Ribonuclease κ and Circular RNAs: A New Mechanism of Aging and Neurodegeneration
Last Updated: 2026-03-21
Overview
Circular RNAs (circRNAs) represent a fascinating class of non-coding RNAs that have transitioned from being considered "junk RNA" to becoming recognized as critical regulators of cellular homeostasis[@kristensen2018]. The 2026 Molecular Cell study first revealed the key function of ribonuclease κ (RNASEK) as an endonuclease that degrades circRNAs in stress granules[@ribonuclease2026]. The research demonstrated that RNASEK expression decreases with age, leading to circRNA accumulation in brain tissue, which may represent a core mechanism of aging and neurodegenerative diseases.
This page provides an in-depth exploration of the biological properties of circRNAs, the mechanism of RNASEK action, age-related changes, and their association with Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS).
Circular RNAs: From Biological Curiosity to Critical Regulators
Biogenesis of Circular RNAs
circRNAs are generated through a process called backsplicing, which differs fundamentally from conventional linear splicing[@salzman2013][@conn2017]. This process involves:
- Backsplicing: The 5' end of an exon connects to the 3' end of the same or a different exon
- Covalent closure: Forms a stable covalently closed circular molecule
- No cap/tail: Produces circular molecules lacking 5' caps and 3' tails
Types of circRNAs
| Type | Description | Prevalence |
|------|-------------|------------|
| Exonic circRNAs (ecircRNAs) | Derived from exons, most common | 80-90% |
| Circular intronic RNAs (ciRNAs) | Retained introns | 5-10% |
| Exon-intron circRNAs (EIciRNAs) | Contain both exons and introns | 2-5% |
| tRNA intronic circRNAs (tricRNAs) | From tRNA splicing | 1-2% |
Properties of circRNAs
circRNAs possess unique biochemical properties that distinguish them from linear RNA:
| Property | circRNA | Linear mRNA |
|----------|---------|-------------|
| Structure | Covalently closed circle | Linear with 5' cap, 3' tail |
| Stability | Highly stable (half-life: days) | Unstable (half-life: hours) |
| Localization | Enriched in brain tissue | Ubiquitous |
| Expression | Often tissue-specific | Ubiquitous |
| Biogenesis | Back-splicing | Canonical splicing |
| Degradation | RNASEK-mediated | Multiple RNases |
circRNA Functions in Cellular Biology
Although circRNAs were initially considered non-functional "junk RNA," research over the past decade has revealed multiple important functions[@hansen2013][@memczak2013]:
1. MicroRNA Sponge Function
circRNAs can act as competitive endogenous RNAs (ceRNAs) that bind microRNAs, regulating gene expression:
- CDR1as (ciRS-7): Contains 74 miR-7 binding sites, acts as an effective miR-7 sponge[@piwecka2017]
- Sry circRNA: Contains 16 miR-135 binding sites[@hansen2013a]
- circHIPK3: Sponges multiple miRNAs including miR-124
2. Protein Sponge/Decoy Function
circRNAs can bind specific proteins, interfering with their normal functions:
- RNA binding protein (RBP) sequestration: Bind and sequester RBPs
- Transcription factor interference: Trap transcription factors
- Splicing factor modulation: Affect spliceosome function
3. Translation Potential
Although most circRNAs are non-coding, certain circRNAs can be translated:
- Internal ribosome entry sites (IRES): Enable cap-independent translation
- circRNA-encoded peptides: Produce novel protein isoforms
- Disease association: Translation products linked to disease states[@pamudurti2017]
4. Regulation of Gene Expression
circRNAs influence gene transcription and chromatin dynamics:
- RNA polymerase II regulation: Modulate transcriptional activity
- Epigenetic modifications: Affect chromatin modifications
- Parent gene expression: Regulate expression of host genes
RNASEK: The CircRNA Degradase
Discovery and Characterization
Ribonuclease κ (RNASEK) was initially described as an enzyme involved in RNA processing. The 2026 study first revealed its central role in circRNA degradation[@ribonuclease2026].
