Hypothesis

It's known that the selective autophagy hierarchy is controlled by a reversible post‑translational switch on autophagy receptors: phosphorylation favors clearance of damaged mitochondria, whereas O‑GlcNAcylation shifts preference toward ferritin and other iron‑storage proteins. In aging immune cells, declining NAD+ reduces kinase activity and elevates O‑GlcNAc transferase (OGT) flux, corrupting the switch and causing non‑selective bulk autophagy that fuels inflammasome activation.

Mechanistic Basis

• Autophagy receptors such as p62/SQSTM1, NIX/BNIP3L, and FTH1‑binding SARs contain serine/threonine residues that are phosphorylated by ULK1 or AMPK, increasing their LC3‑interacting motif (LIM) affinity for ubiquitinated mitochondria [1][2].
• The same residues are substrates of OGT; O‑GlcNAc addition sterically blocks phosphorylation and reduces affinity for mitochondrial cargo while enhancing binding to ferritin heavy chain via a newly identified O‑GlcNAc‑dependent interface (hypothetical).
• NAD+‑dependent sirtuins (SIRT1/2) deacetylate and activate kinases that counteract OGT; with age, NAD+ drop diminishes this brake, tipping the balance toward O‑GlcNAcylation [3][4].
• Consequently, autophagosomes engulf ferritin instead of mitochondria, releasing free iron that activates the NLRP3 inflammasome and drives SASP production [5][6][7].

Testable Predictions

1. In young immune cells, phosphorylation of p62 at Ser403 exceeds O‑GlcNAcylation at the same site; the ratio reverses in aged cells.
2. Pharmacological inhibition of OGT or supplementation with NAD+ precursors restores the phosphorylation/O‑GlcNAc ratio, rescues mitochondrial selectivity (measured by mt‑Keima reporter), and reduces intracellular iron and IL‑1β release.
3. Mutating the phosphorylation site to alanine mimics the aged O‑GlcNAc‑dominant state and confers iron overload even in young cells.

Experimental Design

• Isolate peritoneal macrophages from 3‑month and 24‑month mice. Treat aged cells with either the OGT inhibitor OSMI‑1 or nicotinamide riboside (NR) for 24 h.
• Western blot with phospho‑specific and O‑GlcNAc‑specific antibodies to quantify the switch at p62 Ser403.
• Ferritinophagy and mitophagy reporters (FTH1‑mCherry‑LC3 and mt‑Keima) measured by flow cytometry.
• Labile iron pool assayed with Calcein‑AM; inflammasome activation assessed by caspase‑1 cleavage and IL‑1β ELISA.
• Expected outcome: OGT inhibition or NR increases phosphorylation, restores mitophagy > ferritinophagy, lowers iron, and cuts IL‑1β by >50 % compared with untreated aged cells.

If these results hold, the hypothesis falsifies the notion that age‑related autophagic decline is merely a loss of flux; instead, it pinpoints a specific signaling switch whose misdirection converts a quality‑control ritual into a source of inflammatory damage.