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categories: ["longevity", "bodies"]categories: ["longevity", "bodies"]tags: ["aging", "stem cells", "regeneration", "clonal hematopoiesis", "niche", "mechanisms"]tags: ["aging", "stem cells", "regeneration", "clonal hematopoiesis", "niche", "mechanisms"]summary: "The age-related decline in the number and regenerative function of adult stem cells across blood, muscle, gut and skin, and the loss of repair capacity that follows."summary: "The age-related decline in the number and regenerative function of adult stem cells across blood, muscle, gut and skin, and the loss of repair capacity that follows."updated: "2026-07-27"updated: "2026-10-29"humanEvidence: "Human sequencing establishes clonal hematopoiesis after 60 and a sharp fall in blood clonal diversity after about 70; the senolytic and reprogramming rejuvenation results are from mice."humanEvidence: "Human sequencing establishes clonal hematopoiesis after 60 and a sharp fall in blood clonal diversity after about 70; the senolytic and reprogramming rejuvenation results are from mice."issues: ["The two conflicting 2018 human hippocampal neurogenesis studies are described without citations."]issues: ["The two conflicting 2018 human hippocampal neurogenesis studies are described without citations."]------lines 42–48 → 42–4828 unchanged lines not shown
### Clonal hematopoiesis### Clonal hematopoiesis The most consequential discovery in this area is clonal hematopoiesis of indeterminate potential, or CHIP: the expansion of a single mutant stem cell clone to a detectable fraction of blood cells in people with no blood disorder. Two 2014 studies identified it in large sequencing datasets, found that it becomes common after age 60, and showed that carriers face elevated risks of haematological malignancy and, unexpectedly, of death from cardiovascular causes.[^jaiswal2014][^genovese2014] The driver mutations cluster in a small set of genes, chiefly *DNMT3A*, *TET2*, *ASXL1*, *JAK2*, *TP53* and *PPM1D* — mostly epigenetic regulators and DNA damage response genes.The most consequential discovery in this area is clonal hematopoiesis of indeterminate potential, or CHIP: the expansion of a single mutant stem cell clone to a detectable fraction of blood cells in people with no blood disorder. Two 2014 studies identified it in large sequencing datasets, found that it becomes common after age 60, and showed that carriers face elevated risks of haematological malignancy and, unexpectedly, of death from cardiovascular causes.[^jaiswal2014][^genovese2014] The driver mutations cluster in a small set of genes, chiefly *DNMT3A*, *TET2*, *ASXL1*, *JAK2*, *TP53* and *PPM1D*, mostly epigenetic regulators and DNA damage response genes. The cardiovascular association is thought to run through inflammation: macrophages descended from a *TET2*-mutant clone secrete more interleukin-1β and interleukin-6, accelerating atherosclerotic plaque development in mice. That connects CHIP directly to [[inflammaging]] and offers one of the few cases where a specific somatic mutation in an aged human is linked to a specific inflammatory mechanism and a specific disease.The cardiovascular association is thought to run through inflammation: macrophages descended from a *TET2*-mutant clone secrete more interleukin-1β and interleukin-6, accelerating atherosclerotic plaque development in mice. That connects CHIP directly to [[inflammaging]] and offers one of the few cases where a specific somatic mutation in an aged human is linked to a specific inflammatory mechanism and a specific disease. lines 53–59 → 53–594 unchanged lines not shown
## Muscle## Muscle Skeletal muscle repair depends on satellite cells, quiescent progenitors under the basal lamina of each fibre. Their number declines modestly with age; their capacity to activate, proliferate and fuse declines more. Some geriatric satellite cells lose quiescence not by activating but by entering [[cellular-senescence|senescence]], a switch associated with de-repression of the p16INK4a locus.[^sousa2014] Sarcopenia — the loss of muscle mass and strength with age — is the visible outcome, and it is the single functional decline most responsive to [[exercise-and-aging|resistance training]].Skeletal muscle repair depends on satellite cells, quiescent progenitors under the basal lamina of each fibre. Their number declines modestly with age; their capacity to activate, proliferate and fuse declines more. Some geriatric satellite cells lose quiescence not by activating but by entering [[cellular-senescence|senescence]], a switch associated with de-repression of the p16INK4a locus.[^sousa2014] Sarcopenia, the loss of muscle mass and strength with age, is the visible outcome, and it is the single functional decline most responsive to [[exercise-and-aging|resistance training]]. ## Gut, skin and pigment## Gut, skin and pigment lines 63–69 → 63–693 unchanged lines not shown
## Nervous system## Nervous system Whether the adult human brain generates new neurons at all remains disputed. Two studies published in 2018 reached opposite conclusions from human hippocampal tissue, one finding that neurogenesis becomes undetectable in adults and the other that it persists into old age; subsequent work has reported abundant immature neurons in healthy adults with a sharp decline in Alzheimer's disease. The disagreement turns substantially on tissue fixation and antibody specificity. Rodent hippocampal neurogenesis clearly declines with age. Whether that finding carries over to humans is precisely what the conflicting human studies leave open.Whether the adult human brain generates new neurons at all remains disputed. Two studies published in 2018 reached opposite conclusions from human hippocampal tissue, one finding that neurogenesis becomes undetectable in adults and the other that it persists into old age; subsequent work has reported abundant immature neurons in healthy adults with a sharp decline in Alzheimer's disease. The disagreement turns substantially on tissue fixation and antibody specificity. Rodent hippocampal neurogenesis clearly declines with age. Whether that carries over to humans is what the conflicting human studies leave open. ## Niche versus cell-intrinsic causes## Niche versus cell-intrinsic causes lines 80–86 → 80–8610 unchanged lines not shown
## Open problems## Open problems The framing question is whether stem cell decline is a cause worth targeting or a readout of everything upstream of it. If aged stem cells fail mainly because their epigenomes have drifted, [[epigenetic-reprogramming|reprogramming]] is the appropriate intervention. If they fail mainly because the niche has become fibrotic and inflamed, the target is the niche. If clonal selection is the dominant process in blood, then the goal is not to restore stem cell function but to prevent the expansion of clones with a fitness advantage — a problem closer to cancer prevention than to regeneration, and one that no current intervention addresses.The framing question is whether stem cell decline is a cause worth targeting or a readout of everything upstream of it. If aged stem cells fail mainly because their epigenomes have drifted, [[epigenetic-reprogramming|reprogramming]] is the appropriate intervention. If they fail mainly because the niche has become fibrotic and inflamed, the target is the niche. If clonal selection is the dominant process in blood, then the goal is not to restore stem cell function but to prevent the expansion of clones with a fitness advantage, a problem closer to cancer prevention than to regeneration, and one that no current intervention addresses. ## See also## See also removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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