PI3K–AKT signaling pathway
The PI3K–AKT pathway is the central survival, growth, and metabolism-control axis downstream of insulin, IGF-1, and most other growth-factor receptors. It acts as the primary transducer from receptor tyrosine kinase (RTK) activation to downstream control of protein synthesis (mtor), apoptosis (apoptosis-pathway), cell-cycle progression, and transcription. In the context of aging, the pathway is most significant as the molecular link between insulin/IGF-1 signaling and mTORC1 activation, and as the kinase that phosphorylates and inactivates FOXO transcription factors — the loss of whose activity appears to shorten lifespan in multiple organisms and is implicated in some of the most-replicated human longevity associations 1.
Naming note: This page covers the PI3K–AKT signaling pathway as a whole. Individual kinase protein pages (
[[pi3k]],[[akt]],[[pdk1]]) are implicit stubs — these wikilinks point to as-yet-unseeded protein pages.
Pathway structure
Class IA PI3K: the lipid kinase generating PIP3
Class IA PI3Ks are heterodimers of a catalytic subunit (p110α/PIK3CA, p110β/PIK3CB, or p110δ/PIK3CD) and a regulatory subunit (p85α/PIK3R1 or p85β/PIK3R2). Upon RTK activation, the regulatory subunit binds phosphotyrosine residues on the receptor or scaffolding proteins, relieving its autoinhibitory effect on p110. Active PI3K phosphorylates PIP2 (PI-4,5-P₂) → PIP3 (PI-3,4,5-P₃) at the inner leaflet of the plasma membrane 2.
Isoform relevance to aging-related research:
- p110α (PIK3CA) — ubiquitous; most-mutated PI3K isoform in cancer (~30% of solid tumors)
- p110β (PIK3CB) — ubiquitous; primary effector downstream of GPCRs and PTEN-null contexts
- p110δ (PIK3CD) — enriched in immune cells and preadipocytes; the SCAP (Survival/Anti-apoptotic pathway) node operative in preadipocyte senolysis (see quercetin and senolytics for the D+Q mechanism detail — the PI3Kδ node is verified per the Zhu et al. preadipocyte data cited there)
PTEN — a lipid phosphatase that directly reverses the PI3K reaction (PIP3 → PIP2) — is the principal negative regulator of this pathway. PTEN is among the most-commonly lost tumor suppressors in human cancer. needs-canonical-id for a dedicated [[pten]] protein page.
AKT recruitment and dual phosphorylation
PIP3 accumulation at the plasma membrane recruits AKT (PKB, three isoforms: AKT1/2/3) via its pleckstrin-homology (PH) domain. Full AKT activation requires two phosphorylation events 3:
| Site | Kinase | Effect |
|---|---|---|
| Thr308 (activation loop) | pdk1 (PDPK1) | Partial activation; required for catalytic activity |
| Ser473 (hydrophobic motif) | [[mtor | mTORC2]] (via rictor) |
Both sites must be phosphorylated for full substrate activity. Acutely, mTORC2 provides the Ser473 phosphorylation; this is why chronic rapamycin (which partially inhibits mTORC2) reduces Ser473-pAKT and accounts for rapamycin’s metabolic side effects 3.
