Tollip Inhibits ST2 Signaling in Airway Epithelial Cells Exposed to Type 2 Cytokines and Rhinovirus

Abstract

The negative immune regulator Tollip inhibits the proinflammatory response to rhinovirus (RV) infection, a contributor to airway neutrophilic inflammation and asthma exacerbations, but the underlying molecular mechanisms are poorly understood. Tollip may inhibit IRAK1, a signaling molecule downstream of ST2, the receptor of IL-33. This study was carried out to determine whether Tollip downregulates ST2 signaling via inhibition of IRAK1, but promotes soluble ST2 (sST2) production, thereby limiting excessive IL-8 production in human airway epithelial cells during RV infection in a type 2 cytokine milieu (e.g., IL-13 and IL-33 stimulation). Tollip- and IRAK1-deficient primary human tracheobronchial epithelial (HTBE) cells and Tollip knockout (KO) HTBE cells were generated using the shRNA knockdown and CRISPR/Cas9 approaches, respectively. Cells were stimulated with IL-13, IL-33, and/or RV16. sST2, activated IRAK1, and IL-8 were measured. A Tollip KO mouse model was utilized to test if Tollip regulates the airway inflammatory response to RV infection in vivo under IL-13 and IL-33 treatment. Following IL-13, IL-33, and RV treatment, Tollip-deficient (vs. -sufficient) HTBE cells produced excessive IL-8, accompanied by decreased sST2 production but increased IRAK1 activation. IL-8 production following IL-13/IL-33/RV exposure was markedly attenuated in IRAK1-deficient HTBE cells, as well as in Tollip KO HTBE cells treated with an IRAK1 inhibitor or a recombinant sST2 protein. Tollip KO (vs. wild-type) mice developed exaggerated airway neutrophilic responses to RV in the context of IL-13 and IL-33 treatment. Collectively, these data demonstrate that Tollip restricts excessive IL-8 production in type 2 cytokine-exposed human airways during RV infection by promoting sST2 production and inhibiting IRAK1 activation. sST2 and IRAK1 may be therapeutic targets for attenuating excessive neutrophilic airway inflammation in asthma, especially during RV infection.

PHLDA1 Suppresses TLR4-Triggered Proinflammatory Cytokine Production by Interaction With Tollip

“…In human, Tollip has four isoforms, namely, isoform A, isoform B, isoform C, and isoform D ( 35 ). Tollip plays a critical role in regulating TLR-mediated innate immune responses ( 36 , 37 ). It was reported that Tollip interacted directly with TLR2 or TLR4 with its C-terminal domain (179–273 aa).…”

IRAK1 Duplication in MECP2 Duplication Syndrome Does Not Increase Canonical NF-κB-Induced Inflammation

“…However, this might be different in other tissues such as lung epithelia. On the one hand, IRAK-1 was shown to be essential for IL-8 production in human airway epithelial cells [77]. On the other hand, IRAK-1 is necessary for the rhinovirus-stimulated induction of CXCL-10 in airway epithelial cells and macrophages [78].…”

Rhinovirus and Innate Immune Function of Airway Epithelium

“…Even though these early pro-inflammatory responses are necessary, they must be tightly regulated to prevent excessive inflammation and subsequent tissue damage. Dual specificity phosphatases, which inhibit various mitogen-activated protein kinase (MAPK), tollinteracting protein (Tollip), a negative regulator of TLR signaling pathway, and TLR2-activation mediated IRAK-1 degradation within a short period after RV infection may all contribute to limiting RV-induced inflammation (Unger et al, 2012;Manley et al, 2019;Dakhama et al, 2020).…”