APOE genotype-dependent differences in human astrocytic energy metabolism.

INTRODUCTION

The main genetic risk factor for Alzheimer's disease (AD) is the presence of the apolipoprotein E4 () allele. While increases the risk of developing AD, the allele is protective and is risk-neutral. In the brain, APOE is primarily expressed by astrocytes and plays a key role in various processes including cholesterol and lipid transport, neuronal growth, synaptic plasticity, immune response and energy metabolism. Disruptions in brain energy metabolism are considered a major contributor to AD pathophysiology, raising a key question about how different APOE isoforms affect the energy metabolism of human astrocytes.

METHODS

In this study, we generated astrocytes (iAstrocytes) from -isogenic human induced pluripotent stem cells (iPSCs), expressing either APOE2, APOE3, APOE4 or carrying an APOE knockout (), and investigated genotype-dependent changes in energy metabolism.

RESULTS

ATP Seahorse assay revealed a reduced mitochondrial and glycolytic ATP production in iAstrocytes. In contrast, glycolysis stress tests demonstrated enhanced glycolysis and glycolytic capacity in iAstrocytes while genetically encoded nanosensor-based FLIM analysis revealed that does not affect lactate dynamics. In agreement with the increased glycolytic activity, iAstrocytes also showed elevated mitochondrial respiration and activity, indicated by proteomic GO enrichment analysis and mitochondrial stress test. This was accompanied by elevated proton leak in iAstrocytes while levels of mitochondrial uncoupling proteins (UCPs) were not affected. Mass spectrometry-based metabolomic analysis identified various energy and glucose metabolism-related pathways that were differentially regulated in compared to the other genotypes, including mitochondrial electron transport chain (ETC) and glycolysis. In general, and iAstrocytes showed a very similar phenotype in all functional assays and differences between / and were stronger than between and .

DISCUSSION

Our study provides evidence for genotype-dependent effects on astrocyte energy metabolism and highlights alterations in the bioenergetic processes of the brain as important pathomechanisms in AD.