TET1 Alleviates Cigarette Smoke Induced Bronchial Epithelial Cell Apoptosis Through Upregulating Nrf2

Nuclear factor erythroid 2-related factor 2 (Nrf2), a key regulator of oxidative stress responses, is downregulated in patients with GOLD stage III-IV chronic obstructive pulmonary disease (COPD). However, the mechanisms underlying the epigenetic regulation of Nrf2 in COPD remain poorly understood.

Protein levels of Nrf2, heme oxygenase-1 (HO-1), ten-eleven translocation methylcytosine dioxygenase 1 (TET1), and DNA methyltransferase 1 (DNMT1) were assessed by Western blotting in peripheral lung tissue and primary bronchial epithelial cells obtained from patients with COPD, never-smokers (control-NS), and smokers without COPD (control-S). CSE-treated human bronchial epithelial (HBE) cells were used as an in vitro model. Nrf2 promoter methylation was evaluated using bisulfite sequencing. Apoptosis of HBE cells was measured by flow cytometry. Chromatin immunoprecipitation (ChIP) was performed to assess the binding of TET1 to the Nrf2 promoter. Malondialdehyde (MDA) and superoxide dismutase (SOD) activity assays were used to quantify oxidative stress and antioxidant capacity.

Nrf2 and HO-1 expression was significantly reduced in both lung tissue and primary epithelial cells from patients with COPD. In vitro, CSE exposure increased Nrf2 promoter methylation in HBE cells. Overexpression of Nrf2 mitigated oxidative stress, increased SOD activity, and reduced apoptosis in response to CSE. TET1 expression was decreased in COPD lungs, and TET1 was shown to bind the Nrf2 promoter and enhance its transcription. TET1 overexpression reduced oxidative damage and apoptosis via Nrf2 upregulation.

Reduced Nrf2 expression in COPD may result from promoter hypermethylation. TET1 directly binds and demethylates the Nrf2 promoter, restoring its expression and attenuating CSE-induced HBE cells apoptosis. These findings identify a potential epigenetic mechanism contributing to COPD pathogenesis and suggest TET1 as a novel therapeutic target.