MMP2/TIMP2 ratio and serum CyA in NS children (r = -0.541, p < 0.01). An imbalance within the MMP2 and TIMP2 and MMP9 and TIMP1 system may play a role in the pathogenesis CyA nephropathy.

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.

Fibrosis and matrix metalloproteinases in rat renal allografts

The temporal activity and gene expression of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinase (TIMP) were investigated in a rat model of chronic allograft nephropathy. Gelatinolytic activity of MMP-2 and -9 were demonstrated by zymography, and MMP-2,-9 and TIMP-3 mRNA by in situ hybridization. The generation of fibrosis was determined as total collagen content/DNA. Significantly more latent and active MMP-2, as well as latent MMP-9, were seen in allografts than in autografts. Intense MMP-2 mRNA expression was demonstrated in the allografts during the first 20 days after transplantation, located mainly in the interstitium of the kidney. In addition, some tubular cells expressed MMP-2 mRNA. After day 20, MMP-2 gene expression was faint. MMP-9 mRNA expression in allografts was located mainly in the glomerulus. TIMP-3 mRNA expression was downregulated in allografts. MMP-2, MMP-9 and TIMP-3 seem to play a critical role in the development of fibrosis in the renal allograft.

The Experimental Agent Pirfenidone Reduces Pro-Fibrotic Gene Expression in a Model of Tacrolimus-Induced Nephrotoxicity

BACKGROUND

Tacrolimus nephrotoxicity is thought to contribute to renal allograft dysfunction and subsequent failure, a process that is underpinned by alterations in mRNA expression of genes involved in matrix metabolism. The new anti-fibrotic pirfenidone was tested for its potential to reverse markers of renal dysfunction.

MATERIALS AND METHODS

Rats were salt-depleted before tacrolimus and pirfenidone treatment. Serum creatinine, urinary protein/creatinine ratio, extracellular matrix deposition (ECM), and mRNA expression of genes involved in matrix turnover were assessed.

RESULTS

Tacrolimus reduced TGF-beta mRNA expression below control levels and treatment with pirfenidone at all doses did not alter this effect. Likewise, TIMP-1 mRNA expression was depressed by the addition of tacrolimus and pirfenidone caused a further decrease in expression. Collagen III, MMP-2, and MMP-9 expression was unchanged by tacrolimus, but pirfenidone reduced collagen III below control levels. ECM was slight (1-4%) and not significantly different between groups.

CONCLUSIONS

These findings suggest that pirfenidone can attenuate the limited fibrotic potential of tacrolimus.

The Where, What and Why of the Developing Renal Stroma

In recent years, a great deal has been learnt about the molecular regulation of kidney development. While most research has focused on the molecular regulation of ureteric branching morphogenesis and nephron formation, significant insights into the definition and functions of the renal stroma have emerged. Many molecules expressed in the developing renal stroma are now known to play significant regulatory roles in kidney development. However, the term 'renal stroma' continues to have different meanings to different researchers. This review clarifies this situation and defines the derivation, location and functions of the stroma in the developing metanephros.

Leptin increases expression and activity of matrix metalloproteinase-2 and does not alter collagen production in rat glomerular mesangial cells

Obesity is a leading risk factor for the development of nephropathy. In nephropathy, one of the major structural alterations found in the kidney is the increase in, or altered profile of, extracellular matrix (ECM) proteins such as collagen. Excessive synthesis and decreased degradation of matrix proteins by proteases such as matrix metalloproteinases (MMPs) may contribute to this process. We hypothesized that alterations observed in nephropathy may be due to alterations in direct effects of leptin, the product of the obesity gene. Here, we investigate the effect of leptin on collagen synthesis and MMP-2 production in rat glomerular mesangial cells. Using quantitative real-time PCR we showed that leptin does not alter the expression of collagen type I and IV mRNA. In keeping with this observation, proline incorporation was not altered by leptin. We also demonstrate that leptin induces MMP-2 expression in glomerular mesangial cells, assessed by quantitative real-time PCR. Analysis of conditioned media by gelatin zymography indicated increased activity at a molecular weight corresponding with that of MMP-2 in leptin-treated samples. In summary, our results indicate that leptin induces MMP-2 expression and activity without altering collagen synthesis, suggesting that normal leptin function has the potential to prevent ECM accumulation.

