SPP1 upregulation in perivascular cells in AD mouse models

PRIMARY OUTCOME

SPP1 expression levels in different cell types

EXPECTED OUTCOMES

- 1. Primary: >3-fold increase in perivascular macrophage SPP1 expression in 5xFAD mice compared to controls (p < 0.001, Cohen's d > 1.5) - 2. Secondary: 60-80% of perivascular macrophages (CD68+) express detectable SPP1 in 5xFAD mice vs <20% in controls - 3. Secondary: 2-fold increase in perivascular fibroblast (PDGFRβ+) SPP1 expression in 5xFAD mice (p < 0.01) - 4. Cellular specificity: <5% of microglia away from vessels express SPP1, confirming perivascular localization pattern - 5. Regional variation: Highest SPP1 upregulation in hippocampal regions with dense amyloid pathology - 6. Protein validation: Western blot confirms 4-6 fold increase in total brain SPP1 protein in 5xFAD mice - 7. Technical validation: RNAscope confirms >85% concordance with immunofluorescence results for cellular localization

SUCCESS CRITERIA

- • Statistical significance: p < 0.01 for primary comparison of perivascular macrophage SPP1 expression between genotypes - • Effect size: Cohen's d > 1.0 for difference in SPP1+ perivascular cell density between 5xFAD and control mice - • Cellular resolution: >90% of SPP1+ perivascular cells successfully identified by cell-type specific markers - • Data quality: Clear vessel identification in >85% of analyzed fields, adequate signal-to-noise ratio (>3:1) for SPP1 detection - • Reproducibility: Consistent findings across ≥3 brain regions per animal and ≥2 independent cohorts - • Technical validation: RNAscope and immunofluorescence results show >80% concordance for cellular localization - • Sample completion: ≥75% of planned animals successfully processed through all analysis phases

PROTOCOL

**Phase 1: Animal Model Preparation and Tissue Collection** — Weeks 1-2 Use aged (12-month-old) 5xFAD mice (The Jackson Laboratory #034840-JAX) and age-matched C57BL/6J controls (n=8 per group, power calculation for Cohen's d=1.2). Perform transcardial perfusion with PBS followed by 4% paraformaldehyde after deep anesthesia with ketamine/xylazine. Collect brain hemispheres: one for fresh-frozen sectioning (-80°C storage) and one for paraffin embedding. Prepare 20μm cryosections and 5μm paraffin sections using standard protocols. Include positive control tissues (kidney, bone) known to express high SPP1 levels. **Phase 2: SPP1 Expression Localization by Immunofluorescence** — Week 3 Perform multiplex immunofluorescence on brain sections to identify SPP1-expressing cell types. Use primary antibodies: goat anti-SPP1 (R&D AF808, 1:200), rabbit anti-CD31 (Abcam ab28364, 1:300) for endothelial cells, mouse anti-PDGFRβ (Abcam ab32570, 1:250) for pericytes, rat anti-CD68 (Bio-Rad MCA1957, 1:400) for macrophages/microglia, and mouse anti-GFAP (Sigma G3893, 1:500) for astrocytes. Apply sequential staining protocol with appropriate blocking steps using 10% normal donkey serum. Use species-specific Alexa Fluor secondary antibodies (1:500) and DAPI nuclear counterstain. Image using confocal microscopy with 40x and 63x objectives, acquiring z-stacks (0.5μm steps) of perivascular regions identified by CD31+ vessels. **Phase 3: Quantitative Analysis of Cellular SPP1 Expression** — Week 4 Perform systematic quantitative analysis of SPP1 expression in different cell populations. Use stereological sampling to analyze perivascular regions (within 50μm of CD31+ vessels) across hippocampus, cortex, and thalamus. Employ colocalization analysis using ImageJ with Coloc2 plugin to determine Manders' colocalization coefficients between SPP1 and cell-type markers. Quantify SPP1+ cell density (cells/mm²) for each cell type and calculate percentage of each cell type expressing SPP1. Include analysis of SPP1 fluorescence intensity using identical imaging parameters and exposure times across all samples. **Phase 4: Single-cell Resolution Analysis and Validation** — Week 5 Perform high-resolution confocal imaging (100x oil objective) to confirm cellular identity of SPP1-expressing perivascular cells. Use orthogonal views and 3D reconstruction to verify colocalization. Validate findings using RNAscope fluorescent in situ hybridization (Advanced Cell Diagnostics) with probes for mouse Spp1 (Cat# 404611), Pdgfrb (Cat# 407131), and Cd68 (Cat# 316541). Process according to manufacturer's protocol with protease treatment and target retrieval. Quantify RNA signals using automated spot counting with minimum 3 spots per cell for positive scoring. **Phase 5: Western Blot Validation and Statistical Analysis** — Week 6 Extract proteins from microdissected perivascular-enriched tissue using RIPA buffer with protease inhibitors. Perform Western blot using anti-SPP1 antibody (Abcam ab8448, 1:1000) with β-actin normalization (Sigma A2228, 1:5000). Use densitometry to quantify protein levels. Apply two-way ANOVA for statistical analysis with factors of genotype (5xFAD vs control) and brain region, followed by Sidak's multiple comparison test. Use unpaired t-tests for pairwise comparisons of cell-type specific SPP1 expression levels between genotypes.

LINKED HYPOTHESES

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