(Hypertension. 1995;26:199-207.)
© 1995 American Heart Association, Inc.
Articles |
Transforming Growth Factor-ß1 Expression and Phenotypic Modulation in the Kidney of Hypertensive Rats
From the Department of Pharmacology, Osaka City University Medical School, and the Department of Drug Safety Research (T.F.), Eisai Co, Ltd, Gifu, Japan.
Correspondence to Shokei Kim, MD, Department of Pharmacology, Osaka City University Medical School, 1-4-54 Asahimachi, Abeno, Osaka 545, Japan.
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Abstract |
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Abstract We have previously reported that renal mRNA levels for transforming growth factor-ß1, 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-ß1 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-ß1 and cellular phenotype was determined by immunohistochemistry. In the kidney of 25-week-old SHRSP, renal transforming growth factor-ß1 mRNA was elevated compared with Wistar-Kyoto rats (WKY), whereas renal collagen mRNAs of SHRSP were not increased. Immunoreactive transforming growth factor-ß1 in SHRSP was mainly localized in glomerular cells. Furthermore,
-smooth
muscle actin and desmin were significantly expressed in SHRSP
glomerular cells, in contrast to negligible expression of
these proteins in WKY. -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-ß1 expression and the cellular
phenotypic modulation and was accompanied by a reduction of urinary
albumin excretion and inhibition of cell proliferation. These
results indicated that sustained hypertension causes the increased
glomerular transforming growth factor-ß1 expression and
cellular phenotypic modulation, which may play an important role in the
progression of glomerulosclerosis and
tubulointerstitial fibrosis in hypertension.
Key Words: transforming growth factor-ß • phenotype • hypertension, genetic • nephrosclerosis • antihypertensive agents
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Hypertension causes nephrosclerosis and accelerates the progression toward end-stage renal failure.1 2 Nephrosclerosis by itself also accelerates high blood pressure and results in a vicious circle of hypertension and renal failure.3 In various renal diseases, including hypertensive nephrosclerosis, major histological changes are extracellular matrix (ECM) expansion and cell proliferation in glomerular and interstitial cells.4 5 6 7 However, the molecular and cellular mechanisms of hypertensive nephrosclerosis remain unclear.
Transforming growth factor-ß1 (TGF-ß1), a multifunctional growth factor, is known to stimulate the synthesis of ECM components such as fibronectin and collagens.8 9 Recent studies show that renal TGF-ß1 is increased in various models of renal disease.10 11 12 13 Furthermore, the inhibition of TGF-ß by neutralizing antibody in vivo prevents glomerular ECM expansion in experimental glomerulonephritic rats.14 These findings support the notion that overexpression of TGF-ß1 can cause renal fibrosis, leading to renal failure.
Recent evidence indicates that cellular phenotypic modulation occurs in experimental15 16 17 18 and human19 renal diseases. Phenotypic changes in glomerular and tubulointerstitial cells have been suggested to be responsible for the cell proliferation and regeneration and the repair process of renal injury.17 18 20 21 However, no information is available on the cellular phenotype in hypertensive renal injury.
Recently, we have demonstrated that the gene expression of types I, III, and IV collagen and fibronectin is significantly increased in stroke-prone spontaneously hypertensive rats (SHRSP)22 and deoxycorticosterone acetate–salt hypertensive rats23 with malignant nephrosclerosis. Interestingly, renal TGF-ß1 mRNA is also increased in the kidney of these hypertensive rats. However, it is unclear whether TGF-ß1 contributes to the increased ECM accumulation in hypertensive nephrosclerosis, and the localization of TGF-ß1 in hypertensive kidney has not yet been determined.
In the present study, we examined the expression and localization of TGF-ß1 and cellular phenotypic modulation in the kidney of SHRSP with moderate renal damage and also examined the effect of antihypertensive drugs on TGF-ß1 and cellular phenotype. We obtained evidence supporting the possibility that TGF-ß1 and cellular phenotypic modulation play an important role in the progression of hypertensive nephrosclerosis.
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Methods |
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Animals
Male SHRSP24 and Wistar-Kyoto rats (WKY), which were maintained by selective mating at Eisai Co, Ltd (Gifu, Japan), were used in the present study. Rats were fed standard laboratory chow (MF, Oriental Kobo) and were given tap water ad libitum.
