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Biomedical subjects

W G Couser

Publications and source records attributed to W G Couser.

At least 55 records · Page 3Linked to original sources
PubMed1997

Overexpression of Crry protects mesangial cells from complement-mediated injury.

Crry is a membrane-associated complement regulatory protein expressed on glomerular mesangial, endothelial, and epithelial cells, which reduces C3/C5 convertase activity. This study utilized an overexpression strategy to determine the functional significance of Crry in cultured rat mesangial cells. A Crry expression vector was constructed and was tagged with a c-myc epitope that allowed transfected Crry to be distinguished from the constitutively expressed protein. In stable clones, overexpressed Crry was clearly detected immunocytochemically both by anti-c-myc and anti-Crry antibody in a membrane localization. The overexpression of Crry was also confirmed by Western blotting and immunoprecipitation. To determine if overexpression of Crry by mesangial cells confers a protective effect from complement attack, complement-mediated cell lysis assays were performed. Crry-transfected mesangial cells demonstrated complete resistance to complement-mediated cell lysis, which was reversed by neutralization of Crry with both monoclonal antibody and F(ab')2 fragments of the antibody. This study also investigated the role of Crry in protecting cells from the effects of sublytic complement attack. Overexpressed Crry suppressed antibody/complement induced production of superoxide, one of the inflammatory mediators induced by sublytic complement attack. Immunocytochemical staining confirmed a reduction in C3 and C5b-9 deposition in Crry-transfected cells. These results demonstrate directly that transfected Crry functions as a potent protector of mesangial cells against complement-mediated injury. Crry may play an important role in modulating the glomerular response to immune injury in vivo.

Animals↗
PubMed1996

The cytoskeletal linking proteins, moesin and radixin, are upregulated by platelet-derived growth factor, but not basic fibroblast growth factor in experimental mesangial proliferative glomerulonephritis.

The expression of the two cytoskeletal linking proteins, moesin and radixin, was examined in experimental mesangial proliferative nephritis in rats (anti-Thy1 model). Moesin and radixin mRNA and protein are constitutively expressed in all cell types of normal rat glomeruli, except podocytes. In the anti-Thy1 model the expression of moesin and radixin was increased in infiltrating macrophages and in activated, alpha-smooth muscle actin-positive mesangial cells and was concentrated in the cellular extensions of mesangial cells in areas of glomerular remodelling. Studies using neutralizing antibodies demonstrated that the increase in moesin and radixin expression by mesangial cells is mediated by PDGF, but not bFGF. The increase in these cytoskeletal proteins appears to be regulated primarily (radixin) or partially (moesin) posttranscriptionally. The data suggest that PDGF mediated upregulation of the cytoskeletal proteins, moesin and radixin, is important for cell migration and other changes that accompany the coordinated restoration of glomerular architecture after injury.

Actins↗
PubMed1996

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

The role of the glomerular visceral epithelial cell in the physiologic turnover and pathologic breakdown of the glomerular extracellular matrix has remained largely unexplored. In this study a 98-kD neutral proteinase secreted by cultured rat visceral glomerular epithelial cells was shown to be a calcium, zinc-dependent enzyme secreted in latent form. In addition, the protein was heavily glycosylated and demonstrated proteolytic activity against Type I gelatin, Type IV collagen gelatin, and fibronectin. The similarity in molecular mass and substrate specificities to the 92-kD human matrix metalloproteinase-9 (MMP-9, or gelatinase B) suggested the identity of this activity, which was confirmed by immunoprecipitation and Northern blot analysis. The differences in molecular mass (98 vs. 92 kD) were not due to species-specific differences in glycosylation patterns, since cultured rat peritoneal macrophages secreted MMP-9 as a 92-kD enzyme. Furthermore, transfection of the human MMP-9 cDNA into rat glomerular epithelial cells yielded the 98-kD product. Using a specific monoclonal anti-MMP-9 antibody and in situ reverse transcription (ISRT) analysis of MMP-9 mRNA, the expression of this enzyme was evaluated in vivo. Normal rat glomeruli expressed little immunohistochemical or ISRT staining for MMP-9, while in rats with passive Heymann nephritis there was a major increase in MMP-9 protein and mRNA staining within the visceral epithelial cells. The temporal patterns of MMP-9 expression correlated with the period of proteinuria associated with this model, suggesting that a causal relationship may exist between GEC MMP-9 expression and changes in glomerular capillary permeability.

