Angiotensin III stimulates ERK1/2 mitogen-activated protein kinases and astrocyte growth in cultured rat astrocytes

Roles of Angiotensin III in the brain and periphery

Angiotensin (Ang) III, a biologically active peptide of the renin angiotensin system (RAS) is predominantly known for its central effects on blood pressure. Our understanding of the RAS has evolved from the simplified, classical RAS, a hormonal system regulating blood pressure to a complex system affecting numerous biological processes. Ang II, the main RAS peptide has been widely studied, and its deleterious effects when overexpressed is well-documented. However, other components of the RAS such as Ang III are not well studied. This review examines the molecular and biological actions of Ang III and provides insight into Ang III's potential role in metabolic diseases.

A Systems-Based Map of Human Brain Cell-Type Enriched Genes and Malignancy-Associated Endothelial Changes

Changes in the endothelium of the cerebral vasculature can contribute to inflammatory, thrombotic, and malignant disorders. The importance of defining cell-type-specific genes and their modification in disease is increasingly recognized. Here, we develop a bioinformatics-based approach to identify normal brain cell-enriched genes, using bulk RNA sequencing (RNA-seq) data from 238 normal human cortex samples from 2 independent cohorts. We compare endothelial cell-enriched gene profiles with astrocyte, oligodendrocyte, neuron, and microglial cell profiles. Endothelial changes in malignant disease are explored using RNA-seq data from 516 lower-grade gliomas and 401 glioblastomas. Lower-grade gliomas appear to be an "endothelial intermediate" between normal brain and glioblastoma. We apply our method for the prediction of glioblastoma-specific endothelial biomarkers, providing potential diagnostic or therapeutic targets. In summary, we provide a roadmap of endothelial cell identity in normal and malignant brain, using a method developed to resolve bulk RNA-seq into constituent cell-type-enriched profiles.

Angiotensin III induces p38 Mitogen-activated protein kinase leading to proliferation of vascular smooth muscle cells

BACKGROUND

Mitogen-activated protein kinases (MAPKs) are essential molecular transducers of extracellular stimuli into intracellular responses. MAPKs are crucial in mediating actions of the renin-angiotensin-aldosterone system (RAAS), in particular, functions mediated by Angiotensin (Ang) II, the main biological peptide produced by this system. We have shown that another biologically active heptapeptide Ang III also induces MAPKs in the central nervous system. The ability of Ang III to induce MAPKs in the periphery is unknown and was the focus of this study.

METHODS

We determined whether Ang III induced p38 MAPK in vascular smooth cells (VSMCs) isolated from Wistar and spontaneously hypertensive rats (SHRs) and compared these actions to those of Ang II. Further, the role of this MAPK in Ang III-mediated VSMC proliferation was also determined.

RESULTS

Both Ang peptides similarly induced p38 MAPK phosphorylation in VSMCs of Wistar VSMCs in a concentration- and time-dependent manner. SHR VSMCs were less sensitive to Ang III, which caused less of an effect on p38 MAPK phosphorylation in these cells. The Ang III effect was specific and occurred by activation of the Ang type 1 (AT1) receptor. The p38 MAPK pathway was also involved in Ang III-induced VSMC growth, as measured by DNA synthesis.

CONCLUSIONS

These findings suggest that the p38 MAPK signaling pathway is an important cascade in regulating the actions of Ang III in VSMCs. Most importantly, dysregulation of Ang III actions in these cells are apparent and may contribute to pathological conditions associated with dysfunctions in VSMCS.

Effects of angiotensin III on c-Jun N terminal kinase in Wistar and hypertensive rat vascular smooth muscle cells