Drugs
Cilazapril, a long-acting angiotensin-converting
enzyme (ACE) inhibitor, was a gift from Nippon Roche, Ltd,
and nifedipine, a calcium channel blocker, was purchased
from Wako Pure Industries, Ltd.
Experimental Protocol
All procedures were in accordance with institutional guidelines
for animal research. Male 13-week-old SHRSP with established
hypertension were divided into three groups. The first group was given
saline (0.5 mL) by gastric gavage once a day (vehicle group); the
second group was given cilazapril (10 mg/kg per day) in saline (0.5 mL)
by gastric gavage once a day; and the third group was given
nifedipine (30 mg/kg per day) mixed with the chow. Drug
treatment of SHRSP was performed for 12 weeks (from the age of 13 to 25
weeks). Control WKY were given saline (0.5 mL) by gastric gavage for
the same period. Blood pressure was measured before and 2, 4, 8, and 12
weeks after the start of drug treatment. Urinary albumin
excretion was measured at 12 weeks after drug administration. A 24-hour
urine sample was collected with the use of metabolic cages.
For measurement of renal mRNA, 25-week-old SHRSP and WKY, at the end of
12 weeks of drug or vehicle treatment, were decapitated, and the kidney
was rapidly removed and weighed. The cortex then was separated from the
medulla, rapidly frozen in liquid nitrogen, and stored at -80°C
until use.
For immunohistochemical examination, rats, treated as described above, were anesthetized with sodium pentobarbital (50 mg/kg IP). A midline abdominal incision was made; a blood sample was collected from the abdominal aorta for measurement of blood urea nitrogen (BUN) and serum creatinine; and the kidney was removed and fixed as described below.
cDNA Probes
cDNA probes used were as follows: rat TGF-ß1 cDNA (1.0-kb
HindIII–Xba I fragment)25 ; rat
fibronectin cDNA (0.27-kb HindIII-EcoRI
fragment)26 ; rat 1 (type I) collagen (1.3-kb
Pst I–BamHI fragment)27 ; mouse 1
(type III) collagen (1.8-kb EcoRI-EcoRI
fragment)28 ; mouse 1 (type IV) collagen (0.83-kb
Aba I–Pst I fragment)29 ; and rat
GAPDH (1.3-kb Pst I–Pst I
fragment).30
Extraction of Renal RNA and Northern Blot Analysis
All procedures were performed as previously
described.22 23 In brief, total RNA was isolated from
renal cortex according to the guanidium thiocyanate/phenol/chloroform
method with minor modification. Twenty-five micrograms of total RNA was
electrophoresed on a 1% agarose gel and transferred to a nylon
membrane (GeneScreen Plus, EI du Pont de Nemours & Co, NEN
Products). The membrane was hybridized with the above-mentioned
cDNA probes, labeled with [32P]dCTP, and then was washed
and finally exposed to Kodak XAR-5 film between two intensifying
screens at -70°C. To evaluate tissue mRNA levels, we digitized
autoradiograms and measured their density using the
public domain National Institutes of Health IMAGE
program. The density of an individual mRNA band was divided by that of
GAPDH mRNA for the correction of the difference in RNA loading and
transfer to a nylon membrane.
Immunohistochemistry
For immunohistochemistry, the kidney, obtained from 25-week-old
SHRSP and WKY subjected to 12 weeks of vehicle or drug treatment, was
fixed in methyl Carnoy's solution (60% methanol, 30% chloroform,
10% acetic acid), embedded in paraffin, and cut into 4-µm-thick
sections. The sections were deparaffinized in xylene and a graded
series of ethanol. Immunostaining was carried out with
the use of the streptavidin/biotin immunoperoxidase method (LSAB kit,
Dako Corp). The sections were immersed in 3% hydrogen peroxide to
quench the endogenous peroxidase activity and then
incubated with phosphate-buffered saline (PBS) containing 1% bovine
serum albumin to reduce the nonspecific background staining.
The sections were rinsed with PBS and incubated with one of the
specific primary antibodies, with appropriate dilution (see below), at
room temperature for 30 minutes. After being washed with PBS, the
sections were incubated with biotinylated goat anti-rabbit, anti-mouse,
or anti-chicken IgG, then washed with PBS, and further incubated with
peroxidase-labeled streptavidin for 10 minutes. Sections were reacted
with 3,3'-diaminobenzidine as the chromogen and counterstained with
hematoxylin.
