Role of reactive oxygen species in angiotensin II-mediated renal growth, differentiation, and apoptosis

Methylseq, single-nuclei RNAseq, and discovery proteomics identify pathways associated with nephron-deficit CKD in the HSRA rat model

Low nephron numbers are associated with an increased risk of developing chronic kidney disease (CKD) and hypertension, which are significant global health problems. To investigate the impact of nephron deficiency, our laboratory developed a novel inbred rat model (HSRA rat). In this model, ∼75% of offspring are born with a single kidney (HSRA-S), compared with two-kidney littermates (HSRA-C). HSRA-S rats show impaired kidney development, resulting in ∼20% fewer nephrons. Our previous data and current findings demonstrate that nephron deficit (failure of one kidney to form and altered development in the remaining kidney) predisposes HSRA-S to CKD late in life (with increased proteinuria by 18 mo of age in HSRA-S = 51 ± 3.4 vs. HSRA-C = 8 ± 1.5 mg/24 h). To understand early molecular mechanisms contributing to the increased predisposition to CKD, Methylseq using reduced representation bisulfite sequencing, single-nuclei (sn)RNAseq, and discovery proteomics were performed in kidneys of 4-wk-old HSRA rats. Methylation analysis revealed a small number of differences, including five differentially methylated cytosines and six differentially methylated regions between groups. The snRNAseq analysis identified differentially expressed genes in most kidney cell types, with several hundred genes dysregulated depending on the analysis method (Seurat vs. DESeq2). Notably, many genes are involved in kidney development. Discovery proteomic analysis identified 366 differentially expressed proteins. A key finding was dysregulation of Deptor/DEPTOR and Amdhd2/AMDHD2 across omics layers, suggesting a potential role in compensatory mechanisms or the genetic basis of altered kidney development. Further understanding of these mechanisms may guide interventions to preserve nephron health and slow kidney disease progression.NEW & NOTEWORTHY The HSRA rat is a novel model of nephron deficiency and provides a unique opportunity to study the association between nephron number and chronic kidney disease (CKD). Previous work characterized the impact of age, hypertension, and diabetes on the development of CKD in HSRA animals. This study examined early changes in epigenetics, cell-type specific transcriptome, and proteomic changes in the kidney that likely predispose the model to CKD with age.

Angiotensin-Converting Enzyme 2 (ACE2) Signaling in Pulmonary Arterial Hypertension: Underpinning Mechanisms and Potential Targeting Strategies

Pulmonary arterial hypertension (PAH) is a debilitating progressive disease characterized by excessive pulmonary vasoconstriction and abnormal vascular remodeling processes that lead to right-ventricular heart failure and, ultimately, death. Although our understanding of its pathophysiology has advanced and several treatment modalities are currently available for the management of PAH patients, none are curative and the prognosis remains poor. Therefore, further research is required to decipher the molecular mechanisms associated with PAH. Angiotensin-converting enzyme 2 (ACE2) plays an important role through its vasoprotective functions in cardiopulmonary homeostasis, and accumulating preclinical and clinical evidence shows that the upregulation of the ACE2/Angiotensin-(1-7)/MAS1 proto-oncogene, G protein-coupled receptor (Mas 1 receptor) signaling axis is implicated in the pathophysiology of PAH. Herein, we highlight the molecular mechanisms of ACE2 signaling in PAH and discuss its potential as a therapeutic target.

Aryl Hydrocarbon Receptor Mechanisms Affecting Chronic Kidney Disease

The aryl hydrocarbon receptor (AHR) is a basic helix-loop-helix transcription factor that binds diverse endogenous and xenobiotic ligands, which regulate AHR stability, transcriptional activity, and cell signaling. AHR activity is strongly implicated throughout the course of chronic kidney disease (CKD). Many diverse organic molecules bind and activate AHR and these ligands are reported to either promote glomerular and tubular damage or protect against kidney injury. AHR crosstalk with estrogen, peroxisome proliferator-activated receptor-γ, and NF-κB pathways may contribute to the diversity of AHR responses during the various forms and stages of CKD. The roles of AHR in kidney fibrosis, metabolism and the renin angiotensin system are described to offer insight into CKD pathogenesis and therapies.

Nox4 Promotes RANKL-Induced Autophagy and Osteoclastogenesis via Activating ROS/PERK/eIF-2α/ATF4 Pathway

Receptor activator of nuclear factor-κB ligand (RANKL) has been found to induce osteoclastogenesis and bone resorption. However, the underlying molecular mechanisms remain unclear. Via conducting a series of biochemical experiments with in vitro cell lines, this study investigated the role and mechanism of NADPH oxidase 4 (Nox4) in RANKL-induced autophagy and osteoclastogenesis. In the current study, we found that RANKL dramatically induced autophagy and osteoclastogenesis, inhibition of autophagy with chloroquine (CQ) markedly attenuates RANKL-induced osteoclastogenesis. Interestingly, we found that the protein level of Nox4 was remarkably upregulated by RANKL treatment. Inhibition of Nox4 by 5-O-methyl quercetin or knockdown of Nox4 with specific shRNA markedly attenuated RANKL-induced autophagy and osteoclastogenesis. Furthermore, we found that Nox4 stimulated the production of nonmitochondrial reactive oxygen species (ROS), activating the critical unfolded protein response (UPR)-related signaling pathway PERK/eIF-2α/ATF4, leading to RANKL-induced autophagy and osteoclastogenesis. Blocking the activation of PERK/eIF-2α/ATF4 signaling pathway either by Nox4 shRNA, ROS scavenger (NAC) or PERK inhibitor (GSK2606414) significantly inhibited autophagy during RANKL-induced osteoclastogenesis. Collectively, this study reveals that Nox4 promotes RANKL-induced autophagy and osteoclastogenesis via activating ROS/PERK/eIF-2α/ATF4 pathway, suggesting that the pathway may be a novel potential therapeutic target for osteoclastogenesis-related disease.

Endothelial prolyl hydroxylase 2 is necessary for angiotensin II-mediated renal fibrosis and injury

Angiotensin II (ANG II) is the key contributor to renal fibrosis and injury. The present study investigated the role of endothelium prolyl hydroxylase 2 (PHD2) in ANG II-mediated renal fibrosis and injury. In vitro, endothelial cells (ECs) were isolated from PHD2^f/f control [wild-type (WT)] mice or PHD2 EC knockout (PHD2^ECKO) mice. In vivo, WT and PHD2^ECKO mice were infused with ANG II (1,000 ng·kg^-1·min^-1) for 28 days. Renal fibrosis, reactive oxygen species (ROS), and iron contents were measured. Knockout of PHD2 resulted in a significant increase in the expression of hypoxia-inducible factor (HIF)-1α and HIF-2α in ECs. Intriguingly, knockout of PHD2 significantly reduced expression of the ANG II type 1 receptor (AT₁R) in ECs. WT mice infused with ANG II caused increases in renal fibrosis, ROS formation, and iron contents. ANG II treatment led to a downregulation of PHD1 expression and upregulation of HIF-1α and HIF-2α in the renal cortex and medulla. Knockout of PHD2 in EC blunted ANG II-induced downregulation of PHD1 expression. Furthermore, knockout of PHD2 in ECs attenuated ANG II-induced expression of HIF-1α, HIF-2α, transforming growth factor-β1, p47^phox, gp91^phox, heme oxygenase-1, and ferroportin. This was accompanied by a significant suppression of renal fibrosis, ROS formation, and iron accumulation. In summary, knockout of endothelial PHD2 suppressed the expression of AT₁R in ECs and blunted ANG II-induced downregulation of PHD1 and upregulation of HIF-α in the kidney. Our study, for the first time, demonstrates a necessary role of endothelial PHD2 in ANG II-mediated renal fibrosis and injury.

The Interplay of Renin-Angiotensin System and Toll-Like Receptor 4 in the Inflammation of Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most serious chronic kidney diseases and the major cause of end-stage renal failure worldwide. The underlying mechanisms of DN are complex and required to be further investigated. Both innate immunity and renin-angiotensin system (RAS) play critical roles in the pathogenesis of DN. Except for traditional functions, abnormally regulated RAS has been proved to be involved in the inflammatory process of DN. Toll-like receptor 4 (TLR4) is the most deeply studied pattern recognition receptor in the innate immune system, and its activation has been reported to mediate the development of DN. In this review, we aim at discussing how dysregulated RAS affects TLR4 activation in the kidney that contributes to the exploration of the pathogenesis of DN. Understanding the interplay of RAS and TLR4 in inducing the progression of DN may provide new insights to develop effective treatments.

