The cardiovascular and other actions of angiotensin II (Ang II) are mediated by AT(1) and AT(2) receptors, which are seven transmembrane glycoproteins with 30% sequence similarity. Most species express a single autosomal AT(1) gene, but two related AT(1A) and AT(1B) receptor genes are expressed in rodents. AT(1) receptors are predominantly coupled to G(q/11), and signal through phospholipases A, C, D, inositol phosphates, calcium channels, and a variety of serine/threonine and tyrosine kinases. Many AT(1)-induced growth responses are mediated by transactivation of growth factor receptors. The receptor binding sites for agonist and nonpeptide antagonist ligands have been defined. The latter compounds are as effective as angiotensin converting enzyme inhibitors in cardiovascular diseases but are better tolerated. The AT(2) receptor is expressed at high density during fetal development. It is much less abundant in adult tissues and is up-regulated in pathological conditions. Its signaling pathways include serine and tyrosine phosphatases, phospholipase A(2), nitric oxide, and cyclic guanosine monophosphate. The AT(2) receptor counteracts several of the growth responses initiated by the AT(1) and growth factor receptors. The AT(4) receptor specifically binds Ang IV (Ang 3-8), and is located in brain and kidney. Its signaling mechanisms are unknown, but it influences local blood flow and is associated with cognitive processes and sensory and motor functions. Although AT(1) receptors mediate most of the known actions of Ang II, the AT(2) receptor contributes to the regulation of blood pressure and renal function. The development of specific nonpeptide receptor antagonists has led to major advances in the physiology, pharmacology, and therapy of the renin-angiotensin system.

https://pharmrev.aspetjournals.org/content/pharmrev/52/3/415.full.pdf

International Union of Pharmacology. XXIII. The Angiotensin II Receptors

The ability to safely and efficiently transfer foreign DNA into cells is a fundamental goal in biotechnology. Toward this end, rapid advances have recently been made in our understanding of mechanisms for DNA stability and transport within cells. Current synthetic DNA delivery systems are versatile and safe, but substantially less efficient than viruses. Indeed, most current systems address only one of the obstacles to DNA delivery by enhancing DNA uptake. In fact, the effectiveness of gene expression is also dependent on several additional factors, including the release of intracellular DNA, stability of DNA in the cytoplasm, unpackaging of the DNA-vector complex, and the targeting of DNA to the nucleus. Delivery systems of the future must fully accommodate all these processes to effectively shepherd DNA across the plasma membrane, through the hostile intracellular environment, and into the nucleus.

Synthetic DNA delivery systems.

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Physiology of local renin-angiotensin systems.

Swynghedauw, Bernard. Molecular Mechanisms of Myocardial Remodeling. Physiol. Rev. 79: 215–262, 1999. — “Remodeling” implies changes that result in rearrangement of normally existing structures. Th...

Molecular Mechanisms of Myocardial Remodeling

The incidence of the metabolic syndrome has taken epidemic proportions in the past decades, contributing to an increased risk of cardiovascular disease and diabetes. The metabolic syndrome can be d...

Role of Bile Acids and Bile Acid Receptors in Metabolic Regulation

The type 1 angiotensin II (AT1) receptor is well characterized but the type 2 (AT2) receptor remains an enigma. We tested the hypothesis that the AT2 receptor can modulate the growth of vascular smooth muscle cells by transfecting an AT2 receptor expression vector into the balloon-injured rat carotid artery and observed that overexpression of the AT2 receptor attenuated neointimal formation. In cultured smooth muscle cells, AT2 receptor transfection reduced proliferation and inhibited mitogen-activated protein kinase activity. Furthermore, we demonstrated that the AT2 receptor mediated the developmentally regulated decrease in aortic DNA synthesis at the latter stages of gestation. These results suggest that the AT2 receptor exerts an antiproliferative effect, counteracting the growth action of AT1 receptor.

https://www.pnas.org/content/pnas/92/23/10663.full.pdf

The angiotensin II type 2 (AT2) receptor antagonizes the growth effects of the AT1 receptor: gain-of-function study using gene transfer

Background The availability of selective antagonists for angiotensin II receptors has focused interest on the gene expression of angiotensin II–receptor subtypes in the human heart. Methods and Res...

AT1 and AT2 Angiotensin Receptor Gene Expression in Human Heart Failure

The application of gene therapy to human disease is currently restricted by the relatively low efficiency and potential hazards of methods of oligonucleotide or gene delivery. Antisense or transcription factor decoy oligonucleotides have been shown to be effective at altering gene expression in cell culture expreriments, but their in vivo application is limited by the efficiency of cellular delivery, the intracellular stability of the compounds, and their duration of activity. We report herein the development of a highly efficient method for naked oligodeoxynucleotide (ODN) transfection into cardiovascular tissues by using controlled, nondistending pressure without the use of viral vectors, lipid formulations, or exposure to other adjunctive, potentially hazardous substances. In this study, we have documented the ability of ex vivo, pressure-mediated transfection to achieve nuclear localization of fluorescent (FITC)-labeled ODN in approximately 90% and 50% of cells in intact human saphenous vein and rat myocardium, respectively. We have further documented that pressure-mediated delivery of antisense ODN can functionally inhibit target gene expression in both of these tissues in a sequence-specific manner at the mRNA and protein levels. This oligonucleotide transfection system may represent a safe means of achieving the intraoperative genetic engineering of failure-resistant human bypass grafts and may provide an avenue for the genetic manipultation of cardiac allograft rejection, allograft vasculopathy, or other transplant diseases.

