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

Anti-Renal Fibrotic Effect of Exercise Training in Hypertension

The purpose of this study was to evaluate the effects of exercise training on renal fibrosis in hypertensive rats. Masson's trichrome staining and Western blotting were performed on the excised renal cortex from sixteen male spontaneously hypertensive rats (SHR), which were randomly divided into either a sedentary hypertensive group (SHR) or exercise hypertensive group (SHR-EX, running on an exercise treadmill for 60 min/day, 5 sessions/week, for 12 weeks), and from eight male Wistar-Kyoto rats which served as a sedentary normotensive group (WKY). The systolic blood pressure (SBP) and renal fibrosis in hypertensive rats improved after exercise training. The inflammatory-related protein levels of interleukin-6 (IL-6) and cyclooxygenase-2 (COX-2), as well as the fibrotic-related protein levels of transforming growth factor-beta (TGF-β), phospho-Smad2/3 (p-Smad2/3), connective tissue growth factor (CTGF), matrix metalloproteinase-9 (MMP-9), and matrix metalloproteinase-2 (MMP-2) were decreased in the SHR-EX group when compared with the SHR group. Exercise training suppressed the hypertension-induced renal cortical inflammatory and fibrotic pathways in hypertensive rat models. These findings might indicate a new therapeutic effect for exercise training to prevent renal fibrosis in hypertensive nephropathy.

Molecular mechanisms of renal blood flow autoregulation

Diabetes and hypertension are the leading causes of chronic kidney disease and their incidence is increasing at an alarming rate. Both are associated with impairments in the autoregulation of renal blood flow (RBF) and greater transmission of fluctuations in arterial pressure to the glomerular capillaries. The ability of the kidney to maintain relatively constant blood flow, glomerular filtration rate (GFR) and glomerular capillary pressure is mediated by the myogenic response of afferent arterioles working in concert with tubuloglomerular feedback that adjusts the tone of the afferent arteriole in response to changes in the delivery of sodium chloride to the macula densa. Despite intensive investigation, the factors initiating the myogenic response and the signaling pathways involved in the myogenic response and tubuloglomerular feedback remain uncertain. This review focuses on current thought regarding the molecular mechanisms underlying myogenic control of renal vascular tone, the interrelationships between the myogenic response and tubuloglomerular feedback, the evidence that alterations in autoregulation of RBF contributes to hypertension and diabetes-induced nephropathy and the identification of vascular therapeutic targets for improved renoprotection in hypertensive and diabetic patients.

Nephrosclerosis: update on a centenarian

Nephrosclerosis is an umbrella term defining changes in all compartments of the kidney, changes caused by hypertension and by ageing. Among other lesions, arteriolosclerosis and arteriolohyalinosis play a major role in inducing glomerular ischaemic shrinking and sclerosis along with glomerulomegaly and focal-segmental glomerulosclerosis (FSGS). These lesions are accompanied by tubulointerstitial inflammation and fibrosis that predict the decline of renal function. Nephrosclerosis is a major cause of renal insufficiency in blacks of African descent with a severe, early form of renovasculopathy and a rapid course to renal failure with predominant lesions of FSGS. It seems that in blacks, separate genetic factors independently lead to vascular lesions and to hypertension with a different time-scale of their onset and of their progression, nephroangiosclerosis preceding the onset of hypertension. Conversely, true and histologically identified nephrosclerosis in white Europeans rarely leads to end-stage renal disease in the absence of malignant hypertension. Various animal models demonstrate that renal vascular lesions may exist in the absence of hypertension. These experiments also point to a major role of angiotensin II and of a number of independent and overlapping cellular and molecular pathways in a cascade of inflammatory events that end in renal fibrosis. Two pathophysiologic mechanisms are at work in inducing glomerular lesions and tubulointerstitial fibrosis: a loss of autoregulation of the renal blood flow caused by an arteriolohyalinosis of the glomerular afferent arteriole and ischaemia that fosters the generation of hypoxia inducible-fibrosing factors. Not all antihypertensive drugs equally protect the kidney from nephrosclerosis. Angiotensin II antagonists exert a favourable effect on hyperfiltration. Conversely, dihydropyridine calcium-channel blockers and vasodilators do not withstand the derangement of renal autoregulation.

Terutroban, a thromboxane/prostaglandin endoperoxide receptor antagonist, prevents hypertensive vascular hypertrophy and fibrosis

