Longevity

The field of longevity and anti-aging has interest in slowing the aging process and completely rejuvenating the human body through engineered negligible senesence. Many different kinds of interventions are considered, including organ transplantation, xenotransplantation, cell therapy, gene therapy, human germline genetic engineering, surgical interventions, pharmaceutical drugs, antibodies, drugs, nutrition, etc. Aging is a disease that should be solved.

Definitions

Anti-Aging: Interventions that prevent or slow the accumulation of damage or the rate of metabolic decline (e.g., caloric restriction or caloric restriction mimetics). These extend healthspan and potentially maximum lifespan but do not reverse the biological clock.

Rejuvenation: Interventions that actively reverse age-related damage, restore youthful gene expression profiles (epigenetic resetting), or replace lost tissue (stem cell therapies), effectively reversing the biological age of the organism.

Genetic interventions

See germline modifications page for substantially more information about proposed germline genetic modifications for longevity, rejuvenation, anti-aging, longer lifespan, etc.

Growth hormone receptor gene disruption in mature‐adult mice improves male insulin sensitivity and extends female lifespan -- Ghr^flox/flox^ mice + tamoxifen-inducible Cre-Lox, activated at 6 months. Robust GH resistance, reduced IGF-1, and increased median and maximal lifespan in females.

Inducible knockdown of pregnancy-associated plasma protein-A gene expression in adult female mice extends life span (2017) -- Floxed Pappa allele (PAPP-A = pregnancy-associated plasma protein-A, an IGF-binding-protein protease), using tamoxifen-inducible Cre recombinase. PAPP-A normally cleaves certain IGF-binding proteins, increasing local IGF bioavailability. Knocking it down reduces IGF signaling; genetically long-lived mice with low GH/IGF signaling (Ames, Snell, GHRKO etc.) show similar phenotypes, and PAPP-A KO has been recognized as a "GH/IGF-pathway" longevity model. (ref)

Intermittent clearance of p21-highly-expressing cells extends lifespan and confers sustained benefits to health and physical function (2024) -- clearance of adult senescent cells using p21Ciphigh as a senescence indicator, and a suicide allele (DTA or similar) under inducible expression.

Adipose eNAMPT overexpression delays aging when activated at a young age.

late-life cardiac-targeted Cisd2 overexpression rejuvenates cardiac structure and function in mice (2021)

Adult somatic gene therapy

See gene therapy for more information about gene therapy techniques.

Aging damage types

Interventions are often categorized by which "hallmark" or damage type they address.

• Genomic Instability: Accumulation of nuclear DNA damage. Future interventions may involve "industrial strength" repair enzymes (e.g., CIRBP from Bowhead whales) or DNA damage repair upregulation (SIRT6).
• Epigenetic Alterations: Loss of histone acetylation and DNA methylation patterns. This is the target of partial reprogramming via Yamanaka factors (OSK).
• Loss of Proteostasis: Accumulation of misfolded proteins (e.g., amyloid, tau) and failure of autophagy/lysosomal degradation.
• Mitochondrial Dysfunction: Decline in ATP production and mitonuclear communication (NAD+/pseudohypoxia).
• Cellular Senescence: Accumulation of "zombie cells" that secrete inflammatory factors (SASP).
• Stem Cell Exhaustion: Depletion of regenerative pools.
• Altered Intercellular Communication: "Inflammaging" and chronic systemic inflammation.
• Extracellular Matrix Stiffening: Accumulation of cross-links (e.g., glucosepane) leading to tissue rigidity (e.g., arteriosclerosis).

Strategies for Engineered Negligible Senescence (SENS)

Proposed by Aubrey de Grey, SENS is a damage-repair paradigm arguing that metabolism is too complex to tweak safely; instead, we should repair the damage metabolism causes. The SENS approach categorizes aging into seven types of damage:

1. Intracellular Junk: (e.g., Lipofuscin). Solution: LysoSENS (microbial enzymes to degrade waste).
2. Extracellular Junk: (e.g., Amyloid). Solution: AmyloSENS (immunotherapy/antibodies to remove aggregates).
3. Extracellular Crosslinks: (e.g., AGEs). Solution: GlycoSENS (enzymes to break crosslinks).
4. Cell Loss: (e.g., Sarcopenia, neurodegeneration). Solution: ReplenSENS (stem cells/tissue engineering).
5. Death-Resistant Cells: (e.g., Senescent cells). Solution: ApoptoSENS (senolytics).
6. Mitochondrial Mutations: (mtDNA deletions). Solution: MitoSENS (Allotopic Expression—moving mitochondrial genes into the safety of the nucleus).
7. Nuclear Epimutations: (Cancer risk). Solution: OncoSENS (WILT—removing telomerase machinery and reseeding stem cells).

Nutritional and Metabolic Interventions

Caloric Restriction (CR) and Mimetics

Calorie restriction is the most robust intervention for lifespan extension in model organisms. It works by downregulating nutrient-sensing pathways (IIS/mTOR) and upregulating maintenance pathways (AMPK/Sirtuins).

