VEGF secretion during hypoxia depends on free radicals-induced Fyn kinase activity in mast cells

Mast cells (MC) have an important role in pathologic conditions such as asthma and chronic obstructive pulmonary disease (COPD), where hypoxia conduce to deleterious inflammatory response. MC contribute to hypoxia-induced angiogenesis producing factors such as vascular endothelial growth factor (VEGF), but the mechanisms behind the control of hypoxia-induced VEGF secretion in this cell type is poorly understood. We used the hypoxia-mimicking agent cobalt chloride (CoCl2) to analyze VEGF secretion in murine bone marrow-derived mast cells (BMMCs). We found that CoCl2 promotes a sustained production of functional VEGF, able to induce proliferation of endothelial cells in vitro. CoCl2-induced VEGF secretion was independent of calcium rise but dependent on tetanus toxin-sensitive vesicle-associated membrane proteins (VAMPs). VEGF exocytosis required free radicals formation and the activation of Src family kinases. Interestingly, an important deficiency on CoCl2-induced VEGF secretion was observed in Fyn kinase-deficient BMMCs. Moreover, Fyn kinase was activated by CoCl2 in WT cells and this activation was prevented by treatment with antioxidants such as Trolox and N-acetylcysteine. Our results show that BMMCs are able to release VEGF under hypoxic conditions through a tetanus toxin-sensitive mechanism, promoted by free radicals-dependent Fyn kinase activation.

Research highlights
► Bone marrow-derived mast cells (BMMCs) secrete functional VEGF but do not degranulate after Cobalt chloride-induced hypoxia.
► CoCl2-induced VEGF secretion in mast cells occurs by a Ca2+-insensitive but brefeldin A and Tetanus toxin-sensitive mechanism.
► Trolox and N-acetylcysteine inhibit hypoxia-induced VEGF secretion but only Trolox inhibits FcεRI-dependent anaphylactic degranulation in mast cells.
► Src family kinase Fyn activation after free radical production is necessary for hypoxia-induced VEGF secretion in mast cells.