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Glomerular Bioengineering Unit, Department of Medicine, University College London Medical School, London, United Kingdom
| Abstract |
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) deactivator, may attenuate M
-mediated acute glomerular
injury. Using stromelysin as an indicator, this study investigated
whether and how endogenous TGF-ß1 modulates the glomerular cell
activation triggered by M
. Rat mesangial cells were stably
transfected with a cDNA encoding the active form of TGF-ß1 and a cDNA
coding for a dominant-negative mutant of the TGF-ßR type II. Compared
with mock-transfected cells, TGF-ß1 transfectants exhibited blunted
expression of stromelysin in response to the M
-derived, inflammatory
cytokine IL-1ß. In contrast, mesangial cells expressing the
dominant-interfering TGF-ßR showed enhanced expression of stromelysin
in response to IL-1ß, suggesting that endogenous TGF-ß functions as
an autocrine inhibitor of the IL-1 response. In isolated, normal rat
glomeruli, externally added TGF-ß1 suppressed the induction of
stromelysin by mediators that were elaborated by activated M
.
Similarly, when isolated, nephritic glomeruli producing the active form
of TGF-ß1 were stimulated by IL-1ß or M
-conditioned medium, the
induction of stromelysin was dramatically suppressed as compared with
normal glomeruli. To investigate whether endogenous TGF-ß1 affects
the glomerular cell activation triggered by M
, a technique for
adoptive M
transfer was used. LPS-stimulated reporter M
were
transferred into either normal rat glomeruli or nephritic glomeruli
expressing active TGF-ß1. In the normal glomeruli, stromelysin
expression was markedly induced in resident cells after the transfer of
activated M
. This induction was substantially repressed in those
glomeruli producing active TGF-ß1. These results reinforce the idea
that TGF-ß1 is an endogenous defender that attenuates certain actions
of infiltrating M
in the glomerulus. | Introduction |
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TGF-ß is known to be a potent regulator of immune systems and
inflammatory processes, and generally functions as an immunosuppressor
(6). This molecule represses B cell proliferation and Ig secretion,
mitogenesis and cytokine production by thymocytes/T lymphocytes, and
function of NK cells. TGF-ß inhibits neutrophil and T cell adhesion
to the endothelium (7) and strongly deactivates macrophages
(M
)3 at picomolar
concentrations (8). Based on the fact that M
play a crucial role in
the generation of various glomerular diseases, TGF-ß may function as
a potential inhibitor of M
-mediated glomerular injury (9). Recent
investigations have provided evidence regarding the beneficial action
of TGF-ß1 in the glomerulus. For example, mesangial cells produce
biologically active TGF-ß1 that inhibits the adhesion of M
on
various substrata and leads to their subsequent deactivation (10).
Mesangial cell-derived TGF-ß1 depresses M
production of injurious
inflammatory mediators, including IL-1ß, IL-6, TNF-
, and monocyte
chemoattractant protein-1 (11, 12). These data indicate that TGF-ß
may inhibit the activation of glomerular cells via suppression of local
M
function.
Stromelysin/transin is a matrix-degrading metalloproteinase
that plays an important role in the metabolism of the extracellular
matrix. Tightly controlled expression of this enzyme supposedly
required for organogenesis and wound healing, and its uncontrolled
expression is associated with certain pathologies, including tumor
invasion/metastasis, inflammation, and atherosclerosis (13, 14, 15).
Stromelysin is a multipotent matrix degrader; i.e., it degrades
collagens, glycoproteins, and proteoglycans (16), which are all
components of the glomerular basement membrane and the mesangial
matrix. Overexpression of stromelysin induces an aberrant breakdown of
the glomerular matrix and thereby contributes to its structural and
functional alteration (17, 18). Mesangial cells have the ability to
produce stromelysin abundantly in response to the M
-derived
proinflammatory cytokine, IL-1ß (19). When stromelysin was
overexpressed via genetic manipulation, mesangial cells exhibited an
altered phenotype: enhanced mitogenesis and migration (20).
Furthermore, when activated M
were transferred into normal rat
glomeruli, stromelysin was substantially induced in resident glomerular
cells (21). These data suggest a pathologic implication of stromelysin
in M
-associated glomerular injury.
