Paracrine signalling during ZEB1-mediated epithelial–mesenchymal transition augments local myofibroblast differentiation in lung fibrosis

Abstract

The contribution of epithelial-mesenchymal transition (EMT) to human lung fibrogenesis is controversial. Here we provide evidence that ZEB1-mediated EMT in human alveolar epithelial type II (ATII) cells contributes to the development of lung fibrosis by paracrine signalling to underlying fibroblasts. Activation of EGFR-RAS-ERK signalling in ATII cells induced EMT via ZEB1. ATII cells had extremely low extracellular matrix gene expression even after induction of EMT, however conditioned media from ATII cells undergoing RAS-induced EMT augmented TGFβ-induced profibrogenic responses in lung fibroblasts. This epithelial-mesenchymal crosstalk was controlled by ZEB1 via the expression of tissue plasminogen activator (tPA). In human fibrotic lung tissue, nuclear ZEB1 expression was detected in alveolar epithelium adjacent to sites of extracellular matrix (ECM) deposition, suggesting that ZEB1-mediated paracrine signalling has the potential to contribute to early fibrotic changes in the lung interstitium. Targeting this novel ZEB1 regulatory axis may be a viable strategy for the treatment of pulmonary fibrosis.

Autophagy inhibition-mediated epithelial–mesenchymal transition augments local myofibroblast differentiation in pulmonary fibrosis

“…However, lineage tracing studies found the number of fibroblasts derived from epithelial cells to be small 43,44 , and these cells were not found to colocalise with α-SMA suggesting they did not transition to myofibroblasts 45,46 . It also been proposed in a number of systems that epithelial cells that have undergone EMT may secrete a range of fibrogenic growth factors and cytokines, with impaired epithelial repair leading to aberrant epithelial-mesenchymal communication contributing to the recruitment and activation of myofibroblasts 18,47,48 . Here, we show that autophagy inhibition in ATII cells can induce EMT, and this contributes to fibrosis via aberrant epithelial-fibroblast crosstalk, rather than as a direct contribution to the fibroblast population.…”

“…6a), indicating this effect is likely dependent on the cellular context. The importance of Snail2 in IPF has been demonstrated with Snail2 being upregulated in IPF lung epithelial cells, but not Snail1 or TWIST1, compared to control epithelial cells 16,18 . Jayachandran et al 54 reported that Snail2-mediated EMT may contribute to the fibroblast pool.…”

“…To investigate its role in alveolar epithelial cells, autophagic activity was first modified using chemical inhibitors. We treated human alveolar epithelial type II (ATII) cells [18][19][20] with an autophagy inhibitor, hydroxychloroquine (HCQ), which is a lysosomotropic autophagy inhibitor. HCQ treatment of ATII cells inhibited autophagic activity, demonstrated by the accumulation of p62/ SQSTM1 ( Fig.…”

Microcystin-LR ameliorates pulmonary fibrosis via modulating CD206+ M2-like macrophage polarization

“…Myofibroblasts, originated from exaggerated activation and abnormal differentiation of fibroblasts via EMT and FMT pathways, are widely considered as the effector cells responsible for fibrosis 33,34 . A prolonged inflammation, M2 macrophages differentiation and increased profibrotic factors, especially TGF-β1/Smad signaling form and maintain the microenvironment of fibrogenesis.…”

Comparing transcriptional dynamics of the epithelial-mesenchymal transition

“…This supports previous observations about the involvement of paracrine signalling during the EMT 11 , which could both coordinate the transition across a population of epithelial cells, and modulate the cells' microenvironment (eg. immunosuppression in cancer) [12][13][14] . Given this, we next established an experimental design to mechanistically assess the dependence of the EMT on paracrine signalling.…”