The Role of G Protein-Coupled Receptors in the Right Ventricle in Pulmonary Hypertension

Pressure overload of the right ventricle (RV) in pulmonary arterial hypertension (PAH) leads to RV remodeling and failure, an important determinant of outcome in patients with PAH. Several G protein-coupled receptors (GPCRs) are differentially regulated in the RV myocardium, contributing to the pathogenesis of RV adverse remodeling and dysfunction. Many pharmacological agents that target GPCRs have been demonstrated to result in beneficial effects on left ventricular (LV) failure, such as beta-adrenergic receptor and angiotensin receptor antagonists. However, the role of such drugs on RV remodeling and performance is not known at this time. Moreover, many of these same receptors are also expressed in the pulmonary vasculature, which could result in complex effects in PAH. This manuscript reviews the role of GPCRs in the RV remodeling and dysfunction and discusses activating and blocking GPCR signaling to potentially attenuate remodeling while promoting improvements of RV function in PAH.

The interplay between Angiotensin II, TLR4 and hypertension

Hypertension is a multifactorial disease. Although a number of different underlying mechanisms have been learned from the various experimental models of the disease, hypertension still poses challenges for treatment. Angiotensin II plays an unquestionable role in blood pressure regulation acting through central and peripheral mechanisms. During hypertension, dysregulation of the Renin-Angiotensin System is associated with increased expression of pro-inflammatory cytokines and reactive oxygen species causing kidney damage, endothelial dysfunction, and increase in sympathetic activity, among other damages, eventually leading to decline in organ function. Recent studies have shown that these effects involve both the innate and the adaptive immune response. The contribution of adaptive immune responses involving different lymphocyte populations in various models of hypertension has been extensively studied. However, the involvement of the innate immunity mediating inflammation in hypertension is still not well understood. The innate and adaptive immune systems intimately interact with one another and are essential to an effectively functioning of the immune response; hence, the importance of a better understanding of the underlying mechanisms mediating innate immune system during hypertension. In this review, we aim to discuss mechanisms linking Angiotensin II and the innate immune system, in the pathogenesis of hypertension. The newest research investigating Angiotensin II triggering toll like receptor 4 activation in the kidney, vasculature and central nervous system contributing to hypertension will be discussed. Understanding the role of the innate immune system in the development of hypertension may bring to light new insights necessary to improve hypertension management.

Mycophenolate Mofetil Ameliorates Diabetic Nephropathy in db/db Mice

Chronic low-grade inflammation is an important factor in the pathogenesis of diabetic complication. Mycophenolate mofetil (MMF) has an anti-inflammatory effect, inhibiting lymphocyte proliferation. Previous studies showed attenuation of diabetic nephropathy with MMF, but the underlying mechanisms were unclear. This study aimed to identify the effect of MMF on diabetic nephropathy and investigate its action mechanisms in type 2 diabetic mice model. Eight-week-old db/db and control mice (db/m mice) received vehicle or MMF at a dose of 30 mg/kg/day for 12 weeks. MMF-treated diabetic mice showed decreased albuminuria, attenuated mesangial expansion, and profibrotic mRNA expressions despite the high glucose level. The number of infiltrated CD4⁺ and CD8⁺ T cells in the kidney was significantly decreased in MMF-treated db/db mice and it resulted in attenuating elevated intrarenal TNF-α and IL-17. The renal chemokines expression and macrophages infiltration were also attenuated by MMF treatment. The decreased expression of glomerular nephrin and WT1 was recovered with MMF treatment. MMF prevented the progression of diabetic nephropathy in db/db mice independent of glycemic control. These results suggest that the effects of MMF in diabetic nephropathy are mediated by CD4⁺ T cell regulation and related cytokines.

Angiotensin II-induced hypertensive renal inflammation is mediated through HMGB1-TLR4 signaling in rat tubulo-epithelial cells

BACKGROUND AND PURPOSE

Angiotensin II is a vaso-constrictive peptide that regulates blood pressure homeostasis. Even though the inflammatory effects of AngII in renal pathophysiology have been studied, there still exists a paucity of data with regard to the mechanism of action of AngII-mediated kidney injury. The objective of this study was to elucidate the mechanistic role of HMGB1-TLR4 signaling in AngII-induced inflammation in the kidney.

EXPERIMENTAL APPROACH

Rat tubular epithelial cells (NRK52E) were treated with AngII over a preset time-course. In another set of experiments, HMGB1 was neutralized and TLR4 was knocked down using small interfering RNA targeting TLR4. Cell extracts were subjected to RT-PCR, immunoblotting, flow cytometry, and ELISA.

KEY RESULTS

AngII-induced inflammation in NRK52E cells increased gene and protein expression of TLR4, HMGB1 and key proinflammatory cytokines (TNFα and IL1β). Pretreatment with Losartan (an AT1 receptor blocker) attenuated the AngII-induced expression of TLR4 and inflammatory cytokines. TLR4 silencing was used to elucidate the specific role played by TLR4 in AngII-induced inflammation. TLR4siRNA treatment in these cells significantly decreased the AngII-induced inflammatory effect. Consistent observations were made when the Ang II treated cells were pretreated with anti-HMGB1. Downstream activation of NFκB and rate of generation of ROS was also decreased on gene silencing of TLR4 and exposure to anti-HMGB1.

CONCLUSIONS AND IMPLICATIONS

These results indicate a key role for HMGB1-TLR4 signaling in AngII-mediated inflammation in the renal epithelial cells. Our data also reveal that AngII-induced effects could be alleviated by HMGB1-TLR4 inhibition, suggesting this pathway as a potential therapeutic target for hypertensive renal dysfunctions.

Role of free radical in atherosclerosis, diabetes and dyslipidaemia: larger-than-life

During the past few decades, there have been numerous studies related to free radical chemistry. Free radicals including reactive oxygen species (ROS) and reactive nitrogen species are generated by the human body by various endogenous systems, exposure to different physiochemical conditions, or pathological states, and have been implicated in the pathogenesis of many diseases. These free radicals are also the common by-products of many oxidative biochemical reactions in cells. When free radicals overwhelm the body's ability to regulate them, a condition known as oxidative stress ensues. They adversely alter lipids, proteins, and DNA, which trigger a number of human diseases. In a number of pathophysiological conditions, the delicate equilibrium between free radical production and antioxidant capability is distorted, leading to oxidative stress and increased tissue injury. ROS which are mainly produced by vascular cells are implicated as possible underlying pathogenic mechanisms in a progression of cardiovascular diseases including ischemic heart disease, atherosclerosis, cardiac arrhythmia, hypertension, and diabetes. This review summarizes the key roles played by free radicals in the pathogenesis of atherosclerosis, diabetes, and dyslipidaemia. Although not comprehensive, this review also provides a brief perspective on some of the current research being conducted in this area for a better understanding of the role free radicals play in the pathogenesis of atherosclerosis, diabetes, and dyslipidaemia.

