Native low density lipoprotein induces pancreatic β cell apoptosis through generating excess reactive oxygen species

Background: The growing evidences demonstrated hyperlipidemia in obesity and type 2 diabetes is characterized by high levels of free fatty acids, low-density lipoprotein (LDL), triglyceride, and cholesterol. Method and Results: We investigated the effect of LDL particles (LDLs) loading on MIN6 cells derived from pancreatic beta cells. Exposure of MIN6 cells to LDLs induced apoptosis in dose and time-dependent manner, demonstrated by the TUNEL in situ apoptotic assay. The immunocytochemical analysis and Western blotting revealed that the LDLs-induced apoptosis is associated with the activation of caspase 3 and upregulation of p53. The intracellular concentration of Reactive Oxygen Species (ROS) measured by use of DCFHDA was significantly increased after loading LDLs, demonstrating the induced apoptosis by LDLs loading was mediated through oxidative stress. Addition of reduced form of Glutathione (GSH) in the medium rescued MIN6 cells from apoptosis. The Cellular cholesterol level was increased significantly after LDLs loading, suggesting that the excess cholesterol induced by LDLs loading might contribute to the apoptosis in MIN6s. Agarose electrophoresis demonstrated that the LDLs added to the medium were not oxidized. Conclusion: Taken together, these results demonstrate that the LDLs loading can induce apoptosis of MIN6 cells mediated by the excess cellular cholesterol and generation of oxidative stress.