Smooth muscle cells orchestrate the endothelial cell response to flow and injury.
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.
Balcells
Mercedes
M
Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA 02139, USA. merche@mit.edu
Martorell
Jordi
J
Olivé
Carla
C
Santacana
Marina
M
Chitalia
Vipul
V
Cardoso
Angelo A
AA
Edelman
Elazer R
ER
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
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
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