AKT substrates and their aging-relevance
Activated AKT is a serine/threonine kinase with >100 described substrates. The aging-relevant subset:
| Substrate | AKT effect | Downstream consequence | Aging relevance |
|---|---|---|---|
| tsc1-tsc2 (TSC2, Thr1462) | Inhibitory phosphorylation | TSC1/2 GAP activity ↓ → Rheb-GTP↑ → [[mtor | mTORC1]] ON |
| FOXO1/FOXO3/FOXO4 | Inhibitory phosphorylation (3 sites) | FOXO nuclear exclusion → 14-3-3 retention in cytoplasm | Blocks pro-longevity / stress-resistance transcription program |
| GSK3β (Ser9) | Inhibitory phosphorylation | GSK3β OFF → glycogen synthesis ↑, reduced tau phosphorylation | Metabolic and neuroprotective |
| BAD (Ser136) | Inhibitory phosphorylation | BAD sequestered by 14-3-3 → BCL-2/bcl-xl freed → apoptosis ↓ | Pro-survival; relevant to senescent cell persistence |
| mdm2 (Ser166/Ser186) | Activating phosphorylation | MDM2 nuclear entry → ubiquitylation of p53 → p53 degraded | Reduces p53-mediated apoptosis and senescence entry |
| PRAS40 | Inhibitory phosphorylation | Releases PRAS40 from mTORC1 → mTORC1 substrate access ↑ | Reinforces mTOR activation |
Role in aging and longevity
Convergence with insulin/IGF-1 signaling (IIS)
The PI3K–AKT pathway is the molecular execution layer of IIS. All known long-lived IIS-pathway mutant organisms reduce flux through PI3K–AKT 2:
| Organism | Genetic perturbation | Lifespan effect |
|---|---|---|
| C. elegans | daf-2 (IGF1R ortholog) LOF | +100–200% (daf-16/FOXO required) |
| Mus musculus | Igf1r +/− heterozygous (129/Sv) | +26% mean lifespan overall (P<0.02, Cox); +33% females (P<0.001); +15.9% males (NS) 4 |
| Mus musculus | GH receptor knockout (Laron) | ~25–55% lifespan extension (range across studies) needs-replication |
| Human GWAS | FOXO3A GG genotype | OR ~2.75 vs TT (Japanese-American centenarian cohort) 1 |
The mechanistic interpretation is that reduced IIS → reduced PI3K–AKT activity → FOXO transcription factors not excluded from the nucleus → pro-longevity gene expression (antioxidant defense, autophagy, DNA repair, proteostasis genes) is upregulated.
| Dimension | Status |
|---|---|
| Pathway conserved in humans? | yes |
| Phenotype (longevity via IIS reduction) conserved in humans? | partial — GWAS associations exist but intervention data absent |
| Replicated in humans? | no (IIS reduction as intervention); FOXO3 GWAS replicated in multiple cohorts |
FOXO transcription factors: the pro-longevity effectors suppressed by AKT
FOXO3 (and its orthologs DAF-16 in worms, dFOXO in flies) is the best-understood pro-longevity transcription factor regulated by PI3K–AKT. When AKT is active, FOXO3 is phosphorylated at three conserved sites — Thr32, Ser253, and Ser315 (N- to C-terminal order) 3. Site-function distinction (per Brunet 1999 verified): only phospho-Thr32 + phospho-Ser253 create the 14-3-3 binding motif (T32A+S253A double mutant abolishes 14-3-3 binding); Ser315 phosphorylation drives CRM1-mediated nuclear export, not 14-3-3 docking. Together these effect cytoplasmic sequestration. When AKT is low (energy stress, caloric restriction, reduced IIS), FOXO3 re-enters the nucleus and activates:
- Superoxide dismutase (SOD2, SOD3) — antioxidant defense
- Catalase — H₂O₂ clearance
- GADD45 — DNA repair
- LC3 / BNIP3 — autophagy genes
The FOXO3A rs2802292 GG genotype was associated with OR ~2.75 for longevity (age 95+) versus TT in a case-control study of Japanese-American men 1. This is among the most-replicated human longevity genetic associations globally; replication has been reported in European, Chinese, and Italian centenarian cohorts. needs-replication — precise OR estimates vary by cohort and genotyping strategy.
PI3K–AKT hyperactivation and aging: pro-aging anabolic drive
While complete PI3K-AKT loss extends lifespan via FOXO, chronically elevated PI3K-AKT activity (as occurs in aging fat tissue, metabolic syndrome, and cancer) accelerates aging-associated pathology through:
- mTORC1 hyperactivation — sustained AKT→TSC2 inhibition → mTORC1 permanently ON → autophagy suppressed → protein aggregate and damaged organelle accumulation → deregulated-nutrient-sensing hallmark.
- MDM2-mediated p53 suppression — AKT→MDM2 axis promotes p53 degradation, reducing apoptotic clearance of damaged cells and potentially facilitating pre-neoplastic cell survival.
- Senescent cell persistence — BAD phosphorylation + BCL-XL liberation protects senescent cells from apoptosis, contributing to SASP and chronic inflammation (cellular-senescence).