• Rapamycin: An mTOR inhibitor that mimics the effects of CR. It is the gold standard for pharmacological lifespan extension in mice.
• Metformin: Activates AMPK and induces a mild energetic stress that upregulates defense mechanisms.
• NAD+ Precursors: (NR, NMN) aimed at restoring levels of NAD+, a critical co-enzyme for Sirtuins that declines with age.

Longevity Vitamins and Triage Theory

Bruce Ames' Triage Theory suggests that the body rations micronutrients (vitamins/minerals) for immediate survival at the expense of long-term repair. Chronic sub-clinical deficiencies lead to "insidious damage" (e.g., DNA breaks).

• PQQ (Pyrroloquinoline quinone): Stimulates mitochondrial biogenesis.
• Ergothioneine: A potent antioxidant transporter.
• Taurine: Decline leads to aging; supplementation extends life in mice.
• Glycine: Not just a structural amino acid, but an epigenetic regulator capable of restoring mitochondrial respiration in aged fibroblasts.

Bioavailability and Feedback Loops

Many potential geroprotectors (e.g., Curcumin, Resveratrol, Quercetin) suffer from poor bioavailability. Furthermore, biological feedback loops often dampen the effect of single-agent interventions.

• The Inflammaging Loop: The NLRP3 inflammasome activates NF-κB, which produces cytokines that further prime the inflammasome.
• The Mitonuclear Loop: Declining NAD+ leads to pseudohypoxia (HIF-1α stabilization), which disrupts nuclear-mitochondrial communication, further reducing NAD+.

Senolytics

Senolytics are a class of therapeutic agents that selectively induce apoptosis in senescent cells, where senescent cells are defined as cells that have permanently exited the cell‑cycle yet remain metabolically active and secrete a pro‑inflammatory cocktail known as the senescence‑associated secretory phenotype (SASP). By clearing these dysfunctional cells, senolytics reduce chronic low‑grade inflammation, restore tissue homeostasis, and improve the function of stem‑cell niches, thereby slowing or mitigating the progression of age‑related physiological decline. Unlike rejuvenation strategies that aim to reverse or "reset" aged tissues, senolytic interventions work within an anti‑aging framework that seeks to preserve existing tissue integrity and extend healthspan by removing a key driver of molecular and cellular damage.

Supplementation

• centrophenoxine
• selegiline (deprenyl)
• epitalon
• metformin
• resveratrol
• rapamycin
• combination of thiamine, nicotinamide, pyridoxamine, piperine, and alpha-lipoic acid designed to reduce appetite and advanced glycation end products
• l-arginine
• cocoa megadosing
• plasma dilution, young blood rejuvenation, blood letting
• fasting mimicking diet, prolon therapy

Theories of aging

Antagonistic pleiotropy theory of aging predicts that alleles conferring developmental fitness become liabilities in post-reproductive life. (ref). The antagonistic pleiotropy theory of aging predicts that alleles conferring developmental fitness become liabilities in post-reproductive life, and the empirical evidence reviewed here strongly supports conditional late-life deactivation of the GH-IGF-1-insulin axis (IGF1R, GHR, GHRH), the mTORC1-S6K1 anabolic cascade, the proliferative transcription factor Myc, the NAD+-depleting ectoenzyme CD38, the pro-inflammatory/pro-fibrotic cytokine IL-11, the senescence-promoting histone acetyltransferase KAT7, the ROS-amplifying adaptor p66Shc, the angiotensin receptor AT1A, the translation-optimizing rRNA methyltransferase NSUN5, adipose-specific insulin receptor signaling, and—with careful dose control—mitochondrial Complex I activity. These pathways share a common pattern: they promote growth, proliferation, and rapid protein synthesis during development when selection pressure is maximal, but their continued activity in aging drives cancer, fibrosis, metabolic dysfunction, senescence accumulation, and oxidative damage. Implementation requires age-gated genetic architectures—whether through inducible degrons, senescence-responsive promoters (e.g., SASP cytokine-activated), telomere-length sensors, or systemic activator administration—that preserve early-life pathway function while enabling late-life suppression, thereby capturing longevity benefits without developmental cost.

The "free radical theory of aging is largely considered defunct or heavily modified. Systemic antioxidant supplementation generally fails to extend life because ROS are signals activating essential repair pathways. Naked Mole Rats, for example, live 30+ years despite having higher levels of oxidative damage than short-lived mice, suggesting that damage tolerance and proteostasis are more critical than oxidative damage prevention.

Disposable soma theory of aging

Damage accumulation theory of aging, including damage to maintenance/repair/resilience mechanisms.

