Expression of smooth muscle cell phenotype by rat mesangial cells in immune complex nephritis. Alpha-smooth muscle actin is a marker of mesangial cell proliferation

Thy-1-mediated phosphatidylinositol turnover in cultured rat glomerular mesangial cell

Thy-1 glycoprotein is expressed in rat glomerular mesangial cells, and anti-Thy-1 nephritis induced by anti-Thy-1 antibodies is a model of human renal diseases. In this study, we examined Thy-1-mediated biological reactions in cultured rat glomerular mesangial cells utilizing two anti-Thy-1 monoclonal antibodies (mAbs), 1-22-3 and OX-7. Incubation of the cells with these mAbs resulted in increased inositol trisphosphate (IP3) levels. The rise in IP3 produced by mAb 1-22-3 was greater than that produced by mAb OX-7 at the same dose. Incubation of mesangial cells with these mAbs resulted in an increase in the intracellular free calcium concentration ([Ca2+]i). mAb 1-22-3 induced a sustained increase in [Ca2+]i, while that induced by mAb OX-7 lasted 1-2 min, then decreased to the basal level. An transient increase in [Ca2+]i was also observed in Ca(2+)-free medium, indicating that these [Ca2+]i increases are due to release of Ca2+ from internal stores by IP3 without calcium flux across cell membrane. When cells were pretreated with protein tyrosine kinase (PTK) inhibitors (herbimycin A or genistein), Thy-1-mediated increases in [Ca2+]i were inhibited. These data suggest that Thy-1 induces the production of IP3 (including inositol 1,4,5-triphosphate, an intracellular Ca(2+)-releasing factor) and that PTKs may contribute to the Thy-1-mediated elevation of [Ca2+]i which presumably results from phospholipase C activation following Thy-1-mediated signaling in rat mesangial cells.

Suppression of mesangial proliferative glomerulonephritis development in rats by inhibitors of cAMP phosphodiesterase isozymes types III and IV

Excessive mesangial cell (MC) proliferation is a hallmark of many glomerulopathies. In our recent study on cultured rat MC (Matousovic, K., J.P. Grande, C.C.S. Chini, E.N. Chini, and T.P. Dousa. 1995. J. Clin. Invest. 96:401-410) we found that inhibition of isozyme cyclic-3',5'-nucleotide phosphodiesterase (PDE) type III (PDE-III) suppressed MC mitogenesis by activating cAMP-dependent protein kinase (PKA) and by decreasing activity of mitogen-activated protein kinase (MAPK). We also found that inhibition of another PDE isozyme, PDE-IV, suppresses superoxide generation in glomeruli (Chini, C.C.S., E.N. Chini, J.M. Williams, K. Matousovic, and T.P. Dousa. 1994. Kidney Int. 46:28-36). We thus explored whether administration in vivo of the selective PDE-III antagonist, lixazinone (LX), together with the specific PDE-IV antagonist, rolipram (RP), can attenuate development of mesangioproliferative glomerulonephritis (MSGN) induced in rats by anti-rat thymocyte serum (ATS). Unlike the vehicle-treated MSGN rats, rats with MSGN treated with LX and RP did not develop proteinuria and maintained normal renal function when examined 5 d after injection of ATS. In PAS-stained kidneys from PDE-antagonists-treated MSGN-rats the morphology of glomeruli showed a reduction in cellularity compared with control rats with ATS. Compared with MSGN rats receiving vehicle, the MSGN rats receiving PDE-antagonists had less glomerular cell proliferation (PCNA delta -65%), a significantly lesser macrophage infiltration (delta -36% ED-1) and a significant reduction of alpha-smooth muscle actin expression by activated MC; in contrast, immunostaining for platelet antigens and laminin were not different. The beneficial effect of PDE inhibitors was not due to a moderate decrease (approximately -20%) in systolic blood pressure (SBP); as a similar decrease in SBP due to administration of hydralazine, a drug devoid of PDE inhibitory effect, did not reduce severity of MSGN in ATS-injected rats. We conclude that antagonists of PDE-III and PDE-IV administered in submicromolar concentrations in vivo to ATS-injected rats can decrease the activation and proliferation of MC, inhibit the macrophage accumulation, and prevent proteinuria in the acute phase of MSGN. We propose that PDE isozyme inhibitors act to block (negative "crosstalk") the mitogen-stimulated intracellular signaling pathway which controls MC proliferation due to activating of the cAMP-PKA pathway. These results suggest that antagonists of PDE-111 and IV may have a suppressive effect in acute phases or relapses of glomerulopathies associated with MC proliferations.

The cellular derivation and the life span of the myofibroblast

The presence of myofibroblasts in granulation tissue and various fibrotic settings is well established. Recent work on this cell has shown that myofibroblasts derive mainly from local fibroblasts, but also from pericytes and smooth muscle cells as well as from specialized cells such as perisinusoidal stellate cells of the liver and mesangial cells of the kidney glomerulus. During the healing of an open wound, myofibroblasts disappear by means of apoptosis when the wound is closed and granulation tissue gradually transforms into scar tissue. The possibility exists that an altered regulation of this process leads to the development of a hypertrophic scar.

CD44 in glomerulonephritis: expression in human renal biopsies, the Thy 1.1 model, and by cultured mesangial cells

CD44 is a transmembrane proteoglycan that serves as a cell adhesion receptor and is involved in cell-cell and cell-matrix interactions, both key events in the pathogenesis of clinical and experimental glomerulonephritis. In addition, recent evidence suggests that the binding of cytokines to proteoglycans could regulate cytokine function. We have, therefore, studied the expression of CD44 by mesangial cells in culture and in experimental (Thy 1.1 model) and human glomerulonephritis. Mesangial expression of CD44 detected by immunohistochemistry was markedly increased four days after induction of the Thy 1.1 model, coinciding with the peak of mesangial cell proliferation and macrophage infiltration. Analysis of 92 human renal biopsies by immunohistochemistry showed that CD44 expression by infiltrating cells within the glomerulus, in focal interstitial infiltrates and within the interstitium (interstitial fibroblasts, and extracellular matrix), was significantly increased in biopsies with a greater degree of histological damage. There was, however, no increase in mesangial staining in diseased kidneys as compared with control sections. In contrast, cultured human mesangial cells expressed CD44 strongly when assayed by immunohistochemistry, immunoprecipitation and Northern blotting. CD44, therefore, is an example of a protein strongly expressed by mesangial cells in vitro and weakly or not at all in vivo, but which is up-regulated in a disease model. In human disease, however, little expression was detected within the glomerular mesangium, which may be related to the greater proliferation and more profound disruption of mesangial architecture seen in the Thy 1.1 model. CD44 expression by infiltrating cells and by components of the interstitium could, however, play an important role in the pathogenesis of chronic progressive renal disease in humans.

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

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

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.