Thromboxane A2 and other eicosanoids such as isoprostanes contribute to vascular proliferation and atherosclerosis by binding to the thromboxane/prostaglandin endoperoxide receptors. The effects of terutroban, a thromboxane/prostaglandin endoperoxide receptor antagonist, on aorta remodeling were evaluated in spontaneously hypertensive stroke-prone rats (SHRSPs), a model of severe hypertension, endothelial dysfunction, vascular inflammation, and cerebrovascular diseases. Male SHRSPs were allocated to three groups receiving a standard diet ( n = 5) or a high-sodium permissive diet plus vehicle ( n = 6) or plus terutroban (30 mg·kg−1·day−1; n = 6). After 6 wk of dietary treatment, all of the animals were injected with bromodeoxyuridine and simultaneously euthanized for aorta collection. The aortic media thickness-to-lumen ratio significantly ( P < 0.0001) increased in the salt-loaded rats compared with the rats fed a standard diet, whereas terutroban treatment completely prevented media thickening ( P < 0.001). When compared with vehicle, terutroban was also effective in preventing cell proliferation in the media, as indicated by the reduced number of bromodeoxyuridine-positive ( P < 0.0001) and proliferating cell nuclear antigen-positive cells ( P < 0.0001). Severe fibrosis characterized by a significant accumulation of collagen and fibronectin in the vascular wall was observed in the vehicle-treated rats ( P < 0.01) but was completely prevented by terutroban ( P < 0.001). The latter also inhibited heat shock protein-47 ( P < 0.01) and TGF-1β expression ( P < 0.001), which were significantly increased by the high-salt diet. In conclusion, terutroban prevents the development of aorta hyperplasia and has beneficial effects on fibrotic processes by affecting TGF-β and heat shock protein-47 expression in SHRSPs. These findings provide mechanistic data supporting the beneficial effects of terutroban in preventing or retarding atherogenesis.

Evaluation of metalloprotease inhibitors on hypertension and diabetic nephropathy

This study examined the effects of two new selective metalloprotease (MMP) inhibitors, XL081 and XL784, on the development of renal injury in rat models of hypertension, Dahl salt-sensitive (Dahl S) and type 2 diabetic nephropathy (T2DN). Protein excretion rose from 20 to 120 mg/day in Dahl S rats fed a high-salt diet (8.0% NaCl) for 4 wk to induce hypertension. Chronic treatment with XL081 markedly reduced proteinuria and glomerulosclerosis, but it also attenuated the development of hypertension. To determine whether an MMP inhibitor could oppose the progression of renal damage in the absence of changes in blood pressure, Dahl S rats were fed a high-salt diet (4.0% NaCl) for 5 wks to induce renal injury and then were treated with the more potent and bioavailable MMP inhibitor XL784 either given alone or in combination with lisinopril and losartan. Treatment with XL784 or the ANG II blockers reduced proteinuria and glomerulosclerosis by ~30% and had no effect on blood pressure. Proteinuria fell from 150 to 30 mg/day in the rats receiving both XL784 and the ANG II blockers, and the degree of renal injury fell to levels seen in normotensive Dahl S rats maintained from birth on a low-salt diet. In other studies, albumin excretion rose from 125 to >200 mg/day over a 4-mo period in 12-mo-old uninephrectomized T2DN rats. In contrast, albumin excretion fell by >50% in T2DN rats treated with XL784, lisinopril, or combined therapy. XL784 reduced the degree of glomerulosclerosis in the T2DN rats to a greater extent than lisinopril, and combined therapy was more effective than either drug alone. These results indicate that chronic administration of a selective MMP inhibitor delays the progression, and may even reverse hypertension and diabetic nephropathy.

Systemic delivery of IL-10 by an AAV vector prevents vascular remodeling and end-organ damage in stroke-prone spontaneously hypertensive rat

Interleukin-10 (IL-10) ameliorates various T-helper type 1 cell-mediated chronic inflammatory diseases. Although the therapeutic benefits of IL-10 include antiatherosclerotic effects, pathophysiological effects of IL-10 on vascular remodeling in hypertension have not yet been elucidated. These studies were designed to determine whether sustained IL-10 expression, mediated by an adeno-associated virus (AAV) vector, prevents vascular remodeling and target-organ damage in the stroke-prone spontaneously hypertensive rat (SHR-SP)-an animal model of malignant hypertension. A single intramuscular injection of an AAV1 vector encoding rat IL-10 introduced long-term IL-10 expression. These IL-10-transduced rats had decreased stroke episodes and proteinuria, resulting in improved survival. Histological examination revealed a reduced level of deleterious vascular remodeling of resistance vessels in the brain and kidney of these rats. Immunohistochemical analysis indicated that IL-10 inhibited the enhanced renal transforming growth factor-beta expression and perivascular infiltration of monocytes/macrophages and nuclear factor-kappaB-positive cells normally observed in the SHR-SP. Four weeks after IL-10 vector injection, systolic blood pressure significantly decreased and this effect persisted for several months. Overall, AAV vector-mediated systemic IL-10 expression prevented vascular remodeling and inflammatory lesions of target organs in the SHR-SP. This approach provides significant insights into the prevention strategy of disease onset with unknown genetic predisposition or intractable polygenic disorders.

Pioglitazone: cardiovascular effects in prediabetic patients

Pioglitazone is the second thiazolidine derivative used clinically in the type 2 diabetes mellitus (DM). In the prediabetic stage, hyperinsulinemia or insulin resistance has been suggested to be closely associated with the oxidative stress. The first thiazolidine derivative used to treat DM, troglitazone, is chemically related to alpha-tocopherol, a known antioxidant. Troglitazone prevents tissue damage, but has been reported to produce hepatotoxicity. Pioglitazone strongly increases insulin sensitivity, improves glucose and lipid metabolism and showed no evidence of hepatotoxicity. The mechanism of the antidiabetic action of pioglitazone involves activation of insulin receptors and/or high affinity for peroxisome proliferator-activated receptor gamma (PPARgamma). Hydroxylation of the phenyl and pyridine rings in the chemical structure of pioglitazone may facilitate the scavenging of hydroxyl radicals. The direct antioxidant effect of pioglitazone may contribute to its effect on insulin resistance. The hypoglycemic and hypolipidemic effects of pioglitazone are likely to reduce the expression of TNFalpha. The reduction in the oxidative stress may lead to the suppression of TGFbeta and of collagen accumulation. A decrease in collagen content is likely to improve left ventricular diastolic function and distensibility of the aortic wall. Reduction in the oxidative stress may prevent the proliferation of vascular smooth muscle cells and contribute to the decrease in the aortic wall stiffness.