TODO

• adult somatic gene therapy interventions
• drug therapy for longevity, rejuvenation, etc
• cell therapy
• gene therapy
• senolytics
• autologous bone marrow self-donation via cryopreservation
• an overview of major research institutions and ventures pursuing longevity (NewLimit, Altos, Calico Life Sciences, Retro biosciences, Insilico Medicine, Methuselah Foundation, SENS Research Foundation except it was recently renamed and I don't remember the new name, ..)
• process things from the Gerontology Research Group
• mitochondrial uncouplers thesis
• Restricting bioenergetic efficiency enhances longevity and mitochondrial redox capacity in Drosophila melanogaster
• eunuch -- human eunuchs live 14-19 years longer especially when castrated young. castration delays epigenetic aging and feminizes DNA methylation patterns. [Sterilization and contraception increase lifespan across vertebrates.
• michael rose's idea of switching diets during reproductive years
• hormone supplementation therapy to circumvent menopause, andropause
• estrogen hormone supplementation
• turn off IGFR or use monoclonal antibody after adolescence?
• elastin repair and remodeling via RNA delivery PMC8239663

Whole body transplantation

Whole body transplantation or human head transplantation to a human clone seems more likely to work in the short-term with less investment compared to other longevity science. The remaining problem is an aging brain, although the natural limits of brain aging (absent the confounders of other systemic aging in the body) are not presently known. It also varies between people: some people lose a lot of brain mass or experience central neurodegeneration while others do not experience dementia or other brain deterioration with aging.

There are several startup companies pursuing whole body transplantation at this time. I think 2 or 3 companies, like R3. See cloning for more information.

See also "bicephalic head transplantation" where you don't have to murder the clone or figure out how to grow (or maintain) anencephalic human clones.

See also Jean Hebert's work on progressive brain tissue replacement, book "Replacing Aging", and company BE Therapeutics.

http://aging.wiki/w/index.php/Head_transplantation

Directed evolution for extreme longevity

The best way to gain longevity is to have a selective pressure for longevity, such as through long-term selective breeding of human families for extreme longevity. The main problem with this approach is not that it will not work, but that it will take a very long time.

However, some longevity progress (using selection and mutation) can be achieved in human cell culture in the interim. For example, simulate high oxidation damage scenarios and select for resistance to oxidative damage.

Advocacy against "fairweather-only" longevity research

Solving longevity and anti-aging might take an exceptionally long time, both for adult therapy but also for human embryo engineering. It may take 300 more years of molecular biology research. In general we should do this work anyway, even if we (the current living adults that are aging) do not directly benefit from this.

Other

advanced senolytics? Cancer immunomodulation using bispecific aptamers (2022) to be combined with senescent cell aptamers

See also mitochondria longevity for information about mitochondria and aging.

Other sites

https://fightaging.org/

https://anti-agingfirewalls.com/

https://aging.biluhuang.com/

Gerontology Research Group (GRG.org)

Random refs

here are some random longevity references:

• Genetics of Human Longevity: From Genetic Variants to Longevity‑Associated Genes and Pathways
• Role of Genetic Variants in Human Longevity and Healthy Aging
• Species‑Specific Differences in Lifespan Extension From Reduced Nutrient Signaling
• Targeting the Biology of Aging With mTOR Inhibitors
• Functionally Significant IGF‑1 Receptor Mutations in Human Longevity
• Functional IGF‑1 Receptor Mutations Associated With Extended Human Lifespan
• Identification of Rare Functional Coding Variants in IGF‑1 Signaling Linked to Longevity
• Discovery of Rare Longevity‑Associated Gene Variants in Centenarians
• Hutchinson–Gilford Progeria Syndrome: Premature Aging Caused by LMNA Mutations
• Progeria Mutant Lamin A Preferentially Targets Human Vascular Cells
• Genetic Mechanisms and Pathophysiology of Laminopathies and Premature Aging
• Epigenetic Reprogramming Restores Youthful Cellular Information in Aged Tissues
• Restoration of Vision Through Epigenetic Reprogramming and Cellular Rejuvenation
• Yamanaka Factors and Their Role in Cellular Reprogramming and Rejuvenation
• Partial Reprogramming via Gene Therapy Extends Lifespan and Rejuvenates Tissues
• Mechanisms and Risks of Reprogramming‑Induced Cellular Rejuvenation
• Epigenetic Rejuvenation Through Partial Cellular Reprogramming: Promise and Challenges
• Chemical Reprogramming Strategies to Reverse Cellular Aging
• Telomerase Gene Therapy Delays Aging and Extends Lifespan in Adult and Old Mice Without Increasing Cancer
• Telomerase Gene Therapy Extends Longevity and Healthspan in Mice
• Telomerase Activation as a Strategy to Delay Aging and Extend Lifespan
• Enhanced DNA Repair Mechanisms in Long‑Lived Mammalian Species
• DNA Repair and Cancer Resistance Mechanisms in Long‑Lived Species
• Molecular Characteristics and Longevity Roles of IGF and IGF1R Genes
• Lifespan Extension of Mice by Up to 35 % Through Targeted Anti‑Aging Interventions
• Median Lifespan Extension in Mice Through Senescent Cell Clearance
• Suicide Gene Therapy Targeting p16Ink4a‑Positive Senescent Cells
• Systemic Senolysis in Naturally Aged Mice Using a FAST‑PLV Platform
• Senolytic Therapies as a Strategy to Reverse Age‑Related Diseases (replace with appropriate URL if available)

