ANG II induces c-Jun NH2-terminal kinase activation and proliferation of human mesangial cells via redox-sensitive transactivation of the EGFR

Angiotensin II triggers RIPK3-MLKL-mediated necroptosis by activating the Fas/FasL signaling pathway in renal tubular cells

Our earlier studies proved that RIPK3-mediated necroptosis might be an important mode of renal tubular cell death in rats with chronic renal injury and the necroptotic cell death can be triggered by tumor necrosis factor-α (TNF-α) in vitro, but the triggering role of angiotensin II (AngII), which exerts notable effects on renal cells for the initiation and progression of renal tubulointerstitial fibrosis, is largely unknown. Here, we identified the presence of necroptotic cell death in the tubular cells of AngII-induced chronic renal injury and fibrosis mice and assessed the percentage of necroptotic renal tubular cell death with the disruption of this necroptosis by the addition of necrostatin-1 (Nec-1). Furthermore, the observation was further confirmed in HK-2 cells treated with AngII and RIPK1/3 or MLKL inhibitors. The detection of Fas and FasL proteins led us to investigate the contribution of the Fas/FasL signaling pathway to AngII-induced necroptosis. Disruption of FasL decreased the percentage of necroptotic cells, suggesting that Fas and FasL are likely key signal molecules in the necroptosis of HK-2 cells induced by AngII. Our data suggest that AngII exposure might trigger RIPK3-MLKL-mediated necroptosis in renal tubular epithelial cells by activating the Fas/FasL signaling pathway in vivo and in vitro.

AT1 and AT2 receptors modulate renal tubular cell necroptosis in angiotensin II-infused renal injury mice

Abnormal renin-angiotensin system (RAS) activation plays a critical role in the initiation and progression of chronic kidney disease (CKD) by directly mediating renal tubular cell apoptosis. Our previous study showed that necroptosis may play a more important role than apoptosis in mediating renal tubular cell loss in chronic renal injury rats, but the mechanism involved remains unknown. Here, we investigate whether blocking the angiotensin II type 1 receptor (AT1R) and/or angiotensin II type 2 receptor (AT2R) beneficially alleviates renal tubular cell necroptosis and chronic kidney injury. In an angiotensin II (Ang II)-induced renal injury mouse model, we found that blocking AT1R and AT2R effectively mitigates Ang II-induced increases in necroptotic tubular epithelial cell percentages, necroptosis-related RIP3 and MLKL protein expression, serum creatinine and blood urea nitrogen levels, and tubular damage scores. Furthermore, inhibition of AT1R and AT2R diminishes Ang II-induced necroptosis in HK-2 cells and the AT2 agonist CGP42112A increases the percentage of necroptotic HK-2 cells. In addition, the current study also demonstrates that Losartan and PD123319 effectively mitigated the Ang II-induced increases in Fas and FasL signaling molecule expression. Importantly, disruption of FasL significantly suppressed Ang II-induced increases in necroptotic HK-2 cell percentages, and necroptosis-related proteins. These results suggest that Fas and FasL, as subsequent signaling molecules of AT1R and AT2R, might involve in Ang II-induced necroptosis. Taken together, our results suggest that Ang II-induced necroptosis of renal tubular cell might be involved both AT1R and AT2R and the subsequent expression of Fas, FasL signaling. Thus, AT1R and AT2R might function as critical mediators.

Arsenic and sulfur dioxide co-exposure induce renal injury via activation of the NF-κB and caspase signaling pathway

Although emerging evidence suggests positive association of arsenic (As) or sulfur dioxide (SO₂) exposure with human diseases, reports concerning the effects of co-exposure of As and SO₂ are lacking. Moreover, there is insufficient information in the literature about As and SO₂ co-exposure to renal injury. In this study, we focus on the environmental problems of excessive As and SO₂ that co-exist in many coal consumption areas. We used both C57BL/6 mice and 293T cells to detect toxicities of As and SO₂ exposure alone or in combination. Our results showed that co-exposure significantly increased the hazard compared with exposure to As or SO₂ alone. Mouse kidney tissue slices showed that co-exposure caused more severe diffuse sclerosing glomerulonephritis than As and SO₂ exposure alone. Meanwhile experiments showed that apoptosis was aggravated by co-exposure of As and SO₂ in 293T cells. Because As and SO₂ cause cell toxicity through increasing oxidative stress, next we detected ROS and other oxidative stress parameters, and the results showed oxidative stress was increased by co-exposure compared with the other three groups. The expression levels of downstream genes in the NF-κB and caspase pathways were higher in the co-exposure group than in the groups of As or SO₂ exposure alone in mice and 293T cells. Based on the above results, co-exposure could induce higher toxicity in vitro and in vivo compared with single exposure to As or SO₂, indicating that people living in places that contaminated by As and SO₂ may have higher chance to get renal injury.

An update on possible pathogenic mechanisms of periodontal pathogens on renal dysfunction

Periodontitis is a potential source of permanent systemic inflammation that initiates renal dysfunction and contributes to the development of chronic kidney diseases (CKDs). Although numerous studies have confirmed the bidirectional role of periodontal infection and renal inflammation, no literature has yet highlighted the sophisticated pathogenic mechanisms by which periodontal pathogens, particularly Porphynomonas Gingivalis, induce renal dysfunction and contributed in the development of CKDs. The present review aims to critically analyze and highlight the novel pathogenesis of periodontitis induced CKDs.

