Hypothesis

Circadian control of mitochondrial dynamics serves as a central executor of the anti‑aging firewall. Disruption of the molecular clock desynchronizes the rhythmic phosphorylation of Drp1 (dynamin‑related protein 1) by casein kinase 1δ/ε (CK1δ/ε), leading to chronic Drp1 activation, excessive mitochondrial fragmentation, impaired mitophagy, and accumulation of damaged mitochondrial DNA. This mtDNA efflux activates the cGAS‑STING pathway, driving a sterile inflammatory response that accelerates inflammaging and shortens lifespan.

Mechanistic Basis

• The core clock component BMAL1:CLOCK drives circadian expression of CK1δ and CK1ε in tissues such as liver, muscle, and brain (1).
• CK1δ/ε phosphorylate Drp1 at Ser616, promoting its GTPase activity and mitochondrial fission. Inverse phosphorylation at Ser637 (by PKA) inhibits fission; this site shows circadian dephosphorylation rhythms.
• When circadian rhythms are flattened (e.g., Bmal1 knockout or chronic jet lag), CK1δ/ε lose their rhythmic expression, causing persistently high Ser616‑phospho‑Drp1 and low Ser637‑phospho‑Drp1.
• Chronic fission skews the mitochondrial network toward fragmented organelles that are poorly sequestered by autophagosomes, reducing mitophagy flux (measured by mt‑Keima or LC3‑colocalization).
• Fragmented mitochondria release oxidized mtDNA into the cytosol, where it binds cGAS, producing cGAMP and activating STING‑TBK1‑IRF3 signaling, culminating in type‑I IFN and NF‑κB‑dependent SASP secretion.
• This inflammatory milieu feeds back to suppress BMAL1 transcription via NF‑κB‑mediated repression, creating a vicious loop that further destabilizes the clock.

Testable Predictions

1. Rhythmic Drp1 phosphorylation: In wild‑type mice, liver lysates collected every 4 h over 24 h will show a significant oscillation in p‑Drp1(S616) (peak at early night) and an anti‑phase oscillation in p‑Drp1(S637). This rhythm will be abolished in Bmal1^−/− mice or in mice subjected to 8‑hour advancing light‑dark cycles every 3 days (chronic jet lag).
2. Mitophagy correlation: The amplitude of p‑Drp1(S616) rhythm will inversely correlate with mitophagy flux (mt‑Keima Red/Green ratio) across Zeitgeber times; loss of rhythm predicts >40 % reduction in basal mitophagy.
3. cGAS‑STING activation: Cytosolic mtDNA levels and phosphorylated STING (p‑STING) will be highest when p‑Drp1(S616) is elevated and will normalize when Drp1 activity is pharmacologically inhibited (e.g., with Mdivi‑1) or when CK1δ/ε is knocked down via siRNA.
4. Lifespan rescue: Chronic treatment with a CK1δ/ε selective inhibitor (or timed administration of Mdivi‑1 to coincide with the predicted peak of Drp1 activity) will restore rhythmic mitophagy, reduce SASP markers (IL‑6, TNF‑α, CXCL10) in aged mice, and extend median lifespan by at least 15 % compared with vehicle‑treated controls.
5. Human translatability: In middle‑aged humans (45‑55 y) wearing Oura Rings, intra‑daily variability (IV) of rest‑activity cycles will negatively correlate with plasma levels of cell‑free mtDNA and positively with circulating SASP cytokines; individuals with IV >0.6 will show a two‑fold increase in cGAS‑STING pathway activation in peripheral monocytes.

Potential Interventions

• Chronotherapy: Deliver mitochondrial fission inhibitors (Mdivi‑1, P110) or CK1δ/ε inhibitors at the circadian phase predicted to maximize Drp1 inhibition (based on individual actigraphy).
• NAD+ boosting: Since NAD+ regulates SIRT1, which can deacetylate and inhibit Drp1, combining NR/NMN supplementation with timed exercise may synergize to reinforce anti‑fission signaling.
• Genetic: Muscle‑specific overexpression of a non‑phosphorylatable Drp1(S616A) mutant should blunt inflammaging and improve healthspan even in a Bmal1 deficient background.

If any of these predictions fail—e.g., Drp1 phosphorylation remains rhythmic despite clock disruption, or inhibiting fission does not lower cGAS‑STING activation—the hypothesis would be falsified, prompting a reassessment of how the circadian anti‑aging firewall interfaces with mitochondrial quality control.