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). However, the molecules/mediators involved in basophil-dependent skin inflammation have yet to be elucidated.
A murine model of prurigo reaction, one of the models of basophil-dependent chronic skin inflammation, features marked eosinophil and basophil infiltration and increased local production of amphiregulin (AREG), an epidermal growth factor-like molecule (
). Here, we assessed the contribution of basophil-derived AREG in murine models of prurigo-like skin inflammation and AD. All animal experiments were approved by the Institutional Animal Care and Use Committee of Tokyo Medical and Dental University.
A mouse model of prurigo-like skin inflammation has been described previously (
); see also the Supplementary Materials online. Repeated local injection of 2,4,6-trinitrophenyl-ovalbumin (TNP-OVA) into the dorsal skin of mice passively immunized with TNP-IgE has been shown to induce prurigo-like nodules. In this study, however, skin inflammation was induced on the ear lobes to permit objective assessment of the magnitude of changes in inflammation. We initially assessed the in vivo effects of AREG small interfering RNA (siRNA) on prurigo-like skin inflammation. Inhibition of local AREG production by repeated administration of the siRNA resulted in a partial, but significant, attenuation of skin responses. Histological findings showed ameliorated infiltration of inflammatory cells and improvement of acanthosis (Figure 1a). We then administered recombinant AREG (rAREG) intradermally into the inflamed ear lobes. rAREG enhanced ear swelling responses in prurigo-like skin inflammation (Figure 1b). In contrast, rAREG failed to elicit inflammation in naive skin (see Supplementary Figure S1 online).
We next focused on basophils as a potential cellular source of AREG. In the lesional skin of prurigo-like skin inflammation, basophils expressed AREG (Figure 1c). To confirm the ability of basophils to secrete AREG, we investigated the mRNA expression of AREG in IL-3– and TSLP-elicited ex vivo bone marrow-derived basophils (BMBas) (
). Both IL-3– and TSLP-elicited BMBas showed higher expression of AREG after exposure to IL-33 or when stimulated with IgE plus IL-3 or TSLP (Figure 1d).
To assess the contribution of basophil-derived AREG to prurigo-like skin inflammation, basophil-depleted mice were reconstituted with basophils derived from wild-type (WT) mice that had been treated with AREG siRNA. Basophils from Mcpt8DTR mice (BALB/c background) specifically express diphtheria toxin (DT) receptors, and thus DT treatment selectively and inducibly abolishes basophils in those mice (see Supplementary Figure S2 online) (
), which were used as the recipient animals in this experiment. DT-induced basophil depletion attenuated prurigo-like skin inflammation in Mcpt8DTR mice (Figure 1e), indicating that basophils contribute to this inflammation. The CD49b+ basophil-enriched cell fraction of spleen cells (primary basophils) from WT mice was adoptively transferred into DT-treated Mcpt8DTR mice on day –1, and prurigo-like skin inflammation was elicited starting on day 0. Reconstitution of basophil-depleted Mcpt8DTR mice with scramble siRNA-treated wild-type (WT) primary basophils restored the inflammation. However, this restoration was abolished when basophil-depleted Mcpt8DTR mice were reconstituted with AREG siRNA-treated primary basophils. Thus, AREG derived from basophils appears to contribute, at least in part, to prurigo-like skin inflammation in mice.
We next examined the involvement of basophil-derived AREG in an MC903-induced murine model of AD, in which basophils mediate inflammation (
) (see Supplementary Materials). Administration of AREG siRNA attenuated ear-swelling responses concomitantly with the inhibition of AREG generation (Figure 2a). These effects were accompanied by decreased numbers of dermal infiltrating cells and reduced epidermal thickness (Figure 2a). On the other hand, lesional administration of rAREG in the inflamed skin exacerbated ear swelling responses (Figure 2b). We observed AREG-expressing basophils in the skin lesions of the MC903-induced murine AD model (Figure 2c).
We then attempted to elicit MC903-induced inflammation in basophil-depleted Mcpt8DTR mice reconstituted with AREG-siRNA–treated WT primary basophils. Basophil depletion with DT in Mcpt8DTR mice (on day –1) ameliorated MC903-induced inflammation (Figure 2d). Adoptive transfer of the scramble siRNA-treated, but not AREG siRNA-treated, primary basophils partially restored MC903-induced inflammation (Figure 2d). Collectively, these results indicate that basophil-derived AREG seems to play a role in MC903-induced basophil-mediated skin inflammation, as seen in prurigo-like skin inflammation.
