APOE genotype-dependent differences in human astrocytic energy metabolism

Higher oxygen consumption together with increased glycolysis while having reduced ATP production is a sign of mitochondrial uncoupling.

“Higher oxygen consumption together with an increased glycolysis while having reduced ATP production is a sign of mitochondrial uncoupling.”

• cites Cadenas, 2018 sourcePartly supported

  The Introduction and §2 (page numbers unavailable) describe uncoupling as respiration that is less efficiently linked to ATP synthesis, supporting the oxygen-consumption and ATP-production parts of the claim. The passages do not establish increased glycolysis as part of that sign; a search for glycolysis found no supporting passage. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites Demine et al., 2019 sourcePartly supported

  Section 2.3 reports that the uncoupler FR58P1 rapidly lowers ATP in MDA-MB-231 cells, followed by a probable glycolytic shift that restores ATP within four hours. The Introduction explains the link between oxygen consumption and mitochondrial electron transfer, but the retrieved passages do not establish increased oxygen consumption alongside those changes as a general sign of uncoupling. (LLM, conf=0.84)

  Experimental — accuracy not yet measured

Young APOE4 carriers or APOE4-knock-in mice with no apparent neurodegenerative pathology show increased brain metabolism and activity.

“Interestingly, several studies in young APOE4 carriers or in APOE4-knock-in mice with no apparent neurodegenerative pathology, revealed increased brain metabolism and activity (Filippini et al., 2009; Evans et al., 2017; Nuriel et al., 2017; Venzi et al., 2017), indicating that the APOE4 effect on brain energy metabolism may differ depending on the degree of pathology.”

• cites Filippini et al., 2009 sourceSupported
• cites Evans et al., 2017 sourcePartly supported

  The Discussion (page unavailable) reports hippocampal overactivation during word encoding in young adult APOE4 carriers, supporting the increased-activity part of the claim. It also reports underactivation during recognition and says the carriers do not show a consistent pattern of overactivity. The paper does not report increased brain metabolism or establish an absence of neurodegenerative pathology in its participants; the mouse studies are attributed to other citations. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites Nuriel et al., 2017 sourceSupported

Human isogenic iPSC-derived astrocytes expressing APOE4 display altered lipid metabolism compared to astrocytes expressing APOE3 or APOE2.

“Human isogenic iPSC-derived astrocytes expressing APOE4 displayed a pro-inflammatory phenotype, reduced beta-amyloid uptake capacity and altered lipid metabolism compared to astrocytes expressing APOE3 or APOE2 (de Leeuw et al., 2022).”

• cites de Leeuw et al., 2022 sourceSupported

Human isogenic iPSC-derived astrocytes expressing APOE4 display reduced beta-amyloid uptake capacity compared to astrocytes expressing APOE3 or APOE2.

“Human isogenic iPSC-derived astrocytes expressing APOE4 displayed a pro-inflammatory phenotype, reduced beta-amyloid uptake capacity and altered lipid metabolism compared to astrocytes expressing APOE3 or APOE2 (de Leeuw et al., 2022).”

• cites de Leeuw et al., 2022 sourcePartly supported

  The Results section (“Homeostatic functions show APOE allele-dependent decline in iAstrocytes”) reports an Aβ42 uptake trend of E2 > E3 ≥ E4, supporting lower uptake in APOE4 than APOE2. It also says the difference between APOE3 and APOE4 did not reach statistical significance (p = 0.054), so the unqualified claim of reduced uptake compared with APOE3 overstates the finding. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

Human isogenic iPSC-derived astrocytes expressing APOE4 display a pro-inflammatory phenotype compared to astrocytes expressing APOE3 or APOE2.

“Human isogenic iPSC-derived astrocytes expressing APOE4 displayed a pro-inflammatory phenotype, reduced beta-amyloid uptake capacity and altered lipid metabolism compared to astrocytes expressing APOE3 or APOE2 (de Leeuw et al., 2022).”

• cites de Leeuw et al., 2022 sourceSupported

HK2 expression differences between APOE variants become more pronounced with increasing passage numbers.