Types of DNA damage

https://en.wikipedia.org/wiki/DNA_damage_theory_of_aging

Oxidative Damage

Reactive Oxygen Species (ROS)-Mediated Damage

Sources: Mitochondrial electron transport chain leakage, enzymatic reactions (xanthine oxidase, NADPH oxidases), Fenton chemistry (Fe²⁺/Cu²⁺), ionizing radiation radiolysis, photosensitizer activation (singlet oxygen ¹O₂)

Chemical mechanisms: Hydrogen atom abstraction from deoxyribose moieties, electrophilic addition to nucleobase π-systems, one-electron oxidation of guanine (lowest ionization potential)

Major lesion classes: - Oxidized purines: 8-oxo-7,8-dihydroguanine (8-oxoG), 8-oxo-7,8-dihydroadenine, formamidopyrimidines (FapyG, FapyA), spiroiminodihydantoin, guanidinohydantoin - Oxidized pyrimidines: Thymine glycol, 5-hydroxy-5-methylhydantoin, 5-hydroxycytosine, 5-hydroxyuracil, 5-hydroxymethyluracil (from ¹O₂-mediated 5-OOH-dT collapse) - Sugar oxidation products: C1′-oxidized abasic sites, C3′-oxidized strand breaks with 3′-phosphoglycolate termini, C4′-oxidized strand breaks with 3′-phospho-α,β-unsaturated aldehyde (PUA) - Clustered damage: Multiple lesions (SSB + oxidized base) within 10 bp helical turn, refractory to base excision repair

Repair: Base excision repair (OGG1, NEIL1/2/3 glycosylases), nucleotide excision repair for bulky oxidation products, 3′-phosphodiesterases (APE1, APE2) for blocked termini

Reactive Nitrogen Species (RNS)-Mediated Damage

Sources: Inducible nitric oxide synthase (iNOS) during inflammation, peroxynitrite (ONOO⁻) from diffusion-controlled •NO + O₂⁻ reaction

Chemical mechanisms: Nitration of nucleobases at C8 position, oxidative deamination, peroxynitrous acid (ONOOH) homolysis generating •OH and •NO₂

Major lesion classes: - Nitrated bases: 8-nitroguanine (depurinates rapidly), 8-nitro-deoxyguanosine - Deamination products: Xanthine (from guanine), hypoxanthine (from adenine) - Secondary oxidation: 8-oxoG formation via ONOO⁻ oxidation

Repair: Base excision repair, spontaneous depurination followed by AP site processing

Reactive Halogen Species-Mediated Damage

Sources: Myeloperoxidase (neutrophils) producing HOCl, eosinophil peroxidase producing HOBr, thyroid peroxidase

Chemical mechanisms: Electrophilic halogenation at C5 of pyrimidines, C8 of purines

Major lesion classes: - Chlorinated bases: 5-chlorocytosine (deaminates to 5-chlorouracil), 8-chloroguanine, 8-chloroadenine - Brominated bases: 5-bromocytosine (deaminates to 5-bromouracil), 8-bromoguanine (adopts syn conformation, mispairs with thymine)

Repair: Thymine DNA glycosylase (TDG) for 5-halouracils, NEIL1 for 8-halogenated purines, MBD4 for 5-bromouracil

Hydrolytic Damage

Spontaneous Depurination/Depyrimidination

Mechanism: N-glycosidic bond hydrolysis, accelerated by elevated temperature, low pH, and base modifications that destabilize the glycosidic linkage

Rates: ~10,000 purines/cell/day (depurination), ~100-500 pyrimidines/cell/day (depyrimidination)

Lesion: Apurinic/apyrimidinic (AP) sites with destabilized deoxyribose prone to β-elimination

Consequences: Replicative polymerase stalling, translesion synthesis recruitment (Pol ζ), mutagenic bypass

Repair: AP endonuclease (APE1) incision, base excision repair

Spontaneous Base Deamination

Mechanism: Hydrolytic removal of exocyclic amino groups

Major conversions: - Cytosine → Uracil (100-500/cell/day) - 5-methylcytosine → Thymine (creates T:G mismatch, major source of CpG→TpG transitions) - Adenine → Hypoxanthine (pairs with cytosine, causes A:T→G:C) - Guanine → Xanthine (pairs ambiguously)

Repair: Uracil-DNA glycosylase (UDG/UNG) for uracil, thymine DNA glycosylase (TDG) for T:G mismatches, AAG/MPG for hypoxanthine

Enzymatic Deamination

Enzymes: Activation-induced cytidine deaminase (AID), APOBEC family cytidine deaminases