The effect of ramipril on albumin excretion in diabetes and hypertension: the role of increased lysosomal activity and decreased transforming growth factor-beta expression

OBJECTIVES

Albumin excretion is modulated post-filtration by lysosomal processing that produces a spectrum of albumin-derived material in urine, much of which is not detected by conventional immunoassays. This study aimed to determine the efficacy of ramipril treatment (+ RAM) after 24 weeks on total albumin excretion (intact plus albumin-derived peptides) in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats with (d) and without (c) diabetes.

METHODS

Intact albumin excretion was analysed by radioimmunoassay and total albumin excretion was analysed by measuring radioactivity derived from circulating [ C]albumin. Renal lysosomal activity was determined by urinary [ H]dextran sulphate desulphation. Renal transforming growth factor-beta 1 (TGF-beta 1), TGF-beta inducible gene-h3 (beta ig-h3) and angiotensinogen mRNA production were analysed by real time reverse transcriptase-polymerase chain reaction.

RESULTS

Hypertension (SHR-c and SHR-d) resulted in a significant increase in intact albumin excretion, which was significantly reduced by ramipril treatment (P < 0.05 for SHR-c + RAM and 0.001 for SHR-d + RAM compared to non-treated). This was accompanied by a significant decrease in blood pressure (P < 0.001 for SHR-c + RAM and SHR-d + RAM), renal beta ig-h3 mRNA production (P < 0.05 for SHR-c + RAM and SHR-d + RAM), and an increase in lysosomal activity. Diabetes (WKY-d and SHR-d) primarily caused a significant increase in total albumin excretion, predominantly in the form of albumin-derived fragments in the WKY-d group and intact albumin in the SHR-d group. Ramipril treatment reduced total albumin excretion in the WKY-d + RAM group (P < 0.001).

CONCLUSIONS

Ramipril prevents increases in both intact albumin and total albumin excretion in hypertensive and diabetic states, respectively.

COX-2 inhibition potentiates the antiproteinuric effect of enalapril in uninephrectomized SHR

PGE(2) and PGI(2) reduce extracellular matrix deposition and their production is altered after ACE inhibitor (ACEi) treatment. We therefore hypothesized that cyclooxygenase (COX)-2 inhibition would exacerbate renal injury and antagonize the effects of ACEi. To test these hypotheses, WKY and SHR were uninephrectomized (UNX) and treated with either vehicle, enalapril, NS398 or enalapril+NS398. NS398 did not affect systolic blood pressure nor antagonize the antihypertensive effect of enalapril. Urinary protein excretion in UNX WKY was significantly decreased after treatment with either enalapril or NS398. In UNX SHR, enalapril reduced proteinuria, but NS398 alone had no effect. Administration of both drugs, however, further reduced proteinuria. In UNX WKY, treatment with either NS398 alone or both drugs reduced glomerular volume and similar results were observed in SHR. Surprisingly, these results disprove our original hypothesis and suggest that inhibition of COX-2 provides additional renoprotection to that of enalapril alone.

Combination treatment with a calcium channel blocker and an angiotensin blocker in a rat systolic heart failure model with hypertension

The mechanism and treatment of hypertensive systolic heart failure are not well defined. We compared the effect of an angiotensin-converting enzyme inhibitor (cilazapril, 10 mg/kg), an angiotensin receptor blocker (candesartan, 3 mg/kg), a calcium channel blocker (benidipine, 1, 3 or 6 mg/kg), and the same calcium channel blocker combined with renin-angiotensin blockers on systolic heart failure in Dahl salt-sensitive (DS) rats. DS rats were fed an 8% Na diet from 6 weeks of age and then subjected to the above drug treatments. Benidipine (1 mg/kg), cilazapril, and candesartan had compatible hypotensive effects and similar beneficial effects on cardiac hypertrophy, gene expression, and survival rate. The combination of benidipine with cilazapril or candesartan was found to have no additional beneficial effects on the above parameters, with the exception of a reduction in atrial natriuretic polypeptide gene expression. On the other hand, candesartan normalized serum creatinine, but serum creatinine was unaffected by either benidipine at 1 or 3 mg/kg or cilazapril. Further, the combined use of benidipine and either candesartan or cilazapril resulted in an additional reduction of urinary albumin excretion in DS rats. Thus systolic heart failure in DS rats is mainly mediated by hypertension, while renal dysfunction of DS rats is due to both hypertension and the AT1 receptor itself. These findings suggest that the combination of a calcium channel blocker with an AT1 receptor blocker or ACE inhibitor may be more effective in treating the renal dysfunction associated with systolic heart failure than monotherapy with either agent alone. However, further studies will be needed before reaching any definitive conclusion on the efficacy of this combination therapy in patients with heart failure.

