Smoking Promotes AT2 Cell Senescence and Exacerbates Pulmonary Fibrosis by Downregulating POT1 via Integratively Inducing CpG Methylation and MECP2-Mediated FOXP2 Transcriptional Binding Inhibition

Smoking is one of the most recognized risk factors for pulmonary fibrosis (PF). However, the underlying mechanism is not well understood. This study reveals smoking increases the risk of developing idiopathic PF (IPF) and that smoked IPF patients exhibit higher levels of senescence markers than non-smoker IPF patients. Moreover, smoking enhances bleomycin (Bleo)-induced PF, along with obvious senescence of type II alveolar (AT2) cells. RNA-seq assay identifies cigarette downregulates protection of telomeres 1 (POT1), which is then validated to decrease in smoked PF patients and mice via upregulating the methyltransferase MECP2. Mechanistically, MECP2 binds to the DNA methyltransferases (DNMTs)-induced methylated CpG island in the POT1 promoter, and smoking inhibits the transcriptional activity of the CpG island. The transcription factor FOXP2 could bind to this CpG island to promote POT1 transcription. However, this process is inhibited by forming a MECP2−FOXP2 complex, which blunts the FOXP2−POT1 DNA binding. siRNA-mediated POT1 knockdown promoted AT2 cell senescence in a p-ATM and p-ATR-dependent manner and secreted inflammatory and profibrotic factors, further promoting fibrotic response in fibroblasts. In vivo, delivery of the adeno-associated virus 9-POT1 (AAV9-POT1) vector inhibits cigarette-induced cell senescence and effectively alleviates PF in mice. These findings demonstrate that POT1 is an essential protector in PF by protecting against AT2 cell senescence.