Exophilin-5 regulates allergic airway inflammation by controlling IL-33–mediated Th2 responses
Katsuhide Okunishi, … , Susumu Nakae, Tetsuro Izumi
Katsuhide Okunishi, … , Susumu Nakae, Tetsuro Izumi
Published April 2, 2020
Citation Information: J Clin Invest. 2020;130(7):3919-3935. https://doi.org/10.1172/JCI127839.
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Exophilin-5 regulates allergic airway inflammation by controlling IL-33–mediated Th2 responses

Abstract

A common variant in the RAB27A gene in adults was recently found to be associated with the fractional exhaled nitric oxide level, a marker of eosinophilic airway inflammation. The small GTPase Rab27 is known to regulate intracellular vesicle traffic, although its role in allergic responses is unclear. We demonstrated that exophilin-5, a Rab27-binding protein, was predominantly expressed in both of the major IL-33 producers, lung epithelial cells, and the specialized IL-5 and IL-13 producers in the CD44hiCD62LloCXCR3lo pathogenic Th2 cell population in mice. Exophilin-5 deficiency increased stimulant-dependent damage and IL-33 secretion by lung epithelial cells. Moreover, it enhanced IL-5 and IL-13 production in response to TCR and IL-33 stimulation from a specific subset of pathogenic Th2 cells that expresses a high level of IL-33 receptor, which exacerbated allergic airway inflammation in a mouse model of asthma. Mechanistically, exophilin-5 regulates extracellular superoxide release, intracellular ROS production, and phosphoinositide 3-kinase activity by controlling intracellular trafficking of Nox2-containing vesicles, which seems to prevent the overactivation of pathogenic Th2 cells mediated by IL-33. This is the first report to our knowledge to establish the significance of the Rab27-related protein exophilin-5 in the development of allergic airway inflammation, and provides insights into the pathophysiology of asthma.

Authors

Katsuhide Okunishi, Hao Wang, Maho Suzukawa, Ray Ishizaki, Eri Kobayashi, Miho Kihara, Takaya Abe, Jun-ichi Miyazaki, Masafumi Horie, Akira Saito, Hirohisa Saito, Susumu Nakae, Tetsuro Izumi

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Figure 1

Exophilin-5 deficiency exacerbates lung inflammation in an OVA-induced mouse model of asthma.

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Exophilin-5 deficiency exacerbates lung inflammation in an OVA-induced m...
(A) Targeted disruption of the exophilin-5 gene on mouse chromosome 9. The blue region in the amino acid sequence of exophilin-5 indicates the Rab-binding domain. Dark and light gray boxes indicate regions used for PCR genotyping of WT and KO alleles, respectively. Middle insert: Genomic Southern hybridization analysis of the backcrossed progenies from a cross of chimeric mice with C57BL/6 mice. The location of the external probe is shown with horizontal closed boxes in the upper panel. The probe hybridizes to ApaI fragments of 9.9 kb and 8.4 kb from WT and KO alleles, respectively. Bottom insert: Expression of exophilin-5 protein in cerebellum from WT and exophilin-5–knockout (Exph5-KO) mice. A blot representative of 3 independent experiments with similar results is shown. (B–D) Phenotypes of Exph5-KO mice in an OVA-induced mouse model of asthma. (B and C) Cytokine production in response to ex vivo OVA restimulation (1 mg/mL) by splenocytes (B) and by lung lymph node cells (C). For dose- and time-dependent cytokine production by these cells, refer to Supplemental Figure 1, C and D. (D) Cytokine levels in the lungs of mice after 3-day OVA aerosol challenges. (E) Cell numbers and differentials in BALF after 3-day 3% OVA inhalation. Cell differentials were determined by counting of cytospin samples stained with Diff-Quik. n = 4–6 mice combined from at least 2 independent experiments in B–E. (F) Mucus production by the epithelia was assessed by PAS staining of sliced paraffin-fixed lung sections. An image representative of 6 samples from 2 independent experiments is shown. Scale bars: 50 μm. (G) Airway hyperresponsiveness assessed as change in lung resistance (RL) in response to methacholine. n = 6 mice combined from 2 independent experiments. *P < 0.05; **P < 0.01 by unpaired t test.