Extracellular Double-Stranded RNA Induces TSLP via an Endosomal Acidification- and NF-κB-Dependent Pathway in Human Keratinocytes

Abstract

Double-stranded RNA (dsRNA) causes keratinocytes to release thymic stromal lymphopoietin (TSLP), which plays a key role in allergic diseases. Endosomal Toll-like receptor 3 (TLR3) and cytosolic RIG-like receptors (RLRs) and PKR have been reported to recognize dsRNA. Here, we demonstrate that dsRNA induces TSLP in keratinocytes via an endosomal acidification-dependent and NF-κB-mediated pathway. After treatment with pharmacologic inhibitors or transfection with small interfering RNAs (siRNAs), primary human keratinocytes were stimulated. Bafilomycin A1, which inhibits endosomal acidification to block the TLR3 pathway, blocked the dsRNA-induced expression of TSLP, IL-8, IFN-β, and other molecules including the dsRNA sensors, whereas it did not inhibit diacyllipopeptide-induced expression of TSLP and IL-8. The dsRNA-induced gene expression of TSLP depended on RelA, a component of NF-κB, but not IRF3, similar to IL-8 but different from IFN-β, which depended on both IRF3 and RelA. The results indicate that endosomal acidification and the subsequent activation of NF-κB are necessary to sense extracellular dsRNA, suggesting the importance of the TLR3-NF-κB axis to trigger production of TSLP against the self dsRNA released from damaged cells or viral dsRNA, in the epidermis, relating to skin inflammation including atopic dermatitis (AD).

Bacterial and Viral Infections in Atopic Dermatitis: a Comprehensive Review

“…Like bacterial skin infections, AD patients are also susceptible to viral skin infection [23]. However, as compared to bacterial skin infections, viral skin infections are relatively less common in AD patients.…”

“…Further studies of TLR functions and MDSC are needed in AD. Stimulation of TLR-3 by double-stranded RNA released from damaged epithelial cells leads to an increased production of thymic stromal lymphopoietin (TSLP) from keratinocytes [23]. TSLP is an IL-7-like cytokine that is highly expressed in AD lesions [24].…”

Long TSLP transcript expression and release of TSLP induced by TLR ligands and cytokines in human keratinocytes

“…In primary human keratinocytes, we recently demonstrated that ligands for some Toll-like receptors (TLRs) (polyI:C for TLR3 [19,20], diacylated lipopeptide FSL-1 and Staphylococcus aureus membrane for TLR2-TLR6 [21], and flagellin for TLR5 [22]) upregulate the expression of the TSLP transcript and induce the release of TSLP. Proinflammatory cytokines such as TNF-a and the T H 2 cytokines IL-4 and IL-13 synergistically induce the release of TSLP in human skin explants [23] and upregulate the TLR liganddependent release of TSLP in primary human keratinocytes [19][20][21][22].…”

“…Proinflammatory cytokines such as TNF-a and the T H 2 cytokines IL-4 and IL-13 synergistically induce the release of TSLP in human skin explants [23] and upregulate the TLR liganddependent release of TSLP in primary human keratinocytes [19][20][21][22]. In mice, topical application of vitamin D receptor (VDR) agonists, calcitriol (1,25-dihydroxyvitamin D 3 , the active form of vitamin D 3 ) and its analog MC903 (calcipotriol; Dovonex), induces the expression of TSLP in epidermal keratinocytes and triggers an atopic dermatitis-like inflammation [24].…”

New insights in the pathogenesis of atopic dermatitis

“…Double-stranded RNA released from damaged epithelial cells may stimulate Toll-like receptor (TLR) 3, leading to the production of TSLP from keratinocytes (29). Deletion of a disintegrin and metalloproteinase 17 (ADAM 17), a transmembrane metalloproteinase that cleaves cell surface proteins and maintains barrier homeostasis, in murine keratinocytes has been shown to result in skin barrier defects and chronic dermatitis in mouse models (30,31).…”