Modulation of experimental mesangial proliferative nephritis by interferon-gamma

Metalloprotease meprin beta in rat kidney: glomerular localization and differential expression in glomerulonephritis

Meprin (EC 3.4.24.18) is an oligomeric metalloendopeptidase found in microvillar membranes of kidney proximal tubular epithelial cells. Here, we present the first report on the expression of meprin beta in rat glomerular epithelial cells and suggest a potential involvement in experimental glomerular disease. We detected meprin beta in glomeruli of immunostained rat kidney sections on the protein level and by quantitative RT-PCR of laser-capture microdissected glomeruli on the mRNA level. Using immuno-gold staining we identified the membrane of podocyte foot processes as the main site of meprin beta expression. The glomerular meprin beta expression pattern was altered in anti-Thy 1.1 and passive Heymann nephritis (PHN). In addition, the meprin beta staining pattern in the latter was reminiscent of immunostaining with the sheep anti-Fx1A antiserum, commonly used in PHN induction. Using Western blot and immunoprecipitation assays we demonstrated that meprin beta is recognized by Fx1A antiserum and may therefore represent an auto-antigen in PHN. In anti-Thy 1.1 glomerulonephritis we observed a striking redistribution of meprin beta in tubular epithelial cells from the apical to the basolateral side and the cytosol. This might point to an involvement of meprin beta in this form of glomerulonephritis.

Morphine induces mesangial cell proliferation and glomerulopathy via kappa-opioid receptors

Morphine sulfate (MS) stimulates mesangial cell (MC) proliferation, a process central to development of glomerular disease. The purpose of this study was to examine whether specific opioid receptors (OR) and signal transducer and activators of transcription 3 (STAT3) signaling are associated with MS-induced MC proliferation. C57Bl/6J and OR-specific knockout (KO) mice were treated for up to 6 wk with PBS, MS (0.7-2.14 mg/kg), naloxone (equimolar to MS), or MS+naloxone (n = 6 per group). Glomerular volume and expression of PCNA, Thy1, and ED1/CD68 were analyzed in kidney sections. Cell proliferation and STAT3 phosphorylation were analyzed by bromodeoxyuridine (BrdU) ELISA and Western blot, respectively, in MCs in vitro. MS treatment led to enlarged kidneys and glomerulopathy and naloxone reversed these effects. MS treatment increased glomerular volume in both mu-OR (MOR) KO and delta-OR (DOR) KO mice, but not in kappa-OR (KOR) KO mice. To ascertain that MS-induced glomerulopathy in vivo was due to MC proliferation, we further examined the OR-specific effects of MS in MCs in vitro. MS-induced MC proliferation in vitro was inhibited by KOR-specific nor-BNI, but not by DOR or MOR-specific antagonists naltrindol or CTOP, respectively. KOR-specific agonist U50488H stimulated proliferation of MCs, but DOR-specific agonist DPDPE and MOR-specific agonist DAMGO did not. MS failed to stimulate proliferation of MCs from KOR KO mice. MS and KOR agonists induced STAT3 phosphorylation, and STAT3 inhibitor blocked KOR agonist-induced MC proliferation. We show that MS stimulates glomerulopathy and MC proliferation via KOR and STAT3 signaling.

Cytokines in Glomerulonephritis

Cytokines play central roles in both innate and adaptive immune responses that lead to renal inflammation. They are involved systemically in cross-talk between antigen-presenting cells, leukocytes, and regulatory cells to initiate and modulate nephritogenic immunity. Within the kidney, cytokines play a central role in signaling between infiltrating leukocytes and intrinsic renal cells and orchestrate the effector responses that lead to renal damage. Glomerulonephritis (GN) is an important cause of renal inflammation leading to renal failure that results from adaptive responses targeted at the kidney. Animal models of GN have shown that cytokines play critical roles in initiation and modulation of renal inflammatory responses through their ability to modulate the T helper 1/T helper 2 balance of nephritogenic immune responses. Evidence from clinical studies is now confirming the importance of this paradigm in directing the inflammatory mechanisms, histologic patterns, and clinical consequences of human GN. Cytokines also have critical intrarenal effector roles in the development, perpetuation, and resolution of GN. The proinflammatory role of intrarenal cytokine production by leukocytes in GN is well recognized, but, more recently, the role of intrinsic renal cell cytokine production in amplifying renal inflammation has been shown in animal models of GN. Studies showing benefits of specific anticytokine therapies directed at tumor necrosis factor in human GN are now appearing.

Distinctive role of Stat3 and Erk-1/2 activation in mediating interferon-gamma inhibition of TGF-beta1 action

Interferon-gamma (IFN-gamma) is a multifunctional cytokine that elicits antifibrotic activity in a variety of organs. In this study, we investigated the potential role and mechanism of IFN-gamma in modulating the fibrogenic action of transforming growth factor (TGF)-beta(1) in tubular epithelial cells. Incubation of human proximal tubular epithelial (HKC) cells with IFN-gamma inhibited TGF-beta(1)-mediated alpha-smooth muscle actin (alpha-SMA) expression. IFN-gamma also abolished TGF-beta(1)-induced fibronectin and plasminogen activator inhibitor-1 (PAI-1) expression. To explore the mechanisms by which INF-gamma inhibits TGF-beta(1) action, the signaling pathways that are critical for mediating the antifibrotic activity of IFN-gamma were studied. Stimulation of HKC cells with IFN-gamma triggered a sustained activation of Erk-1/2 and signal transducer and activator of transcription-3 (Stat3). Blockade of Erk-1/2 activation with an Mek1 inhibitor abolished the inhibitory effect of IFN-gamma on alpha-SMA expression, whereas inhibition of Stat3 activation had no influence. Constitutive activation of Erk-1/2 by ectopic expression of activated Mek1 mimicked IFN-gamma and suppressed TGF-beta(1)-mediated alpha-SMA expression. Interestingly, inhibition of Stat3 activation abolished the ability of IFN-gamma to attenuate TGF-beta(1)-mediated PAI-1 and fibronectin expression in HKC cells. These findings indicate that IFN-gamma is capable of antagonizing the fibrogenic actions of TGF-beta(1) in renal tubular epithelial cells. The antifibrotic action of IFN-gamma appears to be mediated through a coordinated activation of both Erk-1/2 and Stat3 signal pathways in a mutually independent fashion.