Using stromelysin as an indicator molecule, the present investigation
examines whether and how endogenous TGF-ß1 modulates the glomerular
cell activation triggered by M
. This study provides evidence that
mesangial cell-derived TGF-ß1 is a glomerular "defender" that
attenuates M
-mediated activation of resident cells.
| Materials and Methods |
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Rat mesangial cells were cultured from the isolated glomeruli of
an adult male Sprague-Dawley rat (22) and identified as being of
mesangial cell phenotype (23). The normal alveolar M
NR8383 (24),
derived from a Sprague-Dawley rat, and the mink lung epithelial cell
line CCL64 (25), were purchased from the American Type Culture
Collection (Rockville, MD). These cells were maintained in DMEM/Hams
F-12 (DMEM-F12) (Life Technologies, Gaithersburg, MD) supplemented with
10 to 15% FCS.
The mesangial cell clone MTG6 that stably expresses the active form of porcine TGF-ß1 was established using the calcium phosphate coprecipitation method (26). This clone produces and secretes high levels of biologically active TGF-ß1 (26). Mock transfectants were established by transfecting mesangial cells with an empty plasmid, pHßAPr-1-neo (27). To abrogate function of the TGF-ßR type II (RII), mesangial cells were cotransfected with pRIIDN (a gift from Dr. R. Derynck, University of California, San Francisco; 28 , which codes for a dominant-negative mutant of TGF-ß RII and pRc/CMV (Invitrogen, Carlsbad, CA) that introduces a neomycin phosphotransferase gene. Overexpression of the mutant receptor gene leads to impaired TGF-ß signaling in a dominant-negative fashion, as demonstrated previously (28). Stable transfectants were selected in the presence of neomycin analogue G418 (750 µg/ml), and clones MRIIDN4 and MRIIDN8 were established. Untransfected cells and mock-transfected cells were used as controls.
Reporter M
BAGMACNR were generated as described
previously (21). These cells express a bacterial ß-galactosidase gene
that is under the control of the long terminal repeat of the Moloney
murine leukemia virus. BAGMACNR cells also express a
neomycin phosphotransferase gene that renders the cells resistant to
G418. In contrast to BAGMACNR cells, resident glomerular
cells are susceptible to G418. This difference allows for the selective
subtraction of resident cell mRNAs from the total mRNAs expressed in
BAGMACNR-containing, chimeric glomeruli (neomycin
subtraction method) (21).
Conditioned media
M
-conditioned media (M
CM) were prepared as follows. NR8383
cells cultured in 1% FCS/DMEM-F12 were stimulated with or without 1
µg/ml of LPS (Escherichia coli 0111:B4; Sigma, St.
Louis, MO) for 6 h. Cells were washed three times and reseeded in
fresh DMEM-F12 containing 1% FCS. After 24 h, the media were
collected and filtered. M
CM diluted at 1:1 (50%) was used for
experiments.
M
CM were prepared from isolated, normal and nephritic glomeruli. To
create the latter, anti-Thy-1 glomerulonephritis was induced in
adult male Sprague-Dawley rats (four rats with a body weight of
250350 g) (23) by a mAb, 1-22-3 (29). Media conditioned by normal or
nephritic (day 7) glomeruli were prepared by incubating isolated
glomeruli (1 x 104) in 1 ml of 0.5% FCS/DMEM-F12 for
24 h. M
CM diluted at 1:4 (20%) was used for the assessment of
TGF-ß bioactivity.
Assessment of TGF-ß activity
A growth inhibition assay of the mink lung epithelial cell line CCL64 was used to measure the bioactivity of TGF-ß (26). In brief, CCL64 cells were seeded in 24-well plates at a density of 5 x 103 cells/well. After incubation for 24 h, cells were further incubated in 1% FCS/DMEM-F12 for 24 h and then exposed to diluted test media. After 48 h, [3H]thymidine (1 µCi/well) was added and incubated for 3 h, and incorporation of radioactivity was subsequently measured by liquid scintillation counting. Human TGF-ß1 (Genzyme, Cambridge, MA) was used as a standard. Assays were performed in quadruplicate.
Northern blot analysis
The expression of stromelysin was examined by Northern blot
analysis. Mesangial cells or isolated glomeruli (
1 x
104) were exposed to 5 to 10 ng/ml of human rIL-1ß
(a gift from Otsuka Pharmaceutical, Tokushima, Japan) or 1:1-diluted
M
CM for 18 h and subjected to analyses. To examine the effect
of TGF-ß, isolated, normal glomeruli were pretreated with TGF-ß1
(20 ng/ml) for 6 h and then stimulated with M
CM. After 18
h, glomeruli were harvested and used for RNA extraction.