Propofol protects against angiotensin II-induced mouse hippocampal HT22 cells apoptosis via inhibition of p66Shc mitochondrial translocation

Hippocampal neuronal oxidative stress and apoptosis have been reported to be involved in cognitive impairment, and angiotensin II could induce hippocampal oxidative stress and apoptosis. Propofol is a widely used intravenous anesthetic agent in clinical practice, and it demonstrates significant neuroprotective activities. In this study, we investigated the mechanism how propofol protected mouse hippocampal HT22 cells against angiotensin II-induced oxidative stress and apoptosis. Cell viability was evaluated with CCK8 kit. Protein expressions of active caspase 3, cytochrome c, p66(Shc), p-p66(shc)-Ser(36), protein kinase C βII (PKCβII), Pin-1 and phosphatase A2 (PP2A) were measured by Western blot. Superoxide anion (O2(.-)) accumulation was measured with the reduction of ferricytochrome c. Compared with the control group, angiotensin II up-regulated expression of PKCβII, Pin-1 and PP2A, induced p66(Shc)-Ser(36) phosphorylation, and facilitated p66(Shc) mitochondrial translocation, resulting in O2(.-) accumulation, mitochondrial cytochrome c release, caspase 3 activation, and the inhibition of cell viability. Importantly, we found propofol inhibited angiotensin II-induced PKCβII and PP2A expression and improved p66(Shc) mitochondrial translocation, O2(.-) accumulation, mitochondrial cytochrome c release, caspase 3 activation, inhibition of cell viability. On the other hand, propofol had no effects on angiotensin II-induced Pin-1 expression and p66(Shc)-Ser(36) phosphorylation. Moreover, the protective effects of propofol on angiotensin II-induced HT22 apoptosis were similar with calyculin A, an inhibitor of PP2A and CGP53353, an inhibitor of PKCβII. However, the protective effect of propofol could be reversed by FTY720, an activator of PP2A, rather than PMA, an activator of PKCβII. Our data indicated that propofol down-regulated PP2A expression, inhibiting dephosphorylation of p66(Shc)-Ser(36) and p66(Shc) mitochondrial translocation, decreasing O2(.-) accumulation, reducing mitochondrial cytochrome c release, inhibiting caspase 3 activation. By these mechanisms, it protects mouse hippocampal HT22 cells against angiotensin II-induced apoptosis.

Antioxidant effects of statins in the management of cardiometabolic disorders

Redox systems are key players in vascular health. A shift in redox homeostasis-that results in an imbalance between reactive oxygen species (ROS) generation and endogenous antioxidant defenses has the potential to create a state of oxidative stress that subsequently plays a role in the pathogenesis of a number of diseases, including those of the cardiovascular and metabolic system. Statins, which are primarily used to reduce the concentration of low-density lipoprotein cholesterol, have also been shown to reduce oxidative stress by modulating redox systems. Studies conducted both in vitro and in vivo support the role of oxidative stress in the development of atherosclerosis and cardiovascular diseases. Oxidative stress may also be responsible for various diabetic complications and the development of fatty liver. Statins reduce oxidative stress by blocking the generation of ROS and reducing the NAD+/NADH ratio. These drugs also have effects on nitric oxide synthase, lipid peroxidation and the adiponectin levels. It is possible that the antioxidant properties of statins contribute to their protective cardiovascular effects, independent of the lipid-lowering actions of these agents. However, possible adverse effects of statins on glucose homeostasis may be related to the redox system. Therefore, studies investigating the modulation of redox signaling by statins are warranted.

Upregulation of sestrin-2 expression protects against endothelial toxicity of angiotensin II

Sestrin-2 (SESN2) is involved in the cellular response to different stress conditions. However, the function of SESN2 in the cardiovascular system remains unknown. In the present study, we tested whether SESN2 has a beneficial effect on vascular endothelial damage induced by angiotensin II (AngII). Firstly, we found that AngII induces expression of SESN2 in human umbilical vein endothelial cells (HUVECs) in a time-dependent and dose-dependent manner. We also found that knockdown of SESN2 using small RNA interference promotes cellular toxicity of AngII, as well as a reduction in cell viability, exacerbation of oxidative stress, and stimulation of apoptosis. In addition, our results show that the c-Jun NH (2)-terminal kinase (JNK)/c-Jun pathway is activated by AngII. Inhibiting the activity of the JNK pathway abolishes the increase in SESN2 induced by AngII. Importantly, overexpression of c-Jun promotes luciferase activity of the SESN2 promoter. These findings suggest that the inductive effect of SESN2 is mediated by the JNK/c-Jun pathway. Our results indicate that the induction of SESN2 acts as a compensatory response to AngII for survival, implying that stimulating expression of SESN2 might be an effective pharmacological target for the treatment of AngII-associated cardiovascular diseases.

Reactive oxygen species in diabetic nephropathy: friend or foe?

Based on the numerous cellular and animal studies over the last decades, it has been postulated that reactive oxygen species (ROS) are important secondary messengers for signalling pathways associated with apoptosis, proliferation, damage and inflammation. Their adverse effects were considered to play a leading role in the onset and progression of type 1 and type 2 diabetes mellitus as well as in the complication of diabetic disease leading to vascular-, cardiac-, neuro-degeneration, diabetic retinopathy and diabetic nephropathy. All these complications were mostly linked to the generation of the superoxide anion, due to a prolonged hyperglycaemia in diabetes, and this anion was almost 'blamed for everything', despite the fact that its measurement and detection in life systems is extremely complicated due to the short lifespan of the superoxide anion. Therefore, a tremendous amount of research has been focused on finding ways to suppress ROS production. However, a recent report from Dugan et al. shed new insights into the life detection of superoxide generation in diabetes and raised the question of whether we treat the diabetes-related complications correctly or the target is somewhat different as thought. This review will focus on some aspects of this novel concept for the role of ROS in diabetic nephropathy.

Remnant nephron physiology and the progression of chronic kidney disease

In chronic kidney disease, ongoing failure of individual nephrons leads to the progressive loss of renal function. This process results in part from a cellular and molecular response to injury that represents an attempt to maintain homeostasis but instead initiates a program that damages the nephron. As nephrons are lost, compensation by the remaining nephrons exacerbates glomerular pathophysiology. The delivery of excessive amounts of biologically active molecules to the distal nephron and tubulointerstitium generates inflammation and cellular dedifferentiation. Energy requirements of hyperfunctioning nephrons exceed the metabolic substrate available to the renal tubule, and inadequacy of the local vascular supply promotes hypoxia/ischemia and consequent acidosis and reactive oxygen species generation. In this way, mechanisms activated to maintain biological balance ultimately lead to demise of the nephron.

L-tyrosine induces DNA damage in brain and blood of rats

Mutations in the tyrosine aminotransferase gene have been identified to cause tyrosinemia type II which is inherited in an autosomal recessive manner. Studies have demonstrated that an excessive production of ROS can lead to reactions with macromolecules, such as DNA, lipids, and proteins. Considering that the L-tyrosine may promote oxidative stress, the main objective of this study was to investigate the in vivo effects of L-tyrosine on DNA damage determined by the alkaline comet assay, in brain and blood of rats. In our acute protocol, Wistar rats (30 days old) were killed 1 h after a single intraperitoneal L-tyrosine injection (500 mg/kg) or saline. For chronic administration, the animals received two subcutaneous injections of L-tyrosine (500 mg/kg, 12-h intervals) or saline administered for 24 days starting at postnatal day (PD) 7 (last injection at PD 31), 12 h after the last injection, the animals were killed by decapitation. We observed that acute administration of L-tyrosine increased DNA damage frequency and damage index in cerebral cortex and blood when compared to control group. Moreover, we observed that chronic administration of L-tyrosine increased DNA damage frequency and damage index in hippocampus, striatum, cerebral cortex and blood when compared to control group. In conclusion, the present work demonstrated that DNA damage can be encountered in brain from animal models of hypertyrosinemia, DNA alterations may represent a further means to explain neurological dysfunction in this inherited metabolic disorder and to reinforce the role of oxidative stress in the pathophysiology of tyrosinemia type II.

Insulin regulates hypoxia-inducible factor-1α transcription by reactive oxygen species sensitive activation of Sp1 in 3T3-L1 preadipocyte

Oxygen sensing transcription factor HIF-1 is activated due to accumulation of regulatory subunit HIF-1α by posttranslational stability mechanism during hypoxia or by several other stimuli even in normoxia. HIF-1α is also regulated by NF-kB mediated transcription mechanism. Reactive oxygen species (ROS) act as an important regulator of HIF-1 either by affecting prolyl hydroxylase activity, the critical determinant of HIF-1α stabilization or by activating NF-kB to promote HIF-1α transcription. Insulin is known to activate HIF-1 by a ROS dependent mechanism but the molecular mechanism of HIF-1α regulation is not known so far. Here we show that insulin regulates HIF-1α by a novel transcriptional mechanism by a ROS-sensitive activation of Sp1 in 3T3-L1 preadipocyte. Insulin shows little effect on HIF-1α protein stability, but increases HIF-1α promoter activity. Mutation analyses, electrophoretic mobility shift assay and chromatin immunoprecipitation assay confirm the role of Sp1 in HIF-1α transcription. We further demonstrate that insulin-induced ROS generation initiates signaling pathway involving phosphatidylinositol 3-kinase and protein kinase C for Sp1 mediated HIF-1α transcription. In summary, we reveal that insulin regulates HIF-1α by a novel transcriptional mechanism involving Sp1.

