APOE genotype-dependent differences in human astrocytic energy metabolism

Area of Science:

• Neuroscience
• Genetics
• Cell Biology

Background:

• The apolipoprotein E4 (APOE4) allele is a major genetic risk factor for Alzheimer's disease (AD).
• APOE isoforms (APOE2, APOE3, APOE4) play crucial roles in brain function, particularly in astrocytes, affecting energy metabolism.
• Disruptions in brain energy metabolism are implicated in AD pathophysiology.

Purpose of the Study:

• To investigate the impact of different APOE genotypes on human astrocyte energy metabolism.
• To determine how APOE2, APOE3, and APOE4 isoforms influence astrocyte bioenergetics.

Main Methods:

• Generation of isogenic human astrocytes (iAstrocytes) from induced pluripotent stem cells (iPSCs) expressing specific APOE isoforms (APOE2, APOE3, APOE4) or APOE knockout (APOE-KO).
• Assessment of cellular energy metabolism using ATP Seahorse assays, glycolysis stress tests, and genetically encoded nanosensor-based FLIM analysis.
• Proteomic and metabolomic analyses (mass spectrometry) to identify differentially regulated pathways.

Main Results:

• APOE4 iAstrocytes exhibited reduced ATP production but enhanced glycolysis and glycolytic capacity compared to other genotypes.
• Mitochondrial respiration and activity were elevated in APOE4 iAstrocytes, with increased proton leak.
• Metabolomic analysis revealed differential regulation of energy and glucose metabolism pathways, including the mitochondrial electron transport chain and glycolysis.
• APOE2 and APOE-KO iAstrocytes displayed similar metabolic phenotypes, distinct from APOE4.

Conclusions:

• APOE genotype significantly influences human astrocyte energy metabolism.
• Alterations in astrocyte bioenergetics associated with APOE4 represent a potential pathomechanism in Alzheimer's disease.
• The study highlights the critical role of APOE in regulating brain energy homeostasis relevant to AD.