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.

Adipocyte lipopolysaccharide binding protein (LBP) is linked to a specific lipidomic signature

“…These previous studies and current data led us to hypothesize that improved mitochondrial function and inflammatory resilience of LBP KD cells could be attributed to decreased inflammatory lipid mediators that induced inflammation and NF‐κB pathway in adipocytes , such as ceramides and arachidonate‐containing glycerolipids, which were reduced in these cells. In fact, these lipid mediators also promoted mitochondrial dysfunction . Inflammation is a crucial pathophysiological underlying factor leading to adipose tissue dysfunction .…”

The Cross-Talk Between Sphingolipids and Insulin-Like Growth Factor Signaling: Significance for Aging and Neurodegeneration

“…Ceramide has been shown to activate fission of mitochondria in various tissues and in a cellular model, acting through modulation of expression levels of BOK (Bcl-2-related ovarian killer protein) [ 251 ]. Ceramide inhibits Akt signaling (synergistically with intracellular amyloid β 42 (Aβ 42 )) and disturbs the fusion-fission regulation in neuronal cell lines through down-regulation of the fusion-promoting proteins mitofusin 1 and OPA1 (optic atrophy 1) [ 252 ] ( Fig. 4 ) .…”

“…4 ) . Ceramide also reduced the levels of the fission regulator dynamin-related protein 1, although in muscle cells its seemed to exert opposite effect [ 252 , 253 ]. Likewise, loss of the ceramide transfer protein CERT results in disturbed transport of ceramides from endoplasmic reticulum to Golgi apparatus, hexosylceramide accumulation in mitochondria, and lower frequency of both fusion and fission [ 254 ].…”

Metabolic Characterization of Intact Cells Reveals Intracellular Amyloid Beta but Not Its Precursor Protein to Reduce Mitochondrial Respiration

“…Amyloid beta is thought to interact with several proteins amongst others some mitochondrial proteins, resulting in an increase in oxidative stress [15] which in turn could increase Aβ levels [16]. Regarding the mitochondrial respiratory system, in vitro studies on isolated mitochondria showed the reduced activity of pyruvate dehydrogenase and Cytochrome c Oxidase after Aβ treatment [17, 18]. Likewise, Aβ treatment of brain homogenate impaired mitochondrial oxygen consumption as well as mitochondrial membrane potential [19].…”