Genetic potential for an acute inflammatory response in IgA glomerulonephritis in mice

Mice selected on the basis of an acute inflammatory response (AIR) can provide information about the immunopathological mechanisms of glomerulonephritis. We studied the differences between mice selected for a maximal AIR (AIRmax that attract more polymorphonuclear cells to the site of injury) or a minimal AIR (AIRmin that attract more mononuclear cells) in an experimental model of IgA nephropathy in order to investigate the effect of genetic background on glomerular disease progression and the participation of the monocyte chemoattractant protein-1 (MCP-1) chemokine. IgA nephropathy was induced by intraperitoneal ovalbumin injection and bile duct ligation in AIRmax and AIRmin mice. Histological changes, urinary protein/creatinine ratio, serum IgA levels, immunofluorescence for IgA, IgG and complement C3 fraction, immunohistochemistry for macrophages and MCP-1, and MCP-1 levels in macerated kidney were determined. Mesangial IgA deposition was seen only in AIRmin mice, which presented more renal lesions. Increased serum IgA levels (1.5 +/- 0.4 vs 0.3 +/- 0.1 mg/mL, P < 0.001), high glomerular MCP-1 expression and decreased monocyte/macrophage infiltration in the interstitial area (0.3 +/- 0.3 vs 1.1 +/- 0.9 macrophages/field, P < 0.05) were detected in AIRmin mice compared to AIRmax mice. No glomerular monocyte/macrophage infiltration was detected in either strain. In spite of the absence of IgA deposition, AIRmax mice presented discrete or absent mesangial proliferation. The study showed that there are differences between mice selected for AIRmax and AIRmin with respect to serum IgA levels, histological damage and MCP-1 chemokine production after ovalbumin injection in combination with bile duct ligation.

Post-inflammatory glomerular remodeling is influenced by transformed mesangial cells

To identify the role of transformed mesangial cells (MC) during glomerular remodeling, anti-thymocyte-1 (Thy1) nephritis; modified Thy1 nephritis (injections of anti-Thy1 antibody four times, weekly); and Thy1 nephritis treated with signal transduction inhibitor 571 (Thy1 + STI); were analyzed. At week 1 the index of MC proliferation in modified Thy1 nephritis and in mesangiolysis in Thy1 + STI nephritis was highest among the three models. From week 4, the index of alpha-smooth muscle actin (alpha-SMA) was significantly higher in modified Thy1 nephritis than the other two models. Production of the mesangial matrix including type IV collagen was increased in modified Thy1 but inhibited in Thy1 + STI nephritis. In contrast to modified Thy1 nephritis, the capillary numbers in glomeruli recovered to normal at week 4 in Thy1, and at week 8 in Thy1 + STI nephritis. At week 12, both the adhesive and sclerotic index was significantly higher in modified Thy1 than in the other two models. Data suggest that a moderate amount of mesangial matrix results in a complete repair of capillary loops. Overproduction of the mesangial matrix retards capillary remodeling and finally induces glomerulosclerosis. Insufficient mesangial matrix delays the repair of capillary loops. In conclusion, transformed MC may influence glomerular remodeling by changing the amount of mesangial matrix.

A linear signal transduction pathway involving phosphatidylinositol 3-kinase, protein kinase Cepsilon, and MAPK in mesangial cells regulates interferon-gamma-induced STAT1alpha transcriptional activation

Interferon-gamma (IFN-gamma) exerts an pleiotropic effect in mesangial cells in inflammatory glomerular diseases. The biologic effect of IFN-gamma is mediated by STAT1alpha. The precise mechanism by which IFN-gamma stimulates the transcriptional activity of STAT1alpha is poorly understood. I investigated the role of protein kinase C (PKC) epsilon in regulating the transcriptional activation of STAT1alpha in mesangial cells. IFN-gamma increased PKCepsilon activity in a time-dependent manner with a concomitant increase in STAT1alpha transcriptional activity. Expression of constitutively active PKCepsilon mimicked the effect of IFN-gamma on STAT1alpha-dependent transcription. Expression of dominant negative PKCepsilon inhibited IFN-gamma-induced STAT1alpha-dependent transcription. Ly294002, a pharmacological inhibitor of phosphatidylinositol (PI) 3-kinase, blocked IFN-gamma-induced PKCepsilon activity and resulted in inhibition of STAT1alpha transcriptional activity but had no effect on STAT1alpha tyrosine phosphorylation and STAT1alpha-DNA complex formation. A PKC inhibitor, H7, also had no effect on STAT1alpha tyrosine phosphorylation and DNA binding. However, Ly294002 and H7 blocked IFN-gamma-induced serine phosphorylation of STAT1alpha. These data indicate that PI 3 kinase-dependent PKCepsilon regulates STAT1alpha transcriptional activity in the absence of any effect on its DNA binding capability. In addition to activating PKCepsilon, IFN-gamma increased MAPK activity, resulting in transcriptional activation of Elk-1, a nuclear target of MAPK. Ly294002 or a dominant negative PI 3-kinase significantly blocked IFN-gamma-induced MAPK activity. On the other hand, ectopic expression of constitutively active PKCepsilon significantly increased MAPK activity. IFN-gamma-stimulated MAPK phosphorylated STAT1alpha in vitro. Inhibition of MAPK activity blocked IFN-gamma-induced serine phosphorylation of STAT1alpha; but its tyrosine phosphorylation and DNA binding were partially inhibited. Finally, expression of dominant negative MAPK significantly inhibited IFN-gamma-induced STAT1alpha-dependent transcription. These data provide the first evidence that IFN-gamma stimulates PKCepsilon in a PI 3-kinase-sensitive manner to activate MAPK, which regulates STAT1alpha transcriptional activity.

