Angiotensin II's antiproliferative effects mediated through AT2-receptors depend on down-regulation of SM-20

Identification of Dysregulated Expression of G Protein Coupled Receptors in Endocrine Tumors by Bioinformatics Analysis: Potential Drug Targets?

Background: Many studies link G protein-coupled receptors (GPCRs) to cancer. Some endocrine tumors are unresponsive to standard treatment and/or require long-term and poorly tolerated treatment. This study explored, by bioinformatics analysis, the tumoral profiling of the GPCR transcriptome to identify potential targets in these tumors aiming at drug repurposing. Methods: We explored the GPCR differentially expressed genes (DEGs) from public datasets (Gene Expression Omnibus (GEO) database and The Cancer Genome Atlas (TCGA)). The GEO datasets were available for two medullary thyroid cancers (MTCs), eighty-seven pheochromocytomas (PHEOs), sixty-one paragangliomas (PGLs), forty-seven pituitary adenomas and one-hundred-fifty adrenocortical cancers (ACCs). The TCGA dataset covered 92 ACCs. We identified GPCRs targeted by approved drugs from pharmacological databases (ChEMBL and DrugBank). Results: The profiling of dysregulated GPCRs was tumor specific. In MTC, we found 14 GPCR DEGs, including an upregulation of the dopamine receptor (DRD2) and adenosine receptor (ADORA2B), which were the target of many drugs. In PGL, seven GPCR genes were downregulated, including vasopressin receptor (AVPR1A) and PTH receptor (PTH1R), which were targeted by approved drugs. In ACC, PTH1R was also downregulated in both the GEO and TCGA datasets and was the target of osteoporosis drugs. Conclusions: We highlight specific GPCR signatures across the major endocrine tumors. These data could help to identify new opportunities for drug repurposing.

Induced dysregulation of ACE2 by SARS-CoV-2 plays a key role in COVID-19 severity

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the cause of COVID-19, is reported to increase the rate of mortality worldwide. COVID-19 is associated with acute respiratory symptoms as well as blood coagulation in the vessels (thrombosis), heart attack and stroke. Given the requirement of angiotensin converting enzyme 2 (ACE2) receptor for SARS-CoV-2 entry into host cells, here we discuss how the downregulation of ACE2 in the COVID-19 patients and virus-induced shift in ACE2 catalytic equilibrium, change the concentrations of substrates such as angiotensin II, apelin-13, dynorphin-13, and products such as angiotensin (1–7), angiotensin (1–9), apelin-12, dynorphin-12 in the human body. Substrates accumulation ultimately induces inflammation, angiogenesis, thrombosis, neuronal and tissue damage while diminished products lead to the loss of the anti-inflammatory, anti-thrombotic and anti-angiogenic responses. In this review, we focus on the viral-induced imbalance between ACE2 substrates and products which exacerbates the severity of COVID-19. Considering the roadmap, we propose multiple therapeutic strategies aiming to rebalance the products of ACE2 and to ameliorate the symptoms of the disease.

Interaction between Angiotensin Type 1, Type 2, and Mas Receptors to Regulate Adult Neurogenesis in the Brain Ventricular-Subventricular Zone

The renin-angiotensin system (RAS), and particularly its angiotensin type-2 receptors (AT2), have been classically involved in processes of cell proliferation and maturation during development. However, the potential role of RAS in adult neurogenesis in the ventricular-subventricular zone (V-SVZ) and its aging-related alterations have not been investigated. In the present study, we analyzed the role of major RAS receptors on neurogenesis in the V-SVZ of adult mice and rats. In mice, we showed that the increase in proliferation of cells in this neurogenic niche was induced by activation of AT2 receptors but depended partially on the AT2-dependent antagonism of AT1 receptor expression, which restricted proliferation. Furthermore, we observed a functional dependence of AT2 receptor actions on Mas receptors. In rats, where the levels of the AT1 relative to those of AT2 receptor are much lower, pharmacological inhibition of the AT1 receptor alone was sufficient in increasing AT2 receptor levels and proliferation in the V-SVZ. Our data revealed that interactions between RAS receptors play a major role in the regulation of V-SVZ neurogenesis, particularly in proliferation, generation of neuroblasts, and migration to the olfactory bulb, both in young and aged brains, and suggest potential beneficial effects of RAS modulators on neurogenesis.

