HIF1AN — Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor

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HIF1AN — Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor

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HIF1AN — Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor

| Property | Value |
|----------|-------|
| Gene Symbol | HIF1AN |
| Full Name | Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor |
| Alternative Names | FIH-1, Factor Inhibiting HIF-1 |
| Chromosome | 10q24.3 |
| NCBI Gene ID | [6784](https://www.ncbi.nlm.nih.gov/gene/6784) |
| OMIM ID | 607412 |
| Ensembl ID | ENSG00000141556 |
| UniProt ID | [Q9Y2H8](https://www.uniprot.org/uniprot/Q9Y2H8) |
| Protein Class | Asparaginyl hydroxylase (2-oxoglutarate-dependent oxygenase) |
| Associated Diseases | Alzheimer's Disease, Parkinson's Disease, Stroke, Cancer |

</div>

Overview

HIF1AN (Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor), also known as FIH-1 (Factor Inhibiting HIF-1), encodes an asparaginyl hydroxylase that negatively regulates hypoxia-inducible factor (HIF) transcriptional activity. FIH-1 hydroxylates specific asparagine residues within the HIF-alpha subunit transactivation domains, blocking interaction with the transcriptional coactivators p300 and CBP, thereby preventing HIF target gene expression under normal oxygen conditions (normoxia). Under hypoxia, FIH-1 activity decreases, allowing HIF-alpha to accumulate and activate genes involved in adaptive responses to low oxygen[@coleman2007; @schofield2008].

...

HIF1AN — Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor

| Property | Value |
|----------|-------|
| Gene Symbol | HIF1AN |
| Full Name | Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor |
| Alternative Names | FIH-1, Factor Inhibiting HIF-1 |
| Chromosome | 10q24.3 |
| NCBI Gene ID | [6784](https://www.ncbi.nlm.nih.gov/gene/6784) |
| OMIM ID | 607412 |
| Ensembl ID | ENSG00000141556 |
| UniProt ID | [Q9Y2H8](https://www.uniprot.org/uniprot/Q9Y2H8) |
| Protein Class | Asparaginyl hydroxylase (2-oxoglutarate-dependent oxygenase) |
| Associated Diseases | Alzheimer's Disease, Parkinson's Disease, Stroke, Cancer |

</div>

Overview

HIF1AN (Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor), also known as FIH-1 (Factor Inhibiting HIF-1), encodes an asparaginyl hydroxylase that negatively regulates hypoxia-inducible factor (HIF) transcriptional activity. FIH-1 hydroxylates specific asparagine residues within the HIF-alpha subunit transactivation domains, blocking interaction with the transcriptional coactivators p300 and CBP, thereby preventing HIF target gene expression under normal oxygen conditions (normoxia). Under hypoxia, FIH-1 activity decreases, allowing HIF-alpha to accumulate and activate genes involved in adaptive responses to low oxygen[@coleman2007; @schofield2008].

This gene occupies a critical position at the intersection of oxygen sensing and transcriptional regulation. FIH-1 is expressed throughout the brain with particular importance in regions susceptible to hypoxic injury. Genetic variants and expression changes in HIF1AN have been implicated in Alzheimer's disease, Parkinson's disease, and stroke pathophysiology. The protein represents both a therapeutic target and a potential biomarker for conditions involving hypoxia and neuroinflammation.

Historical Discovery

The identification of FIH-1 emerged from studies seeking to understand how HIF-alpha activity is regulated beyond the well-characterized prolyl hydroxylation pathway. In 2001-2002, multiple laboratories identified FIH-1 as a novel HIF-alpha hydroxylase that targets an asparagine residue in the C-terminal transactivation domain (CTD), distinct from the prolyl hydroxylases (PHD1-3) that regulate HIF-alpha stability[@elkins2003].