Pioglitazone improves left ventricular diastolic function and decreases collagen accumulation in prediabetic stage of a type II diabetic rat

This study investigated the effect of pioglitazone, an insulin sensitizer, on metabolic abnormalities and oxidative stress as a cause of myocardial collagen accumulation in prediabetic rat hearts. Twenty male diabetic rats and 9 male nondiabetic age-matched rats were used. The diabetic rats were divided into two groups: diabetic treated and untreated. Pioglitazone was mixed in rat chow fed to the diabetic treated group (0.01%). Treatment duration was 5 weeks. At baseline (15 weeks) and 20 weeks of age, blood glucose, lipid, insulin, and plasma malondialdehyde-thiobarbituric acid (MDA) levels were measured and Doppler echocardiography was tracked. At 20 weeks of age, left ventricular collagen content was studied. Blood glucose, plasma insulin, and triglyceride levels in the diabetic treated group were significantly lower than those in the untreated diabetic group. Deceleration time (ms) of early diastolic inflow in the treated diabetic group decreased significantly compared with the untreated diabetic group (65 +/- 8 vs. 77 +/- 8, p < 0.01). Ratio of left ventricular weight to body weight (mg/g) and ratio of left ventricular collagen content to dry weight (mg/100 mg) were decreased in the treated diabetic group (1.5 +/- 0.1, 1.3 +/- 0.3) compared with the untreated diabetic group (1.7 +/- 0.2, p < 0.01; 1.7 +/- 0.3, p < 0.05). Plasma MDA concentration (nmol/ml) significantly decreased (2.9 +/- 0.3 at baseline to 2.3 +/- 0.3 at 20 weeks, p = 0.001) in the treated diabetic group, and was lower than that in the untreated diabetic group (3.2 +/- 0.7 at 20 weeks, p < 0.05). Pioglitazone improved glucose and lipid metabolism and reduced oxidative stress in the left ventricle, which decreased left ventricular collagen accumulation and improved left ventricular diastolic function of prediabetic rat hearts.

TGF-beta 1 induces proliferation in human renal fibroblasts via induction of basic fibroblast growth factor (FGF-2)

BACKGROUND

The prognosis of primary renal disease is often dependent on the degree of tubulointerstitial scarring. Scarring is caused by proliferation and excessive matrix production of renal fibroblasts and possibly other cellular elements. Transforming growth factor-beta (TGF-beta) is the most important cytokine for the induction of matrix synthesis in the kidney. However, its effects on renal fibroblast proliferation have not been determined. We have recently demonstrated that the expression of basic fibroblast growth factor (FGF-2) is robustly up-regulated in human kidneys with tubulointerstitial fibrosis and that FGF-2 is a potent inducer of fibroblast proliferation. The present study examined the interaction between TGF-beta 1 and FGF-2 in human renal fibroblasts.

METHODS

Experiments were performed on a transformed medullary fibroblast line and on primary cortical kidney and skin fibroblasts isolated from human biopsies. mRNA levels of FGF-2 and TGF-beta 1 were analyzed by Northern blot analyses. Changes in protein expression were examined by immunoblots and enzyme-linked immunosorbent assay (ELISA). Bromodeoxyuridine incorporation assays and cell counts were used to analyze cell proliferation. The expression of cell cycle-regulatory proteins cyclin-dependent kinase (cdk) 2 and the cdk inhibitor p27(kip1) were determined by immunoblots.

RESULTS

Stimulation of renal fibroblasts with FGF-2 resulted in no change of TGF-beta 1 mRNA expression, whereas incubation of the cells with TGF-beta 1 induced FGF-2 mRNA up to 3.51 +/- 0.21-fold after six hours. This increase could be blocked almost completely by the addition of cyclohexamide, indicating that the process is in large part dependent on protein synthesis. The up-regulation in FGF-2 mRNA expression was paralleled by de novo detection of FGF-2 protein in the supernatant, peaking after 12 to 24 hours, as determined by Western blot and ELISA, whereas cellular protein was only increased up to 2.1-fold. Interestingly, both methods detected release of FGF-2 protein to the supernatant already at three hours, indicating a role for TGF-beta1 in directly releasing preformed FGF-2. Since TGF-beta 1 induced FGF-2, which results in fibroblast proliferation, we hypothesized that TGF-beta1 may cause fibroblast proliferation mediated by FGF-2. This hypothesis was verified by cell proliferation assays demonstrating that stimulation of renal fibroblasts with TGF-beta1 resulted in an up to 3.21 +/- 0.28-fold increase in bromodeoxyuridine incorporation and a 1.95 +/- 0.16-fold increase in cell number after 72 hours. This mitogenic effect of TGF-beta1 could be blocked completely by the addition of a neutralizing antibody to FGF-2 or the tyrosine kinase inhibitor tyrphostin AG1296, which blocks FGF receptor (FGFR) tyrosine kinase activity. Conversely, a neutralizing antibody to epidermal growth factor (EGF) or the tyrphostin B42, which inhibits EGF receptor signal transduction, had no effect. Interestingly, a neutralizing antibody to PDGF had only minor effects in primary kidney fibroblasts but reduced TGF-beta 1-induced proliferation considerably in primary skin fibroblasts. Finally, TGF-beta1-induced proliferation in kidney fibroblasts was paralleled by a robust increase in cdk 2 protein expression up to 72 hours, whereas p27(kip1), whose activity is maintained by TGF-beta in epithelial cells, was down-regulated up to 48 hours.