Northern blot analysis was performed as previously described (20). In brief, total RNA was extracted by a single-step method (30), and RNA samples were electrophoresed on 1.2% agarose gels and transferred onto nitrocellulose membranes. For hybridization, a truncated human TGF-ß RII cDNA (28) and a rat stromelysin-1 cDNA (31) were labeled with [32P]deoxy-CTP using the random priming method. As loading controls, a chicken ß-actin cDNA and a rat glyceraldehyde-3-phosphate dehydrogenase cDNA were used. The membranes were hybridized with probes at 65°C overnight in a solution containing 4x SSC (600 mM sodium chloride, 60 mM sodium citrate), 5x Denhardts solution, 10% dextran sulfate, 50 µg/ml herring sperm DNA, and 50 µg/ml poly(A). These membranes were subsequently washed at 50°C and exposed to Kodak XAR films at -80°C. Densitometric analysis was performed using a computerized program, the National Institutes of Health Image program. The intensity of each message normalized by the density level of ß-actin mRNA was used to compare data in different groups.
Adoptive transfer of activated M
into the glomerulus
To investigate the role of M
in the expression of stromelysin
in normal and nephritic glomeruli, a technique for in vivo M
transfer was used (21). Via the renal circulation,
BAGMACNR cells that had been stimulated by 1 µg/ml
LPS for 16 h (1 x 106 cells) were transferred
into normal rat glomeruli or into glomeruli that were in the
regeneration phase of acute anti-Thy-1 glomerulonephritis (day 7),
in which TGF-ß1 is up-regulated (a total of 16 Sprague-Dawley rats
with a body weight of 250350 g). Immediately after the cell
injection, both kidneys were removed and processed for glomerular
isolation. One-third (0.51 x 104) of the glomeruli
isolated from each kidney were immediately frozen at -80°C. The
remaining glomeruli were incubated for 24 h in 1% FCS/DMEM-F12
with or without G418 (200 µg/ml) and then stored at -80°C. The
induction of stromelysin was examined by Northern blot analysis. In
this experimental setting, mRNA expression in resident glomerular
cells, but not in BAGMACNR cells, is selectively abolished
by G418 (21).
X-gal assay
To evaluate cell transfer efficiency, isolated glomeruli containing BAG MACNR cells were subjected to 5-bromo-4-chloro-3-indolyl ß-D-galactopyranoside (X-gal) assay (23, 32). In brief, isolated glomeruli were fixed in 0.5% glutaraldehyde, 2 mM MgCl2, and 1.25 mM EGTA in PBS at 4°C overnight and then incubated at 37°C for 1 to 2 h in a reaction buffer containing 1 mg/ml X-gal (Sigma), 20 mM K3Fe(CN)6, 20 mM K4Fe(CN)6 · 3H2O, 2 mM MgCl2, 0.01% sodium desoxycholate, and 0.02% Nonidet P-40 in PBS. More than 100 glomeruli were randomly selected, and percentages of X-gal-positive glomeruli were determined by light microscopy.
Data presentation
All experiments were repeated two to four times, and representative results are shown. Data are expressed as means ± SE. Statistical analyses were performed using the nonparametric Mann-Whitney U test. A p value of <0.05 was used to indicate a statistically significant difference.
| Results |
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Cultured mesangial cells have the ability to produce biologically
active TGF-ß1 (10, 11, 33). To investigate whether the overexpression
of TGF-ß modulates the responsiveness of mesangial cells to
M
-derived cytokines, rat mesangial cells were stably transfected
with a cDNA encoding the active form of TGF-ß1. The established MTG6
cells expressed a transgene transcript, produced higher levels of
active TGF-ß, and exhibited lower mitogenic activity than
mock-transfected cells (26). Using these transfectants, the expression
of stromelysin in response to IL-1ß was examined. Northern blot
analysis revealed that IL-1ß markedly induced stromelysin gene
expression in mock-transfected cells. In contrast, this induction was
dramatically depressed in MTG6 cells overexpressing active TGF-ß1
(Fig. 1
).
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Cultured mesangial cells express stromelysin in response to
M
-derived cytokines (19). However, it is undetermined whether
glomeruli that are stimulated by cytokines express this
metalloproteinase. To examine this possibility, isolated, normal rat
glomeruli were stimulated with either IL-1ß or medium conditioned by
activated M
, and the expression of stromelysin was examined by
Northern blot analysis. A modest expression of stromelysin was observed
in unstimulated glomeruli. This expression was substantially
up-regulated when the glomeruli were stimulated by either IL-1ß or
M
CM (Fig. 3
A).
