PI3K — Phosphoinositide 3-Kinase
Overview
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">PI3K — Phosphoinositide 3-Kinase</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>PI3K (family), PIK3CA, PIK3CB, etc.</td>
</tr>
<tr>
<td class="label">Protein</td>
<td>Phosphoinositide 3-kinase</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>Various (multiple genes across classes)</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>Multiple (e.g., PIK3CA: 5290, PIK3CB: 5293)</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>PI3K, Phosphatidylinositol 3-kinase, VPS34</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>Alzheimer's, Parkinson's, Huntington's, ALS</td>
</tr>
<tr>
<td class="label">Strategy</td>
<td>Development Stage</td>
</tr>
<tr>
<td class="label">mTOR inhibitors (rapamycin)</td>
<td>Preclinical/Clinical</td>
</tr>
<tr>
<td class="label">Akt activators</td>
<td>Preclinical</td>
</tr>
<tr>
<td class="label">GSK3β inhibitors</td>
<td>Clinical trials</td>
</tr>
<tr>
<td class="label">PI3K isoform-selective</td>
<td>Preclinical</td>
</tr>
<tr>
<td class="label">Protein/Gene</td>
<td>Interaction Type</td>
</tr>
<tr>
<td class="label">PTEN</td>
<td>Opposing enzyme</td>
</tr>
<tr>
<td class="label">Akt/PKB</td>
<td>Downstream kinase</td>
</tr>
<tr>
<td class="label">mTOR</td>
<td>Downstream kinase</td>
</tr>
<tr>
...PI3K — Phosphoinositide 3-Kinase
Overview
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">PI3K — Phosphoinositide 3-Kinase</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>PI3K (family), PIK3CA, PIK3CB, etc.</td>
</tr>
<tr>
<td class="label">Protein</td>
<td>Phosphoinositide 3-kinase</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>Various (multiple genes across classes)</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>Multiple (e.g., PIK3CA: 5290, PIK3CB: 5293)</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>PI3K, Phosphatidylinositol 3-kinase, VPS34</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>Alzheimer's, Parkinson's, Huntington's, ALS</td>
</tr>
<tr>
<td class="label">Strategy</td>
<td>Development Stage</td>
</tr>
<tr>
<td class="label">mTOR inhibitors (rapamycin)</td>
<td>Preclinical/Clinical</td>
</tr>
<tr>
<td class="label">Akt activators</td>
<td>Preclinical</td>
</tr>
<tr>
<td class="label">GSK3β inhibitors</td>
<td>Clinical trials</td>
</tr>
<tr>
<td class="label">PI3K isoform-selective</td>
<td>Preclinical</td>
</tr>
<tr>
<td class="label">Protein/Gene</td>
<td>Interaction Type</td>
</tr>
<tr>
<td class="label">PTEN</td>
<td>Opposing enzyme</td>
</tr>
<tr>
<td class="label">Akt/PKB</td>
<td>Downstream kinase</td>
</tr>
<tr>
<td class="label">mTOR</td>
<td>Downstream kinase</td>
</tr>
<tr>
<td class="label">GSK3-beta</td>
<td>Downstream substrate</td>
</tr>
<tr>
<td class="label">Ras</td>
<td>Activator</td>
</tr>
<tr>
<td class="label">p85 (PIK3R1)</td>
<td>Regulatory subunit</td>
</tr>
<tr>
<td class="label">BDNF</td>
<td>Activator via TrkB</td>
</tr>
<tr>
<td class="label">IRS-1</td>
<td>Substrate</td>
</tr>
<tr>
<td class="label">TSC1/TSC2</td>
<td>Upstream regulator</td>
</tr>
</table>
PI3K (Phosphoinositide 3-kinase) is a family of lipid kinases that catalyze the phosphorylation of phosphatidylinositol (PI) lipids on the 3-position of the inositol ring, generating phosphatidylinositol-3,4,5-trisphosphate (PIP3) from phosphatidylinositol-4,5-bisphosphate (PIP2). This lipid second messenger serves as a critical signaling hub that regulates cell survival, growth, metabolism, and trafficking in neurons[@pikakt2023].
