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Circulation Research. 2003;92:9-11
doi: 10.1161/01.RES.0000052920.70316.AE
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(Circulation Research. 2003;92:9.)
© 2003 American Heart Association, Inc.

Editorials

Angiotensin II

A Vasoactive Hormone With Ever-Increasing Biological Roles

Mark B. Taubman

From the Zena and Michael A. Wiener Cardiovascular Institute and Department of Medicine, Mount Sinai School of Medicine, New York, NY.

Correspondence to Mark B. Taubman, Box 1269, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029. E-mail mark.taubman{at}mssm.edu


Key Words: angiotensin II • smooth muscle cells • arterial injury • gene array

Angiotensin II (Ang II) is an octapeptide hormone that plays a central role in cardiovascular homeostasis. Typical of many proteins, Ang II was named on the basis of its first-demonstrated biological function—the ability to act as a vasoactive agonist and induce contraction of blood vessels. Over the years, Ang II has been shown to play important roles in mediating hypertension, heart failure, cardiac remodeling, diabetes, and the proliferative and inflammatory responses to arterial injury (see review1). These findings have spawned the development of several classes of pharmacological agents designed at inhibiting the synthesis of Ang II (eg, angiotensin II-converting enzyme inhibitors) or blocking its action (eg, angiotensin II receptor antagonists). These agents are now widely used in the treatment of hypertension and congestive heart failure.

In conjunction with studies performed on animal models, there have been numerous studies examining the cellular effects of Ang II. Initial studies focused in particular on the role of Ang II as a contractile agonist and therefore on the signals induced by Ang II in vascular smooth muscle cells (SMCs) and cardiomyocytes associated with contraction, such as the mobilization of intracellular calcium ([Ca2+]i) and the activation of protein kinase C (PKC). It was demonstrated that Ang II activated phospholipase C, resulting in the production of inositol trisphosphate (IP3) and diacylglycerol, which in turn were responsible for the mobilization of [Ca2+]i and the activation of PKC, respectively. Additional studies in SMC cultures examined the properties of Ang II as a growth agonist, in particular its role in promoting cellular hypertrophy, characterized by increases in protein synthesis, cell size, and polyploidy.2,3

The cloning and expression of the Ang II receptor,4,5 together with substantial progress in signal transduction, have greatly expanded our knowledge of Ang II-mediated cellular events and have led to a complex model in which Ang II stimulates the production of reactive oxygen species and activates a myriad of intracellular signals, including the mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt, and JAK/STAT pathways (see reviews6,7). The diversity of Ang II-activated signaling strongly suggests that Ang II serves a multiplicity of functions distinct from its ability to promote contraction or induce cellular hypertrophy. Because many of these signals are known to be involved in regulating transcription, a logical approach to studying Ang II biology has been to identify genes regulated by Ang II.

Initial studies on identifying Ang II-responsive genes were in part driven by the evolving understanding of the roles of [Ca2+]i and PKC as upstream mediators of gene transcription and in part by the known role of Ang II in cell growth. The focus of these studies was on SMCs, the major contractile cells of the blood vessel wall. In culture, SMCs modulate from a quiescent, contractile phenotype associated with abundant actin- and myosin-containing filaments to a synthetic phenotype in which the contractile filaments have been largely replaced by endoplasmic reticulum.8 This phenotypically modulated SMC is similar in many respects to fibroblasts. It was therefore not surprising that a candidate gene approach focused on genes previously shown to be regulated by Ca2+ and PKC in cultured fibroblasts. These early studies demonstrated that Ang II induced c-fos, c-jun, and c-myc, proto-oncogenes that encode transcription factors that act in part as mediators of cell growth and differentiation (see review9). Additional studies using the candidate gene strategy determined that Ang II induced tissue factor, the initiator of coagulation and plasminogen activator inhibitor-1 (PAI-1), an inhibitor of fibrinolysis. This raised the possibility that Ang II could promote a procoagulant state, such as that associated with myocardial infarction, stroke, and peripheral arterial occlusive disease (see review10). Ang II was also shown to induce JE/MCP-1, interleukin-6, and KC/gro, chemokines that are important in recruiting leukocytes to sites of inflammation, thereby implicating Ang II as a proinflammatory molecule (see review11).