Animals↗
PubMed1996

Differential expression of transforming growth factor-beta isoforms and receptors in experimental membranous nephropathy.

In membranous nephropathy (MN) overproduction of matrix by glomerular epithelial cells (GEC) is believed to be responsible for glomerular basement membrane thickening and spikes. We studied experimental MN in rats (passive Heymann nephritis, PHN) at 5, 10 and 30 days. PHN rats exhibited a marked increase in GEC immunostaining for TGF-beta 2 at all time points. TGF-beta 3 staining was increased at day 10 only, and TGF-beta 1 was unchanged. Glomerular mRNA for TGF-beta 2 and -beta 3 was increased by day 5 when urine protein increased, whereas TGF-beta 1 was not. TGF-beta 2 bioactivity was increased at day 5. There was also a marked increase in GEC immunostaining for TGF-beta receptor type I (T beta IR) and TGF-beta receptor type II (T beta IIR) at all time points in PHN. mRNA levels for both receptors increased at day 5. Increases in protein expression and mRNA levels for the TGF-beta 2 and -beta 3 isoforms, and T beta IR and T beta RII were prevented by complement depletion. We conclude that complement-mediated injury to the GEC in vivo is associated with the up-regulation of TGF-beta 2 and -beta 3 isoforms, an increase in TGF-beta 2 bioactivity, and an increase in T beta RI and T beta RII expression. This contrasts with changes in TGF-beta 1 reported in mesangial disease, suggesting that TGF-beta 2 and -beta 3 may be important in diseases of the GEC. The differential expression of TGF-beta isoforms and receptors may be important determinants of the GEC response to injury.

Animals↗
PubMed1996

Transfected CD59 protects mesangial cells from injury induced by antibody and complement.

CD59 is a complement regulatory protein on the glomerular cells that inhibits C5b-9 assembly and insertion. We employed an overexpression strategy to determine the functional significance of CD59 in mesangial cells. We made a CD59 expression vector tagged with FLAG utilizing site-directed mutagenesis and PCR, which allows transfected CD59 to be distinguished from the constitutively expressed protein. In stable clones, overexpressed CD59 was clearly detected immunocytochemically both by anti-FLAG and anti-CD59 antibody in a granular pattern. The overexpression of CD59 was also confirmed by Western blotting. To determine if overexpression of CD59 by mesangial cells protected these cells from C5b-9 attack, we performed complement-mediated cell lysis assays. CD59-transfected mesangial cells demonstrated marked resistance to complement-mediated cell lysis which was reversed in the presence of antibody to CD59. We also investigated the role of CD59 in protecting cells from the effects of membrane insertion of sublytic quantities of C5b-9. Overexpressed CD59 suppressed production of superoxide, one of the inflammatory mediators induced by sublytic C5b-9 attack. These results demonstrate directly that transfected CD59 functions as a potent protector of mesangial cells against both lytic and sublytic attack by C5b-9. CD59 may be an important regulator of complement-mediated disease in the glomerular mesangium.

Animals↗
PubMed1996

Changes in cell-cycle protein expression during experimental mesangial proliferative glomerulonephritis.

