CD98 is critical for a conserved inflammatory response to diverse injury stimuli relevant to IPF exacerbations and COVID pneumonitis

Progressive fibrosing interstitial lung diseases (PFILDs) cause substantial morbidity and mortality. Antifibrotic agents slow progression, but most of the clinical need remains unmet. The archetypal PFILD is idiopathic pulmonary fibrosis (IPF). Chronic progression is driven by transforming growth factor (TGF-)β1 signalling. It is punctuated by inflammatory flares known as acute exacerbations (AE-IPF), which are associated with accelerated decline and high mortality. We hypothesized that acute injury responses underlying exacerbations and the mechanisms of chronic fibrosis overlap at the molecular level, via a cell surface assembly nucleated by galectin-3 that we term the ‘gal-3-fibrosome’. We focused upon a putative pro-inflammatory galectin-3 ligand, the CD98:integrin complex. Our data indicate CD98 and β1-integrin co-localise with galectin-3 within epithelial cells in IPF lung tissue, and within 40 nm in human lung tissue treated with TGF-β1 compared to controls. CD98 is required for interleukin (IL-)6 and IL-8 responses to biochemical and biophysical conditions mimicking stimuli of AE-IPF in vivo , ex vivo and in cells, and for an interstitial neutrophilic response in a mouse model. We demonstrate this pathway progresses via intracellular influx of Ca2+ mediated by TRPV4, and NF-κB activation, operating in positive feedback. Lastly we show the CD98- and galectin-3-dependence of IL-6 and IL-8 responses to the SARS-CoV-2 spike protein receptor binding domain and the conservation of this response pattern between lung epithelial cells and monocyte-derived macrophages. Taken together our findings identify CD98 as a key mediator of both pro-fibrotic and acute inflammatory responses in the lung with relevance to AE- and chronic progression of IPF, and the priming of fibrotic lungs for acute inflammatory responses. They similarly implicate CD98 and galectin-3 as mediators of COVID pneumonitis and worse outcomes in ILD patients with COVID. ### Competing Interest Statement Research in this work was supported by funding from the British Lung Foundation and Asthma+Lung UK, MRC (UK) (including Confidence in Concept award administered by Leicester Drug and Diagnostics Discovery (LD3) scheme), BBSRC, the Wellcome Trust, Guy's & St Thomas' Charity. Funding for the mechanobiology facilities used in this study came from EPSRC and Queen Mary strategic equipment funding. The work was supported in part by the National Institute for Health Research (NIHR) Leicester Biomedical Research Centre - Respiratory. The views expressed are those of the authors and not necessarily those of the funders or affiliated bodies. PB has received research funding from Genentech, Inc. via the University Hospitals of Leicester NHS Trust and from DEShawResearch via the University of Leicester, consultancies for Boehringer-Ingelheim (BI) and Genentech via the University of Leicester. Support to attend scientific meetings from Chiesi, Teva and Sanofi Genzyme. AM is a shareholder and employee of Galecto, Inc. BG has received consultancy fees from Vertex, and GSK, and research support in kind from Galecto, Inc. MMK currently has industry funding from Emulate for the Queen Mary and Emulate Organs-on-chips Centre and related research activity (https://www.cpm.qmul.ac.uk/emulate/).