Electronic nicotine delivery systems, or e.cigarettes utilise a liquid solution that normally contains propylene glycol (PG) and vegetable glycerine (VG) to generate vapour and act as a carrier for nicotine and flavourings. Evidence indicated these 'carriers' reduced growth and survival of epithelial cells including those of the airway. We hypothesised that 3% PG or PG mixed with VG (3% PG:VG, 55:45) inhibited glucose uptake in human airway epithelial cells as a first step to reducing airway cell survival. Exposure of H441 or human bronchiolar epithelial cells (HBEC) to PG and PG/VG (30-60 minutes) inhibited glucose uptake and mitochondrial ATP synthesis. PG/VG inhibited glycolysis. PG/VG and mannitol reduced cell volume and height of air-liquid interface cultures. Mannitol but not PG/VG increased phosphorylation of p38 MAPK. PG/VG reduced TEER which was associated with increased transepithelial solute permeability. PG/VG decreased FRAP of GFP linked glucose transporters GLUT1 and GLUT10 indicating that glucose transport function was compromised. Puffing PG/VG vapour onto the apical surface of primary HBEC for 10 mins to mimic the effect of e.cigarette smoking also reduced glucose transport. In conclusion, short term exposure to PG/VG, key components of e.cigarettes, decreased glucose transport and metabolism in airway cells. We propose that this was a result of PG/VG reduced cell volume and membrane fluidity, with further consequences on epithelial barrier function. Taken together, we suggest these factors contribute to reduced defensive properties of the epithelium. We propose that repeated/chronic exposure to these agents are likely to contribute to airway damage in e-cigarette users.

Background Idiopathic pulmonary fibrosis (IPF) is a fatal respiratory disease characterized by aberrant fibroblast activation and progressive fibrotic remodelling of the lungs. Though the exact pathophysiological mechanisms of IPF remain unknown, TGF-β1 is thought to act as a main driver of the disease by mediating fibroblast-to-myofibroblast transformation (FMT). Recent reports have indicated that a metabolic shift towards aerobic glycolysis takes place during FMT and that metabolic shifts can directly influence aberrant cell function. This has led to the hypothesis that inhibition of lactate dehydrogenase 5 (LDH5), an enzyme responsible for converting pyruvate into lactate, could constitute a therapeutic concept for IPF. Methods In this study, we investigated the potential link between aerobic glycolysis and FMT using a potent LDH5 inhibitor (Compound 408, Genentech). Seahorse analysis was performed to determine the effect of Compound 408 on TGF-β1-driven glycolysis in WI-38 fibroblasts. TGF-β1-mediated FMT was measured by quantifying α-smooth muscle actin (α-SMA) and fibronectin in primary human lung fibroblasts following treatment with Compound 408. Lactate and pyruvate levels in the cell culture supernatant were assessed by LC-MS/MS. In addition to pharmacological LDH5 inhibition, the effect of siRNA-mediated knockdown of LDHA and LDHB on FMT was examined. Results We show that treatment of lung fibroblasts with Compound 408 efficiently inhibits LDH5 and attenuates the TGF-β1-mediated metabolic shift towards aerobic glycolysis. Additionally, we demonstrate that LDH5 inhibition has no significant effect on TGF-β1-mediated FMT in primary human lung fibroblasts by analysing α-SMA fibre formation and fibronectin expression. Conclusions Our data strongly suggest that while LDH5 inhibition can prevent metabolic shifts in fibroblasts, it has no influence on FMT and therefore glycolytic dysregulation is unlikely to be the sole driver of FMT. Electronic supplementary material The online version of this article (10.1186/s12931-019-1058-2) contains supplementary material, which is available to authorized users.