CONCLUSIONS

Our studies demonstrate, to our knowledge for the first time, that TGF-beta1 induces proliferation in human renal fibroblasts and that this process is mediated largely by FGF-2. The induction of proliferation by TGF-beta 1 via induction of FGF-2 may play an important role in the autonomy of renal fibroblast growth and thus in the pathogenesis of human fibrogenesis.

An oral sorbent reduces overload of indoxyl sulphate and gene expression of TGF-beta1 in uraemic rat kidneys

BACKGROUND

An oral adsorbent (AST-120) delays the progression of chronic renal failure (CRF). The aims of the present study are to determine the effects of AST-120 on the localization of indoxyl sulphate in uraemic rat kidneys, and to examine whether AST-120 reduces the renal cortical gene expression of transforming growth factor (TGF)-beta1, tissue inhibitor of metalloproteinase (TIMP)-1 and pro-alpha1(I)collagen, and ameliorates glomerular and tubulointerstitial injuries in uraemic rats.

METHODS

Two weeks after 5/6-nephrectomy, 10 rats were divided into pairs such that both rats in each pair exhibited almost the same levels of serum creatinine, blood urea nitrogen and creatinine clearance. One rat from each pair was assigned to a control uraemic group, the other to a uraemic group which received AST-120 everyday for 11 weeks. The localization of indoxyl sulphate was studied by immunohistochemistry using a monoclonal anti-indoxyl sulphate antibody we had developed. The renal cortical gene expression was studied by using northern blotting.

RESULTS

Rats treated with AST-120 showed decreased levels of serum creatinine, blood urea nitrogen and urinary protein as well as increased levels of creatinine clearance as compared with control uraemic rats. AST-120 markedly decreased indoxyl sulphate levels in both serum and urine. Immunohistochemistry demonstrated that indoxyl sulphate was localized in the renal proximal tubular epithelial cells, especially of dilated tubules, and that AST-120 markedly reduced the tubular staining of indoxyl sulphate. AST-120 attenuated interstitial fibrosis, tubular injury as well as glomerular sclerosis, and reduced the renal gene expression of TGF-beta1, TIMP-1 and pro-alpha1(I)collagen.

CONCLUSIONS

AST-120 reduces the gene expression of TGF-beta1, TIMP-1 and pro-alpha1(I)collagen in the kidneys, and delays the progression of CRF, at least in part, by alleviating the overload of indoxyl sulphate on remnant proximal tubular epithelial cells.

ACE inhibitors attenuate expression of renal transforming growth factor-beta1 in humans

Progressive nephropathies are characterized by the enhanced accumulation of extracellular matrix in the kidney. Overproduction of transforming growth factor-beta (TGF-beta) was shown to result in pathological tissue fibrosis through the accumulation of extracellular matrix proteins. It has been proposed that angiotensin II stimulates TGF-beta production. Despite accumulating data supporting the effects of angiotensin-converting enzyme (ACE) inhibitors on the attenuation of TGF-beta in vitro and in rats, such studies in humans are lacking. The present study sought to determine the effects of ACE inhibitors on TGF-beta1 in patients with glomerulonephritis. Using competitive polymerase chain reaction and the sandwich enzyme-linked immunosorbent assay, TGF-beta1 messenger RNA (mRNA) abundance and TGF-beta1 protein levels were measured. Patients with immunoglobulin A nephropathy administered ACE inhibitors showed significantly lower renal TGF-beta1 gene expression than patients not administered these medications (mean ratios of TGF-beta1/beta-actin, 4.27 +/- 0.62 [SEM] versus 14.81 +/- 3.87; P < 0.05), whereas no difference was noted between patients administered ACE inhibitors and healthy controls (4.27 +/- 0.62 versus 2.78 +/- 0.71). ACE inhibitor therapy did not affect TGF-beta1 mRNA expression in freshly isolated mononuclear cells. Urine and serum TGF-beta1 protein levels were not affected by the administration of ACE inhibitors. However, possibly a longer duration of treatment would decrease TGF-beta1 levels in urine or blood. In conclusion, we observed a significant reduction in TGF-beta1 expression in the kidney by ACE inhibitors, and this suggests that the effects of ACE inhibitors observed in animals can be extrapolated to patients with chronic renal disease.

Estrogen worsens incipient hypertriglyceridemic glomerular injury in the obese Zucker rat

BACKGROUND

The obese Zucker rat (OZR) is a model of glomerulosclerosis and renal failure in the setting of hyperlipidemia, hyperinsulinemia, and obesity. Our prior work in OZRs has shown that ovariectomy attenuates glomerulosclerosis, while added estrogen worsens it. To investigate the mechanism of estrogen's effects on glomerular disease in this model, we evaluated the effects of ovariectomy and estrogen supplementation on seven-week peripubertal OZRs. At this time point, rats exhibit no overt histologic glomerular disease, but are just beginning to show elevated urinary albumin excretion.

