IL-17 Induced Autophagy Regulates Mitochondrial Dysfunction and Fibrosis in Severe Asthmatic Bronchial Fibroblasts.

Rakhee K Ramakrishnan,Surendra Rawat,Bassam Mahboub,Saba Al Heialy,Laila Salameh,Ibrahim Y Hachim,Abdul Wahid Ansari,Rifat Hamoudi,Mahmood Y Hachim,Rabih Halwani,Khuloud Bajbouj,Qutayba Hamid,Ronald Olivenstein

doi:10.3389/fimmu.2020.01002

Abstract

The accumulation of fibroblasts, their synthesis of extracellular matrix (ECM) proteins and their innate resistance to apoptosis are characteristics of subepithelial fibrosis observed in severe asthma. Interleukin-17 (IL-17) is an important regulator of airway remodeling in asthma. However, the contribution of IL-17 to the pro-fibrotic phenotype of bronchial fibroblasts is not well-characterized. In this study, we investigated whether IL-17 induced autophagy regulates mitochondrial and pro-fibrotic function in bronchial fibroblasts. The primary cultured bronchial fibroblasts isolated from non-asthmatic (NHBF) and severe asthmatic (DHBF) subjects were treated with IL-17 in order to ascertain its effect on mitochondrial function, mitochondrial quality control, and apoptosis using immunoblotting and flow cytometric analyses. At baseline, DHBF exhibited higher levels of mitophagy and mitochondrial biogenesis compared to NHBF. Immunohistochemical evaluation of bronchial biopsies showed intense PINK1 immunoreactivity in severe asthma than in control. IL-17 intensified the mitochondrial dysfunction and impaired the mitochondrial quality control machinery in NHBF and DHBF. Moreover, IL-17 augmented a pro-fibrotic and anti-apoptotic response in both group of fibroblasts. Inhibition of autophagy using bafilomycin-A1 reduced PINK1 expression in NHBF and restored the IL-17 mediated changes in PINK1 to their basal levels in DHBF. Bafilomycin-A1 also reversed the IL-17 associated fibrotic response in these fibroblasts, suggesting a role for IL-17 induced autophagy in the induction of fibrosis in bronchial fibroblasts. Taken together, our findings suggest that IL-17 induced autophagy promotes mitochondrial dysfunction and fibrosis in bronchial fibroblasts from both non-asthmatic and severe asthmatic subjects. Our study provides insights into the therapeutic potential of targeting autophagy in ameliorating fibrosis, particularly in severe asthmatic individuals.

Highlights

Fibroblasts, the effector cells of fibrosis, exhibit a bio-synthetic, contractile, adhesive, and pro-inflammatory phenotype for effective wound healing
Using bronchial fibroblasts isolated from severe asthmatic (S-As) and non-asthmatic subjects, we show increased autophagy, mitochondrial dysfunction, and fibrotic gene expression in S-As fibroblasts which was exacerbated upon stimulation with IL-17, thereby contributing to the pathobiology of subepithelial fibrosis in severe asthma
To investigate the state of mitochondrial dysfunction in S-As fibroblasts, the mitochondrial quality control (QC) mechanisms were examined in S-As fibroblasts (DHBF) and non-asthmatic fibroblasts (NHBF) isolated from endobronchial biopsy tissues

Summary

Introduction

Fibroblasts, the effector cells of fibrosis, exhibit a bio-synthetic, contractile, adhesive, and pro-inflammatory phenotype for effective wound healing As opposed to their self-limited and tightly regulated repair in response to tissue injury, under pathological conditions, persistent fibroblast activation paves way to extracellular matrix (ECM) accumulation, and remodeling along with their differentiation into apoptosisresistant myofibroblasts. Chronic lung diseases, such as asthma, chronic obstructive pulmonary disease (COPD), and idiopathic pulmonary fibrosis (IPF), exhibit phenotypically different fibroblasts that are responsible for the loss of the typical airway architecture and impair airway function [1]. Fibroblasts and their role in asthma pathogenesis have been relatively undervalued and understudied

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