Role of endothelin as a mitogen in experimental glomerulonephritis in rats

Recent studies have revealed that endothelin-1 (ET-1) is a potent mitogen for mesangial cells in vitro. To determine whether ET-1 exerts the mitogenic action on mesangial cells in vivo, we examined the glomerular expression of ET-1 and its receptors in a rat model of mesangial proliferative glomerulonephritis and assessed the effect of a specific endothelin A (ET(A)) receptor antagonist, FR139317, on mesangial cell proliferation in this model. The levels of preproET-1 mRNA expression and ET-1 protein production in glomeruli increased markedly on days 4 and 7 after disease induction, and the levels changed in concordance with the glomerular cell proliferation. In contrast, the level of ET(A) receptor mRNA initially decreased on day 1, and thereafter increased on days 4 and 7. Administration of FR139317 to rats with experimental glomerulonephritis induced a significant reduction in mesangial cell proliferation. In addition, in situ hybridization of preproET-1 mRNA and double-immunolabeling of ED-1 and OX-7 in a mirror image section revealed that the principal cell expressing ET-1 in glomeruli were infiltrating macrophages on day 1, and they were replaced by mesangial cells on day 4. These findings indicate that ET-1 functions as a potent mitogen for mesangial cells in vivo in an autocrine or paracrine fashion.

Expression of a nonmuscle myosin heavy chain in glomerular cells differentiates various types of glomerular disease in rats

To characterize the phenotypic modulation of mesangial and glomerular epithelial cells, we investigated the expression of a nonmuscle type myosin heavy chain, SMemb, and alpha-smooth muscle actin (alpha-SM actin) in rat experimental glomerular diseases, which included anti-Thy 1 nephritis, 5/6 nephrectomy, diabetes, and anti-glomerular basement membrane nephritis. SMemb was only slightly expressed in normal glomerular epithelial cells but not in mesangial cells. In the anti-Thy 1 nephritis rats, both SMemb and alpha-SM actin were most conspicuously induced in mesangial cells. However, the expression profile was shifted from alpha-SM actin to SMemb dominant pattern over the course of glomerulonephritis. The expression of SMemb was also increased in epithelial cells in this model. In the other three models, glomerular cells did not express alpha-SM actin, but did so for SMemb. In the nephrectomized and the diabetic rats SMemb was newly expressed in mesangial cells at earlier stages, but at later stages was remarkably enhanced in epithelial cells when severe glomerular hypertrophy developed. In the anti-GBM nephritis rats, SMemb expression was increased in epithelial cells. In all models examined, mesangial and epithelial expression of SMemb was confirmed by immunoelectron microscopy, and enhanced expression of SMemb mRNA in glomeruli was verified by RNase protection assay. We conclude from these results that glomerular cells change their phenotypes differently depending on various types of glomerular diseases. These phenotypic changes in glomerular cells can be revealed by the combined immunostaining for SMemb and alpha-SM actin. SMemb is especially useful to detect both mesangial and glomerular epithelial cell activation in these glomerular disease models. Understanding the functional difference and regulatory mechanisms of these cytoskeletal proteins will provide insight into the pathogenesis and progression of glomerular diseases.

Increased expression of a brain/embryo-type myosin heavy chain isoform (MIIB2) in mesangial proliferative glomerulonephritis

Proliferation of mesangial cells is frequently found in glomerulonephritis, such as IgA glomerulonephritis. Recent reports suggest that a brain/embryo-type myosin isoform (MIIB2) is involved in cell proliferation. We have studied the expression of MIIB2 in renal biopsy samples from patients with various renal diseases and in the renal tissues from the rat model of mesangial proliferative glomerulonephritis induced with anti-Thy 1.1 antibody. Immunohistochemical analysis of the biopsy samples using an anti-brain-type myosin heavy chain-specific monoclonal antibody (HBM1) indicated that 92% of the samples from patients with IgA glomerulonephritis contained a significant population of mesangial cells that reacted with the antibody. Most of the samples from patients with other types of proliferative glomerular diseases also contained HBM1-reactive mesangial cells, while none of the samples from patients with non-proliferative glomerular diseases contained a significant population of HBM1-reactive mesangial cells. The expression of a brain/embryo-type myosin heavy chain isoform (MIIB2) in the mesangial cells began at five days after injection of anti-Thy 1.1 antibody and peaked at the tenth day. On the other hand, the expression of the proliferating cell nuclear antigen in the mesangial cells was induced at two days after injection of anti-Thy 1.1 antibody and was maximal at the fourth day. These results indicate that the expression of the MIIB2 isoform by mesangial cells is accelerated in proliferative glomerulonephritis and suggest that the myosin isoform is involved in the phenotypic transformations of the glomerular tissues rather than in the cell proliferation.

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.

Platelet-derived growth factor-BB induces renal tubulointerstitial myofibroblast formation and tubulointerstitial fibrosis

Tubulointerstitial fibrosis correlates closely with renal function, although the mechanism regulating tubulointerstitial fibrogenesis remains poorly understood. Since platelet-derived growth factor (PDGF) is a growth factor for fibroblasts, we examined the effect of daily (for 7 days) PDGF-AA or PDGF-BB administration on renal tubulointerstitial architecture in rats. PDGF-AA administration at a dose of 5 mg/kg did not affect the renal tubulointerstitium. By comparison, PDGF-BB induced dose-dependent renal tubulointerstitial cell proliferation and fibrosis. At 5 mg/kg, PDGF-BB increased BrdU labeling in tubulointerstitial fibroblasts at 24 hours (19-fold), which peaked at 72 hours (23-fold) with bromodeoxyuridine uptake returning to control values by 7 days. Tubulointerstitial proliferation was associated with the differentiation of these cells into myofibroblasts as evidenced by alpha-smooth muscle actin expression beginning on day 3. The expression of alpha-smooth muscle actin peaked on day 5 and had markedly declined by day 21. In addition, apoptotic cells were identified within the tubulointerstitium on day 3 and progressively increased through day 7, suggesting that the disappearance of myofibroblasts may have occurred through apoptosis. These changes were accompanied by increased expression of alpha 1 (III) collagen mRNA and interstitial accumulation of type III collagen within the renal cortex. By morphometric analysis, an approximately twofold increase in collagen III immunolabeling within the interstitial compartment was evident at 24 hours and peaked on days 5 to 7 (approximately fourfold). These data suggest that PDGF-BB may be an important mediator of tubulointerstitial hyperplasia and fibrosis.

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.

Proto-oncogene expression in human glomerular diseases

The expression of the protein products and mRNA of c-fos, c-myc, p53, and c-raf was examined in normal renal tissues and biopsy specimens from 73 patients with various glomerular diseases. Immunofluorescent staining showed that there were cell nuclei stained for c-Fos, c-Myc, and p53, and cytoplasm positive for c-Raf, in the glomeruli of patients with proliferative types of glomerulonephritis, including IgA nephritis and lupus nephritis, and in patients with focal glomerular sclerosis. Glomerular expression of c-fos and c-myc mRNA was detected by in situ hybridization. The number of proto-oncogene-positive glomerular cells was significantly higher in lupus nephritis, IgA nephritis, and focal segmental sclerosis, as compared with minimal change nephrotic syndrome and normal specimens. In IgA nephritis, the population of glomerular cells positive for c-Fos and c-Myc and the grade of c-Raf immunoreactivity were significantly correlated with the proportion of proliferating cell nuclear antigen (PCNA)-positive glomerular cells, with histological grading of mesangial hypercellularity and matrix increase, and with the magnitude of proteinuria. These data indicate that proto-oncogene expression is associated with mesangial proliferation and matrix expansion in proliferative types of glomerulonephritis and in focal glomerular sclerosis.

