Amyloid-β Aggregates Cause Alterations of Astrocytic Metabolic Phenotype: Impact on Neuronal Viability

Abstract

Amyloid-␤(A␤)peptidesplayakeyroleinthepathogenesisofAlzheimer'sdiseaseandexertvarioustoxiceffectsonneurons;however,relatively littleisknownabouttheirinfluenceonglialcells.Astrocytesplayapivotalroleinbrainhomeostasis,contributingtotheregulationoflocalenergy metabolism and oxidative stress defense, two aspects of importance for neuronal viability and function. In the present study, we explored the effects of A␤ peptides on glucose metabolism in cultured astrocytes. Following A␤ 25-35 exposure, we observed an increase in glucose uptake and its various metabolic fates, i.e., glycolysis (coupled to lactate release), tricarboxylic acid cycle, pentose phosphate pathway, and incorporation into glycogen. A␤ increased hydrogen peroxide production as well as glutathione release into the extracellular space without affecting intracellular glutathione content. A causal link between the effects of A␤ on glucose metabolism and its aggregation and internalization into astrocytes through binding to members of the class A scavenger receptor family could be demonstrated. Using astrocyte-neuron cocultures, we observed that the overall modifications of astrocyte metabolism induced by A␤ impair neuronal viability. The effects of the A␤ 25-35 fragment were reproduced by A␤ 1-42 but not by A␤ 1-40 . Finally, the phosphoinositide 3-kinase (PI3-kinase) pathway appears to be crucial in these events since both the changes in glucose utilization and the decrease in neuronal viability are prevented by LY294002, a PI3-kinase inhibitor. This set of observations indicates that A␤ aggregation and internalization into astrocytes profoundly alter their metabolic phenotype with deleterious consequences for neuronal viability.

Aβ42 Neurotoxicity Is Mediated by Ongoing Nucleated Polymerization Process Rather than by Discrete Aβ42 Species

“…Similarly, we show that an ongoing A␤42 polymerization process, rather than distinct A␤42 aggregate states, also underlies previously reported alterations in astrocyte metabolic phenotypes (25). These findings contribute significantly to the understanding of amyloid formation and propagation in AD, provide novel insight into the mechanisms of A␤ protofibril toxicity, and carry important implications for designing anti-amyloid therapies.…”

“…Crude A␤42 Preparations, but Not Monomers, Protofibrils, or Fibrils Alone, Increased Glucose Utilization by Cultured Astrocytes-We have previously reported that treatment of cultured astrocytes with A␤42, at comparable concentrations as used for cell viability measurements in the experiments described above, does not induce significant cell death but alters the astrocyte metabolic activity (25). We observed that A␤42 significantly enhances glucose utilization (uptake and phosphorylation), as assessed by 2-[ 3 H]DG uptake, by cultured astrocytes as compared with A␤40 (25).…”

“…Primary Astrocyte Cell Cultures-Primary cortical astrocyte cultures were prepared as established previously using 1-2-day-old Swiss Albino mice (OF1, Charles River Laboratories) (25). After removing the meninges, cortices were isolated and dissociated by passage through needles of decreasing gauges (1.2 ϫ 40 mm, 0.8 ϫ 40 mm, and 0.5 ϫ 16 mm) using a 10-ml syringe.…”

Astrocytes in Alzheimer's Disease

“…[193][194][195] In contrast, treatment with A␤ significantly increased glucose use in cultured astroglial cells by enhancing the activity of all major glucose metabolism pathways and glycogenesis. 196 Furthermore, co-culturing neurons with astrocytes pre-treated with A␤ significantly decreased neuronal survival as compared with co-culturing with naive astrocytes. 196 Analysis of the activity of metabolic enzymes similarly yielded controversial results: both decrease 197,198 and increase 195,199 in the activity of enzymes associated with glucose metabolism have been reported in AD brain preparations.…”

“…196 Furthermore, co-culturing neurons with astrocytes pre-treated with A␤ significantly decreased neuronal survival as compared with co-culturing with naive astrocytes. 196 Analysis of the activity of metabolic enzymes similarly yielded controversial results: both decrease 197,198 and increase 195,199 in the activity of enzymes associated with glucose metabolism have been reported in AD brain preparations. These discrepancies may reflect opposite cell-specific changes in glucose metabolism developing at different stages of AD.…”