Proliferation of vascular smooth muscle cells (VSMCs) and inflammation are well known actions associated with hypertension. Angiotensin (Ang) II mediates these physiological actions through the c-Jun N terminal Kinase (JNK), mitogen-activated proteins kinase (MAPK) pathway. Ang III effects on this pathway in VSMCs are unknown. The aim of this study was to determine whether Ang III activates JNK MAPK in Wistar VSMCs and determined whether the response was different in spontaneously hypertensive rat (SHR) VSMCs. We also ascertained whether this effect leads to VSMC proliferation. Western blots were used to determine the time and concentration effects of Ang II on JNK MAPK phosphorylation in Wistar VSMCs. Similar studies were conducted for Ang III in Wistar and SHR VSMCs. Both peptides induced JNK phosphorylation in a concentration- and time-dependent manner in Wistar VSMCs. Ang III also increased JNK phosphorylation in a concentration- and time-dependent fashion in SHR VSMCs as well. However, the ability of Ang III to induce JNK MAPK was different in SHR VSMCs as the phosphorylation levels of JNK were significantly higher in Wistar VSMCs as compared to SHR VSMCs at several time points and concentrations. Further, Ang III-mediated DNA synthesis, a measure of VSMC proliferation, occurred through activation of JNK MAPK. This study is the first to show Ang III effects on the JNK MAPK pathway in VSMCs and the role of JNK in Ang III-mediated cellular proliferation. These findings impart key information for the understanding of Ang III functions, especially in VSMCs and possible cardiovascular diseases.

Angiotensin III Induces JAK2/STAT3 Leading to IL-6 Production in Rat Vascular Smooth Muscle Cells

The Janus kinase-2/ signal transducer and activators of transcription-3 (JAK2/STAT3) pathway and interleukin-6 (IL-6) are pleiotropic signal transduction systems that are responsible for induction of many cytokines and growth factors. It is unknown whether the renin angiotensin aldosterone system (RAAS) peptide, angiotensin (Ang) III induces JAK2/STAT3 and IL-6 in vascular smooth muscle cells (VSMCs). Thus, the purpose of this study was to investigate whether Ang III induces the JAK2/STAT3 pathway leading to IL-6 production in cultured VSMCs isolated from Wistar rats and determine whether differences exist in spontaneously hypertensive rat (SHR) VSMCs. We gauged Ang III’s effects on this pathway by measuring its action on STAT3 as well as IL-6 production. Ang III behaved similarly as Ang II in stimulation of STAT3 phosphorylation in Wistar and SHR VSMCs. Moreover, there were no differences in this Ang III effect in SHR versus Wistar VSMCs. In Wistar VSMCs, Ang II and Ang III significantly induced IL-6 protein secretion and mRNA expression. However, IL-6 protein secretions mediated by these peptides were significantly greater in SHR VSMCs. Ang III induced the JAK2/STAT3 pathway, leading to IL-6 protein secretion and IL-6 mRNA expression via actions on AT₁Rs. Moreover, the actions of Ang III to induce IL-6 production was dysregulated in SHR VSMCs. These findings suggest that Ang III acts on AT₁Rs to induce JAK2/STAT3, leading to an increase in IL-6 in cultured VSMCs. These findings are important in establishing Ang III as an important physiologically relevant peptide in VSMCs.

Angiotensin II induces cyclooxygenase 2 expression in rat astrocytes via the angiotensin type 1 receptor

We previously showed that Angiotensin (Ang) II stimulated pro-inflammatory and mitogenic actions in astrocytes suggesting that astrocytes are emerging as key players in neuroinflammation. Evidence suggests that neuroinflammation may contribute to central sympathetic overactivity and elevated blood pressure. Further, cyclooxygenase (Cox)-derived prostanoids were implicated in Ang II-dependent hypertension. Cox2 is one of two Cox isoenzymes that is responsible for the formation of prostanoids from arachidonic acid. Constitutively expressed Cox2 has a protective and homeostatic role in the cardiovascular and renal systems. Inducible Cox2 has been associated with pathogenic stimuli resulting in inflammatory conditions and cancers. In this study, we investigated the effect of Ang II on Cox2 protein and mRNA expression in brainstem and cerebellum astrocytes, and determined whether any differences in Cox2 expression exist in spontaneously hypertensive rat (SHR) astrocytes compared to their normotensive control Wistar rats. We demonstrated that Ang II increased Cox2 protein and mRNA levels relative to untreated controls in a time-dependent manner, in Wistar and SHR brainstem and cerebellum astrocytes. Increases in Cox2 protein expression were evident within 4 h, with subsequent sustained elevation for several hours followed by a decline at 48 h. Ang II-induced Cox2 protein levels were higher in Wistar compared to SHRs in both brainstem and cerebellum astrocytes for the majority of time points examined. The Ang II-induced Cox2 mRNA levels increased within 8 h followed by a rapid decline to almost basal levels at later time points. At the earlier time points, Cox2 mRNA elevation were higher in SHR compared to Wistar rat astrocytes. These Ang II actions were mediated by the Ang type I receptor. Our results corroborate previous reports of Ang II's ability to stimulate neuroinflammatory mediators in astrocytes. Cox2-derived prostaglandins might play a role in brain-renin angiotensin system associated hypertension, and astrocytes could be significant players.

