Angiotensin II stimulates hypoxia-inducible factor 1alpha accumulation in glomerular mesangial cells

Mutual Regulation between Redox and Hypoxia-Inducible Factors in Cardiovascular and Renal Complications of Diabetes

Oxidative stress and hypoxia-inducible factors (HIFs) have been implicated in the pathogenesis of diabetic cardiovascular and renal diseases. Reactive oxygen species (ROS) mediate physiological and pathophysiological processes, being involved in the modulation of cell signaling, differentiation, and survival, but also in cyto- and genotoxic damage. As master regulators of glycolytic metabolism and oxygen homeostasis, HIFs have been largely studied for their role in cell survival in hypoxic conditions. However, in addition to hypoxia, other stimuli can regulate HIFs stability and transcriptional activity, even in normoxic conditions. Among these, a regulatory role of ROS and their byproducts on HIFs, particularly the HIF-1α isoform, has received growing attention in recent years. On the other hand, HIF-1α and HIF-2α exert mutually antagonistic effects on oxidative damage. In diabetes, redox-mediated HIF-1α deregulation contributes to the onset and progression of cardiovascular and renal complications, and recent findings suggest that deranged HIF signaling induced by hyperglycemia and other cellular stressors associated with metabolic disorders may cause mitochondrial dysfunction, oxidative stress, and inflammation. Understanding the mechanisms of mutual regulation between HIFs and redox factors and the specific contribution of the two main isoforms of HIF-α is fundamental to identify new therapeutic targets for vascular complications of diabetes.

Hypoxia-induced angiotensin II by the lactate-chymase-dependent mechanism mediates radioresistance of hypoxic tumor cells

The renin-angiotensin system (RAS) is a principal determinant of arterial blood pressure and fluid and electrolyte balance. RAS component dysregulation was recently found in some malignancies and correlated with poor patient outcomes. However, the exact mechanism of local RAS activation in tumors is still unclear. Here, we find that the local angiotensin II predominantly exists in the hypoxic regions of tumor formed by nasopharyngeal carcinoma CNE2 cells and breast cancer MDA-MB-231 cells, where these tumor cells autocrinely produce angiotensin II by a chymase-dependent rather than an angiotensin converting enzyme-dependent mechanism. We further demonstrate in nasopharyngeal carcinoma CNE2 and 5–8F cells that this chymase-dependent effect is mediated by increased levels of lactate, a by-product of glycolytic metabolism. Finally, we show that the enhanced angiotensin II plays an important role in the intracellular accumulation of HIF-1α of hypoxic nasopharyngeal carcinoma cells and mediates the radiation-resistant phenotype of these nasopharyngeal carcinoma cells. Thus, our findings reveal the critical role of hypoxia in producing local angiotensin II by a lactate-chymase-dependent mechanism and highlight the importance of local angiotensin II in regulating radioresistance of hypoxic tumor cells.

Diabetes-Induced Reactive Oxygen Species: Mechanism of Their Generation and Role in Renal Injury

Diabetes induces the onset and progression of renal injury through causing hemodynamic dysregulation along with abnormal morphological and functional nephron changes. The most important event that precedes renal injury is an increase in permeability of plasma proteins such as albumin through a damaged glomerular filtration barrier resulting in excessive urinary albumin excretion (UAE). Moreover, once enhanced UAE begins, it may advance renal injury from progression of abnormal renal hemodynamics, increased glomerular basement membrane (GBM) thickness, mesangial expansion, extracellular matrix accumulation, and glomerulosclerosis to eventual end-stage renal damage. Interestingly, all these pathological changes are predominantly driven by diabetes-induced reactive oxygen species (ROS) and abnormal downstream signaling molecules. In diabetic kidney, NADPH oxidase (enzymatic) and mitochondrial electron transport chain (nonenzymatic) are the prominent sources of ROS, which are believed to cause the onset of albuminuria followed by progression to renal damage through podocyte depletion. Chronic hyperglycemia and consequent ROS production can trigger abnormal signaling pathways involving diverse signaling mediators such as transcription factors, inflammatory cytokines, chemokines, and vasoactive substances. Persistently, increased expression and activation of these signaling molecules contribute to the irreversible functional and structural changes in the kidney resulting in critically decreased glomerular filtration rate leading to eventual renal failure.