|
CM. Northern blot analysis revealed
that TGF-ß1 inhibited the induction of stromelysin in the glomerulus
(Fig. 3
To examine whether endogenous TGF-ß1 is able to inhibit the
expression of stromelysin in the glomerulus, an acute model of
anti-Thy-1 glomerulonephritis was used. In this model, TGF-ß1 is
up-regulated in activated mesangial cells during the regeneration of
the glomerulus (34). Glomeruli were isolated from normal rat kidneys or
kidneys that were subjected to the anti-Thy-1 glomerulonephritis
(day 7). Compared with normal glomeruli, the regenerating glomeruli
produced higher levels of biologically active TGF-ß, as evidenced by
the inhibition of [3H]thymidine incorporation by CCL64
cells (7.5 ± 12.3% inhibition (not significant) in normal
glomeruli and 34.5 ± 6.7% inhibition (p
< 0.05) in nephritic glomeruli). Isolated glomeruli were subsequently
stimulated by IL-1ß or M
CM, and the expression of stromelysin was
examined by Northern blot analysis. Consistent with the effect of
externally added TGF-ß1, the induction of stromelysin was
dramatically suppressed in the glomeruli producing active TGF-ß1
(Fig. 3
C).
Inhibitory effect of endogenous TGF-ß on the M
-triggered
stromelysin expression in the glomerulus
Using a technique for in vivo M
transfer, we previously
reported that activated M
induce stromelysin expression in the
normal glomerulus (21). To examine whether the M
-triggered
stromelysin expression is inhibited by endogenous TGF-ß1,
BAGMACNR M
stimulated with LPS were transferred
into normal rat glomeruli or into glomeruli that had been subjected to
acute anti-Thy-1 glomerulonephritis (day 7). After the cell
transfer, glomeruli were isolated and used for X-gal assay and Northern
blot analysis. X-gal assay on isolated glomeruli showed that there was
no significant difference in the percentages of X-gal-positive
glomeruli between normal (73.2 ± 3.4%, n = 10)
and nephritic conditions (71.0 ± 2.9%, n = 6).
The expression of stromelysin in isolated chimeric glomeruli was
subsequently examined by Northern blot analysis (Fig. 4
). Immediately after the cell transfer,
the stromelysin transcript was not detectable in both normal and
inflamed glomeruli. After ex vivo incubation of these chimeric
glomeruli, stromelysin mRNA was induced in M
-transferred, normal
glomeruli. This induction was abolished by the treatment of glomeruli
with G418, indicating that resident cells, but not transferred M
,
are responsible for the expression of stromelysin. In the regenerating
glomeruli that express TGF-ß1, the stromelysin expression triggered
by M
was markedly suppressed (19.1 ± 2.4%, n
= 3) compared with its induction in normal glomeruli (100%).
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| Discussion |
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. IL-1 stimulates resident glomerular cells to cell
proliferation, aberrant matrix metabolism, and the release of
inflammatory mediators (35). The injection of IL-1 exacerbates, but the
blocking of IL-1 activity attenuates, experimental glomerulonephritis,
suggesting its crucial pathologic contribution (36). IL-1 induces
metalloproteinase stromelysin in glomerular cells (19). Using this
molecule as an indicator, the present study investigated how endogenous
TGF-ß modulates the stimulatory effect of M
-derived cytokines on
the glomerulus. In both mesangial cells and isolated, normal glomeruli,
externally supplied or internally produced TGF-ß inhibited the
expression of stromelysin in response to M
-derived factors,
including IL-1ß. Consistent with these results, the glomeruli
producing the active form of TGF-ß1 exhibited resistance against the
M
-triggered stromelysin induction. This effect may be due to the
suppressive effect of TGF-ß1 on the production of cytokines by
activated M
(10, 11). Another explanation could be that TGF-ß
inhibited the cytokine response of glomerular cells via intervention in
certain signaling pathways (26). In support of this possibility,
transfection experiments showed that the dominant-negative inhibition
of TGF-ß signaling enhanced the IL-1 response of mesangial cells. The biologic actions of TGF-ß are mediated by specific cell surface receptors, TGF-ßR type I (RI) and RII. TGF-ß1 initially binds to RII that has a constitutively active kinase. RI is then recruited to the complex and phosphorylated by RII, leading to the propagation of the signal to downstream substrates (37). Based on this current dogma, both RI and RII are required for TGF-ß signaling, and the functional inhibition of either RI or RII should abrogate the biologic actions of TGF-ß. However, some early reports suggested separate signaling pathways for the antiproliferative and matrix-regulatory effects of TGF-ß. For example, the functional inactivation of RII did inhibit the TGF-ß regulation of mitogenesis, but it did not affect the stimulatory effects of TGF-ß on the synthesis of fibronectin and plasminogen activator inhibitor I (28). It has been suggested that RII is essential for the control of mitogenesis by TGF-ß but might be not necessary for its regulation of the genes associated with matrix turnover. The present study showed that the dominant-negative inactivation of RII abrogated the effect of TGF-ß on the expression of stromelysin in mesangial cells. Therefore, RII is required in certain cell types for the TGF-ß regulation of genes involved in matrix turnover. This finding is consistent with a recent report using primary hepatocytes derived from dominant-negative RII-transgenic mice (38).