Physiological role: Somatic hypermutation, class switch recombination, retroviral restriction

Pathological consequences: Off-target deamination causing kataegis (localized hypermutation clusters), APOBEC signature mutations in cancer

Alkylation Damage

Direct Alkylation by Small Electrophiles

Sources: Endogenous S-adenosylmethionine (SAM) non-enzymatic transfer, environmental alkylating agents (tobacco nitrosamines), chemotherapeutic agents (temozolomide, MMS, EMS, MNNG)

Mechanism: SN1 (carbocation intermediate) and SN2 (direct displacement) nucleophilic substitution at nucleophilic centers

Major lesion classes by site: - N7-guanine (70-80%): 7-methylguanine, 7-ethylguanine—destabilizes glycosidic bond, leads to depurination - N3-adenine (10%): 3-methyladenine—cytotoxic, blocks replication - O6-guanine (5-10%): O6-methylguanine—highly mutagenic, mispairs with thymine causing G:C→A:T transitions - N1-adenine, N3-cytosine: Block Watson-Crick base pairing - Phosphotriester formation: Alkylation of phosphate backbone

Repair: Direct reversal by O6-methylguanine-DNA methyltransferase (MGMT/AGT), AlkB family dioxygenases (ALKBH2/3), base excision repair via AAG/MPG glycosylase

Exocyclic Adducts from Bifunctional Aldehydes

Sources: Lipid peroxidation products (malondialdehyde, 4-hydroxynonenal, 4-oxononenal, acrolein), acetaldehyde (ethanol metabolism), formaldehyde (one-carbon metabolism, histone demethylation), glyoxal/methylglyoxal (glycolysis byproducts), retinaldehyde, ketone bodies

Mechanism: Michael addition and Schiff base formation with exocyclic amino groups, often followed by cyclization

Major lesion classes: - Etheno adducts: 1,N⁶-etheno-dA (εdA), 3,N⁴-etheno-dC (εdC), 1,N²-etheno-dG (εdG)—from vinyl chloride metabolites and lipid peroxidation - Propano adducts: 1,N²-propano-dG from acrolein, malondialdehyde-dG (M1dG) - Hydroxypropano adducts: From 4-HNE and 4-ONE, helix-distorting - Carboxyethyl adducts: N²-carboxyethyl-dG (CEdG) from methylglyoxal - Acetaldehyde adducts: N²-ethyl-dG, N²-ethylidene-dG, interstrand crosslinks

Repair: Base excision repair (NEIL1, AAG for some), nucleotide excision repair for bulky/helix-distorting adducts

Glycation-Derived Adducts (Advanced Glycation End Products)

Sources: Reducing sugars, methylglyoxal, glyoxal from glycolysis and glucose autoxidation

Mechanism: Carbonyl condensation with nucleobase amino groups, Amadori rearrangement, oxidative fragmentation

Lesions: Carboxymethyl-dG, carboxyethyl-dG, carboxyethyl-dA, various crosslinked structures

Repair: NEIL1 glycosylase, nucleotide excision repair

Bulky/Helix-Distorting Adducts

Polycyclic Aromatic Hydrocarbon (PAH) Adducts

Sources: Tobacco smoke, combustion products, grilled/charred food, environmental pollution

Mechanism: Cytochrome P450 (CYP1A1/1B1) epoxidation followed by epoxide hydrolase activation to diol-epoxides; electrophilic attack on purine exocyclic amino groups

Major lesions: (+)-anti-BPDE-N²-dG (benzo[a]pyrene), bay-region diol epoxide adducts of various PAHs

Structural consequence: Major groove protrusion, helix distortion, replication/transcription blockage

Repair: Global genome and transcription-coupled nucleotide excision repair (XPC-RAD23B recognition, TFIIH unwinding, XPF-ERCC1/XPG dual incision)

Aromatic Amine Adducts

Sources: Heterocyclic aromatic amines from cooked meat (IQ, PhIP, MeIQx), occupational exposures (benzidine, 2-naphthylamine)

Mechanism: N-hydroxylation by CYP1A2, O-acetylation by NAT1/2, formation of nitrenium ion intermediates

Major lesions: C8-dG adducts (major), N²-dG adducts (minor)

Repair: Nucleotide excision repair, error-prone translesion synthesis by Pol κ

Mycotoxin and Natural Product Adducts

Sources: Aflatoxin B1 (Aspergillus contamination), aristolochic acid (herbal remedies), pyrrolizidine alkaloids

Mechanism: Metabolic activation to reactive epoxides or nitrenium ions

Major lesions: AFB1-N7-dG (depurinates to AFB1-formamidopyrimidine), aristolactam-dA adducts

Mutagenic signature: Characteristic G→T transversions (aflatoxin), A→T transversions (aristolochic acid)

Repair: Nucleotide excision repair

Dietary and Xenobiotic Electrophile Adducts

Sources: Isothiocyanates (cruciferous vegetables), various plant secondary metabolites, drug metabolites

