Hypothesis

In aged endometrium, senescent endometrial stromal cells (ESCs) actively suppress autophagy in neighboring decidualizing cells not only via mTORC1 hyperactivation but also through a novel lysosomal sequestration mechanism that traps essential autophagy initiators (e.g., ULK1 complex) in senescent-derived extracellular vesicles, thereby locking downstream flux in a repressed state.

Mechanistic Model

1. Senescent ESC secretome – Besides SASP cytokines, aged ESCs release exosomes enriched in lysosomal-associated membrane protein 1 (LAMP1) and phosphorylated ULK1 (Ser757) 1 2.
2. Vesicular uptake – Decidualizing stromal cells internalize these exosomes via clathrin-mediated endocytosis, delivering active ULK1‑phosphorylating kinases (e.g., mTORC1) directly to the autophagosome initiation site.
3. Lysosomal sequestration – Internalized LAMP1‑positive vesicles fuse with endogenous lysosomes, raising lysosomal pH and impairing cathepsin activity, which blocks autophagosome‑lysosome fusion 3.
4. Feedback loop – Reduced autophagy leads to accumulation of damaged mitochondria, increasing ROS, which further stabilizes the senescent phenotype and amplifies exosome release 4.
5. Hormonal amplification – Estradiol‑ERα signaling in aged endometrium upregulates RAB27A, enhancing exosome release from senescent ESCs, linking endocrine cues to the suppression mechanism 5.

Testable Predictions

• Prediction 1: Isolating exosomes from senescent ESCs of old mice and incubating them with young endometrial stromal cells will decrease LC3‑II turnover and increase p62 accumulation, an effect blocked by GW4869 (exosome release inhibitor).
• Prediction 2: Immunofluorescence will show colocalization of exosomal LAMP1 with lysosomal markers (LAMP2) and reduced Lysotracker signal in recipient cells, indicating lysosomal alkalinization.
• Prediction 3: Genetic knockdown of RAB27A in senescent ESCs will restore autophagy flux and improve decidualization markers (PRL, IGFBP1) in co‑culture assays, even without senolytic treatment.
• Prediction 4: In vivo, administering a lysosomal acidifier (e.g., low‑dose chloroquine analog that reacidifies lysosomes) to aged mice will rescue autophagy flux and improve litter size despite persistent senescent ESC burden.

Potential Implications

If validated, this model shifts the therapeutic focus from merely eliminating senescent cells or inhibiting mTORC1 to blocking pathogenic exosome‑mediated lysosomal dysregulation. Combined senolytic‑exosome blockade or lysosomal reacidification strategies could restore autophagic competence and extend reproductive lifespan.