“This discrepancy may be attributed to the fact that HK2 expression differences between APOE variants become more pronounced with increasing passage numbers (Zhang et al., 2023).”

• cites Zhang et al., 2023 sourceSupported

GSEA of proteomic data showed a tendency to downregulation in APOE2 compared to APOE3.

“Gene set enrichment analysis (GSEA) of proteomic data showed strong upregulation of pathways involved in OXPHOS as well as mitochondrial structure and function in APOE4 compared to APOE2 and a tendency to downregulation in APOE2 compared to APOE3 (Figures 4A,B; Supplementary Table S1).”

• cites de Leeuw et al., 2022 sourceCould not verify

  The Results sections on cholesterol and lipid metabolism and on lysosomal function (pages unavailable) report GSEA comparisons among APOE genotypes, but do not report a tendency for OXPHOS or mitochondrial pathways to be downregulated in APOE2 versus APOE3. Searches for oxidative phosphorylation, mitochondrial function, and the claimed downregulation found no passage addressing that specific result. (LLM, conf=0.72)

  Experimental — accuracy not yet measured

The effects of APOE on OCR and ECAR in APOE4 astrocytes were not prominent after 1 month but became evident after 2 months of culture.

“Similarly, Fang and colleagues found that the effects of APOE on OCR and ECAR in APOE4 astrocytes were not prominent after 1 month but became evident after 2 months of culture (Fang et al., 2021).”

• cites Fang et al., 2021 sourceSupported

APOE isoforms differentially affect astrocyte function.

“APOE isoforms differentially affect astrocyte function (de Leeuw and Tackenberg, 2019).”

• cites de Leeuw and Tackenberg, 2019 sourceSupported

GSEA of proteomic data showed strong upregulation of pathways involved in OXPHOS as well as mitochondrial structure and function in APOE4 compared to APOE2.

“Gene set enrichment analysis (GSEA) of proteomic data showed strong upregulation of pathways involved in OXPHOS as well as mitochondrial structure and function in APOE4 compared to APOE2 and a tendency to downregulation in APOE2 compared to APOE3 (Figures 4A,B; Supplementary Table S1).”

• cites de Leeuw et al., 2022 sourceCould not verify

  The Results sections on cholesterol and lipid metabolism and on lysosomal function describe GSEA of proteomic data, but do not report upregulation of OXPHOS or mitochondrial structure and function pathways in APOE4 versus APOE2. Searches for OXPHOS, oxidative phosphorylation, and mitochondrial pathways found no passage addressing that finding in our copy. (LLM, conf=0.74)

  Experimental — accuracy not yet measured

APOE-KO and APOE2 may promote a more robust glycolytic energy profile compared to APOE3 cells.

“This suggests that APOE-KO and APOE2 may promote a more robust glycolytic energy profile compared to APOE3 cells (Wu et al., 2018; Zhang et al., 2023).”

• cites Wu et al., 2018Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Zhang et al., 2023 sourcePartly supported

  Results §3.3 reports that ApoE2-expressing cells had higher maximum glycolytic capacity than ApoE3-expressing cells at P15, supporting the ApoE2 comparison. The paper does not report an APOE-knockout cell comparison with APOE3, so it does not support that part of the sentence. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

When comparing APOE4 to APOE2, the malate-aspartate shuttle ranked among the top 25 enriched metabolic pathways.

“When comparing APOE4 to APOE2, the malate–aspartate shuttle ranked among the top 25 enriched metabolic pathways (Supplementary Figure S5A) and in the APOE4 versus APOE3 comparison mitochondrial beta-oxidation was among the top 25 enriched pathways (Supplementary Figure S5B).”

Levels of mitochondrial fission marker mitochondrial fission 1 protein (FIS1) were higher in APOE3 compared to APOE-KO and APOE2.

“However, levels of mitochondrial fission marker mitochondrial fission 1 protein (FIS1) were higher in APOE3 compared to APOE-KO and APOE2 (Supplementary Figure S3F).”

Translocase of outer mitochondrial membrane 20 (TOMM20) did not show APOE genotype-specific differences.