Oxidation of heat shock protein 60 and protein disulfide isomerase activates ERK and migration of human hepatocellular carcinoma HepG2

Hepatocyte growth factor (HGF) and its receptor c-Met were frequently deregulated in hepatocellular carcinoma (HCC). Signaling pathways activated by HGF-c-Met are promising targets for preventing HCC progression. HGF can induce the reactive oxygen species (ROS) signaling for cell adhesion, migration and invasion of tumors including HCC. On the other hand, extracellular signal-regulated kinases (ERK), member of mitogen activated kinase, can be activated by ROS for a lot of cellular processes. As expected, HGF-induced phosphorylation of ERK and progression of HCC cell HepG2 were suppressed by ROS scavengers. By N-(biotinoyl)-N'-(iodoacetyl)-ethylenediamine (BIAM) labeling method, a lot of cysteine (-SH)-containing proteins with M.W. 50-75 kD were decreased in HepG2 treated with HGF or two other ROS generators, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and phenazine methosulfate. These redox sensitive proteins were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. Among them, two chaperones, heat shock protein 60 (HSP60) and protein disulfide isomerase (PDI), were found to be the most common redox sensitive proteins in responding to all three agonists. Affinity blot of BIAM-labeled, immunoprecipitated HSP60 and PDI verified that HGF can decrease the cysteine (-SH) containing HSP60 and PDI. On the other hand, HGF and TPA increased cysteinyl glutathione-containing HSP60, consistent with the decrease of cysteine (-SH)-containing HSP60. Moreover, depletion of HSP60 and PDI or expression of dominant negative mutant of HSP60 with alteration of Cys, effectively prevented HGF-induced ERK phosphorylation and HepG2 migration.In conclusion, the redox sensitive HSP60 and PDI are required for HGF-induced ROS signaling and potential targets for preventing HCC progressions.

Smad7 alleviates glomerular mesangial cell proliferation via the ROS-NF-κB pathway

OBJECTIVE

The aim of this study was to demonstrate that altered gene expression of Smad7regulated NF-κB expression and ROS production on Ang II (Angiotensin II)-induced rat glomerular mesangial cell (GMC) proliferation.

METHODS

pAdTrack-CMV-Smad7 was transduced into rat GMC by adeno-transduction using an ADV (adenovirus)-mediated vector in vivo. Diphenylene iodonium chloride (DPI) pre-treated GMC, and blocked ROS generation as determined by DCFH-DA method. Altered expressions of IκBα and p65 were monitored by Western blot analysis and immunofluorescence. GMC proliferation was tested by the Cell Counting Kit-8 assay. Apoptosis of GMC was detected by flow cytometric analysis.

RESULTS

Over-expression of Smad7 dampened the ability of Ang II to promote ROS synthesis and inhibited the ability of Ang II to decrease functional expression of IκBα. Moreover, Smad7 increased nuclear IκBα expression. Smad7 did not significantly influence the capacity of Ang II to increase protein expression of NF-κB p65. However, immunofluorescence analysis showed that Smad7 reduced nuclear NF-κB p65 level. Further, over-expression of Smad7 promoted GMC apoptosis by inhibiting NF-κB activation, which alleviated the Ang II-promoted proliferation of GMC.

CONCLUSIONS

Smad7 influenced NF-κB expression by regulating ROS generation, and induced GMC apoptosis to counter the Ang II-promoted proliferation.

Angiotensin II induces interleukin-6 expression in astrocytes: Role of reactive oxygen species and NF-κB

Previously, we showed that the bio-peptide angiotensin (Ang) II induces interleukin-6 (IL-6) in cultured astrocytes; however, the mechanism(s) involved in this effect were unknown. In the current study, we determined in brainstem and cerebellum astrocytes from the spontaneously hypertensive rat (SHR), the effect of Ang II to induce IL-6 as well as reactive oxygen species (ROS) generation. Results from this study showed that Ang II significantly induced the differential expression of IL-6 mRNA and protein levels in astrocytes from both regions of Wistar and SHRs. There were differences in the ability of Ang II to induce IL-6 mRNA and protein levels, but these differences were not apparent at all time points examined. Ang II also induced ROS generation, but there were no significant differences between ROS generation in SHR samples as compared to the Wistar samples. Ang II-induced IL-6 levels were mediated via the AT₁/Nuclear Factor Kappa beta/ROS pathway. Overall, our findings suggest that there may be dysregulation in IL-6 production from astrocytes, contributing to differences observed in SHRs versus its normotensive control. Elucidating the mechanisms involved in Ang II pro-inflammatory effects in the central nervous system may lead to the development of novel therapeutic strategies that can be harnessed not just to treat hypertension, but other Ang II-mediated diseases as well.

Systemic Redox Imbalance in Chronic Kidney Disease: A Systematic Review

Patients with chronic kidney disease (CKD) experience imbalance between oxygen reactive species (ROS) production and antioxidant defenses leading to cell and tissue damage. However, it remains unclear at which stage of renal insufficiency the redox imbalance becomes more profound. The aim of this systematic review was to provide an update on recent advances in our understanding of how the redox status changes in the progression of renal disease from predialysis stages 1 to 4 to end stage 5 and whether the various treatments and dialysis modalities influence the redox balance. A systematic review was conducted searching PubMed and Scopus by using the Cochrane and PRISMA guidelines. In total, thirty-nine studies met the inclusion criteria and were reviewed. Even from an early stage, imbalance in redox status is evident and as the kidney function worsens it becomes more profound. Hemodialysis therapy per se seems to negatively influence the redox status by the elevation of lipid peroxidation markers, protein carbonylation, and impairing erythrocyte antioxidant defense. However, other dialysis modalities do not so far appear to confer advantages. Supplementation with antioxidants might assist and should be considered as an early intervention to halt premature atherogenesis development at an early stage of CKD.

Oxidant Mechanisms in Renal Injury and Disease

SIGNIFICANCE

A common link between all forms of acute and chronic kidney injuries, regardless of species, is enhanced generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) during injury/disease progression. While low levels of ROS and RNS are required for prosurvival signaling, cell proliferation and growth, and vasoreactivity regulation, an imbalance of ROS and RNS generation and elimination leads to inflammation, cell death, tissue damage, and disease/injury progression.

RECENT ADVANCES

Many aspects of renal oxidative stress still require investigation, including clarification of the mechanisms which prompt ROS/RNS generation and subsequent renal damage. However, we currently have a basic understanding of the major features of oxidative stress pathology and its link to kidney injury/disease, which this review summarizes.

CRITICAL ISSUES

The review summarizes the critical sources of oxidative stress in the kidney during injury/disease, including generation of ROS and RNS from mitochondria, NADPH oxidase, and inducible nitric oxide synthase. The review next summarizes the renal antioxidant systems that protect against oxidative stress, including superoxide dismutase and catalase, the glutathione and thioredoxin systems, and others. Next, we describe how oxidative stress affects kidney function and promotes damage in every nephron segment, including the renal vessels, glomeruli, and tubules.