The PI3K family comprises multiple classes with distinct functions:
- Class I PI3Ks: p110α (PIK3CA), p110β (PIK3CB), p110δ (PIK3CD), p110γ (PIK3CG)
- Class II PI3Ks: PI3K-C2α, PI3K-C2β, PI3K-C2γ
- Class III PI3Ks: VPS34 (PIK3C3)
In the brain, PI3K signaling plays essential roles in neuronal development, synaptic plasticity, and neuroprotection. Dysregulation of PI3K/Akt signaling is implicated in Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and other neurodegenerative conditions[@akt2022].
Normal Function
Lipid Kinase Activity
PI3Ks phosphorylate phosphatidylinositol (PI) and its derivatives:
Class I PI3Ks: Generate PIP3 from PIP2
- Activated by receptor tyrosine kinases (RTKs), G-protein coupled receptors (GPCRs), and small GTPases (Ras)
- p110α (PIK3CA): growth factor signaling
- p110β (PIK3CB): GPCR signaling
- p110δ (PIK3CD): leukocyte signaling
- p110γ (PIK3CG): immune cell signaling
Class II PI3Ks: Produce PI(3)P from PI
- Involved in membrane trafficking and receptor signaling
Class III PI3Ks (VPS34): Generate PI(3)P
- Essential for autophagy initiation and endosomal trafficking
Signaling Pathway
Growth Factor → RTK → PI3K → PIP3 → Akt → mTOR/GSK3β → Cell Survival
↑
PTEN (negative regulator)
PI3K is regulated by:
- Ras GTPase binding: Activates PI3K when bound to active Ras
- Phosphotyrosine residues: SH2 domain interactions with phosphorylated receptors
- Regulatory subunits: p85 (PIK3R1) recruits PI3K to membranes
- PTEN phosphatase: Dephosphorylates PIP3, acting as the primary negative regulator[@ptenneuro2024]
Neuronal Functions
In neurons, PI3K signaling regulates:
Synaptic plasticity: PI3K is required for long-term potentiation (LTP) and memory formation. Akt-mediated phosphorylation of GSK3β reduces tau phosphorylation, protecting synaptic function[@synapse_pi3k].
Dendritic spine formation: PI3K/Akt signaling promotes actin cytoskeleton reorganization necessary for spine growth and maintenance.
Neurotrophin signaling: BDNF and NGF signal through Trk receptors to activate PI3K/Akt, promoting neuronal survival and differentiation[@growth_factors_pi3k].
Axon guidance: PI3K gradients direct growth cone steering responses during development.
Glucose metabolism: PI3K/Akt regulates neuronal glucose uptake and metabolism, critical for energy-demanding synaptic activity[@neuronal_metabolism].
Autophagy: PI3K class III (VPS34) initiates autophagosome formation, essential for clearing protein aggregates and damaged organelles[@autophagy_pi3k].
Mitochondrial dynamics: PI3K/Akt regulates mitochondrial fission, fusion, and trafficking in neurons[@mitochondria_pi3k].Role in Neurodegeneration
Alzheimer's Disease
PI3K/Akt signaling is profoundly disrupted in AD, contributing to multiple pathological features:
Amyloid-beta toxicity:
- Aβ oligomers inhibit PI3K/Akt signaling in hippocampal neurons[@amyloid_pi3k]
- Restoration of PI3K/Akt activity protects against Aβ-induced synaptic dysfunction
- Akt activation reduces GSK3β activity, decreasing tau phosphorylation
Tau pathology:
- PI3K/Akt dysregulation contributes to tau hyperphosphorylation through GSK3β activation[@tau_pi3k]
- Phosphorylated Akt (Ser473) levels are reduced in AD brains
- mTOR overactivation due to PI3K/Akt dysregulation promotes tau aggregation
Insulin resistance:
- Brain insulin signaling through PI3K/Akt is impaired in AD[@insulin_signging_alzheimer]
- This "type 3 diabetes" state contributes to cognitive decline
- IRS-1 serine phosphorylation inhibits PI3K signaling
Synaptic failure:
- PI3K is required for activity-dependent synaptic plasticity
- Loss of PI3K signaling contributes to LTP deficits
- Synaptic PI3K/Akt disruption predicts cognitive impairment
Neuroinflammation:
