Cellular
Senescence
Senescent cells refuse to die and refuse to do their jobs. They secrete a toxic inflammatory cocktail called the SASP — and after age 60, they accumulate fast enough to drive tissue dysfunction across every organ system.
The Mechanism
The zombie cell crisis — and why the SASP is the real problem
Cellular senescence is a tumor suppression mechanism gone wrong at scale. When a cell sustains irreparable DNA damage, excessive oxidative stress, or oncogene activation, p53 and p16INK4a trigger permanent cell cycle arrest — the cell stops dividing, preventing it from passing on mutations.
In youth, immune surveillance (NK cells, macrophages) efficiently clear senescent cells within days. After age 40, immune clearance declines — and senescent cells accumulate exponentially. By age 70, senescent cells constitute 8–10% of cells in some tissues, up from under 1% at 30.
The Senescence-Associated Secretory Phenotype (SASP) is what makes senescent cells dangerous neighbors. They secrete IL-6, IL-1β, TNF-α, MMP-3, MMP-9, and dozens of other pro-inflammatory factors — converting surrounding healthy cells to senescence in a paracrine cascade known as the “bystander effect.”
SASP drives: tissue fibrosis (via TGF-β), cancer microenvironment formation (via MMP-mediated ECM breakdown), adipose inflammation (via PAI-1), and neuroinflammation (via astrocyte senescence and microglial priming). Virtually every age-related disease has senescent cell accumulation as a contributing driver.
Two Therapeutic Strategies
Senolytics
Kill senescent cells by blocking their survival pathways (BCL-2, PI3K/AKT). Goal: reduce total burden. Examples: Fisetin, D+Q, ABT-263.
Senomorphics
Suppress SASP secretion without killing senescent cells. Goal: reduce inflammatory output. Examples: Rapamycin (mTOR), Navitoclax (BCL-2), Metformin (NF-κB).
Monitoring
Biomarkers that track senescent burden
Evidence-Graded Interventions
Senolytics & senomorphics with clinical evidence
Tier A = human RCT evidence. Tier B = at least one human trial + mechanistic data. Tier C = preclinical only.
Fisetin
Tier BFisetin selectively kills senescent cells via pro-apoptotic Bcl-2 family modulation — it downregulates BCL-XL and BCL-W, which senescent cells overexpress to resist apoptosis. A 2019 Mayo Clinic paper (PMID: 31395257) showed reduction in senescent cell burden and circulating SASP markers in older adults.
Quercetin + Dasatinib (D+Q)
Tier AThe first senolytic combination with human RCT evidence. D+Q disrupts the senescent survival pathway by inhibiting SRC kinase (dasatinib) and PI3K/AKT via quercetin. The 2019 Mayo RCT (PMID: 32107278) showed reduced senescent cell burden in diabetic kidney disease patients at 3 days dosing. Dasatinib is prescription-only.
Navitoclax (ABT-263)
Tier CPan-BCL-2 inhibitor with potent senolytic activity in mice. Cleared senescent hematopoietic stem cells and extended median lifespan 7–11% in aged mice. Thrombocytopenia limits human use — included here for mechanistic completeness.
Rapamycin (intermittent)
Tier BmTORC1 inhibition reduces SASP secretion from already-senescent cells (senomorphic effect) without killing them. Also suppresses conversion of normal cells to senescent state by reducing replicative stress. Human longevity data from the PEARL trial (PMID: 36855074) is ongoing.
Build a senolytic protocol.
The Stack Architect shows which compounds target cellular senescence, their evidence tiers, and interactions with everything else in your stack.