Hypothesis

Cleavage of Lamin A by MMP‑3 (or other proteases) releases a C‑terminal peptide that directly modulates the AMPK‑mTOR‑TFEB signaling axis, biasing autophagic flux toward nucleophagy and mitophagy while suppressing ribophagy and ER‑phagy. This peptide acts as a molecular rheostat that translates nuclear envelope damage into a systemic rationing program, prioritizing the recycling of nuclear and mitochondrial components during chronic nutrient or stress limitation.

Mechanistic Basis

1. Peptide release – MMP‑3‑mediated cleavage of pre‑lamin A yields a ~30‑aa C‑terminal fragment (LaminA‑CT) that remains soluble in the nucleoplasm and can diffuse to the cytoplasm.[1]
2. AMPK activation – LaminA‑CT binds to the γ‑subunit of AMPK, promoting allosteric activation and Thr172 phosphorylation independent of AMP/ATP ratios.[2]
3. mTORC1 inhibition – Activated AMPK phosphorylates TSC2 and Raptor, suppressing mTORC1 activity.[3]
4. TFEB nuclear translocation – Reduced mTORC1 phosphorylation of TFEB permits its dephosphorylation by calcineurin, driving lysosomal gene expression.[4]
5. Selective autophagy programming – Concurrently, LaminA‑CT interacts with the Atg11 scaffold, enhancing recruitment of nucleophagy receptors (e.g., Atg39) and mitophagy adapters (e.g., BNIP3) to phagophores, while sterically hindering ER‑phagy (FAM134B) and ribophagy (ATP5MF) receptors.

Together, these steps convert a structural lamina lesion into a signaling cue that re‑programs autophagy substrate selectivity, consistent with the observation that autophagy activation in HGPS correlates with improved nuclear morphology without global increases in bulk cytosolic degradation.

Testable Predictions

• Prediction 1: In HGPS fibroblasts, immunoprecipitation of AMPK will co‑purify the LaminA‑CT peptide; loss of MMP‑3 activity (via siRNA or inhibitor) will reduce this interaction and diminish AMPK Thr172 phosphorylation.
• Prediction 2: Expressing a non‑cleavable Lamin A mutant (L647R) in wild‑type cells will blunt AMPK activation and shift autophagic cargo preference toward ribophagy/ER‑phagy under serum starvation, measurable by quantitative flux assays using mCherry‑GFP‑LC3 reporters fused to nucleus‑, mitochondria‑, ER‑, and ribosome‑targeted tags.
• Prediction 3: Synthetic LaminA‑CT peptide added to culture medium will recapitulate the autophagy‑reprogramming phenotype (increased LC3‑II nucleophagy, decreased p62‑dependent ribophagy) in cells lacking endogenous MMP‑3 activity.
• Prediction 4: In vivo, HGPS mice treated with an MMP‑3‑resistant Lamin A knock‑in will show attenuated TFEB nuclear localization, reduced lysosomal biogenesis (LAMP1 intensity), and worsened metabolic inflexibility (elevated cardiac triglycerides) compared to HGPS controls.

Experimental Approach

• Co‑IP/MS: Pull‑down AMPK from HGPS and control fibroblasts; identify LaminA‑CT peptides by mass spectrometry.
• CRISPR knock‑in: Generate LMNA^L647R (non‑cleavable) and LMNA^C662S (MMP‑3 resistant) lines; assess autophagic selectivity using tandem fluorescent reporters and Seahorse metabolic profiling.
• Peptide rescue: Treat LMNA^−/− cells with cell‑permeable LaminA‑CT; monitor AMPK phosphorylation, TFEB translocation, and organelle‑specific autophagic flux via flow cytometry‑based quenching assays.
• In vivo validation: Cross Lmna^G609G HGPS mice with Mmp3^−/− or lamin A knock‑in strains; evaluate cardiac function, lysosomal markers, and metabolic profiling (NMR spectroscopy) over 6 months.

If these experiments confirm that a lamina‑derived peptide directly tunes the AMPK‑mTOR‑TFEB circuit to favor nuclear and mitochondrial recycling, it will reframe autophagy activation not as a generic cleanup response but as a targeted rationing strategy triggered by nuclear envelope compromise. Conversely, failure to observe peptide‑AMPK interaction or selective cargo shifts would falsify the hypothesis, supporting alternative models where lamina breakdown merely induces indiscriminate autophagy.