A characteristic response to mesangial cell injury is proliferation, which is closely linked to mesangial matrix accumulation and the progression of glomerular disease. Cell proliferation in non-renal cells in vitro is regulated at the level of the cell-cycle by specific cyclins and their catalytic partners, cyclin dependent kinases (CDK). Cyclin kinase inhibitors (CKI) prevent proliferation by inhibiting cell-cycle progression. However, the expression of cell-cycle regulatory proteins in the kidney and in renal disease is unknown. To determine this we studied the expression of cell-cycle proteins in vivo in normal rats and rats with experimental mesangial proliferative glomerulonephritis (Thy1 model). Normal quiescent rat glomeruli have a differential expression for CKI's, where p27Kip1 is highly expressed, and the levels for p21 (Cip1, Waf1, Sdi1, Cap20) (p21) are low. The onset of mesangial cell proliferation in Thy1 glomerulonephritis is associated with a reduction in p27Kip1 levels when mesangial cell proliferation is maximal. Mesangial cell proliferation in vivo is also associated with an increase in glomerular expression of cyclin A, and an increase in expression and activity for CDK2. The resolution of mesangial cell proliferation was associated with a return to baseline levels for p27Kip1, while the expression for p21 increased substantially. Furthermore, mesangial cell p21 expression was maintained following the resolution of proliferation. These results provide evidence for a complex interplay of cell-cycle regulatory proteins during the glomerular response to injury in vivo. The marked increase in CDK2 expression during mesangial cell proliferation and the sustained increase in p21 expression following the resolution of mesangial cell proliferation suggests that the in vivo expression of certain cell-cycle proteins may differ from that described in non-renal cells in vitro.

Animals↗
PubMed1996

Role of the complement membrane attack complex (C5b-9) in mediating experimental mesangioproliferative glomerulonephritis.

Previous studies have demonstrated that most pathologic changes in the antithymocyte serum (ATS) model of mesangioproliferative glomerulonephritis are complement-dependent. These include mesangiolysis, glomerular platelet infiltration, mesangial cell proliferation, mesangial cell production of growth factors and phenotypic change to express alpha-actin, glomerular macrophage infiltrate, mesangial matrix expansion, and proteinuria. The mechanism by which complement mediates these effects has not been defined. Because neutrophils do not participate in the ATS model, we hypothesized that the complement effects observed are consequent to glomerular cell insertion of the C5b-9 membrane attack complex of complement. This hypothesis was tested utilizing PVG rats which exhibit an absence of C6 inherited in an autosomal recessive pattern. C6 deficient (C-) PVG rat serum activated by zymosan produced normal amounts of C5a compared to normocomplementemic (C+) PVG rat controls but no C5b-9. When ATS was induced, C- PVG rats had a significant and marked reduction in mesangiolysis, platelet infiltration, mesangial cell proliferation, alpha-actin expression, macrophage infiltration, collagen IV deposition, and proteinuria compared to C+ controls. The reduction in each of these parameters was comparable to that achieved by systemic complement depletion of C+ PVG rats with cobra venom factor. These findings establish the role of C5b-9 in mediating each of the complement-dependent features of the ATS model and indicate that C5b-9 accounts for all of the complement-mediated effects observed. This study provides the first documentation of a functional role for C5b-9 in mediating a non-membranous inflammatory type of glomerular injury in vivo.

Animals↗
PubMed1996

SPARC is expressed in renal interstitial fibrosis and in renal vascular injury.

Tubulointerstitial inflammation and fibrosis are critical determinants for renal function and prognosis in a variety of human nephropathies. Yet, the pathophysiology of the injury remains obscure. We investigated the expression of SPARC (secreted protein acidic and rich in cysteine) by immunohistochemistry and in situ hybridization in experimental models characterized by tubulointerstitial fibrosis and matrix expansion in rats. SPARC is a secreted glycoprotein that has been demonstrated to affect cellular interaction with matrix proteins, modulate cell proliferation, bind to and/or inhibit growth factors such as PDGF and bFGF, and regulate angiogenesis. Interstitial expression of SPARC was most prominent in passive Heyman nephritis (PHN), chronic cyclosporine A (CsA) nephropathy, and the remnant kidney model and, to a lesser extent, in angiotensin II (Ang II)-infused animals. SPARC protein and mRNA were substantially increased at sites of tubulointerstitial fibrosis/matrix expansion. In the PHN model, SPARC protein was expressed by interstitial fibroblasts that also produced alpha-smooth muscle actin ("myofibroblasts") and correlated both temporally (r = 0.97) and spatially with sites of type I collagen deposition. Interstitial cell proliferation preceded the development of interstitial fibrosis, and maximal SPARC expression (d15) coincided with the initial decline in interstitial proliferation. In the Ang II-infusion model, which is characterized by arteriolopathy and tubulointerstitial injury, an increase in SPARC protein and mRNA was also seen in injured blood vessels. SPARC was shown to be expressed by vascular smooth muscle cells and also by cells in the adventitia of hypertrophied arteries. In summary, SPARC was transiently expressed by interstitial fibroblasts at sites of tubulointerstitial injury and fibrosis, and by smooth muscle cells and cells in the adventitia of injured arteries in the Ang II-model. In addition to its proposed role in extracellular matrix deposition. the antiproliferative properties of SPARC might contribute to the resolution of interstitial fibroblast proliferation in the PHN model.

