COPD Small Airway Fibroblasts show reduced proliferation rate and are arrested in G1 phase

<b>Rationale:</b> Pulmonary fibroblasts proliferate and produce extracellular matrix to repair the lung environment. In COPD, parenchymal-derived fibroblasts exhibit reduced proliferation possibly due to growth arrest via cellular senescence. However, the proliferative capabilities of small airway fibroblasts (SAF) are unknown. <b>Aim:</b> To investigate the proliferative capacity of SAF from COPD patients and age-matched non-smoker and smoker controls. <b>Method:</b> SAF were isolated from surgical lung resections from non-smokers, smokers and COPD patients. iCELLigence technology and propidium iodide (PI) staining were used to investigate SAF proliferation and phase of cell cycle arrest, respectively. Senescence was identified using Senescence Associated-β-Galactosidase (SA-β-Gal) staining and potential mechanisms studied by qPCR for gene expression of cell cycle checkpoints. <b>Results:</b> SAF from COPD patients showed significantly reduced proliferation rate compared to non-smokers and smokers (p&lt;0.05 and p&lt;0.001 respectively, n=4-7). PI staining suggested more COPD SAF were G1 phase arrested compared to NS SAF (p&lt;0.01), and fewer in G2 (p&lt;0.05, n=4-5). Senescence could be driving this, since more COPD SAF stained positive for SA-β-Gal compared to non-smokers (21% vs 11%, p&lt;0.05, n=4-5). However, there was no change in p21, p16, p27 or CDK4 expression; but a trend in increased p15 (+116%, p=0.28) and p53 (+44%, p&lt;0.05, n=7-11) expression. <b>Conclusion:</b> These data suggest COPD SAF display reduced proliferation compared to controls, arresting in G1 phase. This may be due to senescence, induced by p15 and p53. Further investigation into cell cycle arrest mechanisms in COPD may provide alternative targets for therapeutics.