title: Smooth muscle cells orchestrate the endothelial cell response to flow and injury.
abstract: BACKGROUND
  Local modulation of vascular mammalian target of rapamycin (mTOR) signaling reduces smooth muscle cell (SMC) proliferation after endovascular interventions but may be associated with endothelial cell (EC) toxicity. The trilaminate vascular architecture juxtaposes ECs and SMCs to enable complex paracrine coregulation but shields SMCs from flow. We hypothesized that flow differentially affects mTOR signaling in ECs and SMCs and that SMCs regulate mTOR in ECs.
  
  
  RESULTS
  SMCs and/or ECs were exposed to coronary artery flow in a perfusion bioreactor. We demonstrated by flow cytometry, immunofluorescence, and immunoblotting that EC expression of phospho-S6 ribosomal protein (p-S6RP), a downstream target of mTOR, was doubled by flow. Conversely, S6RP in SMCs was growth factor but not flow responsive, and SMCs eliminated the flow sensitivity of ECs. Temsirolimus, a sirolimus analog, eliminated the effect of growth factor on SMCs and of flow on ECs, reducing p-S6RP below basal levels and inhibiting endothelial recovery. EC p-S6RP expression in stented porcine arteries confirmed our in vitro findings: Phosphorylation was greatest in ECs farthest from intact SMCs in metal stented arteries and altogether absent after sirolimus stent elution.
  
  
  CONCLUSIONS
  The mTOR pathway is activated in ECs in response to luminal flow. SMCs inhibit this flow-induced stimulation of endothelial mTOR pathway. Thus, we now define a novel external stimulus regulating phosphorylation of S6RP and another level of EC-SMC crosstalk. These interactions may explain the impact of local antiproliferative delivery that targets SMC proliferation and suggest that future stents integrate design influences on flow and drug effects on their molecular targets.
authors.affiliation: Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA 02139, USA. merche@mit.edu
authors.forename: Mercedes
authors.initials: M
authors.lastname: Balcells
authors.forename: Jordi
authors.initials: J
authors.lastname: Martorell
authors.forename: Carla
authors.initials: C
authors.lastname: Olivé
authors.forename: Marina
authors.initials: M
authors.lastname: Santacana
authors.forename: Vipul
authors.initials: V
authors.lastname: Chitalia
authors.forename: Angelo A
authors.initials: AA
authors.lastname: Cardoso
authors.forename: Elazer R
authors.initials: ER
authors.lastname: Edelman
mesh_terms: D000818:Animals; D001011:Aorta / Q000502:physiology; D001158:Arteries / Q000502:physiology* / Q000503:physiopathology; D002450:Cell Communication / Q000502:physiology*; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000502:physiology; D042783:Endothelial Cells / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000473:pathology / Q000503:physiopathology; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D038601:Ribosomal Protein S6 / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D015607:Stents / Q000009:adverse effects; D013552:Swine; D013556:Swine, Miniature; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000378:metabolism
chemical_list: C500984:CRTC1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D038601:Ribosomal Protein S6; D014157:Transcription Factors; C401859:temsirolimus; C546842:MTOR protein, human; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus
references.citation: Circulation. 2005 Sep 27;112(13):2002-11
references.pmid: 16172265
references.citation: Nat Cell Biol. 2008 Oct;10(10):1208-16
references.pmid: 18806787
references.citation: J Surg Res. 1997 Feb 1;67(2):169-78
