TIGAR — TP53-Induced Glycolysis and Apoptosis Regulator
<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">TP53-Induced Glycolysis and Apoptosis Regulator</th></tr> [@tigar2020]
<tr><td><strong>Gene Symbol</strong></td><td>TIGAR</td></tr> [@metabolic2022]
<tr><td><strong>Full Name</strong></td><td>TP53 induced glycolysis and apoptosis regulator</td></tr> [@tigar2021a]
<tr><td><strong>Chromosome</strong></td><td>12p15</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[2063](https://www.ncbi.nlm.nih.gov/gene/2063)</td></tr>
<tr><td><strong>OMIM</strong></td><td>610335</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000148231</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9Y2H7](https://www.uniprot.org/uniprot/Q9Y2H7)</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>[Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis), [Parkinson's Disease](/diseases/parkinsons-disease), Cancer</td></tr>
</table>
</div>
Overview
TIGAR (TP53-Induced Glycolysis and [Apoptosis](/entities/apoptosis) Regulator) is a gene encoding a bifunctional enzyme with fructose-2,6-bisphosphatase activity. Originally discovered as a p53-regulated gene, TIGAR functions as a metabolic regulator that directs glucose flux between glycolysis and the pentose phosphate pathway (PPP). This dual function makes TIGAR a critical regulator of cellular metabolism, redox balance, and cell survival under stress conditions. In the nervous system, TIGAR plays important roles in neuronal metabolism, stress responses, and has been implicated in the pathogenesis of neurodegenerative diseases including [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease-disease), and amyotrophic lateral sclerosis (ALS)[@tigar2021].
Gene Structure and Expression
Genomic Organization
The TIGAR gene spans approximately 22 kb on chromosome 12p13.1 and contains 6 exons[@chen2019]. The gene is transcriptionally activated by [p53](/genes/tp53) through a canonical p53 response element in its promoter region, and also responds to other stress-activated transcription factors including p73, [HIF-1α](/genes/hif1a), and FOXO3[@rojasrivera2020].
Brain Expression Pattern
TIGAR is expressed throughout the brain with particularly high levels in regions vulnerable to neurodegeneration[@liu2020][@yang2021]:
- Hippocampus: High expression in CA1 pyramidal neurons, dentate granule cells — regions critical for memory that are affected early in AD
- Cerebral cortex: Layer 5 pyramidal neurons show prominent TIGAR expression
- Substantia nigra: Dopaminergic neurons express TIGAR, where it may modulate vulnerability to PD pathology
- Spinal cord: Motor neurons express TIGAR at high levels; ALS-linked mutations directly affect these cells
- Cerebellum: Purkinje cells and cerebellar granule neurons express TIGAR
Cellular localization is primarily cytoplasmic and mitochondrial, consistent with its metabolic functions[@nishida2021].
Protein Structure and Biochemistry
Enzyme Mechanism
TIGAR belongs to the F2,6BPase family, which includes the PFKFB (6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase) enzymes. Unlike PFKFB isoforms which have both kinase and phosphatase activities, TIGAR is a dedicated bisphosphatase that catalyzes the hydrolysis of fructose-2,6-bisphosphate to fructose-6-phosphate and inorganic phosphate[@tang2021]:
F2,6BP + H₂O → F6P + Pi
The reaction proceeds through a histidine intermediate in the active site, requiring divalent metal ions (Mg²⁺ or Mn²⁺) for catalysis.
