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

Abstract

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.

Defining the mechanism of galectin-3–mediated TGF-β1 activation and its role in lung fibrosis

“…Exposure of lung fibroblasts to a fibrotic environment, for example, stimulation with TGFβ for 24 h may potentiate both αvβ1 expression and galectin-3 release from on fibroblasts in vitro increasing the likelihood that sufficient stochastic galectin-3–αvβ1 interactions are detected by PLA to visualize the signal. Our observations are consistent with nonpeer reviewed results showing that although colocalization of galectin-3 and the β1 integrin by PLA was also not detected in untreated lung ex vivo human lung tissue ( 60 ), it was detectable in TGF-β1–treated lung tissue samples created using a validated model of lung fibrogenesis ( 61 ). Stimulation with TGF-β1 increased the signal in both IPF and non-IPF fibroblasts, although more markedly in the IPF tissue–derived cells, and this response could be entirely abrogated by antagonism of galectin-3 glycan binding using the small molecule inhibitor GB0139.…”

Defining the mechanism of galectin-3-mediated TGF-β1 activation and its role in lung fibrosis

“…In the absence of TGF-β1 stimulation, such colocalization was detectable by this method in IPF HLFs but not non-IPF, suggesting that the proteins are inherently more closely associated in the disease state. These observations are consistent with non-peer reviewed results showing that colocalization of galectin-3 and the β1 integrin within 40 nm but was not detected by this method in untreated lung ex vivo human lung tissue (59), but was detectable in TGF-β1 treated lung tissue samples created using a validated model of lung fibrogenesis (60). Stimulation with TGF-β1 increased the signal in both cell types, more markedly in the IPF tissue-derived cells, and could be entirely abrogated by antagonism of galectin-3 glycan binding using the small molecule inhibitor GB0139.…”