Role of Aberrant Iron Homeostasis in the Upregulation of Transforming Growth Factor-β1 in the Kidney of Angiotensin II-Induced Hypertensive Rats

Role of ferroptosis in fibrosis: From mechanism to potential therapy

ABSTRACT

Fibrosis, which is a manifestation of the physiological response to injury characterized by excessive accumulation of extracellular matrix components, is a ubiquitous outcome of the repair process. However, in cases of repetitive or severe injury, fibrosis may become dysregulated, leading to a pathological state and organ failure. In recent years, a novel form of regulated cell death, referred to as ferroptosis, has been identified as a possible contributor to fibrosis; it is characterized by iron-mediated lipid peroxidation. It has garnered attention due to the growing body of evidence linking ferroptosis and fibrogenesis, which is believed to be driven by underlying inflammation and immune responses. Despite the increasing interest in the relationship between ferroptosis and fibrosis, a comprehensive understanding of the precise role that ferroptosis plays in the formation of fibrotic tissue remains limited. This review seeks to synthesize previous research related to the topic. We categorized the different direct and indirect mechanisms by which ferroptosis may contribute to fibrosis into three categories: (1) iron overload toxicity; (2) ferroptosis-evoked necroinflammation, with a focus on ferroptosis and macrophage interplay; and (3) ferroptosis-associated pro-fibrotic factors and pathways. Furthermore, the review considers the potential implications of these findings and highlights the utilization of ferroptosis-targeted therapies as a promising strategy for mitigating the progression of fibrosis. In conclusion, novel anti-fibrotic treatments targeting ferroptosis could be an effective treatment for fibrosis.

Animal models of kidney iron overload and ferroptosis: a review of the literature

In recent years, it has been identified that excess iron contributes to the development of various pathologies and their complications. Kidney diseases do not escape the toxic effects of iron, and ferroptosis is identified as a pathophysiological mechanism that could be a therapeutic target to avoid damage or progression of kidney disease. Ferroptosis is cell death associated with iron-dependent oxidative stress. To study the effects of iron overload (IOL) in the kidney, numerous animal models have been developed. The methodological differences between these models should reflect the IOL-generating mechanisms associated with human IOL diseases. A careful choice of animal model should be considered for translational purposes.

Protective Role for Smooth Muscle Cell Hepcidin in Abdominal Aortic Aneurysm

BACKGROUND

Hepcidin is a liver-derived hormone that controls systemic iron homeostasis, by inhibiting the iron exporter ferroportin in the gut and spleen, respective sites of iron absorption and recycling. Hepcidin is also expressed ectopically in the context of cardiovascular disease. However, the precise role of ectopic hepcidin in underlying pathophysiology is unknown. In patients with abdominal aortic aneurysm (AAA), hepcidin is markedly induced in smooth muscle cells (SMCs) of the aneurysm wall and inversely correlated with the expression of LCN2 (lipocalin-2), a protein implicated in AAA pathology. In addition, plasma hepcidin levels were inversely correlated with aneurysm growth, suggesting hepcidin has a potential disease-modifying role.

METHODS

To probe the role of SMC-derived hepcidin in the setting of AAA, we applied AngII (Angiotensin-II)-induced AAA model to mice harbouring an inducible, SMC-specific deletion of hepcidin. To determine whether SMC-derived hepcidin acted cell-autonomously, we also used mice harboring an inducible SMC-specific knock-in of hepcidin-resistant ferroportinC326Y. The involvement of LCN2 was established using a LCN2-neutralizing antibody.

RESULTS

Mice with SMC-specific deletion of hepcidin or knock-in of hepcidin-resistant ferroportinC326Y had a heightened AAA phenotype compared with controls. In both models, SMCs exhibited raised ferroportin expression and reduced iron retention, accompanied by failure to suppress LCN2, impaired autophagy in SMCs, and greater aortic neutrophil infiltration. Pretreatment with LCN2-neutralizing antibody restored autophagy, reduced neutrophil infiltration, and prevented the heightened AAA phenotype. Finally, plasma hepcidin levels were consistently lower in mice with SMC-specific deletion of hepcidin than in controls, indicating that SMC-derived hepcidin contributes to the circulating pool in AAA.

CONCLUSIONS

Hepcidin elevation in SMCs plays a protective role in the setting of AAA. These findings are the first demonstration of a protective rather than deleterious role for hepcidin in cardiovascular disease. They highlight the need to further explore the prognostic and therapeutic value of hepcidin outside disorders of iron homeostasis.