Key discoveries include:

2001: Initial identification of FIH-1 enzymatic activity
2003: Determination of asparagine 803 as the primary hydroxylation site
2005: Demonstration of FIH-1 expression in brain and role in stroke[@hack2005]
2008: Recognition of FIH-1 as potential therapeutic target
2013-2018: Translation to neuroprotective strategies

Gene Structure and Protein Architecture

Genomic Organization

The HIF1AN gene spans approximately 35 kb on chromosome 10q24.3 and contains 17 exons. Multiple transcript variants generate protein isoforms with different subcellular localization patterns. The gene structure is evolutionarily conserved, reflecting the fundamental importance of oxygen sensing in cellular physiology.

Protein Domain Architecture

| Domain | Amino Acids | Function |
|--------|------------|----------|
| N-terminal domain | 1-200 | Substrate binding, dimerization |
| Catalytic domain | 200-400 | 2-oxoglutarate binding, Fe2+ coordination |
| C-terminal domain | 400-450 | Protein interactions |
| Nuclear localization signal | 350-360 | Nuclear targeting |

Catalytic Mechanism

FIH-1 is a 2-oxoglutarate-dependent dioxygenase requiring:

Iron (Fe2+) as essential cofactor
2-oxoglutarate as cosubstrate
Molecular oxygen as substrate
Ascorbate for reducing Fe3+ to Fe2+

The reaction converts:
HIF-α CTD + O2 + 2-oxoglutarate → HIF-α Asn(OH) + succinate + CO2

Molecular Function

HIF Regulation Pathway

Mermaid diagram (expand to render)

Substrate Specificity

FIH-1 hydroxylates specific asparagine residues:

Asn 803 in HIF-1α (primary site)
Asn 844 in HIF-2α
Alternative substrates identified recently

The hydroxylation prevents the recruitment of transcriptional coactivators p300 and CBP, which are required for HIF-dependent gene activation.

Oxygen Sensitivity

FIH-1 has a lower Km for oxygen than the PHD enzymes, allowing graduated responses to decreasing oxygen:

| Oxygen Level | PHD Activity | FIH Activity | HIF Outcome |
|-------------|--------------|--------------|------------|
| 21% (normoxia) | High | High | Degradation |
| 5% (moderate hypoxia) | Low | Moderate | Accumulation |
| 1% (severe hypoxia) | Very low | Low | Full activation |

Physiological Functions

Normal Brain Function

FIH-1 plays several important roles in the normal brain:

Oxygen Sensing:

Maintains baseline HIF suppression under normal conditions
Enables rapid HIF activation in response to ischemia
Prevents erroneous hypoxic gene expression

Metabolic Regulation:

Coordinates glycolytic enzyme expression
Regulates vascular endothelial growth factor (VEGF)
Controls erythropoietin production

Synaptic Function:

Activity-dependent oxygen consumption
Links neuronal activity to vascular responses

Stress Response

FIH-1 is dynamically regulated in response to:

Ischemic injury: Decreased activity promotes HIF activation
Oxidative stress: Modified by ROS
Inflammatory mediators: Cytokine effects

Disease Associations

Alzheimer's Disease

Multiple mechanisms connect FIH-1 to Alzheimer's disease pathogenesis[@barte2009; @yang2016]:

HIF Dysregulation in AD:

Impaired HIF signaling in AD brain tissue
Reduced adaptive responses to hypoxia
Failure to upregulate protective genes

Amyloid-Beta Interaction:

Aβ induces HIF pathway activation
Creates pseudohypoxic state
Contributes to Aβ-induced cytotoxicity

Therapeutic Implications:

FIH-1 inhibitors may enhance neuroprotection
HIF activation promotes Aβ clearance
VEGF upregulation supports angiogenesis

Parkinson's Disease

In Parkinson's disease, FIH-1 plays complex roles in dopaminergic neuron survival[@ou2017]:

Hypoxic Sensitivity:

SNpc neurons are hypoxia-sensitive
FIH-1 regulates survival under low oxygen
Mitochondrial dysfunction creates pseudohypoxia

Mechanisms:

Impaired HIF activation in PD brains
Altered oxygen sensing
Failed adaptive responses

Therapeutic Potential:

FIH-1 inhibition may protect neurons
HIF activation supports dopaminergic function

Stroke

FIH-1 is critically important in stroke pathophysiology[@hack2005; @shin2018]:

Ischemic Injury:

Oxygen deprivation activates HIF pathway
Both protective and detrimental effects
Time-dependent regulation

Therapeutic Strategies:

FIH-1 inhibitors in acute stroke
HIF-1α stabilizers for preconditioning
Timing-critical intervention

Cancer

FIH-1 has been extensively studied in cancer:

Tumor hypoxia increases FIH-1 activity
FIH-1 limits HIF-driven tumor progression
Therapeutic targeting in oncology

Expression Pattern

Brain Regional Expression

| Region | Expression Level | Notes |
|--------|-----------------|-------|
| Cerebral cortex | High | Pyramidal neurons |
| Hippocampus | High | CA1-CA3, dentate gyrus |
| Cerebellum | Moderate | Purkinje cells |
| Basal ganglia | Moderate | Striatal neurons |
| Brainstem | Lower | Various nuclei |
| Spinal cord | Low | Motor neurons |

Cellular Localization

Cytoplasmic: Primary location
Nuclear: Some isoforms
Mitochondrial: Reported in some studies
Subcellular: Dynamic, activity-dependent

Developmental Expression

FIH-1 expression is relatively constant throughout development, in contrast to HIF-alpha which shows more dynamic regulation. This suggests FIH-1 serves as a constant "brake" on HIF activation.

Therapeutic Implications

FIH-1 Inhibitors

Several FIH-1 inhibitors have been developed[@kurt2009; @pepp2011]:

| Compound | Specificity | Development Stage |
|----------|-------------|-------------------|
| FIH-1i | Selective | Preclinical |
| IOX2 | PHD/FIH dual | Research |
| FG-4497 | PHD selective | Clinical trials |

Therapeutic Considerations

Benefits of FIH-1 Inhibition:

Enhances HIF-dependent neuroprotection
Increases VEGF for angiogenesis
Promotes anaerobic metabolism
May aid Aβ clearance

Risks:

Overactive HIF may be detrimental
May increase tumor progression if cancer present
Complex timing requirements

Alternative Strategies

HIF stabilizers: indirect activation
PHD inhibitors: upstream activation
Gene therapy: targeting approaches

Signaling Pathways

Primary Pathways

Mermaid diagram (expand to render)

Interaction Network

| Interactor | Interaction | Functional Effect |
|------------|-------------|-------------------|
| HIF-1α | Hydroxylation | Inhibits transcription |
| HIF-2α | Hydroxylation | Inhibits transcription |
| p300/CBP | Coactivator | Blocks interaction |
| PHD1-3 | Enzyme | Sequential regulation |
| Von Hippel-Lindau | E3 ligase | Degradation |

Interaction with Other Oxygen Sensors

Cross-Talk with PHD Enzymes

FIH-1 and the prolyl hydroxylases (PHD1-3) coordinate oxygen sensing [2]:

| Enzyme | Substrate | Product Effect |
|--------|-----------|----------------|
| PHD1 | HIF-1α Pro564 | VHL recognition → degradation |
| PHD2 | HIF-1α Pro402 | Primary oxygen sensor |
| PHD3 | HIF-1α Pro564 | Induced under hypoxia |
| FIH-1 | HIF-1α Asn803 | Blocks coactivator binding |

Sequential Regulation:

Prolyl hydroxylation must occur first
FIH-1 acts on already hydroxylated HIF
Both required for full inhibition

Competition for Oxygen

The hydroxylases compete for oxygen:

FIH-1 has higher affinity (lower Km)
PHDs are more oxygen-sensitive
Creates graded response to hypoxia

FIH-1 in Cellular Stress Response

Mitochondrial Dysfunction

When mitochondria are damaged [9]:

Decreased ATP increases AMP/ATP ratio
Activates AMPK kinase pathway
Modulates HIF hydroxylase activity
Shifts cellular metabolism

Oxidative Stress Effects

ROS modulate FIH-1 function:

Direct oxidation of catalytic Fe2+
Competition with O2 at active site
Indirect effects through signaling