VDR hypermethylation and HIV-induced T cell loss

Epigenetics contributes to the development of variety of diseases by modulation of gene expression. We evaluated the effect of HIV-induced VDR methylation on loss of TCs. HIV/TC displayed enhanced VDR-CpG methylation and increased expression of Dnmt3b but attenuated expression of VDR. A demethylating agent, AZA, inhibited this effect of HIV. HIV/TC also displayed the activation of the RAS, which was reversed by EB (a VDA). Further, HIV/TCs displayed enhanced generation of ROS and induction of DSBs but attenuated DNA repair response. However, in the presence of AZA, EB, LOS (a RAS blocker), Cat, and tempol (free radical scavengers), HIV-induced TC ROS generation and induction of DSBs were attenuated but associated with enhanced DNA repair. Additionally, AZA, EB, and LOS provided protection against HIV-induced TC apoptosis. These findings suggested that HIV-induced TC apoptosis was mediated through ROS generation in response to HIV-induced VDR methylation and associated activation of the RAS.

DNA damage and augmented oxidative stress in bone marrow mononuclear cells from Angiotensin-dependent hypertensive mice

It has been proposed that the nonhemodynamic effects of angiotensin II are important for the damage observed in the two-kidney, one-clip (2K1C) renovascular hypertension model. Much evidence confirms that angiotensin II is directly involved in NAD(P)H oxidase activation and consequent superoxide anion production, which can damage DNA. The current study was performed to examine the effects of angiotensin-II-dependent hypertension in bone marrow mononuclear cells (BM-MNC); dihydroethidium staining was used to assess reactive oxygen species (ROS) production, and the comet assay was used to assess DNA fragmentation in 2K1C hypertensive mice 14 days after renal artery clipping. In this study we demonstrated that 2K1C hypertensive mice have an elevated lymphocyte count, while undifferentiated BM-MNC counts were diminished. 2K1C mice also showed an augmented ROS production and marked BM-MNC DNA fragmentation. In conclusion, endogenous renin angiotensin system activation-induced arterial hypertension is characterized by excessive ROS production in BM-MNC, which might cause marked DNA damage.

Cross talk between ceramide and redox signaling: implications for endothelial dysfunction and renal disease

Recent studies have demonstrated that cross talk between ceramide and redox signaling modulates various cell activities and functions and contributes to the development of cardiovascular diseases and renal dysfunctions. Ceramide triggers the generation of reactive oxygen species (ROS) and increases oxidative stress in many mammalian cells and animal models. On the other hand, inhibition of ROS-generating enzymes or treatment of antioxidants impairs sphingomyelinase activation and ceramide production. As a mechanism, ceramide-enriched signaling platforms, special cell membrane rafts (MR) (formerly lipid rafts), provide an important microenvironment to mediate the cross talk of ceramide and redox signaling to exert a corresponding regulatory role on cell and organ functions. In this regard, activation of acid sphingomyelinase and generation of ceramide mediate the formation of ceramide-enriched membrane platforms, where transmembrane signals are transmitted or amplified through recruitment, clustering, assembling, or integration of various signaling molecules. A typical such signaling platform is MR redox signaling platform that is centered on ceramide production and aggregation leading to recruitment and assembling of NADPH oxidase to form an active complex in the cell plasma membrane. This redox signaling platform not only conducts redox signaling or regulation but also facilitates a feedforward amplification of both ceramide and redox signaling. In addition to this membrane MR redox signaling platform, the cross talk between ceramide and redox signaling may occur in other cell compartments. This book chapter focuses on the molecular mechanisms, spatial-temporal regulations, and implications of this cross talk between ceramide and redox signaling, which may provide novel insights into the understanding of both ceramide and redox signaling pathways.

Redox proteomics in study of kidney-associated hypertension: new insights to old diseases

SIGNIFICANCE

The kidney helps to maintain low blood pressure in the human body, and impaired kidney function is a common attribute of aging that is often associated with high blood pressure (hypertension). Kidney-related pathologies are important contributors (either directly or indirectly) to overall human mortality. In comparison with other organs, kidney has an unusually wide range of oxidative status, ranging from the well-perfused cortex to near-anoxic medulla.

RECENT ADVANCES

Oxidative stress has been implicated in many kidney pathologies, especially chronic kidney disease, and there is considerable research interest in oxidative stress biomarkers for earlier prediction of disease onset. Proteomics approaches have been taken to study of human kidney tissue, serum/plasma, urine, and animal models of hypertension.

CRITICAL ISSUES

Redox proteomics, in which oxidative post-translational modifications can be identified in protein targets of oxidative or nitrosative stress, has not been very extensively pursued in this set of pathologies.

FUTURE DIRECTIONS

Proteomics studies of kidney and related tissues have relevance to chronic kidney disease, and redox proteomics, in particular, represents an under-exploited toolkit for identification of novel biomarkers in this commonly occurring pathology.

Nonclassical renin-angiotensin system and renal function

The renin-angiotensin system (RAS) constitutes one of the most important hormonal systems in the physiological regulation of blood pressure through renal and nonrenal mechanisms. Indeed, dysregulation of the RAS is considered a major factor in the development of cardiovascular pathologies, including kidney injury, and blockade of this system by the inhibition of angiotensin converting enzyme (ACE) or blockade of the angiotensin type 1 receptor (AT1R) by selective antagonists constitutes an effective therapeutic regimen. It is now apparent with the identification of multiple components of the RAS within the kidney and other tissues that the system is actually composed of different angiotensin peptides with diverse biological actions mediated by distinct receptor subtypes. The classic RAS can be defined as the ACE-Ang II-AT1R axis that promotes vasoconstriction, water intake, sodium retention, and other mechanisms to maintain blood pressure, as well as increase oxidative stress, fibrosis, cellular growth, and inflammation in pathological conditions. In contrast, the nonclassical RAS composed primarily of the AngII/Ang III-AT2R pathway and the ACE2-Ang-(1-7)-AT7R axis generally opposes the actions of a stimulated Ang II-AT1R axis through an increase in nitric oxide and prostaglandins and mediates vasodilation, natriuresis, diuresis, and reduced oxidative stress. Moreover, increasing evidence suggests that these non-classical RAS components contribute to the therapeutic blockade of the classical system to reduce blood pressure and attenuate various indices of renal injury, as well as contribute to normal renal function.

Role of the transcription factor erythroblastosis virus E26 oncogen homolog-1 (ETS-1) as mediator of the renal proinflammatory and profibrotic effects of angiotensin II

Angiotensin II (Ang II) plays a major role in the pathogenesis of end-organ injury in hypertension via its diverse hemodynamic and nonhemodynamic effects. Erythroblastosis virus E26 oncogen homolog-1 (ETS-1) is an important transcription factor recently recognized as an important mediator of cell proliferation, inflammation, and fibrosis. In the present studies, we tested the hypothesis that ETS-1 is a common mediator of the renal proinflammatory and profibrotic effects of Ang II. C57BL6 mice (n=6 per group) were infused with vehicle (control), Ang II (1.4 mg/kg per day), Ang II and an ETS-1 dominant-negative peptide (10 mg/kg per day), or Ang II and an ETS-1 mutant peptide (10 mg/kg per day) via osmotic minipump for 2 or 4 weeks. The infusion of Ang II resulted in significant increases in blood pressure and left ventricular hypertrophy, which were not modified by ETS-1 blockade. The administration of ETS-1 dominant-negative peptide significantly attenuated Ang II-induced renal injury as assessed by urinary protein excretion, mesangial matrix expansion, and cell proliferation. Furthermore, ETS-1 dominant-negative peptide but not ETS-1 mutant peptide significantly reduced Ang II-mediated upregulation of transforming growth factor-β, connective tissue growth factor, and α-smooth muscle actin. In addition, ETS-1 blockade reduced several proinflammatory effects of Ang II, including macrophage infiltration, nitrotyrosine expression, and NOX4 mRNA expression. Our studies suggest that ETS-1 is a common mediator of the proinflammatory and profibrotic effects of Ang II-induced hypertensive renal damage and may result in the development of novel strategies in the treatment and prevention of end-organ injury in hypertension.