FUTURE DIRECTIONS

Despite the limited success associated with the application of antioxidants for treatment of kidney injury/disease thus far, preventing the generation and accumulation of ROS and RNS provides an ideal target for potential therapeutic treatments. The review discusses the shortcomings of antioxidant treatments previously used and the potential promise of new ones. Antioxid. Redox Signal. 25, 119-146.

The simultaneous control of hyperglycemia and GLP-1 infusion normalize endothelial function in type 1 diabetes

BACKGROUND

To test the effect of normoglycemia and glucagon-like peptide-1 (GLP-1), alone or in combination, on the possible normalization of endothelial function in type 1 diabetes.

METHODS

Fifteen people with type 1 diabetes participated in three experiments: reaching and maintaining normoglycemia for 4h; reaching and maintaining hyperglycemia plus GLP-1 infusion for 4h; and reaching and maintaining normoglycemia for 4h with simultaneous infusion of GLP-1.

RESULTS

Both normoglycemia and GLP-1 infusion restored endothelial function and decreased and plasma 8-iso prostaglandin F2α levels. However, only the combination of normoglycemia and GLP-1 was able to normalize endothelial function.

CONCLUSIONS

This study confirms that long-lasting hyperglycemia in type 1 diabetes induces a permanent alteration which contributes to maintaining endothelial dysfunction even when glycemia is normalized, and that in the presence of normoglycemia, GLP-1 can contribute to normalizing endothelial function.

Induction of epithelial-mesenchymal transition via activation of epidermal growth factor receptor contributes to sunitinib resistance in human renal cell carcinoma cell lines

Sunitinib is widely used for treating renal cell carcinoma (RCC). However, some patients do not respond to treatment with this drug. We aimed to study the association between sunitinib sensitivity and epithelial-mesenchymal transition (EMT) regulation via epidermal growth factor receptor (EGFR) signaling, which is a mechanism of resistance to anticancer drugs. Three RCC cell lines (786-O, ACHN, and Caki-1) were used, and then we evaluated cell viability, EMT regulatory proteins, and signal transduction with sunitinib treatment. Cell viability of 786-O cells was maintained after treatment with sunitinib. After treatment with sunitinib, EGFR phosphorylation increased in 786-O cells, resulting in an increase in the phosphorylation of extracellular signal-regulated kinase, nuclear translocation of β-catenin, and expression of mesenchymal markers. These results suggest that sunitinib induced EMT via activation of EGFR in 786-O cells, but not in ACHN and Caki-1 cells. Caki-1/SN cells, a resistant cell line generated by continuous exposure to sunitinib, displayed increased phosphorylation of EGFR. Cell viability in the presence of sunitinib was decreased by erlotinib, as the selective inhibitor of EGFR, treatment in 786-O and Caki-1/SN cells. Similarly, erlotinib suppressed sunitinib-induced EGFR activation and upregulated mesenchymal markers. Thus, we postulate that resistance to sunitinib in RCC may be associated with EMT caused by activation of EGFR.

Kallistatin inhibits TGF-β-induced endothelial-mesenchymal transition by differential regulation of microRNA-21 and eNOS expression

Kallistatin, an endogenous protein, consists of two structural elements: active site and heparin-binding domain. Kallistatin exerts beneficial effects on fibrosis by suppressing transforming growth factor (TGF)-β synthesis in animal models. TGF-β is the most potent inducer of endothelial-mesenchymal transition (EndMT), which contributes to fibrosis and cancer. MicroRNA (miR)-21 is an important player in organ fibrosis and tumor invasion. Here we investigated the potential role of kallistatin in EndMT via modulation of miR-21 in endothelial cells. Human kallistatin treatment blocked TGF-β-induced EndMT, as evidenced by morphological changes as well as increased endothelial and reduced mesenchymal marker expression. Kallistatin also inhibited TGF-β-mediated reactive oxygen species (ROS) formation and NADPH oxidase expression and activity. Moreover, kallistatin antagonized TGF-β-induced miR-21 and Snail1 synthesis, Akt phosphorylation, NF-κB activation, and matrix metalloproteinase 2 (MMP2) synthesis and activation. Kallistatin via its heparin-binding site blocked TGF-β-induced miR-21, Snail1 expression, and ROS formation, as wild-type kallistatin, but not heparin-binding site mutant kallistatin, exerted the effect. Conversely, kallistatin through its active site stimulated the synthesis of endothelial nitric oxide synthase (eNOS), sirtuin 1 (Sirt1) and forkhead box O1 (FoxO1); however, these effects were blocked by genistein, a tyrosine kinase inhibitor. This is the first study to demonstrate that kallistatin's heparin-binding site is crucial for preventing TGF-β-induced miR-21 and oxidative stress, while its active site is key for stimulating the expression of antioxidant genes via interaction with an endothelial surface tyrosine kinase. These findings reveal novel mechanisms of kallistatin in protection against fibrosis and cancer by suppressing EndMT.

Upstream regulators and downstream effectors of NADPH oxidases as novel therapeutic targets for diabetic kidney disease

Oxidative stress has been linked to the pathogenesis of diabetic nephropathy, the complication of diabetes in the kidney. NADPH oxidases of the Nox family, and in particular the homologue Nox4, are a major source of reactive oxygen species in the diabetic kidney and are critical mediators of redox signaling in glomerular and tubulointerstitial cells exposed to the diabetic milieu. Here, we present an overview of the current knowledge related to the understanding of the role of Nox enzymes in the processes that control mesangial cell, podocyte and tubulointerstitial cell injury induced by hyperglycemia and other predominant factors enhanced in the diabetic milieu, including the renin-angiotensin system and transforming growth factor-β. The nature of the upstream modulators of Nox enzymes as well as the downstream targets of the Nox NADPH oxidases implicated in the propagation of the redox processes that alter renal biology in diabetes will be highlighted.

