Hypothesis\n\nCaloric restriction lowers ventricular extracellular matrix (ECM) stiffness, thereby blocking the microglial transition to a senescent disease‑associated microglia (DAM) state.\n\n### Mechanistic rationale\n\n- Aging‑associated accumulation of ECM components such as collagen IV (Col4a1/Col4a2) and hyaluronan (Has2, Has3) increases tissue stiffness in the ventricles and white matter.\n- Elevated stiffness activates microglial mechanosensors Piezo1 and Piezo2, driving NF‑κB signaling and up‑regulating senescence effectors Cdkn1a and Cdkn1c.\n- This mechanotransduction pathway converges on the DAM transcriptional program (C4b, Axl, Trem2) identified by Zhang et al. Zhang et al..\n- Caloric restriction suppresses TGF‑β signaling and induces matrix metalloproteinases (Mmp2, Mmp9), reducing ECM deposition and restoring compliance.\n\n### Testable predictions\n\n1. Spatial correlation – In 24‑month‑old mouse brains, spatial transcriptomics will show ventricular spots with high Col4a1/Has2 expression also exhibit elevated SenMayo scores and DAM markers (C4b, Piezo2) Zhang et al..\n2. Pharmacological mimic – Intraventricular injection of hyaluronidase or collagenase in aged mice will reduce ventricular stiffness, lower Piezo1/2 activity, and decrease Cdkn1a/Cdkn1c expression without altering food intake.\n3. Temporal order – Longitudinal IRISeq at 18, 21, and 24 months will reveal ECM gene upregulation preceding the rise of DAM‑associated transcripts; caloric restriction initiated at 18 months will blunt this ECM rise and prevent later microglial senescence.\n4. Genetic test – Microglia‑specific knockout of Piezo1 will abolish the ECM‑stiffness‑driven increase in senescence markers, making CR redundant for microglial rescue in ventricular regions.\n\n### Falsifiability\n\nIf ventricular ECM composition and stiffness do not correlate with senescence/DAM signatures, or if ECM degradation fails to rescue the microglial phenotype in aged mice, the hypothesis is refuted.\n\n### Implications\n\nLinking biomechanical cues to microglial senescence provides a unified explanation for the regional specificity of CR benefits and offers a mechanistic entry point for therapies targeting the ECM‑microglia axis in neurodegenerative aging.
