Abstract
Background. Sodium palmitate causes apoptosis of β-cells, and the anti-apoptotic protein Bcl-2 has been shown to counteract this event. However, the exact mechanisms that underlie palmitate-induced pancreatic β-cell apoptosis and through which pathway Bcl-2 executes the protective effect are still unclear.Methods. A stable Bcl-2-overexpressing RINm5F cell clone (BMG) and its negative control (B45) were exposed to palmitate for up to 8 h, and cell viability, mitochondrial membrane potential (Δψm), reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, and NF-κB activation were studied in time course experiments.Results. Palmitate exposure for 8 h resulted in increased cell death rates, and this event was partially counteracted by Bcl-2. Bcl-2 overexpression promoted in parallel also a delayed induction of GADD153/CHOP and a weaker phosphorylation of BimEL in palmitate-exposed cells. At earlier time points (2–4 h) palmitate exposure resulted in increased generation of ROS, a decrease in mitochondrial membrane potential (Δψm), and a modest increase in the phosphorylation of eIF2α and IRE1α. BMG cells produced similar amounts of ROS and displayed the same eIF2α and IRE1α phosphorylation rates as B45 cells. However, the palmitate-induced dissipation of Δψm was partially counteracted by Bcl-2. In addition, basal NF-κB activity was increased in BMG cells.Conclusions. Our results indicate that Bcl-2 counteracts palmitate-induced β-cell death by maintaining mitochondrial membrane integrity and augmenting NF-κB activity, but not by affecting ROS production and ER stress.
Highlights
Type 2 diabetes is often associated with obesity and increased plasma free fatty acid (FFA) levels
Our results indicate that Bcl-2 counteracts palmitate-induced b-cell death by maintaining mitochondrial membrane integrity and augmenting NF-kB activity, but not by affecting reactive oxygen species (ROS) production and endoplasmic reticulum (ER) stress
To confirm the possibility that overexpression of Bcl-2 might increase resistance to palmitate-induced b-cells death and to investigate through which mechanism Bcl-2 overexpression might execute its protective effect, a bcl-2-transfected insulin-producing rat pancreatic RINm5F cell line BMG was used in subsequent experiments [10]
Summary
Type 2 diabetes is often associated with obesity and increased plasma free fatty acid (FFA) levels. In non-b-cells, palmitate-induced apoptosis was associated with dissipation of the mitochondrial membrane potential (Dym), two events that were counteracted by Bcl-2 overexpression [6]. The uncoupling effect of FFAs is associated with a decreased Dym, and increased respiration, enhanced reactive oxygen species (ROS) generation, lower ATP levels, and mitochondrial swelling [3]. A stable Bcl-2-overexpressing RINm5F cell clone (BMG) and its negative control (B45) were exposed to palmitate for up to 8 h, and cell viability, mitochondrial membrane potential (Dym), reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, and NF-kB activation were studied in time course experiments. At earlier time points (2–4 h) palmitate exposure resulted in increased generation of ROS, a decrease in mitochondrial membrane potential (Dym), and a modest increase in the phosphorylation of eIF2a and IRE1a. Our results indicate that Bcl-2 counteracts palmitate-induced b-cell death by maintaining mitochondrial membrane integrity and augmenting NF-kB activity, but not by affecting ROS production and ER stress
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