The Decrement of Hemoglobin Concentration with Angiotensin II Receptor Blocker Treatment Is Correlated with the Reduction of Albuminuria in Non-Diabetic Hypertensive Patients: Post-Hoc Analysis of ESPECIAL Trial

Blockade of the renin-angiotensin-aldosterone system exhibits a renoprotective effect; however, blockade of this system may also decrease hemoglobin (Hb) and erythropoietin (EPO) levels. We evaluated the correlation between reduced albuminuria and decreased hemoglobin concentrations after treatment with an angiotensin II receptor blocker (ARB). Two hundred forty-five non-diabetic hypertensive participants with established albuminuria and relatively preserved renal function were treated with an ARB (40 mg/day olmesartan) for eight weeks. Subsequent changes in various clinical parameters, including Hb, EPO, and albuminuria, were analyzed following treatment. After the 8-week treatment with an ARB, Hb and EPO levels significantly decreased. Patients with a greater decrease in Hb exhibited a greater reduction in 24-hour urinary albumin excretion compared with patients with less of a decrease or no decrease in Hb, whereas no associations with a decline in renal function and EPO levels were noted. Multivariate logistic regression analysis demonstrated a correlation between the reduction of urine albumin excretion and the decrease in Hb levels (after natural logarithm transformation, adjusted odds ratio 1.76, 95% confidence interval 1.21-2.56, P = 0.003). Linear regression analysis also supported this positive correlation (Pearson correlation analysis; R = 0.24, P < 0.001). Decreased Hb concentrations following ARB treatment were positively correlated with reduced albuminuria in non-diabetic hypertensive patients, regardless of decreased blood pressure and EPO levels or renal function decline.

Hypoxia-independent upregulation of placental hypoxia inducible factor-1α gene expression contributes to the pathogenesis of preeclampsia

Accumulation of hypoxia inducible factor-1α (HIF-1α) is commonly an acute and beneficial response to hypoxia, whereas chronically elevated HIF-1α is associated with multiple disease conditions, including preeclampsia, a serious hypertensive disease of pregnancy. However, the molecular basis underlying the persistent elevation of placental HIF-1α in preeclampsia and its role in the pathogenesis of preeclampsia are poorly understood. Here we report that Hif-1α mRNA and HIF-1α protein were elevated in the placentas of pregnant mice infused with angiotensin II type I receptor agonistic autoantibody, a pathogenic factor in preeclampsia. Knockdown of placental Hif-1α mRNA by specific siRNA significantly attenuated hallmark features of preeclampsia induced by angiotensin II type I receptor agonistic autoantibody in pregnant mice, including hypertension, proteinuria, kidney damage, impaired placental vasculature, and elevated maternal circulating soluble fms-like tyrosine kinase-1 levels. Next, we discovered that Hif-1α mRNA levels and HIF-1α protein levels were induced in an independent preeclampsia model with infusion of the inflammatory cytokine tumor necrosis factor superfamily member 14 (LIGHT). SiRNA knockdown experiments also demonstrated that elevated HIF-1α contributed to LIGHT-induced preeclampsia features. Translational studies with human placentas showed that angiotensin II type I receptor agonistic autoantibody or LIGHT is capable of inducing HIF-1α in a hypoxia-independent manner. Moreover, increased HIF-1α was found to be responsible for angiotensin II type I receptor agonistic autoantibody or LIGHT-induced elevation of Flt-1 gene expression and production of soluble fms-like tyrosine kinase-1 in human villous explants. Overall, we demonstrated that hypoxia-independent stimulation of HIF-1α gene expression in the placenta is a common pathogenic mechanism promoting disease progression. Our findings reveal new insight to preeclampsia and highlight novel therapeutic possibilities for the disease.

