129 Involvement of the Hypoxia-Inducible Factor-1 Transcription Complex in the Inflammatory Responses of Human Mast Cells and Basophils

BACKGROUND: We recently found that hypoxia-inducible factor 1 (HIF-1) plays a crucial role in the pro-allergic functions of human basophils by transcriptional control of energy metabolism via glycolysis as well as directly triggering the expression of the angiogenic cytokine vascular endothelial growth factor (VEGF). Here, we investigated whether there is an overarching principle of HIF-1 involvement in controlling the synthesis of angiogenic and inflammatory cytokines from various human effector cells stimulated by IgE-dependent or innate immune triggers. METHODS: LAD2 human mast cells,1 primary human basophils, and THP-1 human myeloid cells were used for investigations of FcεRI and Toll-like receptor (TLR) ligand-induced responses. Quantitative real-time PCR, Western blot analysis, ELISA, fluorometry, luminometry and fluorescence microscopy were used to run the assays. RESULTS: In contrast to basophils, LAD2 mast cells expressed high background levels of HIF-1α, which was largely independent of the effects of stem cell factor (SCF).2 Both mast cells and basophils expressed TLR2 and 4, albeit weakly compared to THP-1 cells. Cytokine production in mast cells following TLR ligand stimulation was markedly reduced by HIF-1α knockdown in LAD2 mast cells. In contrast, although HIF-1 is involved in IgE-mediated IL-4 secretion from basophils, it was not clearly induced by the TLR2 ligand PGN. CONCLUSIONS: HIF-1α accumulation is fundamentally important for sustaining human allergic effector cell survival and function. This transcription complex facilitates the generation of both pro-angiogenic and inflammatory cytokines in mast cells but has a differential role in basophil stimulation comparing IgE-dependent triggering with innate immune stimuli.