“Another mitochondrial marker, translocase of outer mitochondrial membrane 20 (TOMM20), did not show APOE genotype-specific differences (Supplementary Figures S3G,H).”

No differences in basal lactate levels were observed between APOE lines.

“No differences in basal lactate levels were observed between the lines (Figure 3D).”

In APOE4 compared to APOE-KO, fructose and mannose degradation and glycolysis were found in the top 25 pathways.

“In APOE4 compared to APOE-KO, fructose and mannose degradation and glycolysis were found in the top 25 pathways (Supplementary Figure S5C).”

Pathways such as the malate-aspartate shuttle, glycolysis, mitochondrial electron transport chain, Warburg effect, and pyruvate metabolism were found in all comparisons between APOE4 and APOE2, APOE3, or APOE-KO.

“Some pathways were only enriched in the comparison of APOE4 to either APOE2, APOE3 or APOE-KO, whereas others, such as the malate–aspartate-shuttle, glycolysis, mitochondrial electron transport chain, Warburg effect or pyruvate metabolism were found in all comparisons.”

Differences between APOE2/APOE-KO and APOE4 are stronger than differences between APOE3 and APOE4.

“In general, APOE2 and APOE-KO iAstrocytes showed a very similar phenotype in all functional assays and differences between APOE2/APOE-KO and APOE4 were stronger than between APOE3 and APOE4.”

We observed an increased proton leak specifically in APOE4 iAstrocytes.

“We observed an increased proton leak specifically in APOE4 iAstrocytes, suggesting that mitochondrial membrane alterations may contribute to the observed uncoupling.”

Mass spectrometry-based metabolomic analysis identified various energy and glucose metabolism-related pathways that are differentially regulated in APOE4 compared to the other genotypes, including mitochondrial electron transport chain and glycolysis.

“Mass spectrometry-based metabolomic analysis identified various energy and glucose metabolism-related pathways that were differentially regulated in APOE4 compared to the other genotypes, including mitochondrial electron transport chain (ETC) and glycolysis.”

The proportion of glycolysis-generated ATP is higher in APOE2 and APOE-KO iAstrocytes (41 and 42%, respectively) than in APOE3 (29%) and APOE4 iAstrocytes (33%).

“Interestingly, the proportion of glycolsis-generated ATP was higher in APOE2 and APOE-KO iAstrocytes (41 and 42%, respectively) than in APOE3 (29%) and APOE4 iAstrocytes (33%; Figure 1G).”

PKM1 protein levels are not affected by APOE genotype.

“Interestingly, levels of pyruvate kinase (PKM1), the enzyme that catalyzes the last step in glycolysis, was not affected by the APOE genotype (Figures 2B,E).”

Levels of mitochondrial uncoupling proteins (UCPs) are not affected in APOE4 iAstrocytes.

“This was accompanied by elevated proton leak in APOE4 iAstrocytes while levels of mitochondrial uncoupling proteins (UCPs) were not affected.”

No differences in HK1 protein levels were observed between APOE lines.

“No differences in HK1 were observed (Figure 2C), while protein levels of HK2 were significantly lower in APOE3 and APOE4 compared to APOE-KO and APOE2 (KO = E2 > E3 = E4; Figure 2D).”

No differences in UCP2 and UCP4 levels were found in the APOE isogenic lines.

“No differences in UCP2 and UCP4 levels were found in the APOE isogenic lines (Figures 4J,K).”

The levels of mitochondrial proteins TOMM20, TOMM40 and TOMM70 were not significantly affected by APOE.

“Additionally, the levels of mitochondrial proteins TOMM20, TOMM40 and TOMM70 were not significantly affected by the APOE, as shown by western blot (TOMM20) and proteomic analysis (TOMM40, TOMM70).”

We did not observe APOE genotype-dependent changes in key mitochondrial fusion and fission proteins.

“In our study, we did not observe APOE genotype-dependent changes in key mitochondrial fusion and fission proteins.”

iAstrocytes predominantly produce lactate.

“The immediate decrease in measured lifetime is equivalent to an increase in intracellular lactate and shows that iAstrocytes predominantly produce lactate.”