Mechanism: Direct electrophilic attack or metabolic activation

Lesions: Variable depending on electrophile structure; generally N²-dG, N⁶-dA, or N⁴-dC adducts

Crosslinks

Intrastrand Crosslinks

Sources: Ultraviolet radiation, platinum chemotherapeutics, endogenous aldehydes

UV-induced lesions: - Cyclobutane pyrimidine dimers (CPDs): [2+2] cycloaddition between adjacent pyrimidines (TT>TC>CT>CC), 70-80% of UV lesions - 6-4 Photoproducts: Non-concerted addition with oxetane/azetidine intermediate, 20-30% of UV lesions - Dewar valence isomers: UVA-induced photoisomerization of 6-4PP

Platinum-induced lesions: - 1,2-d(GpG) intrastrand crosslinks (65%): Major cisplatin adduct, 35° helix bend - 1,2-d(ApG) intrastrand crosslinks (25%): Similar geometry - 1,3-d(GpNpG) intrastrand crosslinks: Minor, more flexible

Repair: Nucleotide excision repair (removes 24-32 nt oligomer), translesion synthesis for replication bypass (Pol η accurate for TT-CPD, error-prone for others)

Interstrand Crosslinks (ICLs)

Sources: Nitrogen mustards (cyclophosphamide, mechlorethamine), mitomycin C, psoralens + UVA, platinum agents (minor), endogenous aldehydes (acetaldehyde, formaldehyde)

Mechanism: Bifunctional alkylation or photochemical addition linking complementary strands

Major lesion types: - N7-G to N7-G crosslinks: Nitrogen mustards - Psoralen-thymine-thymine: Furan-side and pyrone-side monoadducts, interstrand crosslink - Aldehyde-mediated: Formaldehyde N²-dG to N²-dG, acetaldehyde crosslinks

Consequence: Absolute block to replication fork progression and transcription bubble opening

Repair: Fanconi anemia (FA) pathway—FANCD2-FANCI monoubiquitination, dual incisions by XPF-ERCC1/SLX4/MUS81-EME1, translesion synthesis, homologous recombination; defects cause Fanconi anemia syndrome

DNA-Protein Crosslinks (DPCs)

Sources: - Enzymatic: Trapped topoisomerase I and II cleavage complexes, methyltransferase intermediates - Non-enzymatic: Formaldehyde, reactive aldehydes, ionizing radiation, chromium compounds - Chromatin-associated: Histone crosslinks via lipid peroxidation products (levuglandin-mediated)

Mechanism: Schiff base formation (aldehydes), tyrosyl-phosphodiester bond (topoisomerases), radical coupling

Repair: - Proteolytic pathway: SPRTN/Spartan metalloprotease (VCP/p97-dependent) degrades protein to peptide - Tyrosyl-DNA phosphodiesterases: TDP1 (TOP1cc), TDP2 (TOP2cc) - Nucleotide excision repair: For small crosslinked peptides after proteolysis

Strand Breaks

Single-Strand Breaks (SSBs)

Sources: Direct ROS attack on deoxyribose, base excision repair intermediates, abortive topoisomerase I activity, ionizing radiation

Terminus chemistry (critical for repair): - Ligatable: 3′-OH and 5′-phosphate - Non-ligatable 3′ termini: 3′-phosphate, 3′-phosphoglycolate (PG), 3′-phospho-α,β-unsaturated aldehyde (PUA), 3′-tyrosyl (TOP1cc) - Non-ligatable 5′ termini: 5′-OH, 5′-aldehyde, 5′-deoxyribose phosphate (dRP)

Processing enzymes: Polynucleotide kinase phosphatase (PNKP), apurinic endonucleases (APE1, APE2), tyrosyl-DNA phosphodiesterase 1 (TDP1), Pol β lyase activity

Repair: Single-strand break repair (SSBR)—XRCC1 scaffold, PARP1 detection

Double-Strand Breaks (DSBs)

Sources: - Direct: Ionizing radiation (clustered damage), restriction endonucleases, RAG1/2 (V(D)J recombination), SPO11 (meiotic recombination) - Indirect: Replication fork collapse at unrepaired lesions, convergent replication forks at ICLs, processing of closely opposed SSBs, TOP2 cleavage complex trapping

Ionizing radiation specifics: - Direct ionization (30-40%): 5-30 eV energy deposition breaking C-O and C-N bonds - Indirect (60-70%): Water radiolysis products (•OH, eaq⁻, H•) clustered within 1-2 nm - Complex damage sites (CDS): DSB + oxidized bases + SSBs within 10-20 bp - High-LET radiation (α-particles): Irreparable CDS with >15 lesions per DSB

Terminus chemistry: Often damaged/blocked termini requiring processing before ligation

