Apolipoprotein E2 Expression Alters Endosomal Pathways in a Mouse Model With Increased Brain Exosome Levels During...

Area of Science:

• Neuroscience
• Genetics
• Cell Biology

Background:

• The apolipoprotein E (APOE) gene significantly influences Alzheimer's disease (AD) risk, with APOE4 increasing risk and APOE2 offering protection.
• The neuronal endosomal system is vital for cellular health and is vulnerable during aging, with APOE4 exacerbating dysfunction by enlarging early endosomes and reducing exosome release.

Purpose of the Study:

• To investigate whether the neuroprotective effects of the APOE2 allele are mediated through the endosomal pathway.
• To compare the impact of APOE2, APOE3, and APOE4 on endosomal function and exosome release during brain aging.

Main Methods:

• Analysis of messenger RNA (mRNA) to assess endosomal pathway enrichment in the brain.
• Examination of age-dependent alterations in endosomal regulatory proteins.
• Morphological and quantitative analysis of early endosomes and retromer-associated vesicles in neurons.
• Measurement of extracellular exosome levels in the brain.

Main Results:

• APOE2 expression enriches endosomal pathways in the brain compared to APOE3 and APOE4.
• Unlike APOE4, APOE2 did not cause early endosome enlargement in aged mice; endosome morphology and abundance were similar to APOE3.
• Aged APOE2 mice exhibited increased extracellular levels of endosome-derived exosomes compared to APOE3 mice, indicating enhanced clearance.

Conclusions:

• APOE2 promotes an enhanced endosomal clearance pathway via increased exosome release during brain aging.
• This APOE2-mediated enhancement of endosomal function may underlie its neuroprotective effects against Alzheimer's disease.
• These findings highlight the critical role of the endosomal system in APOE's influence on AD risk and brain aging.