Reversing oxidative stress-induced senescence in small airway epithelial cells using the mTOR inhibitor AZD8055

<bold>Background:</bold> Increased oxidative stress induced by smoking in the lungs of COPD patients results in premature senescence of small airway epithelial cells (SAECs). Oxidative stress activates mammalian target of rapamycin (mTOR) signalling leading to a reduction in the key anti-ageing protein sirtuin-1 (SIRT1). Therefore, direct inhibition of mTOR by AZD8055 (dual mTORC1/2 inhibitor) may induce an increase in SIRT1 protein and reverse senescence in SAECs. <bold>Aim:</bold> To understand the effect of AZD8055 on SIRT1 protein expression and markers of senescence in oxidative stress-induced senescent SAECs. <bold>Methods:</bold> SAECs isolated from non-smokers were cultured with or without 300µM H₂O₂ for 48h, followed by addition of 10⁻¹²-10⁻⁵M AZD8055 for 24h. Protein expression of SIRT1 and p21^CIP1 (marker of cell cycle arrest) was quantified using Western blot. CXCL8 protein expression was measured using ELISA. <bold>Results:</bold> H₂O₂ treatment significantly reduced SIRT1 protein (65%, p<0.01, n=3), increased CXCL8 (75%, p<0.01, n=5) and p21^CIP1 (119%, p<0.01, n=3). AZD8055 exhibited a concentration dependent effect, 10^-7M treatment increased SIRT1 protein expression (184%, p<0.05, n=6), reduced CXCL8 protein release (43%, p<0.05, n=5) and p21^CIP1 protein expression (50%, p<0.05, n=4). <bold>Conclusion:</bold> Direct inhibition of mTOR via AZD8055 reverses oxidative-stress induced senescence in SAECs. Further investigation into the effect of AZD8055 on SIRT1 activity will help confirm a direct interaction on SIRT1.