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.

Identification of platelet-derived growth factor A and B chains in human renal vascular rejection

Platelet-derived growth factor (PDGF) exists as a dimer composed of two homologous but distinct peptides termed PDGF-A and -B chains, and may exist as AA, AB, and BB isoforms. The PDGF-B chain has been implicated as a mediator of renal vascular rejection by virtue of up-regulated expression of its receptor, PDGF beta-receptor, in affected arteries. A role for PDGF-A chain in mediating intimal proliferation has been suggested in human atherosclerosis (Rekhter MD, Gordon D: Does platelet-derived growth factor-A chain stimulate proliferation of arterial mesenchymal cells in human atherosclerotic plaques? Circ Res 1994, 75:410), but no studies of this molecule in human renal allograft injury have been reported to date. We used two polyclonal antisera to detect expression of PDGF-A chain and one monoclonal antibody to detect PDGF-B chain by immunohistochemistry in fixed, paraffin-embedded tissue from 1) normal adult kidneys, 2) a series of renal transplant biopsies chosen to emphasize features of vascular rejection, and 3) allograft nephrectomies. Immunohistochemistry was correlated with in situ hybridization on adjacent, formalin fixed tissue sections from nephrectomies utilizing riboprobes made from PDGF-A and -B chain cDNA. PDGF-A chain is widely expressed by medial smooth muscle cells of normal and rejecting renal arterial vessels of all sizes by immunohistochemistry and in situ hybridization. PDGF-A chain is also expressed by a population of smooth muscle cells (shown by double immunolabeling with an antibody to alpha-smooth muscle actin) comprising the intima in chronic vascular rejection. In arteries demonstrating acute rejection, up-regulated expression of PDGF-A chain by endothelial cells was detected by both immunohistochemistry and in situ hybridization. In contrast, PDGF-B chain was identified principally in infiltrating monocytes within the rejecting arteries, similar to its localization in infiltrating monocytes in human atherosclerosis. Although less prominent than the case for PDGF-A chain, PDGF-B chain also was present in medial and intimal smooth muscle cells in both rejecting and nonrejecting renal arteries. PDGF-A and -B chains have now been localized at both the mRNA and protein levels to the intimal proliferative lesions of vascular rejection. These peptides, which are known stimuli for smooth muscle cell migration and proliferation in experimental vascular injury, may have similar stimulatory effects on smooth muscle cells in an autocrine and/or paracrine manner to promote further intimal expansion and lesion progression in this form of human vasculopathy.

Basic fibroblast growth factor augments podocyte injury and induces glomerulosclerosis in rats with experimental membranous nephropathy

Podocyte injury is believed to contribute to glomerulosclerosis in membranous nephropathy. To identify the factors involved, we investigated the effects of basic fibroblast growth factor (bFGF), a cytokine produced by podocytes, on rats with membranous nephropathy (passive Heymann nephritis [PHN]). All rats received a daily i.v. bolus of 10 microg bFGF or vehicle from days 3-8 after PHN induction. In proteinuric PHN rats on day 8, bFGF injections further increased proteinuria. Podocytes of bFGF-injected PHN rats showed dramatic increases in mitoses, pseudocyst formation, foot process retraction, focal detachment from the glomerular basement membrane, and desmin expression. bFGF injections in PHN rats did not alter antibody or complement deposition or glomerular leukocyte influx. bFGF-injected PHN rats developed increased glomerulosclerosis when compared with control PHN rats. Also, bFGF induced proteinuria and podocyte damage in rats injected with 10% of the regular PHN-serum dose. None of these changes occurred in bFGF-injected normal rats, complement-depleted PHN rats or rats injected with 5% of the regular PHN serum dose. These divergent bFGF effects were explained in part by upregulated glomerular bFGF receptor expression, induced by PHN serum. Thus, bFGF can augment podocyte damage, resulting in increased glomerular protein permeability and accelerated glomerulosclerosis. This bFGF action is confined to previously injured podocytes. Release of bFGF from glomerular sources (including podocytes themselves) during injury may represent an important mechanism by which podocyte damage is enhanced or becomes self sustained.

Thrombospondin 1 is expressed by proliferating mesangial cells and is up-regulated by PDGF and bFGF in vivo

Thrombospondin 1 has been shown to be linked to PDGF-mediated mesangial cell proliferation and migration in vitro, but little is known regarding its expression or regulation in glomerular disease. Experimental mesangial proliferative nephritis was induced in rats by injection of anti-Thy1 antibody. Mesangial cell proliferation was associated with de novo expression of thrombospondin 1 mRNA (detected by Northern blot and in situ hybridization) and protein (by Western blot and immunostaining). Although some thrombospondin 1 was expressed by platelets and macrophages, double labeling showed that most thrombospondin 1 mRNA and protein were expressed by proliferating alpha-actin-positive mesangial cells. Thrombospondin 1 expression in anti-Thy1 nephritis was complement-dependent and could be reduced by treatment with anti-PDGF or anti-bFGF antibodies. Thrombospondin 1 could also be induced in normal rats by infusion of PDGF and in rats which were primed with low dose anti-Thy1 antibody by infusion of PDGF of bFGF. Thus, this study demonstrates that proliferating mesangial cells express thrombospondin 1 de novo in disease and that thrombospondin 1 expression in vivo is regulated by PDGF and bFGF.

Participation of glomerular endothelial cells in the capillary repair of glomerulonephritis

In many glomerular diseases severe injury to the mesangium may occur, leading to matrix dissolution and damage to the glomerular capillaries. Although the destruction of glomerular architecture may lead to permanent injury, in some cases spontaneous recovery occurs. The mechanisms that mediate this recovery are unknown. In this study we provide evidence for glomerular capillary repair (angiogenesis) in the adult injured glomerulus. Injection of anti-Thy 1 antibody into rats results in severe mesangiolysis with capillary ballooning, microaneurysm formation, and loss of endothelial cells in addition to mesangial cells. Although mesangial proliferation is a major response to injury, proliferation of endothelial cells also can be documented from days 2 to 14 in association with repair of the capillaries. The endothelial cell proliferation peaks on days 2 and 7, when it is seven- to ninefold greater than normal. Many of the endothelial cells display morphological features of angiogenesis. The initial wave of endothelial cell proliferation can be reduced by 40% with neutralizing anti-basic fibroblast growth factor antibodies (P < 0.001). The later glomerular endothelial cell proliferation is associated with upregulated expression of vascular permeability factor/endothelial cell growth factor (VPF/VEGF) and an increase of flk, a VPF/VEGF receptor. Although PDGF is expressed in this model, anti-PDGF antibody treatment did not affect the endothelial cell proliferative response. In summary, glomerular endothelial cells have an active role in the glomerular response to injury. Glomeruli are capable of healing microaneurysms, and the mechanism involves basic fibroblast growth factor- and VPF/VEGF-mediated endothelial proliferative responses.