High-Mobility Group Box-1 Modulates the Expression of Inflammatory and Angiogenic Signaling Pathways in Diabetic Retina

PURPOSE

The expression of high-mobility group box-1 (HMGB1) is upregulated in epiretinal membranes and vitreous fluid from patients with proliferative diabetic retinopathy and in the diabetic retina. HMGB1 mediates inflammation, breakdown of the blood-retinal barrier and apoptosis in the diabetic retina. Here, we investigated inflammatory and angiogenic signaling pathways activated by HMGB1 in diabetic retina.

METHODS

Human retinal microvascular endothelial cells (HRMEC) and retinas from 1-month diabetic rats and normal rats intravitreally injected with HMGB1 were studied using RT-PCR, Western blot analysis and co-immunoprecipitation. We also studied the effect of the HMGB1 inhibitor glycyrrhizin on diabetes-induced biochemical changes in the retina.

RESULTS

Diabetes and intravitreal injection of HMGB1 in normal rats induced significant upregulation of the mRNA levels of the chemokine stromal cell-derived factor-1 (SDF-1/CXCL12) receptor CXCR4 and protein levels of hypoxia-inducible factor-1α, early growth response-1, tyrosine kinase 2 and the CXCL12/CXCR4 chemokine axis. Constant glycyrrhizin intake from onset of diabetes did not affect the metabolic status of the diabetic rats, but it restored these increased mediators to control values. Stimulation of HRMEC with HMGB1 and intraviteral injection of HMGB1 significantly increased the expression of vascular endothelial growth factor (VEGF) and VEGF receptor-2. Co-immunoprecipitation studies showed that diabetes increased the interaction between CXCL12 and CXCR4 and between HMGB1 and receptor for advanced glycation end products (RAGE), but not between HMGB1 and the CXCL12/CXCR4 chemokine axis.

CONCLUSIONS

Our findings suggest that HMGB1 activates inflammatory and angiogenic signaling pathways in diabetic retina mediated by RAGE.

The role of hypoxia-induced genes in ovarian angiogenesis

The hypoxic microenvironment that occurs in fast-growing tissue such as the corpus luteum (CL) is a major contributor to its ability to survive via the induction of an intricate vascular network. Cellular responses to hypoxia are mediated by hypoxia-inducible factor-1 (HIF-1), an oxygen-regulated transcriptional activator. HIF-1, a heterodimer consisting of a constitutively-expressed β subunit and an oxygen-regulated α subunit, binds to the hypoxia responsive element (HRE) present in the promoter regions of responsive genes. This review summarises evidence for the involvement of hypoxia and HIF-1α in CL development and function. Special emphasis is given to hypoxia-induced, luteal cell-specific expression of multiple genes (vascular endothelial growth factor A (VEGFA), fibroblast growth factor 2 (FGF-2), prokineticin receptor 2 (PK-R2), stanniocalcin 1 (STC-1) and endothelin 2 (EDN-2) that participate in the angiogenic process during CL formation.

Reverse translation of phase I biomarker findings links the activity of angiotensin-(1-7) to repression of hypoxia inducible factor-1α in vascular sarcomas

Background

In a phase I study of angiotensin-(1–7) [Ang-(1–7)], clinical benefit was associated with reduction in plasma placental growth factor (PlGF) concentrations. The current study examines Ang-(1–7) induced changes in biomarkers according to cancer type and investigates mechanisms of action engaged in vitro.

Methods

Plasma biomarkers were measured prior to Ang-(1–7) administration as well as 1, 2, 3, 4, and 6 hours after treatment. Tests for interaction were performed to determine the impact of cancer type on angiogenic hormone levels. If a positive interaction was detected, treatment-induced biomarker changes for individual cancer types were assessed. To investigate mechanisms of action, in vitro growth assays were performed using a murine endothelioma cell line (EOMA). PCR arrays were performed to identify and statistically validate genes that were altered by Ang-(1–7) treatment in these cells.

Results

Tests for interaction controlled for dose cohort and clinical response indicated a significant impact of cancer type on post-treatment VEGF and PlGF levels. Following treatment, PlGF levels decreased over time in patients with sarcoma (P = .007). Treatment of EOMA cells with increasing doses of Ang-(1–7) led to significant growth suppression at doses as low as 100 nM. PCR arrays identified 18 genes that appeared to have altered expression after Ang-(1–7) treatment. Replicate analyses confirmed significant changes in 8 genes including reduction in PlGF (P = .04) and hypoxia inducible factor 1α (HIF-1α) expression (P < .001).