references.pmid: 9073564
references.citation: J Cell Physiol. 2005 Jul;204(1):329-35
references.pmid: 15700266
references.citation: Arteriosclerosis. 1986 Nov-Dec;6(6):664-9
references.pmid: 3778309
references.citation: Ann Biomed Eng. 2004 Apr;32(4):537-43
references.pmid: 15117027
references.citation: J Control Release. 2008 Nov 12;131(3):173-80
references.pmid: 18713645
references.citation: Circ Res. 2007 Mar 2;100(4):564-71
references.pmid: 17272808
references.citation: Cell Biochem Biophys. 2008;52(1):37-46
references.pmid: 18766304
references.citation: Mol Cell. 2006 Apr 21;22(2):159-68
references.pmid: 16603397
references.citation: Circulation. 2005 Jun 7;111(22):2958-65
references.pmid: 15927969
references.citation: Methods Enzymol. 1990;192:280-300
references.pmid: 2074793
references.citation: Blood. 2006 Jan 1;107(1):285-92
references.pmid: 16141350
references.citation: J Control Release. 2009 Jan 5;133(1):24-30
references.pmid: 18926864
references.citation: Surgery. 1996 Aug;120(2):418-25; discussion 425-6
references.pmid: 8751613
references.citation: Am J Physiol Heart Circ Physiol. 2007 Sep;293(3):H1978-86
references.pmid: 17644568
references.citation: J Biomech Eng. 2002 Aug;124(4):397-407
references.pmid: 12188206
references.citation: Drug Resist Updat. 2008 Jun;11(3):63-76
references.pmid: 18440854
references.citation: J Control Release. 2007 Nov 6;123(2):100-8
references.pmid: 17868948
references.citation: Circ J. 2008 May;72(5):832-8
references.pmid: 18441467
references.citation: Circ Res. 2009 Feb 13;104(3):380-7
references.pmid: 19096032
references.citation: Yonsei Med J. 2000 Dec;41(6):740-55
references.pmid: 11204825
references.citation: J Am Coll Cardiol. 2006 Jul 4;48(1):193-202
references.pmid: 16814667
references.citation: J Interv Cardiol. 2006 Dec;19(6):493-9
references.pmid: 17107363
references.citation: Trends Cardiovasc Med. 2006 Jul;16(5):153-6
references.pmid: 16781948
references.citation: Blood. 2007 Apr 15;109(8):3509-12
references.pmid: 17179228
references.citation: Eur Surg Res. 2008;40(4):325-32
references.pmid: 18303268
references.citation: Eur Heart J. 2010 Jan;31(2):236-42
references.pmid: 19567381
references.citation: Nat Clin Pract Cardiovasc Med. 2006 Dec;3(12):637
references.pmid: 17122790
references.citation: Arteriosclerosis. 1987 Sep-Oct;7(5):463-9
references.pmid: 3675305
references.citation: J Biomech. 2004 Apr;37(4):531-9
references.pmid: 14996565
references.citation: Biosci Rep. 1999 Aug;19(4):235-51
references.pmid: 10589989
references.citation: Arterioscler Thromb Vasc Biol. 2006 Jun;26(6):1215-25
references.pmid: 16543495
references.citation: An R Acad Nac Med (Madr). 1998;115(2):317-31
references.pmid: 9882827
references.citation: Endothelium. 2002;9(1):11-23
references.pmid: 12901357
references.citation: Handb Exp Pharmacol. 2006;(176 Pt 2):79-95
references.pmid: 16999225
references.citation: Am J Physiol Heart Circ Physiol. 2007 May;292(5):H2167-75
references.pmid: 17209004
references.citation: J Biomed Mater Res A. 2008 Mar 1;84(3):661-71
references.pmid: 17635014
references.citation: Eur J Cell Biol. 2009 Nov;88(11):701-9
references.pmid: 19581021
references.citation: Circ Res. 2005 Sep 30;97(7):725-33
references.pmid: 16123336
references.citation: Circ Res. 2008 Aug 15;103(4):405-12
references.pmid: 18617695
references.citation: J Biol Chem. 2009 Mar 27;284(13):8412-20
references.pmid: 19047056
references.citation: Hypertension. 2009 Aug;54(2):427-33
references.pmid: 19564543
references.citation: Blood. 2003 Apr 1;101(7):2667-74
references.pmid: 12468429