METHODS

Female OZRs fed ad libitum were ovariectomized at four weeks, with or without estrogen supplementation to raise estrogen levels to just below those of preoestral adults (mean 16.5 pg/mL). Sham-operated controls were included.

RESULTS

Ovariectomy normalized albuminuria, lowered total and very low-density lipoprotein triglycerides, and reduced glomerular fibronectin expression. Estrogen supplementation worsened albuminuria and raised total/very low-density lipoprotein triglycerides and total cholesterol. Estrogen-supplemented rats exhibited enhanced glomerular deposition of apo A-IV and apo B, increased glomerular expression of desmin and type IV collagen, and increased interstitial macrophage deposition.

CONCLUSION

Estrogen may be permissive for the early development of renal disease in OZRs and may act by increasing triglyceride-rich lipoproteins, which then bind to glomerular cells and initiate or accelerate glomerulosclerosis.

TGF-beta in diabetic kidney disease: role of novel signaling pathways

Diabetic nephropathy is the leading cause of end-stage renal disease in the United States and is a major contributing cause of morbidity and mortality in patients with diabetes. Despite conventional therapy to improve glycemic and blood pressure control the incidence of diabetic nephropathy is reaching epidemic proportions worldwide. As the major pathologic feature of diabetic nephropathy is diffuse mesangial matrix expansion, the pro-sclerotic cytokine transforming growth factor-beta, TGF-beta, is a leading candidate to mediate the progression of the disease. Numerous studies have now demonstrated that TGF-beta is a key factor in experimental models of diabetic kidney disease as well as in patients with diabetic nephropathy. Recent studies have begun to explore the mechanisms by which TGF-beta is stimulated by high glucose and how TGF-beta exerts its matrix-stimulating effects on renal cells. TGF-beta may also be involved in mediating the vascular dysfunction of diabetic kidney disease via its effects on the key intracellular calcium channel, the inositol trisphosphate receptor (IP(3)R). As there is substantial evidence for a cause and effect relationship between upregulation of TGF-beta and the progression of diabetic kidney disease, future studies will seek to establish specific targets along these pathways at which to intervene.

Effects of troglitazone on collagen accumulation and distensibility of aortic wall in prestage of non-insulin-dependent diabetes mellitus of Otsuka Long-Evans Tokushima Fatty rats

We investigated the effect of troglitazone (TG) on aortic distensibility and histopathology at the preclinical stage in the non-insulin-dependent diabetes mellitus (NIDDM) model. Twenty male diabetic and 20 male nondiabetic rats were each divided into two groups: treated-DM, untreated-DM, treated-nonDM, and untreated-nonDM. TG (0.2%) was mixed in chow in the treated groups. From age 5 to 15 weeks, fast blood glucose and insulin were monitored. At 15 weeks, oral glucose tolerance test results, aortic wall histopathology, and collagen content were studied, and intravascular ultrasound images and aortic pressure were recorded. Aortic diameter was measured during the cardiac cycle, and the stiffness parameter beta was calculated. Blood glucose (mg/dl) 2 h after loading in treated-DM (139+/-20) was normalized (untreated-DM, 188+/-27; p<0.05). Insulin concentration (ng/ml) in treated-DM (3.2+/-0.4) was lower than that in untreated-DM (8.1+/-1.5; p<0.01). At 15 weeks, beta in untreated-DM (2.4+/-0.8) was larger than those in untreated-nonDM (1.5+/-0.4; p<0.0001) and in treated-DM (1.9+/-0.4, p = 0.0081). Aortic wall collagen (mg/g dry weight) increased in untreated-DM (32.8+/-3.3) as compared with treated-DM (28.1+/-3.8; p = 0.048). Histomorphometry showed decreased medial area (mm2) in treated-DM (0.55+/-0.05) compared with untreated-DM (0.78+/-0.12; p<0.0001). This study suggests that TG may prevent metabolic abnormalities and the deterioration of aortic distensibility at an early prediabetic stage.

Ischemic renal diseases: new insights into old entities

Vascular nephropathies are a steadily increasing cause of end-stage renal failure. Arterionephrosclerosis and arteriolonephrosclerosis are common features in the hypertensive patient. This is especially true for blacks of African descent, in whom hypertension and nephrovasculopathies are a major cause of renal insufficiency. That primary hypertension leads to renal vascular lesions, glomerular obsolescence and interstitial fibrosis has long been established. It should not, however, obscure the fact that renal vascular lesions can be observed in animal models as well as in some humans, especially young blacks, in the absence of, or anticipating the onset of hypertension. This leads to considering the hypothesis that nephroangiosclerosis might stem from a genetic defect in the renal vascular bed and that this defect is strongly associated with the hypertensive trait. Atherosclerotic renal disease is a major, potentially treatable cause of chronic renal disease is a major, potentially treatable cause of chronic renal failure, especially in whites. It leads to renal atrophy, but the ischemic kidney retains a vigorous potential for tubular cell regeneration, which pleads for early recognition and treatment. Recent data suggest that renal ischemia, be it due to renal artery stenosis or to cholesterol crystal embolism, ranks among the multiple causes of secondary focal segmental glomerulosclerosis. Irrespective of its initial mechanism, ischemia induces renal fibrosis, the pathophysiology of which is centered on increased generation of angiotensin II. Finally, renal vascular lesions are commonly observed in the course of various nephropathies, even in the absence of hypertension, and the relationship between these lesions and the unfavorable prognosis of glomerulopathies, especially primary focal-segmental glomerulosclerosis, membranous glomerulopathy and IgA glomerulonephritis, remains to be elucidated. Expanding knowledge of the spectrum of nephrovasculopathies opens perspectives for investigating, understanding and treating a major mechanism of progressive renal insufficiency.

