Basic Science and Pathogenesis.

Area of Science:

• Neuroscience
• Genetics
• Cell Biology

Background:

• Genome-Wide Association Studies (GWAS) linked phospholipase-C-γ2 (PLCG2) variants to late-onset Alzheimer's Disease (LOAD).
• PLCG2 is implicated in microglial function and Aβ pathology, but its role in tau pathology and other cell types remains unclear.
• PLCG2's known role as a second messenger suggests a potential link to tau phosphorylation and the autophagy-lysosomal pathway (ALP).

Purpose of the Study:

• To investigate the role of PLCG2 and its variants in tau pathology within excitatory neurons.
• To determine if PLCG2 deficiency exacerbates tau aggregation and propagation.
• To explore the impact of PLCG2 on the autophagy-lysosomal pathway (ALP) in the context of Alzheimer's Disease (AD).

Main Methods:

• Western blot and immunofluorescence staining on human post-mortem brains and PS19 tau mice.
• Stereotaxic injection of AAV8-CaMKIIa-cre and tau seeds in PLCG2-floxed mice to quantify tau spreading after PLCG2 knockdown.
• Generation of human neural organoids from iPSCs with CRISPR/Cas9-edited PLCG2 P522R knock-in (KI) and wild-type controls, utilizing a FUW-mCherry-GFP-LC3 reporter assay to investigate ALP dynamics.

Main Results:

• Global PLCG2 protein levels were elevated in human AD cases and PS19 mice, yet reduced in tau-positive cells.
• Knockdown of PLCG2 in excitatory neurons led to increased tau spreading in PLCG2-floxed mice.
• P522R KI organoids exhibited increased autophagy flux, even in the presence of an autophagy inhibitor (Bafilomyacin-A1), compared to wild-type organoids.

Conclusions:

• Repression or dysfunction of PLCG2 in excitatory neurons may contribute to tau pathology in Alzheimer's Disease (AD).
• PLCG2 likely influences tau pathology through the regulation of the autophagy-lysosomal pathway (ALP).
• These findings highlight a novel cellular mechanism involving PLCG2 in AD pathogenesis beyond microglial involvement.