Pressure-mediated oligonucleotide transfection of rat and human cardiovascular tissues.

Objective: While natriuretic peptides can inhibit growth of vascular smooth muscle cells (VSMC), controversy exists as to whether this effect is mediated via the guanylate cyclase-coupled receptors, NPR-A and NPR-B, or the clearance receptor, NPR-C. The original aim of this study was to examine the mechanism by which the NPR-C receptor regulates growth. Methods: Rat VSMC were characterized with regard to natriuretic peptide receptor expression by RT/PCR and radioligand binding studies. The effect on growth following addition of the peptides and the ligands for NPR-C was measured by [3H]thymidine incorporation. Cyclic guanosine monophosphate (cGMP) levels were determined by radioimmunoassay and mitogen activating protein kinase activity was based on the phosphorylation of myelin basic protein. Results: In rat VSMC, passages 4–12, both atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) dose-dependently inhibited serum and PDGF-induced VSMC growth. In contrast, NPR-C specific ligands alone had no effect on cell growth but enhanced growth inhibition when co-administered with ANP and CNP. ANP and CNP also decreased PDGF-BB-stimulated MAP kinase activity. Once again, NPR-C specific ligands alone had no effect but enhanced the effects of ANP. Furthermore, a cGMP specific phosphodiesterase inhibitor dose-dependently inhibited VSMC growth and markedly enhanced natriuretic-peptide-induced inhibition at low peptide concentrations. To examine a potential mechanism for the controversy concerning the NPR-C, we investigated the autocrine expression of ANP and CNP by VSMC and found that mRNA encoding both peptides could be detected by RT/PCR. Conclusion: Our findings indicate that the guanylyl-cyclase-linked receptors mediate the antiproliferative actions of the natriuretic peptides on vascular smooth muscle cell growth. Moreover, we hypothesize that the apparent inhibition of growth by NPR-C specific ligands reported by others may be due to stabilization of natriuretic peptides produced by the cultured VSMC and subsequent action of these peptides at guanylyl-cyclase-linked receptors.

/pdf/mechanisms-of-natriuretic-peptide-induced-growth-inhibition-nral4hxj9h.pdf

Mechanisms of natriuretic-peptide-induced growth inhibition of vascular smooth muscle cells

Objective: To examine the exact profile of expression and to determine the functional significance of the angiotensin II (Ang II), type 1 (AT1) and type 2 (AT2) receptors during rat aortic development and following rat carotid artery balloon injury. Methods: AT1 and AT2 mRNA levels in rat aortae were measured using a quantitative reverse transcription polymerase chain reaction technique. Ang II receptor function was assessed by quantitating the effects of AT1 (DuP753) and AT2 (PD123319) receptor antagonists during these processes. Results: During aortic development, AT1 expression was detected on gestational day 14, increased until embryonic day 16 (E16), after which, levels were similar throughout postnatal development. Conversely, AT2 mRNA first appeared at E16, reached maximal levels between E19 and neonatal day 1, and decreased thereafter. DNA synthesis rates decreased with aortic development (high at E15, 73.8±3.1%; dropping to 37.5±2.3% by E21). Whereas AT1 receptor antagonism accelerated this developmentally regulated decrease in DNA synthesis, AT2 receptor antagonism blunted this decrease. Because activated adult medial smooth muscle cells express a neonatal phenotype after vascular injury, we assessed Ang II receptor levels and function after carotid artery balloon injury. Both receptor subtypes increased; however, AT2 receptor mRNA expression peaked earlier than AT1 (48 to 72 h after injury). As with aortic development, DNA synthesis occurring between 24 to 48 h after injury (when AT2 receptors constitute 10% of the Ang II receptor population) decreased in DuP753-treated animals and increased in PD123319-treated animals. Conclusion: These results indicate that Ang II receptors play a role in vascular development by promoting opposing effects on vascular smooth muscle cell growth.

Howard G. Hutchinson

Papers

The angiotensin II type 2 (AT2) receptor antagonizes the growth effects of the AT1 receptor: gain-of-function study using gene transfer

AT1 and AT2 Angiotensin Receptor Gene Expression in Human Heart Failure

Pressure-mediated oligonucleotide transfection of rat and human cardiovascular tissues.

Mechanisms of natriuretic-peptide-induced growth inhibition of vascular smooth muscle cells

Modulation of vascular development and injury by angiotensin II