Iron chelation suppresses secondary bleeding after intracerebral hemorrhage in angiotensin II-infused mice

AIMS

Secondary bleeding and further hematoma expansion (HE) aggravate brain injury after intracerebral hemorrhage (ICH). The majority of HE results from hypertensive ICH. Previous study reported higher iron content in the brains of hypertensive patients. Iron overload exacerbates the risk of hemorrhagic transformation in thromboembolic stroke mice. Whether iron overload during the process of hypertension participates in secondary bleeding of hypertensive ICH remains unclear.

METHODS

Hypertension was induced by continuous infusion of angiotensin II (Ang II) with an osmotic pump into C57BL/6 mice. ICH was simulated by intrastriatal injection of the liquid polymer Onyx-18. Iron chelation and iron overload was achieved by deferoxamine mesylate or iron dextran injection. Secondary bleeding was quantified by measuring the hemoglobin content in the ipsilateral brain hemisphere.

RESULTS

Ang II-induced hypertensive mice showed increased iron accumulation in the brain and expanded secondary hemorrhage after ICH modeling. Moreover, iron chelation suppressed while iron overload aggravated secondary bleeding. Mechanistically, iron exacerbated the loss of contractile cerebral vascular smooth muscle cells (VSMCs), aggravated blood-brain barrier (BBB) leakage in Ang II-induced hypertensive mice, and increased glial and MMP9 accumulation after ICH.

CONCLUSION

Iron overload plays a key role in secondary bleeding after ICH in Ang II-induced hypertensive mice. Iron chelation during the process of Ang II-induced hypertension suppresses secondary bleeding after ICH.

Molecular and Cellular Effect of Angiotensin 1-7 on Hypertensive Kidney Disease

BACKGROUND

Studies implicate that angiotensin 1-7 (Ang1-7) imparts protective effects in the kidney. However, its relevance in hypertensive kidney disease is not fully understood. The purpose of this study was to explore the role of Ang1-7 on renal damage/remodeling during hypertension and its potential underlying molecular-cellular mechanisms.

METHODS

Hypertension was induced in adult Sprague-Dawley rats by infusion of aldosterone (ALDO; 0.75 μg/hour) for 4 weeks with or without co-treatment of Ang1-7 (1 mg/kg/day). Untreated rats served as controls. Systolic blood pressure was monitored by tail-cuff technique. Renal fibrosis was evaluated by picrosirius red staining and renal collagen volume fraction was quantitated using imaging analyzing system. The expression of profibrotic factors [transforming growth factor-β1 (TGF-β1), platelet-derived growth factor-D (PDGF-D), fibroblast growth factor-1 (FGF-1), vascular endothelial growth factor-D (VEGF-D), and tissue inhibitors of metalloproteinases (TIMPs)] and free radical producing enzymes (inducible nitric oxide synthase and nicotinamide adenine dinucleotide phosphate [NADPH] oxidase) in the kidney were examined by reverse transcription-polymerase chain reaction and western blot. Renal oxidative stress was assessed by malondialdehyde (MDA) measurement.

RESULTS

Chronic ALDO infusion caused hypertension and hypertensive renal disease represented as glomerular damage/sclerosis. Ang1-7 co-treatment did not affect blood pressure in ALDO-treated rats, but significantly attenuated the glomerular damage/fibrosis. ALDO treatment significantly elevated renal expression of profibrogenic factors, including TGF-β1, TIMP-1/TIMP-2, FGF-1, PDGF-D, and VEGF-D, whereas Ang1-7 co-treatment significantly reduced renal TGF-β1, TIMP-1/TIMP-2, and FGF-1, but not PDGF-D and VEGF-D. Furthermore, ALDO infusion elevated NADPH oxidase (gp91phox) and MDA in the kidney, which was attenuated by Ang1-7 co-treatment.

CONCLUSIONS

Ang1-7 plays a protective role in the hypertensive kidney disease independent of blood pressure. The beneficial effects of Ang1-7 are likely mediated via suppressing TGF-β/FGF-1 pathways and oxidative stress.

Dietary iron restriction alleviates renal tubulointerstitial injury induced by protein overload in mice

