MiR-29b level-mediated regulation of Klotho methylation via DNMT3A targeting in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a chronic lung disease characterized by chronic bronchitis and emphysema. Cigarette smoke extract (CSE) is the predominant cause of COPD. This study aimed to investigate the effects of miR-29b and their underlying mechanisms in a COPD cell model. MiR-29b and DNMT3A expression in lung tissue samples (taken at least 5 cm away from the tumor lesion) of NSCLC cases with smoking (n = 30), without smoking (n = 30), and with COPD (with smoking) (n = 30) was researched by qRT-PCR. A medium containing 10 % CSE was employed to induce murine alveolar macrophage MH-S cells to establish COPD cells. 5-Aza-cdr (5-AZA-2'-deoxycytidine) was used to block DNMT3A. The relationship and interaction between miR-29b and DNMT3A were validated through the dual luciferase reporter assay. The expression levels of macrophage M1 polarization marker proteins iNOS and TNF-α, DNMT3A, and Klotho protein were monitored using western blotting. The methylation levels of the miR-29b precursor gene and Klotho promoter were detected by quantitative methylation-specific PCR (MS-qPCR). The levels of IL-1β, IL-6, and TNF-α in cell culture medium were detected via ELISA. It was found that the expression of miR-29b was downregulated, as a result of increased DNA methylation, and that of DNMT3A was upregulated in the lung tissues of NSCLC cases with COPD (with smoking). DNMT3A expression was negatively correlated with miR-29b expression in the lung tissues of NSCLC cases with COPD (with smoking). In addition, miR-29b expression was distinctly downregulated in CSE-induced MH-S cells and inhibited CSE-induced M1 polarization and inflammation. Importantly, DNMT3A was identified as a direct target gene of miR-29b. MiR-29b is negatively regulated by DNMT3A-mediated DNA methylation. Moreover, Klotho expression was downregulated and the Klotho promoter methylation level was increased in lung tissues of NSCLC cases with COPD (with smoking). The negative feedback between miR-29b and DNMT3A modulates CSE-induced M1 polarization and inflammation in macrophages as well as Klotho promoter methylation in CSE-mediated MH-S. Collectively, these findings indicate that the miR-29b level in COPD controls Klotho methylation via DNMT3, which maybe a promising target for the treatment of COPD.