CD33 and clusterin interact biophysically and genetically to modulate Alzheimer risk

Area of Science:

• Neuroscience
• Genetics
• Immunology

Background:

• Alzheimer's disease (AD) is a neurodegenerative disorder with complex genetic underpinnings.
• The CD33 gene, encoding a sialic acid-binding receptor, has been implicated in AD risk.
• Microglia play a crucial role in brain homeostasis and AD pathogenesis, including amyloid-beta (Aβ) plaque clearance.

Purpose of the Study:

• To investigate the structural, functional, and genetic mechanisms by which CD33 influences Alzheimer's disease risk.
• To elucidate the role of CD33 isoforms and their interactions with AD-related proteins in disease pathogenesis.
• To explore the potential of genetic variations in CD33 and CLU for personalized AD therapeutics.

Main Methods:

• Structural and functional studies of the CD33 receptor.
• Genetic analyses, including human brain expression quantitative trait loci (eQTL) and causal mediation analyses.
• Investigation of CD33 interactions with AD-related proteins like clusterin and Aβ.

Main Results:

• Non-coding AD-risk alleles upregulate the full-length CD33 M isoform, which forms dimers and interacts with clusterin and Aβ.
• CD33 M dimerization inhibits microglial phagocytosis of amyloid plaques, impairing a protective function.
• Genetic interactions between CLU and CD33 genotypes modulate AD phenotypes, suggesting personalized therapeutic strategies.

Conclusions:

• CD33 M plays a critical role in AD pathogenesis by suppressing microglial clearance of amyloid plaques.
• Genetic variations in CD33 and CLU offer potential biomarkers for AD risk stratification and personalized treatment approaches.
• Novel soluble CD33 M fragments were identified, indicating new avenues for understanding CD33 biology.