Increased proteinuria causes tubulointerstitial injury due to inflammation in chronic kidney disease (CKD). Iron restriction exhibits protective effects against renal dysfunction; however, its effects against protein overload-induced tubulointerstitial damage remain unclear. Here, we investigated dietary iron restriction effect on tubulointerstitial damage in mice with protein-overload tubulointerstitial injury. Renal tubulointerstitial injury in animal model was induced by intraperitoneal injection of an overdose of bovine serum albumin (BSA). We divided mice into three groups: normal saline + normal diet (ND), BSA + ND, and BSA + iron-restricted diet (IRD). BSA overload induced renal tubulointerstitial injury in the ND mice, which was ameliorated in the IRD mice. Inflammatory cytokines and extracellular matrix mRNA expression was upregulated in BSA + ND mice kidneys and was inhibited by IRD. BSA-induced increase in renal superoxide production, NADPH oxidase activity, and p22^phox expression was diminished in the IRD mice. IRD suppression increased BSA-induced renal macrophage infiltration. Moreover, BSA mice exhibited nucleotide-binding oligomerisation domain-like receptor pyrin domain-containing protein (NLRP) inflammasome activation, which was inhibited by IRD. Ferrous iron increased in kidneys with BSA overload and was inhibited by IRD. Thus, iron restriction inhibited oxidative stress and inflammatory changes, contributing to the protective effect against BSA overload-induced tubulointerstitial injury.

Ovine uterine space restriction causes dysregulation of the renin-angiotensin system in fetal kidneys

In ovine pregnancy, uterine space restriction (USR) resulting from decreased space for placental attachment caused intrauterine growth restriction and impaired nephrogenesis. The fetal kidney renin-angiotensin system (RAS) is involved in nephrogenesis, fluid balance, and iron deposition. Angiotensin II exerts its effects via multiple receptors: angiotensin II 1-8 receptor type 1 (AT 1 R) and type 2 (AT 2 R), and angiotensin II 1-7 Mas receptor (MASR).

Objective

: To test the hypothesis that ovine USR is associated with dysregulation of the fetal renal RAS.

Methods

: Multiparous pregnant ewes (n = 32), 16 with surgical bifurcated disconnection of one uterine horn to further reduce placental attachment sites, were studied. USR (n = 31) ovine fetuses were compared to nonspace restricted (NSR) singleton controls (n = 22) on gestational day (GD) 120 or GD130, term GD147. Fetal plasma was collected to evaluate plasma renin activity and iron indices. Fetal kidney AT 1 R, AT 2 R, and MASR proteins were assessed by Western immunoblotting and immunohistochemistry.

Results

: AT 1 R, AT 2 R, and MASR protein expression was higher in USR at GD130 than aged-matched NSR and USR at GD120, ( P < 0.05 all). AT 1 R and AT 2 R localization was homogenous throughout proximal and distal tubules in both USR and NSR at both gestational dates. MASR localization was punctate throughout renal cortical structures including tubules and glomeruli in both USR and NSR, shifted to intranuclear at GD130. Plasma renin activity was inversely related to plasma osmolarity ( P < 0.02) and was downregulated in USR at GD130 ( P < 0.05).

Conclusions

: By late gestation, USR upregulated renal angiotensin receptor expression, an effect with potential functional implications.

Altered iron homeostasis in an animal model of hypertensive nephropathy: stroke-prone rats

BACKGROUND AND AIM

Iron is the most abundant metal in mammalian cells, and plays a pivotal role in many metabolic processes. Dysregulated iron homeostasis is involved in the cause of a number of pathological processes including renal diseases.

METHODS AND RESULTS

Longitudinal MRI scans of salt-loaded spontaneously hypertensive stroke-prone rats (SHRSP), an animal model that spontaneously develops hypertensive nephropathy, showed a decrease in renal and hepatic T2 SI (a sign of iron accumulation) of, respectively, 42.3 ± 2.5% (P < 0.01) and 60.4 ± 15.1% (P < 0.01) in comparison with SHRSP fed a standard diet. This was accompanied by the development of renal inflammation and oxidative stress (as evaluated by immunohistochemical and proteomic analyses), mitochondrial dysfunction, massive proteinuria and sustained intravascular hemolysis with the subsequent depletion of plasma haptoglobin, which was responsible for the renal uptake of hemoglobin and iron accumulation. In order to investigate the role of iron in these pathological processes, we subcutaneously treated the salt-loaded rats with the iron chelator deferoxamine (200 mg/kg per day). The pharmacological treatment prevented iron tissue accumulation, as indicated by the increase in renal and hepatic T2 SI of, respectively, 120.0 ± 10.1% (P < 0.01) and 73.9 ± 4.4% (P < 0.01) in comparison with salt-loaded rats treated with vehicle alone. Deferoxamine also preserved renal morphology and function, the renal infiltration of ED-1-positive macrophages/monocytes, and the expression of MCP-1 and TGF-β mRNA, reduced the level of reactive oxygen species, and improved the activity of mitochondrial cytochrome c oxidase.

CONCLUSION

These findings suggest that iron dysmetabolism is involved in the development of hypertensive nephropathy in SHRSP.