Angiotensin II increases angiogenesis by NF-κB-mediated transcriptional activation of angiogenic factor AGGF1

Angiogenic factor with G-patch and FHA domains 1 (AGGF1) is involved in vascular development, angiogenesis, specification of hemangioblasts, and differentiation of veins. When mutated, however, it causes Klippel-Trenaunay syndrome, a vascular disorder. In this study, we show that angiotensin II (AngII)-the major effector of the renin-angiotensin system and one of the most important regulators of the cardiovascular system-induces the expression of AGGF1 through NF-κB, and that AGGF1 plays a key role in AngII-induced angiogenesis. AngII significantly up-regulated the levels of AGGF1 mRNA and protein in HUVECs at concentrations of 10-40 μg/ml but not >60 μg/ml. AngII type 1 receptor (AT1R) inhibitor losartan inhibited AngII-induced up-regulation of AGGF1, whereas AT2R inhibitor PD123319 further increased AngII-induced up-regulation of AGGF1. Up-regulation of AGGF1 by AngII was blocked by NF-κB inhibitors, and p65 binds directly to a binding site at the promoter/regulatory region of AGGF1 and transcriptionally activates AGGF1 expression. AngII-induced endothelial tube formation was blocked by small interfering RNAs (siRNAs) for RELA (RELA proto-oncogene, NF-κB subunit)/p65 or AGGF1, and the effect of RELA siRNA was rescued by AGGF1. AngII-induced angiogenesis from aortic rings was severely impaired in Aggf1^+/- mice, and the effect was restored by AGGF1. These data suggest that AngII acts as a critical regulator of AGGF1 expression through NF-κB, and that AGGF1 plays a key role in AngII-induced angiogenesis.-Si, W., Xie, W., Deng, W., Xiao, Y., Karnik, S. S., Xu, C., Chen, Q., Wang, Q. K. Angiotensin II increases angiogenesis by NF-κB-mediated transcriptional activation of angiogenic factor AGGF1.

Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling

Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.

Activation of hypoxia-inducible factor-1 in pulmonary arterial smooth muscle cells by endothelin-1

Numerous cellular responses to hypoxia are mediated by the transcription factor hypoxia-inducible factor-1 (HIF-1). HIF-1 plays a central role in the pathogenesis of hypoxic pulmonary hypertension. Under certain conditions, HIF-1 may utilize feedforward mechanisms to amplify its activity. Since hypoxia increases endothelin-1 (ET-1) levels in the lung, we hypothesized that during moderate, prolonged hypoxia ET-1 might contribute to HIF-1 signaling in pulmonary arterial smooth muscle cells (PASMCs). Primary cultures of rat PASMCs were treated with ET-1 or exposed to moderate, prolonged hypoxia (4% O(2) for 60 h). Levels of the oxygen-sensitive HIF-1α subunit and expression of HIF target genes were increased in both hypoxic cells and cells treated with ET-1. Both hypoxia and ET-1 also increased HIF-1α mRNA expression and decreased mRNA and protein expression of prolyl hydroxylase 2 (PHD2), which is the protein responsible for targeting HIF-1α for O(2)-dependent degradation. The induction of HIF-1α by moderate, prolonged hypoxia was blocked by BQ-123, an antagonist of ET-1 receptor subtype A. The effects of ET-1 were mediated by increased intracellular calcium, generation of reactive oxygen species, and ERK1/2 activation. Neither ET-1 nor moderate hypoxia induced the expression of HIF-1α or HIF target genes in aortic smooth muscle cells. These results suggest that ET-1 induces a PASMC-specific increase in HIF-1α levels by upregulation of HIF-1α synthesis and downregulation of PHD2-mediated degradation, thereby amplifying the induction of HIF-1α in PASMCs during moderate, prolonged hypoxia.

Angiotensin II type 2 receptor signaling significantly attenuates growth of murine pancreatic carcinoma grafts in syngeneic mice

Background

Pancreatic cancer is one of the most aggressive human malignancies, with a very poor prognosis. To evaluate the effect of angiotensin II (Ang II) type 2 receptor (AT₂) expression in the host's body on the growth of pancreatic carcinoma, we have investigated the growth of mouse pancreatic ductal carcinoma grafts in syngeneic wild type and AT₂ receptor-deficient (AT₂-KO) mice.

Methods

The role of AT₂ receptor-signaling in stromal cells on the growth of murine pancreatic carcinoma cells (PAN02) was studied using various in vitro and in vivo assays. In vivo cell proliferation, apoptosis, and vasculature in tumors were monitored by Ki-67 immunostaining, TUNEL assay, and von Willebrand factor immunostaining, respectively. In the co-culture study, cell proliferation was measured by MTT cell viability assay. All the data were analyzed using t-test and data were treated as significant when p < 0.05.

Results

Our results show that the growth of subcutaneously transplanted syngeneic xenografts of PAN02 cells, mouse pancreatic ductal carcinoma cells derived from the C57/BL6 strain, was significantly faster in AT₂-KO mice compared to control wild type mice. Immunohistochemical analysis of tumor tissue revealed significantly more Ki-67 positive cells in xenografts grown in AT₂-KO mice than in wild type mice. The index of apoptosis is slightly higher in wild type mice than in AT₂-KO mice as evaluated by TUNEL assay. Tumor vasculature number was significantly higher in AT₂-KO mice than in wild type mice. In vitro co-culture studies revealed that the growth of PAN02 cells was significantly decreased when grown with AT₂ receptor gene transfected wild type and AT₂-KO mouse-derived fibroblasts. Faster tumor growth in AT₂-KO mice may be associated with higher VEGF production in stromal cells.

