Mast cells (MC) are critical for allergic reactions, but are also important in inflammatory processes. Stimulation by neuropeptides, such as substance P (SP) and neurotensin (NT) leads to release of pre-formed molecules stored in numerous MC secretory granules and newly-synthesized pro-inflammatory mediators, including tumor necrosis factor (TNF), interleukin 8 (CXCL8) and vascular endothelial growth factor (VEGF). Here, we investigate the role of mammalian target of rapamycin (mTOR) signaling in the stimulation of cultured human LAD2 MC by NT or SP, and the inhibitory effect of the natural flavonoids 3′,4′,5,7-tetrahydroxyflavone (luteolin) and its novel structural analog 3 ′,4′,5,7-tetramethoxyluteolin (methoxyluteolin). Stimulation by NT (10[micro]M) or SP (1[micro]M) increases (p <0.001) the gene expression (after 6 h) and release (after 24 h) of TNF, CXCL8 and VEGF. This occurs via activation of both mTOR complexes, as denoted by the increased phosphorylated (p) protein levels (p<0.0001) of the downstream mTORC1 substrate pp70S6KThr389 and mTORC2 component pmTORSer2448. Pre-treatment of human MC using the mTORC1 inhibitor rapamycin or the mTORC1/mTORC2 inhibitor Torin1 or the two flavonoids decreases both gene expression and release (p<0.0001) of all three mediators. Methoxyluteolin is more potent human MC inhibitor than luteolin or Torin1, implicating other MC protein targets in addition to the mTOR complex. The present findings indicate that mTOR is partially involved in the neuropeptide-stimulation of MC, but the novel flavonoid methoxyluteolin inhibits the response entirely suggesting, that it may be developed for treatment of allergic and inflammatory diseases.
- The American Society for Pharmacology and Experimental Therapeutics