Ovine fetal renal development impacted by multiple fetuses and uterine space restriction

Intrauterine growth restriction (IUGR) from uteroplacental dysfunction causes impaired nephrogenesis and ultimately hypertension, but it is unknown whether IUGR caused by insufficient space for placental development seen in uterine anomalies and/or multifetal gestation exerts the same effects. Fetal renal development and metabolism were studied in an ovine space-restriction model by combining unilateral horn surgical ligation and/or multifetal gestation. Reduced placental attachment sites and placental weight per fetus defined space-restricted (USR) v. control nonrestricted (NSR) fetuses. Space-restricted fetuses exhibited evidence for decreased plasma volume, with higher hematocrit and plasma albumin at gestational day (GD) 120, followed by lower blood pO2, and higher osmolarity and creatinine at GD130, P < 0.05 for all. By combining treatments, fetal kidney weight relative to fetal weight was inversely related to both fetal weight and plasma creatinine levels, P < 0.05 for both. At GD130, space-restricted fetal kidney weights, cortical depths and glomerular generations were decreased, P < 0.05 for all. Space-restricted kidneys underwent an adaptive response by prolonging active nephrogenesis and increasing maculae densa number, P < 0.05 for both. The major renal adaptations in space-restricted IUGR fetuses included immaturity in both development and endocrine function, with evidence for impaired renal excretory function.

Iron chelation by deferoxamine prevents renal interstitial fibrosis in mice with unilateral ureteral obstruction

Renal fibrosis plays an important role in the onset and progression of chronic kidney diseases (CKD). Although several mechanisms underlying renal fibrosis and candidate drugs for its treatment have been identified, the effect of iron chelator on renal fibrosis remains unclear. In the present study, we examined the effect of an iron chelator, deferoxamine (DFO), on renal fibrosis in mice with surgically induced unilateral ureter obstruction (UUO). Mice were divided into 4 groups: UUO with vehicle, UUO with DFO, sham with vehicle, and sham with DFO. One week after surgery, augmented renal tubulointerstitial fibrosis and the expression of collagen I, III, and IV increased in mice with UUO; these changes were suppressed by DFO treatment. Similarly, UUO-induced macrophage infiltration of renal interstitial tubules was reduced in UUO mice treated with DFO. UUO-induced expression of inflammatory cytokines and extracellular matrix proteins was abrogated by DFO treatment. DFO inhibited the activation of the transforming growth factor-β1 (TGF-β1)-Smad3 pathway in UUO mice. UUO-induced NADPH oxidase activity and p22^phox expression were attenuated by DFO. In the kidneys of UUO mice, divalent metal transporter 1, ferroportin, and ferritin expression was higher and transferrin receptor expression was lower than in sham-operated mice. Increased renal iron content was observed in UUO mice, which was reduced by DFO treatment. These results suggest that iron reduction by DFO prevents renal tubulointerstitial fibrosis by regulating TGF-β-Smad signaling, oxidative stress, and inflammatory responses.

Heme oxygenase activity as a determinant of the renal hemodynamic response to low-dose ANG II

ANG II causes renal injury through hemodynamic and other effects, and pressor doses of ANG II induce heme oxygenase-1 (HO-1) as a protective response. The present studies examined the hemodynamic effects of more clinically relevant, lower doses of ANG II and the role of HO activity in influencing these effects. Under euvolemic conditions, ANG II increased arterial pressure and renal vascular resistance. ANG II did not induce oxidative stress, inflammation/injury-related gene expression, or proteinuria and did not alter extrarenal vascular reactivity. At these doses, ANG II failed to increase HO-1 or HO-2 mRNA expression or HO activity. Inhibiting HO activity in ANG II-treated rats by tin mesoporphyrin further increased renal vascular resistances, decreased renal blood flow, and blunted the rise in arterial pressure without inducing oxidative stress or altering expression of selected vasoactive/injury/inflammation-related genes; tin mesoporphyrin did not alter vasorelaxation of mesenteric resistor vessels. We conclude that in this model renal vasoconstriction occurs without the recognized adverse effects of ANG II on glomerular filtration rate, renal blood flow, oxidative stress, vascular reactivity, proteinuria, and injury-related gene expression; renal HO activity is essential in preserving perfusion of the ANG II-exposed kidney. These findings represent an uncommon example wherein function of a stressed organ (by ANG II), but not that of the unstressed organ, requires intact renal HO activity, even when the imposed stress neither induces HO-1 nor HO activity. These findings may be germane to conditions attended by heightened ANG II levels, ineffective renal perfusion, and susceptibility to acute kidney injury.

