Protective function of interleukin‐22 in pulmonary fibrosis

Abstract

Abstract Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive scarring disease with unknown etiology. The evidence of a pathogenic role for transforming growth factor‐beta (TGF‐β) in the development and progression of IPF is overwhelming. In the present study, we investigated the role of interleukin‐22 (IL‐22) in the pathogenesis of IPF by regulating the TGF‐β pathway. We measured parameters and tissue samples from a clinical cohort of IPF. IL‐22R knock out (IL‐22RA1−/−) and IL‐22 supplementation mouse models were used to determine if IL‐22 is protective in vivo. For the mechanistic study, we tested A549, primary mouse type II alveolar epithelial cell, human embryonic lung fibroblast, and primary fibroblast for their responses to IL‐22 and/or TGF‐β1. In a clinical cohort, the expression level of IL‐22 in the peripheral blood and lung tissues of IPF patients was lower than healthy controls, and the lower IL‐22 expression was associated with poorer pulmonary function. IL‐22R−/− mice demonstrated exacerbated inflammation and fibrosis. Reciprocally, IL‐22 augmentation by intranasal instillation of recombinant IL‐22 repressed inflammation and fibrotic phenotype. In vitro, IL‐22 treatment repressed TGF‐β1 induced gene markers representing epithelial‐mesenchymal‐transition and fibroblast‐myofibroblast‐transition, likely via the inhibition of TGF‐β receptor expression and subsequent Smad2/3 activation. IL‐22 appears to be protective against pulmonary fibrosis by inhibiting TGF‐β1 signaling, and IL‐22 augmentation may be a promising approach to treat IPF.