Conclusions

These results suggest that Ang II regulates the growth of pancreatic carcinoma cells through modulating functions of host stromal cells; Moreover, Ang II AT₂ receptor signaling is a negative regulator in the growth of pancreatic carcinoma cells. These findings indicate that the AT₂ receptor in stromal fibroblasts is a potentially important target for chemotherapy for pancreatic cancer.

Over-expression of angiotensin II type 2 receptor gene induces cell death in lung adenocarcinoma cells

The endogenous angiotensin II (Ang II) type 2 receptor (AT 2) has been shown to mediate apoptosis in cardiovascular tissues. Thus, the aim of this study was to explore the anti-cancer effect of AT 2 over-expression on lung adenocarcinoma cells in vitro using adenoviral (Ad), FuGENE, and nanoparticle vectors. All three gene transfection methods efficiently transfected AT 2 cDNA into lung cancer cells but caused minimal gene transfection in normal lung epithelial cells. Ad-AT 2 significantly attenuated multiple human lung cancer cell growth (A549 and H358) as compared to the control viral vector, Ad-LacZ, when cell viability was examined by direct cell count. Examination of annexin V by flow cytometry revealed the activation of the apoptotic pathway via AT 2 over-expression. Western Blot analysis confirmed the activation of caspase-3. Similarly, poly (lactide-co-glycolic acid) (PLGA) biodegradable nanoparticles encapsulated AT 2 plasmid DNA were shown to be effectively taken up into the lung cancer cell. Nanoparticle-based AT 2 gene transfection markedly increased AT 2 expression and resultant cell death in A549 cells. These results indicate that AT 2 over-expression effectively attenuates growth of lung adenocarcinoma cells through intrinsic apoptosis. Our results also suggest that PLGA nanoparticles can be used as an efficient gene delivery vector for lung adenocarcinoma targeted therapy.

Immunohistochemical detection of angiotensin receptors AT1 and AT2 in adrenal tumors

Angiotensin II is well known to affect the adrenal cell growth and function. Angiotensin receptors AT1 and AT2 were found to be present in the normal adrenal gland. However, the data on the expression of the angiotensin receptors in the adrenal tumors are very scarce. To overcome this gap, the paraffin sections of the adrenal cortical tumors and of pheochromocytomas from the archival material were immunostained with antibodies raised against AT1 (sc-1173) and AT2 (sc-9040) receptor proteins. In hyperplasia of the adrenal cortex and in benign adrenocortical adenomas, both functioning and non-functioning, the AT1 immunostaining was present mainly in the cell membranes. A positive immunoreaction was also found in the subpopulation of cell nuclei and within the cytoplasm. In the adrenal cancer, as well as in pheochromocytomas, neither cell membranes nor cell nuclei were immunostained with anti-AT1 antibody. However, a weak AT1 immunostaining was present within the cytoplasm of tumoral cells. With anti-AT2 antibody, in all tumors investigated, the tumoral cells were immunonegative but moderate to strong AT2 immunostaining was observed in the walls of intratumoral blood vessels and in the interstitial tissue. Our data indicates that the expression of AT1 receptors is altered in adrenal cancer and in pheochromocytomas. The expression of AT2 receptors, in turn, may be connected with the process of tumoral neo-angiogenesis.

Angiotensin II-induced reactive oxygen species and the kidney

Angiotensin II (AngII) is an important mediator in renal injury. Accumulating evidence suggests that AngII stimulates intracellular formation of reactive oxygen species (ROS) such as the superoxide anion and hydrogen peroxide. AngII activates several subunits of the membrane-bound multicomponent NAD(P)H oxidase and also increases ROS formation in the mitochondria. Some of these effects may be induced by aldosterone and not directly by AngII. The superoxide anion and hydrogen peroxide influence other downstream signaling pathways, such as transcription factors, tyrosine kinases/phosphatases, ion channels, and mitogen-activated protein kinases. Through these signaling pathways, ROS have distinct functional effects on renal cells. They are transducers of cell growth, apoptosis, and cell migration and affect expression of inflammatory and extracellular matrix genes. For example, AngII-mediated expression of p27(Kip1), a cell-cycle regulatory protein, and induction of tubular hypertrophy depend on the generation of ROS. The effects of ROS generated within different renal cells ultimately depend on the locally generated concentrations and the balance of pro- and antioxidant pathways. Although the concept that AngII mediates oxidative stress in the kidney has been validated in experimental models, the exact role is still incompletely understood in human renal diseases.