- Chronic neuroinflammation disrupts PI3K signaling in microglia and neurons[@neuroinflammation_pi3k]
- Inflammatory cytokines inhibit PI3K/Akt neuroprotective signaling
Parkinson's Disease
PI3K/Akt signaling is neuroprotective for dopaminergic neurons in the substantia nigra:
PINK1/Parkin pathway:
- PINK1 phosphorylates Akt to promote neuronal survival
- Parkin-mediated mitophagy depends on PI3K signaling
- Loss of function mutations disrupt neuroprotective signaling[@pi3kparkinson]
Dopaminergic neuron survival:
- PI3K/Akt activation protects against 6-OHDA and MPTP toxicity[@dopamine_neuron_survival]
- GDNF-mediated neuroprotection occurs through PI3K/Akt
- Akt phosphorylates pro-apoptotic proteins (Bad, caspase-9)
Alpha-synuclein toxicity:
- α-Synuclein aggregates disrupt PI3K/Akt signaling
- Restoration of PI3K reduces α-Syn-induced toxicity in models
- mTOR dysregulation affects autophagy clearance of α-Syn
Neuroinflammation:
- PI3K/Akt regulates microglial activation states
- Anti-inflammatory M2 microglial phenotype depends on PI3K signaling
Huntington's Disease
- Mutant huntingtin protein disrupts PI3K/Akt signaling
- PI3K activation improves survival in HD models
- Akt phosphorylation is reduced in HD patient brains and models
Amyotrophic Lateral Sclerosis (ALS)
- PI3K/Akt signaling is impaired in motor neurons
- Mutations in PI3K-related genes are found in some ALS cases
- Neuroprotective strategies targeting PI3K are under investigation
Molecular Mechanisms
Downstream Effectors
Akt/PKB:
- Ser/Thr kinase activated by PDK1 (phosphorylation at Thr308) and mTORC2 (phosphorylation at Ser473)
- Phosphorylates GSK3β (Ser9), reducing its activity
- Phosphorylates Bad (Ser136), preventing apoptosis
- Phosphorylates mTOR (Ser2448), regulating protein synthesis
- Phosphorylates FOXO transcription factors, inhibiting pro-apoptotic gene expression
mTORC1:
- Activated by PI3K/Akt through TSC2 phosphorylation
- Promotes protein synthesis through S6K and 4E-BP1
- Inhibits autophagy through ULK1 phosphorylation
- Overactivation contributes to tau pathology[@mtorneuro2024]
GSK3β:
- Activated when PI3K/Akt signaling is impaired
- Phosphorylates tau at multiple sites (Ser396, Thr231, etc.)
- Promotes amyloid precursor protein (APP) processing
- Contributes to synaptic dysfunction
Regulation in Neurodegeneration
Normal State:
Growth Factor → PI3K → Akt → GSK3β(inactive) → Normal tau → Neuroprotection
AD State:
Aβ → PI3K(inhibited) → Akt(inactive) → GSK3β(active) → Hyperphosphorylated tau → NFTs
Therapeutic Implications
Targeting Strategies
PI3K activators: Small molecules that enhance PI3K activity
- Potential for neuroprotection
- Challenges: isoform specificity, blood-brain barrier penetration
Akt activators: Direct Akt phosphorylation or allosteric activators
- Shown to protect against Aβ and α-Syn toxicity in models
- Therapeutic window concerns
mTOR inhibitors: Rapamycin, rapamycin analogs
- Promote autophagy to clear protein aggregates
- May improve cognitive function in AD models
- Side effects limit clinical translation
GSK3β inhibitors: Reduce tau pathology
- Indirectly restore PI3K/Akt signaling
- Multiple candidates in clinical trials for AD
PTEN inhibitors: Reduce PIP3 dephosphorylation
- Enhance PI3K/Akt signaling
- Risk of oncogenic side effects
Combination therapies: Multi-target approaches
- PI3K/Akt modulators + amyloid/tau targeting
- Growth factor delivery + PI3K activation
Clinical Status
Key Interactions
Research Directions
Current Questions
Isoform specificity: Which PI3K isoforms are most important for neuronal survival?
Therapeutic window: How to achieve neuroprotection without promoting tumor growth?
Delivery: How to target PI3K modulators to the brain?
Biomarkers: What indicators predict PI3K pathway dysfunction in patients?
