Inactivation of mammalian target of rapamycin (mTOR) by rapamycin in a murine model of lipopolysaccharide-induced acute lung injury.

BACKGROUND: The mammalian target of rapamycin (mTOR) pathway, a key cellular signaling pathway associated with various cellular functions, has distinct roles in the inflammatory process. In this study, the mTOR inhibitor rapamycin (Rapa) was used to test whether inhibition of mTOR activation attenuates lipopolysaccharide (LPS)-induced acute lung injury (ALI) in a murine model. METHODS: Mice pretreated with Rapa or vehicle were given LPS intratracheally. Local cell numbers and inflammatory cytokines present in the bronchoalveolar lavage fluid (BAL), wet-to-dry weight ratio, histopathology of the lungs, and survival were evaluated. RESULTS: The phosphorylation of S6, a major downstream target of mTOR, had a 3-fold increase in lung tissue after LPS stimulation, but the increase was blocked by Rapa. Rapa reduced the levels of TNF-α (LPS vs. LPS + Rapa, (1672.74 ± 193.73) vs. (539.17 ± 140.48) pg/ml, respectively; P < 0.01) and IL-6 (LPS vs. LPS + Rapa: (7790.88 ± 1170.54) vs. (1968.57 ± 474.62) pg/ml, respectively; P < 0.01) in the BAL fluid. However, Rapa had limited effects on the overall severity of ALI, as determined by the wet-to-dry weight ratio of the lungs, number of neutrophils in the BAL fluid, and changes in histopathology. In addition, Rapa failed to reduce mortality in the LPS-induced ALI model. CONCLUSIONS: We confirmed that mTOR was activated during LPS-induced ALI and strongly inhibited by Rapa. Although Rapa reduced the levels of the mediators of inflammation, the overall severity and survival of the ALI murine model were unchanged.