Cytokines Stimulated by IL-33 in Human Skin Mast Cells: Involvement of NF-κB and p38 at Distinct Levels and Potent Co-Operation with FcεRI and MRGPRX2

Abstract

The IL-1 family cytokine IL-33 activates and re-shapes mast cells (MCs), but whether and by what mechanisms it elicits cytokines in MCs from human skin remains poorly understood. The current study found that IL-33 activates CCL1, CCL2, IL-5, IL-8, IL-13, and TNF-α, while IL-1β, IL-6, IL-31, and VEGFA remain unaffected in cutaneous MCs, highlighting that each MC subset responds to IL-33 with a unique cytokine profile. Mechanistically, IL-33 induced the rapid (1–2 min) and durable (2 h) phosphorylation of p38, whereas the phosphorylation of JNK was weaker and more transient. Moreover, the NF-κB pathway was potently activated, as revealed by IκB degradation, increased nuclear abundance of p50/p65, and vigorous phosphorylation of p65. The activation of NF-κB occurred independently of p38 or JNK. The induced transcription of the cytokines selected for further study (CCL1, CCL2, IL-8, TNF-α) was abolished by interference with NF-κB, while p38/JNK had only some cytokine-selective effects. Surprisingly, at the level of the secreted protein products, p38 was nearly as effective as NF-κB for all entities, suggesting post-transcriptional involvement. IL-33 did not only instruct skin MCs to produce selected cytokines, but it also efficiently co-operated with the allergic and pseudo-allergic/neurogenic activation networks in the production of IL-8, TNF-α, CCL1, and CCL2. Synergism was more pronounced at the protein than at the mRNA level and appeared stronger for MRGPRX2 ligands than for FcεRI. Our results underscore the pro-inflammatory nature of an acute IL-33 stimulus and imply that especially in combination with allergens or MRGPRX2 agonists, IL-33 will efficiently amplify skin inflammation and thereby aggravate inflammatory dermatoses.

Therapeutic Potential of MRGPRX2 Inhibitors on Mast Cells

“…MRGPRX2 ligands SP and LL-37 activate downstream signals of MRGPRX2, such as Erk1/2, JNK, p38, and PI3K/AKT, to produce TNF-α, IL-6, IL-8, and IL-13 [ 48 , 49 , 50 ], and LL-37 is involved in cytokine production by activating the NF-κB pathway through MRGPRX2 [ 39 , 51 ]. IL-33, a member of the IL-1 family, induces cytokine production in MCs through its downstream signals NF-κB and p38/JNK MAPK, and efficiently co-operates with MRGPRX2-mediated MC activation in the production of IL-8, TNF-α, chemokine ligand (CCL) 1, and CCL2 [ 52 ]. These studies indicate that NF-κB and p38/JNK signaling plays an important role in MRGPRX2-mediated MC cytokine production.…”

The Implications of Pruritogens in the Pathogenesis of Atopic Dermatitis

“…Another group also reported that the expression of IL-33 in keratinocytes was correlated with the severity of pruritus and the degree of lichenification (thick and leathery skin) in patients with AD [78]. IL-33 is a potent MC activator and can stimulate ILC2s and basophils to release Th2 cytokines such as IL-5 and IL-13, which in turn exacerbate inflammation in AD [79,80]. Transgenic mice with IL-33 overexpression in keratinocytes showed AD-like inflammation, which is dependent on the innate immune response mediated by ILC2s and basophils [80].…”

Mast Cells in the Mammalian Testis and Epididymis—Animal Models and Detection Methods

“…The functional characterization of MCs is complex due to their distribution, but also to their dual behavior in the organism since they can act simultaneously as “sensors” [ 22 ] and effective “warriors”.…”

“…The inducers and tissue-specific supporters of MC active response remain incompletely characterized, despite recently proposed candidates. One of them is interleukin IL-33, a constitutively expressed IL-1 family member, having above mentioned the dual role of activation and support of MCs with a significant emphasis on their inflammatory response [ 22 ].…”