Hypothesis

Loss of tropoelastin in aging vessels generates bioactive peptide fragments that normally suppress mTORC1 activity and inhibit Rubicon‑mediated blockade of autophagosome‑lysosome fusion. When tropoelastin declines, this inhibitory tone is lost, leading to mTORC1 hyperactivation, cytoplasmic sequestration of TFEB, and Rubicon upregulation—collectively suppressing autophagy. Restoring tropoelastin or its specific peptide domains should reactivate autophagy in vascular smooth muscle cells (VSMCs) by re‑engaging AKT‑dependent feedback inhibition of mTORC1 and reducing Rubicon expression.

Mechanistic Rationale

Extracellular matrix (ECM) proteins can act as signaling ligands through integrin receptors. Prior work shows exogenous tropoelastin delays senescence via AKT activation [3]. AKT phosphorylates and inhibits the TSC complex, which paradoxically can lead to feedback inhibition of mTORC1 through S6K‑mediated IRS‑1 inhibition—a well‑characterized homeostatic loop. We propose that tropoelastin‑derived peptides engage integrin‑αvβ3, triggering a transient AKT pulse that activates mTORC2‑dependent phosphorylation of FOXO3, which in turn transcriptionally represses Rubicon [2]. Simultaneously, AKT‑mediated phosphorylation of PRAS40 relieves its inhibition of mTORC1, but the ensuing S6K‑IRS‑1 negative feedback dampens mTORC1 signaling sufficiently to allow TFEB nuclear translocation [1]. This dual action—reducing Rubicon and easing TFEB sequestration—would restore autophagic flux without requiring rapamycin.

Predictions and Experimental Design

1. Peptide specificity: Synthetic peptides matching the tropoelastin domains that bind integrin‑αvβ3 will reduce phospho‑S6K (a readout of mTORC1 activity) and Rubicon protein levels in senescent human aortic VSMCs, whereas scrambled peptides will not.
2. Autophagy flux: Treatment with active peptides will increase LC3‑II turnover in the presence of bafilomycin A1 and enhance TFEB nuclear localization, measurable by immunofluorescence and subcellular fractionation.
3. Functional readout: Peptide‑treated VSMCs will exhibit lower senescence‑associated β‑galactosidase activity and reduced secretion of proinflammatory cytokines (IL‑6, MCP‑1) compared with vehicle.
4. In vivo relevance: Administration of tropoelastin peptides to aged mice (via osmotic pump) will decrease aortic wall mTORC1 signaling, increase lysosomal cathepsin activity, and attenuate atherosclerotic plaque formation in ApoE‑/‑ mice fed a high‑fat diet.

Experiments will use VSMCs isolated from young (3‑month) and aged (24‑month) mice, as well as cultured human aortic VSMCs induced to senesce by repeated passaging or oxidative stress. Pharmacological controls include rapamycin (mTORC1 inhibitor) and CQD (Rubicon siRNA) to benchmark expected outcomes.

Potential Implications

If validated, this hypothesis reframes autophagy suppression in aging not as a passive breakdown but as an active loss of ECM‑derived inhibitory signals. It suggests that replenishing specific matrikrine peptides could re‑tune nutrient‑sensing pathways to re‑engage lysosomal degradation, offering a tissue‑targeted strategy to mitigate vascular aging and atherosclerosis without chronic mTORC1 inhibition, which often compromises immunity and metabolism.