Activation of the EGFR/p38/JNK pathway by mitochondrial-derived hydrogen peroxide contributes to oxygen-induced contraction of ductus arteriosus

Oxygen-induced contraction of the ductus arteriosus (DA) involves a mitochondrial oxygen sensor, which signals pO2 in the DA smooth muscle cell (DASMC) by increasing production of diffusible hydrogen peroxide (H2O2). H2O2 stimulates vasoconstriction by regulating ion channels and Rho kinase, leading to calcium influx and calcium sensitization. Because epidermal growth factor receptor (EGFR) signaling is also redox regulated and participates in oxygen sensing and vasoconstriction in other systems, we explored the role of the EGFR and its signaling cascade (p38 and c-Jun N-amino-terminal kinase (JNK)) in DA contraction. Experiments were performed in DA rings isolated from full-term New Zealand white rabbits and human DASMC. In human DASMCs, increasing pO2 from hypoxia to normoxia (40 to 100 mmHg) significantly increased cytosolic calcium, p < 0.01. This normoxic rise in intracellular calcium was mimicked by EGF and inhibited by EGFR siRNA. In DA rings, EGF caused contraction while the specific EGFR inhibitor (AG1478) and the tyrosine kinase inhibitors (genistein or tyrphostin A23) selectively attenuated oxygen-induced contraction (p < 0.01). Conversely, orthovanadate, a tyrosine phosphatase inhibitor known to activate EGFR signaling, caused dose-dependent contraction of hypoxic DA and superimposed increases in oxygen caused minimal additional contraction. Anisomycin, an activator of EGFR's downstream kinases, p38 and JNK, caused DA contraction; conversely, oxygen-induced DA contraction was blocked by inhibitors of p38 mitogen-activated protein kinases (MAPK) (SB203580) or JNK (JNK inhibitor II). O2-induced phosphorylation of EGFR occurred within 5 min of increasing pO2 and was inhibited by mitochondrial-targeted overexpression of catalase. AG1478 prevented the oxygen-induced p38 and JNK phosphorylation. In conclusion, O2-induced EGFR transactivation initiates p38/JNK-mediated increases in cytosolic calcium and contributes to DA contraction. The EGFR/p38/JNK pathway is regulated by mitochondrial redox signaling and is a promising therapeutic target for modulation of the patent ductus arteriosus.

KEY MESSAGES

Oxygen activates epidermal growth factor receptor (EGFR) in ductus arteriosus (DA) smooth muscle cells. EGFR inhibition selectively attenuates O2-induced DA constriction. pO2-induced EGFR activation is mediated by mitochondrial-derived hydrogen peroxide. p38 MAPK and JNK mediated EGFR's effects on oxygen-induced DA contraction. Tyrosine kinases and phosphatases participate in oxygen sensing in the DA. The EGFR pathway offers new therapeutic targets to modulate patency of the ductus arteriosus.

Lignans from the bark of Eucommia ulmoides inhibited Ang II-stimulated extracellular matrix biosynthesis in mesangial cells

Background

Tree bark of Eucommia ulmoides Oliv., (commonly well-known as “Du-zhong” in China), has been used to treat hypertension, hypercholesterolemia, hyperglycemia, hepatic fibrosis and renal injury. This study aims to investigate the effects of lignans extracted from the bark of Eucommia ulmoides Oliv. on Ang II-induced proliferation and extracellular matrix biosynthesis in rat mesangial cells.

Methods

Rat mesangial cells (RMCs) were cultured in vitro and divided into six groups (control, Ang II, losartan, and low, middle and high concentration lignans groups). RMC proliferation was measured by MTT assay. RT-qPCR and western blotting were used to detect mRNA and protein expression of collagen type I (Col I), collagen type III (Col III), collagen type IV (Col IV), fibronectin and aldose reductase (AR).

Results

Cellular proliferation induced by Ang II was significantly suppressed by Eucommia lignans of different concentrations (P = 0.034, P < 0.001, and P < 0.001). Treatment of cells with Ang II increased Col I, Col III, Col IV, and fibronectin mRNA expression, which was observed at the protein level (P < 0.001, P < 0.001, P = 0.004, and P = 0.004, respectively). The increased mRNA expression and protein levels of Col I, Col III, Col IV, and fibronectin were diminished remarkably with by treatment Eucommia lignans, and elevated AR expression stimulated by Ang II was significantly inhibited by Eucommia lignans.

Conclusions

Eucommia lignans (Du-zhong) inhibited Ang II-stimulated extracellular matrix biosynthesis in mesangial cells.

Nox4 and diabetic nephropathy: with a friend like this, who needs enemies?

Oxidative stress has been linked to the pathogenesis of diabetic nephropathy, a complication of diabetes in the kidney. NADPH oxidases of the Nox family are a major source of reactive oxygen species in the diabetic kidney and are critical mediators of redox signaling in glomerular and tubulointerstitial cells exposed to the diabetic milieu. Here, we present an overview of the current understanding of the roles of Nox catalytic and regulatory subunits in the processes that control mesangial cell, podocyte, and tubulointerstitial cell injury induced by hyperglycemia and other predominant factors enhanced in the diabetic milieu, including the renin-angiotensin system and transforming growth factor-β. The role of the Nox isoform Nox4 in the redox processes that alter renal biology in diabetes is highlighted.

Protein Arginine Methyltransferases (PRMTs): promising targets for the treatment of pulmonary disorders

Protein arginine methylation is a novel posttranslational modification that plays a pivotal role in a variety of intracellular events, such as signal transduction, protein-protein interaction and transcriptional regulation, either by the direct regulation of protein function or by metabolic products originating from protein arginine methylation that influence nitric oxide (NO)-dependent processes. A growing body of evidence suggests that both mechanisms are implicated in cardiovascular and pulmonary diseases. This review will present and discuss recent research on PRMTs and the methylation of non-histone proteins and its consequences for the pathogenesis of various lung disorders, including lung cancer, pulmonary fibrosis, pulmonary hypertension, chronic obstructive pulmonary disease and asthma. This article will also highlight novel directions for possible future investigations to evaluate the functional contribution of arginine methylation in lung homeostasis and disease.

