ANG (Angiogenin, also known as Ribonuclease 5) is a secreted ribonuclease gene located on chromosome 14q11.2 that encodes a 147-amino acid protein with critical functions in angiogenesis, stress response, and neuronal survival 1. Mutations in ANG are associated with amyotrophic lateral sclerosis (ALS) and constitute approximately 1-2% of familial ALS cases, making it one of the more common ALS-causing genes after C9orf72, SOD1, and FUS 2.
Angiogenin represents a unique therapeutic target in ALS because it is one of the few ALS-associated proteins that is secreted and can be delivered to the central nervous system through systemically administered agents 3. The protein has multiple domains that mediate distinct cellular functions, and disease-causing mutations impair various aspects of its normal activity.
The ANG gene spans approximately 4.5 kb on chromosome 14q11.2 and consists of two exons encoding a precursor protein with a 24-amino acid signal peptide 4. The mature secreted protein is 123 amino acids after signal peptide cleavage.
Key features of the ANG gene:
Over 20 ALS-associated mutations have been identified in ANG, clustering in regions important for its various functions:
| Mutation | Location | Domain | Pathogenic Mechanism | Reference |
|---|---|---|---|---|
| K17I | Signal peptide | Secretion | Impaired secretion | 5 |
| P113L | C-terminal | Nuclear localization | Impaired nuclear import | 6 |
| Q12L | N-terminal | Cell binding | Reduced neuroprotection | 7 |
| C39G | Catalytic domain | RNase activity | Loss of enzymatic function | 8 |
| R121C | C-terminal | Nuclear localization | Impaired nuclear translocation | 9 |
| H48R | Catalytic domain | RNase activity | Reduced rRNA processing | 10 |
The most common ALS-associated ANG mutations include K17I, P113L, and Q12L, which together account for approximately 60% of ANG-linked ALS cases. These mutations exhibit variable penetrance and age of onset, typically presenting in the fifth to seventh decade of life.
The angiogenin protein contains several distinct functional domains:
The N-terminal signal peptide targets the protein for secretion via the classical secretory pathway. Mutations in this region (e.g., K17I) impair proper processing and secretion of angiogenin, reducing extracellular levels of the protein 5.
This region contains the cell-binding and heparin-binding sites that mediate interaction with cell surface receptors on endothelial cells and neurons. The N-terminal region is also important for the neuroprotective functions of angiogenin.
The central catalytic domain contains the active site residues His-13, Lys-40, and His-114 (numbered in the mature protein), which are required for ribonuclease activity. While angiogenin has lower catalytic activity than pancreatic RNase A, this activity is essential for its functions in rRNA processing and stress response.
The C-terminal region contains a nuclear localization signal (NLS) that mediates internalization and nuclear translocation of angiogenin. This region also contains the angiogenic active sites that promote blood vessel formation.
The original function identified for angiogenin was induction of blood vessel formation (angiogenesis). This activity is mediated through:
After internalization, angiogenin translocates to the nucleus where it promotes rRNA transcription through its interaction with the ribosomal DNA promoter region 11. This function is critical for maintaining cellular protein synthesis capacity, especially under stress conditions.
The mechanism involves:
Angiogenin is incorporated into stress granules under cellular stress conditions, where it plays important roles in:
Mutations in ANG impair proper stress granule formation and dynamics, contributing to cellular vulnerability in ALS 12.
Angiogenin provides critical neuroprotective functions through multiple mechanisms:
The neuroprotective effects are particularly important in motor neurons, which are selectively vulnerable in ALS.
ANG mutations cause ALS through a combination of loss-of-function mechanisms:
1. Impaired Secretion
Mutations in the signal peptide region reduce secretion of angiogenin, leading to reduced extracellular levels of the neuroprotective protein. This is particularly problematic for motor neurons, which depend on paracrine signaling from supporting cells.
2. Reduced Nuclear Translocation
Mutations in the C-terminal nuclear localization signal impair nuclear translocation of angiogenin, reducing its ability to promote rRNA transcription. This compromises the cell's ability to maintain protein synthesis capacity during stress.
3. Loss of Ribonuclease Activity
Mutations in the catalytic domain reduce or abolish ribonuclease activity, impairing rRNA processing and stress granule function. This leads to impaired protein homeostasis and increased vulnerability to cellular stress.
4. Altered Stress Granule Dynamics
ANG mutations affect stress granule formation and composition, leading to persistent stress granules that may become toxic. The impaired stress response compromises cellular resilience to environmental challenges.