Idiopathic pulmonary fibrosis (IPF) is a fatal disease of unknown cause that is characterized by progressive fibrotic lung remodeling. An abnormal emergence of airway epithelial‐like cells within the alveolar compartments of the lung, herein termed bronchiolization, is often observed in IPF. However, the origin of this dysfunctional distal lung epithelium remains unknown due to a lack of suitable human model systems. In this study, we established a human induced pluripotent stem cell (iPSC)‐derived air‐liquid interface (ALI) model of alveolar epithelial type II (ATII)‐like cell differentiation that allows us to investigate alveolar epithelial progenitor cell differentiation in vitro. We treated this system with an IPF‐relevant cocktail (IPF‐RC) to mimic the pro‐fibrotic cytokine milieu present in IPF lungs. Stimulation with IPF‐RC during differentiation increases secretion of IPF biomarkers and RNA sequencing (RNA‐seq) of these cultures reveals significant overlap with human IPF patient data. IPF‐RC treatment further impairs ATII differentiation by driving a shift toward an airway epithelial‐like expression signature, providing evidence that a pro‐fibrotic cytokine environment can influence the proximo‐distal differentiation pattern of human lung epithelial cells. In conclusion, we show for the first time, the establishment of a human model system that recapitulates aspects of IPF‐associated bronchiolization of the lung epithelium in vitro.

Unveiling the molecular mechanisms of tissue remodelling following injury is imperative to elucidate its regenerative capacity and aberrant repair in disease. Using different omics approaches, we identified enhancer of zester homolog 2 (EZH2) as a key regulator of fibrosis in injured lung epithelium. Epithelial injury drives an enrichment of nuclear transforming growth factor‐β‐activated kinase 1 (TAK1) that mediates EZH2 phosphorylation to facilitate its liberation from polycomb repressive complex 2 (PRC2). This process results in the establishment of a transcriptional complex of EZH2, RNA‐polymerase II (POL2) and nuclear actin, which orchestrates aberrant epithelial repair programmes. The liberation of EZH2 from PRC2 is accompanied by an EZH2‐EZH1 switch to preserve H3K27me3 deposition at non‐target genes. Loss of epithelial TAK1, EZH2 or blocking nuclear actin influx attenuates the fibrotic cascade and restores respiratory homeostasis. Accordingly, EZH2 inhibition significantly improves outcomes in a pulmonary fibrosis mouse model. Our results reveal an important non‐canonical function of EZH2, paving the way for new therapeutic interventions in fibrotic lung diseases.

The airway epithelium maintains differential glucose concentrations between the airway surface liquid (ASL, ~0.4 mM) and the blood/interstitium (5–6 mM), which is important for defense against infection. Glucose primarily moves from the blood to the ASL via paracellular movement, down its concentration gradient, across the tight junctions. However, there is evidence that glucose can move transcellularly across epithelial cells. Using a Förster resonance energy transfer sensor for glucose, we investigated intracellular glucose concentrations in airway epithelial cells and the role of hexokinases in regulating intracellular glucose concentrations in normoglycemic and hyperglycemic conditions. Our findings indicated that in airway epithelial cells (H441 or primary human bronchial epithelial cells) exposed to 5 mM glucose (normoglycemia), intracellular glucose concentration is in the micromolar range. Inhibition of facilitative glucose transporters (GLUTs) with cytochalasin B reduced intracellular glucose concentration. When cells were exposed to 15 mM glucose (hyperglycemia), intracellular glucose concentration was reduced. Airway cells expressed hexokinases I, II, and III. Inhibition with 3-bromopyruvate decreased hexokinase activity by 25% and elevated intracellular glucose concentration, but levels remained in the micromolar range. Exposure to hyperglycemia increased glycolysis, glycogen, and sorbitol. Thus, glucose enters the airway cell via GLUTs and is then rapidly processed by hexokinase-dependent and hexokinase-independent metabolic pathways to maintain low intracellular glucose concentrations. We propose that this prevents transcellular transport and aids the removal of glucose from the ASL and that the main route of entry for glucose into the ASL is via the paracellular pathway.