Biochemical Properties
| Property | Description |
|----------|-------------|
| Enzyme Type | Endoribonuclease |
| Substrate | Circular RNAs (not linear mRNAs) |
| Location | Stress granules |
| Species conservation | C. elegans, mice, humans |
| Mechanism | Endonucleolytic cleavage within circRNA |
Mechanism of Action
RNASEK degrades circRNAs through the following mechanism:
Stress Granule Localization: RNASEK is enriched in stress granules (SGs), which are RNA-protein complexes that form in cells under stress conditions[@wolfe2022]
Substrate Recognition: RNASEK specifically recognizes the circular structure of circRNAs, which allows it to distinguish circRNAs from linear RNA
Cleavage Activity: RNASEK performs endonucleolytic cleavage within the circRNA, producing linearized degradation products
Granule Dynamics: Normal circRNA degradation is necessary for proper stress granule disassemblyResearch shows that RNASEK expression significantly decreases with age[@ribonuclease2026]:
- C. elegans: RNASEK expression decreases with age
- Mice: Age-related expression decline
- Human: Age-related decline in brain tissue
This age-related decline leads to:
- circRNA accumulation in tissues
- Impaired stress granule disassembly
- Cellular homeostasis disruption
The Aging-circRNA Connection
circRNA Accumulation with Age
circRNAs significantly accumulate during aging[@gruner2019][@dlouhy2021]:
- circRNA levels increase 2-5-fold in elderly brain tissue
- Similar phenomena observed in multiple tissues
- Correlates with biological age
Possible mechanisms for circRNA accumulation:
RNASEK decline: Reduced degradase activity
Increased synthesis: Age-related splicing changes may increase circRNA production
Reduced excretion: Decreased extracellular vesicle-mediated clearance
Cell death: Release of more circRNAs into tissuesConsequences of circRNA Accumulation
Pathological consequences of circRNA accumulation include:
Stress Granule Dysfunction
circRNA accumulation disrupts normal stress granule dynamics[@ribonuclease2026]:
- Delayed granule disassembly
- Abnormal RNA-protein complexes
- Impaired protein translation
Protein Aggregation
circRNAs can form pathological complexes with proteins:
- Interaction with stress granule proteins
- May promote abnormal protein aggregation
- Associated with TDP-43, tau, and other pathologies
RNA Homeostasis Disruption
Cellular RNA homeostasis disruption:
- Abnormal protein synthesis
- Dysregulated gene expression
- Abnormal cellular stress responses
Disease Implications
Alzheimer's Disease (AD)
circRNA accumulation is closely related to AD pathology[@dube2021][@zhang2022]:
TDP-43 Connection
TDP-43 proteinopathy is a significant feature of AD[@josephs2018]:
- TDP-43 is enriched in stress granules
- circRNA accumulation may affect TDP-43 function
- TDP-43 pathology correlates with cognitive decline
Tau Pathology
Tau protein abnormal aggregation is a core feature of AD[@wang2023]:
- circRNAs may interact with tau pathology
- Stress granule dysfunction affects tau phosphorylation
- May accelerate tau pathology spread
Biomarker Potential
circRNAs show promise as AD biomarkers:
- Can be detected in blood and cerebrospinal fluid
- Correlates with disease progression
- May reflect RNASEK activity
Parkinson's Disease (PD)
The relationship between circRNAs and PD is increasingly recognized[@kumar2021][@hanan2022]:
Alpha-Synuclein Connection
Alpha-synuclein is the core pathological protein in PD:
- circRNAs may affect alpha-synuclein expression
- Associated with Lewy body formation
- May serve as PD biomarkers
Mitochondrial Function
circRNAs affect mitochondrial function:
- Regulate mitochondrial gene expression
- Related to mitochondrial dysfunction in PD
Dopaminergic Neuron Vulnerability
Dopaminergic neurons are particularly sensitive to circRNA accumulation:
- circRNA accumulation in substantia nigra
- May accelerate neuronal death
Amyotrophic Lateral Sclerosis (ALS)
Research on the relationship between ALS and circRNAs is deepening[@liu2023]:
ALS-related gene mutations affect stress granules:
- TDP-43 (TARDBP)