Expression of alternatively spliced fibronectin variants during remodeling in proliferative glomerulonephritis

Fibronectin (Fn) plays an important role in tissue remodeling during embryogenesis, wound repair, and vascular disease, and is thought to regulate cellular processes such as cell adhesion, migration, proliferation, and differentiation through specialized domains within the molecule. In addition, Fn can be alternatively spliced at three regions: extradomains EIIIA, EIIIB, and a variable segment V, potentially giving rise to functionally distinct variants of the molecule. We have previously shown a sequential expression of cellular Fn first by platelets, followed by macrophages, then mesangial cells in habu snake venom-induced proliferative glomerulonephritis (Am J Pathol 145: 585-597, 1994). These studies examined the cellular sources and glomerular localization of Fn in general but did not distinguish between the various alternatively spliced isoforms. In this study, we examine by in situ hybridization and immunohistochemistry the temporal expression and cellular sources of EIIIA, EIIIB, and V in a model of proliferation glomerulonephritis that has cell migration, proliferation, and extracellular matrix synthesis as features of tissue remodeling. Macrophages were the first cells to express Fn mRNA showing an EIIIA+, EIIIB-, and V95+ pattern beginning at 8 hours after habu snake venom injection. Migrating mesangial cells at the margins of early lesions (8 and 24 hours) did not overexpress mRNA encoding these Fn variants, but immunofluorescence microscopy revealed V95 and EIIIA protein at the margins of lesions. EIIIB was absent in lesions at this time. At 48 hours and peaking at 72 hours after habu snake venom injection, mesangial cells in central aspects of glomerular lesions expressed abundant mRNA and protein for V95 and EIIIA. EIIIB mRNA and protein was slight in the mesangium at these times. Parietal epithelial cells, particularly adjacent to glomerular lesions, also expressed abundant mRNA and protein for all three variants throughout the course of the disease, beginning at 24 hours after habu snake venom injection. Expression of mRNA and protein for all three isoforms declined by 2 weeks after habu snake venom injection. These studies show that migrating mesangial cells do not require their own synthesis of Fn and suggest that they might rely on exogenous sources of Fn, particularly V95+ and EIIIA+ forms. Commencement of enhanced expression of EIIIA and EIIIB mRNA and protein by resident glomerular cells coincided with the temporal course of cell proliferation, acquisition of alpha-smooth muscle cell actin phenotype, and matrix synthesis, suggesting that Fn isoforms have specific functions during the course of glomerular remodeling.

Endothelial regeneration during the repair process following Habu-snake venom induced glomerular injury

In this study, the kinetics of glomerular endothelial cells during the repair process following glomerular injury was investigated in a model of mesangial proliferative glomerulonephritis induced by Habu-snake venom (HSV) in rats. Intravenous injection of HSV led to a cystic ballooning type lesion at day 1. Subsequently a marked segmental proliferative lesion was observed in the cystic areas at day 5. Thereafter cellularity decreased and reconstruction of the glomerular tuft was gradually observed with time. The histological structure of the glomeruli had almost returned to normal 21 days following HSV injection. After prominent depletion at day 1, the number of endothelial cells increased rapidly and reached a plateau at day 7, not significantly different from that of the control group. Morphologically endothelial cell elongation from the vascular pole into the cystic lesion was seen together with premature capillary formation in the proliferative lesion. Accompanying the reduction of mesangial expansion, the endothelial cells gradually formed definite capillary lumens. We conclude that the mesangial proliferative glomerulonephritis induced by HSV recovers to its original structural state and that the migration and proliferation of endothelial cells with accompanying capillary formation are essential for the repair process, in addition to mesangial cell proliferation.

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.

Macrophages in childhood IgA nephropathy

The role of glomerular macrophages in IgA nephropathy in children was investigated using a new monoclonal antibody (KP1) as a probe. The average number of glomerular macrophages per patient (ANM/P) was closely correlated with the degree of hematuria (P < 0.01) as well as with the degree of leukocyturia (P < 0.01) in the absence of any correlation with proteinuria, serum IgA levels or the interval between the detection of urine abnormalities and renal biopsy. ANM/P was significantly higher in patients diagnosed pathologically as having focal and diffuse proliferative glomerulonephritis than in patients with minor glomerular abnormalities or advanced sclerosis (P < 0.05). Among various types of glomerular morphology in individual patients, macrophages predominantly infiltrated glomeruli with cell-proliferative lesions despite an absence of any increase in glomeruli with minor abnormalities or with sclerosis. Macrophages were mainly localized within the capillary lumen in association with endocapillary proliferative lesions (tuft necrosis), they accumulated in areas of mesangial proliferation, and they were attached to Bowman's capsule in segmental lesions. Macrophages were less evident in sclerosis. Furthermore, ultrastructural analysis revealed macrophages in the paramesangial areas in close proximity to lytic changes in the glomerular basement membrane and effacement of epithelial foot processes. In addition, some cases in repeat biopsy shows prolonged or increased values of ANM/P after several years of interval in association with progression of proliferative lesions. These results suggest that macrophages infiltrate glomeruli during acute glomerular inflammation, and that they are involved in mesangial proliferation or the development of extracapillary lesions in the absence of apparent clinical symptoms. Furthermore, recurrence or prolonged infiltration may promote progression of IgA nephropathy.

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)

Endothelial cell injury initiates glomerular sclerosis in the rat remnant kidney

The development of progressive glomerulosclerosis in the renal ablation model has been ascribed to a number of humoral and hemodynamic events, including the peptide growth factor, transforming growth factor-beta 1 (TGF-beta 1). An important role has also been attributed to angiotensin II (AII), which, in addition to its hemodynamic effects, can stimulate transcription of TGF-beta 1. We postulated that increased glomerular production of AII, resulting from enhanced intrinsic angiotensinogen expression, stimulates local TGF-beta 1 synthesis, activating glomerular matrix protein synthesis, and leads to sclerosis. Using in situ reverse transcription, the glomerular cell sites of alpha-1 (IV) collagen, fibronectin, laminin B1, angiotensinogen, and TGF-beta 1 mRNA synthesis were determined at sequential periods following renal ablation. The early hypertrophic phase was associated with global, but transient, increases in the mRNA for alpha-1 (IV) collagen. No changes were noted for fibronectin, TGF-beta 1, and angiotensinogen mRNAs. At 24 d after ablation, at which time sclerosis is not evident, endothelial cells, particularly in the dilated capillaries at the vascular pole, expressed angiotensinogen and TGF-beta 1 mRNAs, as well as fibronectin and laminin B1 RNA transcripts. By 74 d after ablation angiotensinogen and TGF-beta 1 mRNAs were widely distributed among endothelial and mesangial cells, and were particularly prominent in regions of evolving sclerosis. These same regions were also notable for enhanced expression of matrix protein mRNAs, particularly fibronectin. All receptor blockade inhibited angiotensinogen, TGF-beta 1, fibronectin, and laminin B1 mRNA expression by the endothelium. We conclude that, as a result of hemodynamic changes, injured or activated endothelium synthesizes angiotensinogen, triggering a cascade of TGF-beta 1 and matrix protein gene expression with resultant development of the segmental glomerular sclerotic lesion.