IL-18 translational inhibition restricts IFN-gamma expression in crescentic glomerulonephritis

BACKGROUND

Interleukin-18 (IL-18), a potent inducer of interferon gamma (IFN-gamma) production, is a cytokine involved in the cell-mediated immune response that is expressed during inflammatory and pathologic conditions. IFN-gamma plays a role in the development of some models of glomerulonephritis (GN); however, the role of IL-18 in the production of IFN-gamma during these pathologies has not been studied.

METHODS

Rat IL-18 cDNA was isolated and the regulation of IL-18 gene expression was studied. IFN-gamma and IL-18 expression were determined in anti-glomerular basement membrane (GBM) antibody (Ab)-induced GN. Recombinant active IL-18 (rIL-18) was used to further identify its effect on IFN-gamma production during this GN. Glomerular injury and levels of IFN-gamma were assayed in Wistar Kyoto (WKY) rats with anti-GBM GN in the presence or absence of rIL-18.

RESULTS

Rat IL-18, similar to the mouse clone, requires processing by the IL-1beta converting enzyme to become activated. A rat IL-18 5'-untranslated region (UTR) translational inhibitor was identified that strongly inhibited the synthesis of IL-18. This translational inhibitor with different lengths (180 and 130 bp) was highly expressed during GN and correlated with minimal IFN-gamma mRNA expression. Injection of recombinant active IL-18 in WKY rats with anti-GBM GN was associated with an increase of glomerular IFN-gamma levels, proliferating cell nuclear antigen (PCNA)-ED1+ cells, and PCNA-CD8+ cells, with worsening of glomerular injury.

CONCLUSION

These data suggest that the translational control of IL-18 expression by its 5'-UTR limits the production of IL-18, resulting in restricted expression of mRNA and protein IFN-gamma in this model of GN. Furthermore, it was suggested that possible IL-18/IFN-gamma induction of local proliferation of macrophages and CD8+ cells might be an important mechanism for amplifying CD8+-mediated macrophage-dependent GN.

Interferon-gamma augments acute macrophage-mediated renal injury via a glucocorticoid-sensitive mechanism

Macrophages have been implicated in causing renal injury in both human and experimental kidney disease. The aim of the current study was to determine whether modulating the state of macrophage activation directly affects the capacity of these cells to cause renal injury. This was investigated using an adoptive transfer model in which macrophage activation can be manipulated in vitro, using interferon-gamma (IFN-gamma) or dexamethasone (Dex), and then macrophage-mediated renal injury determined in vivo. In this model, rats were made leukopenic by administration of cyclophosphamide (CyPh). Two days later (day 0), animals were injected with sheep anti-GBM serum followed by a single injection of rat NR8383 macrophages on day 1 and then killed 3 or 24 h after cell transfer. NR8383 macrophages were incubated IFN-gamma and/or Dex before adoptive transfer into animals. Induction of proteinuria and glomerular cell proliferation (PCNA+ cells) in this model was dependent on transfer of NR8383 macrophages. Exposure of macrophages to IFN-gamma for 18 h (but not 3 h) before transfer caused a twofold increase in the degree of proteinuria and glomerular cell proliferation compared with unstimulated cells (Nil versus IFN-gamma; P < 0.001). This was due to an increase in the number of transferred macrophages within the glomerulus and a significant increase in degree of renal injury per transferred glomerular macrophage. IFN-gamma increased iNOS and PDGF-B gene expression and upregulated adhesion molecule expression in NR8383 macrophages. In contrast, exposure of NR8383 cells to Dex for 18 h (but not 1 h) abrogated renal injury due to a failure of transferred macrophages to accumulate within the glomerulus. In addition, Dex abrogated renal injury caused by IFN-gamma-stimulated macrophages. In conclusion, activation of macrophages by IFN-gamma, independent of any effect on other leukocytes or renal cells, can substantially augment macrophage-mediated renal injury. This IFN-gamma augmentation of renal injury is sensitive to the action of glucocorticoids, which act directly on macrophages to prevent their recruitment to the inflamed glomerulus. This study provides the first evidence that it is possible to directly modulate macrophage-mediated renal injury.

Interleukin-10 inhibits experimental mesangial proliferative glomerulonephritis

Conflicting reports exist regarding the effects of interleukin-10 (IL-10) on mesangial cells. There have been reports of both proliferative and antiproliferative effects, and both proinflammatory and anti-inflammatory effects of IL-10 on mesangial cells. However, the potential for IL-10 to affect glomerulonephritis characterized by mesangial proliferation is not known. To test the hypothesis that IL-10 would limit experimental mesangial proliferative glomerulonephritis, IL-10 was administered to rats in which mesangial proliferative glomerulonephritis was induced by administration of anti-Thy 1 antibody. Compared to control treated rats, IL-10 treated rats showed less proliferation, with fewer cells in glomeruli. Glomerular cellular proliferation was reduced, assessed by the numbers of cells within glomeruli expressing either proliferating cell nuclear antigen (PCNA) or bromodeoxyuridine. Glomerular macrophage influx (but not the proportion of glomerular macrophages that were PCNA positive) was reduced by IL-10 administration. There was no significant reduction in glomerular alpha-smooth muscle actin staining. IL-10 treatment resulted in reduced renal IL-1beta mRNA expression and reduced glomerular ICAM-1 expression, but renal expression of MCP-1 and osteopontin mRNA was unaltered. This study demonstrates that in experimental mesangial proliferative glomerulonephritis IL-10 diminishes inflammatory cell recruitment and mesangial cell proliferation. The effects of IL-10 in inhibiting mesangial cell proliferation are likely to be due to a combination of direct effects of IL-10 on mesangial cells and effects mediated by macrophages.

