Palmitic acid stimulates energy metabolism and inhibits insulin/PI3K/AKT signaling in differentiated human neuroblastoma cells: The role of mTOR activation and mitochondrial ROS production

•Palmitic acid decreases NAD/NADH ratio in neurons.•Short-term exposure to palmitic acid inhibits insulin signaling.•Palmitic acid activates mTor kinase in neurons.•Inhibition of mitochondrial ROS prevents the effect of palmitic acid on insulin signaling.

The high consumption of saturated lipids has been largely associated with the increasing prevalence of metabolic diseases. In particular, saturated fatty acids such as palmitic acid (PA) have been implicated in the development of insulin resistance in peripheral tissues. However, how neurons develop insulin resistance in response to lipid overload is not fully understood. Here, we used cultured rat cortical neurons and differentiated human neuroblastoma cells to demonstrate that PA blocks insulin-induced metabolic activation, inhibits the activation of the insulin/PI3K/Akt pathway and activates mTOR kinase downstream of Akt. Despite the fact that fatty acids are not normally used as a significant source of fuel by neural cells, we also found that short-term neuronal exposure to PA reduces the NAD+/NADH ratio, indicating that PA modifies the neuronal energy balance. Finally, inhibiting mitochondrial ROS production with mitoTEMPO prevented the deleterious effect of PA on insulin signaling. This work provides novel evidence of the mechanisms behind saturated fatty acid-induced insulin resistance and its metabolic consequences on neuronal cells.