Downregulation of Sirt3 contributes to ß-cell dedifferentiation via FoxO1 in type 2 diabetic mellitus.

AIMS: FoxO1 is an important factor in the ß-cell differentiation in type 2 diabetes mellitus (T2DM). Sirt3 is found to be involved in FoxO1 function. This study investigated the role of Sirt3 in the ß-cell dedifferentiation and its mechanism. METHODS: Twelve-week-old db/db mice and INS1 cells transfected with Sirt3-specific short hairpin RNA (shSirt3) were used to evaluate the dedifferentiation of ß-cell. Insulin levels were measured by enzyme linked immunosorbent assay. The proteins of Sirt3, T-FoxO1, Ac-FoxO1 and differentiation indexes such as NGN3, OCT4, MAFA were determined by western blot or immunofluorescence staining. The combination of Sirt3 and FoxO1 was determined by the co-immunoprecipitation assay. The transcriptional activity of FoxO1 was detected by dual luciferase reporter assay. RESULTS: Both the in vivo and in vitro results showed that Sirt3 was decreased along with ß-cell dedifferentiation and decreased function of insulin secretion under high glucose conditions. When Sirt3 was knocked down in INS1 cells, increased ß-cell dedifferentiation and lowered insulin secretion were observed. This effect was closely related to the amount loss and the decreased deacetylation of FoxO1, which resulted in a reduction in transcriptional activity. CONCLUSION: Downregulation of Sirt3 contributes to ß-cell dedifferentiation in high glucose via FoxO1. Intervention of Sirt3 may be an effective approach to prevent ß-cell failure in T2DM.

Decreased Sirt3 contributes to cyclic production of reactive oxygen species and islet ß-cell apoptosis in high glucose conditions.

BACKGROUND: Reactive oxygen species (ROS) plays a vital role in the apoptosis of islet ß-cells in type 2 diabetes mellitus (T2DM). Sirt3 (Sirtuin 3, a deacetylase) and FoxO1 (a transcription factor) might be involved in ROS production. This study was to investigate mechanism of ROS production and ß-cell apoptosis in T2DM. METHODS: Oxidative stress and apoptosis in islets of db/db mice and high glucose cultured ß-cells were observed by terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) assay and western blotting. Then, H2O2 was used to ascertain the effect of ROS on the expression of Sirt3. Meanwhile, FoxO1, antioxidant enzymes - catalase (CAT) and manganese superoxide dismutase (MnSOD) and ß-cell apoptosis were also determined by western blotting. Finally, Sirt3 was knocked down to evaluate the effect on oxidative stress and apoptosis of ß-cells. RESULTS: Under high glucose environment, enhanced ROS made a decrease of Sirt3 expression, which increased acetylation of FoxO1, thus reduced the expression of its target proteins -MnSOD and CAT, and further significantly increased ROS levels. Increased ROS finally led to the apoptosis of ß-cells. CONCLUSION: Down-regulation of Sirt3 plays an important role in the cyclic production of ROS and ß-cell apoptosis. Targeting Sirt3 may be favorable for the treatment of T2DM.