The prevailing model treats mTOR as a universal dial whose chronic inhibition promotes longevity. This overlooks a critical finding: the dynamic range of mTOR oscillation is tissue-specific and may itself be a biomarker of resilience. Hypothesis: Aging is driven not merely by elevated mTOR activity, but by a collapse in the tissue-specific temporal plasticity of mTOR signaling—its ability to rhythmically switch between anabolic and catabolic states in response to nutrient cues.

Mechanistic Core: Senescent cells exhibit constitutive, starvation-insensitive mTORC1 due to elevated basal autophagy sustaining intracellular amino acid pools [1]. This isn't just elevated signaling; it's a loss of switch function. Chronic rapamycin can further disrupt homeostasis by suppressing mTORC2 and impairing tissue health [2]. The emerging picture is that healthy aging requires not low mTOR, but responsive mTOR.

Novel Extension – The Tissue-Mosaic Model: We propose different tissues maintain distinct optimal mTOR rhythm frequencies (e.g., hepatic rhythms tied to feeding/fasting cycles, neuronal rhythms tied to synaptic activity). Aging represents a phase decoherence of these tissue-specific clocks, leading to systemic dysregulation. Support:

• mTORC1 acts as a key autophagy suppressor [3]; erratic mTOR rhythms would cause mistimed catabolic clearance.
• Aberrant mTOR in aging may be a compensatory response to mitochondrial dysfunction [4], suggesting cells are desperately trying to maintain a rhythm against noise.
• The failure of continuous rapamycin—which imposes an artificial, monotonous state—underscores the need for physiological variability.

Testable Predictions & Falsifiability:

1. Quantifying Rhythm: Using phospho-specific antibodies and serial biopsies in model organisms, we predict aged tissues show reduced amplitude (peak/trough ratio) and increased variability in mTORC1/2 activity cycles compared to young controls, even if time-averaged activity is similar.
2. Rescue Paradigm: Intermittent mTOR inhibition (e.g., every-other-day rapamycin) will extend healthspan more effectively than chronic low-dose treatment in mice, by preserving rhythmic amplitude. Outcome measures: stress resilience (e.g., ischemia-reperfusion injury), not just lifespan.
3. Tissue-Specific Knockouts: Selectively disrupting nutrient-sensing feedback (e.g., TSC complex) in one tissue (e.g., liver) should induce phase decoherence in other tissues (e.g., muscle, brain) via circulating factors, accelerating systemic aging hallmarks. This would test the mosaic's interdependence.
4. Falsification: If aged tissues maintain normal mTOR oscillation amplitude and phase coherence despite functional decline, the hypothesis fails. Similarly, if chronic mtor inhibition without any rhythmic component fully recapitulates the benefits of caloric restriction (which imposes strong rhythms), the rhythm component is non-essential.

Implication: Longevity interventions should aim to restore dynamic range, not just suppress signaling. This shifts the focus from 'how low can you go' to 'how well can you still swing.'

[1] Narita et al., 2011 [2] Jun et al., 2018 [3] Gallagher et al., 2025 [4] Nacarelli & Sell, 2017