De novo kidney transplantation without use of calcineurin inhibitors preserves renal structure and function at two years

We performed a randomized prospective trial comparing calcineurin inhibitor (CNI)-free to CNI-based immunosuppression to determine the impact on renal function, structure and gene expression. Sixty-one kidney recipients treated with basiliximab mycophenolate mofetil (MMF) and prednisone (P) were randomly assigned to concentration-controlled sirolimus or cyclosporine. Two years post-transplant 55 patients underwent renal function studies, 48 (87%) underwent transplant biopsies; all classified by Banff scoring and 41 by DNA microarrays. Comparing sirolimus/MMF/P to cyclosporine/MMF/P there was a significantly lower serum creatinine (1.35 vs. 1.81 mg/dL; p = 0.008), higher Cockroft-Gault glomerular filtration rate (GFR) (80.4 vs. 63.4 mL/min; p = 0.008), iothalamate GFR (60.6 vs. 49.2 mL/min; p = 0.018) and Banff 0 (normal) biopsies (66.6 vs. 20.8%; p = 0.013). Regression analysis of calculated GFRs from 1 to 36 months yielded a positive slope for sirolimus of 3.36 mL/min/year, and a negative slope for cyclosporine of -1.58 mL/min/year (p = 0.008). Gene expression profiles from kidneys with higher Banff chronic allograft nephropathy (CAN) scores confirmed significant up-regulation of genes responsible for immune/inflammation and fibrosis/tissue remodeling. At 2 years the sirolimus-treated recipients have better renal function, a diminished prevalence of CAN and down-regulated expression of genes responsible for progression of CAN. All may provide for an alternative natural history with improved graft survival.

Differentiation between chronic rejection and chronic cyclosporine toxicity by analysis of renal cortical mRNA

BACKGROUND

In kidney transplantation, chronic allograft nephropathy (CAN) is the major cause of graft loss. Causes of CAN include chronic rejection and chronic cyclosporine A (CsA) nephrotoxicity. It is necessary to differentiate between these two entities in order to apply the appropriate therapeutic regimen for the individual patient, but this is hampered by the lack of discriminating functional and morphologic parameters. We investigated whether renal cortical mRNA levels for several matrix proteins can serve as discriminating parameters.

METHODS

Patients with chronic rejection (N= 19) and chronic CsA toxicity (N= 17) were selected by clinical and histologic criteria. Protocol biopsies without histologic abnormalities, taken at 6 months after transplantation from patients receiving CsA, were used as controls (N= 6). Total RNA was extracted from the renal biopsy tissue, and mRNA levels of transforming growth factor-beta (TGF-beta) and the extracellular matrix (ECM) molecules collagen Ialpha1, IIIalpha1, IValpha3, decorin, fibronectin, and laminin beta2 were measured by real-time polymerase chain reaction (PCR).

RESULTS

In both patient groups, the mean collagen IValpha3 and fibronectin mRNA levels were significantly elevated compared to those in controls, whereas only in CsA toxicity were the laminin beta2 and TGF-beta mRNA levels significantly increased. The increase of laminin beta2 and TGF-beta mRNA levels was significantly higher in the CsA toxicity group than in the chronic rejection group (P < 0.001 and P= 0.004, respectively). Receiver-operating characteristic (ROC) curve analysis showed that with a 15.6-fold increase in laminin beta2 mRNA expression as cut-off point, the presence of CsA toxicity could be predicted with an 87% sensitivity and an 88% specificity.

CONCLUSION

Renal laminin beta2 and TGF-beta mRNA levels can be used to differentiate between chronic rejection and chronic CsA toxicity in renal transplants. The method of mRNA quantification might be applicable as an additional diagnostic tool in clinical practice.

Modulation of matrix gelatinases and metalloproteinase-activating process in acute kidney rejection

Changes in matrix metalloproteinase (MMP) activities would contribute to the accumulation of extracellular matrix during acute kidney allograft rejection. MMP-2 and MMP-9 and other gelatinolytic activities were examined in the rejected graft and the urine of a rat model of acute kidney rejection (orthotopic allotransplantation from a Buffalo donor to a Wistar-Furth recipient) by either zymography or fluorescence assay. MMP-2, membrane type 1 (MT1)-MMP, and tissue inhibitor of metalloproteinase (TIMP)-2 were also examined by immunodetection. The proMMP-2 activity and protein level increased in the graft during rejection when compared with normal Buffalo kidney, whereas activated MMP-2 decreased. TIMP-2 protein levels were markedly decreased and MT1-MMP proteolytic fragments (44-40 kDa) were undetectable. This suggests an altered MT1-MMP-dependent processing of proMMP-2 into active MMP-2 due to a diminished TIMP-2 level in acute kidney rejection. In the urine the overall gelatinolytic activity decreased considerably, although activity associated with an as yet unidentified 78-kDa protein appeared 6 days after transplantation.