IP-10 and Mig production by glomerular cells in human proliferative glomerulonephritis and regulation by nitric oxide

High levels of expression of mRNA and protein for the chemokines interferon-gamma (IFN-gamma)-inducible protein of 10 kD (IP-10) (CXCL10) and the monokine induced by IFN-gamma (Mig) (CXCL9) were observed, by using in situ hybridization and immunohistochemical analyses, in kidney biopsy specimens from patients with glomerulonephritis (GN), particularly those with membranoproliferative or crescentic GN, but not in normal kidneys. Double-immunostaining or combined in situ hybridization and immunohistochemical analyses for IP-10, Mig, and proliferating cell nuclear antigen (PCNA) or alpha-smooth muscle actin (alpha-SMA) revealed that IP-10 and Mig production by resident glomerular cells was a selective property of glomeruli in which mesangial cells demonstrated active proliferation. IP-10 and Mig mRNA and protein were also expressed by primary cultures of human mesangial cells and human visceral epithelial cells after stimulation with IFN- gamma or with IFN-gamma plus tumor necrosis factor-alpha (TNF-alpha) (which produced greater stimulation). The induction of IP-10 and Mig mRNA and protein expression by IFN-gamma plus TNF-alpha was strongly inhibited by nitric oxide (NO) donors, such as sodium nitroprusside or S-nitroso-N-acetylpenicillamine, but not by cGMP analogues. Electrophoretic mobility shift assays demonstrated that NO donors repressed IP-10 gene transcription induced by IFN-gamma plus TNF-alpha through the inhibition of NF-kappaB activation. These data demonstrate that resident glomerular cells in kidneys of patients with proliferative GN produce large amounts of IP-10 and Mig, which may play important pathogenic roles in this disease. These data also indicate that the production of IP-10 and Mig by human mesangial cells can be downregulated by NO donors through cGMP-independent inhibition of NF-kappaB activation.

Effects of retinoids on the TGF-beta system and extracellular matrix in experimental glomerulonephritis

Transforming growth factor-beta1 (TGF-beta 1) overexpression plays a key role in the glomerular accumulation of extracellular matrix proteins in renal disease. Retinoids have previously been shown to significantly limit glomerular damage in rat experimental glomerulonephritis. Therefore, the effects of all-trans retinoic acid and isotretinoin on the components of the TGF-beta system and extracellular matrix proteins in anti-Thy1.1-nephritis (Thy-GN) were investigated. Vehicle-injected control rats were compared with rats treated with daily subcutaneous injections of 10 mg/kg body wt all-trans retinoic acid or 40 mg/kg body wt isotretinoin (n = 9 per group) either with a pretreatment (day -2 through 8) or posttreatment protocol (day +3 through 8), i.e., starting before or after induction of Thy-GN, respectively. Urinary TGF-beta 1 excretion was 60% lower in all-trans retinoic acid-treated animals with Thy-GN (P < 0.025). The increase of cortical TGF-beta 1 gene expression in Thy-GN rats was significantly attenuated with all-trans retinoic acid and even more with isotretinoin treatment as compared with untreated animals (P < 0.025). Cortical expression of TGF receptor II, but not receptor I gene expression, was significantly lower in animals treated with all-trans retinoic acid or isotretinoin (P < 0.05). In all-trans retinoic acid-treated animals with Thy-GN, the increase of glomerular TGF-beta 1 protein (P < 0.008) and TGF-beta 1 (P < 0.025) and TGF receptor II mRNA (P < 0.015) was significantly less. Immunohistochemistry revealed less glomerular staining for TGF-beta 1 and TGF receptor II in the presence of all-trans retinoic acid. TGF-beta 1 immunostaining was not restricted to monocytes and macrophages, as indicated by double-staining. Glomerular staining for collagen IV and collagen III was less in animals treated with isotretinoin (P < 0.02 for both) in contrast to all-trans retinoic acid, whereas fibronectin remained unchanged. It was concluded that the beneficial effects of retinoids on glomerular damage are presumably due to a marked reduction in renal TGF-beta 1 and TGF receptor II expression.

Effects of all-trans retinoic acid on renin-angiotensin system in rats with experimental nephritis

We previously demonstrated that all-trans retinoic acid (RA) preserves glomerular structure and function in anti-Thy1.1 nephritis (Wagner J, Dechow C, Morath C, Lehrke I, Amann K, Floege J, and Ritz E. J Am Soc Nephrol 11: 1479-1489, 2000). Because the renin-angiotensin system (RAS) contributes to renal damage, we 1) studied retinoid-specific effects on its components and 2) compared the effects of all-trans-RA with those of the AT(1)-receptor blocker candesartan. Rats were pretreated for 3 days before injection of the OX-7 antibody and continued with treatment with either vehicle or daily injections of 10 mg/kg all-trans-RA only (study 1) or 10 mg/kg body wt all-trans-RA, 1 mg/kg candesartan, or both (study 2) for an additional 7 days. The blood pressure increase observed in anti-Thy1.1 nephritic rats was equally normalized by all-trans-RA and candesartan (P < 0.05). In nephritic rats, mRNAs of angiotensinogen and angiotensin-converting enzyme (ACE) in the kidney were unchanged, but renin mRNA was lower (P < 0.01). Renal and glomerular AT(1)-receptor gene and protein expression levels were higher in anti-Thy1.1 nephritic rats (P < 0.05). In the renal cortex of nephritic rats, pretreatment with all-trans-RA significantly reduced mRNAs of all the examined RAS components, but in the glomeruli it increased ACE gene and protein expression (P < 0.01). In nephritic rats, candesartan reduced the number of glomerular cells and mitoses (P < 0.05) less efficiently than all-trans-RA (P < 0.01). Both substances reduced cellular proliferation (proliferating cell nuclear antigen) significantly (P < 0.05). No additive effects were noted when both compounds were combined. In conclusion, all-trans-RA influences the renal RAS in anti-Thy1.1 nephritis by decreasing ANG II synthesis and receptor expression. The beneficial effect of retinoids may be explained, at least in part, by reduction of RAS activity.