Pharmacological stimulation of sigma-1 receptor promotes activation of astrocyte via ERK1/2 and GSK3β signaling pathway

Astrocyte is considered to be a type of passive supportive cells that preserves neuronal activity and survival. The dysfunction of astrocytes is involved in the pathological processes of major depression. Recent studies implicate sigma-1 receptors as putative therapeutic targets for current available antidepressant drugs. However, it is absent of direct evidences whether sigma-1 receptor could promote activation of astrocyte. In the present study, we took advantage of primary astrocyte culture and a highly selective agonist of sigma-1 receptor, (+)SKF-10047 to determine the effect of sigma-1 receptor on Brdu (bromodeoxyuridine) labeling positive cells, migration as well as GFAP (glial fibrillary acidic protein) expression of astrocyte. The results showed that (+)SKF-10047 notably increased the number of Brdu labeling positive cells, migration, and the expression of GFAP in primary astrocytes, which were blocked by antagonist of sigma-1 receptor. Moreover, we also found that (+)SKF-10047 increased the phosphorylation of ERK1/2 (extracellular signal-regulated kinases 1/2) and GSK3β (glycogen synthase kinase 3β) (ser 9) in the primary astrocytes. In addition, pharmacological inhibition of ERK1/2 and GSK3β (ser 9) abolished sigma-1 receptor-promoted activation of astrocyte. Therefore, sigma-1 receptor could be considerate as a new pattern for modulating astrocytic function might emerge as therapeutic strategies.

Dopamine modulates astroglial and microglial activity via glial renin-angiotensin system in cultures

Dopamine is an immunomodulatory molecule that acts on immune effector cells both in the CNS and peripheral tissues. However, the role of changes in dopamine levels in the neuroinflammatory response is controversial. The local/paracrine renin-angiotensin system (RAS) plays a major role in inflammatory processes in peripheral tissues and brain. In the present study, we investigated the possible role of the brain RAS in the effects of dopamine on the glial inflammatory responses. Astrocytes are the major source of the precursor protein angiotensinogen and angiotensin II (AII) in the brain. Neurotoxins such as MPP⁺ (1-methyl-4-phenylpyridinium) can act directly on astrocytes to increase levels of angiotensinogen and AII. Conversely, dopamine, via type-2 (D2) receptors, inhibited production of angiotensinogen, decreased expression of angiotensin type-1 (AT1) receptors and increased expression of AT2 receptors. In microglia, dopamine and dopamine agonists also regulated RAS activity. First, indirectly, via downregulation of the astrocyte-derived AII. Second, via dopamine-induced regulation of microglial angiotensin receptors. Dopamine decreased the microglial AT1/AT2 ratio leading to inhibition of the pro-inflammatory AT1/NADPH-oxidase/superoxide axis. D2 receptors were particularly responsible for microglial RAS inhibition in basal culture conditions. However, both D1 and D2 agonists inhibited the AT1/NADPH-oxidase axis in lipopolysaccharide-treated (LPS; i.e. activated) microglia. The results indicate that the decrease in dopamine levels observed in early stages of Parkinson's disease and aging may promote neuroinflammation and disease progression via glial RAS exacerbation.

Angiotensin III induces signal transducer and activator of transcription 3 and interleukin-6 mRNA levels in cultured rat astrocytes

INTRODUCTION

Recently we established that pro-inflammatory actions of angiotensin (Ang) II in astrocytes involved Janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), and interleukin-6 (IL-6).

MATERIALS AND METHODS

In our current study, we determined in brainstem and cerebellum whether Ang III also activates STAT3 leading to IL-6 mRNA expression and astrocyte proliferation.