Catalytic Properties
TIGAR's bisphosphatase activity has several distinctive features[@rojasrivera2020]:
- Substrate specificity: TIGAR acts exclusively on F2,6BP; it does not hydrolyze fructose-1,6-bisphosphate or other phosphate esters
- Kinetic parameters: Km approximately 5-10 μM (comparable to PFKFB enzymes), kcat approximately 0.5-1 s⁻¹
- Regulation: TIGAR activity is modulated by pH (optimal pH ~7.5), ionic strength, and post-translational modifications
- Structural features: The active site contains a histidine-aspartate dyad that participates in phosphoester bond hydrolysis
Comparison with PFKFB Enzymes
| Property | TIGAR | PFKFB2 | PFKFB3 |
|----------|-------|--------|--------|
| Kinase activity | None | Present | Present |
| Phosphatase activity | Yes | Yes | Yes |
| F2,6BP affinity (Km) | ~8 μM | ~5 μM | ~10 μM |
| Tissue expression | Ubiquitous, brain-high | Heart, brain | Brain, cancer |
| Regulation | p53, stress | Insulin, hypoxia | HIF-1α, cAMP |
The F2,6BP Rheostat
F2,6BP is one of the most potent allosteric activators of 6-phosphofructo-1-kinase (PFK-1), the rate-limiting enzyme of glycolysis. By hydrolyzing F2,6BP, TIGAR reduces PFK-1 activity and redirects glucose metabolism[@chen2019][@nishida2021]:
Mermaid diagram (expand to render)
Pentose Phosphate Pathway Shunt
When TIGAR is active, glucose-6-phosphate entering the PPP generates[@nishida2021][@zhang2018]:
NADPH for antioxidant defense: The oxidative branch of the PPP produces 2 NADPH molecules per glucose-6-phosphate, supporting glutathione and thioredoxin reduction
Ribose-5-phosphate for nucleotide synthesis: The non-oxidative branch provides ribose-5-P for ATP, NAD+, and DNA/RNA synthesis
Metabolic intermediates: Sedoheptulose-7-phosphate and erythrose-4-phosphate for biosynthesisInteraction with PFKFB3
TIGAR functionally competes with PFKFB3 (a HIF-1α-inducible enzyme with strong kinase activity) for F2,6BP metabolism. In neurons, PFKFB3 is expressed and promotes glycolysis under hypoxic or inflammatory conditions. TIGAR activation counteracts this, redirecting metabolism toward PPP[@park2019].
Normal Physiological Functions
TIGAR functions as a metabolic stress sensor by coupling p53 activation to metabolic reprogramming[@chen2019][@wang2016]:
- Basal conditions: Low TIGAR expression permits high glycolytic flux to meet the high ATP demands of neurons
- Stress conditions: DNA damage, ROS, or metabolic stress activates p53, inducing TIGAR expression
- Metabolic shift: TIGAR activation reduces F2,6BP levels, decreasing glycolysis and increasing PPP flux
- NADPH generation: PPP-derived NADPH supports the glutathione system, protecting neurons from oxidative damage
Neuronal Survival Under Oxidative Stress
Neurons are particularly vulnerable to oxidative stress due to their high metabolic rate, abundant iron content, and high proportion of polyunsaturated fatty acids in membrane lipids. TIGAR provides neuroprotection through[@wang2016][@zhang2018]:
- NADPH-supported glutathione system: Increased PPP flux generates NADPH that keeps glutathione in its reduced state (GSH)
- Mitochondrial protection: NADPH supports thioredoxin reductase, protecting mitochondrial proteins from oxidative damage
- Reduced ROS accumulation: Enhanced antioxidant capacity limits lipid peroxidation and protein oxidation
- Prevention of mitochondrial apoptosis: Reduced oxidative damage to mitochondria prevents cytochrome c release
Autophagy and Protein Quality Control
TIGAR modulates [autophagy](/mechanisms/autophagy-lysosome-dysfunction) through multiple mechanisms[@xie2022][@li2017]:
- AMPK activation: TIGAR-mediated reduction in glycolytic flux increases AMP/ATP ratio, activating AMPK
- mTOR inhibition: AMPK activation inhibits mTORC1, releasing its suppression of autophagy initiation
- Mitophagy enhancement: AMPK activation also stimulates PINK1/Parkin-mediated mitophagy
- Selective autophagy: TIGAR supports the clearance of damaged proteins and organelles through autophagy
DNA Damage Response