Participation of endothelial cells and transformed mesangial cells in remodeling of glomerular capillary loops in Thy-1 nephritis

The relationship between mesangial cells (MC) and endothelial cells (EC) in the remodeling of glomerular capillary loops was investigated in a rat model of anti-Thy-1 antibody (Ab)-induced glomerulonephritis. Immunohistochemical analysis showed that cells positive for alpha-smooth muscle actin (alpha-SMA) appeared in the mesangial stalks at day three, and had increased in number at day seven, after injection of Thy-1 Ab. Double staining for alpha-SMA and proliferating cell nuclear antigen (PCNA) showed that some MC expressing PCNA were negative for alpha-SMA at day three, but by day seven almost all PCNA-positive MC expressed alpha-SMA. Western blotting for alpha-SMA from isolated glomeruli was negative at day one after injection of Thy-1 Ab, but positive at day seven. Type III collagen appeared at day seven, followed by an increase of EC in the capillary loops, as determined by double immunofluorescent staining for rat endothelial cell antigen-1 (RECA-1) and type III collagen. RECA-1-positive cells increased rapidly in number after day seven and eventually showed the same distribution pattern as that in control rats. Both type I and type III collagens were expressed in the mesangial and the ballooning area of the glomerulus at day seven. Electron microscopy revealed that immature MC and EC forming small capillary lumina appeared in the enlarged mesangial area at day seven. In accordance with the increase of capillaries and the enlargement of the lumina, the number of MC and the amount of mesangial matrix decreased gradually, and most of the glomeruli returned to a normal structure by week 4. These data show that type I and type III collagen produced by transformed MC may be of benefit to proliferation of EC and remodeling of the capillary in Thy-1-induced nephritis.

Effects of pentoxifylline, pentifylline and gamma-interferon on proliferation, differentiation, and matrix synthesis of human renal fibroblasts

BACKGROUND

Kidneys that progress to end-stage renal failure are almost invariably characterized by the presence of tubulointerstitial fibrosis. Therapeutic interventions to halt the progressive deterioration of renal function are still limited. Pentoxifylline, pentifylline, and gamma-interferon have shown a potential benefit in the treatment of fibrotic processes in the skin and lung. Thus, the aim of the present study was the analysis of potential anti-fibrotic effects of these substances on human kidney fibroblasts in vitro.

METHODS

Primary renal fibroblasts were established from human kidney biopsies and were studied in addition to two renal fibroblast cell lines. Cells were first growth arrested by withdrawal of fetal calf serum (FCS) and subsequently stimulated with 10% FCS in the presence of different concentrations of pentoxifylline (PTX), pentifylline (PTF), or gamma-interferon (IFN-gamma). Fibroblast proliferation was determined by bromodeoxyuridine incorporation and cell counts. Northern and western blot hybridizations for basic fibroblast growth factor (FGF)-2 and transforming growth factor (TGF)-beta1 were performed to analyse inhibitory effects. The effects of all three substances on matrix synthesis were evaluated by immunoblot analyses and ELISA for collagen type I and fibronectin after stimulation with TGF-beta1. Finally, differentiation into myofibroblasts was examined by double immunofluorescence staining for alpha-smooth-muscle actin and Hoechst dye H33258.

RESULTS

PTX and PTF resulted in a dose- and time-dependent inhibition of proliferation in all fibroblast lines (maximum 78.9+/-6.2% at 500 microg/ml PTX). Conversely, IFN-gamma had only modest effects on fibroblast proliferation, resulting in a maximum of 36.0+/-6.1% inhibition at 500 U/ml. Northern blot hybridizations determined that FGF-2 mRNA levels in fibroblasts were decreased up to 73.7 and 91.5% by PTX (1000 microg/ml) and PTF (100 microg/ml), whereas IFN-gamma led to a reduction of 46.2% at 1000 U/ml, indicating that the inhibitory effects of all three substances may be mediated through inhibition of FGF-2 synthesis. These findings were corroborated by immunoblot analyses where again PTX and PTF had the strongest inhibitory effects. No change in TGF-beta1 mRNA levels was noted. Synthesis of cellular and secreted collagen type I was robustly inhibited by PTX and PTF, whereas IFN-gamma exerted the strongest inhibitory effect on fibronectin synthesis and secretion. In addition, IFN-gamma down-regulated the expression of alpha-smooth-muscle actin up to 73.3% (at 1000 U/ml) whereas PTX and PTF resulted in a down-regulation of up to 49.7+/-1.8 and 80.0+/-4.4% (at 1000 and 100 microg/ml) respectively. PTF was in all experiments about 10 times more potent than equimolar concentrations of PTX.

CONCLUSIONS

PTX and PTF exerted robust inhibitory effects on fibroblast proliferation, extracellular matrix synthesis, and myofibroblastic differentiation. Conversely, IFN-gamma caused strong inhibition of fibronectin synthesis and alpha-smooth-muscle cell actin expression but had only weak inhibitory influences on fibroblast proliferation and collagen type I synthesis. Inhibitory effects of all three substances on proliferation may be mediated through inhibition of FGF-2 synthesis.

Platelet-derived growth factor, basic fibroblast growth factor, and interferon gamma increase type IV collagen production in human fetal mesangial cells via a transforming growth factor-beta-dependent mechanism

BACKGROUND

Glomerulosclerosis is characterized by glomerular accumulation of extracellular matrix following mesangial cell proliferation. The precise pathomechanism of glomerulosclerosis is still undetermined. Platelet-derived growth factor (PDGF) and basic fibroblast growth factor (b-FGF) are known to be mitogenic for mesangial cells, and interferon gamma (IFN-gamma) is known to have an inhibitory effect on mesangial cell proliferation. We attempted to clarify the role of these cytokines on mesangial matrix production using cultured human fetal mesangial cells (HMC).