In this work, we showed that basophils contribute to inflammation in murine models of prurigo and AD via the release of AREG. Previous research has shown that IL-3–elicited basophils are activated by FcεRI crosslinking to release cytokines/chemokines, and TSLP-elicited basophils respond to IL-18 and IL-33 (
). In this study, IL-3–elicited BMBas showed higher levels of AREG when stimulated with IgE than did TSLP-elicited BMBas. In contrast, TSLP-elicited BMBas were more responsive to IL-33 than were IL-3–elicited BMBas. The types of basophils that develop in the murine models of prurigo and AD are uncertain. However, the immunological environment in these models appeared to be ideal for AREG generation irrespective of the types of basophil, because both of these models showed increased local production of IL-33 and TSLP, along with elevated serum IgE (
) may contribute to increased generation of IL-33 and TSLP from epidermal cells. Nonetheless, our results indicate that basophil-derived AREG may be a therapeutic target for chronic skin inflammation, including that occurring in prurigo and AD.
The authors thank Chiyako Miyagishi for technical assistance. This work was supported by the Japan Society for the Promotion of Science KAKENHI Grant-in-Aid for Young Scientists (B) (no. 17K16328) and by a GlaxoSmithKline Japan Research Grant 2016.
TH: conceptualization, data curation, formal analysis, funding acquisition, investigation, methodology, project administration, resources, validation, visualization, and writing (the draft). TS: methodology, project administration, supervision, and writing (review and editing). HK: methodology, resources, supervision, and writing (review and editing). HY: funding acquisition, project administration, supervision, and writing (review and editing). All authors have read the manuscript and approved this submission.
Supplementary Materials and Methods
Six- to 9-week-old male and female C57BL/6 mice, BALB/c mice, and BALB/c-nu/nu mice were obtained from Sankyo Lab Service (Tokyo, Japan). Mast cell protease 8-diphtheria toxin receptor (Mcpt8DTR) mice (BALB/c background) were generated as described previously (
). Both male and female mice showed similar results in the experiments of this work. Mice were maintained under specific pathogen free conditions in our animal facility. All animal experiments were approved by the Institutional Animal Care and Use Committee of Tokyo Medical and Dental University (protocols A2018-299A, A2018-199A, A2018-298A, and A2018-237A).
Mcpt8DTR mice were administered DT intravenously (750 ng/20 g body weight) (Sigma-Aldrich, St. Louis, MO) as described previously (
TNP-IgE was collected from ascites of BALB/c-nu/nu mice by intraperitoneal injection of IgELb4 cell hybridoma (American Type Culture Collection, Manassas, VA). Supernatants were precipitated with 55% saturated ammonium sulfate, followed by phosphate buffered saline(–) dialysis. The concentration of IgE was determined with an ELISA kit (Yamasa Co., Tokyo, Japan) as described previously (
Mice were passively immunized with TNP-IgE (120 μg/mouse) on days –1, 2, and 5, followed by subcutaneous administration of TNP(12)-OVA (100 μg/site; Biosearch Technologies, Petaluma, CA) into the ear lobes on days 0, 3, and 6 (
). On day 7, animals were euthanized, and ear samples were collected.
Anti-amphiregulin antibody (H-155) was obtained from Santa Cruz Biotechnology (Dallas, TX). Anti-mouse basophil-specific antibody (TUG8) was purchased from BioLegend (San Diego, CA)
Formalin-fixed paraffin-embedded samples (5-μm-thick sections) were pretreated with proteinase K (Dako, Glostrup, Denmark). The treated sections then were incubated with a combination of the indicated antibodies, followed by a reaction with Alexa Fluor 488- or 568-conjugated secondary antibodies (Abcam) and mounted with Fluoroshield with DAPI (GeneTex, TX). Photomicrographs were captured with a TCS SP8 confocal microscope (Leica Microsystems, Tokyo, Japan).
