Hypothesis

The successful decidualization of endometrial stromal cells depends on a temporal hierarchy of selective autophagy: ER‑phagy precedes mitophagy, which precedes aggrephagy. Disrupting this order—by inducing mitophagy before ER‑phagy stalls—triggers a senescence‑like state that impairs decidualization, providing a mechanistic link between autophagy sequencing errors and reproductive aging.

Rationale

Recent work shows autophagy is essential for decidualization, with ATG5/ATG7 loss blocking the process[1]. Selective pathways are known: ER‑phagy via FAM134B[2], mitophagy via PINK1/Parkin[2], and aggrephagy for protein aggregates[3]. In other remodeling contexts, inflammation‑induced muscle atrophy displays a ordered ER clearance before mitochondrial turnover[5]. Yet no study has mapped when each selective autophagy pathway peaks during endometrial decidualization or how aging reshapes that timeline.

We propose that the cell treats autophagy as a cannibalism ritual where the order of cargo degradation encodes a survival program. Early ER‑phagy reduces unfolded protein load, safeguarding the secretory burst needed for decidual factors. Only after ER stress is mitigated does mitophagy remove damaged mitochondria, preventing ROS‑driven DNA damage. Finally, aggrephagy clears lingering aggregates, completing the remodeling. If mitophagy is activated prematurely—say by stress‑induced PINK1 stabilization before ER‑phagy finishes—the cell loses mitochondrial ATP while still burdened with ER stress, pushing p53‑AMPK‑mTOR toward senescence[4]. This mismatched sequence would explain why global autophagy inhibition and specific receptor knockouts both cause senescence, yet the phenotypes differ.

Testable Predictions

1. Temporal ordering – Using fluorescent reporters (e.g., mCherry‑GFP‑LC3 for general autophagy coupled to organelle‑specific tags: Sec61‑BFP for ER, mito‑Keima for mitochondria, p62‑YFP for aggregates) in primary human endometrial stromal cells undergoing decidualization, we will observe a sequential peak: ER‑phagy signal rises first (0‑12 h), mitophagy follows (12‑24 h), aggrephagy appears last (24‑48 h).

2. Order disruption induces senescence – Premature activation of mitophagy via mito‑targeted Parkin overexpression (or ER‑phagy inhibition with FAM134B siRNA) will shift the mitophagy peak earlier, resulting in:

   • Increased SA‑β‑gal staining and p16^INK4a^ expression[4].
   • Reduced decidual markers (PRL, IGFBP1) and impaired stromal‑cell differentiation.
   • Rescue by restoring ER‑phagy first (overexpressing FAM134B) before inducing mitophagy.

3. Aging alters hierarchy – Stromal cells from older donors will show a blunted or inverted ER‑phagy peak and elevated basal mitophagy, correlating with lower autophagy flux[1] and higher senescence markers. Pharmacological enhancement of ER‑phagy (e.g., with spermidine) should re‑establish the correct order and improve decidualization in aged cells.

Experimental Approach

• Isolate endometrial stromal cells from young (<35 y) and pre‑menopausal (>45 y) donors.
• Transduce with the three reporters; treat with estradiol + medroxyprogesterone acetate to induce decidualization.
• Live‑cell imaging every 2 h for 48 h; quantify reporter colocalization with LC3.
• Apply perturbations: siRNA against FAM134B, overexpression of Parkin mito‑target, or rapamycin to modulate mTOR.
• Measure senescence (SA‑β‑gal, p16), decidualization (PRL ELISA), and autophagy flux (bafilomycin A1 chase).
• Statistical analysis via two‑way ANOVA (age × treatment) with post‑hoc tests.

Falsification

If the reporters show simultaneous activation of all selective autophagy pathways, or if altering the order does not change senescence or decidualization outcomes, the hypothesis is falsified. Likewise, if aged cells retain the youthful temporal order despite functional decline, the proposed link between hierarchy loss and aging fails.

This framework converts the metaphor of autophagy as a cannibalism ritual into a concrete, testable model of how the sequence of self‑digestion governs endometrial fate and reproductive longevity.