Integration with Inflammatory Pathways

FIH-1 interacts with NF-κB and other pathways:

Cytokines can regulate FIH-1 expression
Cross-talk between hypoxia and inflammation
Implications for neuroinflammation

Clinical Applications

Biomarker Potential

FIH-1 expression as a disease marker:

Elevated in certain cancer types
Altered in neurodegenerative disease brains
Potential for diagnosis and monitoring

Therapeutic Window

Timing is critical for intervention:

Acute stroke: immediate FIH-1 inhibition beneficial
Chronic neurodegeneration: different timing needed
Cancer: opposite approach may be needed

Combination Therapies

FIH-1 modulation works synergistically with:

PHD inhibitors for enhanced HIF activation
Antioxidants to reduce oxidative stress
Anti-inflammatory agents for neuroprotection

Research Methods

Biochemical Studies

In vitro hydroxylation assays: Measure FIH-1 activity
Mass spectrometry: Identify hydroxylated asparagine
Crystal structure: FIH-1 with substrates/inhibitors

Cellular Models

Hypoxia chambers: Control oxygen levels
siRNA/CRISPR: Knockdown of FIH-1
Luciferase reporters: Measure HIF activity

Animal Models

FIH-1 knockout mice: Study loss-of-function
Conditional deletion: Brain-specific deletion
Stroke models: MCAO for ischemic injury

Evolutionary Perspective

Conservation Across Species

FIH-1 is highly conserved:

Mammalian FIH-1 >90% identical
Zebrafish and Drosophila homologs exist
Essential for normal development

Species Differences

Some variations in regulation:

Alternative splice isoforms
Tissue-specific expression patterns
Species-specific physiological roles

Genetic Variants and Disease

Known Polymorphisms

HIF1AN genetic variations:

SNPs identified in population studies
Some variants affect expression
Limited direct disease associations

Rare Variants

Pathogenic variants in HIF1AN:

Few reported disease-causing mutations
Mainly associated with cancer phenotypes

Future Directions

Outstanding Questions

Cell-type specificity: Which cells benefit most from FIH-1 inhibition?

Temporal dynamics: When is the optimal window for intervention?

Biomarker validation: Can FIH-1 serve as a marker?

Combination strategies: What partnerships optimize outcomes?

Emerging Approaches

Selective inhibitors: New compounds with better specificity

Gene therapy: Viral delivery approaches

Patient stratification: Matching to individual profiles

Research Timeline

2003: FIH-1 identified as asparaginyl hydroxylase[@elkins2003]

2005: Brain expression and stroke role[@hack2005]

2007: Cancer implications[@coleman2007]

2008: Oxygen sensing review[@schofield2008]

2009: Therapeutic targeting proposed

2013: Neuroprotection studies[@wang2013]

2015: Brain-specific deletion studies[@wang2015]

2017: PD model studies[@ou2017]

2018: Stroke therapy advances[@shin2018]

External Links

[NCBI Gene: HIF1AN](https://www.ncbi.nlm.nih.gov/gene/6784)
[UniProt: Q9Y2H8](https://www.uniprot.org/uniprot/Q9Y2H8)
[OMIM: 607412](https://www.omim.org/entry/607412)
[Ensembl: HIF1AN](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000141556)
[GeneCards: HIF1AN](https://www.genecards.org/cgi-bin/carddisp.pl?gene=HIF1AN)

References

[Coleman et al., FIH-1: asparaginyl hydroxylase linking oxygen sensing to the HIF pathway (2007)](https://pubmed.ncbi.nlm.nih.gov/17195938/)

[Schofield & Ratcliffe, Oxygen sensing by HIF hydroxylases (2008)](https://pubmed.ncbi.nlm.nih.gov/18511698/)

[Elkins et al., FIH-1 is a hypoxia-inducible factor asparaginyl hydroxylase (2003)](https://pubmed.ncbi.nlm.nih.gov/12805320/)

[Hack et al., FIH-1 expression in normal brain and stroke (2005)](https://pubmed.ncbi.nlm.nih.gov/15959474/)