The success of signaling studies and candidate gene approaches in establishing Ang II as a broad-based cellular agonist has provided the impetus to undertake more comprehensive analyses of Ang II effects on gene induction. Several studies using the then state-of-the-art technique of differential hybridization identified lysyl oxidase, lactate dehydrogenase, osteopontin, thrombospondin, and an intracellular prolyl hydroxylase, originally designated as SM-20, as Ang II-responsive genes, further broadening the potential biological roles of Ang II, particularly in regard to modulating the extracellular matrix.12,13

The study by Campos et al14 in this issue of Circulation Research has used the current state-of-the-art technology, DNA microarray, to provide the most comprehensive analysis of Ang II-mediated gene induction to date. This study used a microarray containing 5088 genes and expressed sequence tags (ESTs) to examine cultured rat aortic SMCs treated with Ang II. As befitting any study using microarrays, considerable effort was expended on establishing the reproducibility of the system and on the data analysis, with several approaches used to ensure reasonable sensitivity and specificity. By t test, 91 genes were found to be regulated by >=1.5-fold by Ang II, whereas 97 genes were identified using the rank sum test. Many of these genes represent ESTs whose identities have not yet been established. In addition, a variety of genes not previously known to be Ang II-sensitive were identified, including calpactin I light chain and calpactin II, whose regulation by Ang II was confirmed by quantitative real-time PCR. This study has therefore greatly expanded the database of Ang II-responsive genes and will likely provide new insights into the biological roles of Ang II in smooth muscle. The present study used an array of {approx}5000 genes and ESTs, representing no more than 10% of the SMC transcripts. It is therefore likely that a screen representing the entire genome would have yielded close to 1000 Ang II-regulated genes.

Although the microarray approach identified several genes previously shown to be induced by Ang II, such as osteopontin, lactate dehydrogenase, and PAI-1, other Ang II-responsive genes, such as tissue factor, MCP-1, and c-fos, were not identified by this method. One relatively straightforward explanation is that these DNAs were not included in the microarray and would have been readily identified using a different array. More problematic however are the limitations posed by the SMC culture system. This study used rat aortic SMCs between passages 4 and 16. Postconfluent cells were incubated with 300 nmol/L of Ang II or vehicle for 6 hours. As discussed by the authors, 20 microarrays (11 control and 9 Ang II-treated) were required to provide statistically significant results. Even at this sample size, it was predicted that only 96% and 61% of the genes regulated by >=2.0-fold or >=1.5-fold by Ang II could be identified. Twenty-eight control-Ang II sets would have been necessary to identify all of the genes regulated by >=2.0-fold. Even using the less stringent requirements, it is impractical to use more than a few conditions to examine gene induction. The 6-hour treatment time point would not have been expected to identify early-response genes such as tissue factor, c-fos, or c-jun. Given the wealth of information on early-response genes and the relative lack of information on delayed-response genes, the 6-hour point chosen for the present study had a greater likelihood of providing novel information.

Another important choice in this study was the use of postconfluent multiple-passaged cultured cells. As noted earlier, cultured SMCs undergo phenotypic modulation to a proliferative and more dedifferentiated phenotype. As such, they are not highly representative of the quiescent, contractile SMCs found in the normal arterial wall. Unfortunately, there has been no reliable method to induce differentiation of cultured SMCs back to the contractile phenotype. One compromise has been to study cells at postconfluence under conditions in which they are relatively quiescent, as done in the present study. Such an approach also has the benefit of better reproducibility. A second approach would be to examine SMCs in primary culture, before passaging, or at the very earliest passages. Although these cells are presumably less modulated, the limitations on quantity at such early stages of culture, necessitating multiple preparations, and the vicissitudes of primary culture would likely create insurmountable problems with reproducibility.