Actins↗
PubMed1996

Beneficial effects of systemic immunoglobulin in experimental membranous nephropathy.

To test the hypothesis that systemic administration of immunoglobulin might reduce glomerular injury in membranous nephropathy through mechanisms involving inhibition of complement activation, we studied the passive Heymann nephritis (PHN) model of membranous nephropathy in rats. The daily administration of immunoglobulin goat IgG (600 mg/kg i.p.) reduced proteinuria by 52%. Quantitative immunohistochemical analysis showed that the glomerular deposition of C3c, an indicator of ongoing complement attack, and of C5b-9 was significantly decreased in the immunoglobulin treated group, while deposition of anti-Fx1A was not affected. Electron microscopic analysis demonstrated that the extent of subepithelial immune complexes did not appreciably differ between treated and control animals. Systemic complement levels were not altered by immunoglobulin treatment. These data suggest that the reduction in proteinuria that resulted from systemic immunoglobulin administration was mediated by modifying the effect of complement induced glomerular injury. This interpretation was further supported by in vitro data that documented a significant reduction in C5b-9 induced glomerular epithelial cell lysis in the presence of both goat and rat IgG. These results indicate that systemic administration of immunoglobulin can substantially reduce ongoing complement activation in the glomerulus in PHN rats and that this effect is associated with a significant reduction in glomerular injury.

Animals↗
PubMed1996

Mechanisms involved in the pathogenesis of tubulointerstitial fibrosis in 5/6-nephrectomized rats.

The 5/6 nephrectomy model is used to study pathogenetic mechanisms underlying chronic renal failure. We previously demonstrated that increased mesangial cell proliferation and glomerular PDGF B-chain expression precede glomerulosclerosis in this model. In the present study we have assessed the concomitant changes in the cortical tubulointerstitium. A wave of tubular and interstitial cell proliferation (as determined by immunostaining for PCNA) occurred at week 1 after 5/6 nephrectomy. This wave preceded the peak glomerular cell proliferation by one week. Tubulointerstitial cell proliferation decreased thereafter and reached control values by week 10. In situ hybridization and immunostaining for PDGF B-chain and beta-receptor in sham-operated controls showed labeling of distal tubules and collecting ducts, while no signal was present in the interstitium. PDGF B-chain mRNA and protein expression was markedly increased in tubules at weeks 2 and 4 after 5/6 nephrectomy and in the interstitium (particularly in areas of inflammatory infiltrates) at weeks 2 to 10. Similar changes occurred with PDGF receptor beta-subunit immunostaining. Interstitial expression of desmin and alpha-smooth muscle actin (markers of myofibroblasts) progressively increased after week 1. Interstitial influx of monocytes/macrophages with focal accentuation started at week 2. Counts of lymphocytes, neutrophils and platelets showed only minor changes. In parallel to the monocyte/macrophage influx, progressive interstitial accumulation of collagens I and IV, laminin, and fibronectin occurred. All of these changes were correlated with the increase in serum creatinine, proteinuria and an index of tubulointerstitial damage. We conclude that tubulointerstitial changes after 5/6 nephrectomy show similarities with those observed in the glomeruli. Tubular and interstitial overexpression of PDGF B-chain and its receptor may play a role in mediating fibroblast migration and/or proliferation in areas of tubulointerstitial injury.