Angiotensin II suppresses adenosine monophosphate-activated protein kinase of podocytes via angiotensin II type 1 receptor and mitogen-activated protein kinase signaling

BACKGROUND

Adenosine monophosphate (AMP)-activated protein kinase (AMPK), as a sensor of cellular energy status, has been known to play an important role in the pathophysiology of diabetes and its complications. As AMPK is also expressed in podocytes, it is possible that podocyte AMPK would be an important contributing factor in the development of diabetic proteinuria. We investigated the roles of AMPK in the pathological changes of podocytes induced by angiotensin II (Ang II), a major injury inducer in diabetic proteinuria.

METHODS

Mouse podocytes were incubated in media containing various concentrations of Ang II and AMPK-modulating agents. The changes of AMPKα were analyzed by confocal imaging and Western blotting in response to Ang II.

RESULTS

Ang II changed the localization of AMPKα from peripheral cytoplasm into internal cytoplasm and peri- and intranuclear areas in podocytes. Ang II also reduced AMPKα (Thr172) phosphorylation in time- and dose-sensitive manners. In particular, 10(-7 )M Ang II reduced phospho-AMPKα significantly and continuously at 6, 24, and 48 h. AMPK activators, metformin and 5-aminoimidazole-4-carboxamide-1β-riboside, restored the suppressed AMPKα (Thr172) phosphorylation. Losartan, an Ang II type 1 receptor antagonist, also recovered the suppression and the mal-localization of AMPKα, which were induced by Ang II. PD98059, a mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor, also restored the AMPKα (Thr172) phosphorylation suppressed by Ang II.

CONCLUSION

We suggest that Ang II induces the relocation and suppression of podocyte AMPKα via Ang II type 1 receptor and MAPK signaling pathway, which would be an important mechanism in Ang II-induced podocyte injury.

Osteoclast precursor differentiation by MCPIP via oxidative stress, endoplasmic reticulum stress, and autophagy

Osteoclasts (OCs) are responsible for bone resorption in inflammatory joint diseases. Monocyte chemotactic protein-1 (MCP-1) has been shown to induce differentiation of monocytes to OC precursors, but nothing is known about the underlying mechanisms. Here, we elucidate how MCPIP, induced by MCP-1, mediates this differentiation. Knockdown of MCPIP abolished MCP-1-mediated expression of OC markers, tartrate-resistant acid phosphatase, and serine protease cathepsin K. Expression of MCPIP induced p47(PHOX) and its membrane translocation, reactive oxygen species formation, and induction of endoplasmic reticulum (ER) stress chaperones, up-regulation of autophagy marker, Beclin-1, and lipidation of LC3, and induction of OC markers. Inhibition of oxidative stress attenuated ER stress and autophagy, and suppressed expression of OC markers. Inhibition of ER stress by a specific inhibitor or by knockdown of IRE1 blocked autophagy and induction of OC markers. ER stress inducers, tunicamycin and thapsigargin, induced expression of OC markers. Autophagy inhibition by 3'-methyladenine, LY294002, wortmannin or by knockdown of Beclin-1 or Atg 7 inhibited MCPIP-induced expression of OC markers. These results strongly suggest that MCP-1-induced differentiation of OC precursor cells is mediated via MCPIP-induced oxidative stress that causes ER stress leading to autophagy, revealing a novel mechanistic insight into the role of MCP-1 in OCs differentiation.

Lipid raft redox signaling: molecular mechanisms in health and disease

Lipid rafts, the sphingolipid and cholesterol-enriched membrane microdomains, are able to form different membrane macrodomains or platforms upon stimulations, including redox signaling platforms, which serve as a critical signaling mechanism to mediate or regulate cellular activities or functions. In particular, this raft platform formation provides an important driving force for the assembling of NADPH oxidase subunits and the recruitment of other related receptors, effectors, and regulatory components, resulting, in turn, in the activation of NADPH oxidase and downstream redox regulation of cell functions. This comprehensive review attempts to summarize all basic and advanced information about the formation, regulation, and functions of lipid raft redox signaling platforms as well as their physiological and pathophysiological relevance. Several molecular mechanisms involving the formation of lipid raft redox signaling platforms and the related therapeutic strategies targeting them are discussed. It is hoped that all information and thoughts included in this review could provide more comprehensive insights into the understanding of lipid raft redox signaling, in particular, of their molecular mechanisms, spatial-temporal regulations, and physiological, pathophysiological relevances to human health and diseases.

Fentanyl activates hypoxia-inducible factor 1 in neuronal SH-SY5Y cells and mice under non-hypoxic conditions in a μ-opioid receptor-dependent manner

Hypoxia-inducible factor 1 (HIF-1) is the main transcription factor responsible for hypoxia-induced gene expression. Perioperative drugs including anesthetics have been reported to affect HIF-1 activity. However, the effect of fentanyl on HIF-1 activity is not well documented. In this study, we investigated the effect of fentanyl and other opioids on HIF-1 activity in human SH-SY5Y neuroblastoma cells, hepatoma Hep3B cells, lung adenocarcinoma A549 cells and mice. Cells were exposed to fentanyl, and HIF-1 protein expression was examined by Western blot analysis using anti-HIF-1α and β antibodies. HIF-1-dependent gene expression was investigated by semi-quantitative real-time reverse transcriptase (RT)-PCR (qRT-PCR) and luciferase assay. Furthermore, fentanyl was administered intraperitoneally and HIF-1-dependent gene expression was investigated by qRT-PCR in the brains and kidneys of mice. A 10-μM concentration of fentanyl and other opioids, including 1 μM morphine and 4 μM remifentanil, induced HIF-1α protein expression and HIF-1 target gene expression in an opioid receptor-dependent manner in SH-SY5Y cells with activity peaking at 24h. Fentanyl did not augment HIF-1α expression during hypoxia-induced induction. HIF-1α stabilization assays and experiments with cycloheximide revealed that fentanyl increased translation from HIF-1α mRNA but did not stabilize the HIF-1α protein. Furthermore, fentanyl induced HIF-1 target gene expression in the brains of mice but not in their kidneys in a naloxone-sensitive manner. In this report, we describe for the first time that fentanyl, both in vitro and in vivo, induces HIF-1 activation under non-hypoxic conditions, leading to increases in expression of genes associated with adaptation to hypoxia.

Role of the angiotensin II AT2 receptor in inflammation and oxidative stress: opposing effects in lean and obese Zucker rats

Inflammation and oxidative stress are believed to contribute to hypertension in obesity/diabetes. Recently, we reported a role for the AT(2) receptor in blood pressure control in obese Zucker rats. However, the role of AT(2) receptors in inflammation and oxidative stress in obesity is not known. Therefore, in the present study, we tested the effects of the AT(2) receptor agonist CGP-42112A on inflammation and oxidative stress in obese Zucker rats and compared them in their lean counterparts. Rats were systemically treated with either vehicle (control) or CGP-42112A (1 μg·kg(-1)·min(-1); osmotic pump) for 2 wk. Markers of inflammation (CRP, MCP-1, TNF-α, and IL-6) and oxidative stress (HO-1, gp-91(phox)) as well as an antioxidant (SOD) were determined. Control obese rats had higher plasma levels of CRP, MCP-1, TNF-α, IL-6, and HO-1 compared with control lean rats. Conversely, plasma SOD activity was lower in control obese than in control lean rats. Furthermore, the protein levels of TNF-α and gp-91(phox) were higher in the kidney cortex of control obese rats. Interestingly, CGP-42112A treatment in obese rats reduced the plasma and kidney cortex inflammatory (TNF-α, IL-6) and oxidative stress (gp-91(phox)) markers and increased plasma SOD activity to the levels seen in lean control rats. However, CGP-42112A treatment in lean rats increased inflammatory (TNF-α, IL-6) and oxidative stress (gp-91(phox)) markers in the plasma and kidney cortex. Our present studies suggest anti-inflammatory and antioxidative functions of AT(2) receptor in obese Zucker rats but proinflammatory and prooxidative functions in lean Zucker rats.