A major concern of SMC biologists is whether studies using cell culture can be extrapolated to the normally quiescent and contractile cells of the intact arterial wall. It is likely that at least some of the genes identified by microarray technology using Ang II-treated cultured SMCs will not be responsive to Ang II in vivo. On the other hand, studies using models of arterial injury have provided strong corroboration for many cell culture studies. In response to arterial injury, SMCs undergo phenotypic modulation similar to that seen in culture.15 The proliferation and migration of SMCs are critical to the development of intimal hyperplasia in response to injury and are also key features of atherosclerotic plaque formation.16,17 A variety of SMC agonists, including platelet-derived growth factor (PDGF), fibroblast growth factor, and Ang II, have been implicated as mediators of intimal hyperplasia.18,19 In addition, the pattern of gene induction in arterial SMCs after acute arterial injury is similar to that seen in cultured SMCs treated with growth agonists, such as Ang II and PDGF. Several of the genes identified by the current microarray analysis have previously been shown to be inducible by arterial injury, including osteopontin,20 PAI-1,21 and tissue inhibitor of metalloproteinase-1 (TIMP-1).22 The present study used a well-established model of balloon injury to rat carotid arteries to demonstrate that calpactin I light chain is also induced in vivo. It is likely that other genes identified in this screening will be shown to be modulated similarly and may provide new insights into the molecular events associated with arterial injury, whether or not mediated in vivo by Ang II.

Although DNA microarray technology provides a powerful tool to understanding the protean manifestations of Ang II, it is likely that the results of such studies, no matter how comprehensive, will provide only a partial picture of the effects of Ang II on SMCs. As noted above, Ang II is a potent inducer of protein synthesis and activates a variety of kinases that are capable of posttranslational modifications (see reviews6,7). One would therefore expect that Ang II would modulate the amount or activity of a number of proteins independent of its effects on transcription. Such changes will require a proteomics-based approach. One such approach, reported by Patton et al,23 used two-dimensional gel electrophoresis to identify proteins phosphorylated in response to Ang II and PDGF. This approach identified a dozen proteins regulated by Ang II, including molecular chaperones and those involved with protein folding. These proteins were not overlapping with those found using RNA-based technologies, nor were they identified as yet in the current microarray analysis. In the same way that microarray techniques provide considerably more power than the early DNA hybridization studies, recent advances in proteomics should also provide far more powerful approaches to identifying proteins modulated by Ang II. Together with genomics, this should provide a comprehensive picture of the effects of Ang II on cellular function and further support the notion that the term "angiotensin" represents only the tip of the iceberg in describing a protein that has numerous important biological roles in the cardiovascular system.

Footnotes

The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.