Actins↗
PubMed1996

Phosphodiesterase inhibitors correct resistance to natriuretic peptides in rats with Heymann Nephritis.

Experimental nephrotic syndrome is characterized by abnormal sodium metabolism, reflected in a blunted natriuretic response both to volume expansion and to infused atrial natriuretic peptide (ANP). The studies presented here examined the relationships among plasma ANP concentration and urinary sodium (VNaV) and cyclic GMP excretion (UcGMPV) in vivo, and the responsiveness of isolated glomeruil and inner medullary collecting duct (IMCD) cells to ANP and urodilatin (renal natriuretic peptide; RNP) in vitro in rats with Heymann nephritis, an immunologically mediated model of nephrotic syndrome. Nine to 14 days after Ip injection of anti-Fx1A antiserum, rats were proteinuric and had a blunted natriuretic response to intravenous infusion of isotonic saline (2% body weight, given over 5 min). Thirty min after the onset of the infusion, plasma ANP concentration was increased to the same extent in both normal and nephritic rats, compared with their respective hydropenic controls. Despite this increase, UcGMPV was significantly less in nephritic rats after the saline infusion. Accumulation of cGMP by isolated glomeruil and IMCD cells from nephritic rats after incubation with ANP and RNP was also significantly reduced, compared with normal rats. This difference was not related to differences in either density or affinity of renal ANP receptors, but was abolished when accumulation of cGMP was measured in the presence of 10(-3) M isobutylmethylxanthine or Zaprinast, two different inhibitors of cyclic nucleotide phosphodiesterases (PDE). Infusion of Zaprinast into one renal artery in nephritic rats normalized both the natriuretic response to volume expansion and the increase in UcGMPV from the infused, but not the contralateral, kidney. Furthermore, cGMP-PDE activity was increased in IMCD cell homogenates from nephritic compared with normal rats (388 +/- 32 versus 198 +/- 93 pmol/min per mg protein, P < 0.03). These results indicate that blunted volume expansion natriuresis accompanied by cellular resistance to ANP in vitro occurs in an immunologic model of renal injury. The resistance is not related to an alteration in ANP release or binding to its renal receptors, but is suppressed by PDE inhibitors and is associated with increased renal cGMP. PDE activity, thus suggesting that enhanced cGMP-PDE activity may account for resistance to the natriuretic actions of ANP observed in vivo. This defect may represent the intrinsic sodium transport abnormality linked to sodium retention in nephrotic syndrome.

1-Methyl-3-isobutylxanthine↗
PubMed1996

SPARC is expressed by mesangial cells in experimental mesangial proliferative nephritis and inhibits platelet-derived-growth-factor-medicated mesangial cell proliferation in vitro.

Mesangial cell proliferation is a characteristic feature of many glomerular diseases and often precedes extracellular matrix expansion and glomerulosclerosis. This study provides the first evidence that SPARC (secreted protein acidic and rich in cysteine) could be an endogenous factor mediating resolution of experimental mesangial proliferative nephritis in the rat. SPARC is a platelet-derived-growth-factor-binding glycoprotein that inhibits proliferation of endothelial cells and fibroblasts. We now show that SPARC is synthesized by mesangial cells in culture and that SPARC mRNA levels are increased by platelet-derived growth factor and basic fibroblast growth factor. Recombinant SPARC or the synthetic SPARC peptide 2.1 inhibited platelet-derived-growth-factor-induced mesangial cell DNA synthesis in vitro. In a model of experimental mesangioproliferative glomerulonephritis, SPARC mRNA was increased 5-fold by day 7 and was identified in the mesangium by in situ hybridization. Similarly, SPARC was increased in glomerular mesangial cells and visceral epithelial cells by day 5 and reached maximal expression levels by day 7. Mesangial cell proliferation increased by 36-fold on day 5 and decreased abruptly on day 7. Maximal expression of SPARC was correlated with the resolution of mesangial cell proliferation. We propose that SPARC functions in part as an endogenous inhibitor of platelet-derived-growth-factor-mediated mesangial cell proliferation in glomerulonephritis and that it could account for the resolution of cellular proliferation in this disease.