Diversity and variability of smooth muscle phenotypes of renal arterioles as revealed by myosin isoform expression

The contractility and distensibility of renal arterioles are important in the regulation of glomerular filtration. However, little is known regarding the characteristics of contractile proteins in these arterioles. Recently it was demonstrated that vascular smooth muscles contain two types of myosin heavy chain (MHC) isoforms, SM1 and SM2, which are unique molecular markers of smooth muscle cell phenotypes. SM1 is constitutively expressed in all types of smooth muscles, whereas SM2 exists only in mature smooth muscles. We characterized the expression of MHC isoforms as well as the ultrastructural myofilament assembly of renal arteriolar smooth muscles in human, rat and rabbit by immunohistochemical techniques. SM1 and alpha-smooth muscle actin were localized in both the preglomerular vessels (including the afferent arterioles) and efferent arterioles, whereas SM2 was present only in the preglomerular vessels. Renin-producing cells in the afferent arterioles (juxtaglomerular granular cells, JG cells) were positive for alpha-smooth muscle actin but negative for SM2. When renin synthesis was stimulated, the more proximal afferent arteriolar smooth muscles turned renin-positive and SM2 disappeared. Glomerular mesangial cells did not show immunoreactivities for SM1, SM2 or alpha-smooth muscle actin. The difference in MHC isoform expression in these arterioles was also reflected by ultrastructures; the afferent arteriolar smooth muscles contained abundant myofilaments including thick filaments, whereas the efferent arteriolar smooth muscles had a few myofilaments composed only of thin microfilaments. The JG cells displayed a myofilament assembly similar to that in the efferent arteriolar smooth muscles. We conclude from these observations that smooth muscles in pre-and postglomerular arterioles, the glomerular mesangial cells and JG cells differ in phenotypes, suggesting that they may have different contractile properties which may be critically involved in the regulation of glomerular filtration.

Transforming growth factor-beta 1 expression and phenotypic modulation in the kidney of hypertensive rats

We have previously reported that renal mRNA levels for transforming growth factor-beta 1, fibronectin, and collagens were increased in 32-week-old stroke-prone spontaneously hypertensive rats (SHRSP) with severe nephrosclerosis. To elucidate the mechanism of hypertension-induced nephrosclerosis, we examined gene expression and localization of transforming growth factor-beta 1 and cellular phenotype in the kidney of 25-week-old SHRSP with moderate renal damage. Renal mRNA was measured by Northern blot analysis. The localization of transforming growth factor-beta 1 and cellular phenotype was determined by immunohistochemistry. In the kidney of 25-week-old SHRSP, renal transforming growth factor-beta 1 mRNA was elevated compared with Wistar-Kyoto rats (WKY), whereas renal collagen mRNAs of SHRSP were not increased. Immunoreactive transforming growth factor-beta 1 in SHRSP was mainly localized in glomerular cells. Furthermore, alpha-smooth muscle actin and desmin were significantly expressed in SHRSP glomerular cells, in contrast to negligible expression of these proteins in WKY. alpha-Smooth muscle actin staining was also observed in interstitial cells, and vimentin, another phenotypic marker, was expressed in atrophic tubular cells of SHRSP, despite no staining of these proteins in WKY. Furthermore, all these phenotypic changes in SHRSP were associated with increased cell proliferation, as shown by the increased number of proliferating cell nuclear antigen-positive cells. Treatment of SHRSP with cilazapril and nifedipine (from the age of 13 to 25 weeks) prevented the increase in transforming growth factor-beta 1 expression and the cellular phenotypic modulation and was accompanied by a reduction of urinary albumin excretion and inhibition of cell proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet-derived growth factor A-chain expression in developing and mature human kidneys and in Wilms' tumor

Regulated expression of PDGF A-chain may be important in kidney development. We employed two polyclonal antisera to detect expression of PDGF A-chain in fetal and normal adult kidneys by immunohistochemistry. Specificity of the antisera was demonstrated by Western blots of fetal and adult kidneys, demonstrating monospecific bands at 10 to 15 kD, and by absorption studies with PDGF-A peptide. PDGF A-chain is uniformly expressed by visceral glomerular epithelial cells and the epithelial cells of the distal nephron, including collecting ducts and contiguous urothelium lining the renal pelvis, in both fetal and adult kidneys. Fetal kidneys also demonstrate expression of PDGF A-chain at the earliest stages of vesicle formation from the metanephric blastema; this expression is then only intermittently detectable in developing glomeruli until differentiation of visceral epithelial cells occurs. Fetal and mature arterial smooth muscle cells, and some express PDGF A-chain. In situ hybridization with a riboprobe made from PDGF A-chain cDNA showed close correlation of mRNA expression with protein immunohistochemistry. PDGF A-chain expression was also identified in epithelial elements of 5/6 Wilms' tumors studied. These are the first studies to localize PDGF A-chain expression in human kidney and suggest sites of activity for PDGF A-chain in development, neoplasia, and in the renal arterial sclerosis of aging.

Hypoxia selectively induces proliferation in a specific subpopulation of smooth muscle cells in the bovine neonatal pulmonary arterial media

Medial thickening of the pulmonary arterial wall, secondary to smooth muscle cell (SMC) hyperplasia, is commonly observed in neonatal hypoxic pulmonary hypertension. Because recent studies have demonstrated the existence of multiple phenotypically distinct SMC populations within the arterial media, we hypothesized that these SMC subpopulations would differ in their proliferative responses to hypoxic pulmonary hypertension and thus contribute in selective ways to the vascular remodeling process. Expression of meta-vinculin, a muscle-specific cytoskeletal protein, has been shown to reliably distinguish two unique SMC subpopulations within the bovine pulmonary arterial media. Therefore, to assess the proliferative responses of phenotypically distinct SMC subpopulations in the setting of neonatal pulmonary hypertension, we performed double immunofluorescence staining on pulmonary artery cryosections from control and hypertensive calves with antibodies against meta-vinculin and the proliferation-associated nuclear antigen, Ki-67. We found that, although neonatal pulmonary hypertension caused significant increases in overall cell replication, proliferation occurred almost exclusively in one, the meta-vinculin-negative SMC population, but not the other SMC population expressing meta-vinculin. We also examined fetal pulmonary arteries, where proliferative rates were high and meta-vinculin expression again reliably distinguished two SMC subpopulations. In contrast to the hypertensive neonate, we found in the fetus that the relative proliferative rates of both SMC subpopulations were equal, thus suggesting the existence of different mechanisms controlling proliferation and expression of cytoskeletal proteins in the fetus and neonate. We conclude that phenotypically distinct SMC populations in the bovine arterial media exhibit specific and selective proliferative responses to neonatal pulmonary hypertension. Distinct SMC subpopulations may, thus, contribute in unique ways to vascular homeostasis under both normal and pathologic conditions.

