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(Circulation Research. 2007;101:542.)
© 2007 American Heart Association, Inc.

Editorials

Interferon- and Intimal Hyperplasia

Marlene L. Rose

From the Imperial College London, UK.

Correspondence to Professor Marlene L. Rose, Imperial College London, National Heart & Lung Institute, Transplant Immunology, Harefield Hospital, Middlesex UB9 6JH, United Kingdom. E-mail marlene.rose{at}imperial.ac.uk

See related article, pages 560–569

Key Words: arteriosclerosis • neointima

Interferon gamma (IFN-) is a pleiotropic interferon, and it is known to regulate 500 genes.¹ It has long been thought to be involved in the pathogenesis of atherosclerosis. The well known properties of IFN- include its ability to induce inflammatory genes (eg, ICAM-1, VCAM-1), cell signaling molecules (CD40, CD80, tissue factor, MHC class II antigen) on endothelial cells, and macrophages.² This results in enhancement of the antigen-presenting properties of macrophages and endothelial cells and induces a proinflammatory phenotype of endothelial cells. IFN- also has effects on cholesterol and lipid trafficking. The consensus is that presence of IFN- in atherosclerotic plaques has a deleterious effect, possibly by enhancing plaque instability and plaque rupture.² In this issue of Circulation Research,³ Wang et al have published a report, the third in a series, which provides compelling evidence that IFN- plays a nonredundant role in pathogenesis of alloimmune-induced vascular intimal hyperplasia, a condition that occurs after cardiac allograft transplantation. The results of this study have therapeutic implications for all vascular diseases where smooth muscle hyperplasia occurs, and the mechanisms of its actions are unrelated to the previously described effects of IFN- on endothelial cells or macrophages.

Cardiac transplantation is a successful therapeutic option for patients with end stage heart failure that cannot be treated by conventional surgery or medication. Whereas 1-year survival has been impacted by improvements in immunosuppression, long-term survival remains relatively unchanged; 10-year survival of combined adult and pediatric transplant recipients is currently 50%.⁴ A major reason for this is development of cardiac graft vasculopathy (CGV), an occlusive vascular disease of grafted vessels which results in altered blood flow in the arteries and ischemia to the heart. Histologically, there are similarities and differences between CGV and nontransplant atherosclerosis.⁵ In CGV affected vessels demonstrate loss of medial cells and an expanded intima consisting of extracellular matrix, infiltrating mononuclear cells, and vascular smooth muscle cells. The presence of proliferating smooth muscle cells is also a feature of in-stent restenosis, and to a lesser extent nontransplant atherosclerosis.

It is paradoxical that although acute rejection is modified by treatment with immunosuppressive drugs in routine use (such as calcineurin inhibitors, and inhibitors of purine synthesis) these drugs have little impact on CGV. In contrast, the recently introduced drug, Everolimus, an mTOR (mammalian target of rapamycin) inhibitor, produces less intimal thickening in the arteries of treated patients.⁶ It is not clear whether the effect of mTOR inhibitors are a direct effect on smooth muscle cell proliferation⁷ or their antiproliferative effects on lymphocytes.⁸ As with all chronic human diseases, it is difficult to produce an adequate model of cardiac graft vasculopathy. In vitro studies using clinical materials are limited by the artificial nature of culture conditions. Experiments in vivo are limited because of the difficulties in extrapolating from animal to human cell–cell interactions. Progress in this area has proceeded using a xenotransplantation model; namely transplantation of human epicardial arteries into C.B-17 severe combined immunodeficient beige mice, followed by repopulation of the mouse with gamma interferon,⁹ human leukocytes,¹⁰ or in the most recent study, replication deficient adenovirus encoding the human transgene for IFN-.³ The advantage of using adenovirus (AAV) to transfer human IFN- was that it produced higher circulating levels of IFN- than were previously achieved by daily injection,⁹ and levels could be maintained for as long as 14 weeks. Four weeks exposure was sufficient to result in an expanded intima of the human epicardial arteries, consisting of matrix and smooth muscle cells; in contrast mice given adenovirus containing a control gene failed to show intimal expansion. The authors went on to explore the pathways involved in IFN-–mediated human vascular SMC proliferation.

Cellular proliferation is associated with activation of the mammalian target of rapamycin, mTOR. mTOR is an evolutionary conserved protein kinase, it was identified and cloned 10 years ago (1994) shortly after its initial discovery in yeast, during a screen for the immusuppressive drug rapamycin. It is now known to be a major effector of cell growth and proliferation via the regulation of protein synthesis.¹¹ It regulates protein synthesis via recruitment of the ribosomal protein S6 and its kinase ribosomal S6 kinase (S6K1). Phosphorylation of S6 is thought to be a general mechanism to signal and induce cell growth and proliferation.¹¹ mTOR may also regulate transcription of ribosomal RNA (rRNA; Figure). The upstream signaling pathway of mTOR is mediated via phosphorylation of phosphatidylinositol 3-kinase (PI3K) at the cell membrane, this leading to phosphorylation of Akt. The PI3K pathway is activated by extracellular signals such as growth factors, hormones, and mitogenic stimuli¹¹ (Figure). Wang et al demonstrate the presence of phosphorylated S6K1 in xenografts from mice treated with AAV/IFN-, but not controls, suggesting activation of the mTOR pathway by IFN-. They showed that SMC proliferation and phosphorylation of S6K1 in the presence of AAV/IFN- was inhibited if animals were treated with 1.5 mg/kg rapamycin/d. In vitro studies of denuded arteries or cultured SMCs confirmed that IFN- caused phosphorylation of mTOR, S6K1, and S6 in a time-dependent and dose-dependent way. The fact that these effects were mediated in SMCs or arteries maintained in serum-free medium is important because it shows that IFN- has a direct effect on SMCs and is not mediated via growth factors (such as platelet-derived growth factor). Finally, as expected, it was demonstrated that IFN-–mediated phosphorylation of mTOR, S6K1, and S6 was inhibited by the PI3K inhibitor LY294002.

View larger version (17K): [in this window] [in a new window]   Activation of the Akt/mTOR pathway. Diagrammatic representation demonstrating that mTOR activation regulates protein synthesis via phosphorylation of ribosomal protein S6 and activation of initiation factors such as eIF4B. In addition, it exerts transcriptional control of ribosomal RNA (rRNA) by modulating various transcription factors and enzymes (RF, or regulatory factors); these will affect global protein synthesis. Inhibitors of this pathway include PTEN, which inhibits PI3K activation and rapamycin which inhibits mTOR. Modified from Ruggero and Sonenberg11 with permission from Macmillan Publishers Ltd, Oncogene, 2005.

It is interesting that early studies (reviewed in²) suggested that IFN- had an inhibitory effect of proliferation of vascular SMC; however, these were short-term in vitro studies using cultured cells, in vivo studies have the advantage of long exposure to circulating cytokines and maintenance of normal vessel architecture.

Wang et al have published that inhibition of IFN- with neutralizing antibodies inhibits intimal expansion induced by allogeneic T cells in SCID-Beige mice¹⁰suggesting a nonredundant role for IFN- in alloimmune induced vascular smooth muscle cell proliferation. This hypothesis is supported by experimental studies which demonstrate decreased cardiac allograft vasculopathy when hearts have been allotransplanted into mice lacking the gene for IFN-.^12,13 One of the questions arising from this notion is the cellular source of the IFN- in the affected arteries. Interferon- is made by CD4+ T cells, CD8+ T cells, activated macrophages, NK cells, B cells, and vascular smooth muscle cells.² With the exception of NK cells, all these cell types are present in the intima and adventitia of coronary arteries from patients with cardiac graft vasculopathy.¹⁴ Indeed the infiltrating cells in the vessel wall occupy a discreet area within the expanded intima which is between the acellular and smooth muscle cell rich component, making them well placed to activate SMC by local secretion of IFN-. It is interesting to speculate whether activation of IFN- producing T lymphocytes occurs locally within the graft; the presence of alloantigen displayed by dendritic cells and endothelial cells in the graft may be sufficient to cause local activation of graft infiltrating memory CD4+ and CD8+ T cells, allowing them to further differentiate and produce IFN-.¹⁵

Taken together^3,9,10 these experiments provide compelling evidence that human IFN- causes smooth muscle cell proliferation in vivo, via activation of the PI3 kinase/mTOR pathway (Figure). IFN- stimulates transcriptional activity through Stat-1complex¹⁶; however, Stat-1–independent mechanisms of IFN- activation also exist. The exact pathways by which IFN- stimulate PI3K are currently not known. There results provide a new mechanistic insight into the role of IFN- in vascular disease and may have therapeutic implications for all vascular disease characterized by smooth muscle cell proliferation. In the cases of flow or mechanically-induced restenosis injury, the question remains whether SMC proliferation is dependent on IFN-.

Finally, as acknowledged by the authors,³ IFN- is unlikely to be the only player in the sequence of immune events which cause CGV. In vitro studies have shown that alloantibody also causes phosphorylation of PI3K and of S6 ribosomal protein in vascular smooth muscle cells,¹⁷ although whether this leads to growth factor–independent cell proliferation has not been determined. S6RP was found in cardiac biopsies to be associated with humoral rejection, rather than cellular rejection.¹⁷In view of the association between alloantibodies and graft vasculopathy,¹⁸ it might be of interest to test for a synergistic effect between alloantibodies and IFN- in SMC proliferation, using this elegant in vivo xenotransplant model.

	Acknowledgments

 
Sources of Funding

Research in the author’s laboratory is supported by the British Heart Foundation.

Disclosures

None.

	Footnotes

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

	References

Top References

 

1. Boehm U, Klamp T, Groot M, Howard JC. Cellular responses to interferon-gamma. Annu Rev Immunol. 1997; 15: 749–795[CrossRef][Medline] [Order article via Infotrieve]
2. Leon ML, Zuckerman SH. Gamma interferon: a central mediator in atherosclerosis. Inflamm Res. 2005; 54: 395–411.[CrossRef][Medline] [Order article via Infotrieve]
3. Wang Y, Bai Y, Qin L, Zhang P, Yi T, Teesdale SA, Zhao L, Pober JS, Tellides G. Interferon-{gamma} induces human vascular smooth muscle cell proliferation and intimal expansion by phosphatidylinositol 3-kinase dependent mammalian target of rapamycin raptor complex 1 activation. Circ Res. 2007; 101: 560–569.[Abstract/Free Full Text]
4. Taylor DO, Edwards LB, Boucek MM, Trulock EP, Waltz DA, Keck BM, Hertz MI. Registry of the International Society for Heart and Lung Transplantation: twenty-third official adult heart transplantation report–2006. J Heart Lung Transplant. 2006; 25: 869–879.[CrossRef][Medline] [Order article via Infotrieve]
5. Rahmani M, Cruz RP, Granville DJ, McManus BM. Allograft vasculopathy versus atherosclerosis. Circ Res. 2006: 99: 801–815.[Abstract/Free Full Text]
6. Eisen HJ, Tuzcu EM, Dorent R, Kobashigawa J, Mancini D, Valantine-von Kaeppler HA, Starling RC, Sorensen K, Hummel M, Lind JM, Abeywickrama KH, Bernhardt P, RAD B253 Study Group. Everolimus for the prevention of allograft rejection and vasculopathy in cardiac-transplant recipients. N Engl J Med. 2003; 349: 847–858.[Abstract/Free Full Text]
7. Marx SO, Marks AR. Bench to bedside: the development of rapamycin and its application to stent restenosis Circulation. 2001; 104: 852–855.[Free Full Text]
8. Easton JB, Houghton PJ. Therapeutic potential of target of rapamycin inhibitors. Expert Opin Ther Targets. 2004; 8: 551–564.[CrossRef][Medline] [Order article via Infotrieve]
9. Tellides G, Tereb DA, Kirkiles-Smith NC, Kim RW, Wilson JH, Schechner JS, Lorber MI, Pober JS. Interferon-gamma elicits arteriosclerosis in the absence of leukocytes. Nature. 2000; 403: 207–211.[CrossRef][Medline] [Order article via Infotrieve]
10. Wang Y, Burns WR, Tang PC, Yi T, Schechner JS, Zerwes HG, Sessa WC, Lorber MI, Pober JS, Tellides G. Interferon-gamma plays a nonredundant role in mediating T cell-dependent outward vascular remodeling of allogeneic human coronary arteries. FASEB J. 2004; 18: 606–608.[Abstract/Free Full Text]
11. Ruggero D, Sonenberg N. The Akt of translational control Oncogene. 2005; 24: 7426–7434.[CrossRef][Medline] [Order article via Infotrieve]
12. Nagano H, Mitchell RN, Taylor MK, Hasegawa S, Tilney NL, Libby P. Interferon-gamma deficiency prevents coronary arteriosclerosis but not myocardial rejection in transplanted mouse hearts. J Clin Invest. 1997; 100: 550–557.[Medline] [Order article via Infotrieve]
13. Raisanen-Sokolowski A, Glysing-Jensen T, Koglin J, Russell ME. Reduced transplant arteriosclerosis in murine cardiac allografts placed in interferon–gamma knockout recipients. Am J Pathol. 1998; 152: 359–365.[Abstract]
14. van Loosdregt J, van Oosterhout MF, Bruggink AH, van Wichen DF, van Kuik J, de Koning E, Baan CC, de Jonge N, Gmelig-Meyling FH, de Weger RA. The chemokine and chemokine receptor profile of infiltrating cells in the wall of arteries with cardiac allograft vasculopathy is indicative of a memory T-helper 1 response. Circulation. 2006; 114: 1599–1607.[Abstract/Free Full Text]
15. Choi J, Enis DR, Koh KP, Shiao SL, Pober JS. T lymphocyte-endothelial cell interactions. Annu Rev Immunol. 2004; 22: 683–709.[CrossRef][Medline] [Order article via Infotrieve]
16. Schroder K, Hertzog PJ, Ravasi T, Hume DA. Interferon-gamma: an overview of signals, mechanisms and functions. J Leukoc Biol. 2004; 75: 163–189.[Abstract/Free Full Text]
17. Lepin EJ, Zhang Q, Zhang X, Jindra PT, Hong LS, Ayele P, Peralta MV, Gjertson DW, Kobashigawa JA, Wallace WD, Fishbein MC, Reed EF. Phosphorylated S6 ribosomal protein: a novel biomarker of antibody-mediated rejection in heart allografts. Am J Transplant. 2006; 6: 1560–1571.[CrossRef][Medline] [Order article via Infotrieve]
18. Wehner J, Morrell CN, Reynolds T, Rodriguez ER, Baldwin WM III. Antibody and complement in transplant vasculopathy Circ Res. 2007; 100: 191–203.[Abstract/Free Full Text]

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