Abstract
Recruitment of circulating leukocytes into inflamed tissues depends on adhesion molecules expressed by endothelial cells (ECs). Here we report that rapamycin pretreatment reduced the ability of TNF-treated ECs to capture T cells under conditions of venular flow. This functional change was caused by inhibition of TNF-induced expression of vascular cell adhesion molecule-1 (VCAM-1) and could be mimicked by knockdown of mammalian target of rapamycin (mTOR) or rictor, but not raptor, implicating mTORC2 as the target of rapamycin for this effect. Mechanistically, mTORC2 acts through Akt to repress Raf1-MEK1/2-ERK1/2 signaling, and inhibition of mTORC2 consequently results in hyperactivation of ERK1/2. Increased ERK1/2 activity antagonizes VCAM-1 expression by repressing TNF induction of the transcription factor IRF-1. Preventing activation of ERK1/2 reduced the ability of rapamycin to inhibit TNF-induced VCAM-1 expression. In vivo, rapamycin inhibited mTORC2 activity and potentiated activation of ERK1/2. These changes correlated with reduced endothelial expression of TNF-induced VCAM-1, which was restored via pharmacological inhibition of ERK1/2. Functionally, rapamycin reduced infiltration of leukocytes into renal glomeruli, an effect which was partially reversed by inhibition of ERK1/2. These data demonstrate a novel mechanism by which rapamycin modulates the ability of vascular endothelium to mediate inflammation and identifies endothelial mTORC2 as a potential therapeutic target.