Opposing Effects of ApoE2 and ApoE4 on Glycolytic Metabolism in Neuronal Aging Supports a Warburg Neuroprotective Cascade against Alzheimer’s Disease

Abstract

Apolipoprotein E4 (ApoE4) is the most recognized genetic risk factor for late-onset Alzheimer’s disease (LOAD), whereas ApoE2 reduces the risk for LOAD. The underlying mechanisms are unclear but may include effects on brain energy metabolism. Here, we used neuro-2a (N2a) cells that stably express human ApoE isoforms (N2a-hApoE), differentiated N2a-hApoE neuronal cells, and humanized ApoE knock-in mouse models to investigate relationships among ApoE isoforms, glycolytic metabolism, and neuronal health and aging. ApoE2-expressing cells retained robust hexokinase (HK) expression and glycolytic activity, whereas these endpoints progressively declined with aging in ApoE4-expressing cells. These divergent ApoE2 and ApoE4 effects on glycolysis directly correlated with markers of cellular wellness. Moreover, ApoE4-expressing cells upregulated phosphofructokinase and pyruvate kinase with the apparent intent of compensating for the HK-dependent glycolysis reduction. The introduction of ApoE2 increased HK levels and glycolysis flux in ApoE4 cells. PI3K/Akt signaling was distinctively regulated by ApoE isoforms but was only partially responsible for the ApoE-mediated effects on HK. Collectively, our findings indicate that human ApoE isoforms differentially modulate neuronal glycolysis through HK regulation, with ApoE2 upregulating and ApoE4 downregulating, which markedly impacts neuronal health during aging. These findings lend compelling support to the emerging inverse-Warburg theory of AD and highlight a therapeutic opportunity for bolstering brain glycolytic resilience to prevent and treat AD.

APOE4 increases energy metabolism in APOE-isogenic iPSC-derived neurons

“…In general, many contradictory results on the impact of APOE on energy metabolism have been published. Some studies found that APOE4 reduced glycolysis [28,39], whereas others observed a shift from oxidative to glycolytic metabolism in APOE4 cells with higher glycolytic activity in APOE4 than APOE3 [40][41][42]. Our study showed enhancement of both, oxidative as well as glycolytic metabolism.…”

“…However, at higher passages APOE4 N2A cells showed impaired glycolysis and glycolytic activity indicating an age-dependent effect of APOE4 on their energy metabolism. This effect could also be observed for hexokinase (HK) expression, which is decreased in APOE4 cells with higher passages whereas APOE2 and APOE3 showed a stable expression of HK over time [28]. Qi and colleagues suggested a cell type-specific APOE effect on glycolysis with showing reduced ATP levels and glycolysis in primary hippocampal neurons and increased glycolytic rates and ATP production in astrocytes [29].…”

Why Is Iron Deficiency/Anemia Linked to Alzheimer’s Disease and Its Comorbidities, and How Is It Prevented?

“…Another transgenic mouse model carrying the human APOEε4 isoform displayed a reduction of about 30% in glucose transport through the blood-brain barrier compared with mice carrying the APOEε2 variant, although Glut1 expression in brain capillaries was unchanged [66]. In line with these results, Zhang observed high neuronal glycolytic activity in APOEε2 transgenic mice but low activity in APOEε4 mice, probably due to the limited glucose uptake [67]. ApoE also influences brain iron homeostasis.…”

How areAPOE4, changes in body weight, and longevity related? Insights from a causal mediation analysis

“…This CMA also revealed that AgeMaxW and SlopeW are factors that may explain only a part (albeit substantial) of the negative association between APOE4 and longevity, because they did not meet the criteria to satisfy ‘complete mediation’ (𝑃𝑀 ≥ 80%) (Kenny 2021). This suggests that there are other causal factors to be discovered, which warrants further investigation of the mechanisms involved in the association between APOE4 and longevity, using other mediators, such as those involved in dysregulations of cholesterol transport, impaired myelination, hypometabolism, and other traits associated with APOE4 that may also affect longevity (Zhang et al 2023; Blanchard et al 2022).…”