The impact of cyclosporine dose reduction with or without the addition of rapamycin on functional, molecular, and histological markers of chronic allograft nephropathy

BACKGROUND

Overexposure to cyclosporine is a risk factor for chronic allograft nephropathy (CAN) and dose reduction has been advocated. The purpose of this study was to determine the impact of adding the non-nephrotoxic immunosuppressant, rapamycin, after cyclosporine dose reduction in renal-allograft recipients with CAN.

METHODS

Thirty-one patients with biopsy-confirmed CAN were prospectively randomized to receive a 40% cyclosporine dose reduction with (rapamycin, n=16) or without (control, n=15) the addition of rapamycin 2 mg/day. Renal function and side-effect parameters were assessed. Patients had renal allograft biopsies taken at recruitment and after 6 months. Glomeruli were isolated from these and underwent total mRNA extraction followed by RT-PCR-ELISA to assess transforming growth factor-beta1, collagen III, TIMP-1, TIMP-2, and matrix metalloproteinase-2 expression. Samples were also stained with Sirius red and the percentage interstitial volume fraction quantified by computerized histomorphometric analysis. Data are presented as mean (+/-SD).

RESULTS

Patient characteristics and cyclosporine trough levels after dose reduction (rapamycin 68 [+/-21] vs. control 56 [+/-19] ng/mL, P=NS) were similar in both groups. Rapamycin patients had a significant fall in Cr-51 radioisotope glomerular filtration rate (31.6 [+/-8.9] to 27.3 [+/-8.6] mL/min, P<0.01) that was not significant in controls (29.5 [+/-10.4] to 27.0 [+/-8.0] mL/min, P=NS). Transforming growth factor-beta1 expression fell over time in control but remained constant in rapamycin patients. Conversely collagen III expression increased over the 6-month follow-up in rapamycin patients but not in controls. Both had comparable increases in TIMP-1 and matrix metalloproteinase-2 but only rapamycin patients developed a significant increase in TIMP-2. Sirius red-stained interstitial volume fraction fell over the study in controls (15.3-11.2%, P=0.06) but not in rapamycin patients (16.2-16.3%, P=NS).

CONCLUSION

Rapamycin (2 mg/day) did not improve functional, molecular, or histological outcome in patients with CAN after cyclosporine dose reduction. Further studies involving larger numbers of patients are necessary to confirm these findings.

Renal transplant fibrosis correlates with intragraft expression of tissue inhibitor of metalloproteinase messenger RNA

BACKGROUND

Chronic renal allograft nephropathy is characterized by an abnormal accumulation of extracellular matrix proteins in the glomeruli and tubulo-interstitium. The aim of this study was to determine the relationship between intragraft expression of the genes controlling the accumulation of extracellular matrix and the development of chronic renal allograft nephropathy in human renal transplants.

METHODS

Forty renal allografts with stable renal function were biopsied 6 months after transplantation. Single glomeruli were plucked from the surface of these protocol biopsies and total messenger RNA (mRNA) was extracted. Reverse transcriptase-polymerase chain reaction was used to study the intragraft expression of several fibrosis-associated genes (collagen III, collagen IValpha2, matrix metalloproteinase (MMP) 2, tissue inhibitors of metalloproteinases (TIMPs) 1 and 2, tenascin and transforming growth factor (TGF) beta1). The level of tubulo-interstitial fibrosis was measured by quantitative immunostaining of collagen III.

RESULTS

There were positive correlations between the level of tubulo-interstitial collagen III immunostaining and intragraft expression of the genes for TIMP-1 (rs= 0.70, P < 0.02) and TIMP-2 (rs = 0.59, P < 0.02). Interstitial fibrosis was also strongly correlated with the levels of TGF-beta mRNA (rs = 0.67, P < 0.002). Finally, TIMP-1 expression increased with TGF-beta expression (rs = 0.77, P < 0.002).

CONCLUSION

Failure of extracellular matrix degradation may be an important molecular mechanism in the pathogenesis of chronic renal allograft damage.

