on May 14, 2009
Published online before print May 14, 2009, doi: 10.1161/ATVBAHA.109.185918
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Submitted on September 13, 2008
Accepted on May 6, 2009
Rapamycin Inhibition of the Akt/mTOR Pathway Blocks Select Stages of VEGF-A164–Driven Angiogenesis, in Part by Blocking S6Kinase
Qi Xue ;
From the Center for Vascular Biology and the Department of Pathology at the Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Mass.
* To whom correspondence should be addressed. E-mail: lbenjami{at}bidmc.harvard.edu.
Objective—We evaluated the stages of VEGF-A164 driven angiogenesis that are inhibited by therapeutic doses of rapamycin and the potential role of S6K1 in that response.
Methods and Results—We assessed the effects of rapamycin on the several stages of angiogensis and lymphangiogenesis induced with an adenovirus expressing VEGF-A164 (Ad-VEGF-A164) in the ears of adult nude mice. Rapamycin (0.5 mg/kg/d) effectively inhibited mTOR and downstream S6K1 signaling and partially inhibited Akt signaling, likely through effects on TORC2. The earliest stages of angiogenesis, including mother vessel formation and increased vascular permeability, were strikingly inhibited by rapamycin, as was subsequent formation of daughter glomeruloid microvasular proliferations. However, later stage formation of vascular malformations and lymphangiogenesis were unaffected. Retrovirally delivered isoforms and shRNAs demonstrated that S6K1 signaling plays an important role in early VEGF-A164-angiogenesis.
Conclusions—Rapamycin potently inhibited early and mid stages of VEGF-A164–driven angiogenesis, but not late-stage angiogenesis or lymphangiogenesis. Rapamycin decreased phosphorylation of both Akt and S6, suggesting that both the TORC1 and TORC2 pathways are impacted. Inhibition of S6K1 signaling downstream of mTOR is a major component of the antiangiogenesis action of rapamycin.
Key words: angiogenesis • VEGF-A • rapamycin • lymphangiogenesis