Comparison of ROCK and EGFR activation pathways in the progression of glomerular injuries in AngII-infused rats

AIM

The roles of rho-kinase (ROCK) and epidermal growth factor receptor (EGFR) were studied using an angiotensin II (AngII)-dependent hypertension rat model.

METHOD

Male Wistar rats were infused with AngII at a rate of 400 ng/kg body weight (BW)/min for 14 days. Effects of ROCK inhibitor, fasudil (20 mg/kg BW), and EGFR inhibitor, gefitinib (3 mg/kg BW), were studied.

RESULTS

AngII infusion increased blood pressure (BP; 220 ± 19 mmHg) as well as the number of proliferating cells in glomeruli judged by Ki67 and proliferating cell nuclear antigen immunostaining and urinary protein excretion (118 ± 19 mg/day). AngII also decreased p27 expression and increased cyclin D1 expression in glomeruli, as well as induced dissociation of the nephrin- and podocin-immunostaining patterns in podocytes. Treatment with fasudil or gefitinib completely inhibited glomerular cell proliferation without changing the BP. Although the decreased p27 expression was reversed by both treatments, cyclin D1 induction was abolished only by gefitinib. Fasudil significantly reduced proteinuria (57.2 ± 17.5 mg/day), but not gefitinib (133.3 ± 30.9 mg/day). The dissociation of podocin and nephrin was ameliorated by fasudil, but not by gefitinib.

CONCLUSION

ROCK and EGFR have distinct roles in proteinuria and glomerular cell proliferation in this model.

Inhibition of the epidermal growth factor receptor preserves podocytes and attenuates albuminuria in experimental diabetic nephropathy

AIM

Early renal enlargement may predict the future development of nephropathy in patients with diabetes. The epidermal growth factor (EGF)-EGF receptor (EGFR) system plays a pivotal role in mediating renal hypertrophy, where it may act to regulate cell growth and proliferation and also to mediate the actions of angiotensin II through transactivation of the EGFR. In the present study we sought to investigate the effects of long-term inhibition of the EGFR tyrosine kinase in an experimental model of diabetes that is characterized by angiotensin II dependent hypertension.

METHODS

Female heterozygous streptozotocin-diabetic TGR(mRen-2)27 rats were treated with the EGFR inhibitor PKI 166 by daily oral dosing for 16 weeks.

RESULTS

Treatment of TGR(mRen-2)27 rats with PKI 166 attenuated the increase in kidney size, glomerular hypertrophy and albuminuria that occurred with diabetes. The reduction in albuminuria, with EGFR inhibition in diabetic TGR(mRen-2)27 rats, was associated with preservation of the number of glomerular cells staining positively for the podocyte nuclear marker, WT1. Immunostaining for WT1 inversely correlated with glomerular volume in diabetic rats. In contrast to agents that block the renin-angiotensin system (RAS), EGFR inhibition had no effect on either the quantity of mesangial matrix or the magnitude of tubular injury in diabetic animals.

CONCLUSION

These observations indicate that inhibition of the tyrosine kinase activity of the EGFR attenuates kidney and glomerular enlargement in association with podocyte preservation and reduction in albuminuria in diabetes. Accordingly, targeting the EGF-EGFR pathway may represent a therapeutic strategy for patients who continue to progress despite RAS-blockade.

The ADMA-Metformin Hypothesis: Linking the Cardiovascular Consequences of the Metabolic Syndrome and Type 2 Diabetes

Metformin and asymmetric dimethylarginine (ADMA) are structural analogs. They have opposite effects at multiple points on complex signaling pathways that coordinate energy, molecular synthesis, growth, and metabolism with nutrient intake. Excess saturated fats and glucose may initiate the methylation of arginine residues in proteins involved in the transcription of genes mediating inflammation, cell proliferation, apoptosis, and oncogenesis. Free ADMA may appear in the circulation after proteolysis of these proteins when the work of transcription is complete and ADMA subsequently functions as a signaling molecule. In children, ADMA levels are not significantly related to the usual metabolic syndrome risk factors but instead there is a significant association between ADMA and alkaline phosphatase - a marker of normal growth. There is only one direct study that shows that ADMA negates the metabolic effects of metformin. There are no investigations that demonstrate that metformin blocks the effect of ADMA and so this review must be considered hypothesis generating. The potential implications of the metformin-ADMA relationship merit further investigation.

Angiotensin II utilizes Janus kinase 2 in hypertension, but not in the physiological control of blood pressure, during low-salt intake

Janus kinase (JAK) 2 is activated by ANG II in vitro and in vivo, and chronic blockade of JAK2 by the JAK2 inhibitor AG-490 has been shown recently to attenuate ANG II hypertension in mice. In this study, AG-490 was infused intravenously in chronically instrumented rats to determine if the blunted hypertension was linked to attenuation of the renal actions of ANG II. In male Sprague-Dawley rats, after a control period, ANG II at 10 ng·kg(-1)·min(-1) was infused intravenously with or without AG-490 at 10 ng·kg(-1)·min(-1) iv for 11 days. ANG II infusion (18 h/day) increased mean arterial pressure from 91 ± 3 to 168 ± 7 mmHg by day 11. That response was attenuated significantly in the ANG II + AG-490 group, with mean arterial pressure increasing only from 92 ± 5 to 127 ± 3 mmHg. ANG II infusion markedly decreased urinary sodium excretion, caused a rapid and sustained decrease in glomerular filtration rate to ∼60% of control, and increased renal JAK2 phosphorylation; all these responses were blocked by AG-490. However, chronic AG-490 treatment had no effect on the ability of a separate group of normal rats to maintain normal blood pressure when they were switched rapidly to a low-sodium diet, whereas blood pressure fell dramatically in losartan-treated rats on a low-sodium diet. These data suggest that activation of the JAK/STAT pathway is critical for the development of ANG II-induced hypertension by mediating its effects on renal sodium excretory capability, but the physiological control of blood pressure by ANG II with a low-salt diet does not require JAK2 activation.

