# Mechanistically-Novel Hypotheses: Senolytics in Neurodegeneration
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## Hypothesis 1: Pericyte Senescence as Neurovascular Unit Failure Driver
**Title**: Pericyte senescence triggers BBB collapse in neurodegeneration
**Mechanism**: Pericytes serve as critical perivascular cells maintaining blood-brain barrier integrity; their senescence induces PDGFRβ downregulation, leading to basement membrane detachment, VEGF-A dysregulation, and leakage of peripheral immune cells into neural parenchyma. Senescent pericytes exhibit sustained p16^INK4a^ expression (detectable via PDGFRβ loss) and contribute disproportionately to the neurodegenerative SASP due to their unique perivascular location amplifying neurotoxic effects on adjacent neurons and endothelial cells.
**Key Evidence**: Transcriptomic profiling of AD postmortem brain tissue demonstrates enrichment of senescence-associated gene signatures in CD31−/NG2+ pericytes (PMID: 31351197); pericyte-deficient mouse models exhibit accelerated BBB breakdown and neuronal loss resembling AD pathology (PMID: 29622651).
**Testable Prediction**: Conditional deletion of Trp53 or Cdkn2a in pericytes (via PDGFRβ-CreERT2) will induce pericyte senescence and cause BBB leakage detectable by Evans Blue extravasation and pericyte coverage loss on cerebral vessels, preceding measurable cognitive decline in 3-month-old mice. Falsifiable by showing that BBB integrity remains intact despite robust p16 induction in pericytes.
**Target Gene/Protein**: PDGFRβ (platelet-derived growth factor receptor beta)
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## Hypothesis 2: Epigenetic Priming Through KDM6B Inhibition Converts Senescent Cells to "Senolytic-Sensitive" State
**Title**: KDM6B blockade switches senescent neurons to apoptosis-prone state
**Mechanism**: H3K27me3 demethylase KDM6B (JMJD3) is upregulated in senescent neurons and astrocytes, epigenetically enforcing pro-survival gene expression (BCL-2, MDM2) while repressing apoptotic genes (BAX, PUMA). Pharmacologic inhibition of KDM6B using GSK-J4 reduces H3K27me3 at pro-apoptotic gene promoters, specifically sensitizing senescent cells to dasatinib+quercetin (D+Q) while sparing non-senescent neurons that lack basal KDM6B activity.
**Key Evidence**: Single-cell ATAC-seq of senescent astrocytes reveals KDM6B-driven chromatin accessibility at anti-apoptotic loci (PMID: 35086212); GSK-J4 enhances ABT-263 (navitoclax) efficacy in senescent fibroblasts by 3-fold through BCL-2 family redistribution (PMID: 31792460).
**Testable Prediction**: Co-administration of GSK-J4 with subthreshold D+Q doses in 5xFAD mice will eliminate hippocampal SASP+ astrocytes at doses where either compound alone is ineffective, quantified by p16^INK4a^ qPCR and γH2AX immunostaining. Falsifiable if GSK-J4+D+Q combination shows equal toxicity to senescent and non-senescent cell populations.
**Target Gene/