Measurement of cytokines
The 8-mm-diameter skin punch samples were homogenized with 200 μl of phosphate buffered saline supplemented with 1% proteinase inhibitor cocktail (Sigma-Aldrich) and then centrifuged at 10,000g for 10 minutes at 4 °C. Levels of AREG in the supernatants of homogenates or of cell cultures were quantified by sandwich ELISA (R&D Systems, Minneapolis, MN).
Preparation of BMBas
BMBas were prepared by culturing bone marrow cells collected from 8-week-old C57BL/6 N mice in RPMI 1640 complete medium supplemented with 10% fetal bovine serum, 100 IU/ml penicillin-streptomycin, and 10 ng/ml recombinant IL-3, or 500 ng/ml recombinant TSLP (eBioscience, San Diego, CA), and incubated for 10 days at 37 °C and 5% CO2. Then, CD49b+ cells were isolated by the use of a magnetically activated cell sorter system with biotinylated anti-CD49b antibody and streptavidin microbeads (Miltenyi Biotec, Auburn, CA).
Stimulation of BMBas
For IgE-mediated stimulation, cells were sensitized with 1 μg/ml TNP-IgE for 1 hour with or without 10 ng/ml IL-3 or 500 ng/mL TSLP, then washed, and stimulated with 20 ng/ml TNP(12)-OVA for 10 hours. BMBas also were incubated with recombinant mouse IL-3 (10 ng/ml), TSLP (500 ng/ml), or IL-33 (10 ng/ml) (eBioscience) for 10 hours. Then, the cells were subjected to total RNA extraction as described below.
Preparation of the CD49b+ basophil-enriched cell fraction from splenocytes
Spleen cells were collected from 8-week-old WT BALB/c mice, and CD49b+ cells were isolated by the use of a magnetically activated cell sorter system as described.
In vivo and ex vivo transfection with AREG siRNA
For in vivo transfection with AREG or scramble siRNA, siRNAs were prepared for transfection using cationic liposomes (Lipofectamine 3000, Life Technologies, Carlsbad, CA), according to the manufacturer’s instructions. Mice were transfected with siRNA by injection into each ear lobe of 0.5 nmol/30 μl/ear diluted with Life Technologies Opti-MEM I (Invitrogen, Waltham, MA)/Lipofectamine 3000 at a ratio of 50:1
For ex vivo transfection, siRNA was transfected into CD49b+ cells by using GenomOne-Si (Ishihara Sangyo Kaisha, Osaka, Japan) in RPMI 1640 complete medium supplemented with 10% fetal bovine serum, 100 IU/ml penicillin-streptomycin, and IL-3 (10 ng/ml) in conjunction with TSLP (500 ng/ml) for 24 hours.
The nucleotide sequences of the sense and antisense strands of mouse AREG siRNA were 5′-GGACCUAUCCAAGAUUGCA-3′ and 5′-UGCAAUCUUGGAUAGGUCC-3′, respectively. The scramble siRNA used as a negative control was constituted from the following two primers: 5′-CCUACGCCACCAAUUUCGU-3′ (sense strand) and 5′-ACGAAAUUGGUGGCGUAGG-3′ (antisense strand) (
Total cellular RNA was extracted from cells using ISOGEN II (Nippon Gene Co., Tokyo, Japan) and reverse-transcribed with SuperScript IV VILO Master Mix with ezDNase enzyme (Thermo Fisher Scientific, Waltham MA). Then quantitative real-time PCR was performed by real-time monitoring of the increase in fluorescence of SYBR Green dye (Brilliant SYBR Green QPCR Master Mix) by using an AriaMx Real-Time PCR System (both from Agilent Technologies Japan, Tokyo, Japan). The primers used for PCR were 5′-GCCATTATGCAGCTGCTTTGGAGC-3′ and 5′- TGTTTTTCTTGGGCTTAATCACCT-3′ for mouse AREG, and 5′-ACCACAGTCCATGCCATCAC-3′ and 5′-TCCACCACCCTGTTGCTGTA-3′ for mouse GAPDH. The levels of mRNA expression were calculated by the comparative ΔΔCt method relative to GAPDH, a housekeeping gene.
The Student t test was used to determine the statistical significance of differences between means. Results were considered significant at P < 0.05.
Protective role of STAT6 in basophil-dependent prurigo-like allergic skin inflammation.