Interactions between collagen IV and collagen-binding integrins in renal cell repair after sublethal injury

Recent studies demonstrate that collagen IV selectively promotes the repair of physiological processes in sublethally injured renal proximal tubular cells (RPTC). We sought to further define the mechanisms of cell repair by measuring the effects of toxicant injury and stimulation of repair by L-ascorbic acid-2-phosphate (AscP), exogenous collagen IV, or function-stimulating integrin antibodies on the expression and subcellular localization of collagen-binding integrins (CBI) in RPTC. Expression of CBI subunits alpha1, alpha2, and beta1 in RPTC was not altered on day 1 after sublethal injury by S-(1,2-dichlorovinyl)-L-cysteine (DCVC). On day 6, expression of alpha1 and beta1 subunits remained unchanged, whereas a 2.2-fold increase in alpha2 expression was evident in injured RPTC. CBI localization in control RPTC was limited exclusively to the basal membrane. On day 1 after injury, RPTC exhibited a marked inhibition of active Na(+) transport and a loss of cell polarity characterized by a decrease in basal CBI localization and the appearance of CBI on the apical membrane. On day 6 after injury, RPTC still exhibited marked inhibition of active Na(+) transport and localization of CBI to the apical membrane. However, DCVC-injured RPTC cultured in pharmacological concentrations of AscP (500 microM) or exogenous collagen IV (50 microg/ml) exhibited an increase in active Na(+) transport, relocalization of CBI to the basal membrane, and the disappearance of CBI from the apical membrane on day 6. Function-stimulating antibodies to CBI beta1 did not promote basal relocalization of CBI despite stimulating the repair of Na(+)/K(+)-ATPase activity on day 6 after injury. These data demonstrate that DCVC disrupts integrin localization and that physiological repair stimulated by AscP or collagen IV is associated with the basal relocalization of CBI in DCVC-injured RPTC. These data also suggest that CBI-mediated repair of physiological functions may occur independently of integrin relocalization.

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.

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.

Fetal partial urethral obstruction causes renal fibrosis and is associated with proteolytic imbalance

PURPOSE

We determine whether fetal bladder outlet obstruction induces renal fibrosis, and is associated with an alteration in the regulation of connective tissue degradation and the presence of fibrogenic interstitial cells.

MATERIALS AND METHODS

Partial bladder outlet obstruction was surgically induced in 33 fetal sheep at 95 days of gestation. These animals and 24 normal age matched controls were sacrificed at 109, 116 and 135 (term) days of gestation, and the kidneys were rapidly retrieved, drained and weighed. Representative whole kidney samples were snap frozen for assessment of deoxyribonucleic acid, protein and collagen content. Morphometric analysis and alpha-smooth muscle actin immunohistochemistry were performed on histological specimens from formalin fixed kidneys. Tissue extract from fresh kidney specimens were analyzed for metalloproteinase and tissue inhibitor of metalloproteinase activity. Urine samples obtained at the time of sacrifice were analyzed for electrolyte, creatinine and N-acetyl glucosaminidase excretion.

RESULTS

All obstructed kidneys were hydronephrotic and larger than age matched controls. Obstructed kidneys at term showed interstitial fibrosis, as measured by increased extracellular matrix volume fraction (45% in male obstructed kidneys versus 2.5% in normal male kidneys, p = 0.0004), increased total collagen content (120 mg./kidney in male obstructed versus 20 mg. in normal male animals, p = 0.016) and collagen/deoxyribonucleic acid content per kidney (2.78 versus 0.53 mg./mg., p = 0.016). Metalloproteinase-1 activity was significantly lower in obstructed kidneys (210 versus 380 U./mg. protein in normal kidneys). Tissue inhibitor of metalloproteinase activity was undetectable in both groups. The presence of an increased population of myofibroblasts often associated with fibrotic processes was seen by alpha-smooth muscle actin staining which was localized to interstitial cells throughout the cortex in obstructed kidneys.

CONCLUSIONS

Fetal partial bladder outlet obstruction induces renal interstitial fibrosis as early as 2 weeks after obstruction. A possible mechanism for this process is a shift in proteolytic activity to reduce matrix degradation in obstructed kidneys. These changes might be mediated by the increased number of fibrogenic interstitial cells. The observations suggest several potential approaches to developing an understanding of congenital obstructive uropathy.

Intragraft expression of transforming growth factor beta1 gene in isolated glomeruli from human renal transplants

BACKGROUND

Experimental evidence suggests that transforming growth factor (TGF) beta1 is a fibrogenic cytokine. The histopathological changes of chronic renal allograft nephropathy are dominated by fibrotic changes and TGF-beta may have an important aetiological role. This study investigated the relationship between intragraft TGF-beta gene expression and extracellular matrix protein deposition in human renal allografts.

METHODS

Sixteen cadaveric renal transplant recipients immunosuppressed with cyclosporin and steroids were studied. Individual glomeruli were isolated from protocol needle-core biopsies and, following messenger RNA extraction, intragraft gene expression was studied by reverse transcriptase-polymerase chain reaction. Collagen III deposition in these renal transplant biopsies was examined by immunohistochemistry and quantified by computerized histomorphometry.