Conclusions

Ang-(1–7) has clinical and pre-clinical activity for vascular sarcomas that is linked to reduced HIF-1α and PlGF expression.

Angiotensin II differentially regulates Morg1 expression in kidney cells

BACKGROUND

The mitogen-activated protein kinase organizer 1 (Morg1) belongs to the WD-40 repeat protein family and is a scaffold molecule for the extracellular regulated kinase signaling pathway. Morg1 also binds to prolyl-hydroxylase 3 (PHD3) and regulates the hypoxia-inducible factor-1α (HIF-1α) expression via PHD3 stabilization. Morg1 has been detected in the kidney as well as in other cell tissues but its expression in renal cells has not been well investigated. It has been widely shown that angiotensin II (ANG II) mediates renal damage. We have previously shown that ANG II downregulates the expression of PHD3 in PC12 cells. The aim of this study was to analyze whether ANG II regulates Morg1 expression in mouse mesangial cells (MMC), mouse proximal tubular cells (MTC) and in differentiated podocytes. The correlation between the expression of Morg1 and PHD3 activity was also addressed.

METHODS

Effect of ANG II on the Morg1 mRNA expression level was assessed by real-time PCR. Morg1 and HIF-1α cellular localization was analyzed by immunohistochemistry. HIF-1α promoter activity was investigated using a reporter gene system. PHD3 hydroxylase activity test was measured with a hydroxylation-coupled decarboxylation assay.

RESULTS

ANG II differentially regulates Morg1 expression in MMC, MTC and differentiated podocytes. We detected a biphasic effect of ANG II on Morg1 mRNA expression which was time dependent. While 9-hour ANG II treatment downregulated Morg1 expression in MMC, it induced Morg1 expression in MTC. Conversely, 24-hour ANG II stimulation upregulated the expression of Morg1 mRNA in MMC, but showed an opposite effect in MTC and differentiated podocytes. In addition, we found that ANG II signals mostly through the AT(1) receptor subtype in MMC and via the AT(2) subtype in MTC. PHD3 activity correlated to Morg1 expression patterns. Our data also demonstrate that HIF-1α transcriptional activity in MTC contrasted to PHD3 activity at 9 and 24 h, whereas in the MMC and in podocytes we did not find any correlation between PHD3 HIF-1α hydroxylation ability and HIF-1α transcriptional activation, suggesting a different mechanism of regulation in these cell types. Interestingly, the reduced expression of Morg1 in mesangial cells isolated from Morg1 (+/-) heterozygous mice correlated with a reduced PHD3 enzymatic activity and an increased HIF-1α transcriptional activity compared with mesangial cells originated from wild-type (Morg1 +/+) mice.

CONCLUSIONS

We show for the first time in various renal cells that ANG II modulates Morg1 expression and HIF-1α transcriptional activity via cell type-specific mechanisms, demonstrating a novel mechanism by which ANG II may contribute to renal disease.

Silencing of hypoxia-inducible factor-1α gene attenuated angiotensin II-induced renal injury in Sprague-Dawley rats

