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

Abstract

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 β-amyloid (Aβ) and insulin resistance on mitochondrial metabolism has not been explored in neuronal cells. We investigated the additive and synergistic effects of intracellular Aβ42 and ceramide-induced insulin resistance on mitochondrial metabolism in SH-SY5Y and Neuro-2a cells. In our model, mitochondria take-up Aβ42 expressed through viral-mediated transfection and exposure of the same cells to ceramide produces resistance to insulin signaling. Ceramide alone increased phosphorylated MAP kinases while decreasing phospho-Akt (Ser473). The combination of Aβ42 and ceramide synergistically decreased phospho-Thr308 on Akt. Aβ42 and ceramide synergistically also decreased mitochondrial complex III activity and ATP generation whereas Aβ 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 Aβ42 expression. Mitochondrial fusion and fission proteins were notably dysregulated by Aβ42 (Mfn1) or Aβ42 plus ceramide (OPA1, Drp1). Antioxidant vitamins blocked the Aβ42 alone-induced ROS production, but did not reverse Aβ42-induced ATP reduction or complex IV inhibition. Aβ expression combined with ceramide exposure had additive effects to decrease cell viability. Taken together, our data demonstrate that Aβ42 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.

Keywords: Alzheimer's disease; Ceramide; Insulin resistance; Mitochondrial dysfunction; β-amyloid.