Autophagy Clears Senescence Proteins to Slow Heart Valve Aging

Myxomatous mitral valve degeneration (MMVD) is a common age-dependent cardiovascular disease affecting 2–3% of humans globally and up to 70% of older dogs. It involves pathological remodeling of the extracellular matrix driven by senescent myofibroblast-like valve interstitial cells (aVICs), largely under the control of TGF-β1 signaling. Despite its prevalence and severity, no pharmacological treatment currently exists to halt or reverse valve deterioration, making mechanistic insights urgently needed.

Using an established canine model of early-to-mid-stage MMVD — which closely mirrors the pre-fibrotic phase of human disease — the researchers compared autophagy activity between quiescent VICs (qVICs) and senescent activated VICs (aVICs). Senescent aVICs showed markedly reduced LC3-II levels during amino acid starvation, impaired autophagy flux as measured by bafilomycin A1 assays, downregulated expression of key ATG genes (ATG3, ATG5, ATG7), and accumulation of SQSTM1/p62 — all consistent with profound autophagy deficiency. Electron microscopy further revealed structurally immature autophagosomes in aVICs.

Pharmacological induction of autophagy via MTOR inhibitors rapamycin and torin-1 significantly reduced the expression of cyclin-dependent kinase inhibitors CDKN1A/p21 and CDKN2A/p16, attenuated senescence markers (SA-β-galactosidase, BrdU incorporation arrest), and suppressed SASP factors. Conversely, genetic knockout of ATG genes exacerbated senescence and SASP, while re-expression of ATG genes in autophagy-deficient aVICs reversed the senescent phenotype. These results establish a bidirectional, causal relationship between autophagy competence and cellular senescence in this disease context.

Most strikingly, the study identified SQSTM1/p62 as the selective autophagy receptor responsible for directly binding and sequestering both CDKN1A and CDKN2A for lysosomal degradation. Co-immunoprecipitation, proximity ligation assays, and colocalization studies confirmed physical interactions between SQSTM1 and these CDK inhibitors at autophagosomes and lysosomes. This degradation was shown to be independent of the ubiquitin-proteasome system, representing a novel, previously undescribed clearance mechanism for these canonical senescence effectors.

These findings have broad translational relevance. Beyond MMVD, the authors propose that SQSTM1-mediated selective autophagic clearance of p16 and p21 may be relevant to Alzheimer disease, Parkinson disease, and other age-related degenerative disorders where autophagy impairment and cellular senescence converge. MTOR inhibitors like rapamycin are already in clinical use, and this work provides a compelling mechanistic rationale for exploring their application in valve disease management.