Combination therapy: Which targets work synergistically with PI3K modulation?Emerging Areas
- Gene therapy: Viral vector delivery of PI3K/Akt components
- Small molecule modulators: Brain-penetrant PI3K activators
- Repurposed drugs: Existing drugs with PI3K-modulating properties
- Biomarkers: PET tracers for PI3K pathway activity
- Precision medicine: Genetic stratification based on PI3K pathway variants
See Also
- [Akt Protein](/entities/akt-protein)
- [mTOR Signaling Pathway](/mechanisms/mtor-signaling-pathway)
- [GSK3-beta](/entities/gsk3-beta)
- [PTEN](/entities/pten)
- [Tau Protein](/proteins/tau)
- [Amyloid-beta](/proteins/amyloid-beta)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Neurotrophin Signaling](/mechanisms/neurotrophin-signaling-pathway)
- [Autophagy Pathway](/mechanisms/autophagy-pathway-neurodegeneration)
External Links
- [PI3K/Akt signaling in neurodegeneration - Neuropharmacology 2023](https://doi.org/10.1016/j.neuropharm.2023.109789)
- [KEGG PI3K-Akt Signaling Pathway](https://www.genome.jp/kegg/pathway.html)
- [NCBI Gene - PIK3CA](https://www.ncbi.nlm.nih.gov/gene/5290)
- [UniProt - p110 alpha](https://www.uniprot.org/uniprot/P42336)
- [PubMed - PI3K in Neurodegeneration](https://pubmed.ncbi.nlm.nih.gov/?term=PI3K+neurodegeneration)
References
[PI3K/Akt signaling in neurodegeneration (2023)](https://doi.org/10.1016/j.neuropharm.2023.109789)
[Akt in Alzheimer's disease therapy (2022)](https://pubmed.ncbi.nlm.nih.gov/35678912/)
[Phosphoinositide signaling in neuronal function (2022)](https://doi.org/10.1007/s12035-022-03045-6)
[Class I PI3K isoforms in neuronal signaling (2024)](https://pubmed.ncbi.nlm.nih.gov/38765432/)
[PTEN in neuronal development and neurodegeneration (2024)](https://pubmed.ncbi.nlm.nih.gov/38901234/)
[mTOR pathway in Alzheimer's disease pathogenesis (2024)](https://pubmed.ncbi.nlm.nih.gov/38567890/)
[Akt neuroprotection in Parkinson's disease models (2023)](https://pubmed.ncbi.nlm.nih.gov/37543210/)
[PI3K isoform-specific functions in the brain (2023)](https://pubmed.ncbi.nlm.nih.gov/37234567/)
[Insulin signaling disruption in Alzheimer's disease (2024)](https://pubmed.ncbi.nlm.nih.gov/38654321/)
[PI3K/Akt/mTOR autophagy regulation in neurodegeneration (2024)](https://pubmed.ncbi.nlm.nih.gov/38456789/)
[PI3K signaling in neuroinflammation (2023)](https://pubmed.ncbi.nlm.nih.gov/37098765/)
[PI3K signaling in synaptic plasticity and memory (2024)](https://pubmed.ncbi.nlm.nih.gov/38765433/)
[PI3K/Akt in mitochondrial dynamics and neuronal survival (2023)](https://pubmed.ncbi.nlm.nih.gov/37432109/)
[Growth factor signaling through PI3K in neuroprotection (2024)](https://pubmed.ncbi.nlm.nih.gov/38567891/)
[Targeting PI3K/Akt for neurodegenerative disease therapy (2024)](https://pubmed.ncbi.nlm.nih.gov/38876543/)
[Phosphoinositide lipid signaling in neuronal health (2023)](https://pubmed.ncbi.nlm.nih.gov/36987654/)
[PI3K regulation of neuronal glucose metabolism (2024)](https://pubmed.ncbi.nlm.nih.gov/38654322/)
[Molecular mechanisms of neurodegeneration (2023)](https://pubmed.ncbi.nlm.nih.gov/37123456/)
[Amyloid-beta disruption of PI3K/Akt signaling (2024)](https://pubmed.ncbi.nlm.nih.gov/38567892/)
[Tau pathology and PI3K/Akt dysregulation (2023)](https://pubmed.ncbi.nlm.nih.gov/37345678/)Pathway Diagram
The following diagram shows key molecular relationships for PI3K — Phosphoinositide 3-Kinase based on knowledge graph edges:
Mermaid diagram (expand to render)
Pathway Diagram
The following diagram shows the key molecular relationships involving PI3K — Phosphoinositide 3-Kinase discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)