Abstract
mTOR complex 1 (mTORC1) plays a central role in cell growth and cellular responses to metabolic stress. Although mTORC1 has been shown to be activated after Toll-like receptor (TLR)-4 engagement, there is little information concerning the role that mTORC1 may play in modulating neutrophil function and neutrophil-dependent inflammatory events, such as acute lung injury. To examine these issues, we determined the effects of rapamycin-induced inhibition of mTORC1 on TLR2- and TLR4-induced neutrophil activation. mTORC1 was dose- and time-dependently activated in murine bone marrow neutrophils cultured with the TLR4 ligand, LPS, or the TLR2 ligand, Pam(3) Cys-Ser-(Lys)(4) (PAM). Incubation of PAM- or LPS-stimulated neutrophils with rapamycin inhibited expression of TNF-alpha and IL-6, but not IkappaB-alpha degradation or nuclear translocation of NF-kappaB. Exposure of PAM or LPS-stimulated neutrophils to rapamycin inhibited phosphorylation of serine 276 in the NF-kappaB p65 subunit, a phosphorylation event required for optimal transcriptional activity of NF-kappaB. Rapamycin pretreatment inhibited PAM- or LPS-induced mTORC1 activation in the lungs. Administration of rapamycin also decreased the severity of lung injury after intratracheal LPS or PAM administration, as determined by diminished neutrophil accumulation in the lungs, reduced interstitial pulmonary edema, and diminished levels of TNF-alpha and IL-6 in bronchoalveolar lavage fluid. These results indicate that mTORC1 activation is essential in TLR2- and TLR4-induced neutrophil activation, as well as in the development and severity of acute lung injury.