Administration of angiotensin II, but not catecholamines, induces accumulation of lipids in the rat heart

Accumulation of lipids in the heart may cause cardiac dysfunction in various disorders, such as obesity and diabetes. In the current study, we have investigated whether administration of angiotensin II or norepinephrine induces accumulation of lipids and/or changes in the expression of genes related to lipid metabolism in the rat heart. Lipid deposition was found in myocardial, vascular wall, and perivascular cells of the angiotensin II-infused rat heart, and superoxide generation was increased in these lipid-positive cells. By contrast, intracardiac lipid deposition was not found in the heart of norepinephrine-induced hypertensive rats. Triglyceride content in the heart tissue of angiotensin II-infused rats increased more than 3-fold as compared with untreated controls. Losartan completely, but hydralazine only partially, suppressed the angiotensin II-induced intracardiac lipid deposition and increase in tissue triglyceride content. Administration of angiotensin II upregulated the mRNA expression of sterol regulatory element-binding protein-1c and fatty acid synthase, but downregulated that of uncoupling protein 2 and 3, in a manner dependent on the angiotensin AT(1) receptor. Collectively, these results suggest that angiotensin II may be involved in modulating both intracardiac lipid content and lipid metabolism-related gene expression, in part via an angiotensin AT(1) receptor-dependent and pressor-independent mechanism.

Reduced expression of heme oxygenase-1 in patients with coronary atherosclerosis

Heme oxigenase-1 (HO-1) is known to be an inducible cytoprotective enzyme that copes with oxidative stress. However, changes in HO-1 expression and their association with human diseases have not been studied. To test the hypothesis that the capacity to upregulate HO-1 in response to oxidative stress is an intrinsic marker for susceptibility to coronary atherosclerosis, we assessed stimulation-induced change in HO-1 expression in blood cells in 110 patients who underwent coronary angiography, comparing the results with the extent of coronary atherosclerosis and (GT)(n) repeat polymorphism in the HO-1 gene promoter region, which is believed to affect the gene expression level. The extent of coronary atherosclerosis was assessed by coronary score. Mononuclear cells were incubated with 10 micromol/l hemin or vehicle for 4 h to maximally stimulate HO-1 expression, then the HO-1 expression level was determined by real-time polymerase chain reaction (PCR). The difference between the HO-1 mRNA levels of hemin- and vehicle-treated cells (DeltaHO-1 mRNA) was taken as an index of the capacity to upregulate HO-1 mRNA. The coefficient of variance of DeltaHO-1 mRNA was 7.2%. Consistent with previous studies, DeltaHO-1 mRNA was significantly lower in patients carrying a long (GT)(n) repeat. DeltaHO-1 mRNA negatively and significantly correlated with the coronary score (r(2)=0.50, p<0.01). In conclusion, the capacity to upregulate HO-1 expression may be determined, at least in part, by genetics, and reduced ability to induce HO-1 may be involved in the mechanism of coronary atherosclerosis.

Angiotensin II-induced regulation of the expression and localization of iron metabolism-related genes in the rat kidney

Due to recent discoveries of novel genes involved in iron metabolism, our understanding of the molecular mechanisms underlying iron metabolism has dramatically increased. We have previously shown that the administration of angiotensin II alters iron homeostasis in the rat kidney, which may in turn aggravate angiotensin II-induced renal damage. Here we have investigated the effect of angiotensin II administration on the localization and expression of transferrin receptor (TfR), divalent metal transporter 1 (DMT1), ferroportin 1 (FPN), and hepcidin mRNA in the rat kidney. Weak expression of TfR, DMT1, FPN, and hepcidin mRNA was observed in the kidneys of control rats. In contrast, after 7 days of angiotensin II infusion by osmotic minipump, the expression of these mRNAs was more widely distributed. Staining of serial sections revealed that some, but not all, of the renal tubular cells positive for these genes contained iron deposits in the kidney of angiotensin II-infused animals. Real-time polymerase chain reaction (PCR) showed that the mRNA expression of TfR, iron-responsive element-negative DMT1, FPN, and hepcidin mRNA increased ~1.9-fold, ~1.7-fold, ~2.3-fold, and ~4.7-fold, respectively, after angiotensin II infusion as compared with that of untreated controls, and that these increases could be suppressed by the concomitant administration of losartan. Our data demonstrate that these genes were unequivocally expressed in the kidney and could be regulated by angiotensin II infusion. The relative contribution, if any, of these genes to renal and/or whole-body iron homeostasis in various disorders in which the renin angiotensin system is activated should be investigated in future studies.