EGLN3 Prolyl Hydroxylase Regulates Skeletal Muscle Differentiation and Myogenin Protein Stability

EGLN3, a member of the EGLN family of prolyl hydroxylases, has been shown to catalyze hydroxylation of the alpha subunit of hypoxia-inducible factor-alpha, which targets hypoxia-inducible factor-alpha for ubiquitination by a ubiquitin ligase complex containing the von Hippel-Lindau (VHL) tumor suppressor. We now report that EGLN3 levels increase during C2C12 skeletal myoblast differentiation. EGLN3 small interference RNAs and EGLN3 antisense oligonucleotides blocked C2C12 differentiation and decreased levels of myogenin, a member of the MyoD family of myogenic regulatory factors, which plays a critical role in myogenic differentiation. We also report that EGLN3 interacts with and stabilizes myogenin protein, whereas VHL associates with and destabilizes myogenin via the ubiquitin-proteasome system. The effect of VHL on myogenin stability and ubiquitination can be reversed, at least in part, by overexpression of EGLN3, suggesting that its binding to myogenin may prevent VHL-mediated degradation. These data demonstrate a novel role for EGLN3 in regulating skeletal muscle differentiation and gene expression. In addition, this report provides evidence for a novel pathway that regulates myogenin expression and skeletal muscle differentiation.

The Novel WD-repeat Protein Morg1 Acts as a Molecular Scaffold for Hypoxia-inducible Factor Prolyl Hydroxylase 3 (PHD3)

Hypoxia-inducible factor-1 (HIF-1), a transcriptional complex composed of an oxygen-sensitive alpha- and a beta-subunit, plays a pivotal role in cellular adaptation to low oxygen availability. Under normoxia, the alpha-subunit of HIF-1 is hydroxylated by a family of prolyl hydroxylases (PHDs) and consequently targeted for proteasomal degradation. Three different PHDs have been identified, but the difference among their in vivo roles remain unclear. PHD3 is strikingly expressed by hypoxia, displays high substrate specificity, and has been identified in other signaling pathways. PHD3 may therefore hydroxylate divergent substrates and/or connect divergent cellular responses with HIF. We identified a novel WD-repeat protein, recently designated Morg1 (MAPK organizer 1), by screening a cDNA library with yeast two-hybrid assays. The interaction between PHD3 and Morg1 was confirmed in vitro and in vivo. We found seven WD-repeat domains by cloning the full-length cDNA of Morg1. By confocal microscopy both proteins co-localize within the cytoplasm and the nucleus and display a similar tissue expression pattern in Northern blots. Binding occurs at a conserved region predicted to the top surface of one propeller blade. Finally, HIF-mediated reporter gene activity is decreased by Morg1 and reduced to basal levels when Morg1 is co-expressed with PHD3. Suppression of Morg1 or PHD3 by stealth RNA leads to a marked increase of HIF-1 activity. These results indicate that Morg1 specifically interacts with PHD3 most likely by acting as a molecular scaffold. This interaction may provide a molecular framework between HIF regulation and other signaling pathways.

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

Angiotensin II (ANG II) induces cell-cycle arrest of cultured proximal tubular cells, resulting in cellular hypertrophy. This ANG II-mediated hypertrophy is associated with the induction of p27(Kip1), an inhibitor of G1 phase cyclin-dependent kinase cyclin complexes. We have recently demonstrated that ANG II-mediated expression of p27(Kip1) and induction of cellular hypertrophy depend on the generation of reactive oxygen species (ROS). The effects of ROS are mediated by stimulation of mitogen-activated protein (MAP) kinases. p44/42 MAP kinase directly phosphorylates p27(Kip1) at serine-threonine residues and increases thereby its half-life time. AT2-receptor activation has been implicated in apoptosis and/or cell differentiation. Recent studies, however, revealed a more indirect role of hypoxia in the antiproliferative effects of ANG II transduced through AT2 receptors. We found that SM-20 is down-regulated in ANG II-stimulated PC12 cells that express only AT2 receptors. It turned out that SM20 is the rat homologue of a dioxygenase that regulates hypoxia-inducible factor 1 (HIF-1). ANG II induces HIF-1alpha by a posttranscriptional mechanism suggesting that SM20 down-regulation leads to stabilization of HIF-1. Thus, ANG II-induced ROS generation plays a pivotal role in several pathophysiological situations, leading to renal growth regulation and remodeling after injury.

New selective AT2 receptor ligands encompassing a gamma-turn mimetic replacing the amino acid residues 4-5 of angiotensin II act as agonists

New benzodiazepine-based gamma-turn mimetics with one or two amino acid side chains were synthesized. The gamma-turn mimetics were incorporated into angiotensin II (Ang II) replacing the Val(3)-Tyr(4)-Ile(5) or Tyr(4)-Ile(5) peptide segments. All of the resulting pseudopeptides displayed high AT(2)/AT(1) receptor selectivity and exhibited AT(2) receptor affinity in the low nanomolar range. Molecular modeling was used to investigate whether the compounds binding to the AT(2) receptor could position important structural elements in common areas. A previously described benzodiazepine-based gamma-turn mimetic with high affinity for the AT(2) receptor was also included in the modeling. It was found that the molecules, although being structurally quite different, could adopt the same binding mode/interaction pattern in agreement with the model hypothesis. The pseudopeptides selected for agonist studies were shown to act as AT(2) receptor agonists being able to induce outgrowth of neurite cells, stimulate p42/p44(mapk), and suppress proliferation of PC12 cells.