By redirecting glucose toward PPP, TIGAR supports nucleotide synthesis for DNA repair[@karim2021]:
- Ribonucleotide reduction: PPP provides ribose-5-P for dNTP synthesis, supporting DNA replication and repair
- NADPH for DNA repair enzymes: Several DNA repair enzymes require NADPH as a cofactor
- p53-mediated repair: TIGAR is induced by p53, linking DNA damage to the metabolic resources needed for repair
Disease Associations
Amyotrophic Lateral Sclerosis (ALS)
TIGAR mutations were identified in ALS patients through whole-exome sequencing, establishing a direct link between TIGAR dysfunction and motor neuron disease[@gersin2020]:
| TIGAR Variant | Effect | ALS Context |
|---------------|--------|-------------|
| R192H | ~50% reduced phosphatase activity | Sporadic ALS |
| R234W | Impaired stress-induced activation | Familial ALS |
| S228P | Partial loss of function | Sporadic ALS |
| N156D | Reduced PPP flux | ALS with frontotemporal dementia |
Pathogenic mechanisms in ALS[@gersin2020][@xie2022]:
Impaired metabolic stress response: Motor neurons require robust PPP activity to handle oxidative stress from high metabolic activity. TIGAR mutations compromise this response
Defective mitophagy: Reduced TIGAR function impairs clearance of damaged mitochondria through the PINK1/Parkin pathway
Increased oxidative damage: Inadequate NADPH production leads to accumulation of ROS and damage to motor neurons
Energy crisis: The combination of reduced glycolysis and impaired PPP flux leads to ATP depletion in motor neurons
Dysregulated autophagy: Impaired AMPK signaling reduces autophagy, allowing accumulation of misfolded proteins (SOD1, TDP-43)Alzheimer's Disease
TIGAR is dysregulated in AD brains and contributes to disease pathogenesis through several mechanisms[@liu2020][@yang2021][@benjamin2021]:
- Expression changes: TIGAR expression is reduced in AD hippocampus and prefrontal cortex compared to age-matched controls
- Amyloid-beta effects: Aβ toxicity activates p53, attempting to induce TIGAR, but this compensatory response is insufficient in AD
- Tau pathology crosstalk: Metabolic dysregulation affects tau kinase/phosphatase balance, influencing NFT formation
- Neurogenesis impairment: TIGAR regulates metabolic support for hippocampal neural stem cells; its dysfunction contributes to reduced neurogenesis in AD
- Therapeutic potential: Enhancing TIGAR activity may protect neurons from Aβ toxicity through improved PPP flux and NADPH generation
Parkinson's Disease
TIGAR plays important roles in dopaminergic neuron survival and PD pathogenesis[@kim2022][@ma2019][@kim2020]:
- Alpha-synuclein interaction: TIGAR haploinsufficiency exacerbates α-synuclein toxicity; α-synuclein overexpression reciprocally downregulates TIGAR
- Dopaminergic neuron vulnerability: The substantia nigra has relatively low PPP enzyme expression, making these neurons particularly dependent on TIGAR for stress protection
- Mitochondrial complex I inhibition: MPTP and other PD-inducing toxins inhibit mitochondrial complex I, generating ROS that requires PPP-generated NADPH for detoxification
- PINK1/Parkin pathway connection: TIGAR interacts with mitophagy regulators; impaired mitophagy in PD is worsened by TIGAR deficiency
- NAD+ metabolism: TIGAR affects NAD+ consumption through PARP activation during DNA repair, linking to broader NAD+ homeostasis in PD[@sun2023]
Cancer
While protective in neurons, dysregulated TIGAR in cancer creates pro-survival advantages[@rojasrivera2020]:
- Warburg effect support: Reduced TIGAR in some cancers shunts glucose toward glycolysis and away from PPP
- Apoptosis resistance: Low TIGAR reduces PPP-mediated NADPH and protects cancer cells from chemotherapeutic oxidative stress
- Therapeutic targeting paradox: TIGAR inhibitors are being developed for cancer, but these would be harmful to neurons — selective targeting is needed
Therapeutic Implications
TIGAR as a Neuroprotective Target
Enhancing TIGAR function represents a promising approach for neurodegenerative disease[@yang2021][@wenger2023]:
