MicroRNA-34a drives small airway fibroblast cellular senescence in COPD

Background: COPD is a disease of accelerated lung aging and is associated with elevated cellular senescence. Increased senescent fibroblasts are seen in small airways of patients with COPD, which may contribute to disease progression via progressive fibrosis and release of pro-inflammatory cytokines. However, mechanisms by which senescence is induced in these cells are unclear. Aims: To investigate the role of miR-34a in small airway fibroblast (SAF) senescence in non-smokers and COPD patients. Methods: SAFs were isolated from human lung resection tissue from non-smokers and COPD patients and the expression of miR-34a and senescence markers measured by qPCR. SAFs were treated with miR-34a inhibitors or mimics and changes in senescence markers compared to the scrambled control. Senescence was detected using β-galactosidase staining and iCELLigence technology used to assess cell proliferation. Results: COPD SAFs (n=5) showed increased expression of miR-34a (2-fold), p21 (6-fold) and p27 (2-fold) compared to non-smokers (n=5). COPD SAFs displayed elevated β-galactosidase staining and impaired proliferation compared to non-smoker SAFs. In non-smoker SAFs (n=3), a miR-34a mimic suppressed SIRT1 expression by 44% but increased p21 and p27 by 1.3-fold. Similarly in COPD SAFs, SIRT1 was reduced by 37% and p21 and p27 elevated 1.4 and 1.7-fold, respectively. Conversely, the miR-34a inhibitor (antagomir, n=5) reduced p21 by 15% and 25% in non-smoker and COPD SAFs respectively. Conclusions: These data suggest greater senescence in COPD SAFs compared to controls, with miR-34a contributing to changes in senescent markers, therefore suggesting miR-34a as a future therapeutic target for accelerated aging disease such as COPD.