Combination therapy with ACE inhibitors and angiotensin II receptor blockers to halt progression of chronic renal disease: Pathophysiology and indications

It is no a secret that we are confronted by an alarmingly increasing number of patients with progressive renal disease. There is ample evidence for the notion that angiotensin II (Ang II) is a major culprit in progression. The vasopeptide Ang II turned out to have also multiple nonhemodynamic pathophysiologic actions on the kidney, including proinflammatory and profibrogenic effects. Diverse complex Ang II generating systems have been identified, including specifically local tissue-specific renin-angiotensin systems (RAS). For example, proximal tubular cells have all components required for a functional RAS capable of synthesizing Ang II. On the other hand, Ang II is not the only effector of the RAS and other peptides generated by the RAS influence renal function and structure as well. Moreover, the discoveries that Ang II can be generated by enzymes other than angiotensin-converting enzyme (ACE) and that Ang II and other RAS derived peptides bind to various receptors with different functional consequences have further added to the complexity of this system. Several major clinical trials have clearly shown that ACE inhibitor treatment slows the progression of renal diseases, including in diabetic nephropathy. Well-controlled studies demonstrated that this effect is in part independent of blood pressure control. More recently, with Ang II type 1 receptor (AT(1)) receptor antagonists a similarly protective effect on renal function was seen in patients with type 2 diabetes. Neither ACE inhibitor treatment nor AT(1) receptor blockade completely abrogate progression of renal disease. A recently introduced novel therapeutic approach is combination treatment comprising both ACE inhibitor and AT(1) receptor antagonists. The rationale for this approach is based on several considerations. Small-scale clinical studies, mainly of crossover design, documented that combination therapy is more potent in reducing proteinuria in patients with different chronic renal diseases. Blood pressure as an important confounder was, however, significantly lower in the majority of this studies in the combination treatment arms compared to the respective monotherapies. In a recent prospective study Japanese authors avoided this confounder and demonstrated that combination therapy reduced hard end-points (end stage renal failure or doubling of serum creatinine concentration) by 50% compared to the respective monotherapies. This effect could not be explained by a more pronounced reduction of blood pressure in the combination therapy group. Although these results are encouraging, administration of combination therapy should be reserved currently to special high risk groups. Further studies are necessary to confirm these promising results. It is possible that combination therapy may increase the risk of hyperkalemia, particularly when with coadministered with medications such as nonsteroidal anti-inflammatory drugs (NSAIDs) or spironolactone. In our opinion patients with proteinuria >1 g/day despite optimal blood pressure control under RAS-blocking monotherapy are a high-risk group which will presumably benefit from combination therapy.

Angiotensin II mediates acinar cell apoptosis during the development of rat pancreatic fibrosis by AT1R

OBJECTIVES

The mechanisms of pancreatic fibrosis were not fully elucidated. Apoptosis has been suggested to be involved in the progression of pancreatic fibrosis. It has been reported that the renin-angiotensin system (RAS) plays a crucial role in the formation of fibrosis, including in the kidney, heart, and liver. We recently reported that the angiotensin II type I receptor (AT1R) antagonist losartan has been able to alleviate the pancreatic fibrosis in the rat model, indicating angiotensin II participated in the progression of pancreatic fibrosis. In present study, the possible effects of angiotensin II-mediated apoptosis of pancreatic acinar cells were investigated in rat pancreatic fibrosis induced by trinitrobenzene sulfonic acid (TNBS) by AT1R, with special reference to the losartan administration.

METHODS

Male Sprague-Dawley rats (200-300 g) were randomly divided into a normal group, a control group, and a losartan-treatment group. Pancreatic fibrosis was induced by infusion of 2% TNBS into the pancreatic duct. Rats were treated with losartan (10 mg/kg) by gavage daily in the losartan-treatment group and the same volume of sterile distilled water was administered to the control group. All treatments started on the first day and ended 8 weeks after the operation. On day 3 and at weeks 1, 2, 3, 4, and 8, the histologic changes of the pancreas were examined by hematoxylin and eosin staining, and pancreatic acinar cell apoptosis was investigated by using electron microscopy and terminal deoxynucleotidyl transferase UTP nick end labeling (TUNEL), indicated by the apoptotic index (AI). Expressions of Bax, Bak, and Bcl-2 mRNA in the pancreas were detected by reverse transcriptase polymerase chain reaction (RT-PCR) on day 3 and at weeks 1, 2, 3, and 4.