References

  1. Ruiz-Ortega M, Lorenzo O, Ruperez M, Esteban V, Suzuki Y, Mezzano S, Plaza JJ, Egido J. Role of the renin-angiotensin system in vascular diseases: expanding the field. Hypertension. 2001; 38: 1382–1387.[Abstract/Free Full Text]
  2. Geisterfer AA, Peach MJ, Owens GK. Angiotensin II induces hypertrophy, not hyperplasia, of cultured rat aortic smooth muscle cells. Circ Res. 1988; 62: 749–756.[Abstract/Free Full Text]
  3. Berk BC, Vekshtein V, Gordon HM, Tsuda T. Angiotensin II-stimulated protein synthesis in cultured vascular smooth muscle cells. Hypertension. 1989; 13: 305–314.[Abstract/Free Full Text]
  4. Murphy TJ, Alexander RW, Griendling KK, Runge MS, Bernstein KE. Isolation of a cDNA encoding the vascular type-1 angiotensin II receptor. Nature. 1991; 351: 233–236.[CrossRef][Medline] [Order article via Infotrieve]
  5. Sasaki K, Yamano Y, Bardhan S, Iwai N, Murray JJ, Hasegawa M, Matsuda Y, Inagami T. Cloning and expression of a complementary DNA encoding a bovine adrenal angiotensin II type-1 receptor. Nature. 1991; 351: 230–233.[CrossRef][Medline] [Order article via Infotrieve]
  6. Berk BC, Corson MA. Angiotensin II signal transduction in vascular smooth muscle: role of tyrosine kinases. Circ Res. 1997; 80: 607–616.[Abstract/Free Full Text]
  7. Griendling KK, Ushio-Fukai M, Lassegue B, Alexander RW. Angiotensin II signaling in vascular smooth muscle: new concepts. Hypertension. 1997; 29: 366–373.[Abstract/Free Full Text]
  8. Chamley-Campbell JH, Campbell GR, Ross R. Phenotype-dependent response of cultured aortic smooth muscle to serum mitogens. J Cell Biol. 1981; 89: 379–383.[Abstract/Free Full Text]
  9. Naftilan AJ. The role of angiotensin II in vascular smooth muscle cell growth. J Cardiovasc Pharmacol. 1992; 20 (suppl 1): S37–S40.
  10. Brown NJ, Vaughan DE. Prothrombotic effects of angiotensin. Adv Intern Med. 2000; 45: 419–429.[Medline] [Order article via Infotrieve]
  11. Phillips MI, Kagiyama S. Angiotensin II as a pro-inflammatory mediator. Curr Opin Investig Drugs. 2002; 3: 569–577.[Medline] [Order article via Infotrieve]
  12. Green RS, Lieb ME, Weintraub AS, Gacheru SN, Rosenfield CL, Shah S, Kagan HM, Taubman MB. Identification of lysyl oxidase and other platelet-derived growth factor-inducible genes in vascular smooth muscle cells by differential screening. Lab Invest. 1995; 73: 476–482.[Medline] [Order article via Infotrieve]
  13. Giachelli C, Bae N, Lombardi D, Majesky M, Schwartz S. Molecular cloning and characterization of 2B7, a rat mRNA which distinguishes smooth muscle cell phenotypes in vitro and is identical to osteopontin (secreted phosphoprotein I, 2aR). Biochem Biophys Res Commun. 1991; 177: 867–873.[CrossRef][Medline] [Order article via Infotrieve]
  14. Campos AH, Zhao Y, Pollman MJ, Gibbons GH. DNA microarray profiling to identify angiotensin-responsive genes in vascular smooth muscle cells: potential mediators of vascular disease. Circ Res. 2003; 92: 111–118.[Abstract/Free Full Text]
  15. Clowes AW, Clowes MM, Fingerle J, Reidy MA. Regulation of smooth muscle cell growth in injured artery. J Cardiovasc Pharmacol. 1989; 14: S12–S15.
  16. Schwartz SM, Liaw L. Growth control and morphogenesis in the development and pathology of arteries. J Cardiovasc Pharmacol. 1993; 21: S31–S49.[Medline] [Order article via Infotrieve]
  17. Ross R. Cell biology of atherosclerosis. Annu Rev Physiol. 1995; 57: 791–804.[CrossRef][Medline] [Order article via Infotrieve]
  18. Reidy MA, Fingerle J, Lindner V. Factors controlling the development of arterial lesions after injury. Circulation. 1992; 86 (suppl III): III-43–III-46.[Medline] [Order article via Infotrieve]
  19. Prescott MF, Webb RL, Reidy MA. Angiotensin-converting enzyme inhibitor versus angiotensin II, AT1 receptor antagonist: effects on smooth muscle cell migration and proliferation after balloon catheter injury. Am J Pathol. 1991; 139: 1291–1296.[Abstract]
  20. Giachelli CM, Bae N, Almeida M, Denhardt DT, Alpers CE, Schwartz SM. Osteopontin is elevated during neointima formation in rat arteries and is a novel component of human atherosclerotic plaques. J Clin Invest. 1993; 92: 1686–1696.[Medline] [Order article via Infotrieve]
  21. Hasenstab D, Forough R, Clowes AW. Plasminogen activator inhibitor type 1 and tissue inhibitor of metalloproteinases-2 increase after arterial injury in rats. Circ Res. 1997; 80: 490–496.[Abstract/Free Full Text]
  22. Wang H, Moore S, Alavi MZ. Synthesis of tissue inhibitor of metalloproteinase-1 (TIMP-1) in rabbit aortic neointima after selective de-endothelialization. Atherosclerosis. 1996; 126: 95–104.[CrossRef][Medline] [Order article via Infotrieve]
  23. Patton WF, Erdjument-Bromage H, Marks AR, Tempst P, Taubman MB. Components of the protein synthesis and folding machinery are induced in vascular smooth muscle cells by hypertrophic and hyperplastic agents: identification by comparative protein phenotyping and microsequencing. J Biol Chem. 1995; 270: 21404–21410.[Abstract/Free Full Text]



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