APOE4 association with TDP-43 pathology in AD

PRIMARY OUTCOME

frequency of TDP-43 pathology by APOE genotype

EXPECTED OUTCOMES

## Primary Outcomes **APOE4-TDP-43 Association**: APOE4+ AD patients show ≥40% higher CSF phospho-TDP-43 levels vs. APOE4- AD patients (p < 0.01). APOE4+ AD group shows ≥2-fold higher odds of TDP-43 pathology at autopsy (OR = 2.3, 95% CI: 1.4-3.8). **Neuroimaging Correlation**: Hippocampal atrophy rate (mL/year) correlates positively with CSF phospho-TDP-43 levels (Spearman ρ = 0.58, p < 0.001). APOE4+ patients show accelerated atrophy (+0.12 mL/year vs. APOE4-). ## Secondary Outcomes **CSF Biomarker Profile**: APOE4+ AD patients show distinct CSF signature: elevated total tau (+25%, p < 0.05) and phospho-tau181 (+30%, p < 0.01) vs. APOE4- AD, without change in Aβ42. This suggests APOE4 accelerates tau pathology independent of amyloid. **TDP-43 Strain Variation**: APOE4-derived TDP-43 aggregates show distinct conformational signatures (ThT kinetics, proteolytic resistance patterns) vs. APOE3-derived aggregates, consistent with APOE isoform-dependent structural templating.

SUCCESS CRITERIA

## Primary Success Criteria **Association Strength**: APOE4 carrier status must associate with ≥1.5-fold increase in TDP-43 pathological burden (CSF or autopsy) vs. non-carriers, with p < 0.01 in logistic regression controlling for age, sex, and disease severity. **Dose-Response**: ε4/ε4 homozygotes show greater TDP-43 burden than ε3/ε4 heterozygotes (≥1.3-fold), confirming gene dose effect consistent with APOE4's known dose-response for AD risk. ## Secondary Success Criteria **Specificity**: APOE4-TDP-43 association must remain significant after adjusting for APOE4's known effects on amyloid pathology (include CSF Aβ42 or PET status as covariate). If association attenuates to ns, APOE4 effect may be mediated entirely through amyloid. **Replication**: Association must replicate in an independent cohort (n≥50 per group) with consistent direction and magnitude (within 30% of discovery effect size).

PROTOCOL

# APOE4 Association with TDP-43 Pathology in Alzheimer's Disease Protocol ## Phase 1: Patient Cohort Recruitment and Sample Collection (Days 1-30) **Cohort Assembly**: Recruit AD patients (n=120, ages 60-85, NINCDS-ADRDA criteria) and age-matched cognitively normal controls (n=60) from memory clinics. Genotype APOE (ε2/ε3/ε4 status) via PCR-RFLP or TaqMan assay. Stratify into APOE4+ (≥1 ε4 allele, n~60) and APOE4- (ε3/ε3, n~60) AD groups plus APOE4- controls (n~40). **CSF Collection**: Perform lumbar puncture (LP) at baseline (25G Sprotte needle, 12 mL CSF, slow withdrawal). Centrifuge at 800×g (10 min, 4°C) within 1 hour. Aliquot into 0.5 mL fractions, store at -80°C. Exclude samples with >500 erythrocytes/μL or signs of blood contamination. **Neuroimaging**: Obtain 3T MRI (T1 MPRAGE, T2 FLAIR, GRE) within 2 weeks of CSF collection. Rate medial temporal atrophy (MTA scale 0-4) and global cortical atrophy (GCA). Process via FreeSurfer for hippocampal volume and cortical thickness measures. ## Phase 2: TDP-43 and Neurodegeneration Biomarker Analysis (Days 31-60) **CSF Biomarker Measurement**: Assay TDP-43 species via ELISA (Fujirebio #NR-25341 for total TDP-43, phospho-TDP-43 #NR-25342). Measure tau/Aβ42 ratio (INNOTEST, Fujirebio). Run all samples in duplicate with internal QC standards (low/medium/high pools). Technicians blinded to APOE/genotype. **蛟Fractionation for TDP-43 States**: Separate soluble vs. insoluble TDP-43 via high-salt extraction (50 mM Tris, 750 mM NaCl, 1% Triton X-100) followed by urea extraction (7M urea). Probe fractions via western blot with pan-TDP-43 (1:1000, Proteintech #10782-2-AP) and phospho-TDP-43 (1:500, Cosmo Bio #TIP-PTD-P01). **APOE4 Effects on TDP-43 Aggregation**: For mechanistic arm, incubate recombinant TDP-43 (0.5 mg/mL) with APOE4 or APOE3 lipoproteins (10 μg/mL) in physiological buffer (37°C, 7 days). Assess aggregate formation via Thioflavin T fluorescence and filter trap assay. ## Phase 3: Neuropathological Correlation (Days 61-90) **Autopsy and Tissue Processing**: For cases coming to autopsy (target n=30), collect fresh frozen brain tissue (dorsolateral prefrontal cortex, DLPFC; hippocampus) and fixed tissue blocks. Sample Brodmann area 46/9 from DLPFC and hippocampal CA1. **Immunohistochemistry**: Stain for phospho-TDP-43 (pS409/410, 1:2000, Cosmo Bio) using standard DAB protocol. Score burden semiquantitatively (0: none, 1: sparse, 2: moderate, 3: frequent, 4: dense). Include TDP-43 inclusion morphology (neuronal cytoplasmic, glial, neuritic). **Co-localization Studies**: Double-label TDP-43 with APOE (1:200, Abcam #ab1904) to assess APOE-TDP-43 physical proximity via confocal microscopy. Use proximity ligation assay (PLA) to detect direct APOE-TDP-43 interaction in situ.

LINKED HYPOTHESES

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