Expression and localization of PDGF-B, PDGF-D, and PDGF receptor in the kidney of angiotensin II-infused rat

Lipid accumulation in the kidney is a marker of tissue damage and may play a role in the development of renal injury. We have previously shown that long-term administration of angiotensin II in rats causes increased expression of transforming growth factor-beta1, coupled with an accumulation of lipids in the tubular and vascular wall cells in the kidney. In this study, we examine the regulation of expression of platelet-derived growth factor (PDGF) and its receptor system and their co-localization with lipid deposits in the kidneys of angiotensin II-infused rats. Real-time RT-PCR showed that expression of PDGF-B, PDGF-D, and PDGF receptor-beta (PDGFR-beta) mRNA was increased by angiotensin II infusion, and in situ hybridization showed the co-localization of these mRNAs. Tubular cells that had increased PDGF-B mRNA expression were positive for lipid deposition and also for cellular proliferation, which was indicated by the presence of proliferating cell nuclear antigen. By contrast, in the kidneys of angiotensin II-infused rats, apoptosis occurred in tubular cells that contained deposits of iron but not lipids. The deposition of lipids and upregulation of PDGF-B, PDGF-D, and PDGFR-beta induced by administration of angiotensin II were all suppressed by the selective angiotensin II type 1 (AT(1)) receptor antagonist losartan, but not by the nonspecific vasodilator hydralazine. The findings that lipid accumulation, upregulation of PDGF-B, PDGF-D, and PDGFR-beta, and cellular proliferation were topologically associated and regulated in an AT(1) receptor-dependent manner in the kidney of angiotensin II-infused rats suggests that these phenomena are related.

Iron sucrose induced morphological and functional changes in the rat kidney

Treatment of anemia in uremic patients requires simultaneous supplementation of erythropoietin and iron. Because of the impaired iron absorption from the gastrointestinal tract in conditions of renal insufficiency, intravenous supplementation is a treatment of choice in such conditions. Iron compounds used for intravenous supplementation induce several systemic side effects, and therefore, we studied the effect of chronic exposure to iron sucrose in rats on renal function. Experiments were performed on male Wistar rats, which were infused intraperitoneally every 4 days, for 28 days with iron sucrose in a dose 1 mg/kg bw or 10 mg/kg bw diluted in 20 mL of the dialysis fluid. Control animals were infused with plain dialysis fluid. Renal function was evaluated at the beginning and at the end of the study. Additionally morphology of the kidneys was evaluated in all animals after 28 days of the study. Chronic exposure of rats to iron sucrose resulted in increased accumulation of PAS-positive material in their glomeruli: + 38% at Fe 1 mg/kg bw P < 0.05 and + 42% at Fe 10 mg/kg/bw P < 0.01 and collagen in the peritubular area: + 40% at Fe 1 mg/kg bw P < 0.005 and + 77% at Fe 10 mg/kg/bw P < 0.001. Only renal clearance of urea was decreased by 53%, P < 0.01 in rats exposed to iron sucrose at a dose of 10 mg/kg bw. Chronic exposure of rats to iron sucrose results in morphologic changes of the kidney; however, mild impairment in renal function was observed only at the highest (10 mg Fe/kg bw) concentration of iron sucrose.

Transforming Growth Factor-.BETA. Signaling Enhances Transdifferentiation of Macrophages into Smooth Muscle-Like Cells

Hemopoietic cells or bone marrow-derived cells contribute to tissue formation, possibly by transdifferentiation into smooth muscle cells (SMCs) or myofibroblasts. In this study our goal is to examine the effects of transforming growth factor-beta1 (TGF-beta1) on the transdifferentiation of the monocyte/macrophage lineage into SMC-like cells. Using rat peritoneal exudate macrophages, we investigated the expression of smooth muscle-specific differentiation markers, such as alpha-smooth muscle actin, embryonic smooth muscle myosin heavy chain, and calponin. The treatment of macrophages with TGF-beta1 enhanced the expression of SMC-specific markers at day 4; after 7 days in culture, a higher level of expression (approximately 3- to 5-fold) was detected on Western blots. In contrast, TGF-beta1 decreased the expression of CD11b, which is a macrophage marker. Furthermore, we examined the effect of the TGF-beta type 1 receptor inhibitor SB-431542 and a replication-defective adenovirus construct expressing Smad7 (Adeno-Smad7), which inhibits TGF-beta signaling by interfering with the activation of other Smad proteins. Both SB-431542 and Adeno-Smad7 suppressed the expression of SMC-specific markers. These results indicated that TGF-beta signaling is essential for the transdifferentiation of macrophages into SMC-like cells. Elucidating the mechanism by which macrophages transdifferentiate into SMC-like cells may reveal new therapeutic targets for preventing vascular diseases.