- Oncogenesis — PI3K–AKT is hyperactivated in ~30–50% of human cancers; somatic gain-of-function mutations in PIK3CA and loss-of-function mutations in PTEN are among the most common cancer driver events 5.
The FOXO3 paradox: context-dependence in aging vs cancer
A key tension: the same AKT→FOXO suppression that accelerates aging in normal tissue enables cancer cell survival. Full PI3K-AKT blockade in aging contexts would restore FOXO-mediated longevity gene expression but might also inappropriately trigger apoptosis in normal tissue. The aging research field therefore focuses on partial or context-specific pathway modulation rather than complete inhibition 5. dose-response-unclear — optimal degree of pathway reduction for geroprotection without cancer risk is not established in humans.
Negative regulation and feedback
- PTEN — dephosphorylates PIP3 → PIP2; acts as a tumor suppressor and longevity-permissive gene 2. Loss of heterozygosity of PTEN increases with age in some tissues. needs-replication
- SHIP1/2 — phosphatases converting PIP3 → PI(3,4)P₂; parallel negative regulators
- AKT → S6K1 → IRS-1 (Ser312/Ser616) — mTORC1/S6K1 feedback phosphorylates insulin receptor substrate-1, reducing IRS-1 binding to PI3K; this negative feedback contributes to insulin resistance in metabolic syndrome
- mTORC1 → GRB10 — an additional negative feedback arm on RTK–PI3K coupling
- PP2A, PHLPP1/2 — phosphatases that directly dephosphorylate AKT Thr308 and Ser473 respectively
Pharmacological targeting
Cancer (high-dose inhibition)
| Drug class | Example agents | Target | Clinical status |
|---|---|---|---|
| PI3K inhibitors (pan) | Copanlisib, buparlisib | All class I PI3K | FDA-approved (hematologic cancers); severe hyperglycemia limits solid tumor use |
| PI3Kα-selective | Alpelisib | p110α | FDA-approved (PIK3CA-mutant breast cancer) |
| PI3Kδ-selective | Idelalisib, umbralisib | p110δ | FDA-approved (CLL, follicular lymphoma) |
| AKT inhibitors | Capivasertib, ipatasertib | Pan-AKT | Phase 2–3; capivasertib FDA-approved 2023 (breast cancer) |
| Dual PI3K/mTOR | Gedatolisib | PI3K + mTOR (catalytic) | Phase 3 (ongoing) |
Hyperglycemia caveat: PI3K/AKT inhibition disrupts insulin signaling in liver and muscle → acute hyperglycemia. This is a major safety concern at anti-cancer doses and renders full-dose PI3K inhibitors inappropriate for aging applications 5.
Aging research (partial modulation strategy)
No PI3K–AKT inhibitor is currently in clinical trials specifically for aging (as of 2026). The aging-relevant pharmacological approach is indirect: compounds that reduce upstream IIS (e.g., metformin via AMPK activation reducing hepatic insulin output) or that activate competing longevity pathways (sirtuins, AMPK). The senolytic use of quercetin targets PI3Kδ selectively in preadipocytes — an example of isoform-selective engagement avoiding systemic AKT inhibition.
long-term-unknown — Whether partial, isoform-selective, or intermittent PI3K-AKT inhibition can extend healthspan in humans without metabolic or immune toxicity is an open question. No interventional human trial with aging healthspan as a primary endpoint has been completed.
Cross-pathway connections
- mtor — direct downstream of AKT via TSC2 phosphorylation; mTORC2 is a direct AKT Ser473 kinase, creating bidirectional coupling
- ampk — antagonizes PI3K-AKT indirectly: AMPK activates TSC2 and inhibits Raptor, reducing mTORC1 even when AKT is active; also, insulin resistance (downstream of PI3K–S6K1 feedback) is countered by AMPK-activating interventions
- p53-pathway — AKT→MDM2 promotes p53 degradation; conversely, p53 can suppress PI3K-AKT by inducing PTEN transcription and PTEN-regulatory lncRNAs
- sirtuin — SIRT1 can deacetylate FOXO3, modifying its transcriptional targets independently of AKT-mediated nuclear exclusion; creates a parallel longevity axis partially independent of IIS
- dna-damage-response — DNA damage activates ATM, which can phosphorylate and stabilize PTEN, suppressing PI3K signaling as part of the DNA damage response
Limitations and gaps
- #gap/needs-human-replication — All lifespan-extension evidence from PI3K-AKT pathway reduction is from model organisms (worms, flies, mice). Human FOXO3 GWAS associations are observational and confounded by LD structure.
