Sirtuin 6 Mitigated LPS-induced Human Umbilical Vein Endothelial Cells Inflammatory Responses Through Modulating Nuclear Factor Erythroid 2-related Factor 2

Background: Nuclear factor erythroid 2-related factor 2 (Nrf2) protects the lung from sepsis-induced injury through activating Nrf2-regulated multiple phase 2 detoxification genes, including NAD(P)H: quinine oxidoreductase-1 (NQO1) and heme oxygenase-1 (HO1). Based on the positive effect of Sirtuin 6 on Nrf2, we aim to explore the potential role of SIRT6 in the mechanism of sepsis-induced acute lung injury (ALI).

Methods: Mouse models of sepsis were constructed by instilling intratracheal of lipopolysaccharide (LPS; 4 ml/kg). After 48-hour treatment, lung tissues were collected to measure the degree of lung injury. The SIRT6, siSIRT6, and siNrf2 plasmids were cotransfected into various concentrations of LPS-treated human umbilical vein endothelial cells (HUVECs; 0, 1, 5, 10, and 50 μg/ml) using Lipofectamine 2000. Tumor necrosis factor-α (TNF-α) and interleukin (IL)-6 levels were determined by enzyme-linked immunosorbent assay. Expression levels of SIRT6, Nrf2, NQO1, and HO1 was measured by quantitative polymerase chain reaction and Western blot analysis. Cell apoptosis was determined by flow cytometry.

Results: Lung tissues in the model group already had basic characteristics of ALI. Compared with the control model, TNF-α and IL-6 levels were much higher (P < 0.01), the levels of SIRT6, Nrf2, and Nrf2-modulated detoxification factors were downregulated (P < 0.01). SIRT6 overexpression decreased the apoptosis below to 10% (P < 0.01), significantly increased the Nrf2 expression, effectively inhibited TNF-α and IL-6 releases, and enhanced NQO1 and HO1 levels (P < 0.01). siNrf2 abolished the protective effects of SIRT6 overexpression, including increasing apoptosis and inhibiting anti-inflammatory and antioxidative genes expressions (P < 0.01).

Conclusions: Our study suggested SIRT6 positively regulated Nrf2 expression and activated Nrf2-regulated anti-inflammatory and antioxidative enzymes, which could effectively mitigate LPS-induced HUVECs inflammatory responses. This might reflect the mechanism of ALI induced by sepsis.