Antibodies
Antibodies used for immunohistochemistry were as follows:
anti–-smooth muscle actin (-SMA) was detected with murine
monoclonal antibody 1A4 (Dako Corp) diluted 1:50; desmin with D33 (Dako
Corp) diluted 1:25; vimentin with V9 (Dako Corp) diluted 1:20;
proliferating cell nuclear antigen (PCNA) with PC10 (Dako Corp) diluted
1:40; TGF-ß1 with chicken IgG antibody AB-101-NA (R&D Systems Inc)
diluted 1:100; and fibronectin with A245 (Dako Corp) diluted 1:400.
Quantitation of Immunohistochemistry
For examination of glomerular phenotype,
semiquantitative analysis for expressions of desmin and -SMA
were performed and graded, according to the method of Floege et
al.18 The scores were as follows: 0=absent or very weak
staining; 1+=staining involving 1% to 25% of the area of the
glomerular tuft; 2+=staining involving 25% to 50% of the
area of the glomerular tuft; 3+=staining involving 50% to
75% of the area of the glomerular tuft; and 4+=staining
involving greater than 75% of the area of the glomerular
tuft.
PCNA, an auxiliary protein to a DNA polymerase-
protein, is a marker
of the G1 to S transition in the cell cycle and hence
mitogenesis.31 The mean number of PCNA-positive cells per
glomerular cross section in each section was determined by
examining 30 glomeruli selected at random. In tubulointerstitium,
the number of PCNA-positive cells was determined by calculating the
total number of positive cells in 30 fields per tissue section at x200
magnification. We used a 1-mm2 grid for this purpose, which
was chosen to exclude blood vessels and glomeruli.
Miscellaneous Measurements
Systolic pressure was measured by the tail-cuff method. Urinary
albumin was measured by radioimmunoassay using specific
anti-rat albumin antibody. BUN and serum creatinine
were measured using their respective kits (Wako Pure Industries,
Ltd).
Statistics
Data are expressed as mean±SEM. Statistical significance was
determined with ANOVA and Duncan's multiple range test. Differences
were considered statistically significant at a value of
P<.05.
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Results |
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Blood Pressure, Urinary Albumin Excretion, BUN, and Plasma Creatinine of WKY and SHRSP
As shown in Fig 1A, 13-week-old SHRSP already had established hypertension, and there was no significant difference in blood pressure among the three groups of SHRSP before the start of drug treatment. Both cilazapril and nifedipine significantly lowered blood pressure in SHRSP throughout the experiments. As shown in Fig 1B, urinary albumin excretion in vehicle-treated 25-week-old SHRSP (8.7±2.3 mg/d) was larger than that in WKY (0.2±0.02 mg/d, P<.01). Both cilazapril and nifedipine significantly reduced urinary albumin excretion of SHRSP. BUN and plasma creatinine in 25-week-old SHRSP were 8.0±0.6 mmol/L of urea and 39.8±2.7 µmol/L, respectively, which were not different from the values of WKY.
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indicates
WKY; 
, vehicle-treated SHRSP; 
, cilazapril-treated SHRSP;
and 
, nifedipine-treated SHRSP. In B, W indicates
WKY; V, vehicle-treated SHRSP; C, cilazapril-treated SHRSP; and N,
nifedipine-treated SHRSP. In A and B, values are mean±SEM
(n=10 or 11 in each group); 
P<.05, *P<.01,
compared with vehicle-treated SHRSP.
TGF-ß1 and Extracellular Matrix mRNA Levels
As shown in Figs 2 and 3A, renal
cortical TGF-ß1 mRNA levels of vehicle-treated SHRSP were 1.2-fold
higher than those of WKY (P<.05). Treatment with cilazapril
or nifedipine decreased renal TGF-ß1 mRNA in SHRSP to
levels similar to those in WKY. As shown in Figs 2 and 3B, renal
cortical fibronectin mRNA levels in vehicle-treated SHRSP were 1.9-fold
higher than in WKY (P<.01). Cilazapril or
nifedipine treatment normalized renal fibronectin mRNA
levels in SHRSP. There was no significant difference in these
inhibitory effects between cilazapril and
nifedipine.
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In contrast to TGF-ß1 and fibronectin, there was no significant difference in renal types I, III, and IV collagen mRNA levels between 25-week-old SHRSP and WKY (data not shown).
