The key role of microRNA-34a in the reduction of sirtuin-1 in COPD

<b>Background:</b> Sirtuin-1 (SIRT1), a NAD⁺-dependent Class III protein deacetylases, known as a putative anti-ageing enzyme, has been shown to be down-regulated in patients with chronic obstructive pulmonary disease (COPD). COPD is characterized by the accelerated ageing of the lung, associated with increased oxidative stress. Both SIRT1 protein and mRNA are reduced in COPD but the mechanisms for this reduction are unknown. <b>Aims:</b> To identify the role of miR-34a, a microRNA previously linked to reduced SIRT1 function, in the regulation of SIRT1 expression in response to oxidative stress. <b>Methods:</b> Protein levels were determined by western blotting and mi/mRNA expression by real-time PCR. Luciferase assays assessed miRNA binding. <b>Results:</b> miR-34a was elevated in peripheral lung samples from patients with COPD (P&lt;0.05, n=23) compared to non-disease controls (n=12) and correlated with decreased SIRT1 mRNA expression (P&lt;0.05). Oxidative stress with H₂O₂ (100µM) reduced both SIRT1 mRNA and protein (n=5, P&lt;0.05), with this correlating with increased expression of miR-34a (n=6, P&lt;0.001) in bronchial epithelial cells (BEAS2B). Over-expression of miR-34a mimics, in combination with SIRT1 39-UTR luciferase reporter constructs, suggests miRNA-34a directly binds (n=4, P&lt;0.01). Over-expression of miR-34a mimics also caused significant reduction in both SIRT1 mRNA and protein (n=5, P&lt;0.05), with increased levels of SIRT1 being observed when miR-34a was inhibited (n=5, P&lt;0.01). <b>Conclusions:</b> Our results indicate that miR-34a is induced by oxidative stress, suggesting a potential new mechanism by which increased oxidative stress in lungs of COPD patients may reduce SIRT1 expression. Funding: Wellcome trust Programme Grant.