METHODS

HMC were incubated with these cytokines for 24-72 h and the levels of type IV collagen and TGF-beta in the cell supernatants were measured by enzyme immunoassay.

RESULTS

PDGF, b-FGF, and IFN-gamma stimulated type IV collagen production by HMC in a dose- and time-dependent manner. The anti-TGF-beta neutralizing antibody clearly inhibited their stimulatory effect on type IV collagen production. PDGF and b-FGF also stimulated TGF-beta production by HMC in a dose-dependent manner, although IFN-gamma did not.

CONCLUSION

PDGF, b-FGF, and IFN-gamma stimulate type IV collagen production in cultured HMC via a TGF-beta-dependent mechanism.

Interferon-gamma inhibits experimental renal fibrosis

Interferon-gamma inhibits experimental renal fibrosis.

BACKGROUND

Recent evidence has implicated myofibroblasts as a cell type responsible for the laying down of extracellular matrix components during fibrosis in a number of organs. In this study, we examined the capacity of interferon-gamma (IFN-gamma) to inhibit the activation of fibroblasts to the myofibroblastic phenotype and hence reduce the extent of renal scarring in the rat subtotal nephrectomy (SNx) model using a novel method of intrarenal delivery.

METHODS

Rats were divided into four groups: sham, SNx (group 1), SNx + drug vehicle (group 2) and SNx + IFN-gamma (400 units/day; group 3) for 30 days. Rats were sacrificed on days 15, 30, 45, and 90 following SNx.

RESULTS

Clinical data showed a marked reduction in proteinuria in the group treated with IFN-gamma (161 vs. 280 mg/24 hr by day 45, P < 0.01) and a preservation of the creatinine clearance (1.16 vs. 0. 84 ml/min by day 45, P < 0.05) when compared to the SNx or SNx + vehicle groups throughout the time course. Immunohistochemical staining for alpha-smooth muscle actin (alpha-SMA) revealed a reduction in myofibroblastic cell types (6.5 +/- 3.1% glomerular alpha-SMA in group 3 compared with 14.8 +/- 4.2% glomerular alpha-SMA in group 2, P < 0.05, 3.8 +/- 1.4% tubulointerstitial alpha-SMA in group 3 compared with 8.8 +/- 2.0% tubulointerstitial alpha-SMA in group 2 on day 45, P < 0.05). There was also a reduction in immunostaining for collagens III and IV in the IFN-gamma-treated group. Scoring for both glomerulosclerosis and tubulointerstitial fibrosis in the IFN-gamma group (group 3) was lower than the other two operated groups.

CONCLUSIONS

We conclude that IFN-gamma, administered at a dose of 400 units/day, has a strong inhibitory effect on myofibroblasts and that as a possible result of this action, renal fibrosis is reduced and renal function is preserved in the rat SNx model. The IFN-gamma renoprotective effect lasted only for the extent of its administration and subsided when discontinued.

Pentoxifylline attenuates experimental mesangial proliferative glomerulonephritis

BACKGROUND

Accumulation of glomerular macrophages, proliferation of mesangial cells (MCs), and deposition of extracellular matrix proteins are pathobiological hallmarks of glomerulonephritis. We previously reported that a clinically available nonselective inhibitor of cyclic 3',5'-nucleotide phosphodiesterase, pentoxifylline (PTX), inhibits proliferation of cultured rat MCs, as well as collagen production by these cells. In this study, we investigated the in vivo effects of PTX on rat anti-Thy1 disease, a model of mesangial proliferative nephritis.

METHODS

Anti-Thy1 nephritis was induced in Sprague-Dawley rats by injecting mouse anti-rat Thy1 antibodies intravenously. Nephritic rats were randomly assigned to receive PTX (0.1 g/kg/day) or vehicle (phosphate-buffered saline) and were sacrificed at various time points. Paraffin kidney sections were stained with hematoxylin and periodic acid-Schiff reagents for glomerular histology. Frozen kidney sections were stained by monoclonal antibodies against proliferating cell nuclear antigen, ED-1, and alpha-smooth muscle actin and were visualized by color development from a horseradish peroxidase reaction. Monocyte chemoattractant protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1), and various extracellular matrix mRNAs were analyzed by Northern blotting. Urine protein concentrations were determined by Lowry's method.

RESULTS

Nephritic rats treated with PTX excreted less urinary protein on day 5 of nephritis than vehicle-treated nephritic rats. In periodic acid-Schiff-stained kidneys from PTX-treated nephritic rats, there was attenuation of both glomerular cellularity and glomerular sclerosis compared with vehicle-treated nephritic rats. PTX decreased the augmented glomerular mRNA levels of MCP-1 and ICAM-1 at two hours and on day 1 of nephritis. Immunoreactive staining showed that PTX reduced the number of proliferating glomerular macrophages on days 1, 2, and 3, but not at two hours of nephritis, compared with vehicle-treated nephritic rats. On day 5, PTX decreased the number of activated proliferating MCs and attenuated the glomerular mRNA levels of type I (alpha1), type III (alpha1), and type IV (alpha1) collagen and fibronectin compared with vehicle-treated nephritic rats.

CONCLUSION

The administration of PTX to rats with anti-Thy1 disease reduces accumulation and proliferation of glomerular macrophages, attenuates proteinuria, suppresses activation and proliferation of MCs, and ameliorates glomerular sclerosis. These results suggest that PTX may have a suppressive effect in acute phases or relapses of mesangial proliferative glomerulonephritis.