Repair pathways: - Non-homologous end joining (NHEJ): Ku70/80 recognition, DNA-PKcs activation, processing (Artemis), ligation (XRCC4-LIG4) - Homologous recombination (HR): MRN-CtIP resection, RPA coating, RAD51 strand invasion, template-directed synthesis - Alternative end joining (alt-EJ/MMEJ): Pol θ-mediated, microhomology-dependent, highly mutagenic

Replication-Associated Damage

Polymerase Errors

Sources: Intrinsic polymerase infidelity, dNTP pool imbalances, damaged template bypass

Error types: - Base-base mismatches: Wrong nucleotide insertion (Pol α error rate ~10⁻⁴, Pol δ/ε ~10⁻⁵ without proofreading) - Insertion/deletion loops (IDLs): Strand slippage in repetitive sequences (microsatellites)

Correction mechanisms: - Proofreading: 3′→5′ exonuclease activity of replicative polymerases - Mismatch repair (MMR): MutSα (MSH2-MSH6) or MutSβ (MSH2-MSH3) recognition, MutLα (MLH1-PMS2) incision, exonuclease resection, resynthesis

Ribonucleotide Incorporation

Source: Cellular rNTP concentrations 30-200× higher than dNTPs; replicative polymerase discrimination imperfect (~1 rNMP per 3,000 nt by Pol ε)

Consequence: Embedded ribonucleotides with 2′-OH sensitize backbone to alkaline hydrolysis, creating SSBs with non-ligatable 3′-phosphate and 5′-OH termini

Repair: RNase H2 incision 5′ to ribonucleotide, strand displacement synthesis, flap cleavage (RER pathway)

Disease association: RNase H2 mutations cause Aicardi-Goutières syndrome (autoimmune/autoinflammatory)

Replication Fork Pathology

Triggers: Unrepaired template lesions, nucleotide depletion, oncogene-induced replication stress, fragile sites, repetitive sequences, transcription-replication conflicts

Structures: - Stalled forks: Polymerase uncoupled from helicase, RPA-coated ssDNA - Reversed forks (chicken-foot): Annealed nascent strands forming Holliday junction-like structure - Collapsed forks: One-ended DSB from fork breakage

Processing: Fork reversal enzymes (SMARCAL1, ZRANB3, HLTF), fork protection (BRCA1/2, RAD51), restart via HR or repriming (PrimPol)

R-Loop-Associated Damage

Source: Co-transcriptional RNA:DNA hybrid formation, especially at G-rich sequences, highly transcribed genes, and sites of transcription-replication collision

Consequences: - Displaced non-template ssDNA susceptible to deamination (AID/APOBEC), oxidation, and nuclease attack - Replication fork stalling and collapse - DSB formation at persistent R-loops

Resolution: RNase H1/H2 degradation of RNA, helicases (Senataxin, Aquarius), topoisomerases

Topoisomerase-Associated Damage

Topoisomerase I-DNA Cleavage Complexes (TOP1cc)

Normal function: Relaxation of torsional stress via transient SSB (3′-phosphotyrosyl covalent intermediate)

Trapping agents: Camptothecin and derivatives (topotecan, irinotecan), endogenous oxidized bases, ribonucleotides, abasic sites

Consequence: Replication fork collision converts TOP1cc to irreversible DSB

Repair: TDP1 hydrolyzes 3′-phosphotyrosyl bond; alternative: endonuclease cleavage (XPF-ERCC1) removes oligonucleotide with attached TOP1

Topoisomerase II-DNA Cleavage Complexes (TOP2cc)

Normal function: Passage of DNA duplex through transient DSB (5′-phosphotyrosyl covalent intermediates on both strands)

Trapping agents: Etoposide, doxorubicin, mitoxantrone, teniposide

Consequence: Persistent DSB with protein-blocked termini

Repair: TDP2 hydrolyzes 5′-phosphotyrosyl bond; alternative: MRN-CtIP endonucleolytic processing; NHEJ or HR for DSB

Epigenetic and Modified Base Damage

TET-Mediated Oxidation Products of 5-Methylcytosine

Pathway: 5-methylcytosine (5mC) → 5-hydroxymethylcytosine (5hmC) → 5-formylcytosine (5fC) → 5-carboxylcytosine (5caC) via TET dioxygenase iterative oxidation

Dual nature: Physiological intermediates in active DNA demethylation; potentially mutagenic if bypassed during replication

Mutagenicity: 5fC read ambiguously by some polymerases (C or T incorporation)

Repair/removal: Thymine DNA glycosylase (TDG) excises 5fC and 5caC, initiating BER and restoration of unmodified cytosine

Aberrant Cytosine Modifications

Sources: AID/APOBEC off-target activity, environmental mutagens, spontaneous deamination of modified bases

Lesions: 5-chlorouracil, 5-bromouracil, 5-hydroxycytosine, 5-hydroxyuracil

Repair: TDG, SMUG1, MBD4 glycosylases (overlapping specificities)