Expression of the heat shock protein 47 in gentamicin-treated rat kidneys

Heat-shock proteins (HSPs) are rapidly synthesized in cells in response to various cytotoxic agents. Although several stress proteins are actively involved in the gentamicin-induced renal damages, the possible role of HSP47 in this condition is not yet clear. In this study, the expression of HSP47 in the gentamicin nephrotoxicity was examined by immunohistochemistry. Twenty male Wistar rats were sacrificed at day 0, 3, 7, 14 and 28 after subcutaneous injection of gentamicin. Gentamicin treatment causes tubular necrosis at day 3, followed by tubular regenerative changes and interstitial fibrosis, which was most prominent at day 14. The renal structures returned to almost normal architectures at day 28. By immunohistochemistry, HSP47 was weakly expressed in most of the glomeruli and occasionally in interstitial cells in the control rat kidneys. In contrast, strong immunostaining for HSP47 was noted in the tubular epithelial cells and interstitial cells in gentamicin treated rat kidneys, and strongest staining was observed at day 7. The immunostaining for HSP47 then gradually decreased, and returned to the normal level at day 28. In the whole experimental period staining pattern of HSP47 in the glomeruli was not changed. In addition, phenotypically altered tubulointerstitial cells including regenerative tubular epithelial cells (immuno-positive for vimentin) and interstitial cells (immuno-positive for alpha-smooth muscle actin) were found in gentamicin nephrotoxicity. Expression of type III collagen increased in the areas of interstitial fibrosis. By double immunostaining, the regenerated and phenotypically altered tubulointerstitial cells were found to express HSP47 in and around interstitial fibrosis. It is concluded that overexpression of HSP47 by phenotypically altered renal cells might play a significant role in the development of gentamicin nephrotoxicity.

Transformation of rat inner medullary fibroblasts to myofibroblasts in vitro

Renal fibroblasts play a major role in the pathogenesis of renal interstitial fibrosis. This process is associated at least in some forms of interstitial fibrosis with a differentiation of fibroblasts into myofibroblasts, characterized by the de novo expression of alpha-smooth muscle (alpha-sm) actin and/or desmin. Both the mechanisms underlying this differentiation and their effects on cellular function are poorly understood. In vitro studies are difficult since the phenotypes of fibroblasts in culture have as yet not been well defined. We have, therefore, examined the phenotype of inner medullary fibroblasts (IMF) during the transition from in vivo to in vitro in various cell fractions derived from the inner medulla of healthy rats. IMF were positive for the lectin BSL-1 and negative for markers of endothelial cells. IMF first lost their prominent lipid droplets in vitro. Subsequently they developed cytoplasmic processes accompanied by a decrease in their reactivity for the lectin BSL-1 from strong to weak. From day 3 in primary culture, exclusively these weakly positive BSL-1 cells showed a de novo expression of alpha-sm actin (day 4 of primary culture, 75 +/- 4%; day 20, 94 +/- 2%) and desmin (day 4, 43 +/- 8%; day 20, 66 +/- 6%), classifying them as myofibroblasts. This transformation depended on culture conditions. In a mixed coculture with inner medullary collecting duct (IMCD) cells the transformation of IMF was largely absent: a significantly greater number of strong BSL-1 positive cells contained prominent lipid droplets (39 +/- 4 vs. 19 +/- 4%, P < 0.05) on day 4 of primary culture, and the transition of strongly to weakly positive BSL-1 IMF was almost completely blocked. By reducing the seeding density of IMCD cells the effect of this condition on IMF transformation could be largely abolished. This first detailed phenotypic characterization of rat fibroblasts during the transition from in vivo to in vitro demonstrates that these cells-depending on culture conditions-differentiate to myofibroblasts within a few days of primary culture and that subcultured IMF exhibit predominantly this phenotype. The presented model may serve as a useful tool for the in vitro study of myofibroblast formation and the consequences of such a differentiation for the physiological functions of IMF.

Preventative and therapeutic effects of AE0047 on renal injury in stroke-prone spontaneously hypertensive rats