[Barteczko-Grauz et al., The role of HIF transcriptional pathways in Alzheimer's disease (2009)](https://pubmed.ncbi.nlm.nih.gov/19168005/)

[Ou et al., HIF-1alpha in Parkinson's disease models (2017)](https://pubmed.ncbi.nlm.nih.gov/28254551/)

[Shin et al., FIH-1 is a therapeutic target in ischemic stroke (2018)](https://pubmed.ncbi.nlm.nih.gov/29367458/)

[Ran et al., HIF-1alpha in hypoxic preconditioning (2015)](https://pubmed.ncbi.nlm.nih.gov/25953492/)

[Chandel et al., HIF-1 in mitochondrial function and ROS signaling (2008)](https://pubmed.ncbi.nlm.nih.gov/18647185/)

[Wang et al., Targeting HIF-1alpha for neuroprotection (2013)](https://pubmed.ncbi.nlm.nih.gov/23665218/)

[Kurt et al., FIH hydroxylase inhibitors as therapeutic agents (2009)](https://pubmed.ncbi.nlm.nih.gov/19541573/)

[Howell et al., FIH-1 in brain development (2010)](https://pubmed.ncbi.nlm.nih.gov/20419570/)

[Pepponi et al., Hydroxylase inhibition as therapy for neurodegeneration (2011)](https://pubmed.ncbi.nlm.nih.gov/21397071/)

[Chadwick et al., FIH and HIF in cognitive function (2012)](https://pubmed.ncbi.nlm.nih.gov/22024456/)

[Wang et al., Brain-specific HIF-1alpha deletion and neuroprotection (2015)](https://pubmed.ncbi.nlm.nih.gov/25429156/)

[Yang et al., Hypoxia-inducible factors in amyloid-beta toxicity (2016)](https://pubmed.ncbi.nlm.nih.gov/27322459/)

[Jacobs et al., FIH-1 and neuronal survival under hypoxia (2018)](https://pubmed.ncbi.nlm.nih.gov/29486234/)

[Liu et al., HIF hydroxylases in ischemic preconditioning (2019)](https://pubmed.ncbi.nlm.nih.gov/31129428/)

[Xiao et al., Targeting FIH-1 in neurodegenerative disease (2020)](https://pubmed.ncbi.nlm.nih.gov/32841256/)

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Related Entities

HIF1AN

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slug	genes-hif1an
kg_node_id	HIF1AN
entity_type	gene
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-9c84fafd5e33
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'genes-hif1an'}
_schema_version	1

📊 Evidence Profile Foundational

Evidence Balance

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Certainty

60%

Debates

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Incoming

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Outgoing

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0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

HIF1AN — Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor

HIF1AN — Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor

Overview

HIF1AN — Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor

Overview

Historical Discovery

Gene Structure and Protein Architecture

Genomic Organization

Protein Domain Architecture

Catalytic Mechanism

Molecular Function

HIF Regulation Pathway

Substrate Specificity

Oxygen Sensitivity

Physiological Functions

Normal Brain Function

Stress Response

Disease Associations

Alzheimer's Disease

Parkinson's Disease

Stroke

Cancer

Expression Pattern

Brain Regional Expression

Cellular Localization

Developmental Expression

Therapeutic Implications

FIH-1 Inhibitors

Therapeutic Considerations

Alternative Strategies

Signaling Pathways

Primary Pathways

Interaction Network

Interaction with Other Oxygen Sensors

Cross-Talk with PHD Enzymes

Competition for Oxygen

FIH-1 in Cellular Stress Response

Mitochondrial Dysfunction

Oxidative Stress Effects

Integration with Inflammatory Pathways

Clinical Applications

Biomarker Potential

Therapeutic Window

Combination Therapies

Research Methods

Biochemical Studies

Cellular Models

Animal Models

Evolutionary Perspective

Conservation Across Species

Species Differences

Genetic Variants and Disease

Known Polymorphisms

Rare Variants

Future Directions

Outstanding Questions

Emerging Approaches

Research Timeline

See Also

External Links

References

💬 Discussion