mTOR regulates vascular smooth muscle cell differentiation from human bone marrow-derived mesenchymal progenitors.
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.


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-alpha-actin, and SM protein 22-alpha (SM22alpha) expression. The PI3K inhibitor Ly294002 abolished Akt and p70S6K phosphorylation and reversed the dedifferentiated phenotype via induction of sm-calponin, sm-alpha-actin, SM22alpha, 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.
Hegner
Björn
B
Clinic for Nephrology and Intensive Care Medicine, Charité Campus Virchow Klinihum, Augustenburger Platz 1, 13353 Berlin, Germany.
Lange
Maria
M
Kusch
Angelika
A
Essin
Kirill
K
Sezer
Orhan
O
Schulze-Lohoff
Eckhard
E
Luft
Friedrich C
FC
Gollasch
Maik
M
Dragun
Duska
D
D001854:Bone Marrow Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D002470:Cell Survival; D002478:Cells, Cultured; D054377:Chemokine CXCL12 / Q000378:metabolism; D002633:Chemotaxis; D002867:Chromones / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D009124:Muscle Proteins / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D013997:Time Factors
D020746:Calcium Channels, L-Type; D054377:Chemokine CXCL12; D002867:Chromones; D009025:Morpholines; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C515255:CXCL12 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546842:MTOR protein, human