Suppression of senescence/SASP (geroconversion), not just autophagy, is the mediator of rapamycin's healthspan benefit

Mechanism-to-outcome gap · confidence 70% · Atlas ID H10

The gap

Rapamycin's anti-ageing benefit is usually credited to boosting autophagy (cellular cleanup), but there is a competing explanation: rapamycin also calms “senescent” cells - old, damaged cells that pump out inflammatory signals. Whether it can do that WITHOUT autophagy is an open question here: this card used to state that it can, but the study behind that claim was never recorded, so the claim has been withdrawn. In humans, a topical version of the drug did reduce a marker of skin-cell senescence, but that is skin, not whole-body ageing. Nobody has directly tested, in one experiment, which of the two explanations actually drives the lifespan benefit.

Technical framing: H4 asks whether autophagy is REQUIRED for the lifespan benefit; this gap proposes a parallel, partly autophagy-INDEPENDENT mediator that is equally untested at the outcome level. Evidence that mTOR gates senescence: DEM2009 rapamycin decelerates cellular senescence (geroconversion from arrest to senescence); BLA2006 framed aging as quasi-programmed mTOR-driven cellular hyperfunction pharmacologically inhibitable by rapamycin; LAB2015 mTOR directly regulates the pro-tumorigenic SASP (via MK2/ZFP36L1 control of secreted-factor mRNAs); CAS2009 mTOR drives Wnt-induced epidermal stem-cell exhaustion; LV2026 links Lamtor5-mTOR to cGAS-driven immunosenescence. WITHDRAWN CLAIM (2026-08-30): this block previously asserted that 'external work shows rapamycin still suppresses SASP in Nrf2-KO fibroblasts WITHOUT activating autophagy'. No study in this corpus supports it, no PMID was recorded, and an uncheckable sentence has no place in a block labelled Established. It has been withdrawn. Whether SASP suppression can occur independently of autophagy is therefore an OPEN question in this Atlas, not a premise - and closing it requires a primary paper entered in the corpus. Human anchor: CHU2019 topical rapamycin REDUCED senescence markers (p16INK4a) in human skin (p=0.008) - the rare direct human PD readout, but on skin, not a systemic aging endpoint. Missing: no study tests whether BLOCKING senescence suppression (or clearing senescent cells independently) reproduces or abolishes rapamycin's mammalian healthspan gain, so autophagy vs geroconversion as the dominant mediator is unresolved.

The hypothesis

Educated guess: it's the slowing of senescent, inflamed cells — not autophagy — that does most of the work. If true, rapamycin should still help mice that can't do autophagy, as long as it can still calm senescent cells; and it should have much less left to offer if those senescent cells are already cleared out by a different drug first.

Technical framing: Rapamycin's healthspan benefit is mediated substantially by suppressing mTOR-driven geroconversion and the SASP - not solely by inducing autophagy. Therefore rapamycin's benefit will persist in autophagy-deficient tissue as long as senescence/SASP suppression is intact, and will be largely OCCLUDED by a senolytic (removing the target senescent-cell burden leaves rapamycin little to suppress).

How it could be tested

Two crossed tests in mice: (i) rapamycin in an inducible autophagy-KO (shared with H4's design) with senescence/SASP burden (p16, IL-6, SA-beta-gal) as the readout - does rapamycin still cut SASP and preserve healthspan without autophagy? (ii) Rapamycin +/- a senolytic (e.g. dasatinib+quercetin): epistasis test - if benefits are non-additive/occluded, senescence suppression is the shared mechanism; if additive, they are parallel. Endpoints: healthspan/frailty index, tissue senescence load, lifespan.

Related studies

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