Hypoxia and monomeric IgE activate common signaling pathways leading to chemokine CCL2 production in mast cells

Abstract

Although presence of mast cells (MCs) to sites with low oxygen concentration (such as inflamed tissues with compromised blood flux and solid tumors) has been reported, the effects of hypoxia on the cytokine profile produced by MCs under those conditions has not been fully explored. We used the murine B16 melanoma model to quantify the presence of MCs in normoxic or hypoxic zones of the tumor and, bone marrow-derived mast cells (BMMCs) subjected to a 1% O2 atmosphere to characterize the production of specific cytokines and chemokines by this cell type in hypoxic conditions. Hypoxic areas of melanoma tumors were identified with hypoxyprobe and the number of MCs was determined by confocal analysis of tryptase positive cells. Using this methodology, important MCs presence in hypoxic zones of the tumor was detected. In vitro, BMMCs subjected to hypoxia were able to produce VEGF and the potent chemokine CCL2. Chemokine production in hypoxia was sensitive to the antioxidant Trolox and the IKK inhibitor BAY117085. CCL2 production was also induce by monomeric IgE by a mechanism also sensitive to Trolox and BAY117085. CCL2 production triggered by hypoxia or monomeric IgE was sensitive to calcium chelator BAPTA and the L-type calcium channel blocker Nifedipine. Our results show that MCs are importantly recruited to hypoxic sites of melanoma tumors and that hypoxia induces the production of the chemokine CCL2 by a mechanism that require the production of reactive oxygen species (ROS) and intracellular calcium rise through the activation of L-type calcium channels. Also, data indicate that monomeric IgE triggers a very similar response than hypoxia does to lead to the production of CCL2 in mast cells.