A PPARγ agonist inhibits aldosterone-induced mesangial cell proliferation by blocking ROS-dependent EGFR intracellular signaling

Mesangial cell (MC) proliferation is a key feature in the pathogenesis of a number of renal diseases. Peroxisome proliferator-activated receptor-γ (PPARγ) has attracted considerable attention for its effects on stimulating cell differentiation and on inducing cell cycle arrest. We previously showed that aldosterone (Aldo) stimulates MC proliferation via the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway, which was dependent on reactive oxygen species (ROS)-mediated epithelial growth factor receptor (EGFR) transactivation (Huang S, Zhang A, Ding G, and Chen R. Am J Physiol Renal Physiol 296: F1323–F1333, 2009). In this study, we examined whether the PPARγ agonist rosiglitazone inhibited Aldo-induced MC proliferation by modulating ROS-dependent EGFR intracellular signaling. Rosiglitazone at 1–10 μM dose dependently inhibited Aldo-induced MC proliferation of cultured mouse MCs. The inhibitory effect was blocked by the PPARγ antagonist PD-68235, indicating that the rosiglitazone effect acted through PPARγ activation. Rosiglitazone also arrested Aldo-induced cell cycle progression and suppressed expression of cyclins D1 and A. Moreover, rosiglitazone dose dependently blocked Aldo-induced ROS production, EGFR phosphorylation, and PI3K/Akt activation. These results suggest that the PPARγ agonist rosiglitazone may inhibit Aldo-induced MC proliferation directly, by affecting ROS/EGFR/PI3K/Akt signaling pathways and cell cycle-regulatory proteins. PPARγ might be a novel therapeutic target against glomerular diseases.

Receptor for AGEs (RAGE) blockade may exert its renoprotective effects in patients with diabetic nephropathy via induction of the angiotensin II type 2 (AT2) receptor

AIMS/HYPOTHESIS

The receptor for AGEs (RAGE) contributes to the development and progression of diabetic nephropathy. In this study, we examined whether the protective effects of RAGE blockade are exerted via modulation of the renal angiotensin II type 2 (AT2) receptor.

METHODS

Control and streptozotocin diabetic mice, wild-type or deficient in the AT2 receptor (At2 knockout [KO]) or RAGE (Rage KO), were studied for 24 weeks. Adenoviral overexpression of full-length Rage in primary rat mesangial cells was also used to determine the effects on AT2 production.

RESULTS

With diabetes, Rage-deficient mice had less albuminuria, and an attenuation of hyperfiltration and glomerulosclerosis as compared with diabetic wild-type and At2 KO mice. Renal gene and protein expression of RAGE was elevated with diabetes. Diabetic Rage KO mice had a greater increase in renal AT2 receptor protein than was seen in diabetic wild-type mice. Diabetes-induced increases in renal cytosolic and mitochondrial superoxide generation were prevented in diabetic Rage KO mice, but enhanced in all At2 KO mice. Adenoviral overexpression of RAGE or AGE treatment decreased cell surface AT2 expression, in association with increasing superoxide generation; both were reversed using antioxidants N-acetylcysteine and apocynin, and soluble RAGE in primary mesangial cells.

CONCLUSIONS/INTERPRETATION

RAGE appears to be a common and key modulator of AT2 receptor expression, a finding that would implicate a newly defined RAGE-AT2 axis in the development and progression of diabetic nephropathy.

SP600125, an inhibitor of c-Jun NH2-terminal kinase, blocks expression of angiotensin II-induced monocyte chemoattractant protein-1 in human mesangial cells

BACKGROUND

We investigated the role of c-Jun NH2-terminal kinase (JNK), a member of the mitogen-activated protein kinase family, in the expression of angiotensin II (Ang II)-induced monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor-1 (TGF-1), and in the production of fibronectin (FN), by human mesangial cells (HMCs).

METHODS

JNK activation in cultured human mesangial cells was determined by Western blotting with an antibody against the phosphorylated Ser63 residue of c-Jun. Binding of the activator protein (AP-1) to the MCP-1 AP-1 motif was detected via the electrophoretic mobility shift assay (EMSA). The transient luciferase reporter was used to examine MCP-1 promoter activity; an RNase protection assay and ELISA were used respectively to detect the expression of MCP-1 mRNA and production of MCP-1, TGF-beta and FN.

RESULTS

Anthra (1,9-cd) pyrazol-6(2H)-one (SP600125), a pharmacological inhibitor of JNK, almost completely abolished Ang II-induced Ser63 phosphorylation of c-Jun at concentrations of 5-20 micromol/L: JNK activity was reduced by 75% with 10 micromol/L SP600125, and by 90% with 20 micromol/L. Ang II increased AP-1 binding to the MCP-1 AP-1 motif in a time-dependent manner, as detected by EMSA, while SP600125 effectively blocked this increased AP-1 binding in a concentration-dependent manner. Treatment with 100 nmol/L Ang II led to a steady increase in MCP-1 mRNA expression, and to an enhanced production of MCP-1, TGF-beta and FN. These effects were blocked by SP60025 in a dose-dependent manner. SP600125 also reduced MCP-1 mRNA stability: the halflife of MCP-1 mRNA was approximately 5 hours in cells treated with Ang II only, but was reduced to 2 hours when treated with a combination of Ang II and SP600125.

CONCLUSIONS

These results show that the JNK/AP-1 pathway is involved in the expression of MCP-1 and TGF-beta, and in extracellular matrix production. JNK is an important therapeutic target for glomerulonephritis and glomerulosclerosis.

