Hypothesis

Aging is accompanied by a progressive loss of robust circadian rhythms, which in turn amplifies the active suppression of autophagy through increased transcriptional activity of the Rubicon gene. We propose that the core circadian repressor BMAL1:CLOCK heterodimer normally binds to E‑box elements in the Rubicon promoter to keep its expression low. With age‑related decline in BMAL1 activity, this repression is lost, leading to elevated Rubicon protein, inhibited VPS34 lipid kinase activity, and a block in autophagosome formation. This mechanistic link explains why interventions that restore circadian strength (e.g., timed feeding, light therapy, or pharmacological activation of REV‑ERB) can rescue autophagy flux even without directly targeting Rubicon.

Rationale

• Rubicon is a known autophagy inhibitor whose expression rises at both mRNA and protein levels in aged tissues across species [1]
• BMAL1 binds to numerous autophagy‑related gene promoters and its loss accelerates aging phenotypes [4]
• Circadian disruption exacerbates mitochondrial oxidative stress, which can further inhibit ATG3/ATG7 via H₂O₂‑mediated oxidation [1]

Testable Predictions

1. ChIP‑seq in young vs. old mouse liver will show reduced BMAL1 occupancy at the Rubicon promoter in aged animals, correlating with higher Rubicon transcript levels.
2. Genetic or pharmacological enhancement of BMAL1 activity in aged mice (e.g., liver‑specific Bmal1 overexpression or treatment with a REV‑ERB agonist) will decrease Rubicon expression, increase LC3‑II turnover, and improve markers of cellular senescence (p16^Ink4a^, SA‑β‑gal) compared with aged controls.
3. Circadian disruption (constant light or jet‑lag model) in young mice will prematurely raise Rubicon levels and suppress autophagy, mimicking the aged phenotype; this effect will be abolished in Rubicon heterozygous knockouts.
4. Parabiosis of a circadian‑disrupted young mouse with an aged wild‑type partner will fail to restore hepatic autophagy flux, indicating that systemic youthful factors cannot overcome cell‑autonomous circadian‑driven Rubicon upregulation.

Experimental Approach

• Use chromatin immunoprecipitation followed by qPCR (ChIP‑qPCR) for BMAL1 at the Rubicon promoter in liver samples from 3‑month and 24‑month mice under entrained conditions.
• Treat aged mice with either a BMAL1 stabilizer (e.g., NAD+ booster) or a REV‑ERB agonist for 4 weeks; measure Rubicon protein by Western blot, autophagic flux via mCherry‑GFP‑LC3 reporter, and senescence markers.
• Implement a chronic jet‑lag regimen (8‑hour advance every 2 days) for 2‑month‑old mice, monitor Rubicon induction and autophagy readouts; rescue experiments with liver‑specific Rubicon shRNA.
• Perform parabiosis surgeries pairing jet‑lagged young mice with aged controls; assess liver autophagy after 2 weeks using tandem fluorescent LC3 and serum metabolites.

Potential Impact

If validated, this hypothesis would reposition circadian health as a upstream regulator of the active autophagy suppression observed in aging. It suggests that strengthening circadian rhythms could be a viable, low‑risk strategy to counteract the deliberate downregulation of cellular cleanup mechanisms, thereby reducing senescent cell burden and extending healthspan.