Arginase-1 (ARG1) is a cytosolic metalloenzyme that catalyzes the hydrolysis of L-arginine to L-ornithine and urea, representing the final step of the urea cycle. While traditionally studied in the liver for its role in ammonia detoxification, arginase-1 has emerged as a critical regulator of various physiological and pathological processes in the nervous system. In the brain, ARG1 plays dual roles—一方面参与正常的神经功能调节，另一方面在神经退行性疾病中发挥复杂的病理作用.
| Attribute | Value |
|-----------|-------|
| Protein Name | Arginase-1 |
| Gene | ARG1 |
| UniProt ID | P05089 |
| PDB ID | 1HQ8, 4HVW |
| Molecular Weight | ~35 kDa (homotrimer: ~105 kDa) |
| Subcellular Localization | Cytoplasm |
| Protein Family | Arginase family (metallohydrolase) |
| Expression | Liver, erythrocytes, brain (astrocytes, microglia, neurons) |
ARG1 is a 322-amino acid protein that forms a homotrimeric complex. Each monomer contains:
- N-terminal region: Involved in trimerization and substrate binding
- Active site: Contains two manganese ions (Mn²⁺) coordinated by aspartate and histidine residues
- C-terminal domain: Contributes to oligomerization interface
The crystal structure of ARG1 reveals a trimeric arrangement with three identical active sites. The active site contains the signature motif "DXHXH" (residues 101-104) that coordinates the binuclear manganese cluster essential for catalytic activity [1].
- Metal binding site: Binuclear Mn²⁺ cluster essential for catalytic function
- Substrate channel: Narrow entrance restricts access to active site
- Allosteric regulation: Slight conformational changes affect enzyme activity
While the complete urea cycle is primarily active in the liver, neurons and astrocytes express key enzymes including ARG1, enabling local arginine metabolism:
- Ammonia detoxification: ARG1 in astrocytes helps neutralize ammonia released during neurotransmission and metabolic processes [2]
- Ornithine production: Provides substrate for polyamine synthesis and proline biosynthesis
- Arginine homeostasis: Regulates local arginine availability for nitric oxide synthesis
ARG1 directly competes with nitric oxide synthase (NOS) for the common substrate L-arginine:
- Substrate competition: By depleting arginine, ARG1 limits NOS activity and NO production [3]
- Neuroprotective vs. harmful NO: ARG1-mediated regulation influences the balance between physiological and pathological nitric oxide signaling
- Coupled regulation: Arginase and NOS activities are reciprocally regulated in response to cellular signals
The L-ornithine produced by ARG1 serves as a precursor for polyamines:
- Ornithine decarboxylase (ODC): Converts ornithine to putrescine
- Polyamine functions: Spermidine and spermine are essential for:
- Synaptic plasticity and memory formation
- Neuronal survival and differentiation
- Protection against oxidative stress
ARG1 is highly expressed in immune cells including microglia and infiltrating monocytes:
- M2 polarization: ARG1 is a marker of anti-inflammatory (M2) microglial phenotype [4]
- T-cell regulation: Arginase activity suppresses T-cell proliferation and function
- Inflammatory resolution: Helps terminate excessive neuroinflammatory responses
- APP processing: Arginine availability influences amyloid precursor protein (APP) processing and amyloid-beta production [5]
- Aβ clearance: Polyamines derived from ARG1 activity may enhance Aβ clearance mechanisms
- Neuroinflammation: M1/M2 microglial polarization, with ARG1-expressing M2 cells, affects Aβ clearance efficiency
- Phosphorylation regulation: Arginine metabolism influences tau phosphorylation through effects on kinase/phosphatase activities [6]
- Neurofibrillary tangles: Ornithine-derived polyamines may interact with tau aggregation pathways
- Glutamate homeostasis: ARG1 affects arginase-derived ornithine that can be converted to glutamate
- Excitotoxicity: Altered arginine metabolism contributes to glutamate-mediated excitotoxic cell death [7]
- Arginase inhibitors: Being explored as potential AD therapeutics to modulate neuroinflammation
- Arginine supplementation: Investigated for enhancing polyamine synthesis and cognitive function [8]
- Metabolic support: ARG1 provides ornithine for energy metabolism in dopaminergic neurons
- Mitochondrial function: Polyamines from ARG1 activity support mitochondrial health and protect against alpha-synuclein toxicity [9]
- Microglial activation: ARG1 expression in microglia correlates with anti-inflammatory responses
- Neuroprotection: M2 microglia expressing ARG1 provide support for dopaminergic neuron survival
- Interaction with L-DOPA: Arginase competes with aromatic amino acid decarboxylase for substrate
- Therapeutic implications: Understanding ARG1 may inform combination therapies [10]
- Energy metabolism: ARG1 supports polyamine synthesis crucial for high energy demands of motor neurons
- Oxidative stress: Polyamines provide protection against ROS in motor neurons [11]
- Astrocyte dysfunction: Altered arginase expression in astrocytes affects motor neuron support
- Microglial polarization: M2 microglia expressing ARG1 may modulate disease progression
¶ Demyelination and Remyelination
- Myelin repair: Polyamines promote oligodendrocyte precursor cell (OPC) differentiation
- Remyelination enhancement: ARG1 activity supports remyelination processes [12]
- T-cell suppression: ARG1 activity in myeloid cells suppresses autoreactive T-cell responses
- Immunomodulation: Potential therapeutic target for MS treatment
- Elevated polyamines: Altered ARG1 activity contributes to polyamine abnormalities in HD
- Neuroprotective effects: Polyamines may offer protection against mutant huntingtin toxicity [13]
- Mitochondrial function: ARG1-derived ornithine supports mitochondrial energy production
- Therapeutic targeting: Modulating arginase activity may benefit HD patients
¶ Diagnostic and Biomarker Potential
- ARG1 activity: Measured in CSF as a marker of:
- Microglial activation status
- Disease progression
- Treatment response
- Ornithine levels: Downstream metabolite reflecting ARG1 activity
- Peripheral ARG1: Monocyte/erythrocyte arginase as peripheral inflammation marker
- Therapeutic monitoring: Potential for tracking treatment efficacy
- Compound development: Small molecule inhibitors targeting ARG1 catalytic activity
- Clinical applications: Being investigated for various neurological conditions
- Challenge: Achieving brain penetration while inhibiting peripheral ARG1
¶ Arginine and Polyamine Supplementation
- Rationale: Enhancing substrate availability for protective pathways
- Clinical trials: Investigating cognitive benefits in aging and AD
- Caution: Must balance multiple arginase isoforms and NOS competition
- AAV delivery: Potential for targeted ARG1 expression in specific cell types
- Cell-type specificity: Focusing on astrocyte or microglial targeting
¶ Interacting Proteins and Pathways
| Partner |
Interaction |
Functional Impact |
| NOS1/nNOS |
Substrate competition |
NO production regulation |
| ODC1 |
Metabolic pathway |
Polyamine synthesis |
| GLS1 |
Metabolic connection |
Glutamate metabolism |
| GFAP |
Cell type expression |
Astrocyte marker |
| CD206 |
Co-expression |
M2 microglial marker |
Arginase-1 (ARG1) is a crucial enzyme in brain metabolism with multifaceted roles in neurodegeneration. Its functions in substrate competition with NOS, polyamine synthesis, and immune regulation make it an important player in Alzheimer's disease, Parkinson's disease, ALS, and other neurological conditions. While excessive ARG1 activity can contribute to pathological processes through polyamine dysregulation and immune suppression, its protective roles in neuroinflammation and metabolic support highlight its complex involvement in neuronal health and disease.