qPCR and western blot analysis of microvascular functional molecules

PRIMARY OUTCOME

expression levels of blood-brain barrier proteins

EXPECTED OUTCOMES

## Expected Outcomes ### Primary Outcomes 1. **Reduced tight junction protein expression:** APP/PS1 mice expected to show 20-40% lower Claudin-5, Occludin, and ZO-1 mRNA and protein in cortical microvessels at 1 month (early AD phenotype) 2. **Decreased Glut1 transporter:** Glucose transporter (Slc2a1) protein reduced 15-30% in APP/PS1 microvessels 3. **Altered P-gp expression:** Compensatory upregulation of P-glycoprotein efflux transporter possible (0-50% increase) ### Secondary Outcomes - Sex-specific effects: female APP/PS1 may show more pronounced BBB disruption markers - Correlation between Aβ burden and tight junction protein levels - Potential elevation of inflammatory markers (VCAM-1, ICAM-1) indicating endothelial activation ### Null Result Interpretation - No difference at 1 month could indicate BBB dysfunction occurs later (3-6 months) - Consider examining older age cohorts (3, 6, 12 months) - May require laser-capture microdissection to isolate pure microvessels

SUCCESS CRITERIA

## Success Criteria ### Primary - [ ] ≥20% reduction in Claudin-5 mRNA in APP/PS1 vs WT (p < 0.05) - [ ] ≥20% reduction in Occludin protein in APP/PS1 vs WT (p < 0.05) - [ ] Western blot confirmation of mRNA changes at protein level ### Secondary - [ ] Glut1 expression validated at both mRNA and protein level - [ ] Reference genes stable across groups (CV < 0.5 for ΔCt) - [ ] Sex as biological variable: analysis includes male/female comparison ### Technical Quality Gates - [ ] ≥7/8 biological replicates per group yield acceptable RNA/western data - [ ] qPCR efficiency 90-110% for all primer pairs - [ ] Single melt curve peak for SYBR Green assays (no primer-dimer) - [ ] Western blot: molecular weight matches expected, no non-specific bands - [ ] Blinded analysis during quantification (analyst unaware of genotype)

PROTOCOL

## Protocol: qPCR and Western Blot Analysis of Blood-Brain Barrier Proteins in APP/PS1 Mice ### Study Design Cross-sectional study comparing blood-brain barrier (BBB) molecular markers in 1-month-old APP/PS1 transgenic AD mice vs age-matched wild-type controls. Assess expression of key BBB integrity proteins in cerebral cortex microvascular fractions. ### Animals and Tissue Preparation 1. APP/PS1 transgenic mice (n=8 per group, equal sex distribution) and WT littermates (n=8) 2. Euthanize by CO2 inhalation at 1 month of age 3. Rapidly dissect brain and place in ice-cold Hibernate-E medium 4. Microvascular fractionation: - Strip meninges, mince cortex in ice-cold PBS - Homogenize with 10 strokes in Dounce homogenizer - Centrifuge at 3,000g for 5 min to remove debris - Collect pellet (crude microvascular fraction) - Percoll gradient purification to isolate microvessels 5. Flash-freeze microvascular pellets in liquid nitrogen, store at -80°C ### RNA Extraction and qPCR 1. Extract total RNA from microvascular fractions using RNeasy Micro Kit 2. Assess RNA integrity (RIN > 7 required for analysis) 3. Reverse transcribe 500 ng RNA using SuperScript IV 4. qPCR reactions (LightCycler 480): - Target genes: Cldn5, Ocln, ZO1 (tight junction), Glut1 (Slc2a1), P-gp (Abcb1a) - Reference gene: Gapdh, β-actin - Use SYBR Green chemistry, triplicate technical replicates - Include no-template and no-RT controls ### Western Blot Analysis 1. Lyse microvascular pellets in RIPA buffer + protease/phosphatase inhibitors 2. Quantify protein (BCA assay) 3. Load 20 µg protein per lane on 4-12% Bis-Tris SDS-PAGE 4. Transfer to PVDF membrane (wet transfer, 100V, 1 hour) 5. Block in 5% BSA/TBST for 1 hour at RT 6. Primary antibodies (overnight, 4°C): - Anti-Claudin-5 (1:500), anti-Occludin (1:500), anti-ZO-1 (1:1000) - Anti-Glut1 (1:1000), anti-P-gp (1:500) - Anti-β-actin (1:5000) as loading control 7. HRP-secondary antibodies (1:10,000), 1 hour RT 8. Develop with ECL substrate, image on ChemiDoc ### Controls - **Positive control:** Adult mouse brain microvessels (known high expression) - **Negative control:** Liver tissue (low BBB marker expression) - **Loading control:** β-actin normalization for each sample - **Technical replicates:** Triplicate qPCR, duplicate western blot lanes ### Expected Outcomes 1. Reduced Claudin-5, Occludin, ZO-1 mRNA and protein in APP/PS1 vs WT (early BBB dysfunction) 2. Decreased Glut1 expression indicating impaired glucose transporter function 3. Potential increase in P-gp (compensatory efflux upregulation) 4. Sex-specific differences possible (females may show earlier BBB breakdown) ### Success Criteria - [ ] RNA yield ≥ 200 ng with RIN > 7 from microvascular fraction - [ ] All target genes amplified with Ct < 35 in ≥ 7/8 biological replicates - [ ] ΔΔCt method with stable reference genes (Gapdh, β-actin; CV < 0.5) - [ ] Western blot: clear bands at expected molecular weights, no saturation - [ ] ≥20% difference in tight junction protein expression between groups (p < 0.05) - [ ] Effect direction consistent between mRNA and protein levels

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