APOE4 iAstrocytes show elevated proton leak.

“This was accompanied by elevated proton leak in APOE4 iAstrocytes while levels of mitochondrial uncoupling proteins (UCPs) were not affected.”

Similar rates of lactate increase through azide treatment were observed between APOE genotypes.

“Similar rates of lactate increase through azide treatment were observed between APOE genotypes (Figure 3F).”

No differences in the mitochondrial fusion proteins mitofusin-1/2 (MFN1/2) and optic atrophy-1 (OPA1) were detected between the APOE-isogenic lines.

“No differences in the mitochondrial fusion proteins mitofusin-1/2 (MFN1/2) and optic atrophy-1 (OPA1) were detected between the APOE-isogenic lines (Supplementary Figure S3C–E).”

Nine pathways related to glucose and energy metabolism were identified when comparing APOE4 to APOE2 iAstrocytes.

“Nine pathways related to glucose and energy metabolism were identified when comparing APOE4 to APOE2 iAstrocytes (Figure 5A), while 7 pathways were identified in APOE4 compared to APOE3 (Figure 5B) and 11 pathways in APOE4 compared to APOE-KO (Figure 5C).”

We did not observe differences in the expression of UCP2 and UCP4 in APOE4 iAstrocytes.

“However, we did not observe differences in the expression of UCP2 and UCP4, two major astrocytic UCPs, in APOE4 iAstrocytes.”

Basal and maximal respiration were significantly higher in APOE4 iAstrocytes compared to the other APOE genotypes.

“Basal and maximal respiration was significantly higher in APOE4 iAstrocytes compared to the genotypes (Figures 4E,F), while spare respiration capacity was increased in APOE4 compared to APOE2 (Figure 4G).”

Seven pathways related to glucose and energy metabolism were identified when comparing APOE4 to APOE3 iAstrocytes.

“Nine pathways related to glucose and energy metabolism were identified when comparing APOE4 to APOE2 iAstrocytes (Figure 5A), while 7 pathways were identified in APOE4 compared to APOE3 (Figure 5B) and 11 pathways in APOE4 compared to APOE-KO (Figure 5C).”

Eleven pathways related to glucose and energy metabolism were identified when comparing APOE4 to APOE-KO iAstrocytes.

“Nine pathways related to glucose and energy metabolism were identified when comparing APOE4 to APOE2 iAstrocytes (Figure 5A), while 7 pathways were identified in APOE4 compared to APOE3 (Figure 5B) and 11 pathways in APOE4 compared to APOE-KO (Figure 5C).”

In the APOE4 versus APOE3 comparison, mitochondrial beta-oxidation was among the top 25 enriched pathways.

“When comparing APOE4 to APOE2, the malate–aspartate shuttle ranked among the top 25 enriched metabolic pathways (Supplementary Figure S5A) and in the APOE4 versus APOE3 comparison mitochondrial beta-oxidation was among the top 25 enriched pathways (Supplementary Figure S5B).”

Mitochondrial ATP production is significantly lower in APOE4 iAstrocytes than in all other APOE lines (E4 < E3 = E2 = KO).

“Mitochondrial ATP production was significantly lower in APOE4 iAstrocytes than in all other APOE lines (E4 < E3 = E2 = KO; Figure 1D).”

APOE genotypes have no observable effect on lactate dynamics.

“Taken together, APOE genotypes differentially affect mitochondrial respiration and glycolysis, but have no observable effect on lactate dynamics.”

Glycolytic reserve remains unchanged between APOE lines.

“APOE4 astrocytes exhibited increased glycolysis and glycolytic capacity compared to APOE-KO and APOE2 (Figures 2H,I), while glycolytic reserve remained unchanged between APOE lines (Figure 2J).”

A significantly elevated proton leak was observed in APOE4 iAstrocytes compared to all other APOE lines.

“Further, a significantly elevated proton leak was observed in APOE4 iAstrocytes compared to all other lines (Figure 4H).”

Similar rates of intracellular lactate increase after inhibition of lactate export through monocarboxylate transporters (AR-C) were observed between APOE-isogenic astrocyte lines.