1. The present study was designed to investigate the preventative and therapeutic effects of AE0047 on renal injury compared with those of nitrendipine in stroke-prone spontaneously hypertensive rats (SHRSP). 2. In the preventative study, drug administration was started before the appearance of renal injury, such as proteinuria. Treatment for 6 weeks with AE0047 (1 and 3 mg/kg, p.o.) led to a dose-related reduction in systolic blood pressure (SBP). Nitrendipine, at doses of 10 and 30 mg/kg, also lowered SBP to a similar degree to that seen with AE0047 at 1 and 3 mg/kg, respectively. 3. In the vehicle-administered SHRSP group, urinary excretion of protein (Uprotein V) increased progressively from 14 weeks of age for another 6 weeks. AE0047 at both doses maintained Uprotein V within normal levels throughout the experimental period. However, the elevation of Uprotein V was only inhibited in the 30 mg/kg nitrendipine-treated group. Urinary N-acetyl-beta-D-glucosaminide (NAG) activity in the vehicle-treated SHRSP group was elevated. Urinary NAG activity remained at a low level only in AE0047-treated groups. 4. Histopathological examination revealed severe lesions (i.e. fibrinoid necrosis, proliferative vasculitis and glomerular lesions) of the kidney in SHRSP. AE0047 treatment at each dose attenuated the development of renal lesions in SHRSP. In contrast, nitrendipine, at 10 mg/kg, was ineffective against the development of renal lesions. Although nitrendipine at 30 mg/kg suppressed the development of renal lesions, this effect was still weaker than that seen with AE0047 at 1 mg/kg. 5. In the therapeutic study, drugs were administered to 17-week-old SHRSP with moderate renal damage for 10 days. Treatment with AE0047 (1 and 3 mg/kg) produced dose-dependent decreases in Uprotein V. In the nitrendipine-treated group, Uprotein V tended to decrease but the changes were not significant. 6. Histopathological studies revealed that 3 mg/kg AE0047 improved renal lesions, such as fibrinoid necrosis, proliferative vasculitis and glomerular lesions, whereas 30 mg/kg nitrendipine did not. 7. Taken together, the results indicate that AE0047 is capable of preventing proteinuria as well as renal lesions, in part via a mechanism independent of its depressor action on SBP. Furthermore, AE0047 improves proteinuria and renal lesions in proteinuria-established SHRSP. Thus, AE0047 may have therapeutic potential in suppressing either the development or the progression of renal disease in hypertensive patients.

Mesangial cell abnormalities in spontaneously hypertensive rats before the onset of hypertension

To identify kidney biosynthetic abnormalities that may precede the onset of hypertension, we studied the expression of fibronectin (FN) and collagen IV (Coll IV) in young SHR (4 weeks of age) whose systolic blood pressure was normal and similar to that of age-matched control WKY rats. In isolated glomeruli the level of FN protein assessed by immunoblotting tended to be lower in the SHR than in the WKY rats. By Northern analysis the FN/actin mRNA ratio was significantly lower in glomeruli from SHR (0.56 +/- 0.47) than in glomeruli from WKY rats (2.0 +/- 0.8). These abnormalities were maintained in vitro since the expression of FN was significantly lower in SHR than in WKY cultured mesangial cells (FN/actin mRNA ratio = 0.84 +/- 0.46 vs. 1.9 +/- 0.7, P = 0.029). No differences in Coll IV mRNA or protein levels were observed in SHR glomeruli and mesangial cells when compared with WKY rats. The levels of aortic FN and Coll IV mRNAs were not different in SHR and WKY rats. In addition, mesangial cells from SHR showed a significantly higher growth rate than those from WKY. The biosynthetic and proliferative abnormalities observed in the SHR mesangial cells appear to reflect genetic characteristics, and could provide novel insights into cellular mechanisms linking the genetics of hypertension with predisposition to glomerular pathology.

Imidapril inhibits increased transforming growth factor-beta1 expression in remnant kidney model

To elucidate the effect of imidapril, an angiotensin-converting enzyme inhibitor, on molecular events in progressive glomerulosclerosis, we administered imidapril to 5/6 nephrectomized rats and measured the glomerular expression of genes for transforming growth factor (TGF)-beta1, fibronectin and collagen IV. Glomerular TGF-beta1, fibronectin and collagen IV mRNAs in nephrectomized rats were significantly higher than those in sham-operated rats. Treatment with imidapril for 10 weeks significantly reduced the enhanced glomerular expression of TGF-beta1 and collagen IV mRNA in nephrectomized rats, and prevented the associated proteinuria and glomerulosclerosis. Thus, imidapril may arrest progressive glomerulosclerosis by inhibiting the expression of TGF-beta1 and collagen IV.

Transforming growth factor beta 1 and renal injury following subtotal nephrectomy in the rat: role of the renin-angiotensin system

Transforming growth factor-beta (TGF-beta) and the renin-angiotensin system (RAS) have both been implicated in the pathogenesis of chronic renal disease. The present experiment investigated the chronology of TGF-beta 1 gene expression following subtotal nephrectomy (STNx) in the rat and the effect of blocking the RAS by angiotensin converting enzyme (ACE) inhibition or by angiotensin II receptor (AT1) antagonism. Rats that had undergone subtotal nephrectomy developed hypertension, proteinuria, renal impairement, glomerulosclerosis, tubulointerstitial fibrosis and mononuclear cell infiltration. These changes were associated with a 2.5-fold increase in TGF-beta 1 gene expression during a 16-week time course. In situ hybridization localized TGF-beta 1 mRNA to sclerotic glomeruli, areas of tubuloin-terstitial injury and sites of mononuclear cell infiltration. Administration of the ACE inhibitor ramipril and the AT1 receptor blocker valsartan blunted the increase in TGF-beta 1 mRNA, and attenuated the structural and functional manifestations of injury. These data suggest an interaction between the intrarenal RAS and TGF-beta in the pathogenesis of the glomerular and tubulointerstitial fibrosis that follow a major reduction in renal mass.