Hypothesis\n\nIn aged vascular cells, mitochondrial-derived reactive oxygen species oxidize cardiolipin, promoting its binding to the Rubicon–VPS34 complex and thereby stabilizing Rubicon’s inhibitory activity on autophagosome‑lysosome fusion. This lipid‑dependent mechanism creates a feed‑forward loop: suppressed autophagy raises mitochondrial stress, which further oxidizes cardiolipin and deepens the block. Consequently, autophagic flux remains actively repressed despite upstream signals that would normally induce it, driving VSMC senescence, calcification, and arterial stiffening.\n\n## Mechanistic Rationale\n\nRubicon is known to increase with age and to impede the final step of autophagy[[https://pubmed.ncbi.nlm.nih.gov/30783089/]]. While transcriptional regulation and mTORC1‑mediated TFEB sequestration[[https://www.imrpress.com/journal/FBL/30/9/10.31083/FBL38730]] explain part of the suppression, they do not account for the rapid, lipid‑sensitive modulation observed in ischemia‑reperfusion models where Rubicon activity spikes within minutes[[https://pmc.ncbi.nlm.nih.gov/articles/PMC4313568/]]. Cardiolipin, a mitochondrial inner‑membrane phospholipid, is highly susceptible to peroxidation by mtROS. Oxidized cardiolipin exhibits a conical shape that promotes membrane curvature and can serve as a platform for protein‑protein interactions. We propose that oxidized cardiolipin directly binds the Rubicon C‑terminal domain, increasing its affinity for VPS34 and preventing the conformational change required for autophagosome‑lysosome tethering. This hypothesis links mitochondrial dysfunction to the autophagy‑suppressive axis identified in vascular aging.\n\n## Testable Predictions\n\n1. Biochemical – Immunoprecipitation of Rubicon from aged aortic extracts will show increased cardiolipin co‑precipitation compared with young tissue; lipid‑oxidation assays will reveal a rise in cardiolipin‑hydroperoxide species.\n2. Imaging – Proximity ligation assays in cultured human aortic smooth muscle cells treated with tert‑butyl hydroperoxide will demonstrate enhanced Rubicon–VPS34 puncta that colocalize with mitochondrial markers, an effect attenuated by the cardiolipin‑protecting peptide SS‑31.\n3. Functional – Knock‑down of cardiolipin synthase (CPT1C) or pharmacological scavenging of mtROS (MitoTEMPO) in aged mice will reduce Rubicon‑VPS34 interaction, restore LC3‑II turnover, decrease p62 accumulation, and lower VSMC senescence markers (SA‑β‑gal, p16^INK4a^).\n4. Phenotypic – Mice with endothelium‑specific expression of a Rubicon mutant incapable of binding cardiolipin (point mutation in the predicted lipid‑binding pocket) will exhibit preserved autophagic flux, reduced medial calcification, and improved pulse‑wave velocity despite normal aging.\n5. Rescue – Exogenous addition of non‑oxidizable cardiolipin analogues (e.g., tetralinoleoyl‑cardiolipin) to cultured aged VSMCs will competitively inhibit oxidized cardiolipin binding to Rubicon, thereby rescuing autophagosome‑lysosome fusion without altering mTORC1 activity.\n\n## Potential Interventions\n\nIf validated, targeting the cardiolipin‑Rubicon interface offers a node distinct from mTOR or TFEB pathways. Small‑molecule inhibitors that block the lipid‑binding pocket, mitochondria‑targeted antioxidants, or cardiolipin‑mimetic peptides could re‑engage autophagy in the vasculature, mitigate senescence‑driven calcification, and improve arterial compliance. Such strategies would complement existing approaches like trehalose‑mediated autophagy induction[[https://doi.org/10.1038/ncomms15750]] or young‑factor plasma exchange[[https://doi.org/10.1007/s11357-020-00180-6]] by addressing the upstream lipid signal that locks Rubicon in its inhibitory state.\n\n## Falsifiability\n\nThe hypothesis is falsifiable if, despite robust oxidation of cardiolipin in aged vasculature, Rubicon‑VPS34 interaction does not increase, or if disrupting cardiolipin binding fails to restore autophagic flux and ameliorate vascular phenotypes. Conversely, confirmation of the predicted lipid‑dependent stabilization would redefine autophagy suppression in aging as a membrane‑centric, redox‑sensitive process rather than solely a transcriptional or kinase‑driven event.
