Differential mast cell activation by transcriptomic signature analysis in the U-BIOPRED severe asthma cohort

<b>Background:</b> Although recognized for its role in allergic reactions, mast cell (MC) involvement in severe asthma (SA) pathogenesis remains ill-defined. <b>Objective:</b> To investigate the role of MCs in SA compared to healthy volunteers (HV) using sputum transcriptomic data from the U-BIOPRED adult cohort. <b>Methods:</b> We analysed transcriptomic data from 61 non-smoking SA patients (SAns), 23 SA patients who were current or ex-smokers (SAsm), 20 subjects with mild-moderate asthma (MMA) and 16 HV. Ten MC transcriptomic signatures that define their response to exogenous stimuli (IgE, IL-33, LPS and IFNγ) were used. We calculated enrichment scores (ESs) across severity and transcriptome-associated clusters (TACs) using gene set variation analysis (GSVA). <b>Results:</b> Despite no increase in sputum mast cell numbers, most MC signatures were significantly enriched in SA vs MMA and HV, using gene signatures derived from mast cells exposed to IgE, IL-33, LPS or IFNg (all adjusted p&lt;0.05). ESs were comparable between MMA and HV. Resting, activated and IgE-exposed MC were significantly enriched in the TAC1 group compared with TAC2 and TAC3 groups, whilst IL-33-, LPS-, and IFNg- were enriched in TAC2 (p&lt;0.001). Tryptase+, tryptase/chymase+ and tryptase/CPA3+ MCs were significantly enriched in TAC1 compared to other TACs (p&lt;0.001). Asthmatics with a high versus low ES for the MC-activated signature were clinically distinct and were defined by the upregulation of 23 genes involved in IL-4, IL-13, IL-6, IL-18 and IL-33 signalling pathways. <b>Conclusions:</b> MCs are highly activated in SA and their distinct activation pathways may point towards potential therapeutic targets.