Transient expression of type I collagen in glomeruli with anti-Thy-1 antibody-induced mesangial proliferative lesions

Glomerular expression of extracellular matrices at the protein and mRNA levels was examined in rats with mesangial proliferative glomerulonephritis induced by the intravenous administration of a monoclonal anti-rat Thy-1 antibody. In close association with the mesangial proliferative lesion, type I collagen was immunostained at day 8 but not demonstrated at day 28 in the glomeruli of the kidneys. Type I collagen mRNA expression prominently increased in the nephritic glomeruli at day 4, prior to the appearance of type I collagen protein. In addition, fibronectin expression was also elevated in the diseased glomeruli at both the protein and mRNA levels. These results indicated that glomerular, probably mesangial cells, change their phenotypes during this disease, to synthesize abnormal extracellular matrices that lead to the progression of glomerular sclerosis.

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.

Myofibroblasts in experimental hydronephrosis

Interstitial fibrosis is a common outcome of longterm ureteral obstruction. One pathological arm of the fibrotic reaction in diverse tissue loci and experimental models is the retraction of granulation tissue. The role of the myofibroblast in granulation tissue contraction and fibrocontractive diseases has been well established, but the mechanisms leading to differentiation of fibroblastic cells into myofibroblasts during the evolution of inflammation are not yet fully clarified. Investigators using other model systems have shown that macrophage-derived transforming growth factor-beta 1 (TGF-beta 1) may be pivotal in the process of myofibroblast modulation. Our laboratory has shown that the unilateral ureteral obstruction in the rat is characterized by a 20-fold increment in infiltrating renal cortical interstitial macrophages, an increase in cortical TGF-beta 1 gene expression, which parallels the infiltrating macrophage burden, and immunolocalization of this peptide growth factor in close proximity to resident interstitial fibroblasts. Because of this model's features, it was our aim to assess whether a myofibroblastic modulation was operant in the renal cortex of obstructed rat kidneys versus the control contralateral unobstructed kidney specimens. Immunolabeling for alpha-smooth muscle actin and the intermediate filament protein, desmin, was detected and steadily intensified from 24 to 96 hours after unilateral ureteral obstruction in obstructed kidneys only. In temporal concert with the detection of alpha-smooth muscle actin protein, the mRNA expression for this cytoskeletal component exhibited 3.7-, 15.7-, and 4.1-fold increments in the renal cortex of obstructed kidneys versus the contralateral unobstructed kidney specimens at 24, 48, and 96 hours after unilateral ureteral obstruction, respectively. Whole body X-irradiation, administered to rats 11 days before proximal left ureteral ligation, significantly lowered cortical interstitial macrophage number, cortical TGF-beta and alpha-smooth muscle actin mRNA levels as well as the intensity of immunolabeling for alpha-smooth muscle actin from 12 to 96 hours after unilateral ureteral obstruction. These data support a postulate that renal cortical TGF-beta 1, derived from the infiltrating macrophage, in part, contributes to the subsequent interstitial fibrosis response to renal injury by fostering the modulation of fibroblasts to myofibroblasts within the renal cortex after ureteral obstruction.

Modulation of experimental mesangial proliferative nephritis by interferon-gamma

The observation that interferon-gamma (IFN-gamma) inhibits cell proliferation and collagen synthesis of a variety of cell types in culture has suggested that IFN-gamma may be useful in the treatment of fibroproliferative diseases. We administered recombinant IFN-gamma subcutaneously (10(5) U/kg/day for 3 days) to rats, beginning one day after the induction of mesangial proliferative nephritis with anti-Thy 1 antibody. IFN-gamma reduced glomerular (primarily mesangial) cell proliferation by 44% at days 2 and 4 compared to vehicle injected control rats with anti-Thy 1 nephritis (that is, proliferating cells that excluded the macrophage marker, ED-1, P < 0.001). Despite the inhibition of mesangial cell proliferation, IFN-gamma did not reduce the overall extracellular matrix deposition (by silver stain) or deposition of type IV collagen or laminin (by immunostaining) at 4 or 7 days, and glomerular type IV collagen and laminin mRNA levels were increased (1.4 and 1.7-fold) at 4 days relative to controls. The inability of IFN-gamma treatment to reduce mesangial matrix expansion may relate to the fact that IFN-gamma treated rats had a twofold increase in glomerular macrophages (that is, ED-1 positive cells, P < 0.001 at 2 and 4 days) with an increase in oxidant producing cells (day 2, P < 0.05) and a 1.6-fold increase in glomerular TGF-beta mRNA expression (4 days). This suggests that the effect of IFN-gamma to inhibit mesangial cell proliferation in glomerulonephritis may be offset by the ability of IFN-gamma to increase glomerular macrophages and TGF-beta expression. These data also show that IFN-gamma can partly dissociate the mesangial proliferative response from the extracellular matrix expansion in glomerulonephritis.

Effects of energy intake on type 1 plasminogen activator inhibitor levels in glomeruli of lupus-prone B/W mice

Calorie restriction (CR) and/or reduced energy intake ameliorates the progression of autoimmune renal disease in (NZB x NZW)F1 (B/W) female mice and increases life span. Like other forms of glomerulonephritis, the lupus-like kidney disease observed in these animals is frequently accompanied by glomerular deposition of fibrin and increased accumulation of mesangial matrix. Because alterations in plasminogen activator inhibitor type 1 (PAI-1) expression or function may be involved in both fibrin deposition and accumulation of extracellular matrix, we have studied the effects of CR on the expression of PAI-1 in kidneys from female B/W mice fed either ad libitum or on a 40% CR diet. By immunohistochemistry and immunoblotting, we found that the glomerular levels of PAI-1 antigen were highest in older ad lib fed animals with more advanced glomerular disease. Increased levels of PAI-1 protein were paralleled by increased levels of PAI-1 mRNA in total RNA extracted from renal cortex and in diseased glomeruli as detected by in situ hybridization. CR diminished the accumulation of PAI-1 protein and reduced the expression of PAI-1 mRNA. Thus, glomeruli from animals fed ad lib showed much greater deposition of PAI-1 protein, increased expression of PAI-1 mRNA, and more severe histological abnormalities than animals on a CR diet. The differences between CR and ad lib animals were more pronounced in animals studied at 9 to 10 months versus those at 3 to 4 months of age. These observations indicate that the ameliorating effects of CR include diminished PAI-1 gene expression and decreased localization of PAI-1 in glomeruli.