Nucleotide Pool Damage and Incorporation

Oxidized Nucleotide Incorporation

Source: Oxidation of dNTP pool (8-oxo-dGTP, 2-OH-dATP)

Mechanism: Oxidized dNTPs escape polymerase discrimination, incorporate opposite wrong template base

Sanitization: MTH1 (NUDT1) hydrolyzes 8-oxo-dGTP to 8-oxo-dGMP, preventing incorporation; NUDT15, NUDT5 for other damaged nucleotides

Consequence if incorporated: G:C→T:A or A:T→C:G transversions

Base and Nucleoside Analog Incorporation

Sources: Chemotherapeutic agents (5-fluorouracil, gemcitabine, cytarabine, fludarabine), antiviral nucleosides, BrdU (experimental)

Mechanisms: - Chain termination: 3′-modified sugars (araC, acyclovir) block extension - Fraudulent bases: 5-FU mispairs, causes futile BER cycling; BrdU photosensitizes, increases fragility - dNTP pool disruption: Thymidylate synthase inhibition (5-FU, methotrexate) causes dUTP accumulation and incorporation

Transposon and Mobile Element-Induced Damage

Retrotransposon Activity (LINE-1)

Mechanism: LINE-1 ORF2p endonuclease creates nick at target site, ORF2p reverse transcriptase synthesizes cDNA using cleaved 3′-OH as primer (target-primed reverse transcription)

Consequences: - Target site DSB formation - Insertional mutagenesis - Genome instability from ectopic recombination between dispersed elements - Aberrant DNA structures (inversions, deletions, duplications)

Regulation: Silenced by DNA methylation, piRNA pathway, APOBEC3 restriction; reactivated in cancer and aging

Endogenous Retrovirus Reactivation

Source: HERV elements derepressed by hypomethylation (cancer, aging, cellular stress)

Consequences: Similar to LINE-1; additionally may produce viral proteins with immunogenic or oncogenic properties

Viral-Induced DNA Damage

Integrating Virus Damage

Examples: Retroviruses (HIV, HTLV-1), HBV (via integration of double-stranded DNA intermediate)

Mechanism: Integrase-mediated strand transfer creates DSBs flanking provirus, repaired by host NHEJ (often with errors)

Consequences: - Insertional mutagenesis (oncogene activation, tumor suppressor disruption) - Genomic instability from multiple integrations - Persistent DSB signaling

Non-Integrating Virus Damage

Mechanisms: - Viral protein-mediated replication stress (HPV E6/E7 deregulating cell cycle, increasing origin firing) - ROS/RNS induction (EBV LMP1, HCV) - Degradation of DNA damage response proteins (HPV E6-p53, E7-Rb)

Biogenic and Metabolic Adducts (Miscellaneous)

Catecholamine and Neurotransmitter Adducts

Sources: Oxidation of dopamine, norepinephrine, serotonin by various oxidases and transition metals

Mechanism: Quinone formation followed by Michael addition to nucleophilic centers on nucleobases

Lesions: N²-dG and N⁶-dA adducts of catechol quinones

Relevance: Potential contribution to neurodegeneration, repaired by NER and AlkB dioxygenases

Polyamine-Derived Adducts

Sources: Spermine/spermidine oxidation by polyamine oxidases, producing aminoaldehydes

Mechanism: Schiff base formation with dG exocyclic amino group

Lesions: N²-(aminopropyl)-dG, N²-(aminobutyl)-dG

Vitamin and Cofactor-Derived Adducts

Examples: Retinaldehyde-dA adducts, biotin-dA adducts (holocarboxylase synthetase-mediated)

Significance: Generally minor, context-dependent pathological relevance

Physical and Mechanical Damage

Torsional Stress-Induced Damage

Source: Replication fork progression, transcription bubble movement, chromatin remodeling

Consequences: Positive supercoiling ahead of forks/bubbles induces topoisomerase activity; failure to resolve leads to DNA breaks, R-loop formation, and illegitimate recombination

Mechanical Shearing

Source: Mitotic chromosome condensation/segregation errors, nuclear envelope rupture during migration through confined spaces

Consequences: DSBs, chromosome fragmentation, chromothripsis

Summary Table: Major Categories and Representative Lesions

DNA damage type TODO

See also DNA damage repair.

TODO: enrich this with information from GRG.

Types of protein damage

• mistranslation
• misfolding
• unfolding
• degradation
• amino acid methylation errors
• ...

See also

https://fightaging.org/

https://grg.org/

https://www.anti-agingfirewalls.com/

https://diyhpl.us/~bryan/irc/chatgpt/conditional-activation-longevity.txt

https://programmed-aging.org/

https://aging-theories.org/

https://www.senescence.info/ (João Pedro de Magalhães)

https://lifespan.io/

Longevity Escape Velocity Foundation (levf.org)

Methuselah Foundation (mfoundation.org)

longecity.org forums

https://www.lesswrong.com/posts/RcifQCKkRc9XTjxC2/anti-aging-state-of-the-art