| Strategy | Mechanism | Status |
|----------|-----------|--------|
| Direct small molecule activators | Increase TIGAR bisphosphatase activity | Preclinical |
| Indirect activation via p53 | MDM2 inhibitors stabilize p53, inducing TIGAR | Phase I/II (oncology) |
| PPP pathway enhancement | Other PPP enzymes synergize with TIGAR | Preclinical |
| NAD+ precursors | Support NADPH-dependent repair alongside TIGAR | Clinical |
| Antioxidant mimetics | Reduce oxidative stress load, complementing TIGAR | Clinical |
| AAV-mediated TIGAR overexpression | Deliver TIGAR gene to vulnerable neurons | Preclinical |
Small Molecule Activators
Several classes of compounds have been identified that enhance TIGAR function[@wenger2023]:
- F2,6BP analogues: Structural mimetics of F2,6BP that bind TIGAR and stabilize its active conformation
- Allosteric activators: Small molecules that bind outside the active site and enhance catalytic activity
- p53 stabilizers: Nutlin-3a and other MDM2 inhibitors increase p53 levels, inducing endogenous TIGAR expression
Delivery Challenges
TIGAR-targeted therapies face several CNS delivery challenges[@wenger2023]:
- Blood-brain barrier: Most small molecules have limited BBB penetration
- Neuronal targeting: Ensuring therapeutic effect reaches neurons vs. glia
- Therapeutic window: Over-activation of TIGAR could excessively reduce glycolysis, impairing neuronal energy metabolism
- APOE4 interaction: APOE4 carriers may have altered lipid metabolism that affects TIGAR-targeted approaches
Biomarker Potential
TIGAR activity markers may have clinical utility[@yeung2022][@sun2023]:
- CSF metabolites: F2,6BP levels in cerebrospinal fluid may reflect neuronal TIGAR activity
- NAD+/NADH ratio: TIGAR activation shifts the cellular redox balance, detectable in blood
- PPP flux markers: Radiolabeled glucose analogs can measure PPP activity in brain imaging
- Genetic testing: TIGAR variant screening could identify at-risk individuals
Animal Models
Tigar Knockout Mice
Complete knockout of Tigar in mice is embryonic lethal due to severe metabolic defects. However, heterozygous knockout mice are viable and show[@rojasrivera2020][@yang2021]:
- Increased oxidative stress: Reduced PPP flux and lower NADPH/GSH levels
- Impaired stress response: Reduced ability to handle oxidative or genotoxic stress
- Accelerated neurodegeneration: Crossed with AD models (APP/PS1), Tigar haploinsufficiency increases amyloid pathology
- Motor neuron vulnerability: In ALS models (SOD1-G93A), Tigar haploinsufficiency accelerates disease onset
- Cognitive deficits: Reduced performance on hippocampal-dependent memory tasks
Conditional Knockout
Neuron-specific Tigar deletion in adult mice reveals[@li2017][@ma2019]:
- Progressive neurodegeneration: Age-dependent neuronal loss in cortex and hippocampus
- Mitochondrial dysfunction: Reduced mitochondrial spare capacity and increased susceptibility to toxins
- Autophagy impairment: Accumulation of p62 and ubiquitinated proteins
- Behavioral deficits: Reduced motor coordination and spatial memory impairment
Transgenic Overexpression
Neuronal Tigar overexpression provides neuroprotection[@yang2021]:
- Reduced oxidative damage: Increased GSH/GSSG ratio and reduced protein carbonylation
- Improved mitochondrial function: Enhanced mitochondrial membrane potential and respiration
- Neuroprotection in AD models: Crossed with APP/PS1 mice, Tigar OE reduces amyloid burden and improves cognition
- Neuroprotection in PD models: Crossed with MPTP-treated mice, Tigar OE protects dopaminergic neurons
Signaling Pathways and Interactions
Upstream Regulators
TIGAR expression and activity are controlled by several signaling pathways[@rojasrivera2020][@chen2019]:
- p53 tumor suppressor: Primary transcriptional activator; DNA damage, oxidative stress, and oncogenic signals activate p53 to induce TIGAR
- p73: p53 family member that can activate TIGAR in neurons, particularly during development