Augmentation of Intrarenal Angiotensin II Levels in Uninephrectomized Aldosterone/Salt-Treated Hypertensive Rats; Renoprotective Effects of an Ultrahigh Dose of Olmesartan

Recent studies have suggested that aldosterone plays a role in the pathogenesis of renal injury. In this study, we investigated whether local angiotensin II (Ang II) activity contributes to the progression of renal injury in aldosterone/salt-induced hypertensive rats. Uninephrectomized rats were treated with 1% NaCl in a drinking solution and one of the following combinations for 6 weeks: vehicle (2% ethanol, s.c.; n=9), aldosterone (0.75 mug/h, s.c.; n=8), aldosterone+Ang II type 1 receptor blocker olmesartan (10 mg/kg/day, p.o.; n=8), or aldosterone+olmesartan (100 mg/kg/day, p.o.; n=9). Aldosterone/salt-treated hypertensive rats exhibited severe proteinuria and renal injury characterized by glomerular sclerosis and tubulointerstitial fibrosis. Aldosterone/salt-induced renal injury was associated with augmented expression of angiotensin converting enzyme and Ang II levels in the renal cortex and medullary tissues. Renal cortical and medullary mRNA expression of transforming growth factor-beta (TGF-beta) and connective tissue growth factor (CTGF) as well as the collagen contents were increased in aldosterone/salt-treated hypertensive rats. Treatment with olmesartan (10 or 100 mg/kg/day) had no effect on blood pressure but attenuated proteinuria in a dose-dependent manner. Olmesartan at 10 mg/kg/day tended to decrease renal cortical and medullary Ang II levels, TGF-beta and CTGF expression, and collagen contents; however, these changes were not significant. On the other hand, an ultrahigh dose of olmesartan (100 mg/kg/day) significantly decreased these values and ameliorated renal injury. These data suggest that augmented local Ang II activity contributes, at least partially, to the progression of aldosterone/salt-dependent renal injury.

Tissue Inhibitor of Metalloproteinase-3 Plays Important Roles in the Kidney Following Unilateral Ureteral Obstruction

Tissue inhibitor of metalloproteinase-3 (Timp-3), an inhibitor of matrix-degrading enzymes, is an important molecule for maintenance of the extracellular matrix. In this study, we generated Timp-3-deficient mice and used them to examine the effect of Timp-3-deficiency on blood pressure and to investigate the role of Timp-3 in the kidney following unilateral ureteral obstruction. The blood pressure and heart rate of Timp-3-deficient mice were not significantly different from those of wild-type mice. On the other hand, the obstructed kidneys of Timp-3-deficient mice developed more severe hydronephrosis than those of wild-type animals. Matrix metalloproteinase activities assessed by in situ zymography and transforming growth factor-beta expression were elevated in Timp-3-deficient mice. The renal tissues were thinner and the ratio of renal medulla to cortex was significantly lower in the obstructed Timp-3-deficient kidneys. These findings indicate that Timp-3-deficiency does not substantially affect the blood pressure in mice, and that Timp-3 plays an important role in the maintenance of renal macrostructure after unilateral ureteral obstruction.

Cardioprotective mechanisms of spironolactone associated with the angiotensin-converting enzyme/epidermal growth factor receptor/extracellular signal-regulated kinases, NAD(P)H oxidase/lectin-like oxidized low-density lipoprotein receptor-1, and Rho-kinase pathways in aldosterone/salt-induced hypertensive rats

Studies were performed to test the hypothesis that the angiotensin-converting enzyme (ACE)/epidermal growth factor receptor (EGFR)/extracellular signal-regulated kinases (ERK) pathway, nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase/lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) pathway, and Rho-kinase pathway contribute to the pathogenesis of aldosterone/salt-induced hypertensive rats. Wistar rats were given 1% NaCl to drink and treated with one of the following combinations for 6 weeks: vehicle; aldosterone (0.75 microg/h); aldosterone plus a mineralocorticoid receptor antagonist, spironolactone (20 mg/kg/day); aldosterone plus an ACE inhibitor, imidapril (1 mg/kg/day); aldosterone plus an NAD(P)H oxidase inhibitor, apocynin (0.5 mmol/l); and aldosterone plus an Rho-kinase inhibitor, Y-27632 (3 mg/kg/day). Upregulated expression of ACE and EGFR and p44/p42ERK phosphorylation were suppressed by spironolactone or imidapril. Upregulated NAD(P)H oxidase subunits and LOX-1 expression were inhibited by spironolactone or apocynin. Increased expression of RhoA and Rho-kinase and myosin light chain phosphorylation were decreased by spironolactone or Y-27632. Moreover, these drugs effectively inhibited the vascular lesion formation, as measured by the medial thickness and level of perivascular fibrosis, and suppressed the expression of transforming growth factor-beta1, type I and III collagen, and monocyte chemoattractant protein-1 mRNA. Spironolactone may be useful as a cardioprotective agent to prevent cardiovascular remodeling via the ACE/EGFR/ERK, NAD(P)H oxidase/LOX-1, and Rho-kinase pathways.