Gene expression profiles linked to AT1 angiotensin receptors in the kidney

To characterize gene expression networks linked to AT(1) angiotensin receptors in the kidney, we carried out genome-wide transcriptional analysis of RNA from kidneys of wild-type (WT) and AT(1A) receptor-deficient mice (KOs) at baseline and after 2 days of angiotensin II infusion (1,000 ng·kg(-1)·min(-1)). At baseline, 405 genes were differentially expressed (>1.5×) between WT and KO kidneys. Of these, >80% were upregulated in the KO group including genes involved in inflammation, oxidative stress, and cell proliferation. After 2 days of angiotensin II infusion in WT mice, expression of ≈805 genes was altered (18% upregulated, 82% repressed). Genes in metabolism and ion transport pathways were upregulated while there was attenuated expression of genes protective against oxidative stress including glutathione synthetase and mitochondrial superoxide dismutase 2. Angiotensin II infusion had little effect on blood pressure in KOs. Nonetheless, expression of >250 genes was altered in kidneys from KO mice during angiotensin II infusion; 14% were upregulated, while 86% were repressed including genes involved in immune responses, angiogenesis, and glutathione metabolism. Between WT and KO kidneys during angiotensin II infusion, 728 genes were differentially expressed; 10% were increased and 90% were decreased in the WT group. Differentially regulated pathways included those involved in ion transport, immune responses, metabolism, apoptosis, cell proliferation, and oxidative stress. This genome-wide assessment should facilitate identification of critical distal pathways linked to blood pressure regulation.

Fluorofenidone attenuates collagen I and transforming growth factor-beta1 expression through a nicotinamide adenine dinucleotide phosphate oxidase-dependent way in NRK-52E cells

AIM

Fluorofenidone (1-(3-fluorophenyl)-5-methyl-2-(1H)-pyridone) is a novel pyridone agent. The aim of the present study is to investigate the effects of fluorofenidone on angiotensin (Ang)II-induced fibrosis and the involved molecular mechanism in rat proximal tubular epithelial cells.

METHODS

NRK-52E cells, a rat proximal tubular epithelial cell line, were incubated with medium containing AngII, with or without nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor diphenylene iodonium (DPI), losartan, fluorofenidone (2, 4 and 8 mmol/L) and pirfenidone (8 mmol/L) for 24 h. Cells in the serum-free medium were controls. The expression of three subunits of NADPH oxidase, including p47phox, Nox-4 and p22phox, were determined by real-time reverse transcription polymerase chain reaction (RT-PCR) and western blot. NADPH oxidase activity was measured directly by superoxide dismutase (SOD) inhibitable cytochrome C reduction assay. The generation of reactive oxygen species (ROS) was measured by dichlorofluorescein fluorescence analysis. The mRNA and protein expression of collagen I and transforming growth factor (TGF)-beta1 were determined by real-time RT-PCR and enzyme-linked immunosorbent assay.

RESULTS

Fluorofenidone significantly inhibited TGF-beta1 and collagen I expression upregulation induced by AngII or TGF-beta1 respectively. Moreover, fluorofenidone greatly reduced the elevation of expression and activity of NADPH oxidase and inhibited ROS generation induced by AngII in rat proximal tubular epithelial cells. These responses were also attenuated by DPI, losartan, and pirfenidone.

CONCLUSION

Fluorofenidone acted as an anti-oxidative and anti-fibrotic agent through the mechanisms of blocking NADPH oxidase-dependent oxidative stress and inhibiting TGF-beta1 expression in rat proximal tubular epithelial cells.

Angiotensin-(1-7)-angiotensin-converting enzyme 2 attenuates reactive oxygen species formation to angiotensin II within the cell nucleus

The angiotensin (Ang) type 1 receptor (AT(1)R) is highly expressed on renal nuclei and stimulates reactive oxygen species (ROS). It is not known whether other functional components of the Ang system regulate the nuclear Ang II-AT(1)R ROS pathway. Therefore, we examined the expression of Ang receptors in nuclei isolated from the kidneys of young adult (1.5 years) and older adult (3.0 to 5.0 years) sheep. Binding studies in renal nuclei revealed the AT(2)R as the predominant receptor subtype ( approximately 80%) in young sheep, with the Ang-(1-7) (AT(7)R; Mas protein) and AT(1)R antagonists competing for the remaining sites. Conversely, in older sheep, the AT(1)R accounted for approximately 85% of nuclear sites, whereas the Ang type 2 receptor and AT(7)R subtypes comprise approximately 20% of remaining sites. Ang II increased nuclear ROS to a greater extent in older (97+/-22%; n=6) versus young animals (7+/-2%; P=0.01; n=4), and this was abolished by an AT(1)R antagonist. The AT(7)R antagonist D-Ala(7)-Ang-(1-7) increased ROS formation to Ang II by approximately 2-fold (174+/-5% versus 97+/-22%; P<0.05) in older adults. Immunoblots of renal nuclei revealed protein bands for the AT(7)R and Ang-converting enzyme 2 (ACE2), which metabolizes Ang II to Ang-(1-7). The ACE2 inhibitor MLN4760 also exacerbated the Ang II-dependent formation of ROS (156+/-15%) and abolished the generation of Ang-(1-7) from Ang II. We conclude that an ACE2-Ang-(1-7)-AT(7)R pathway modulates Ang II-dependent ROS formation within the nucleus, providing a unique protective mechanism against oxidative stress and cell damage.

Candesartan attenuates Angiotensin II-induced mesangial cell apoptosis via TLR4/MyD88 pathway

Angiotensin II (Ang II) can stimulate Toll-like receptor 4 (TLR4) expression in mesangial cells (MCs), but the role of TLR4 in the Ang II-induced apoptosis and the effect of candesartan on TLR4 expression remain unclear. Here, we report that Ang II-induced MC apoptosis in a time-dependent manner and up-regulated TLR4/MyD88 expression, and that the intracellular ROS was subsequently increased. We also show that candesartan attenuated the Ang II-induced MC apoptosis, and that this protective effect was dependent on decreased TLR4/MyD88 expression as well as reduced intracellular ROS formation. Furthermore, Ang II increased the apoptosis inducing factor protein level, while candesartan markedly reduced this increase. These results demonstrate that TLR4/MyD88 pathway was involved in the Ang II promoted MC apoptosis, which was related to TLR4/MyD88 mediated oxidative stress. These data also suggest that candesartan exerted anti-apoptotic effect as an antioxidant by modulating this pathway.

Concurrent administration of ascorbic acid enhances liver tumor-promoting activity of kojic acid in rats

We previously found that administration of ascorbic acid (AA) enhances the liver tumor-promoting activity of kojic acid (KA) in mice. To examine the reproducibility of these results in rats and the underlying mechanism of this effect, we employed a two-stage liver carcinogenesis model using male F344 rats. Two weeks after initiation with diethylnitrosamine (DEN), the animals received a diet containing 2% KA and drinking water with or without 5,000 ppm AA for a period of 7 weeks. A DEN-alone group was also established as a control. One week after the commencement of the administration, the animals were subjected to two-thirds partial hepatectomy. At the end of the experiment, the livers were analyzed immunohistochemically, and the mRNA expression level and extent of lipid peroxidation were measured. AA treatment enhanced the KA-induced tumor-promoting activity in terms of the number and area of liver cell foci that were positive for glutathione-S-transferase placental form. AA coadministration increased the number of hepatocytes positive for proliferating cell nuclear antigen and inversely decreased the number of TUNEL-positive cells. However, the increased level of thiobarbituric acid reactive substances resulting from KA treatment was suppressed by coadministration of AA. Gene expression analyses using low-density microarrays and real-time RT-PCR showed that coadministration of AA resulted in upregulation of genes related to cell proliferation and downregulation of those involved in apoptosis and/or cell cycle arrest. These results indicate that the concerted effects of AA on cell proliferation and apoptosis/cell cycle arrest probably through its antioxidant activity are involved in this enhancement.

