Human apoE isoforms differentially regulate brain amyloid-β peptide clearance.

Area of Science:

• Neuroscience
• Genetics
• Biochemistry

Background:

• The apolipoprotein E (APOE) ε4 allele is a significant genetic risk factor for late-onset Alzheimer's disease (AD), increasing risk and lowering age of onset, likely due to its impact on amyloid-beta (Aβ) peptide accumulation.
• While the APOE ε2 allele appears protective, the precise mechanisms by which different APOE isoforms influence Aβ accumulation in sporadic AD remain unclear.

Purpose of the Study:

• To investigate how human apolipoprotein E (apoE) isoforms differentially affect amyloid-beta (Aβ) clearance and synthesis in vivo.
• To determine if apoE isoform-dependent differences in Aβ metabolism precede Aβ deposition in a mouse model of Alzheimer's disease.

Main Methods:

• Utilized a mouse model (PDAPP/TRE) expressing human apoE isoforms and performed in vivo microdialysis to measure soluble Aβ concentration and clearance in brain interstitial fluid.
• Employed in vivo stable isotopic labeling kinetics to assess amyloid precursor protein processing and Aβ synthesis rates across different apoE isoforms in young mice.

Main Results:

• Brain interstitial fluid concentration and clearance of soluble Aβ were dependent on the expressed apoE isoform in the PDAPP/TRE mouse model.
• These apoE isoform-dependent metabolic differences were observed in both young and aged mice, predating significant amyloid plaque deposition.
• Amyloidogenic processing and Aβ synthesis rates did not vary by apoE isoform in young mice, indicating clearance, not production, is differentially regulated.

Conclusions:

• APOE alleles influence Alzheimer's disease risk by differentially regulating the clearance of Aβ from the brain.
• Targeting Aβ clearance pathways presents a promising therapeutic strategy for Alzheimer's disease prevention.