Increased Susceptibility to Immunologically Mediated Glomerulonephritis in IFN-γ-Deficient Mice

It is postulated that IFN-γ confers susceptibility to immunologically mediated tissue injury. To test this hypothesis, we compared the intensity of accelerated anti-glomerular basement membrane glomerulonephritis between wild-type (IFN-γ+/+) and IFN-γ gene knockout (IFN-γ−/−) mice. This disease model is initiated by binding of heterologous (sheep) anti-glomerular basement membrane Abs to the glomeruli of mice preimmunized with sheep IgG. The secondary cellular and humoral immune responses to the planted Ag then lead to albuminuria and glomerular pathology. We found that IFN-γ−/− mice or IFN-γ+/+ mice injected with IFN-γ-neutralizing Ab develop worse albuminuria and glomerular pathology than IFN-γ+/+ mice. The humoral response to sheep IgG (serum mouse anti-sheep IgG titers and intraglomerular mouse IgG deposits) was comparable in the IFN-γ+/+ and IFN-γ−/− groups. In contrast, IFN-γ−/− mice mounted a stronger cellular immune response (cutaneous delayed-type hypersensitivity reaction) to sheep IgG than IFN-γ+/+ mice. These findings provide evidence that endogenous IFN-γ has a protective role in immunologically mediated glomerulonephritis initiated by foreign Ags.

Expression of interferon-inducible Mx-proteins in patients with IgA nephropathy or Henoch-Schönlein purpura

Both viral infections and dysregulated cytokine synthesis have been implicated in the pathogenesis of immunoglobulin A nephropathy (IgAN) and Henoch-Schönlein purpura (HSP). Mx proteins are specifically induced by type I interferons (IFN-alpha, -beta, -omega) and are very sensitive in detecting, for example, virus-induced, in vivo production of IFN-alpha/-beta, because the biological half-life of Mx (approximately 3 days) markedly exceeds that of IFN-alpha/-beta (20 to 90 minutes). Mx concentrations in leukocytes were measured by enzyme-linked immunosorbent assay (ELISA) in 79 blood samples of 35 patients with IgAN and five with HSP. No patient showed symptoms of infections at the time of the examination. Compared with normal leukocyte Mx concentrations (<2 mU/1,000 leukocytes), only 3 of 79 samples of IgAN/HSP patients showed mildly elevated Mx concentrations (range, 2.2 to 3 mU/1,000 leukocytes). By contrast, patients with increased endogenous IFN production (lupus erythematosus) or patients treated with IFN-alpha2 showed leukocyte Mx concentrations of up to 35 mU/1,000 leukocytes. In patients with IgAN and HSP, leukocyte Mx concentrations were not correlated with various clinical parameters. Immunohistochemically, no renal Mx expression could be detected in eight renal biopsy specimens of patients with various stages of IgAN, whereas control specimens (skin of patients treated with IFN-alpha2) showed abundant cellular Mx expression. Furthermore, human mesangial cells in vitro showed marked Mx production after exposure to IFN-alpha or IFN-beta. We conclude that, in patients with IgAN/HSP, no evidence of an activation or dysregulation of the type I interferon system can be detected.

Anti-angiogenic compound (TNP-470) inhibits mesangial cell proliferation in vitro and in vivo

Growth factors, especially basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), and transforming growth factor-beta (TGF-beta) are known to play key roles in the pathogenesis of mesangial proliferative glomerulonephritis. TNP-470 (AGM-1470), a potent anti-angiogenic compound, has anti-growth factor properties and inhibits the activation of cyclin-dependent kinase (cdk) 2 and phosphorylation of RB protein. We investigated whether TNP-470 could suppress growth factor induced mesangial cell proliferation in vitro and experimental model of mesangial proliferative glomerulonephritis in vivo. TNP-470 inhibited potently PDGF- and bFGF-stimulated proliferation of rat mesangial cells in vitro (IC50 = 50 pg/ml). In anti-Thy 1.1 glomerulonephritis, high dose use of TNP-470 (20 mg/kg/day) markedly suppressed mesangial cell proliferation and mesangial matrix expansion on day 6; however, mesangiolysis remained. Low dose use of TNP-470 (10 mg/kg/day) moderately inhibited mesangial cell proliferation and mesangial matrix synthesis, and induced appropriate glomerular healing on day 14 in anti-Thy 1.1 glomerulonephritis. Thus, TNP-470 potently inhibits growth factor-induced proliferation of mesangial cells in vitro, and mesangial cell proliferation and extracellular matrix expansion in anti-Thy 1.1 glomerulonephritis in vivo. These results suggest a novel therapeutic potential of TNP-470 in mesangial proliferative glomerulonephritis.

Role of serotonin in nephrotoxic serum nephritis in WKY rats

Our objective was to determine whether serotonin is involved in inducing nephrotoxic serum nephritis in WKY rats. After injection of antiglomerular basement membrane antiserum, urinary protein excretion was significantly decreased in rats treated with the serotonin receptor antagonist, MCI-9042, and in rats treated with p-chlorophenylalanine. Similarly, severe necrotizing lesions and crescent formation were inhibited in a dose-dependent manner by treatment with MCI-9042 and p-chlorophenylalanine. The number of intraglomerular ED-1-positive cells was increased on day 3 and thereafter in the placebo group. A significant increase in the number of crescent lesions was observed in the placebo group on day 7 and thereafter. Neither adenosine diphosphate- nor collagen-induced platelet aggregations were inhibited in platelet-rich plasma from rats treated with MCI-9042. No significant differences were observed in the production of circulating antibody and antibody deposition in rat glomeruli among the study groups. These results indicate that pathologic changes and urinary protein excretion are closely related to the presence of serotonin in nephrotoxic serum nephritis of WKY rats. Thus serotonin may play a key role in the glomerular injury in this model. Studies on the mode of action of MCI-9042 on platelet aggregation in vivo indicate that the antiplatelet effect of this drug did not contribute to the inhibition of renal injury in this experimental model. This study suggests that serotonin participates in macrophage-mediated immune injury in nephrotoxic serum nephritis of WKY rats.

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.