AGER1 regulates endothelial cell NADPH oxidase-dependent oxidant stress via PKC-delta: implications for vascular disease

Advanced glycated end-product receptor 1 (AGER1) protects against vascular disease promoted by oxidants, such as advanced glycated end products (AGEs), via inhibition of reactive oxygen species (ROS). However, the specific AGEs, sources, and pathways involved remain undefined. The mechanism of cellular NADPH oxidase (NOX)-dependent ROS generation by defined AGEs, N(epsilon)-carboxymethyl-lysine- and methylglyoxal (MG)-modified BSA, was assessed in AGER1 overexpressing (AGER1(+) EC) or knockdown (sh-mRNA-AGER1(+) EC) human aortic endothelial (EC) and ECV304 cells, and aortic segments from old (18 mo) C57BL6-F(2) mice, propagated on low-AGE diet (LAGE), or LAGE supplemented with MG (LAGE+MG). Wild-type EC and sh-mRNA-AGER1(+) EC, but not AGER1(+) EC, had high NOX p47(phox) and gp91(phox) activity, superoxide anions, and NF-kappaB p65 nuclear translocation in response to MG and N(epsilon)-carboxymethyl-lysine. These events involved epidermal growth factor receptor-dependent PKC-delta redox-sensitive Tyr-311 and Tyr-332 phosphorylation and were suppressed in AGER1(+) ECs and enhanced in sh-mRNA-AGER1(+) ECs. Aortic ROS, PKC-delta Tyr-311, and Tyr-332 phosphorylation, NOX expression, and nuclear p65 in older LAGE+MG mice were significantly increased above that in age-matched LAGE mice, which had higher levels of AGER1. In conclusion, circulating AGEs induce NADPH-dependent ROS generation in vascular aging in both in vitro and in vivo models. Furthermore, AGER1 provides protection against AGE-induced ROS generation via NADPH.

Blockade of endogenous tissue kallikrein aggravates renal injury by enhancing oxidative stress and inhibiting matrix degradation

Levels of tissue kallikrein (TK) are significantly lower in the urine of patients with kidney failure, and TK expression is specifically diminished in rat kidney after recovery from ischemia-reperfusion injury. In this study, we investigated the functional consequence of blocking endogenous TK activity in a rat model of chronic kidney disease. Inhibition of endogenous TK levels for 10 days by neutralizing TK antibody injection in DOCA-salt rats caused a significant increase in blood urea nitrogen and urinary protein levels, and a decrease in creatinine clearance. Kidney sections from anti-TK antibody-treated rats displayed a marked rise in tubular dilation and protein cast accumulation as well as glomerular sclerosis and size. TK blockade also increased inflammatory cell infiltration, myofibroblast and collagen accumulation, and collagen fraction volume. Elevated renal inflammation and fibrosis by anti-TK antibody were associated with increased expression of tumor necrosis factor-alpha, intercellular adhesion molecule-1, tissue inhibitor of metalloproteinase-2 (TIMP-2), and plasminogen activator inhibitor-1 (PAI-1). Moreover, the detrimental effect of TK blockade resulted in reduced nitric oxide (NO) levels as well as increased serum lipid peroxidation, renal NADH oxidase activity, and superoxide formation. In cultured proximal tubular cells, TK inhibited angiotensin II-induced superoxide production and NADH oxidase activity via NO formation. In addition, TK markedly increased matrix metalloproteinase-2 activity with a parallel reduction of TIMP-2 and PAI-1 synthesis. These findings indicate that endogenous TK has the propensity to preserve kidney structure and function in rats with chronic renal disease by inhibiting oxidative stress and activating matrix degradation pathways.

Role of c-Jun N-terminal kinase in the regulation of vascular tone

The c-Jun N-terminal kinases (JNKs) belong to the mitogen-activated protein kinases superfamily, which play an important role in the pathogenesis of cardiovascular and metabolic diseases. However, it is still unclear whether JNK participates in the regulation of vascular tone. We investigated the effect of JNK inhibitors on vascular reactivity in aortic rings in organ bath and on angiotensin (Ang) II-induced pressor responses in vivo in Sprague-Dawley (SD) rats. In aortic rings from SD rats, KCl, norepinephrine (NE), Ang II, or endothelin 1 (ET)-1 induced a dose-dependent vasoconstriction. Preincubation with the JNK inhibitor SP600125 (20 micromol/L) slightly inhibited KCl-induced vasoconstriction (Emax: -19%) and markedly inhibited vasoconstriction to NE (-42%), Ang II (-54%), and ET-1 (-42%). SP600125 induced a dose-dependent relaxation in the NE-preconstricted aortic rings (-54%) but exerted minimal relaxation in the KCI-preconstriction rings. To exclude the nonspecific effect of SP600125, we performed additional experiments using JNK peptide inhibitor 1, L-stereoisomer (L-JNKI1), a cell-permeable peptide inhibitor specific for JNK. Compared to SP600125, L-JNKI1 (20 micromol/L) had a smaller but still significant inhibitory effect on NE-induced vasoconstriction (-18%) and did not inhibit KCI-induced vasoconstriction. Next, we investigated the effect of L-JNKI1 (5 mg/kg intravenously [IV]) in vivo on Ang II-induced pressor responses in SD rats. Ang II induces a dose-dependent increase in systolic blood pressure and L-JNKI1 slightly attenuated the Ang II-induced pressor response. These results suggest that JNK signaling plays a role in the regulation of vascular tone.

Contribution of epidermal growth factor receptor transactivation in angiotensin II-induced enhanced expression of Gi protein and proliferation in A10 vascular smooth muscle cellsThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

We have recently shown that vasoactive peptides such as angiotensin II (Ang II) and endothelin-1 (ET-1) increased the expression of Gi proteins and proliferation of A10 vascular smooth muscle cells (VSMC) through MAP kinase / PI3 kinase pathways. The present study was undertaken to examine the implication of growth factor receptor activation in Ang II-induced enhanced expression of Gi proteins and proliferation of A10 VSMC and to further investigate the underlying mechanisms responsible for these increases. Cell proliferation was determined by [3H]thymidine incorporation, and the expression of Gi proteins and the phosphorylation of ERK1/2 and epidermal growth factor receptor (EGFR) was determined by Western blotting. Treatment of A10 VSMC with Ang II enhanced the expression of Gi proteins, which was attenuated by Ang II AT1 receptor antagonist but not by AT2 receptor antagonist. The inhibitor of EGFR also attenuated the enhanced expression of Gi proteins induced by Ang II to control levels. In addition, Ang II enhanced the phosphorylation of EGFR in A10 VSMC, and this was restored to control levels by the EGFR inhibitor and antioxidants. Furthermore, Ang II also augmented the proliferation and ERK1/2 phosphorylation of A10 VSMC, which were restored to control levels by the EGFR inhibitor. These data suggest that the Ang II-induced increase in oxidative stress transactivates EGFR, which through MAP kinase signaling may contribute to the enhanced expression of Gi proteins and thereby to the increased proliferation of A10 VSMC.