- HIF-1α: Hypoxia-inducible factor can modulate TIGAR expression in a p53-independent manner
- FOXO3: Forkhead transcription factor activates TIGAR under oxidative stress
- AMPK: Energy sensor that can regulate TIGAR post-translationally
Key Protein Interactions
TIGAR physically and functionally interacts with[@park2019][@xie2022][@kim2020]:
- PFKFB3: Competition for F2,6BP substrate; functionally opposite roles in metabolic regulation
- PFK-1: TIGAR indirectly affects PFK-1 activity through F2,6BP modulation
- Parkin (PRKN): Functional interaction in mitophagy regulation
- PINK1: TIGAR supports the energetic requirements of PINK1/Parkin-mediated mitophagy
- AMPK: Bidirectional regulation — TIGAR affects AMPK activation through metabolic changes, and AMPK can influence TIGAR
- p53: Direct transcriptional activation; also physical interaction reported
Signaling Network
Mermaid diagram (expand to render)
Research Directions
Current Priorities
Key areas of TIGAR research include[@benjamin2021][@yang2021][@wenger2023]:
Structure-function studies: High-resolution structure of TIGAR to enable rational drug design
CNS-specific activators: Developing BBB-penetrant small molecules with neuronal selectivity
Gene therapy approaches: AAV vectors for neuronal TIGAR delivery in ALS and PD
Combination strategies: TIGAR enhancement with antioxidant, autophagy, or disease-modifying therapies
Biomarker development: Non-invasive markers of TIGAR activity for patient stratification
ALS variant functional studies: Characterizing each ALS-linked TIGAR mutationEmerging Questions
- What determines the therapeutic window for TIGAR activation — how much PPP shunting is neuroprotective vs. harmful?
- Can TIGAR-targeted approaches work in APOE4 carriers given their altered lipid metabolism?
- Do the ALS-linked TIGAR mutations share a common mechanism or represent distinct pathomechanisms?
- How does TIGAR interact with other metabolic regulators in neurons (PFKFB3, AMPK, SIRT3)?
- Can TIGAR enhancement protect against TDP-43 proteinopathy specifically?
Summary
TIGAR encodes a bisphosphatase enzyme that redirects glucose metabolism from glycolysis toward the pentose phosphate pathway, generating NADPH for antioxidant defense and ribose-5-phosphate for nucleotide synthesis. As a p53-regulated metabolic stress sensor, TIGAR is essential for neuronal survival under conditions of oxidative stress, DNA damage, and metabolic challenge. TIGAR mutations cause ALS through impaired PPP flux and reduced neuroprotection, while reduced TIGAR expression in AD and PD brains contributes to disease pathogenesis through inadequate antioxidant defense and mitochondrial dysfunction. Enhancing TIGAR function through small molecules, gene therapy, or metabolic modulation represents a promising therapeutic strategy for multiple neurodegenerative diseases.
See Also
- [TP53](/genes/tp53)
- [Metabolism](/mechanisms/cellular-metabolism)
- [Pentose Phosphate Pathway](/mechanisms/pentose-phosphate-pathway)
- [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Oxidative Stress](/mechanisms/oxidative-stress)
- [Autophagy](/mechanisms/autophagy)
- [Mitochondrial Dynamics](/mechanisms/mitochondrial-dynamics)
Background
The study of Tigar Tp53 Induced Glycolysis And Apoptosis Regulator has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
External Links
- [TIGAR - NCBI Gene](https://www.ncbi.nlm.nih.gov/gene/2063)
- [TIGAR Protein - UniProt](https://www.uniprot.org/uniprotkb/Q9Y2H7)
- [TIGAR - GeneCards](https://www.genecards.org/cgi-bin/carddisp.pl?gene=C12ORF5)
- [OMIM: 610335](https://www.omim.org/entry/610335)
- [Ensembl: ENSG00000148231](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000148231)
- [C6orf120 (TIGAR) - HGNC](https://www.genenames.org/data/hgnc_data.php?hgnc_id=28832)
Pathway Diagram
The following diagram shows the key molecular relationships involving TIGAR - TP53-Induced Glycolysis and Apoptosis Regulator discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)