Hypothesis

Aged microglia lose lysosomal competence, which blocks phagocytic removal of epigenetically silenced neurons; restoring lysosomal function via TFEB activation before OSK-mediated partial reprogramming clears deleterious neurons and lowers oncogenic risk.

Mechanistic Rationale

Microglial phagocytosis depends on lysosomal acidification and cathepsin activity, both decline with age [1]. Simultaneously, aged neurons accumulate DNA damage that triggers SIRT1-dependent epigenetic silencing rather than apoptosis, making them resistant to death signals [2]. When microglia cannot degrade engulfed material, they secrete pro‑inflammatory cytokines and adopt a disease‑associated state that further impairs neurogenic niches [3]. This creates a feed‑forward loop: damaged neurons persist, lysosomal stress in microglia rises, and the tissue becomes permissive to aberrant proliferation when OSK factors are introduced. By pharmacologically boosting TFEB— the master regulator of lysosomal biogenesis— before OSK delivery, we predict microglial phagocytic flux will increase, clearing senescent neurons and reducing the substrate for malignant transformation.

Testable Predictions

1. TFEB overexpression in aged mice will increase lysosomal markers (LAMP1, cathepsin D) in Iba1+ microglia and elevate phagocytic beads uptake ex vivo.
2. Microglial-specific TFEB activation will reduce the number of SIRT1‑high, γH2AX‑low neurons in the cortex and hippocampus without inducing apoptosis.
3. Prior TFEB activation will lower the incidence of hyperplasia or tumor formation following OSK-induced partial reprogramming in the subventricular zone, compared with OSK alone.
4. The protective effect will be abrogated by pharmacological lysosomal inhibition (e.g., chloroquine) or microglia‑specific TFEB knockout.

Experimental Design

• Use Cx3cr1‑CreER;TFEB^fl/fl mice to delete TFEB in microglia and Cx3cr1‑CreER;TFEB^OE mice for overexpression.
• Treat 20‑month‑old mice with either vehicle, TFEB activator (e.g., trehalose or small‑molecule TBE‑31), or chloroquine for two weeks.
• Quantify microglial lysosomal activity (LysoTracker, cathepsin D immunofluorescence) and phagocytic pHrodo‑labeled synaptosome clearance.
• Assess neuronal burden: immunostaining for SIRT1, γH2AX, and NeuN; quantify co‑localized cells.
• Administer OSK via AAV‑Flex‑OSK under a doxycycline‑inducible system to the SVZ for three weeks.
• Monitor proliferation (Ki67), dysplasia (p53, Ki67+/Sox2+ clusters), and tumor formation over six months.
• Include control groups: OSK only, TFEB modulation only, and combined.
• Statistical analysis via two‑way ANOVA with post‑hoc Tukey; n≥6 per group for adequate power.

If TFEB‑mediated lysosomal restoration clears damaged neurons and reduces oncogenic events after OSK, the hypothesis is supported; failure to improve clearance or persistent tumor formation would falsify it.