Tafazzin Modulates Allergen-Induced Mast Cell Inflammatory Mediator Secretion.

Allergic inflammatory diseases are a steadily growing health concern. Mast cells, a driving force behind allergic pathologies, modulate metabolic pathways to carry out various functions following IgE-FcεRI-mediated activation. Tafazzin (TAZ) is a cardiolipin transacylase that functions to remodel, and thereby mature, cardiolipin, which is important for efficient energy production through oxidative phosphorylation. In this study, we aimed to evaluate the contribution of TAZ in IgE-mediated mast cell activation. Fetal liver-derived mast cells (FLMCs) were differentiated from mice with a doxycycline (dox)-inducible TAZ short hairpin RNA (shRNA) cassette (TAZ shRNA+/+) and littermate wild-types (WTs). TAZ knockdown in FLMCs following dox treatment was confirmed by Western blotting (99.1% by day 5), whereas flow cytometry confirmed FLMC phenotype (c-kit+ FcεRI+) and retention of receptor expression post-dox. Five-day dox-treated WT and TAZ shRNA+/+ FLMCs were activated via allergen-bound IgE cross-linking of FcεRI under stem cell factor potentiation. With dox, and in response to allergen, TAZ shRNA+/+ FLMCs displayed a 25% reduction in oxygen consumption and a significant 31% reduction in mast cell degranulation compared with dox-treated WT FLMCs. Secretion of TNF, CCL1, and CCL2 were significantly reduced, with CCL9 also impaired. Notably, gene expression was not impaired for any inflammatory mediator measured. Functionally, this suggests that TAZ is a contributor to mast cell degranulation and inflammatory mediator secretion. Given unimpacted induced gene expression for mediators measured, we propose that TAZ reduction impairs mast cell exocytosis mechanisms. We thus identify a potential new contributor to immunometabolism that enhances our understanding of mast cell signaling metabolic pathway interactions during allergic inflammation.

TAK1 signaling activity links the mast cell cytokine response and degranulation in allergic inflammation.

Mast cells drive the inappropriate immune response characteristic of allergic inflammatory disorders via release of pro-inflammatory mediators in response to environmental cues detected by the IgE-FcεRI complex. The role of TGF-ß-activated kinase 1 (TAK1), a participant in related signaling in other contexts, remains unknown in allergy. We detect novel activation of TAK1 at Ser412 in response to IgE-mediated activation under SCF-c-kit potentiation in a mast cell-driven response characteristic of allergic inflammation, which is potently blocked by TAK1 inhibitor 5Z-7-oxozeaenol (OZ). We, therefore, interrogated the role of TAK1 in a series of mast cell-mediated responses using IgE-sensitized murine bone marrow-derived mast cells, stimulated with allergen under several TAK1 inhibition strategies. TAK1 inhibition by OZ resulted in significant impairment in the phosphorylation of MAPKs p38, ERK, and JNK; and mediation of the NF-κB pathway via IκBα. Impaired gene expression and near abrogation in release of pro-inflammatory cytokines TNF, IL-6, IL-13, and chemokines CCL1, and CCL2 was detected. Finally, a significant inhibition of mast cell degranulation, accompanied by an impairment in calcium mobilization, was observed in TAK1-inhibited cells. These results suggest that TAK1 acts as a signaling node, not only linking the MAPK and NF-κB pathways in driving the late-phase response, but also initiation of the degranulation mechanism of the mast cell early-phase response following allergen recognition and may warrant consideration in future therapeutic development.