Metformin regulates sirtuin expression in airway epithelial cells

<b>Background:</b> COPD is now recognised as a disease of accelerated lung aging, associated with increased cellular senescence, mTOR (mammalian target of rapamycin) signalling and decreased expression of anti-aging molecules, such as sirtuin-1/6. AMPK (5' AMP-activated protein kinase) activation inhibits mTOR, and has been associated with longevity, however its role in regulating senescence in COPD is unclear. <b>Aim:</b> Identify the role of AMPK activation via a pharmacological activator, metformin, on oxidative stress-induced cellular senescence in epithelial cells. <b>Methods:</b> BEAS2B bronchial epithelial cells were exposed to H₂O₂ (100µM) for 48h +/- metformin. Expression of senescence markers and senescence-associated secretory phenotype (SASP) markers were determined by qPCR and Western blotting. <b>Results:</b> Oxidative stress (H₂O₂) increased the expression of senescence markers p21 (9-fold, P&lt;0.01) and p16 (3-fold), SASP proteins CXCL-8 (6-fold, P&lt;0.05) and IL-6 (8-fold) as well as ̴ 75% reduction in expression of <i>SIRT1</i> and <i>SIRT6</i> (P&lt;0.05) (n=5). Metformin treatment reduced H₂O₂ induced IL-6 ( ̴ 74%, P&lt;0.05), CXCL-8 ( ̴ 88%, P&lt;0.05) and p16 ( ̴ 61%), with increased expression of <i>SIRT1</i> (3-fold, P&lt;0.05) and <i>SIRT6</i> (3-fold) (n=5). At the protein level (n=4), H₂O₂ increased p21 (18-fold, P&lt;0.05) and p16 (3-fold) but decreased SIRT6 ( ̴ 56%, P&lt;0.05). Metformin treatment inhibited p16 ( ̴ 67%) and p21 ( ̴ 77%) induction, whilst increasing sirtuin-6 (2-fold). <b>Conclusion:</b> These data suggest that metformin reverses oxidative stress-induced suppression of sirtuin-1/6 at both the mRNA and protein level, thereby modulating senescence markers. Metformin maybe beneficial in treating accelerated aging in COPD patients.