RESULTS

There was a positive correlation between renal cortical collagen III immunostaining and the levels of glomerular complementary DNA for TGF-beta1.

CONCLUSION

TGF-beta1 is a profibrotic influence in human renal transplants. The methods described should prove of benefit in investigating the mechanisms of chronic renal allograft damage.

Computerized histomorphometric assessment of protocol renal transplant biopsy specimens for surrogate markers of chronic rejection

BACKGROUND

Chronic transplant rejection has emerged as the commonest cause of long-term renal allograft failure, and early identification of those grafts at risk could allow the targeting of specific therapies aimed at delaying this process. This study explores the usefulness of quantitative immunohistochemistry in defining biopsy-based surrogate markers of allograft damage.

METHODS

A consecutive series of 52 renal transplant recipients immunosuppressed with cyclosporine were studied. Needle core transplant biopsies were performed at 1, 3, and 6 months postoperatively. Immunostaining for collagen III, and smooth muscle actin, tenascin, and infiltrating leukocytes was performed using an indirect immunoperoxidase technique. The interstitial area stained (%) was measured using a semiautomatic image analysis system. The results were related to glomerular filtration rates (GFR) measured at 6, 12, and 24 months after transplantation using rank correlation coefficients.

RESULTS

The area fraction of immunostained collagen III correlated with 6-month GFR (r=-0.42, P=0.005) and was predictive of 12-month GFR (r=-0.32, P=0.03). An area fraction of immunostained collagen III of >40% at 6 months was associated with a significantly lower GFR at 24 months, compared with a percentage area of < or =40% (31+/-4 versus 45+/-4 ml/min/1.73 m2, P=0.01). Furthermore, a collagen III of >40% at 6 months identified patients who were at risk of progressive deterioration in graft function.

CONCLUSIONS

Grafts with poorer long-term function can be predicted using 6-month protocol biopsy specimens immunostained for collagen III. This should prove to be a useful ad interim surrogate marker of allograft damage in studies addressing the effects of new immunosuppressive agents on the development of chronic rejection.

Noncollagenous Matrix Proteins Controlling Mineralization

Biomineralization is a highly controlled process that is believed to be regulated by noncollagenous proteins found in the organic matrix of bone. Dystrophic calcification possesses several features of bone, including the presence of noncollagenous proteins, which are also thought to regulate pathologic calcification. Noncollagenous proteins have been demonstrated to be present in a wide variety of tissues. They are also believed to play a role in the pathogenesis of a number of disease processes, including atherosclerosis, restenosis, valvular stenosis, nephrolithiasis, glomerulonephritis, malignant transformation, and metastasis. This review discusses the structure, function, and possible roles of noncollagenous proteins in physiologic and pathologic processes.

Semiautomatic quantitation of macrophages in human renal biopsy specimens in proteinuric states

AIMS

To develop and validate a rapid and economical semiautomated approach to the measurement of immunostainable tissue components which is applicable to routine diagnostic practice. To apply this approach to the measurement of macrophages in renal biopsy specimens in nephrotic states, as protein in the renal tubules may induce macrophage infiltration, and the morphology of macrophages in tissue sections does not lend itself to cell counting.

METHODS

Macrophages were identified by immunostaining with a pan-macrophage marker, followed by digital image capture and analysis using a macro procedure written for the freeware image analysis program NIH-Image.

RESULTS

The method was rapid, robust and accurate to within the limits imposed by sampling error inherent in the use of small needle biopsy specimens. Very few macrophages are found in normal kidney (mean volume fraction (+/- 95% confidence limits) 0.04% (0.02%)) but infiltration of macrophages was detected in minimal change nephropathy (0.29% (0.12%)) and in membranous glomerulonephritis (0.42% (0.11%)). A statistically significant correlation was found between macrophage volume fraction and weight of proteinuria in minimal change nephropathy but not in membranous glomerulonephritis. Correlations were found in both diseases between macrophage volume fraction and serum creatinine at time of biopsy.

CONCLUSIONS

The equipment is inexpensive and measurement takes less than one minute per biopsy specimen. The results indicate that macrophage infiltration is part of the pathological process in minimal change nephropathy and membranous glomerulonephritis. The correlation with creatinine at time of biopsy suggests that renal impairment in minimal change nephropathy may result from infiltration by immunologically active cells and not merely from haemodynamic changes in nephrons. However, the correlation is not close, indicating that the relation between macrophage infiltration and disease severity is not a simple one.