Amino Acid Sequence↗
PubMed1995

Cellular events in the evolution of experimental diabetic nephropathy.

In several models of progressive glomerular disease, mesangial cell proliferation, phenotypic change and increased growth factor expression precede up-regulation of genes for extracellular matrix components (ECM) and mesangial expansion. To examine these events in diabetic nephropathy (DN) we conducted sequential studies of glomeruli in rats with streptozotocin induced DN. We found prominent mesangial cell proliferation at three days (4.34 +/- 2.24 PCNA + cells/glom vs. 1.6 +/- 0.74 in controls, P < 0.001) associated with increased alpha-actin expression. PDGF B-chain mRNA was slightly increased at day one, and PDGF B-chain immunostaining was slightly increased at days one and six. Staining for bFGF was significantly increased at three days (2.2 +/- 0.6 vs. 1.2 +/- 0.1 in controls, P < 0.01). There was also an early increase in platelets in glomeruli of diabetic animals, and platelet depletion significantly inhibited the early phase of proliferation. In addition to mesangial cell proliferation, a prominent glomerular macrophage infiltration began at day three and peaked at day 30 (3.94 +/- 1.47 vs. 2.08 +/- 1.13 in controls, P < 0.01). TGF-beta mRNA increased at days 14 and 30. Insulin treatment prevented mesangial cell proliferation, actin expression, and macrophage infiltration, and normalized TGF-beta expression at 14 and 30 days. These multiple cellular events preceded any detectable increases in glomerular gene expression or deposition of collagen I, IV or laminin.

Animals↗
PubMed1995

Non-iron mediated alteration in hepatic transferrin gene expression in the nephrotic rat.

Both transferrin and the iron it carries are lost in the urine in the nephrotic syndrome. Patients may develop hypochromic microcytic anemia and synthesis of transferrin, a protein regulated in large part by iron availability, is increased. Transferrin synthesis has also been reported to be increased in liver slices from rats with hereditary analbuminemia, and their plasma transferrin levels are increased, suggesting that transferrin synthesis may be stimulated by processes other than iron depletion in this hypoalbuminemic condition. Transferrin metabolism was studied in rats with Heymann nephritis (HN), in a strain of Sprague-Dawley (SD) rats with hereditary analbuminemia [Nagase analbuminemic rats (NAR)], and in normal SD rats. Plasma transferrin concentration and mass was decreased significantly in HN, but increased in NAR. Transferrin synthesis was increased both in NAR (measured either as the disappearance of [125I] labeled transferrin or as the incorporation of [3H] phenylalanine) and in HN (incorporation of [3H] phenylalanine). The fractional rate of transferrin catabolism was unchanged in NAR. Thus transferrin mass was increased in NAR entirely as a consequence of increased synthesis. Transferrin and albumin synthesis correlated with one another in both HN and SD (P < 0.001). Transferrin mRNA was increased in both HN and NAR and was unaffected by administration of iron to HN. Hepatic transferrin and albumin mRNA levels were also correlated positively in HN and SD, suggesting that increased hepatic synthesis of both proteins might be responding to the same stimuli. Transferrin gene transcription was increased in both HN and NAR and was unaffected by administration of iron to HN. Transferrin mRNA was not increased in the testis in either HN or NAR, suggesting that augmentation in transferrin gene expression is driven by a non-iron dependent process and is confined to the liver.

Albumins↗
PubMed1995

Cyclosporine A induced arteriolopathy in a rat model of chronic cyclosporine nephropathy.