RESULTS

Ang III induced STAT3 phosphorylation in a concentration- and time-dependent manner. Significant STAT3 phosphorylation was rapid and was maximal within 10 min, and with 100 nM Ang III. The Ang AT1 receptor was shown to mediate this action of Ang III. Ang III also significantly induced IL-6 mRNA expression within an hour, and maximal Ang III-mediated IL-6 mRNA expression occurred in the presence of 100 nM Ang III. Ang III-mediated IL-6 mRNA expression occurred by the interaction of the peptide with the Ang AT1 receptor and was mediated by STAT3. In addition, STAT3 was shown to mediate Ang III astrocyte proliferation.

CONCLUSIONS

These findings suggest that Ang III, similar to Ang II, has pro-inflammatory effects since it induces STAT3 leading to an induction of IL-6 mRNA expression, outcomes that lend relevance to the physiological importance of central Ang III.

Angiotensin III: a physiological relevant peptide of the renin angiotensin system

The renin angiotensin system (RAS) is a peptide hormone system that plays an important role in the pathophysiology of various diseases, including congestive heart failure, hypertension, myocardial infarction, and diabetic nephropathy. This has led researchers to focus extensively on this system, leading to the discovery of various peptides, peptidases, receptors and signal transduction mechanisms intrinsic to the RAS. Angiotensinogen (AGT), angiotensin (Ang) II, Ang III, Ang IV, and Ang-(1-7) are the main biologically active peptides of RAS. However, most of the available studies have focused on Ang II as the likely key peptide from the RAS that directly and indirectly regulates physiological functions leading to pathological conditions. However, data from recent studies suggest that Ang III may produce physiologically relevant effects that are similar to those produced by Ang II. Hence, this review focuses on Ang III and the myriad of physiological effects that it produces in the body.

Distinct Molecular Effects of Angiotensin II and Angiotensin III in Rat Astrocytes

It is postulated that central effects of angiotensin (Ang) II may be indirect due to rapid conversion to Ang III by aminopeptidase A (APA). Previously, we showed that Ang II and Ang III induced mitogen-activated protein (MAP) kinases ERK1/2 and stress-activated protein kinase/Jun-terminal kinases (SAPK/JNK) phosphorylation in cultured rat astrocytes. Most importantly, both peptides were equipotent in causing phosphorylation of these MAP kinases. In these studies, we used brainstem and cerebellum astrocytes to determine whether Ang II's phosphorylation of these MAP kinases is due to the conversion of the peptide to Ang III. We pretreated astrocytes with 10  μ M amastatin A or 100  μ M glutamate phosphonate, selective APA inhibitors, prior to stimulating with either Ang II or Ang III. Both peptides were equipotent in stimulating ERK1/2 and SAPK/JNK phosphorylation. The APA inhibitors failed to prevent Ang II- and Ang III-mediated phosphorylation of the MAP kinases. Further, pretreatment of astrocytes with the APA inhibitors did not affect Ang II- or Ang III-induced astrocyte growth. These findings suggest that both peptides directly induce phosphorylation of these MAP kinases as well as induce astrocyte growth. These studies establish both peptides as biologically active with similar intracellular and physiological effects.

Angiotensins inhibit cell growth in GH3 lactosomatotroph pituitary tumor cell culture: a possible involvement of the p44/42 and p38 MAPK pathways

The local renin-angiotensin system is present in the pituitary. We investigated the effects of angiotensins on GH3 lactosomatotroph cells proliferation in vitro and the involvement of p44/42 and p38 MAPK inhibitors in the growth-regulatory effects of angiotensins. Materials and Methods. Cell viability using the Mosmann method and proliferation by the measurement of BrdU incorporation during DNA synthesis were estimated. Results. Ang II and ang IV decreased the viability and proliferation of GH3 cells. Inhibitor of p44/42 MAPK attenuated the effects of ang II on cell viability and proliferation but did not affect the ang 5-8-dependent actions. Inhibitor of p38 MAPK prevented the decrease in the number of GH3 cells in ang-II- and ang-IV-treated groups. Conclusions. The growth-inhibitory effect of ang II is possibly mediated by the p44/42 MAPK. The p38 MAPK appears to mediate the inhibitory effects of both ang II and ang 5-8 upon cell survival.