Hypothesis

Age‑dependent loss of the m6A writers METTL3 and METTL14 in neurons directly impairs autophagy by destabilizing m6A‑modified transcripts of essential autophagy genes (ATG5, ATG7, BECN1), thereby linking writer decline to a third arm of proteostatic collapse beyond UPR and proteasome dysfunction.

Mechanistic Rationale

• METTL3 and METTL14 are degraded through distinct proteasomal pathways (Parkin‑mediated K48‑ubiquitination of METTL3 at K164; STUB1‑mediated ubiquitination of METTL14 stabilized by METTL3) [1][2].
• In dopaminergic neurons, METTL14 loss reduces m6A on Atp2a3 (SERCA3) mRNA, compromising ER calcium homeostasis and triggering chronic UPR [3]; this establishes a precedent that writer loss can destabilize specific transcripts via loss of m6A.
• Autophagy genes are known to harbor m6A peaks in their 3’UTRs that enhance transcript stability and translation efficiency in other cell types. If METTL3/14 decline similarly erodes m6A on ATG5, ATG7, or BECN1 transcripts in aged neurons, these mRNAs would undergo accelerated decay, diminishing autophagosome formation and lysosomal degradation.
• The resulting autophagy deficit would exacerbate accumulation of damaged proteins and organelles, feeding back to amplify ER stress and proteasome overload, thus creating a vicious cycle of proteostatic failure.
• Cell‑type specificity is plausible: vascular senescence shows METTL14 upregulation [5], suggesting that neuronal contexts uniquely favor writer degradation, perhaps due to high oxidative stress or distinct E3 ligase repertoires.

Testable Predictions

1. In aged mouse or human cortical/hippocampal neurons, METTL3 and METTL14 protein levels will correlate positively with m6A occupancy on ATG5, ATG7, and BECN1 transcripts (measured by MeRIP‑qPCR or m6A‑CLIP).
2. Neuronal knockdown of METTL3 or METTL14 in young adult brains will reduce m6A on these autophagy transcripts, decrease their half‑life (actinomycin D chase), and lower protein levels without affecting transcription rates.
3. Consequently, autophagy flux (LC3‑II turnover with bafilomycin A1, p62/SQSTM1 accumulation) will be significantly impaired in METTL3/14‑deficient aged neurons compared to controls.
4. Rescue experiments—overexpression of catalytically active METTL3/METTL14 or transfection of m6A‑modified ATG5/7/BECN1 mimics—will restore autophagy flux and alleviate p62 accumulation, even when proteasome activity remains compromised.
5. Pharmacological induction of autophagy (e.g., rapamycin or Tat‑Beclin1 peptide) will partially rescue neuronal survival and reduce UPR markers in METTL3/14‑deficient aged neurons, indicating that autophagy loss is a contributory, not merely correlative, factor.

Experimental Design

• Model: Primary cultured neurons from young (2 mo) and aged (18‑24 mo) mice; alternatively, iPSC‑derived cortical neurons treated with senescence‑inducing agents (e.g., low‑dose etoposide) to mimic aging.
• Interventions: siRNA/shRNA knockdown of METTL3 or METTL14; CRISPR‑based activation (CRISPRa) to boost expression; lentiviral delivery of synthetic m6A‑modified ATG5/7/BECN1 3’UTR reporters.
• Readouts: Western blot for METTL3/14, LC3‑I/II, p62, ATG5/7/BECN1; qPCR for transcript stability; MeRIP‑seq for m6A mapping; immunofluorescence for autophagosome/lysosome colocalization; cell viability assays (caspase‑3 cleavage, LDH release).
• Controls: Non‑targeting siRNA, catalytically dead METTL3/14 mutants, and autophagy‑inhibited (chloroquine) conditions to confirm flux dependence.

If the data show that METTL3/14 loss directly diminishes m6A on autophagy transcripts, reduces their stability, and impairs flux—rescuable by writer restoration or m6A‑mimic transcripts—the hypothesis will be supported. Conversely, if autophagy parameters remain unchanged despite writer loss, the hypothesis would be falsified, prompting investigation of alternative mechanisms linking m6A writers to neuronal proteostasis.