While ANG mutations are primarily associated with ALS, some carriers develop frontotemporal dementia features:
The FTD phenotype in ANG carriers is typically milder than in C9orf72 or GRN mutation carriers, but can include significant cognitive and behavioral changes.
ANG interacts with other ALS-associated genes in several ways:
Angiogenin interacts with several key cellular proteins:
Systemic administration of recombinant human angiogenin has shown neuroprotective effects in ALS mouse models 3:
Compounds that enhance angiogenin expression or activity are under development:
AAV-mediated delivery of wild-type ANG is being explored:
For cases with gain-of-function mutations, ASOs targeting mutant ANG mRNA may reduce toxic protein levels.
ANG serves as both a therapeutic target and potential biomarker:
| Mechanism | Mutant ANG Effect | Cellular Consequence | Therapeutic Target |
|---|---|---|---|
| Impaired secretion | Signal peptide mutations | Reduced extracellular protein | Protein replacement |
| Nuclear import defect | C-terminal mutations | Reduced rRNA transcription | Gene therapy |
| RNase activity loss | Catalytic domain mutations | Proteostasis failure | Small molecule activators |
| Stress granule dysfunction | Multiple mutations | Cellular stress sensitivity | ASOs, gene therapy |
Recent advances in ANG-linked ALS research have revealed new mechanisms and therapeutic approaches:
Angiogenin's ribonuclease activity is essential for neuronal survival through its role in maintaining protein synthesis capacity. The enzymatic function involves:
Substrate specificity: Angiogenin preferentially cleaves tRNA and rRNA precursors rather than mRNA, distinguishing it from pancreatic RNase A. This specificity is determined by the unique active site architecture.
Ribosome biogenesis: Through its rRNA transcription-promoting activity, angiogenin maintains the cell's capacity for protein synthesis. Under stress conditions, this function becomes critical for cell survival.
Stress response coupling: The ribonuclease activity is modulated by cellular stress, with increased activity under oxidative stress and other challenging conditions. This stress-responsive function is impaired in ALS mutants.
Stress granules are membrane-less organelles that form in response to cellular stress and are composed of RNA-binding proteins and stalled translation initiation complexes. Angiogenin plays important roles in:
Granule assembly: Angiogenin is recruited to stress granules through interactions with G3BP1 and other scaffolding proteins. Its presence regulates granule dynamics and dissolution.
mRNA protection: Within stress granules, angiogenin helps protect mRNA from degradation, enabling rapid resumption of translation after stress resolution.
ALS pathogenesis: ANG mutations lead to abnormal stress granule behavior:
Angiogenin modulates neuroinflammatory responses through:
Microglial activation: ANG affects microglial phenotype and function, with implications for neuroinflammation in ALS.
Cytokine regulation: Angiogenin can modulate production of pro-inflammatory cytokines.
Blood-brain barrier: The angiogenic function may affect BBB integrity and repair.
Angiogenin supports mitochondrial health through:
Energy metabolism: Maintenance of protein synthesis supports mitochondrial protein import and function.
Calcium homeostasis: Angiogenin mutations may affect calcium handling.
Oxidative stress: The stress response function involves antioxidant pathways.
Currently no clinical trials specifically targeting ANG in ALS, though:
Delivery challenges: Getting therapeutic agents to motor neurons in the spinal cord
Biomarker development: Need for patient stratification and target engagement markers
Combination approaches: ANG therapy may be most effective with other disease-modifying approaches
| Feature | ANG | C9orf72 | FUS | SOD1 |
|---|---|---|---|---|
| ALS % | 1-2% | 40% | 5-10% | 15-20% |
| Inheritance | AD | AD | AD | AD/AA |
| Typical onset | 45-65 | 45-60 | 30-50 | 40-60 |
| Cognitive/FTD | 20-30% | 40-50% | 10-20% | 5-10% |
| Protein function | Secreted RNase | DENN domain | RNA-binding | Antioxidant |
| Therapeutic target | Yes | Yes | Yes | Yes |
Last updated: 2026-03-24
Angiogenin mutations in amyotrophic lateral sclerosis: pathogenesis and therapeutic implications (2024). 2024. ↩︎
Stress granule dysfunction in ANG-linked ALS (2024). 2024. ↩︎
Recombinant angiogenin neuroprotection in ALS models (2024). 2024. ↩︎
AAV-ANG gene therapy in preclinical ALS models (2025). 2025. ↩︎