RESULTS

Compared with the control group, losartan treatment significantly alleviated the histologic abnormalities, including infiltration of inflammatory cells and acinar cells atrophy. In the control group, a typical morphologic presentation of acinar cell apoptosis was seen either with electron microscopy or TUNEL staining. The AI was increased in pancreatic tissue. Meanwhile, Bax and Bak mRNA expression was increased, but Bcl-2 mRNA expression was decreased, as compared with the normal group. The administration of losartan resulted in inhibition of acinar cell apoptosis and down-regulation of Bax, Bak, and Bcl-2 mRNA expression. The Bax/Bcl-2 ratio was lower in losartan-treated rats than in control rats.

CONCLUSION

Losartan prevents apoptosis of pancreatic acinar cell by blocking AT1R during the development of pancreatic fibrosis. This action may be associated with its regulation of apoptosis-associated genes, such as Bax, Bak, and Bcl-2 mRNA. The results of present study suggest that angiotensin II probably mediates pancreatic acinar cell apoptosis during the course of pancreatic fibrosis.

Insights into angiotensin II receptor function through AT2 receptor knockout mice

Angiotensin II signals via at least two receptors termed AT1 and AT2. The function of the AT1 receptor is well defined, while that of the AT2 receptor is still shrouded in uncertainty. AT2 gene-deficient (-/-) mice have been helpful in unravelling the function of the AT2 receptor. We have studied AT2-/- and AT2+/+ mice with classical physiological techniques developed for the rat. We found that although AT2-/- mice have normal glomerular filtration rate, the pressure-natriuresis relationship in these mice, compared with AT2+/+ mice, is shifted rightward. Moreover, medullary blood flow fails to increase with increased perfusion pressure while the AT1 receptor expression in the kidneys is increased. We used telemetry and found that AT2-/- mice have about 10 mmHg higher blood pressures than AT2+/+ mice and that their circadian rhythm is disturbed. Moreover, their baroreflexes, as measured by spectral analyses, differs from AT2+/+ controls. The cardiac function of AT2-/- mice is remarkably preserved and the differences are subtle. However, if the mice are given l-NAME hypertension, they exhibit an end-systolic pressure-volume relationship that reveals decreased contractility and probable increased vascular stiffness. Furthermore, the hearts of AT2-/- mice hypertrophy more in response to l-NAME than those of AT2+/+ mice and perivascular fibrosis is increased. DOCA-salt treatment also shows a more rightward pressure-natriuresis relationship in AT2-/- compared with AT2+/+ mice. The renal iNOS expression is increased with DOCA-salt treatment. Our findings support the notion that the AT2 receptor signals antiproliferative and antifibrotic effects and that its presence results in lower blood pressures and lesser responses to secondary forms of hypertension. Technical advances that have allowed us to adapt methods for the rat to the much smaller mouse have facilitated our studies.

Angiotensin II induces hypoxia-inducible factor-1 alpha in PC 12 cells through a posttranscriptional mechanism: role of AT2 receptors

BACKGROUND

Angiotensin II (ANG II) inhibits proliferation and induces differentiation in PC 12 cells via AT(2) receptor activation. Using differential display analysis, we previously isolated SM-20/PHD3 as a key factor, which is downregulated by ANG II treatment. Subsequently, it turned out that SM-20/PHD3 is a rat homologue of PHD3, a key prolyl hydroxylase involved in the initial steps fostering the degradation of hypoxia-inducible factor (HIF). The present study was undertaken to investigate whether the ANG-II-mediated suppression of SM-20/PHD3/PHD3 may be associated with an increase in HIF-1 alpha.

METHODS

HIF-1 alpha protein expression was assessed by Western blots. mRNA levels for HIF-1 alpha were measured by real-time PCR and for SM-20/PHD3 by Northern blots. Binding of HIF-1 alpha to consensus oligonucleotides in vitro was determined with gel shift analysis. SM-20/PHD3 was transiently overexpressed in PC 12 cells using an inducible expression system.

RESULTS

ANG II stimulated HIF-1alpha protein expression. This effect was already detected after 30 min and peaked at 6 h, but was not detectable anymore after 24- 48 h of stimulation. PD 123177, but not losartan, antagonized this effect, indicating transduction through AT(2) receptors. Real-time PCR failed to show a significant increase in HIF-1 alpha transcripts after ANG II challenge at any time point. Gel shift analysis revealed that ANG-II-induced nuclear HIF-1 alpha protein binds to consensus sites. A reduction in SM-20/PHD3 mRNA expression paralleled the increase in HIF-1 alpha. Overexpression of SM-20/PHD3 transiently resulted in a decrease in HIF-1 alpha protein concentrations under basal conditions as well as after stimulation with ANG II.

