Hypothesis

Age‑related decline in autophagy‑lysosomal pathway (ALP) activity reduces the intracellular clearance of nuclear DNA fragments generated during basal turnover or stress‑induced apoptosis. When lysosomal degradation is impaired, these DNA pieces escape autophagic sequestration, are exported to the extracellular space as longer cfDNA fragments, and retain a hypomethylated state that fuels TLR9/RAGE‑mediated inflamm‑aging.

Mechanistic Model

1. Autophagy as a nuclear‑DNA quality‑control route – In addition to cytosolic cargos, ALP can engulf micronuclei, chromatin bridges, or apoptotic DNA‑containing vesicles via LC3‑associated phagocytosis (LAP) and deliver them to lysosomes for degradation【4】【5】.
2. Lysosomal bottleneck in aging – Reduced LAMP2A‑mediated chaperone‑mediated autophagy and lower RAB7A/ATP6V1G1 expression diminish lysosomal acidification and proteolytic capacity【6】. This creates a backlog of autophagosomes that fail to fuse or degrade their cargo.
3. Escape of undegraded DNA – Stalled autophagosomes undergo alternative secretion pathways (exocytosis or extracellular vesicle release), releasing their DNA load as cfDNA. Because lysosomal nucleases (e.g., DNase II) normally trim DNA to <150 bp fragments, incomplete degradation yields a skew toward longer cfDNA pieces (>200 bp).
4. Methylation preservation – Lysosomal degradation also strips protective histone marks and exposes DNA to cytosolic nucleases that favor demethylated regions; when degradation is blocked, the original methylation landscape of the nuclear donor is retained, preserving age‑associated hypomethylation at CpG sites linked to inflamm‑aging.
5. Inflamm‑aging amplification – The longer, hypomethylated cfDNA acts as a potent DAMP, activating TLR9 in myeloid cells and RAGE on endothelium, sustaining NF‑κB signaling and cytokine release【1】【2】.

Testable Predictions

• Prediction 1: In vitro inhibition of autophagy (e.g., Bafilomycin A1, ATG5/7 siRNA) in primary human fibroblasts or hepatocytes will increase the proportion of cfDNA fragments >200 bp and elevate hypomethylation at the 48‑CpG aging clock sites relative to controls.
• Prediction 2: Enhancing lysosomal function (e.g., TFEB overexpression or trehalose treatment) in aged mouse models will shift plasma cfDNA toward shorter fragments (<150 bp) and restore methylation patterns, reducing TLR9‑dependent cytokine production.
• Prediction 3: Individuals with genetic variants causing lysosomal storage disorders (e.g., GBA mutations) will exhibit higher plasma cfDNA concentrations, a longer fragment size distribution, and accelerated epigenetic aging clocks compared with age‑matched controls.

Experimental Design

1. Cell culture: Treat young and senescent human hepatocyte lines with autophagy inhibitors or activators; collect media at 6 h, 12 h, 24 h; quantify cfDNA concentration (Qubit), fragment size (TapeStation), and methylation status (targeted bisulfite sequencing of the 48‑CpG clock).
2. In vivo: Use aged (20‑month) C57BL/6 mice; administer AAV‑TFEB or vehicle; after 4 weeks, collect plasma for cfDNA analytics and measure serum IL‑6, TNF‑α as inflamm‑aging readouts.
3. Human cohort: Recruit patients with clinically confirmed lysosomal disorders and matched controls; draw plasma, perform low‑pass cfDNA sequencing and methylation array; correlate cfDNA features with GrimAge acceleration.

Potential Confounds

• Apoptosis vs. necrosis contributions: Use caspase‑3 activity assays and HMGB1 release to distinguish death modes.
• Cell‑type specificity: Perform cell‑of‑origin deconvolution of cfDNA methylation to confirm hepatocyte/monocyte signatures.

Implications

If validated, this hypothesis reframes autophagy activation not merely as a bulk recycling boost but as a targeted gatekeeper that prevents nuclear DNA from becoming a pro‑inflammatory cfDNA signal. Therapeutic strategies aimed at restoring lysosomal competence—rather than globally inducing autophagy—could normalize cfDNA signatures and attenuate inflamm‑aging.