Apoptosis in the repair process of experimental proliferative glomerulonephritis

The recovery from the proliferative glomerulonephritis (GN) with reduction of hypercellularity is known in various experimental and human GN. To elucidate the participation of apoptosis in GN, we studied the experimental Thy-1.1 GN for six weeks. Apoptosis was recognized by both light and electron microscopy, and the biochemical expression of apoptosis was morphologically confirmed by in situ end-labeling method of fragmented DNA, using terminal deoxy-transferase. Mesangioproliferative GN was induced by a single administration of anti-Thy-1.1 monoclonal antibody in a rat. Mesangial cell proliferation started early in the process and the number of glomerular cells peaked from day 7 to day 10. Subsequently, the degree of proliferative lesion diminished with obvious reconstruction of the capillary structure, as well as decrease in the number of glomerular cells. During this period, proliferated mesangial cells returned to their original level of cellularity and apoptosis apparently increased in number among the glomeruli. Apoptosis was significantly noted from day 7 to week 4 and was in its maximum at day 10 to week 2. Following this period, by week 6 most of the glomeruli reverted to their original structure. The number of infiltrated neutrophils and macrophages in the glomeruli slowly decreased during the course of the disease, and a few apoptosis were also observed. It is concluded that proliferated glomerular cells regress by apoptosis in the repairing process of GN. Apoptosis plays an essential role in the recovery to the original glomerular structure in GN.

Mesangial cell apoptosis: the major mechanism for resolution of glomerular hypercellularity in experimental mesangial proliferative nephritis

Increases in mesangial cell number may herald glomerular scarring, but they are not irreversible. This study sought mechanisms by which surplus glomerular mesangial cells can be cleared. A small proportion of cultured mesangial cells exhibited typical morphological features of apoptosis (programmed cell death), which was increased by growth factor deprivation or exposure to cycloheximide, stimuli known to increase apoptosis in other cell types. Apoptosis was confirmed by typical internucleosomal chromatin cleavage. In vivo, clear morphological evidence of mesangial apoptosis leading to phagocytosis by neighboring mesangial cells was obtained in self-limited mesangial proliferation induced in rats by Thy1.1 antibody, apoptosis occurring approximately 10-fold more frequently than in the healthy rat glomerulus. Indeed, changes in glomerular cell number in Thy1.1 nephritis strongly suggested that apoptosis is the major cell clearance mechanism counterbalancing cell division, thereby mediating resolution of glomerular hypercellularity in experimental mesangial proliferation.

Treatment with a glycosaminoglycan formulation ameliorates experimental diabetic nephropathy

Previous studies have indicated that administration of glycosaminoglycans can prevent some of the morphological and physiological alterations which occur in experimental diabetic nephropathy. The aims of this study were to further elucidate the effect of these drugs on glomerular basement membrane permeability by dextran clearance studies, to test the ability of glycosaminoglycans to revert established diabetic nephropathy and to examine the effect of glycosaminoglycans on renal extracellular matrix synthesis. Five groups of Sprague-Dawley rats were studied for 12 months: two control groups (treated or untreated non-diabetic), three streptozotocin diabetic animal groups, two of which received a glycosaminoglycan formulation, one from the induction of diabetes and the other after the fifth month of diabetes. At five months the 35S-sulfate glomerular incorporation, albuminuria, glomerular basement membrane thickness and anionic charge density were determined. At 12 months albuminuria, renal collagen IV and perlecan mRNA levels, anionic and neutral dextran clearances, glomerular basement membrane morphometry, and mesangial cell proliferation were evaluated. We demonstrate that long-term administration of glycosaminoglycans prevents renal morphological and functional alterations in diabetic rats and appears to revert established diabetic renal lesions. Glycosaminoglycan administration modified renal matrix composition by the normalization of collagen gene expression and increasing glomerular 35S-sulfate incorporation.

Sequential expression of cellular fibronectin by platelets, macrophages, and mesangial cells in proliferative glomerulonephritis

Fibronectin (Fn) regulates cell migration, proliferation, and extracellular matrix formation during embryogenesis, angiogenesis, and wound healing. Fn also promotes mesangial cell migration and proliferation in vitro and contributes to extracellular matrix formation and tissue remodeling during glomerular disease. In this study, we examined, by immunohistochemistry and in situ hybridization, the temporal glomerular localization and cellular sources of Fn in Habu snake venom (HSV)-induced proliferative glomerulonephritis. Early HSV-induced glomerular lesions consisted of microaneurysms devoid of resident glomerular cells and filled with platelets, leukocytes, and erythrocytes. Over the course of the disease, mesangial cells migrated into the lesions, proliferated, and formed a confluent cellular mass. Fn was present in lesions beginning at 8 hours, with highest intensity at 72 hours and diminishing at 2 weeks after HSV. Staining for Fn at 8 and 24 hours after HSV was attributed to platelets and macrophages. In situ hybridization and phenotypic identification of cell types within lesions revealed macrophages as the predominant source of cellular Fn mRNA at these times. At 48 hours after HSV, Fn mRNA was expressed in proliferating mesangial cells in addition to macrophages. Most cells in lesions at 72 hours after HSV were mesangial, at a time when expression of Fn mRNA peaked. Cellular expression for Fn mRNA and translated protein declined at 2 weeks after HSV. These studies support the hypothesis that Fn, derived from platelets and macrophages, provides a provisional matrix involved with mesangial cell migration into glomerular lesions. Fn produced by mesangial cells might contribute to the formation of a stable extracellular matrix.

Ultrastructural and immunohistochemical studies in callitrichid renal glomeruli

The "normal" mesangium of callitrichids exhibits certain features pointing to enhanced activity. Protrusions of the mesangial cellular cytoplasm (blebs) into the capillary lumen were observed very frequently as were electron-dense granules in mesangial matrix channels. Histochemical, alpha-actin expression was invariably observed in the mesangial cells of callitrichids.

Heterogeneity of myofibroblast phenotypic features: an example of fibroblastic cell plasticity

Granulation tissue fibroblasts (myofibroblasts) develop several ultrastructural and biochemical features of smooth muscle (SM) cells, including the presence of microfilament bundles and the expression of alpha-SM actin, the actin isoform present in SM cells and myoepithelial cells and particularly abundant in vascular SM cells. Myofibroblasts have been suggested to play a role in wound contraction and in retractile phenomena observed during fibrotic diseases. When contraction stops and the wound is fully epithelialized, myofibroblasts containing alpha-SM actin disappear, probably as a result of apoptosis, and the scar classically becomes less cellular and composed of typical fibroblasts with well-developed rough endoplasmic reticulum but with no more microfilaments. In contrast, alpha-SM actin expressing myofibroblasts persist in hypertrophic scars and in fibrotic lesions of many organs, including stroma reaction to epithelial tumours, where they are allegedly involved in retractile phenomena as well as in extracellular matrix accumulation. The mechanisms leading to the development of myofibroblastic features remain to be investigated. In vivo and in vitro investigations have shown that gamma-interferon exerts an antifibrotic activity at least in part by decreasing alpha-SM actin expression whereas heparin increases the proportion of alpha-SM actin positive cells. Recently, we have observed that the subcutaneous administration of transforming growth factor-beta 1 to rats results in the formation of a granulation tissue in which alpha-SM actin expressing myofibroblasts are particularly abundant. Other cytokines and growth factors, such as platelet-derived growth factor, basic fibroblast growth factor and tumour necrosis factor-alpha, despite their profibrotic activity, do not induce alpha-SM actin in myofibroblasts. In conclusion, fibroblastic cells are relatively undifferentiated and can assume a particular phenotype according to the physiological needs and/or the microenvironmental stimuli. Further studies on fibroblast adaptation phenomena appear to be useful for the understanding of the mechanisms of development and regression of pathological processes such as wound healing and fibrocontractive diseases.