Although it has been shown that upregulation of hypoxia-inducible factor (HIF)-1α is protective in acute ischemic renal injury, long-term overactivation of HIF-1α is implicated to be injurious in chronic kidney diseases. Angiotensin II (Ang II) is a well-known pathogenic factor producing chronic renal injury and has also been shown to increase HIF-1α. However, the contribution of HIF-1α to Ang II-induced renal injury has not been evidenced. The present study tested the hypothesis that HIF-1α mediates Ang II-induced renal injury in Sprague-Dawley rats. Chronic renal injury was induced by Ang II infusion (200 ng/kg per minute) for 2 weeks in uninephrectomized rats. Transfection of vectors expressing HIF-1α small hairpin RNA into the kidneys knocked down HIF-1α gene expression by 70%, blocked Ang II-induced HIF-1α activation, and significantly attenuated Ang II-induced albuminuria, which was accompanied by inhibition of Ang II-induced vascular endothelial growth factor, a known glomerular permeability factor, in glomeruli. HIF-1α small hairpin RNA also significantly improved the glomerular morphological damage induced by Ang II. Furthermore, HIF-1α small hairpin RNA blocked Ang II-induced upregulation of collagen and α-smooth muscle actin in tubulointerstitial region. There was no difference in creatinine clearance and Ang II-induced increase in blood pressure. HIF-1α small hairpin RNA had no effect on Ang II-induced reduction in renal blood flow and hypoxia in the kidneys. These data suggested that overactivation of HIF-1α-mediated gene regulation in the kidney is a pathogenic pathway mediating Ang II-induced chronic renal injuries, and normalization of overactivated HIF-1α may be used as a treatment strategy for chronic kidney damages associated with excessive Ang II.

Chinese medicine Tongxinluo modulates vascular endothelial function by inducing eNOS expression via the PI-3K/Akt/HIF-dependent signaling pathway

AIM OF THE STUDY

To investigate the molecular mechanisms whereby the Chinese medicinal compound Tongxinluo improves vascular endothelial function through studying the induction of endothelial nitric oxide synthase (eNOS) and its upstream signaling pathway.

MATERIALS AND METHODS

Hyperhomocysteinemia was induced in Wistar rats by a methionine-rich diet followed by Tongxinluo treatment. The aorta ring was isolated for measuring vascular dilation of aorta and eNOS expression. Human umbilical vein endothelial cells (HUVECs) were transfected with AP-1, NF-κB, HRE or eNOS reporter plasmid followed by Tongxinluo exposure. Expression of the reporter genes was measured by luciferase assay. The level of eNOS was studied by western blot and the nitric oxide content was measured using the nitrate reductase method. HUVECs were also transiently transfected with the dominant negative mutant of HIF-1, PI-3K or Akt to explore the role of HIF and PI-3K/Akt pathway in eNOS induction by Tongxinluo.

RESULTS

Tongxinluo could significantly up-regulate the expression of eNOS in the aortic tissue and improve the endothelium-dependent vasodilation of the aorta ring. Additionally, Tongxinluo at various doses could significantly enhance the expression of HRE and eNOS reporter gene as well as up-regulate the protein level of eNOS. Meanwhile, Tongxinluo caused a dose-dependent increase in the NO content in the supernatant of HUVECs. Suppression of HIF-1 activation by DN-HIF or inhibition of PI-3K/Akt pathway by ΔP85 or DN-Akt both attenuated HRE reporter gene activation and eNOS induction by Tongxinluo.

CONCLUSION

Tongxinluo, a compound Chinese traditional medicine, up-regulates the expression of eNOS via the PI-3K/Akt/HIF-dependent signaling pathway, thus improving the endothelium-dependent vasodilation.

Hypoxia-inducible factor-1α contributes to the profibrotic action of angiotensin II in renal medullary interstitial cells

To examine whether hypoxia-inducible factor (HIF)-1α mediates the profibrotic effects of angiotensin II, we treated cultured renal medullary interstitial cells with angiotensin II and found that it increased HIF-1α levels. This was accompanied by a significant upregulation of collagen I/III, the tissue inhibitor of metalloproteinase-1, elevation of the proliferation marker proliferating cell nuclear antigen, and a transdifferentiation marker vimentin. All these effects of angiotensin II were completely blocked by siRNA for HIF-1α but not HIF-2α. Overexpression of a prolyl-hydroxylase domain-containing protein 2 (PHD2) transgene, the predominant renal HIF prolyl-hydroxylase, attenuated the effects of angiotensin II and its gene silencing enhanced the effects of angiotensin II. Removal of hydrogen peroxide eliminated angiotensin II-induced profibrotic effects. A 2-week infusion of rats with angiotensin II increased the expression of HIF-1α and α-smooth muscle actin, another marker of transdifferentiation, in renal medullary interstitial cells in vivo. Thus, our study suggests that HIF-1α mediates angiotensin II-induced profibrotic effects through activation of cell transdifferentiation. We propose that redox regulation of prolyl-PHD2 plays a critical role in angiotensin II-induced activation of HIF-1α in renal cells.