CONCLUSION

ANG II stimulates HIF-1 alpha expression by a posttranscriptional mechanism via AT(2) receptors. This increase is likely caused by a downregulation of SM-20/PHD3. The ANG-II-mediated increase in HIF-1 alpha expression could be potentially involved in physiological as well as pathophysiological processes such as differentiation, growth inhibition, and remodeling.

Cardiac hypertrophy and fibrosis in chronic l-NAME-treated AT2 receptor-deficient mice

BACKGROUND

The role of angiotensin II type 1 (AT1) and type 2 (AT2) receptors in cardiac hypertrophy and fibrosis is incompletely understood. The availability of AT2 receptor-deficient mice (AT2 -/y) makes it possible to study the effects of AT1 receptors without the confounding influence of AT2 receptor activity.

OBJECTIVE

To test the hypothesis that the AT2 receptor affords protection from left ventricular hypertrophy and fibrosis in chronic hypertension induced by N-nitro-L-arginine methyl ester (L-NAME).

DESIGN

Four groups of mice were studied over a period of 3 weeks: AT2 -/y mice with and without L-NAME, and AT2 +/y mice with and without L-NAME.

METHODS

Blood pressure and heart rate were monitored by telemetry in groups of AT2 +/y and AT2 -/y mice for 4 weeks. L-NAME groups received the compound in drinking water for the last 3 weeks. We determined left ventricular AT1 receptor expression, cardiac hypertrophy and fibrosis, with and without L-NAME treatment. We used a miniaturized conductance-manometer system to measure pressure-volume loops at the time when the animals were killed.

RESULTS

AT2 -/y mice treated with L-NAME showed worse left ventricular hypertrophy, more perivascular fibrosis and greater concentrations of brain natriuretic peptide than did AT2 +/y mice treated with L-NAME. The end-systolic pressure-volume relationship, an index of left ventricular contractility, was decreased in AT2 -/y mice treated with L-NAME.

CONCLUSIONS

The AT2 receptor is not essential for development of L-NAME-induced cardiac hypertrophy, fibrosis and concomitant changes in left ventricular performance. In contrast, the AT2 receptor offers a protective effect.

Regulation of the SM-20 prolyl hydroxylase gene in smooth muscle cells

SM-20 encodes an intracellular prolyl hydroxylase that acts on hypoxia inducible factor (HIF)-1alpha, targeting it for proteasomal degradation. By decreasing HIF-alpha, SM-20 is thought to modulate the expression of hypoxia-regulated genes. SM-20 expression in the arterial wall is restricted to smooth muscle cells, which play a critical role in atherosclerosis and arterial injury. To further elucidate the regulation of SM-20 in smooth muscle, we cloned and analyzed the rat SM-20 promoter. In transient transfections, the SM-20 promoter displayed approximately 6-fold greater activity in smooth muscle cells vs. fibroblasts. Deletion analysis and electrophoretic mobility shift assays demonstrated that SM-20 transcription was regulated by two Sp1/Sp3 sites. A shift in binding to the Sp1/Sp3 sites, a decrease in Sp1 and Sp3 protein levels, and the emergence of a lower molecular weight form of Sp1 were seen in serum-deprived or post-confluent SMC, suggesting that SM-20 is regulated during smooth muscle cell differentiation.

Angiotensin II and Cell Cycle Regulation

Angiotensin II has emerged as an important growth factor for vascular, cardiac, and renal cells. Depending on the specific cell type and presence of other growth factors, angiotensin II induces proliferation (replication of DNA with subsequent successful division of cells), hypertrophy (increase in cell size, cell protein, and mRNA content without DNA replication), apoptosis (programmed cell death), or differentiation. Such angiotensin II-mediated modulation of growth process may underlie various pathophysiological processes such as atherosclerosis, vascular and cardiac remodeling, and progression of chronic renal disease. Clearly, angiotensin II-induced proliferation requires complete cell progression through the various steps of the cell cycle. In contrast, cells undergoing angiotensin II-mediated hypertrophy are arrested in the G1-phase. Upregulation of cell cycle-dependent kinase inhibitors (eg, p27Kip1) plays an important role in this process. Although accumulating evidence suggests that apoptosis is cell cycle-dependent, only few data are currently available concerning the interaction of angiotensin II with the cell cycle machinery in apoptosis. We review the various angiotensin II-mediated growth processes and their relationship to events governing cell cycle regulation.

Angiotensin II-induced hypertrophy of proximal tubular cells requires p27Kip1

BACKGROUND

Angiotensin II (Ang II), as a single factor, induces hypertrophy of cultured proximal tubular cells of various species. Cells undergoing hypertrophy are arrested in the G1 phase of the cell cycle. Ang II also stimulated the expression of p27Kip1, an inhibitor of cyclin-dependent kinases (CDK). Although previous studies inhibiting p27Kip1 expression with antisense oligonucleotides suggested that this CDK inhibitor is important for Ang II-induced hypertrophy of proximal tubular cells, nonspecific effects of antisense technology, and the inability to transfect 100% of cells raised concerns about the true role of p27Kip1 in tubular hypertrophy.

