Hypothesis

In aged erythroid progenitors, chronic autophagy activated by niche‑derived inflammation selectively degrades the EPO receptor (EPOR) and associated JAK2/STAT5 signaling proteins, producing functional EPO resistance that contributes to age‑related anemia.

Mechanistic Basis

Aged bone marrow stromal cells exhibit mTORC1 hyperactivation (phospho‑ULK1 Ser757) that suppresses autophagy, raises mitochondrial ROS, and secretes IL‑6/TNF‑α (1, 2, 3). These cytokines engage JAK/STAT and NF‑κB pathways in erythroid progenitors, leading to FoxO3 activation and upregulation of autophagy initiators (ULK1 Ser317/777) despite declining AMPK activity (4). Simultaneously, oxidative stress promotes phosphorylation of EPOR on Tyr residues, creating a degron recognized by selective autophagy receptors such as p62/SQSTM1 and NBR1. Consequently, EPOR‑JAK2 complexes are sequestered into autophagosomes and degraded, attenuating STAT5 phosphorylation and reducing erythroid survival and proliferation signals.

Testable Predictions

1. Aged erythroid progenitors will show increased LC3‑II/LC3‑I ratio and higher colocalization of EPOR with autophagosomes compared with young cells.
2. Pharmacological inhibition of autophagy (chloroquine or bafilomycin A1) or genetic ablation of Atg7 in the erythroid lineage will restore EPOR protein levels, increase p‑STAT5 after EPO stimulation, and improve colony‑forming unit‑erythroid (CFU‑E) output in aged mice.
3. Mice with erythroid‑specific overexpression of a non‑degradable EPOR mutant (resistant to p62 binding) will resist age‑related anemia despite persistent niche inflammation and mTORC1 hyperactivity in stromal cells.

Experimental Approach

• Isolate Ter119⁺CD71⁺ erythroid progenitors from young (3 mo) and aged (24 mo) mice.
• Measure autophagy flux using mCherry‑GFP‑LC3 reporter and Western blot for LC3‑II, p62.
• Assess EPOR stability by cycloheximide chase ± autophagy inhibitors; quantify EPOR‑p62 interaction by co‑immunoprecipitation.
• Determine signaling output: p‑JAK2, p‑STAT5 levels after EPO stimulation (flow cytometry or phospho‑specific Western).
• Functional assay: CFU‑E colonies in methylcellulose with EPO; compare conditions.
• In vivo: Generate Vav‑Cre‑Atg7fl/fl (erythroid‑specific autophagy knockout) and EPOR‑knock‑in mice resistant to autophagy; monitor hemoglobin, reticulocyte count, and spleen histology across lifespan.

If autophagy inhibition or EPOR rescue normalizes EPO signaling and erythropoiesis in aged mice, the hypothesis is supported; failure to restore signaling would falsify the proposed mechanism.