Prostaglandin E1 inhibits collagen expression in anti-thymocyte antibody-induced glomerulonephritis: possible role of TGF beta

To test whether or not prostaglandins mediate extracellular matrix formation in immune-mediated glomerular disease, rats with anti-thymocyte antibody-induced glomerulonephritis were treated with prostaglandin E1 (PGE1) (250 micrograms/twice daily/s.c.). Glomerular expression of collagen types III and IV was assessed by Northern blotting, immunohistology and Western blotting. Proliferation of glomerular cells was evaluated by staining for the proliferating cell nuclear antigen (PCNA) and consecutive cell counting. At day five after induction of the disease, glomerular mRNA levels of collagen types III and IV were three- to fivefold higher compared with non-nephritic controls. Similarly glomerular deposition of these collagens was markedly increased when assessed by immunohistology. The treatment of nephritic rats with PGE1 reduced the increased glomerular mRNA levels as well as the protein concentration and the deposition of extracellular collagens. The number of PCNA positive cells which was significantly higher in nephritic rats when compared with control animals (24 hr, nephritis 2.53 +/- 0.33 and Control 0.26 +/- 0.06, P = 0.011; 5 days, nephritis 5.10 +/- 1.13 and Control 0.75 +/- 0.08, cells per glomerular cross section, P = 0.03) was reduced by PGE1 (24 hr, nephritis+PGE1 0.44 +/- 0.30, P = 0.0001; 5 days, nephritis +/- PGE1 1.91 +/- 1.84 cells per glomerular cross section, P = 0.001). Prostaglandin E1 also ameliorated the glomerular infiltration of monocytes at 24 hours (nephritis 4.36 +/- 2.82, nephritis + PGE1 2.20 +/- 1.82, cells per glomerular cross section) and five days (nephritis 1.51 +/- 0.58, nephritis+PGE1 1.12 +/- 0.61, cells per glomerular cross section). To further characterize possible mechanisms by which PGE1 reduces extracellular matrix deposition, the glomerular expression of transforming growth factor (TGF-beta), and interleukin 1 beta (IL-1 beta) was assessed by Northern blotting. Nephritic glomeruli showed increased mRNA levels of TGF-beta at day 5 and IL-1 beta at 24 hours when compared with control kidneys. Treatment of the animals with PGE1 inhibited the mRNA expression of TGF-beta and IL-1 beta. These data demonstrate that PGE1 reduces the glomerular expression of extracellular matrix proteins in anti-thymocyte antibody-induced glomerulonephritis, suggesting a beneficial role of prostaglandins in this proliferative glomerular immune injury. The effects of PGE1 might be mediated by inhibition of TGF-beta and IL-1 beta production.

Dissociation of glomerular hypertrophy, cell proliferation, and glomerulosclerosis in mouse strains heterozygous for a mutation (Os) which induces a 50% reduction in nephron number

We reported that the Os mutation in ROP mice induced a 50% reduction in nephron number, glomerular hypertrophy, and severe glomerulosclerosis. We examined two mouse strains with the Os mutation, ROP Os/+ and C57 Os/+ mice, to determine whether the genetic background influenced the development of glomerulosclerosis. Nephron number was decreased by 50% in both ROP Os/+ and C57 Os/+ mice, and a glomerular volume and labeling index were two- to threefold increased in both. Whereas glomerulosclerosis was severe in ROP Os/+ mice, it was absent or minimal in C57 Os/+ mice. ROP Os/+ glomeruli had two- to threefold more type IV collagen, laminin, and tenascin than C57 Os/+ by immunofluorescence microscopy. Glomerular alpha 1IV collagen and tenascin mRNA levels were increased (2.8- and 1.7-fold) in ROP Os/+ and in C57 Os/+ (1.7- and 1.4-fold) mice. Both ROP Os/+ and C57 Os/+ mice had a slight increase (1.5- and 1.7-fold) in 72-kD collagenase mRNA levels. Whereas laminin B1 mRNA levels were twofold higher in ROP +/+ than in C57 +/+ mice, there was no further change in the presence of the Os mutation. Thus, the response to the Os mutation depended on the mouse strain, since severe glomerulosclerosis occurred only in ROP Os/+ mice, even though cell proliferation and glomerular hypertrophy also were present in C57 Os/+ mice.

Local macrophage proliferation in the progression of glomerular and tubulointerstitial injury in rat anti-GBM glomerulonephritis

The aim of this study was to examine the contribution of local proliferation in the development of macrophage accumulation and macrophage-mediated injury in rat anti-GBM glomerulonephritis. Using double immunohistochemistry staining of monocyte/macrophages plus the proliferating cell nuclear antigen (PCNA) or bromodeoxyuridine (BrdU) incorporation, we found that the initial accumulation of ED1+ macrophages in the kidney on day 1 of disease was due to an influx of circulating monocytes. However, large numbers of proliferating macrophages (ED1+PCNA+cells), including mitotic macrophages, were present within the glomerulus and interstitium during disease progression (days 7 to 21), accounting for up to 62% of the total macrophage population and giving an excellent correlation with total macrophage accumulation (glomerulus, r = 0.92; interstitium, r = 0.94; both P < 0.001). These proliferating cells had a monocyte phenotype (ED1+ED2-ED3-), but this marked proliferative activity was restricted to the diseased kidney since no PCNA expression or BrdU incorporation was evident within circulating blood monocytes. Proliferating macrophages were almost exclusively localized in areas of severe tissue damage and they correlated significantly with glomerular and tubulointerstitial lesions (P < 0.001), proteinuria (P < 0.001) and creatinine clearance (P < 0.01). In marked contrast, glomerular PCNA- macrophages failed to correlate with these parameters. In conclusion, this study has demonstrated that local macrophage proliferation is the major mechanism of macrophage accumulation during the progression of rat anti-GBM glomerulonephritis. Furthermore, it suggests that proliferating macrophages are potent local effector cells in the mediation of progressive renal injury in this disease.