Immunohistochemistry of TGF-ß1 and Fibronectin
Immunohistochemical results indicated that immunoreactive TGF-ß1
expression was only slightly detected in glomerular cells
(mainly epithelial cells) in the kidney of WKY (Fig 4A and 4B). On the other hand, in vehicle-treated SHRSP (Fig 4C and 4D), a significant amount of TGF-ß1 staining was detected in
glomerular cells (mainly epithelial cells). In addition, a
faint staining for TGF-ß1 could be detected in renal tubules of SHRSP
and WKY, although no difference was found between the two groups.
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As shown in Fig 5, immunoreactive fibronectin deposition was increased in glomerular cells in the kidney of vehicle-treated SHRSP (Fig 5B and 5C) compared with WKY (Fig 5A). Furthermore, staining for fibronectin was marked in the area of SHRSP renal interstitium, despite the absence of significant staining for fibronectin in WKY interstitium.
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Expression of Immunoreactive -SMA, Desmin, and Vimentin in the
Kidney
Figs 6 through 9 show the phenotypic modulation of
intraglomerular and tubulointerstitial
cells of SHRSP. In WKY, the expression of -SMA was localized in
renal vascular smooth muscle cells but was either absent or negligible
in glomerular cells (Fig 6A). In contrast,
in vehicle-treated SHRSP, significant amounts of -SMA were detected
in glomerular cells (mainly in mesangial cells)
as well as vascular smooth muscle cells (Fig 6B). This increase in
glomerular -SMA staining in SHRSP was significantly
suppressed by treatment with cilazapril or nifedipine
(P<.05, Fig 8A).
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As shown in Figs 7 and 8B, in contrast to only a faint staining for desmin in glomerular cells of WKY, glomerular cells (epithelial and mesangial cells) of vehicle-treated SHRSP expressed a significant amount of desmin. Treatment with cilazapril or nifedipine significantly reduced desmin expression in SHRSP glomerular cells (P<.01, Fig 8B).
Furthermore, the phenotypic changes of SHRSP were observed not only for
glomerular cells but also for
tubulointerstitial cells (Figs 6C and 9). In SHRSP, marked staining for -SMA was observed
not only in glomerular cells but also in
interstitial cells located around the atrophic tubules (Fig 6C), despite no staining for -SMA in WKY interstitial
cells. However, treatment of SHRSP with cilazapril or
nifedipine completely prevented the appearance of
-SMA–positive interstitial cells (data not shown).
As shown in Fig 9A, staining for vimentin was seen exclusively in WKY glomerular cells and not in tubular cells. On the other hand, in SHRSP a marked staining for vimentin was found in atrophic tubular epithelial cells and proliferative arterial cells as well as glomerular cells (Fig 9B and 9C). There was no staining for vimentin in tubular and arterial cells of cilazapril- or nifedipine-treated SHRSP.
Cell Proliferation
For determination of the proliferation of glomerular
and tubulointerstitial cells, tissue sections were
immunostained for PCNA (Fig 10). The number
of PCNA-positive cells in glomeruli and tubulointerstitium of
vehicle-treated SHRSP was approximately twofold and sixfold,
respectively, greater than in WKY. The majority of PCNA-positive cells
in tubulointerstitium of SHRSP were vimentin-positive atrophic
tubular cells or -SMA–positive interstitial cells.
Cilazapril and nifedipine treatment significantly reduced
the number of PCNA-positive cells in glomeruli and
tubulointerstitium of SHRSP (Table).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Our present data show that TGF-ß1 expression was enhanced in glomerular cells of SHRSP with moderate renal damage and that the phenotypic modulations, which were associated with increased cell proliferation, occurred in glomerular and tubulointerstitial cells of SHRSP. Furthermore, the above-mentioned changes in SHRSP were prevented by treatment with an ACE inhibitor or calcium channel blocker and were accompanied by a reduction of urinary albumin excretion and suppression of cell proliferation. We also examined TGF-ß1 expression and cellular phenotype of 8-week-old SHRSP without significant hypertension and found that there was no increase in glomerular TGF-ß1 and no cellular phenotypic modulation in SHRSP at this prehypertensive age (data not shown). These results provide evidence that sustained hypertension leads to the induction of glomerular TGF-ß1 expression and cellular phenotypic modulation and suggest that these changes in SHRSP may be responsible for the progression of nephrosclerosis.