Perindopril attenuates tubular hypoxia and inflammation in an experimental model of diabetic nephropathy in transgenic Ren-2 rats

BACKGROUND

Renal hypoxia plays a role in the development of diabetic nephropathy, and may be mediated by overactivity of the renin-angiotensin-aldosterone system (RAAS). In this study the localization of cellular hypoxia in an experimental model of diabetic nephropathy was assessed, and the effect of the angiotensin-converting enzyme inhibitor perindopril on hypoxia evaluated.

METHODS

Female Sprague-Dawley rats heterozygous for the Ren-2 gene were randomized to three groups (n = 8 per group)--controls, diabetes or diabetes + perindopril. Diabetes was induced by injection of streptozotocin at 6 weeks of age. Perindopril was administered at a dose of 2 mg/kg daily from 6 weeks. Subjects were culled after 16 weeks. Areas of tissue hypoxia were localized using immunohistochemistry to detect pimonidazole uptake.

RESULTS

Diabetic rat kidneys were characterized by increases in tubulointerstitial collagen deposition compared with controls. Tubular hypoxia was significantly greater in diabetic rats, indicated by a 2.5-fold increase in the proportional area of pimonidazole immunostaining (P < 0.001). Immunohistochemical staining for pimonidazole co-localized with osteopontin, and was associated with higher numbers of ED-1-positive cells (macrophages) within the tubulointerstitium. Treatment with perindopril ameliorated structural changes of diabetic nephropathy and reduced the amount of pimonidazole and ED-1 immunostaining to levels similar to that of controls.

CONCLUSION

In diabetic Ren-2 rats the development of diabetic nephropathy was associated with tubular hypoxia. Co-localization of osteopontin with hypoxic cells suggests that tubular hypoxia may be involved in the pathogenesis of diabetic nephropathy. The degree of hypoxia and fibrosis was attenuated by treatment with perindopril.

Regulation of endothelial proliferation by the renin–angiotensin system in human umbilical vein endothelial cells

This study was performed in order to evaluate the role of angiotensin II in physiological angiogenesis. Human umbilical vein endothelial cells (HUVEC) were stained for angiotensin II type 1 receptor (AGTR1) immunocytochemically and for gene expression of renin–angiotensin system (RAS) components. The regulation of the angiogenesis-associated genes vascular endothelial growth factor (VEGF) and angiopoietins (ANGPT1andANGPT2) were studied using quantitative RT-PCR. Furthermore, we examined the effect of angiotensin II on the proliferation of HUVEC using Ki-67 as well as BrdU immunocytochemistry and investigated whether the administration of the AGTR1 blocker candesartan or the VEGF antagonist FLT1-Fc could suppress the observed angiotensin II-dependent proangiogenic effect. AGTR1 was expressed in HUVEC and the administration of angiotensin II significantly increased the gene expression ofVEGFand decreased the gene expression ofANGPT1. Since the expression ofANGPT2was not affected significantly the ratio of ANGPT1/ANGPT2 was decreased. In addition, a significantly increased endothelial cell proliferation was observed after stimulation with angiotensin II, which was suppressed by the simultaneous administration of candesartan or the VEGF antagonist FLT1-Fc. These results indicate the potential capacity of angiotensin II in influencing angiogenesis by the regulation of angiogenesis-associated genes via AGTR1. Since VEGF blockade opposed the effect of angiotensin II on cell proliferation, it is hypothesised that VEGF mediates the angiotensin II-dependent effect in concert with the changes in angiopoietin expression. This is the first report of the RAS on the regulation of angiogenesis-associated genes in physiology.

Potential role of Renin-Angiotensin-system for tumor angiogenesis in receptor negative breast cancer

OBJECTIVE

This study examined the potential role of Angiotensin II for the regulation of angiogenesis associated genes in receptor positive and negative human breast cancer.