“Similar rates of lactate increase through AR-C were observed between APOE lines.”

The degree of pathway enrichment varied between the APOE lines.

“However, the degree of pathway enrichment varied between the lines.”

APOE2 and APOE-KO iAstrocytes show a very similar phenotype in all functional assays.

“In general, APOE2 and APOE-KO iAstrocytes showed a very similar phenotype in all functional assays and differences between APOE2/APOE-KO and APOE4 were stronger than between APOE3 and APOE4.”

APOE4 astrocytes exhibit increased glycolysis compared to APOE-KO and APOE2.

“APOE4 astrocytes exhibited increased glycolysis and glycolytic capacity compared to APOE-KO and APOE2 (Figures 2H,I), while glycolytic reserve remained unchanged between APOE lines (Figure 2J).”

HK2 protein levels are significantly lower in APOE3 and APOE4 compared to APOE-KO and APOE2 (KO = E2 > E3 = E4).

“No differences in HK1 were observed (Figure 2C), while protein levels of HK2 were significantly lower in APOE3 and APOE4 compared to APOE-KO and APOE2 (KO = E2 > E3 = E4; Figure 2D).”

APOE4 astrocytes exhibit increased glycolytic capacity compared to APOE-KO and APOE2.

“APOE4 astrocytes exhibited increased glycolysis and glycolytic capacity compared to APOE-KO and APOE2 (Figures 2H,I), while glycolytic reserve remained unchanged between APOE lines (Figure 2J).”

Spare respiratory capacity was increased in APOE4 iAstrocytes compared to APOE2.

“Basal and maximal respiration was significantly higher in APOE4 iAstrocytes compared to the genotypes (Figures 4E,F), while spare respiration capacity was increased in APOE4 compared to APOE2 (Figure 4G).”

A noticeable trend is observed in the glyco/mitoATP production ratio, with glycolytic ATP production being higher in APOE-KO and APOE2 compared to APOE3 and APOE4.

“A noticeable trend is observed in the glyco/mitoATP production ratio, with glycolytic ATP production being higher in APOE-KO and APOE2 compared to APOE3 and APOE4.”

APOE4 iAstrocytes display reduced ATP production.

“Despite exhibiting increased mitochondrial respiration and glycolysis, APOE4 iAstrocytes display reduced ATP production, likely due to mitochondrial dysfunction, as indicated by a significant proton leak.”

Immunostaining confirmed expression of astrocyte markers s100β and GJA1 in differentiated iAstrocytes.

“To verify successful iAstrocytes differentiation, immunostaining was performed confirming the expression of astrocyte markers s100β and GJA1 (Supplementary Figure S1A).”

Post-mortem analysis of Alzheimer's disease brains found lower levels of neuronal glucose transporter GLUT3.

“Further, post-mortem analysis of AD brains discovered higher brain tissue glucose concentration, reduced glycolytic flux and lower levels of neuronal glucose transporter GLUT3 but no effect on astrocytic glucose transporter GLUT1, suggesting cell type specific metabolic alterations in AD (An et al., 2018).”

• cites An et al., 2018Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Differentiation efficiency reached >97% for all cell lines.

“Differentiation efficiency was calculated as s100β-positive cells per total DAPI counts and reached >97% for all cell lines (Supplementary Figure S1B).”

APOE genotypes differentially affect mitochondrial respiration and glycolysis.

“Taken together, APOE genotypes differentially affect mitochondrial respiration and glycolysis, but have no observable effect on lactate dynamics.”

APOE4 expression leads to an increase in mitochondrial respiration.

“Our data demonstrates that APOE4 expression leads to an increase in both mitochondrial respiration and glycolysis; however, this is accompanied by inefficient ATP production.”

APOE4 expression leads to an increase in glycolysis.

“Our data demonstrates that APOE4 expression leads to an increase in both mitochondrial respiration and glycolysis; however, this is accompanied by inefficient ATP production.”

APOE genotype has dependent effects on astrocyte energy metabolism.

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

LC-MS-based metabolomic analysis indicates that APOE4 has a major impact on human astrocyte energy metabolism.