Evidence of cytokeratin expression in canine visceral glomerular epithelial cells in vivo

Visceral glomerular epithelial cells (vGECs) originate from a mesenchymal blastema and transiently express cytokeratin during embryogenesis. There are no reports of cytokeratin expression in vGECs of mature, normal or damaged, human or other mammalian kidneys in vivo, but in vitro studies have provided evidence of the synthesis of cytokeratin in cultured vGECs. Cytokeratin expression was observed in vGECs in the damaged kidneys of four dogs with spontaneous renal diseases and, by using monoclonal antibodies, type 18 cytokeratin was identified. vGECs are apparently able to (re-) activate in vivo a mechanism for switching on the synthesis of cytokeratin in damaged glomeruli.

Myofibroblasts and their role in lung collagen gene expression during pulmonary fibrosis. A combined immunohistochemical and in situ hybridization study

Appearance of contractile filament-laden stromal cells or myofibroblasts is a characteristic of lung fibrotic lesions. The role of these cells in fibrosis and their cytoskeletal phenotype are not fully delineated. This study was undertaken to further investigate these issues using a model of lung fibrosis. Rats were treated endotracheally with bleomycin on day 0, and their lungs examined at various time points by in situ hybridization for alpha 1(I) procollagen mRNA expression and by immunohistochemistry for desmin and alpha-smooth muscle actin expression. The results show an increase in the number of cells resembling fibroblasts and strongly positive for alpha-smooth muscle actin, desmin and procollagen mRNA expression in lungs of animals treated with bleomycin, with the increase being maximal between days 7 and 14 after bleomycin treatment. Two types of newly positive cells could be discerned. The first expressing alpha-smooth muscle actin, desmin, and procollagen mRNA was localized in active fibrotic lesions. The second expressing only alpha-smooth muscle actin and procollagen mRNA was localized in fibrotic submesothelial areas. Almost all of the newly reactive alpha-smooth muscle actin-positive cells strongly express procollagen mRNA, and they constituted most of the cells actively expressing procollagen. These findings suggest that the newly appearing myofibroblast characterized by alpha-smooth muscle actin and/or desmin expression may be responsible for most if not all of the increased lung collagen gene expression in pulmonary fibrosis.

Intraglomerular expression of alpha-smooth muscle actin in aging mice

To determine whether chronic treatment with enalapril initiated early in life prevents glomerular injury secondary to normal aging, CF1 mice received enalapril (20 mg/L, n = 10) or nifedipine (40 mg/L, n = 10) in their drinking water from the time of weaning to 12 months of life. Control mice (n = 10) received tap water ad libitum. Immunocytochemical detection of renin confirmed that angiotensin-converting enzyme inhibition resulted in recruitment of renin-containing cells along the preglomerular vessels. Morphometric analysis of glomeruli included assessment of glomerular diameter and the percentage of mesangial area per glomerulus. Glomerular diameter and mesangial area were higher in control mice (99.7 +/- 0.5 microns, 12.7 +/- 0.3%) than in enalapril-treated mice (88 +/- 0.8 microns, 8.6 +/- 0.6%) (P < .05). Glomerular diameter and mesangial area in the nifedipine-treated group (99.1 +/- 0.9 microns, 12.4 +/- 0.9%) were not different from control mice. These results demonstrate that angiotensin-converting enzyme inhibition prevents the glomerular enlargement and mesangial expansion observed during natural aging. In addition, control glomeruli expressed alpha-smooth muscle actin in a mesangial distribution. This effect was prevented by enalapril treatment but not by nifedipine. We conclude that long-term treatment with enalapril from early life prevents the early changes associated with glomerular injury and expression of alpha-smooth muscle actin in the glomerulus. alpha-Smooth muscle actin may participate in and serve as an early marker of the glomerular injury during the normal aging process.

New insights into mechanisms of immune glomerular injury

Although glomerular disease remains the most common cause of end-stage renal disease worldwide, major advances have been made recently in understanding the cellular and molecular mechanisms that mediate these disorders. The nephrotic syndrome in noninflammatory lesions such as minimal change or focal sclerosis and membranous nephropathy results from disorders of the glomerular epithelial cell that can be simulated in animal models by antibodies to various epithelial cell membrane epitopes. Clarification of how these antibodies affect epithelial cells to induce a loss of glomerular barrier function should substantially improve understanding of the pathogenesis of minimal change or focal sclerosis. In membranous nephropathy, proteinuria is mediated primarily by the C5b-9 complex through similar mechanisms that also involve glomerular epithelial cells as targets. Inflammatory glomerular lesions are induced by circulating inflammatory cells or proliferating resident glomerular cells. Understanding of how these cells induce tissue injury has also evolved considerably over the past decade. Neutrophil-induced disease involves leukocyte adhesion molecules in regulating neutrophil localization; proteases, oxidants, and myeloperoxidase in mediating injury; and platelets in augmenting these processes. The activated mesangial cell exhibits altered phenotype and proliferation with the release of oxidants and proteases. Mesangial cell proliferation may be initiated by basic fibroblast growth factor and is maintained by an autocrine mechanism involving platelet-derived growth factor. Transforming growth factor beta is important in the subsequent development of sclerosis.

Tubulointerstitial disease in glomerulonephritis. Potential role of osteopontin (uropontin)

Interstitial inflammation and tubular injury accompany most types of glomerulonephritis and are likely to mediate progressive renal injury. We hypothesized that the interstitial monocyte/macrophage accumulation in nephritis involves osteopontin, a cell attachment glycoprotein that avidly binds macrophages in vitro and induces a macrophage-rich infiltrate on subcutaneous injection in mice (Singh et al, J Exp Med, 1990, 171: 1931). In this study, we demonstrate that osteopontin messenger RNA and protein levels are up-regulated in a proportion of proximal and distal tubules in three experimental models of glomerulonephritis. In all three models, the expression of osteopontin initially precedes histological evidence of tubular injury, but is correlated with subsequent sites of monocyte/macrophage accumulation and tubular damage. Osteopontin expression also correlates with the severity of the tubulointerstitial injury, being greatest in amino-nucleoside nephrosis. These data suggest that 1) osteopontin is up-regulated in tubules in glomerular disease; 2) osteopontin may be important for macrophage accumulation at specific sites in diseased tissue; and 3) osteopontin may therefore have a role in the pathogenesis of the tubulointerstitial injury that accompanies glomerulonephritis.