Deficiency of BMAL1 promotes ROS generation and enhances IgE-dependent degranulation in mast cells

Background: Bmal1 (Brain and muscle arnt-like, or Arntl) is a bHLH/PAS domain transcription factor central to the transcription/translation feedback loop of the circadian clock. Mast cells are crucial for effector functions in allergic reaction and their activity follows a circadian rhythm. However, the functional roles of Bmal1 in mast cells remain to be determined. Purpose: This study aimed to elucidate the specific roles of Bmal1 in IgE-dependent mast cell degranulation. Results: IgE-dependent degranulation was enhanced in bone marrow-derived mast cells (BMMCs) derived from Bmal1-deficient mice (Bmal1-KO mice) compared to that in BMMCs derived from wild-type mice (WT mice) in the absence of 2-Mercaptoethanol (2-ME) in culture. Mast cell-deficient KitW-sh mice reconstituted with Bmal1KO BMMCs showed more robust passive cutaneous anaphylactic (PCA) reactions, an in vivo model of IgEdependent mast cell degranulation, than KitW-sh mice reconstituted with WT BMMCs. In the absence of 2-ME in culture, the mRNA expression of the anti-oxidative genes NF-E2-related factor 2 (Nrf2), superoxide dismutase 2 (SOD2), and heme oxygenase-1 (HO-1) was lower and reactive oxygen species (ROS) generation was higher in Bmal1-KO BMMCs than in WT BMMCs at steady state. The IgE-dependent ROS generation and degranulation were enhanced in Bmal1-KO BMMCs compared to WT BMMCs in the absence of 2-ME in culture. The addition of 2-ME into the culture abrogated or weakened the differences in anti-oxidative gene expression, ROS generation, and IgE-dependent degranulation between WT and Bmal1-KO BMMCs. Conclusion: The current findings suggest that Bmal1 controls the expression of anti-oxidative genes in mast cells and Bmal1 deficiency enhanced IgE-dependent degranulation associated with promotion of ROS generation. Thus, Bmal1 may function as a key molecule that integrates redox homeostasis and effector functions in mast cells.