- #gap/dose-response-unclear — Optimal level of PI3K–AKT attenuation for geroprotection is unknown; too little → no benefit; too much → insulin resistance, immune impairment, apoptosis dysregulation.
- #gap/contradictory-evidence — PI3K-AKT inhibition can both promote (via FOXO target genes) and reduce (via MDM2-p53 suppression removal) tumor suppression, making the net oncogenicity risk of partial inhibition for aging unclear.
- #gap/needs-canonical-id — Dedicated protein pages for
[[pten]],[[akt]],[[pdk1]],[[foxo3]],[[gsk3b]],[[bad]],[[pi3k]]have not been seeded yet. These are implicit stubs. - Long-term PI3K delta isoform role — PI3Kδ’s role outside immune and preadipocyte contexts in aging is understudied. long-term-unknown
Footnotes
Footnotes
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doi:10.1073/pnas.0801030105 · willcox-2008-foxo3-longevity · nested case-control · n=615 total (213 cases survived to ≥95y, mean attained age 97.9y; 402 controls died before age 81, mean attained age 78.5y) · model: Japanese-American men (Honolulu Heart Program / HAAS cohort, Oahu) · Willcox BJ et al. · PNAS 2008 · FOXO3A rs2802292 GG vs TT: OR=2.75 (95% CI 1.51–5.02, P=0.0007); TG vs TT: OR=1.91 (95% CI 1.34–2.72, P=0.0003); overall genotype frequency difference P=0.00009 (Pearson exact chi-sq), Bonferroni-corrected P=0.00135 · archive: locally downloaded ↩ ↩2 ↩3
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doi:10.1038/nrg1879 · engelman-luo-cantley-2006-pi3k-review · review · model: multi-organism (yeast, worm, fly, mouse, human) · Engelman JA, Luo J, Cantley LC · Nature Reviews Genetics 2006 · 3,271 citations · archive: locally downloaded ↩ ↩2 ↩3
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doi:10.1016/j.cell.2017.04.001 · manning-toker-2017-akt-signaling · review · model: human (cellular and biochemical) · Manning BD, Toker A · Cell 2017; 169(3):381–405 · 3,500+ citations; comprehensive network-level AKT review; confirms dual AKT phosphorylation (PDK1/Thr308 + mTORC2/Ser473) and three conserved FOXO3A AKT-phosphorylation sites (Thr32, Ser253, Ser315) · archive: locally downloaded ↩ ↩2 ↩3
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doi:10.1038/nature01298 · holzenberger-2002-igf1r-lifespan · in-vivo · n=65 (cohort 1: 20 Igf1r+/- + 17 WT females; 12 Igf1r+/- + 16 WT males) plus cohorts 2 and 3 for metabolic/oxidative studies · model: Mus musculus (129/Sv background, Igf1r +/−) · Holzenberger M et al. · Nature 2003 (published online Dec 2002, print 9 Jan 2003) · Igf1r+/- mice lived 26% longer overall (P<0.02, Cox); females +33% (756±46 vs 568±49 days, P<0.001 t-test); males +15.9% (679±80 vs 585±69 days, NS) · archive: locally downloaded ↩
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doi:10.1038/s41571-022-00633-1 · vasan-cantley-2022-pi3k-cancer · review · model: human (clinical + preclinical) · Vasan N, Cantley LC · Nature Reviews Clinical Oncology 2022 · 164 citations · covers PI3K inhibitor toxicity (hyperglycemia — alpelisib causes grade ≥3 hyperglycemia in ~37% of patients via on-target insulin-signaling inhibition), feedback mechanisms, and clinical trial lessons · claims verified via PMC11215755 (green OA); full PDF not locally cached ↩ ↩2 ↩3