TGF-ß1, a multifunctional growth factor, plays an important role in tissue repair by regulating cell proliferation and differentiation.9 Recent evidence supports the hypothesis that TGF-ß1 is involved in fibrotic diseases by stimulating the synthesis of ECM.8 TGF-ß1 causes mesangial cell proliferation in vitro by stimulating platelet-derived growth factor expression.32 The inhibition of TGF-ß by neutralizing antibody in vivo prevents glomerular matrix expansion in experimental glomerulonephritic rats.14 Transfection of TGF-ß gene into the rat kidney in vivo, which causes sustained glomerular expression of TGF-ß1, induces glomerulosclerosis, with increased glomerular collagen accumulation.33 Furthermore, TGF-ß1 and ECM mRNAs are reported to be elevated in various experimental renal diseases, including glomerulonephritis,11 diabetic nephropathy,10 12 and adriamycin-induced nephropathy.13 Thus, TGF-ß1 may play a central role in the development of glomerulosclerosis and tubulointerstitial fibrosis.8 However, the role of TGF-ß1 in the progression of hypertensive nephrosclerosis is poorly understood.
We have recently investigated the gene expression of TGF-ß1 and ECM in the kidney of 32-week-old SHRSP with malignant nephrosclerosis, characterized by increased BUN and serum creatinine levels, glomerular fibrinoid necrosis, and severe tubulointerstitial fibrosis.22 In the kidney of 32-week-old SHRSP, mRNA levels for types I, III, and IV collagen and fibronectin were significantly elevated compared with levels in WKY. Of further interest, renal TGF-ß1 mRNA was also significantly increased in 32-week-old SHRSP.22 The increased renal TGF-ß1 in hypertensive rats is at least in part mediated by the activation of the intrarenal renin-angiotensin system.22 23 However, our previous study did not allow us to determine whether the increase in TGF-ß1 in SHRSP precedes the increase in ECM; we also did not determine the localization of TGF-ß1 in the kidney of SHRSP. In the present study, using 25-week-old SHRSP with moderate renal damage, we obtained evidence that the increase in renal TGF-ß1 mRNA preceded the increase in collagen gene expression and that the increased TGF-ß1 expression was due to glomerular cells. These observations suggest that TGF-ß1 may be responsible for glomerulosclerosis in hypertension. Although the increase in cortical TGF-ß1 mRNA of SHRSP was small in the present study (1.2-fold), glomerular TGF-ß1 mRNA of SHRSP might be more significantly increased, because glomeruli comprise less than 1% of kidney cortex. However, further study with the use of in situ hybridization or isolated glomeruli is necessary to confirm our proposal, because the immunohistochemical technique allows for semiquantitative analysis but not quantitative analysis.
Interestingly, fibronectin mRNA was also increased in 25-week-old SHRSP, preceding the increase in collagen gene expression. Furthermore, increased fibronectin deposition was seen in the glomerulus and interstitium of SHRSP. These observations, taken together with the in vitro data that fibronectin acts as a scaffold for collagen deposition34 35 and activates the integrin-mediated cellular signal transduction pathway,36 suggest that the increased fibronectin deposition may be responsible for the increase in collagen accumulation and cellular proliferation and migration in hypertensive kidney.
Previous reports show that glomerular injury, including
mesangial proliferative nephritis15 and the
remnant kidney model,18 causes the dramatic expression of
-SMA and desmin in glomerular cells. This phenotypic
change of glomerular cells has also been demonstrated in
human glomerular diseases.19 At present,
the significance of glomerular phenotypic changes remains
to be elucidated. Previous reports suggest that the expression of
-SMA may be responsible for the proliferation of
glomerular cells15 18 19 ; however, the
cellular phenotype in hypertensive kidney has not yet been
examined. Our study provides the first evidence that hypertension leads
to phenotypic modulation of glomerular cells, accompanied
by glomerular cell proliferation, thereby supporting the
notion that glomerular phenotypic changes in hypertension
may also contribute to cell proliferation. Furthermore, the
glomerular mesangial cell is a contractile cell
and plays an important role in the regulation of glomerular
filtration.37 38 As -SMA is a contractile protein, the
increased expression of this protein may change mesangial
contractility, thereby affecting glomerular
filtration rate. Thus, the mesangial phenotypic change may
participate in the regulation of cell proliferation and
glomerular filtration rate. However, further study is
needed to elucidate this proposal.
