Mechanically Activated Calcium Channel PIEZO1 Modulates Radiation-Induced Epithelial-Mesenchymal Transition by Forming a Positive Feedback With TGF-β1

TGF-beta-centered epithelial-mesenchymal transition (EMT) is a key process involved in radiation-induced pulmonary injury (RIPI) and pulmonary fibrosis. PIEZO1, a mechanosensitive calcium channel, is expressed in myeloid cell and has been found to play an important role in bleomycin-induced pulmonary fibrosis. Whether PIEZO1 is related with radiation-induced EMT remains elusive. Herein, we found that PIEZO1 is functional in rat primary type II epithelial cells and RLE-6TN cells. After irradiation, PIEZO1 expression was increased in rat lung alveolar type II epithelial cells and RLE-6TN cell line, which was accompanied with EMT changes evidenced by increased TGF-beta 1, N-cadherin, Vimentin, Fibronectin, and alpha-SMA expression and decreased E-cadherin expression. Addition of exogenous TGF-beta 1 further enhanced these phenomena in vitro. Knockdown of PIEZO1 partly reverses radiation-induced EMT in vitro. Mechanistically, we found that activation of PIEZO1 could upregulate TGF-beta 1 expression and promote EMT through Ca2+/HIF-1 alpha signaling. Knockdown of HIF-1 alpha partly reverses enhanced TGF-beta 1 expression caused by radiation. Meanwhile, the expression of PIEZO1 was up-regulated after TGF-beta 1 co-culture, and the mechanism could be traced to the inhibition of transcription factor C/EBP beta expression by TGF-beta 1. Irradiation also caused a decrease in C/EBP beta expression in RLE-6TN cells. Dual luciferase reporter assay and chromatin immunoprecipitation assay (ChIP) confirmed that C/EBP beta represses PIEZO1 expression by binding to the PIEZO1 promoter. Furthermore, overexpression of C/EBP beta by using the synonymous mutation to C/EBP beta siRNA could reverse siRNA-induced upregulation of PIEZO1. In summary, our research suggests a critical role of PIEZO1 signaling in radiation-induced EMT by forming positive feedback with TGF-beta 1.

Automated summary

This study demonstrates the critical role of PIEZO1 signaling in radiation-induced epithelial-mesenchymal transition (EMT) by forming a positive feedback loop with TGF-beta 1. Activation of PIEZO1 can upregulate TGF-beta 1 expression and promote EMT through the Ca2+/HIF-1 alpha signaling pathway, while knockdown of PIEZO1 or HIF-1 alpha partially reverses radiation-induced EMT. Additionally, the expression of PIEZO1 is regulated by the transcription factor C/EBP beta, which further influences the EMT process in response to radiation and TGF-beta 1.