Drug Development.

Area of Science:

• Neuroscience
• Immunology
• Genetics

Background:

• The APOE ε4 allele is a major genetic risk factor for Alzheimer's disease (AD), linked to earlier onset.
• ApoE4 is implicated in amyloid-beta (Aβ) aggregation and lipid droplet formation in early AD pathogenesis.
• The role of ApoE in Aβ phagocytosis and its differential effects based on isoform remain unclear.

Purpose of the Study:

• To investigate the impact of Apolipoprotein E3 (ApoE3) and Apolipoprotein E4 (ApoE4) on Aβ phagocytosis by immune cells.
• To determine if ApoE isoforms differentially affect Aβ clearance mechanisms.
• To explore the relationship between ApoE, lipid droplet formation, and phagocytic activity.

Main Methods:

• Utilized HEK293 cells expressing ApoE3 or ApoE4 to isolate proteins.
• Employed real-time flow cytometry with THP-1 monocytes and fluorescent beads to assess phagocytosis.
• Used BV2 microglia with pHrodo-red Aβ oligomers and LipidSpot staining to evaluate Aβ endocytosis and lipid droplet formation.

Main Results:

• Both ApoE3 and ApoE4 dose-dependently inhibited phagocytosis of beads by monocytes.
• ApoE isoforms reduced Aβ oligomer endocytosis and acidification in microglia.
• ApoE4 demonstrated decreased binding of Aβ oligomers compared to ApoE3, while both isoforms reduced lipid droplet formation.

Conclusions:

• ApoE isoforms inhibit phagocytic activity in monocytes and microglia, irrespective of the specific isoform.
• Reduced Aβ surface binding by ApoE4 suggests impaired Aβ chaperoning, potentially contributing to initial Aβ aggregation in AD.
• These findings reveal isoform-specific mechanisms of ApoE in Alzheimer's disease pathogenesis.