Iron Chelation Suppresses Ferritin Upregulation and Attenuates Vascular Dysfunction in the Aorta of Angiotensin II–Infused Rats

Objective— We have investigated whether long-term administration of angiotensin (Ang) II causes ferritin induction and iron accumulation in the rat aorta, and their possible relation to regulatory effects on gene expression and vascular function in Ang II-infused animals.

Methods and Results— Sprague-Dawley rats were given Ang II for 7 days via subcutaneously implanted osmotic minipumps. Ang II infusion caused a >20-fold increase in ferritin protein expression over control values. Immunohistochemistry showed that Ang II infusion markedly increased the ferritin expression in the aortic endothelial and adventitial cells, with some of the latter being identified as monocytes/macrophages. Prussian blue staining showed that stainable iron was observed in the adventitial layer of aorta from Ang II-infused animals, but not in the endothelial layer. Chelation of iron suppressed aortic induction of ferritin and also the oxidative stress markers, heme oxygenase-1 and 4-hydroxynonenal-modified protein adducts. In addition, iron chelation attenuated Ang II-induced impairment of aortic relaxations in response to acetylcholine and sodium nitroprusside and suppressed upregulation of mRNA levels of monocyte chemoattractant protein-1. Iron chelation also partially attenuated the medial thickening and perivascular fibrosis induced by Ang II infusion for 4 weeks.

Conclusion— Ang II infusion caused ferritin induction and iron deposition in the aortas. These phenomena might have a role in the regulation of gene expression, impairment of vascular function, and arterial remodeling induced by Ang II, which are presumably mediated in part by enhancement of oxidative stress.

Lipid accumulation and transforming growth factor-beta upregulation in the kidneys of rats administered angiotensin II

Abnormal lipid metabolism may play a role in progressive renal failure. We studied whether lipid accumulation occurs and whether lipid deposits are colocalized with transforming growth factor-beta1 (TGF-beta1) in the kidney of angiotensin II-infused animals. Oil red O staining showed marked lipid deposition in the tubular epithelial and vascular wall cells of angiotensin II-treated but not in norepinephrine-treated rats. Histological analyses showed that increased amounts of superoxide and intense TGF-beta1 mRNA expression were present in lipid-positive tubular epithelial cells in angiotensin II-infused animals. Protein expression of sterol regulatory element-binding protein 1 (SREBP-1) and mRNA expression of fatty acid synthase in the kidney were &3 times and 1.5 times, respectively, higher in angiotensin II-treated rats than in controls. Treatment of angiotensin II-infused animals with an iron chelator, deferoxamine, attenuated the angiotensin II-induced increases in renal expression of SREBP-1 and fatty acid synthase and normalized the lipid content in the renal cortical tissues. Abnormal lipid metabolism may be associated with upregulation of TGF-beta1 expression and aberrant iron homeostasis in the kidneys of angiotensin II-infused animals.

Diastolic Dysfunction in Hypertensive Hearts: Roles of Perivascular Inflammation and Reactive Myocardial Fibrosis

There is increasing evidence that myocardial fibrosis plays a role in the pathogenesis of diastolic dysfunction in hypertensive heart disease. However, it has been difficult to explore the mechanisms of isolated diastolic dysfunction in hypertensive hearts because of the lack of adequate animal models. Recently, we demonstrated that Wistar rats with a suprarenal aortic constriction (AC) can be used as a model of cardiac hypertrophy associated with preserved systolic, but impaired diastolic function without overt congestive heart failure. In this model, acute pressure elevation induces reactive myocardial fibrosis (perivascular fibrosis followed by intermuscular interstitial fibrosis) and myocyte/left ventricular (LV) hypertrophy. Perivascular macrophage infiltration, which is mediated by monocyte chemoattractant protein-1 (MCP-1) and intercellular adhesion molecule-1, exerts a key role in myocardial fibrosis, but not in myocyte/LV hypertrophy. Transforming growth factor (TGF)-beta is crucial for reactive fibrosis in AC rats. MCP-1 function blocking not only inhibits macrophage infiltration and TGF-beta induction but also prevents reactive fibrosis and diastolic dysfunction, without affecting blood pressure, myocyte/LV hypertrophy, or systolic function. Accordingly, a substantial role of inflammation is indicated in myocardial fibrosis and diastolic dysfunction in hypertensive hearts. Currently, the precise mechanisms whereby acute pressure elevation triggers inflammation remain unknown, but it is likely that activation of the tissue angiotensin system is involved in the induction of the inflammatory process.