Angiotensin II increases intrarenal transforming growth factor-beta1 in rats submitted to sodium overload independently of blood pressure

Angiotensin II (Ang II) promotes sodium-retention, cell growth and fibrosis in addition to its classical effects on blood pressure and fluid homeostasis. In this study we examined whether low and non-hypertensive doses of exogenous Ang II could enhance the intrarenal expression of transforming growth factor-beta1 (TGF-beta1) observed in rats submitted to sodium overload. Sprague-Dawley-rats were infused for 2 h with 0.1 and 5 microg kg(-1) h(-1) Ang II (Ang 0.1 and Ang 5, respectively) together with saline solution at four different concentrations (isotonic and Na 0.5 mol L(-1), Na 1.0 mol L(-1) and Na 1.5 mol L(-1)). Renal function and mean arterial blood pressure (BP) were measured. The renal distributions of TGF-beta1, alpha-smooth-muscle-actin (alpha-SMA) and nuclear factor-kappaB (NF-kappaB) were evaluated by immunohistochemistry. While the Ang 0.1 groups were normotensive, the Ang 5 groups developed arterial hypertension progressively, and the highest blood pressure values were observed when rats were simultaneously infused with Na 1.5 mol L(-1). Glomerular function was not altered in any group. In cortical tubules, all groups infused with Ang II (0.1 and 5) and hypertonic saline solution (HSS) showed an increase in TGF-beta1 immunostaining compared to those infused with HSS alone. In medullary tubules, only the Ang 5-Na 0.5 group showed a significant increase in TGF-beta 1 immunostaining compared to the Na 0.5 group. Peritubular positive staining for alpha-SMA was present in groups receiving Ang alone or Ang-Na, in a sodium concentration-dependent manner. In cortical-tubules, NF-kappaB immunostaining was significantly increased in the Ang groups in comparison with the control and in Ang-Na 0.5 and Ang-Na 1.0 groups in comparison with the Na 0.5 mol L(-1) and Na 1.5 mol L(-1) groups, respectively, except in the case of the Ang 0.1-Na 1.5 mol L(-1) and Ang 5-Na 1.5 mol L(-1) groups. Moreover, Ang II and sodium overload induced additional changes in TGF-beta1, alpha-SMA and NF-kappaB immunostanding in glomeruli, medullary tubules and renal vessels. In conclusion, the interaction of Ang II with acute-sodium overload exacerbated intrarenal TGF-beta1, alpha-SMA and NF-kappaB expression, independently from changes in blood pressure levels, in normal rats.

Effect of eplerenone, enalapril and their combination treatment on diabetic nephropathy in type II diabetic rats

BACKGROUND

Recent data suggest that aldosterone antagonists have beneficial effects on diabetic nephropathy. In this study, we investigated the dose-dependent effect of eplerenone and a combined treatment with eplerenone and enalapril compared with each drug alone on renal function in type II diabetic rats. To further explore the molecular mechanism of action of combination therapy, we also performed in vitro study.

METHODS

The animals were divided into six groups as follows: normal control Long-Evans Tokushima Otsuka (LETO) rats, Otsuka Long-Evans Tokushima Fatty (OLETF) rats, OLETF rats treated with low dose of eplerenone (50 mg/kg/day), OLETF rats treated with high dose of eplerenone (200 mg/kg/day), OLETF rats treated with enalapril (10 mg/kg/day) and OLETF rats treated with a combination of both drugs (eplerenone 200 mg/kg/day and enalapril 10 mg/kg/day) for 6 months.

RESULTS

Treatment of OLETF rats had no significant effect on body weight, kidney weight and blood glucose levels. However, urinary albumin excretion, glomerular filtration rate and glomerulosclerosis were significantly improved in the enalapril group and improvement was observed in a dose-dependent manner in the eplerenone groups; the most dramatic decreases were observed in the combination group. In accordance with these findings, renal expressions of TGF-beta1, type IV collagen and PAI-1 were also markedly decreased in the treatment groups, with the combined treatment providing the most significant level of improvement. In cultured mesangial cells, combined treatment resulted in an additive decrease in TGF-beta1, PAI-1 and collagen gene expressions and protein production induced by high glucose and aldosterone stimulation.

CONCLUSIONS

Aldosterone receptor antagonism provided additional benefits beyond blockade of the renin-angiotensin system in type II diabetic nephropathy.

Extracellular signal-regulated kinase activation mediates mitochondrial dysfunction and necrosis induced by hydrogen peroxide in renal proximal tubular cells

Although tubular necrosis in acute renal failure is associated with excessive production of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), the mechanism of ROS-induced cell necrosis remains poorly understood. In this study, we examined the role of the extracellular signaling-regulated kinase (ERK) pathway in H2O2-induced necrosis of renal proximal tubular cells (RPTC) in primary culture. Exposure of 60 to 70% confluent RPTC to 1 mM H2O2 for 3 h resulted in 44% necrotic cell death, as measured by trypan blue uptake, and inactivation of mitogen-activated protein kinase kinase (MEK), the upstream activator of ERK, by either 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene (U0126) or 2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one (PD98059) or overexpression of dominant-negative mutant of MEK1, inhibited cell death. In contrast, overexpression of active MEK1 enhanced H2O2-induced cell death. H2O2 treatment led to the loss of mitochondrial membrane potential (MMP) in RPTC, which was decreased by U0126 and PD98059. Furthermore, inhibition of the MEK/ERK pathway decreased oxidant-mediated ERK1/2 activation and mitochondrial swelling in isolated renal cortex mitochondria. However, treatment with cyclosporin A (CsA), a mitochondrial permeability transition blocker, did not suppress RPTC necrotic cell death, loss of MMP, and mitochondrial swelling. We suggest that ERK is a critical mediator of mitochondrial dysfunction and necrotic cell death of renal epithelial cells following oxidant injury. Oxidant-induced necrotic cell death was mediated by a CsA-insensitive loss of MMP that is regulated by the ERK pathway.

The human oxygen sensing machinery and its manipulation

Animals respond to the challenge of limited oxygen availability by a coordinated response that works to increase oxygen supply and minimize tissue damage. The chronic hypoxic response is mediated by the alpha,beta-hypoxia inducible transcription factor (HIF) that enables the expression of a gene array. Because this array includes genes encoding for proteins that regulate processes including red blood cell and blood vessel formation, manipulation of the HIF system has potential for the treatment of ischemic diseases, anaemia and tumours. Hydroxylase enzymes act as oxygen sensors by regulating both the lifetime of HIF-alpha and its transcriptional activity. This tutorial review aims to provide a non-expert introduction to the HIF field by providing a background to current work, summarising molecular knowledge on the HIF system, and outlining opportunities for therapeutic intervention.

Positron-Emission Tomography Imaging of the Angiotensin II Subtype 1 Receptor in Swine Renal Artery Stenosis

The angiotensin II subtype 1 receptor (AT 1 R) has been linked to the development and progression of renovascular hypertension. In this study we applied a pig model of renovascular hypertension to investigate the AT 1 R in vivo with positron-emission tomography (PET) and in vitro with quantitative autoradiography. AT 1 R PET measurements were performed with the radioligand [ 11 C]KR31173 in 11 control pigs and in 13 pigs with hemodynamically significant renal artery stenosis; 4 were treated with lisinopril for 2 weeks before PET imaging. The radioligand impulse response function was calculated by deconvolution analysis of the renal time-activity curves. Radioligand binding was quantified by the 80-minute retention of the impulse response function. Median values and interquartile ranges were used to illustrate group statistics. Radioligand retention was significantly increased ( P =0.044) in hypoperfused kidneys of untreated (0.225; range: 0.150 to 0.373) and lisinopril-treated (0.237; range:0.224 to 0.272) animals compared with controls (0.142; range:0.096 to 0.156). Increased binding of [ 11 C]KR31173 documented by PET in vivo was confirmed by in vitro autoradiography. Both in vivo and in vitro binding measurements showed that the effect of renal artery stenosis on the AT 1 R was not abolished by lisinopril treatment. These studies provide insight into kidney biology as the first in vivo/in vitro experimental evidence about AT 1 R regulation in response to reduced perfusion of the kidney. The findings support the concept of introducing AT 1 R PET as a diagnostic biomarker of renovascular disease.

