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‐β‐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.
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.
Large artery stiffness is an independent predictor of cardiovascular disease (CVD) and all‐cause mortality. Stiffening of the large arteries (e.g., the aorta) is characterized by a marked reduction in the elastin‐collagen ratio in the extracellular matrix (ECM) of the arterial wall, and is largely the result of fatigue and fragmentation of ECM components due to cyclic stress. Matrix metalloproteinases (MMPs), a family of zinc‐dependent endopeptidases, may be important in the progression of arterial stiffness due to their involvement in ECM homeostasis and arterial wall remodeling. MMP‐3 may be of particular importance in arterial wall remodeling due to its ability to degrade numerous constituents of the arterial ECM, such as elastin and collagen. Previous studies have examined the effects of MMP‐3 genotype and expression on arterial wall stiffness in different disease populations; however, none have examined the association between MMP‐3 expression and large artery stiffness in a population of healthy young adults. Thus, the purpose of this study was to examine the association between serum MMP‐3 and carotid‐femoral pulse wave velocity (cfPWV), a non‐invasive measure of large artery stiffness, in a sample of healthy young adults. It is expected that individuals with higher serum MMP‐3 levels will present with larger cfPWVs. 156 participants (n = 68 males) aged 20–25 years were recruited as part of the Niagara Longitudinal Heart Study (NLHS), and all participants were free of any clinically diagnosed CVD. cfPWV (m/s) was determined using applanation tonometry as a non‐invasive surrogate of large artery stiffness. Serum MMP‐3 concentrations (pg/mL) were measured using standard ELISA techniques. Linear regression analyses were used to investigate the cross‐sectional association between serum MMP‐3 and cfPWV. Analyses were adjusted for age, sex, mean arterial pressure (MAP), body mass index (BMI), and smoking status. Data on cfPWV and MMP‐3 were available on 139 participants (n = 63 males), and were subsequently used in analysis. After adjustment for age, sex, MAP, BMI, and smoking status, serum MMP‐3 was significantly and positively associated with cfPWV (p = 0.038). cfPWV was also significantly and positively associated with MAP and smoking status (both p < 0.001), but not age (p = 0.336). The association between cfPWV and both sex and BMI showed a positive trend, but only reached borderline significance (p = 0.059 and p = 0.054, respectively). Together, MAP, smoking status and serum MMP‐3 predicted 22% of the variation in cfPWV (adjusted R2 = 0.220, p < 0.001). These data suggest that greater serum MMP‐3 levels are associated with larger cfPWVs and thus, greater large artery stiffness. Physiologic MMP‐3 levels function to maintain ECM homeostasis; however, greater MMP‐3 levels may exacerbate ECM degradation and contribute to stiffening of the large arteries. Future research should examine the potential functional role of MMP‐3 in CVD progression. Support or Funding Information The NLHS is funded by the Canadian In...
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