The infiltration of monocytes/M
is a common pathologic feature of a
wide range of human and experimental glomerular diseases (39). M
infiltration is correlated with both structural and functional changes
of the glomerulus, and depletion of M
attenuates glomerular damage
and proteinuria in several forms of experimental glomerulonephritis
(39). However, in the process of acute inflammation, the M
-initiated
pathologic change is self-limiting. Endogenous, antiinflammatory
machinery may exist to turn off the inflammatory process toward
resolution. The TGF-ß1 produced by activated mesangial cells is a
possible molecular switch (9). Together with the fact that TGF-ß1 is
an autocrine inhibitor of mesangial cell proliferation (26, 33), the
present results further support the possibility that TGF-ß1 is a
glomerular defender that attenuates M
-mediated glomerular cell
activation.
Several cytokines are regarded as deactivators of M
. Those include
IL-4, IL-10, IL-13, and TGF-ß (40). In the present study, the role of
TGF-ß was highlighted, but other cytokines could also function
against the inflammatory process initiated by M
. Recent
investigations have shown that, under pathologic circumstances,
glomeruli express IL-4, IL-10, and IL-13 (41, 42, 43, 44). When these cytokines
are administered into animals that have been subjected to experimental
glomerulonephritis, histopathologic changes are attenuated (45).
Although these cytokines are regarded as "Th2 factors" released by
Th cells, recent reports have disclosed the ability of resident
glomerular cells, especially mesangial cells, to produce IL-4 and IL-13
(44, 46). At inflammatory sites, the cooperation of these M
deactivators released from mesangial cells may play a role in the
prevention of or recovery from glomerulonephritis.
The role of TGF-ß in glomerular pathophysiology is still undefined.
Normally, constitutive expression of TGF-ß1 is observed in the
glomerulus (34, 47, 48, 49). This expression is up-regulated in a wide
range of glomerular diseases, especially in glomerulonephritis, where
mesangial cells are activated (5). Under these pathologic conditions,
TGF-ß1 stimulates matrix production by glomerular cells and is
thereby postulated to be a molecule responsible for the generation of
glomerulosclerosis (5). In addition to this effect, however, TGF-ß1
is potentially antiinflammatory through its suppressive effects on
M
, the "blackguards" in glomerular injury (9). The present
results reinforce the idea of a beneficial potential of TGF-ß1 in
M
-mediated, early glomerular inflammation.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Masanori Kitamura, Glomerular Bioengineering Unit, Department of Medicine, University College London Medical School, The Rayne Institute, 5 University Street, London WC1E 6JJ, U.K. E-mail address: ![]()
3 Abbreviations used in this paper: M
, macrophages; M
CM, M
-conditioned medium; RII, receptor type II; RI, receptor type I; DMEM-F12, DMEM/Hams F-12; X-gal, 5-bromo-4-chloro-3-indolyl ß-D-galactopyranoside. ![]()
Received for publication November 3, 1997. Accepted for publication January 26, 1998.
| References |
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, TGF-ß, IGF-I, IL-4, and IL-6. Nephrol. Dial. Transplant. 9:1545.This article has been cited by other articles:
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J. S. Duffield, P. G. Tipping, T. Kipari, J.-F. Cailhier, S. Clay, R. Lang, J. V. Bonventre, and J. Hughes Conditional Ablation of Macrophages Halts Progression of Crescentic Glomerulonephritis Am. J. Pathol., November 1, 2005; 167(5): 1207 - 1219. [Abstract] [Full Text] [PDF] |
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Y. Ishikawa, T. Konta, and M. Kitamura Spontaneous shift in transcriptional profile of explanted glomeruli via activation of the MAP kinase family Am J Physiol Renal Physiol, November 1, 2000; 279(5): F954 - F959. [Abstract] [Full Text] [PDF] |
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M. KITAMURA Renal Transfer of Genetically Engineered Cells J. Am. Soc. Nephrol., November 1, 2000; 11(90002): 154S - 158. [Abstract] [Full Text] |
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