IL1A — Interleukin 1 Alpha

IL1A — Interleukin 1 Alpha

Overview

IL1A — Interleukin 1 Alpha

Overview

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">IL1A — Interleukin 1 Alpha</th>
</tr>
<tr>
<td class="label">Cell Type</td>
<td>Expression Pattern</td>
</tr>
<tr>
<td class="label">Microglia</td>
<td>Constitutive low, dramatically upregulated by injury/pathology</td>
</tr>
<tr>
<td class="label">Astrocytes</td>
<td>Moderate constitutive, stress-induced upregulation</td>
</tr>
<tr>
<td class="label">Neurons</td>
<td>Low constitutive, pathological induction</td>
</tr>
<tr>
<td class="label">Oligodendrocytes</td>
<td>Stress-responsive</td>
</tr>
<tr>
<td class="label">Endothelial cells</td>
<td>Low, upregulated in inflammation</td>
</tr>
<tr>
<td class="label">Drug</td>
<td>Mechanism</td>
</tr>
<tr>
<td class="label">Anakinra (Kineret)</td>
<td>IL1R1 blockade (recombinant IL-1RA)</td>
</tr>
<tr>
<td class="label">Canakinumab (Ilaris)</td>
<td>Anti-IL-1beta monoclonal</td>
</tr>
<tr>
<td class="label">Rilonacept (Arcalyst)</td>
<td>IL-1 trap (IL1R1+IL1R2 ectodomain fusion)</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/atherosclerosis" style="color:#ef9a9a">Atherosclerosis</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a>, <a href="/wiki/carcinoma" style="color:#ef9a9a">Carcinoma</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">109 edges</a></td>
</tr>
</table>

IL1A encodes interleukin-1 alpha, a pleiotropic pro-inflammatory cytokine and founding member of the interleukin-1 family. Located on chromosome 2q14.1, IL1A is expressed across multiple tissues including the brain, where it serves as a master regulator of neuroinflammatory responses. IL1A plays a critical role in the neuroinflammation that characterizes Alzheimer's disease, Parkinson's disease, multiple sclerosis, and other neurodegenerative conditions["@mrak2006"][@rogers2002].

Unlike its close relative IL1B, which is secreted as a mature active protein after inflammasome-mediated cleavage, IL1A is biologically active in both its pro-form (31 kDa) and mature form (17 kDa). This allows IL1A to function both intracellularly and extracellularly, contributing to both autocrine and paracrine inflammatory signaling["@schroder2023"].

Function

Pro-inflammatory Cytokine Signaling

IL1A is a potent pleiotropic cytokine that initiates and amplifies inflammatory responses[@mrak2006]. Unlike IL1B which is secreted as a mature protein, IL1A is active in both its pro-form and mature form. The cytokine functions include:

• Autocrine activation: IL1A acts on the same cell that produces it, creating a self-amplifying inflammatory loop[@rogers2002]
• Paracrine signaling: IL1A from microglia and astrocytes activates neighboring cells including neurons, other glia, and endothelial cells[@mhy2011]
• Systemic effects: IL1A can access the hypothalamus via the organum vasculosum of the lamina terminalis to induce fever and sickness behavior[@schroder2023]
• Intracellular signaling: Full-length pro-IL1A can signal from within the nucleus, where it may regulate gene expression independently of receptor engagement

Receptor Interactions

IL1A signals through multiple receptor interactions[@patel2023]:

• IL1R1 (signaling): The functional signaling receptor, requires the accessory protein IL1RAP for signal transduction. Binding triggers MyD88-dependent signaling cascade leading to NF-κB and MAPK activation
• IL1R2 (decoy): A soluble or membrane-bound receptor that lacks a TIR domain and cannot signal. Acts as a natural inhibitor by sequestering IL1A and IL1B
• IL-1RA (antagonist): The IL-1 receptor antagonist (anakinra) competes for IL1R1 binding without triggering signaling

Cell-Type Specific Expression

IL1A in Brain Physiology

Under normal conditions, IL1A is tightly regulated in the brain:

• Low baseline expression in microglia maintains surveillance state
• Neuronal IL1A expression is nearly absent but induced by injury
• Astrocyte IL1A production is triggered by pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs)
• Constitutive IL1R2 expression in healthy brain limits accidental IL1A signaling

Disease Associations

Alzheimer's Disease

IL1A is strongly implicated in AD pathogenesis through multiple mechanisms[@liccini2019][@zhang2021]:

• Genetic susceptibility: IL1A promoter polymorphisms (-889C/T, rs1800587) associated with increased AD risk in meta-analyses of over 10,000 subjects
• Inflammasome activation: IL1A activates the NLRP3 inflammasome in microglia, driving chronic neuroinflammation and IL1B release[@schroder2023]
• Amyloid interaction: IL1A enhances amyloid precursor protein (APP) processing and Aβ production through NF-κB-mediated BACE1 upregulation[@mrak2006]
• Tau pathology: IL1A drives tau hyperphosphorylation through GSK3β and CDK5 activation; IL1A levels correlate with Braak staging[@zhang2021]
• Synaptic dysfunction: IL1A impairs long-term potentiation (LTP) and synaptic plasticity through NMDA receptor modulation
• Brain region vulnerability: IL1A is highest in hippocampus and entorhinal cortex, matching early AD pathology
• Therapeutic relevance: IL-1 receptor blockade reduces AD-like pathology in 3xTg and 5xFAD mouse models

Parkinson's Disease

IL1A drives neuroinflammation and dopaminergic degeneration in PD[@mhy2011][@patel2023]:

• Elevated in PD brain: IL1A mRNA and protein are increased 3-5 fold in the substantia nigra pars compacta of PD patients
• CSF biomarkers: IL1A is elevated in PD CSF and correlates with disease severity (UPDRS-III scores)
• Dopaminergic toxicity: IL1A synergizes with MPTP, 6-OHDA, and alpha-synuclein to kill dopaminergic neurons
• Microglial activation: IL1A is a key trigger of the pro-inflammatory M1 microglial phenotype
• αSyn propagation: IL1A-induced neuroinflammation may facilitate the cell-to-cell spreading of alpha-synuclein pathology[@schroder2023]
• Genetic evidence: IL1A promoter variants modify PD age at onset in GWAS studies

Multiple Sclerosis

IL1A contributes to demyelination and disease progression in MS[@grillaki2021]:

• Blood-brain barrier disruption: IL1A increases BBB permeability through VEGF and MMP-9 upregulation, allowing immune cell infiltration
• Oligodendrocyte toxicity: IL1A directly damages oligodendrocytes through caspase-1-dependent apoptosis
• T-cell activation: IL1A promotes Th17 differentiation and autoimmune responses in the CNS
• EAE models: IL1A-deficient mice are resistant to experimental autoimmune encephalomyelitis (EAE)

Amyotrophic Lateral Sclerosis

IL1A is elevated in ALS CSF and contributes to motor neuron vulnerability[@simon2020]:

• CSF IL1A levels are significantly elevated in ALS patients compared to controls
• Genetic variants in the IL1A/IL1B pathway modify disease onset and progression
• Microglial IL1A drives neuroinflammation in SOD1G93A and other ALS mouse models

Molecular Mechanisms

NF-κB Signaling Pathway

IL1A binding to IL1R1 triggers the canonical NF-κB pathway[@patel2023]:

Target genes include:

• Pro-inflammatory cytokines: IL6, TNF-α, IL1B itself (creating amplification loop)
• Chemokines: CCL2 (MCP-1), CXCL1 (GRO-α), CXCL8 (IL-8) (recruiting immune cells)
• Adhesion molecules: VCAM1, ICAM1 (facilitating leukocyte extravasation)
• Enzymes: COX2 (producing prostaglandins), iNOS (producing NO)

Inflammasome Cross-Talk

IL1A directly activates the NLRP3 inflammasome in primed cells[@schroder2023]:

• IL1A-induced ROS production provides signal 1 for NLRP3 priming (NF-κB-dependent pro-caspase-1 and pro-IL1B transcription)
• IL1A primes cells for enhanced NLRP3 response to secondary triggers (ATP, nigericin, αSyn oligomers)
• This creates a feed-forward loop: IL1A → NF-κB → NLRP3 priming → caspase-1 activation → IL1B release → more IL1A

Impact on Glial Cells

IL1A has profound effects on neuroglial cells[@pare2022]:

• Microglia: Converts resting microglia to the pro-inflammatory M1 phenotype through STAT1 and NF-κB activation; increases phagocytosis initially but impairs debris clearance over time
• Astrocytes: Induces reactive astrogliosis (A1 phenotype) with enhanced inflammatory profile; disrupts astrocyte support of neuronal function and glutamate uptake
• Oligodendrocytes: Direct toxicity through activation of apoptotic pathways; impairs differentiation of oligodendrocyte precursor cells

Interaction with Neurodegeneration Pathways

IL1A intersects with multiple pathways central to neurodegeneration:

• Protein aggregation: NF-κB activation upregulates APP and BACE1, increasing Aβ production; IL1A promotes tau phosphorylation through GSK3β
• Mitochondrial dysfunction: IL1A impairs mitochondrial respiration and promotes mitochondrial permeability transition
• Oxidative stress: IL1A induces iNOS and NADPH oxidase, generating reactive oxygen and nitrogen species
• Autophagy dysregulation: IL1A inhibits autophagic flux, reducing clearance of protein aggregates

Therapeutic Approaches

IL-1 Receptor Antagonists

Challenges and Considerations

• IL-1A has both pro-inflammatory and homeostatic functions; complete blockade may impair beneficial CNS immune surveillance
• The blood-brain barrier limits access of large biologics; new approaches needed (nanobodies, small molecules)
• Timing is critical: early blockade may prevent pathology, late intervention may have limited benefit
• Biomarker-guided patient selection may be needed (IL1A-high patients most likely to benefit)

Clinical Trials

• NCT04735770: Anakinra in Alzheimer's disease (Phase 2, 12-month treatment)
• NCT04059874: Canakinumab cognitive outcomes in post-MI patients (subgroup analysis for neurodegeneration biomarkers)
• NCT04163107: IL-1 blockade in Parkinson's disease (observational study)
• NCT03806456: Anakinra in ALS (Phase 2, safety and biomarker study)

See Also

• [Interleukin-1](/mechanisms/il-1-signaling-pathway)
• [NLRP3 Inflammasome](/mechanisms/nlrp3-inflammasome-neuroinflammation)
• [Neuroinflammation](/mechanisms/neuroinflammation-pathway)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [IL1B](/genes/il1b)
• [TNF-alpha](/mechanisms/tnf-alpha-neuroinflammation)
• [Microglia and Neuroinflammation](/mechanisms/microglia-neuroinflammation)

External Links

• [NCBI Gene: IL1A](https://www.ncbi.nlm.nih.gov/gene/3552)
• [UniProt: IL1A](https://www.uniprot.org/uniprot/P01583)
• [GeneCards: IL1A](https://www.genecards.org/cgi-bin/carddisp.pl?gene=IL1A)
• [OMIM: IL1A](https://www.omim.org/entry/147450)
• [Reactome: IL-1 signaling](https://reactome.org/content-detail/R-HSA-449147)

Pathway Diagram

The following diagram shows the key molecular relationships involving IL1A — Interleukin 1 Alpha discovered through SciDEX knowledge graph analysis: