Research Profile
The main areas of our research are smooth muscle physiology and pharmacology; pathophysiology of hypertension, restenosis and coronary artery disease; vascular smooth muscle contraction and growth; Ca2+-dependent and Ca2+-independent mechanisms of cell activation; Ca2+ homeostasis in living cells; signal transduction, G proteins, protein kinase C and kinase cascades; fluorescent probes, immunocytochemistry; digital imaging microscopy and confocal microscopy.
We use traditional and advanced techniques to address important questions in cardiovascular physiology and cell biology. We measure isometric contraction in vascular strips using tissue bath bioassay systems. We measure cell contraction in isolated living smooth muscle cells. We measure intracellular ions and pH using fluorescent probes and double excitation double emission spectrofluorometry. We measure the expression and activity of intracellular enzymes and proteins using enzyme assays, immunoprecipitation and Western blot analysis. We image the distribution of intracellular enzymes and proteins using fluorescently labeled antibodies. The acquired images are further processed using the nearest neighbor, no neighbor or quadratic regularization mathematical deconvolution algorithms installed on a SUN SPARC work station. The enhanced images are used for 3-D reconstruction and visualization of vascular cells. We have also developed mathematical algorithms to analyze the cell images quantitatively and to determine the subcellular localization of different enzymes and proteins.
We have had the opportunity to mentor and train more than 20 U.S. and international undergraduate, graduate, medical and postdoctoral trainees. They have been very successful in their training and have published several peer-reviewed articles and competed successfully for several national and international awards.
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Projects
Signaling mechanisms of coronary vascular tone in healthy and spastic arteries (NIH HL-52696).
| Coronary smooth muscle contraction can not be fully explained by activation of Ca2+-dependent myosin light chain kinase, and a role for protein kinase C (PKC) activation has been suggested. In this project we test whether activation of specific PKC isoforms is a major step in the signal transduction cascade leading to maintained contraction of coronary smooth muscle. We measure contraction and [Ca2+]i in isolated coronary smooth muscle cells. We measure PKC distribution and activity using radioactive enzyme assays and Western blot analysis. These studies should help to understand the cellular mechanisms underlying coronary smooth muscle contraction and shed light on the pathophysiological basis of coronary vasospasm. |
Role of endothelin A and endothelin B receptors in maintaining vascular tone during high salt diet (AHA, Established Investigator Award 2002-2006).
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High salt diet is associated with increased vascular resistance and arterial pressure in salt-sensitive individuals. In normal individuals, high salt diet does not increase the arterial pressure, suggesting possible vascular protective mechanisms. Endothelin-1 (ET-1), a potent vasoconstrictor, activates ETA and ETB receptors. Although the role of ETA receptors in vascular contraction and hypertension has been studied, the importance of ETB receptors in modulating the vascular function and arterial pressure particularly during high salt diet is unclear. In this project we test the possibility that normally during high salt diet an increase in ET-1 production and enhancement of ETA-mediated vascular contraction are counterbalanced by enhanced ETB-mediated vascular relaxation pathways, thus preventing excessive increases in vascular resistance and arterial pressure. These studies should help understand the vascular protective mechanisms during high salt diet in normal individuals. The studies will also shed light on the pathophysiological basis of the increased vascular resistance in salt-sensitive forms of hypertension.
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Mechanisms of gender differences in regulation of vascular tone, and the vascular protective effects of estrogen in hypertension and coronary artery disease.
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The greater incidence of cardiovascular diseases in men and postmenopausal women compared with premenopausal women has suggested potential vascular effects of sex hormones. Estrogen, progesterone and testosterone receptors have been identified in the cytosol and nuclear compartment of the endothelium and smooth muscle. The interaction of sex hormones with cytosolic/nuclear receptors initiates long-term genomic effects that stimulate endothelial cell growth, but inhibit smooth muscle proliferation. In this project we test whether sex hormones also activate specific receptors on the plasma membrane and trigger acute non-genomic effects that stimulate endothelium-dependent mechanisms of vascular relaxation and inhibit the signaling mechanisms of vascular smooth muscle contraction. These potential vascular effects of sex hormones should be taken into account when considering hormone replacement therapy during natural and surgically-induced deficiencies of gonadal hormones particularly in hypertensive subjects.
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Vascular and cellular mechanisms of hypertension in pregnancy and preeclampsia (NIH HL-65998, 2002-2006).
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Normal pregnancy is associated with reduction in vascular resistance and arterial pressure. These beneficial hemodynamic changes do not occur in women with preeclampsia; instead severe increase in blood pressure is observed; however, the vascular mechanisms involved are unclear. Reduction in uterine perfusion pressure and the ensuing placental ischemia/hypoxia trigger the release of placental factors such as TNF-a and reactive oxygen species. We test whether increases in placental factors lead to endothelial cell dysfunction and reduction in vasodilator substances such as nitric oxide (NO), prostacyclin (PGI2) and EDHF. The placental factors may also increase the release of contracting factors such as endothelin and thromboxane, which could increase [Ca2+]i and stimulate Ca2+-dependent contraction, or increase the activity of protein kinases, and enhance the myofilament sensitivity to [Ca2+]i and smooth muscle contraction. The decreased endothelium-dependent vascular relaxation and increased vascular contraction represent plausible causes of the increased vascular resistance and arterial pressure in preeclampsia.
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Vascular and Cellular Mechanisms underlying Aneurysm Formation (BWH Research Funds).
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Abdominal aortic aneurysm (AAA) is a slow and progressive disease. The late stages of AAA are characterized by increased plasma and tissue levels of matrix metalloproteinases (MMPs) and degenerative changes in the extracellular matrix and smooth muscle components of the aortic wall. In this project we test whether MMPs may have additional inhibitory effects on the Ca2+ entry mechanisms of aortic smooth muscle contraction, even in the absence of extracellular matrix degradation. The MMPs-induced inhibition of aortic contraction may further explain the role of increased MMP activity particularly during the early development of AAA. Chronic exposure to MMPs may lead to protracted inhibition of aortic contraction, progressive aortic dilation and aneurysm formation. MMPs may represent potential less invasive targets for treatment of small AAA, and specific inhibitors of MMPs may be beneficial in controlling the progress of aneurysm formation.
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Labs
A multidisciplinary approach to the study of vascular disease. We are focusing mainly on the molecular mechanisms and potential therapeutic targets which govern lower extremity bypass graft failure, restenosis and hypertension
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Funding
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Publications
For the latest articles by Dr. Raouf Khalil, please visit 
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Christov C, Chretien F, Khalil RA, Bassez G, Vallet G, Authier FJ, Bassaglia Y, Shinin V, Tajbakhsh S, Chazaud B, Gherardi RK. Muscle Satellite Cells and Endothelial Cells: Close Neighbors and Privileged Partners. Mol Biol Cell. 2007 Feb.
Raffetto JD, Ross RL, Khalil RA. Matrix metalloproteinase 2-induced venous dilation via hyperpolarization and activation of K(+) channels: Relevance to varicose vein formation. J Vasc Surg. 2007 Feb;45(2):373-80.
Hynynen MM, Khalil RA. The Vascular Endothelin System in Hypertension - Recent Patents and Discoveries. Recent Pat Cardiovas Drug Discov. 2006 Jan;1(1):95-108.
Stennett AK, Khalil RA. Neurovascular mechanisms of hypertension in pregnancy. Curr Neurovasc Res. 2006 May;3(2):131-48. Review.
Koledova VV, Khalil RA. Ca2+, calmodulin, and cyclins in vascular smooth muscle cell cycle. Circ Res. 2006 May 26;98(10):1240-3. Review.
Khalil RA. Dietary salt and hypertension: new molecular targets add more spice. Am J Physiol Regul Integr Comp Physiol. 2006 Mar;290(3):R509-13. Review.
Salamanca DA, Khalil RA. Protein kinase C isoforms as specific targets for modulation of vascular smooth muscle function in hypertension. Biochem Pharmacol. 2005;70(11):1537-47.
Khalil RA. Sex hormones as potential modulators of vascular function in hypertension. Hypertension. 2005;46(2):249-54.
Chew DK, Conte MS, Khalil RA. Matrix metalloproteinase-specific inhibition of Ca2+ entry mechanisms of vascular contraction. J Vasc Surg. 2004 Nov;40(5):1001-10.
Orshal JM, Khalil RA. Interleukin-6 impairs endothelium-dependent NO-cGMP-mediated relaxation and enhances contraction in systemic vessels of pregnant rats. Am J Physiol Regul Integr Comp Physiol. 2004 Jun;286(6):R1013-23.
Chew DK, Orshal JM, Khalil RA. Elastase promotes aortic dilation by inhibiting Ca2+ influx into vascular smooth muscle. J Cardiovasc Pharmacol. 2004 Apr;43(4):504-13.
McNair LL, Salamanca DA, Khalil RA. Endothelin-1 promotes Ca2+ antagonist-insensitive coronary smooth muscle contraction via activation of epsilon-protein kinase C. Hypertension. 2004 Apr;43(4):897-904. Epub 2004 Feb 23.
Orshal JM, Khalil RA. Reduced endothelial NO-cGMP-mediated vascular relaxation and hypertension in IL-6-infused pregnant rats. Hypertension. 2004 Feb;43(2):434-44. Epub 2004 Jan 05.
Orshal JM, Khalil RA. Gender, sex hormones, and vascular tone. Am J Physiol Regul Integr Comp Physiol. 2004 Feb;286(2):R233-49. Review.
Dallas A, Khalil RA. Ca2+ antagonist-insensitive coronary smooth muscle contraction involves activation of epsilon-protein kinase C-dependent pathway. Am J Physiol Cell Physiol. 2003 Dec;285(6):C1454-63.
Chew DK, Orshal JM, Khalil RA. Elastase-induced suppression of endothelin-mediated Ca2+ entry mechanisms of vascular contraction. Hypertension. 2003 Oct;42(4):818-24. Epub 2003 Aug 04.
Wynne FL, Khalil RA. Testosterone and coronary vascular tone: implications in coronary artery disease. J Endocrinol Invest. 2003 Feb;26(2):181-6. Review.
Thompson J, Khalil RA. Gender differences in the regulation of vascular tone. Clin Exp Pharmacol Physiol. 2003 Jan-Feb;30(1-2):1-15. Review.
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Contact
Raouf A. Khalil, M.D., Ph.D.
Harvard Medical School
Brigham and Women's Hospital
Division of Vascular Surgery
75 Francis Street
Boston, MA 02115
Office Tel: 617-525-8530
Lab Tel: 617-525-8531
Fax: 617-264-5124
E-mail: raouf_khalil@hms.harvard.edu
rkhalil@partners.org
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Send Feedback to: Department of Surgery at bwhsurgery@partners.org
