Tumor Necrosis Factor-alpha (TNF-α) Enhances miR-155-Mediated Endothelial Senescence by Targeting Sirtuin1 (SIRT1).

BACKGROUND Sirtuin1 (SIRT1) participates in a wide variety of cellular processes, but the molecular mechanism remains largely unknown. miR-155 is an element of the inflammatory signaling pathway in atherosclerosis. Therefore, we tested the hypothesis that TNF-alpha stimulates miR-155 to target SIRT1 and thereby regulates endothelial senescence, and we also explored the function of miR-155 as a regulator of cardiovascular diseases. MATERIAL AND METHODS TNF-alpha was used to stimulate human umbilical vein endothelial cells (HUVECs), after which protein and gene expression were assessed via Western blotting and RT-qPCR. miR-155 targeting of SIRT1 was confirmed via luciferase reporter assays, while MTT and senescence-associated ß-galactosidase (SA-ß-gal) assays were used for quantifying cellular proliferation and senescence. RESULTS We found that miR-155 was upregulated in response to TNF-alpha treatment, in addition to inducing marked changes in SIRT1/FoxO-1/p21 pathway protein level. When we overexpressed miR-155 mimics, SIRT1 was markedly reduced, whereas miR-155 inhibition had the opposite effect in TNF-alpha-treated cells. We additionally confirmed that miR-155 was able to directly bind to SIRT1 3'-UTR, and that inhibition of miR-155 reduced the ability of TNF-alpha to induce senescence in HUVECs, thereby leading to their enhanced proliferation. Simvastatin was associated with suppression of miR-155 expression in HUVECs following TNF-alpha treatment, and with a corresponding reduction in TNF-alpha-induced senescence, whereas miR-155 overexpression had the opposite effect. CONCLUSIONS Our findings suggest that TNF-alpha upregulates miR-155, which then targets SIRT1, suppressing its expression and driving HUVEC apoptosis. Simvastatin disrupted this senescence mechanism via the miR-155/SIRT1/FoxO-1/p21 pathway signaling. Hence, miR-155 is a possible therapeutic approach to endothelial senescence in the development of cardiovascular diseases.