The present study did not permit us to elucidate the mechanism by
which sustained hypertension causes glomerular phenotypic
modulation. Johnson et al39 reported that long-term
infusion of angiotensin II to normal rats in vivo induces
glomerular phenotypic modulation. In vivo transfection of
TGF-ß1 gene into the rat kidney causes the expression of -SMA in
mesangial cells, thereby indicating phenotypic changes of
mesangial cells by TGF-ß1.40 Therefore, it
is possible that the activation of the intrarenal
renin-angiotensin system and/or the increased TGF-ß1
induced by hypertension may be responsible for glomerular
phenotypic modulation in SHRSP.
Phenotypic modulation was also found for SHRSP interstitial
and tubular cells, as indicated by the expression of -SMA in
interstitial cells and vimentin in atrophic tubular cells.
The same phenotypic changes of tubulointerstitial
cells also have been reported in rats with gentamicin-induced tubular
injury17 and human renal diseases such as hydronephrosis
and pyelonephritis.21 The expression of -SMA in
interstitial cells indicates that these cells acquire
myofibroblast phenotype41 and can produce
fibronectin.42 Furthermore, -SMA–positive
interstitial cells of SHRSP were proliferative cells, as
indicated by the positive staining of PCNA. These findings suggest that
-SMA–positive interstitial cells may play a central
role in the increased fibronectin deposition in the interstitium of
SHRSP. In the present study, vimentin-positive tubular cells were
found in SHRSP and were associated with the positive staining of PCNA.
Witzgall et al,43 who examined the vimentin and PCNA
expression in the rat kidney of ischemic acute renal failure,
found that after ischemia, damaged tubular cells express
vimentin and actively proliferate, thereby indicating that
vimentin-expressing tubular cells can be regarded as regenerating or
proliferating damaged tubular cells. All these findings, taken together
with a report by Mai et al7 that
tubulointerstitial cells are important for the
progression of hypertensive nephrosclerosis as well as
glomerular cells, suggest that the phenotypic changes of
tubulointerstitial cells may also participate in
the progression of tubulointerstitial fibrosis.
ACE inhibitors and calcium antagonists are the most popular antihypertensive drugs and have been shown to have beneficial effects on various human44 and animal45 46 47 48 49 renal diseases. Although these renal protective effects may be due to the improvement of hemodynamics, such as the reduction of systemic or glomerular hypertension, the detailed mechanism remains to be determined. To examine the mechanism of the renal protective effects of ACE inhibitors and calcium antagonists at the molecular and cellular levels, we studied the effect of cilazapril and nifedipine on TGF-ß1 and ECM expressions and cellular phenotype in the kidney of SHRSP. We found that cilazapril and nifedipine suppressed the increase in TGF-ß1 and fibronectin gene expressions and prevented the phenotypic modulation of glomerular and tubulointerstitial cells in SHRSP, associated with a reduction of urinary albumin excretion and reduction of renal cell proliferation. Our previous study showed that angiotensin II type I receptor antagonists can decrease renal TGF-ß1 and ECM gene expressions in SHRSP22 and deoxycorticosterone acetate–salt hypertensive rats23 independent of its hypotensive effect. Furthermore, it has been reported that calcium antagonists significantly block the intrarenal actions of angiotensin II in vivo.50 These findings, taken together with our present observation that the hypotensive effect of cilazapril and nifedipine in SHRSP was modest, suggest that the inhibitory effects of these drugs on TGF-ß1 expression and cellular phenotypic modulation in SHRSP may be in part due to the direct inhibition of the intrarenal renin-angiotensin system.
In conclusion, we obtained evidence that the increase in glomerular TGF-ß1 expression and the phenotypic modulations of glomerular and tubulointerstitial cells occurred in hypertensive rats with moderate renal damage. These changes may contribute to the progression of hypertensive glomerulosclerosis and tubulointerstitial fibrosis. The suppression of TGF-ß1 expression and phenotypic modulation by an ACE inhibitor and calcium channel blocker may be partially mediated by the inhibition of the intrarenal renin-angiotensin system.
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Acknowledgments |
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This work was supported in part by a Grant-in-Aid for Scientific Research (05670100) from the Ministry of Education, Science, and Culture, and by Osaka City University Medical Research Foundation Fund for Medical Research.
Received November 30, 1994; first decision January 13, 1995; accepted April 3, 1995.
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