Synergistic effects of β-amyloid and ceramide-induced insulin resistance on mitochondrial metabolism in neuronal cells

A large body of evidence support major roles of mitochondrial dysfunction and insulin action in the Alzheimer's disease (AD) brain. However, interaction between cellular expression of beta-amyloid (A beta) and insulin resistance on mitochondrial metabolism has not been explored in neuronal cells. We investigated the additive and synergistic effects of intracellular A beta 42 and ceramide-induced insulin resistance on mitochondrial metabolism in SH-SY5Y and Neuro-2a cells. In our model, mitochondria take-up A beta 42 expressed through viral-mediated transfection and exposure of the same cells to ceramide produces resistance to insulin signaling. Ceramide alone increased phosphotylated MAP kinases while decreasing phospho-Akt (Ser473). The combination of A beta 42 and ceramide synergistically decreased phospho-Thr308 on Akt. A beta 42 and ceramide synergistically also decreased mitochondrial complex III activity and ATP generation whereas A beta alone was largely responsible for complex IV inhibition and increases in mitochondrial reactive oxygen species production (ROS). Proteomic analysis showed that a number of mitochondrial respiratory chain and tricarboxylic acid cycle enzymes were additively or synergistically decreased by ceramide in combination with A beta 42 expression. Mitochondrial fusion and fission proteins were notably dysregulated by A beta 42 (Mfn1) or A beta 42 plus ceramide (OPA1, Drp1). Antioxidant vitamins blocked the A beta 42 alone-induced ROS production, but did not reverse A beta 42-induced ATP reduction or complex IV inhibition. A beta expression combined with ceramide exposure had additive effects to decrease cell viability. Taken together, our data demonstrate that A beta 42 expression and ceramide-induced insulin resistance synergistically interact to exacerbate mitochondrial damage and that therapeutic efforts to reduce insulin resistance could lessen failures of energy production and mitochondrial dynamics. (C) 2015 Elsevier B.V. All rights reserved.