Chronic cyclosporine (CsA) nephrotoxicity is a major complication of heart, bone marrow, and renal transplantation, and is characterized in humans by striped interstitial fibrosis, tubular dilatation and atrophy, and hyalinization of hilar arterioles. This last feature is highly specific for cyclosporine injury and has been difficult to reproduce in normotensive animal models. Salt-depletion has been shown to sensitize rodents to the effects of CsA and accelerate the disease process. We conducted sequential studies in chronically salt depleted, pair fed rats treated with CsA (15 mg/kg, s.c.) or an equivalent dose of olive oil vehicle, and found a histologic lesion associated with CsA that consisted of striped cortical interstitial fibrosis, tubular dilatation and atrophy, and hyalinization of many afferent arterioles. The arteriolopathy was first detected at day 10 with progressive hyalinization of arterioles continuing until termination of the study at day 35. The arteriolopathy consisted initially of eosinophilic granular transformation of smooth muscle cells comprising afferent hilar glomerular arterioles, and progressed to foci of smooth muscle cell vacuolization and accumulation of discrete hyaline deposits in vessel walls. Electron microscopy demonstrated marked accumulation of typical renin granules throughout the smooth muscle cell cytoplasm, corresponding to the eosinophilic granular transformation revealed histologically. Immunocytochemistry confirmed the up-regulated production of renin in these vessels. This study documents a rodent model for CsA arteriolopathy and CsA-associated interstitial fibrosis that strikingly reproduces the most characteristic nephropathic effects of cyclosporine found in human patients treated with this agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Cellular proliferation and macrophage influx precede interstitial fibrosis in cyclosporine nephrotoxicity.

Chronic cyclosporine (CsA) nephrotoxicity is a major complication of solid organ transplantation, and is characterized histologically by striped tubulointerstitial fibrosis, tubular atrophy, and hyalinization of the afferent arteriole, a highly specific finding in cyclosporine injury. The salt-depleted rat model of chronic cyclosporine nephropathy mimics these lesions in humans. We conducted sequential studies of this model in groups of pair fed rats (N = 6) treated with CsA (15 mg/kg, s.q.) or an equivalent dose of olive oil. Proliferation of tubular and interstitial cells was documented early in the medulla by day 5 (3.2 +/- 2.1 vs. 0.81 +/- 0.4 cells/HPF in CsA vs. control, P < 0.02), and was maximal in areas of interstitial fibrosis by day 35 (7.9 +/- 3.7 vs. 0.52 +/- 0.2 cells/HPF in CsA vs. control, P < 0.005). The interstitial fibrosis was associated with a significant macrophage influx by day 35 (13.9 +/- 3.5 vs. 1.5 +/- 0.32 cells/HPF, CsA vs. control, P < 0.005), which correlated with increased cortical tubular staining for the macrophage adhesion protein, osteopontin. Elevated serum creatinine correlated with interstitial fibrosis at day 35 (0.85 +/- 0.11 vs. 0.40 +/- 0.03 mg/dl Cr, CsA vs. control, P < 0.005) by linear regression (r = 0.9, P < 0.05). Medullary proliferation and interstitial fibrosis correlated with decreased tubular concentrating ability, and higher urinary volume. Cortical interstitial fibrosis was maximal at day 35 and was associated with an increase in type I and type IV collagen deposition, while tubular injury was associated with increased vimentin expression. Tubular interstitial cells also expressed increased vimentin early in the medulla (day 10) and later in the cortex. Both groups remained normotensive despite significantly elevated juxtaglomerular (JG) apparatus renin expression in CsA treated animals, implicating the intrarenal-renal renin-angiotensin system in this disease. We conclude that cyclosporine nephrotoxicity is associated with early tubular and interstitial cell proliferation, and a significant macrophage influx that precedes the development of cortical interstitial fibrosis and afferent arteriolar hyalinosis. These early cellular changes correlate with functional abnormalities including decreased creatinine clearance (CCr) and decreased medullary concentrating ability, which stabilized despite progressive fibrosis. These cellular events may be important in the pathogenesis of chronic CsA nephrotoxicity.

Animals↗