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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2009;29:232.)
© 2009 American Heart Association, Inc.

Cell Biology/Signaling

mTOR Regulates Vascular Smooth Muscle Cell Differentiation From Human Bone Marrow–Derived Mesenchymal Progenitors

Björn Hegner; Maria Lange; Angelika Kusch; Kirill Essin; Orhan Sezer; Eckhard Schulze-Lohoff; Friedrich C. Luft; Maik Gollasch; Duska Dragun

From the Clinic for Nephrology and Intensive Care Medicine (B.H., M.L., A.K., K.E., M.G., D.D.), Charité Campus Virchow-Klinikum, the Center for Cardiovascular Research (B.H., M.L., A.K., D.D.), Experimental and Clinical Research Center (K.E., F.C.L., M.G.), Clinic for Hematology and Oncology (O.S.), Charité Campus Mitte, Berlin; the Department of Medicine I (E.S.-L.), Cologne General Hospital, Cologne; and Max-Delbrück Center for Molecular Medicine and HELIOS Klinikum (F.C.L.), Berlin, Germany.

Correspondence to Dr Duska Dragun, Clinic for Nephrology and Intensive Care Medicine, Charité Campus Virchow Klinihum, Augustenburger Platz 1, 13353 Berlin, Germany. E-mail duska.dragun{at}charite.de

Objective— Vascular smooth muscle cells (VSMCs) and circulating mesenchymal progenitor cells (MSCs) with a VSMC phenotype contribute to neointima formation and lumen loss after angioplasty and during allograft arteriosclerosis. We hypothesized that phosphoinositol-Akt-mammalian target of rapamycin-p70S6 kinase (PI3K/Akt/mTOR/p70S6K) pathway activation regulates VSMC differentiation from MSCs.

Methods and Results— We studied effects of PI3K/Akt/mTOR signaling on phenotypic modulation of MSC and VSMC marker expression, including L-type Ca(2+) channels. Phosphorylation of Akt and p70S6K featured downregulation of VSMC markers in dedifferentiated MSCs. mTOR inhibition with rapamycin at below pharmacological concentrations blocked p70S6K phosphorylation and induced a differentiated contractile phenotype with smooth muscle (sm)-calponin, sm--actin, and SM protein 22-alpha (SM22) expression. The PI3K inhibitor Ly294002 abolished Akt and p70S6K phosphorylation and reversed the dedifferentiated phenotype via induction of sm-calponin, sm--actin, SM22, and myosin light chain kinase. Rapamycin acted antiproliferative without impairing MSC viability. In VSMCs, rapamycin increased a homing chemokine for MSCs, stromal cell–derived factor-1–alpha, at mRNA and protein levels. The CXCR4-mediated MSC migration toward conditioned medium of rapamycin-treated VSMCs was enhanced.

Conclusions— We describe novel pleiotropic effects of rapamycin at very low concentrations that stabilized differentiated contractile VSMCs from MSCs in addition to exerting antiproliferative and enhanced homing effects.