“In summary, LC–MS-based metabolomic analysis indicates that APOE4 has a major impact on human astrocyte energy metabolism, confirming our observations from proteomic analysis and functional assays.”

APOE4 expression is accompanied by inefficient ATP production.

“Our data demonstrates that APOE4 expression leads to an increase in both mitochondrial respiration and glycolysis; however, this is accompanied by inefficient ATP production.”

Mitochondrial membrane alterations may contribute to the observed uncoupling in APOE4 iAstrocytes.

“We observed an increased proton leak specifically in APOE4 iAstrocytes, suggesting that mitochondrial membrane alterations may contribute to the observed uncoupling.”

Alterations in the bioenergetic processes of the brain are important pathomechanisms in Alzheimer's disease.

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

• AssumptionRests on an assumption: Disruptions in brain energy metabolism are a major contributor to Alzheimer's disease pathophysiology.
• AssumptionRests on an assumption: The in vitro metabolic phenotype of APOE-isogenic iAstrocytes is relevant to Alzheimer's disease pathomechanisms in the human brain.

APOE has a specific effect on distinct glycolytic enzymes rather than a general up/downregulation of glycolytic proteins.

“We show that APOE4 iAstrocytes exhibit lower expression of HK2 but not of HK1 or PKM1, suggesting a specific APOE effect on distinct enzymes rather than a general up/downregulation of glycolytic proteins.”

Post-mortem analysis of Alzheimer's disease brains found reduced glycolytic flux.

“Further, post-mortem analysis of AD brains discovered higher brain tissue glucose concentration, reduced glycolytic flux and lower levels of neuronal glucose transporter GLUT3 but no effect on astrocytic glucose transporter GLUT1, suggesting cell type specific metabolic alterations in AD (An et al., 2018).”

• cites An et al., 2018Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Mitochondrial uncoupling in APOE4 iAstrocytes occurs independently of UCPs.

“This suggests that mitochondrial uncoupling in APOE4 iAstrocytes occurs independently of UCPs.”

APOE4 may induce mitochondrial uncoupling.

“supporting our hypothesis of APOE4 may induce mitochondrial uncoupling”

APOE does not affect lactate dynamics in iAstrocytes.

“while genetically encoded nanosensor-based FLIM analysis revealed that APOE does not affect lactate dynamics.”

Rather than leading to excessive lactate accumulation, glycolysis appears to be upregulated just enough to maintain metabolic balance in APOE4 iAstrocytes.

“However, rather than leading to excessive lactate accumulation, glycolysis appears to be upregulated just enough to maintain metabolic balance.”

APOE-KO and APOE2 cells rely more on glycolysis compared to APOE3.

“This indicates that APOE-KO and APOE2 cells rely more on glycolysis compared to APOE3.”

A compensatory mechanism exists where pyruvate is preferentially directed toward mitochondrial oxidation rather than lactate production, thereby preserving stable intracellular lactate dynamics.

“This implies a compensatory mechanism where pyruvate is preferentially directed toward mitochondrial oxidation rather than lactate production, thereby preserving stable intracellular lactate dynamics.”

APOE variants differentially affect human astrocyte energy metabolism at the proteomic, metabolomic and functional level.

“Our study provides compelling evidence that APOE variants differentially affect human astrocyte energy metabolism at the proteomic, metabolomic and functional level.”

• AssumptionRests on an assumption: The APOE-isogenic iAstrocytes used in this study are a valid model for human astrocytes in vivo.

APOE4 displays a gain-of-function rather than a loss-of-function effect on astrocyte metabolism.

“This indicates that APOE4 displays a gain-of-function rather than a loss-of-function effect on astrocyte metabolism.”

APOE4 drives metabolic dysregulation in iAstrocytes through a gain-of-function mechanism.

“Specifically, we demonstrate that APOE4 drives metabolic dysregulation in iAstrocytes through a gain-of-function mechanism.”

The lower APOE protein levels in APOE4 iAstrocytes are not the cause for the metabolic phenotype observed in this cell line.

“However, the lower protein levels in APOE4 iAstrocytes are not the cause for the metabolic phenotype observed in this cell line.”