Aldosterone-induced mesangial cell proliferation is mediated by EGF receptor transactivation

Aldosterone (Aldo) stimulates glomerular mesangial cell (MC) proliferation, in part, through an ERK1/2-dependent pathway. In this study, we examined whether Aldo activation of ERK1/2 in MC is mediated through redox-dependent EGF receptor (EGFR) transactivation, as well as the involvement of other signaling mechanisms in Aldo-induced MC proliferation. Aldo increased human MC proliferation, as determined by [3H]thymidine incorporation and cell counts. This increase in proliferation was blocked by inhibition of the mineralocorticoid receptor (MR). Continuing our observations downstream in the signaling pathway, we examined the ability of Aldo to activate both the Ras/MAPK and the PI3K signaling pathways. Aldo increased Ki-RasA and Ki-RasA:GTP levels, and sequentially phosphorylated c-Raf, MAPK kinase (MEK1/2), and ERK1/2. Ki-RasA small interfering RNA (siRNA), the c-Raf inhibitor GW5074, and the MEK1/2 inhibitor PD98059 reduced Aldo-induced cell proliferation by ∼65%. Aldo also increased phosphorylation of PI3K, Akt, the mammalian target of rapamycin (mTOR), and the 70-kDa ribosomal S6 kinase (p70S6K1). Inhibition of the PI3K pathways by the selective PI3K inhibitor LY 294002, an Akt inhibitor, or the mTOR inhibitor rapamycin reduced cell proliferation by 51%. Combining LY 294002 and PD98059 completely blocked Aldo-induced MC proliferation. Next, we confirmed that Aldo exerts its effect on MAPK and PI3K activation, as well as on cell proliferation, by activating the EGFR. Pretreatment with the EGFR antagonist AG1478 inhibited MC proliferation, as well as the activation of Ras/MAPK and PI3K/Akt, suggesting that Ras/MAPK and PI3K/Akt activation occur downstream of EGFR activation. Finally, we examined the role of reactive oxygen species (ROS) in Aldo-induced transactivation of the EGFR. Aldo-induced ROS were predominantly generated by mitochondria. Pretreatment with the antioxidant N-acetyl-l-cysteine, catalase, SOD, mitochondrial respiratory chain complex I inhibitor rotenone (Rot), NADPH oxidase inhibitor apocynin, and DPI significantly inhibited Aldo-stimulated MC proliferation as well as EGFR transactivation. However, Rot reduced MC proliferation more potently than apocynin and DPI. In conclusion, Aldo stimulated cell proliferation through MR-mediated, redox-sensitive EGFR transactivation, which was dependent on the Ki-RasA/c-Raf/MEK/ERK and PI3K/Akt/mTOR/p70S6K1 signaling pathways in human MCs.

NADPH oxidases and angiotensin II receptor signaling

Over the last decade many studies have demonstrated the importance of reactive oxygen species (ROS) production by NADPH oxidases in angiotensin II (Ang II) signaling, as well as a role for ROS in the development of different diseases in which Ang II is a central component. In this review, we summarize the mechanism of activation of NADPH oxidases by Ang II and describe the molecular targets of ROS in Ang II signaling in the vasculature, kidney and brain. We also discuss the effects of genetic manipulation of NADPH oxidase function on the physiology and pathophysiology of the renin-angiotensin system.

Redox control of renal function and hypertension

Loss of redox homeostasis and formation of excessive free radicals play an important role in the pathogenesis of kidney disease and hypertension. Free radicals such as reactive oxygen species (ROS) are necessary in physiologic processes. However, loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney, which in turn lead to reduced vascular compliance and proteinuria. The kidney is susceptible to the influence of various extracellular and intracellular cues, including the renin-angiotensin-aldosterone system (RAAS), hyperglycemia, lipid peroxidation, inflammatory cytokines, and growth factors. Redox control of kidney function is a dynamic process with reversible pro- and anti-free radical processes. The imbalance of redox homeostasis within the kidney is integral in hypertension and the progression of kidney disease. An emerging paradigm exists for renal redox contribution to hypertension.

Salutary Effect of Kallistatin in Salt-Induced Renal Injury, Inflammation, and Fibrosis via Antioxidative Stress

An inverse relationship exists between kallistatin levels and salt-induced oxidative stress in Dahl-salt sensitive rats. We further investigated the role of kallistatin in inhibiting inflammation and fibrosis through antioxidative stress in Dahl-salt sensitive rats and cultured renal cells. High-salt intake in Dahl-salt sensitive rats induced elevation of thiobarbituric acid reactive substances (an indicator of lipid peroxidation), malondialdehyde levels, reduced nicotinamide-adenine dinucleotide phosphate oxidase activity, and superoxide formation, whereas kallistatin gene delivery significantly reduced these oxidative stress parameters. Kallistatin treatment improved renal function and reduced kidney damage as evidenced by diminished proteinuria and serum urea nitrogen levels, glomerular sclerosis, tubular damage, and protein cast formation. Kallistatin significantly decreased interstitial monocyte-macrophage infiltration and the expression of tumor necrosis factor-α, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1. Kallistain also reduced collagen fraction volume and the deposition and expression of collagen types I and III. Renal protection by kallistatin was associated with increased NO levels and endothelial NO synthase expression and decreased p38 mitogen-activated protein kinase, extracellular signal-regulated kinase phosphorylation, and transforming growth factor-β1 expression. Moreover, kallistatin attenuated tumor necrosis factor-α–induced intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression via inhibition of reactive oxygen species formation and p38 mitogen-activated protein kinase and nuclear factor-κB activation in cultured proximal tubular cells. Kallistatin inhibited fibronectin and collagen expression by suppressing angiotensin II–induced reactive oxygen species generation and transforming growth factor-β1 expression in cultured mesangial cells. These combined findings reveal that kallistatin is a novel antioxidant, which prevents salt-induced kidney injury, inflammation, and fibrosis by inhibiting reactive oxygen species–induced proinflammatory cytokine and transforming growth factor-β1 expression.