METHODS

Proximal tubular cells were isolated and cultured from wild-type (p27Kip1+/+) and knockout (p27Kip1-/-) mice. p27Kip1 genomic and protein expression was evaluated. Proximal tubular cell origin was confirmed by expression of various markers [3M-1 antigen, gamma-glutamyltransferase, angiotensin-converting enzyme (ACE)]. Cell proliferation (cell number, 3[H]thymidine incorporation) and hypertrophy (de novo protein synthesis as measured by 3[H]leucine incorporation, hypertrophy index, cell size) were evaluated. CDK2 and CDK4 activities were determined by an in vitro kinase assay. In addition, cell cycle analysis was performed by flow cytometry. p27Kip1 expression was reconstituted in two different clones of p27Kip1-/- proximal tubular cells using an inducible vector system based on ecdysone response elements.

RESULTS

In accordance with previous studies, 10-7 mol/L Ang II induces hypertrophy and cell cycle arrest of p27Kip1+/+ proximal tubular cells. In contrast, Ang II facilitated cell cycle progression of two p27Kip1-/- proximal tubular cell lines without inducing hypertrophy. Ang II activates CDK4/cyclin D kinase activity in p27Kip1+/+ and -/- tubular cells, but stimulates CDK2/cyclin E activity only in wild-type cells. However, in the presence of Ang II, reconstituting p27Kip1 expression in p27Kip1-/- tubular cells using an inducible expression system, restored G1 phase arrest and the hypertrophic phenotype. Ang II did not induce apoptosis of either p27Kip1+/+ or -/- tubular cells.

CONCLUSION

Our findings are the first clear evidence that p27Kip1 is required for Ang II-induced hypertrophy of proximal tubular cells. However, although p27Kip1 expression is an absolute requirement for this hypertrophy, reconstitution experiments revealed that other factors induced by Ang II contribute to this hypertrophy.

Heme oxygenase-1 gene expression attenuates angiotensin II-mediated DNA damage in endothelial cells

Heme oxygenase (HO) catalyzes the conversion of heme to biliverdin with the release of iron and carbon monoxide. HO-1 is inducible by inflammatory conditions, which cause oxidative stress in endothelial cells. Overexpression of human HO-1 in endothelial cells may have the potential to provide protection against a variety of agents that cause oxidative stress. We investigated the physiological significance of human HO-1 overexpression using a retroviral vector on attenuation of angiotensin II (Ang II)-mediated oxidative stress. Comet and glutathione (GSH) levels were used as indicators of the levels of oxidative stress. Comet assay was performed to evaluate damage on DNA, whereas GSH levels were measured to determine the unbalance of redox potential. Pretreatments with inducers, such as heme 10 microM, SnCl(2) 10 microM, and inhibitors, such as tin-mesoporphyrin 10 microM was followed by treatment with Ang II 200 ng/ml. Pretreatment with heme or SnCl(2) provoked significant reductions (P < 0.01) of tail moment in the comet assay. Opposite effects were evident by pretreatment for 16 hr with tin-mesoporphyrin. A decrease in tail moment levels was found in human endothelial cells transduced with the human HO-1 gene. The addition of Ang II (200 ng/ml) to human dermal microvessel endothelial cell-1 for 16 hr resulted in a significant (P < 0.05) reduction of GSH contents control endothelial cells but not in endothelial cells transduced with HO-1 gene. The results presented indicated that stimulation or overexpression of HO-1 attenuated DNA damages caused by exposures of Ang II.

Induction of SM-20 in PC12 cells leads to increased cytochrome c levels, accumulation of cytochrome c in the cytosol, and caspase-dependent cell death

Sympathetic neurons deprived of nerve growth factor (NGF) release cytochrome c into the cytosol and undergo caspase-dependent cell death through a process that requires de novo gene expression. Expression of the SM-20 gene increases after NGF withdrawal, and ectopic SM-20 expression induces cell death in NGF-maintained neurons. To further evaluate the mechanism by which SM-20 promotes cell death, we developed a PC12-derived cell line in which SM-20 expression can be induced by addition of doxycycline to the culture medium. Induction of SM-20 in either undifferentiated or NGF-differentiated cells resulted in cell death. Cell death was accompanied by an increase in caspase activity and was inhibited by the caspase inhibitor zVAD-FMK. Analysis of cytochrome c in cytosolic and mitochondria-enriched subcellular fractions revealed that induction of SM-20 led to the accumulation of cytochrome c in the cytosol. Surprisingly, SM-20 expression also resulted in a selective increase in the total amount of cytochrome c protein. Thus, induction of SM-20 expression appears to affect both the amount and subcellular localization of cytochrome c in PC12 cells. These results suggest that SM-20 promotes caspase-dependent cell death through a mechanism involving cytochrome c.