METHODS

Expression of different Renin-Angiotensin system (RAS) components in human breast cancer tissue was investigated using immunofluorescence, and in a receptor positive (MCF-7) and receptor negative (MDA-MB 468) breast cancer cell line by performing immunocytochemistry and RT-PCR. Both cell lines were stimulated with Angiotensin II and Angiotensin II receptor type 1 (At(1)R) blocker Candesartan, and gene expression of vascular endothelial growth factor (VEGF), Angiopoietin 1 and 2 (Ang-1 and Ang-2), tissue inhibitor of matrix metalloproteinases 1 (TIMP-1), and hypoxia inducible transcription factor 2alpha (HIF-2alpha) were quantified by TaqMan-Real-Time PCR analysis.

RESULTS

RAS components, Angiotensinogen, Renin, Angiotensin I-converting enzyme (ACE), and At(1)R and At(2)R were expressed in hormone-receptor negative and positive human breast cancer tissue as well as in MDA-MB 468 and in MCF-7 human breast cancer cells. In addition, we found expression of VEGF, Ang-1, TIMP-1, and HIF-2alpha in both cell lines. However, only in receptor negative MDA-MB 468 cells, did Angiotensin II significantly increase gene expression of VEGF, HIF-2alpha, and TIMP-1. This effect was completely inhibited by Candesartan.

CONCLUSION

In conclusion, it is hypothesized that Angiotensin II may be involved in regulation of tumor angiogenesis especially in receptor negative breast cancer by regulation of angiogenesis associated genes via At(1)R. These findings are the first evidence for targeting tumor angiogenesis by inhibition of At(1)R in receptor negative human breast cancer cells and may lead to new therapeutical anticancer strategies based upon inhibition of At(1)R.

Angiotensin II Induces Angiogenesis in the Hypoxic Adult Mouse Heart In Vitro Through an AT 2 –B2 Receptor Pathway

Angiotensin II is a vasoactive peptide that may affect vascularization of the ischemic heart via angiogenesis. In this study we aimed at studying the mechanisms underlying the angiogenic effects of angiotensin II under hypoxia in the mouse heart in vitro. Endothelial sprout formation from pieces of mouse hearts was assessed under normoxia (21% O 2 ) and hypoxia (1% O 2 ) during a 7-day period of in vitro culture. Only under hypoxia did angiotensin II dose-dependently induce endothelial sprout formation, peaking at 10 −7 mol/L of angiotensin II. Angiotensin II type 1 (AT 1 ) receptor blockade by losartan did not affect angiotensin II–induced sprouting in wild-type mice. Conversely, the angiotensin II type 2 (AT 2 ) receptor antagonist PD 123319 blocked this response. In hearts from AT 1 −/− mice, angiotensin II–elicited sprouting was preserved but blocked again by AT 2 receptor antagonism. In contrast, no angiotensin II–induced sprouting was found in preparations from hearts of AT 2 −/− mice. Angiotensin II–mediated angiogenesis was also abolished by a specific inhibitor of the B2 kinin receptor in both wild-type and AT 1 −/− mice. Furthermore, angiotensin II failed to induce endothelial sprout formation in hearts from B2 −/− mice. Finally, NO inhibition completely blunted sprouting in hearts from wild-type mice, whereas NO donors could restore sprouting in AT 2 −/− and B2 −/− hearts. This in vitro study suggests the obligatory role of hypoxia in the angiogenic effect of angiotensin II in the mouse heart via the AT 2 receptor through a mechanism that involves bradykinin, its B2 receptor, and NO as a downstream effector.

Current understanding of HIF in renal disease

Hypoxia-inducible factors (HIF) are ubiquitous transcription factors regulated by oxygen-dependent proteolysis, and hence rapidly mount an adaptational response to hypoxia. The HIF system is apparently more complex than initially considered in the perspective of the increasing number of HIF target genes, and the inter-relationship with various additional regulatory pathways. Regional hypoxia is believed to play a major role in renal disease. Experimental data confirm a role for HIF in renal pathophysiology. The discovery of HIF prolyl-hydroxylases as key enzymes of oxygen sensing and HIF proteolysis offer new possibilities to therapeutically target HIF. Herein, we review basic concepts of HIF regulation, and existing data on HIF activation in renal disease.