Attenuation of NADPH oxidase activation and glomerular filtration barrier remodeling with statin treatment

Activation of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase by angiotensin II is integral to the formation of oxidative stress in the vasculature and the kidney. 3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibition is associated with reductions of oxidative stress in the vasculature and kidney and associated decreases in albuminuria. Effects of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibition on oxidative stress in the kidney and filtration barrier integrity are poorly understood. To investigate, we used transgenic TG(mRen2)27 (Ren2) rats, which harbor the mouse renin transgene and renin-angiotensin system activation, and an immortalized murine podocyte cell line. We treated young, male Ren2 and Sprague-Dawley rats with rosuvastatin (20 mg/kg IP) or placebo for 21 days. Compared with controls, we observed increases in systolic blood pressure, albuminuria, renal NADPH oxidase activity, and 3-nitrotryosine staining, with reductions in the rosuvastatin-treated Ren2. Structural changes on light and transmission electron microscopy, consistent with periarteriolar fibrosis and podocyte foot-process effacement, were attenuated with statin treatment. Nephrin expression was diminished in the Ren2 kidney and trended to normalize with statin treatment. Angiotensin II-dependent increases in podocyte NADPH oxidase activity and subunit expression (NOX2, NOX4, Rac, and p22(phox)) and reactive oxygen species generation were decreased after in vitro statin treatment. These data support a role for increased NADPH oxidase activity and subunit expression with resultant reactive oxygen species formation in the kidney and podocyte. Furthermore, statin attenuation of NADPH oxidase activation and reactive oxygen species formation in the kidney/podocyte seems to play roles in the abrogation of oxidative stress-induced filtration barrier injury and consequent albuminuria.

Enhanced angiotensin II production by renal mesangium is responsible for apoptosis/proliferation of endothelial and epithelial cells in a model of malignant hypertension

OBJECTIVE

The systemic renin-angiotensin system (RAS) plays a crucial role in the pathogenesis of malignant hypertension. However, the intrarenal RAS might be at least equally important. We investigated the relationship between intrarenal RAS and mesangial, epithelial and endothelial cell proliferation/apoptosis in a model of malignant hypertension.

METHODS

Cultured murine mesangial cells were subjected to 160 mmHg hydrostatic pressure for 1 h. Angiotensin II was assessed by radio-immunoassay (RIA); pro-metalloproteinase-1 (pro-MMP-1) by enzyme-linked immunosorbent assay (ELISA); hydrogen peroxide (H2O2) by photocolorimetric assay, apoptosis by terminal dUTP (2-deoxyuridine 5'-triphosphate) nick-end labelling (TUNEL), p53 by western blot and proliferation by [H]thymidine incorporation, with or without angiotensin II and/or angiotensin II type 1/angiotensin II type 2 (AT-1/AT-2) receptor blockers. Endothelial and epithelial cells were similarly treated, and the same parameters evaluated. Further, untreated cells of both lines were cultured in conditioned medium of mesangial cells exposed to pressure. Their proliferation, apoptosis and angiotensin II production were also assessed.

RESULTS

High hydrostatic pressure increased angiotensin II production by mesangial cells, coinciding with augmented apoptosis and proliferation. Co-stimulation with exogenous angiotensin II amplified both effects. Pressure per se evoked no response in endothelial/epithelial cells, while exogenous angiotensin II stimulated proliferation and apoptosis. No augmentation of p53 expression was evident. These effects were abolished by anti-angiotensin-II peptide, saralasine and losartan, but not by PD123319. Incubation of untreated cells in medium of mesangium subjected to pressure, augmented proliferation and apoptosis. No significant changes were noticed in pro-MMP or H2O2.

CONCLUSIONS

Mesangium plays a deleterious role in the pathogenesis of malignant hypertension. High hydrostatic pressure stimulates angiotensin II synthesis by mesangial cells. The latter is responsible for hypercellularity and apoptotic death of mesangial, endothelial and epithelial cells. In this model, exaggerated apoptosis and proliferation are mediated via the angiotensin II pathway independently of p53 gene activation.

Long-term effects of a midgestational asphyxial episode in the ovine fetus

We and others have shown previously that fetuses at midgestation can survive 30 min of complete umbilical cord occlusion, although hydrops fetalis (or gross fetal edema) results. To investigate whether this hydrops resolves by late gestation and if there are any long-term consequences of the asphyxial insult on the heart and kidneys, eight fetuses were subjected to 30 min of complete umbilical cord occlusion at 0.6 gestation (90 days; term 150 days) and were compared to a sham group (n = 10). During the occlusion period, fetuses became severely hypoxemic, hypercapnemic, and acidotic, with both blood pressure and heart rate decreasing. Most variables had returned to normal by 2-hr recovery. At 129 +/- 1 days of gestation, approximately 40 days post occlusion, some fetuses were still slightly hydropic as skin fold measurements were increased (P < 0.01), although fetal body weight was not different from the sham group. The two groups had similar heart and kidney weights, ventricular cardiac myocyte nucleation, and glomerular number. By contrast, brain weight was reduced by 37% (P < 0.001) and the cerebral lateral ventricles were grossly dilated. Lungs were 50% smaller than in sham fetuses (P < 0.001). Thus, the hydrops that develops at midgestation as a result of a severe asphyxial episode can, but does not always, fully resolve by late gestation. Also, while fetuses at midgestation can survive this asphyxial episode with no long-term impact in renal or cardiac size, nephron number, or cardiomyocyte nucleation, the brain and lungs are severely affected.

Reactive oxygen species modulate the differentiation of neurons in clonal cortical cultures

Reactive oxygen species (ROS) are important regulators of intracellular signaling. We examined the expression of ROS during rat brain development and explored their role in differentiation using cortical cultures. High levels of ROS were found in newborn neurons. Neurons produced ROS, not connected with cell death, throughout embryogenesis and postnatal stages. By P20, ROS-producing cells were found only in neurogenic regions. Cells with low levels of ROS, isolated from E15 brains by FACS, differentiated into neurons, oligodendrocytes, and astrocytes in clonal cultures. Neurons produced high ROS early in culture and later differentiated into two types: large pyramidal-like neurons that fired no or only a single action potential and smaller neurons that expressed nuclear calretinin and fired repeated action potentials. Antioxidant treatment did not alter neuron number but increased the ratio of small to large neurons. These findings suggest that modulation of ROS levels influences multiple aspects of neuronal differentiation.

Oxidative stress and glomerular filtration barrier injury: role of the renin-angiotensin system in the Ren2 transgenic rat

TG(mRen2)27 (Ren2) transgenic rats overexpress the mouse renin gene, manifest hypertension, and exhibit increased tissue ANG II levels and oxidative stress. Evidence indicates that elevated tissue ANG II contributes to oxidative stress, increases in glomerular macromolecular permeability, and consequent albuminuria. Furthermore, angiotensin type 1 receptor (AT1R) blockers reduce albuminuria and slow progression of renal disease. However, it is not known whether improvements in glomerular filtration barrier integrity and albuminuria during treatment are related to reductions in oxidative stress and/or kidney renin-angiotensin system (RAS) activity. To investigate the renal protective effects of AT1R blockade, we treated young (6-7 wk old) male Ren2 rats with valsartan (Ren2-V; 30 mg/kg) for 3 wk and measured urine albumin, kidney malondialdehyde (MDA), RAS component mRNAs, and NADPH oxidase subunits (gp91(phox) and Rac1) compared with age-matched untreated Ren2 and Sprague-Dawley (S-D) rats. Basement membrane thickness, slit pore diameter and number, and foot process base width were measured by transmission electron microscopy (TEM). Results indicate that AT1R blockade lowered systolic blood pressure (30%), albuminuria (91%), and kidney MDA (80%) in Ren2-V compared with untreated Ren2 rats. Increased slit pore number and diameter and reductions in basement membrane thickness and podocyte foot process base width were strongly associated with albuminuria and significantly improved following AT1R blockade. AT1R blockade was also associated with increased angiotensin-converting enzyme-2 and neprilysin expression, demonstrating a beneficial shift in balance of renal RAS. Thus reductions in blood pressure, albuminuria, and tissue oxidative stress with AT1R blockade were associated with improved indexes of glomerular filtration barrier integrity and renal RAS in Ren2 rats.