Hypothesis

Timed feeding (TF) administered during the active phase re‑aligns peripheral circadian clocks in intestinal epithelial cells, boosting CLOCK/BMAL1 transcription, restoring β‑catenin nuclear levels, and consequently inhibiting MMP‑2/9 activity. This dual action prevents proteolytic degradation of ZO‑1 and occludin while simultaneously lowering miR‑191‑5p expression via CB1 up‑regulation, thereby tightening the gut barrier and reducing systemic LPS‑driven inflammaging in aged organisms.

Mechanistic Rationale

• Circadian disruption lowers CLOCK/BMAL1 → less β‑catenin → MMP‑2/9 activation → TJ protein loss.
• Aging adds a CB1‑miR‑191‑5p axis that directly degrades ZO‑1 mRNA and fuels NF‑κB.
• TF synchronizes feeding‑driven insulin/IGF‑1 signals that enhance CLOCK/BMAL1 transcription independently of the light‑entrained SCN, as shown in liver and intestine.
• Elevated β‑catenin sequesters MMP‑2/9 promoters via TCF/LEF sites, reducing their transcription.
• Restored CB1 signaling diminishes miR‑191‑5p maturation, relieving repression of ZO‑1 mRNA and attenuating NF‑κB‑mediated cytokine production.

Together, these mechanisms create a positive feedback loop where a robust circadian rhythm preserves TJ integrity, and a tight barrier limits inflammagenic ligands that would otherwise further destabilize the clock.

Testable Predictions

1. Molecular read‑outs – In aged mice (20‑24 mo) subjected to 12 h TF (food available only during the dark phase) for 4 weeks, intestinal CLOCK and BMAL1 mRNA will increase ≥1.5‑fold vs ad‑libitum fed controls, β‑catenin protein will rise ≥1.4‑fold (Western blot), and MMP‑2/9 activity (gelatin zymography) will drop ≥40 %.
2. Barrier function – FITC‑dextran flux across colonic explants will decrease ≥30 % and ZO‑1/occludin immunofluorescence at the apical junction will show ≥25 % higher membrane localization.
3. Inflammaging markers – Serum LPS‑binding protein, IL‑6, and TNF‑α will fall ≥25 %; fecal calprotectin will decline ≥20 %; and colonic miR‑191‑5p levels will be reduced ≥35 % (qPCR).
4. Rescue specificity – Co‑administration of an MMP‑2/9 inhibitor (e.g., SB‑3CT) with TF will not provide additional barrier improvement beyond TF alone, indicating that TF’s effect operates primarily through MMP suppression. Conversely, CB1 antagonism (rimonabant) will abolish the TF‑mediated increase in ZO‑1 mRNA, confirming the CB1‑miR‑191‑5p arm.

Experimental Design (brief)

• Animals: Male and female C57BL/6 mice, young (3‑4 mo) and aged (20‑24 mo).
• Groups: (1) Young ad‑libitum, (2) Young TF, (3) Aged ad‑libitum, (4) Aged TF, (5) Aged TF + MMP‑2/9 inhibitor, (6) Aged TF + CB1 antagonist.
• Duration: 4 weeks of TF (food access 19:00‑07:00).
• Outcomes: qPCR/Western for clock components, β‑catenin, MMPs; zymography for MMP activity; immunofluorescence for TJ proteins; FITC‑dextran permeability assay; cytokine ELISA; miR‑191‑5q quantification.

Falsifiability

If TF fails to elevate CLOCK/BMAL1 or β‑catenin in aged intestine, or if barrier permeability and inflammaging markers remain unchanged despite molecular rescue, the hypothesis would be refuted. Likewise, if MMP inhibition does not mimic TF’s barrier benefits, or CB1 blockade does not block TF’s effect on ZO‑1, the proposed mechanistic links would be unsupported.

Potential Impact

Demonstrating that a simple feeding schedule can reinstate the circadian‑tight‑junction axis offers a low‑cost, non‑pharmacological strategy to mitigate gut‑derived inflammaging. It positions circadian alignment not merely as a correlative biomarker but as an actionable lever to preserve epithelial homeostasis and delay age‑related systemic decline.