- [FUS](/genes/fus)
- [C9orf72](/genes/c9orf72)
RNA Toxicity
Hexanucleotide repeat expansion in the C9orf72 gene:
- Produces toxic RNA foci
- circRNAs may be involved in this process
Other Neurodegenerative Diseases
Huntington's Disease
circRNAs are abnormally expressed in Huntington's disease[@cai2021]
Frontotemporal Dementia
Shares pathological mechanisms with ALS; circRNAs may be involved
Therapeutic Strategies
RNASEK-Based Therapies
Gene Therapy
- Deliver RNASEK gene to aging brain
- AAV-mediated expression
- Potential disease-modifying treatment
Small Molecule Activators
Screen for small molecules that enhance RNASEK activity:
- High-throughput screening
- Virtual screening
- Structure-guided design
Protein Replacement
Direct delivery of functional RNASEK protein
circRNA-Targeting Approaches
Reduce circRNA Production
- Target backsplicing mechanisms
- Inhibit circRNA formation
Enhance circRNA Clearance
- Promote excretion
- Enhance degradation pathways
Antisense Oligonucleotides
- ASOs target specific circRNAs
- LNA modifications enhance effect
Combination Approaches
The most effective strategy may be combination therapy:
Enhance RNASEK activity + reduce circRNA production
Target circRNA + target protein aggregation
Biomarker monitoring + personalized treatmentResearch Directions
Mechanistic Studies
circRNA Toxicity Mechanisms
- Detailed mechanisms of circRNA-protein interactions
- Cell type-specific effects
- Consequences of long-term accumulation
RNASEK Regulation
- Transcriptional regulation mechanisms
- Post-translational modifications
- Activity regulatory factors
Therapeutic Development
Drug Discovery
- Preclinical development of RNASEK activators
- Pharmacokinetic optimization
- Safety assessment
Delivery Systems
- Brain delivery technologies
- Blood-brain barrier penetration
- Targeting specific cell types
Biomarker Development
Diagnostic Markers
- circRNAs as early markers
- Blood/CSF detection
- Multi-panel combinations
Disease Progression
- Monitor treatment effects
- Predict disease progression
- Personalized medicine
circRNA Database Resources
Research Databases
| Database | Description | URL |
|----------|-------------|-----|
| circBase | circRNA sequences and annotations | circbase.org |
| circRNADb | Comprehensive circRNA database | circrnadb.idrx.org |
| CSCD | Cancer-specific circRNA database | mircirc.com/cscd |
| circAtlas | circRNA in multiple species | circatlas.bioinf.org |
- circRNA finder: Identify circRNAs from RNA-seq data
- CIRCexplorer: Annotate circRNAs
- PSPA: Predict protein-binding sites
Exosomal circRNAs
circRNAs can be packaged into extracellular vesicles:
- Protected from RNase degradation
- May serve as intercellular messengers
- Potential disease biomarkers
Clinical Applications
- Detectable in blood, urine, CSF
- Reflect tissue-specific pathology
- Non-invasive diagnostic potential
circRNA and Epigenetics
Chromatin Regulation
circRNAs can influence chromatin states:
- Interact with chromatin modifiers
- Regulate gene expression epigenetically
- May affect transgenerational inheritance
DNA Damage Response
circRNAs are involved in DNA damage responses:
- Regulate DNA repair genes
- Affected by genotoxic stress
- May influence genomic stability
circRNA in Other Diseases
Cancer
- Many circRNAs are dysregulated in cancer
- Can act as oncogenes or tumor suppressors
- Potential therapeutic targets
Cardiovascular Disease
- circRNAs in heart disease
- Regulate cardiac function
- Biomarker potential
Diabetes
- circRNAs in pancreatic beta cells
- Affect insulin secretion
- Metabolic disease links
Future Perspectives
The discovery of circRNAs and RNASEK provides a new framework for understanding neurodegenerative diseases. As research deepens, we anticipate:
Mechanistic elucidation: More detailed understanding of circRNA accumulation toxicity mechanisms
Therapeutic development: Clinical translation of RNASEK activators or circRNA-targeted treatments
Biomarkers: circRNAs as tools for disease diagnosis and monitoring
Precision medicine: Personalized treatment based on circRNA characteristicsSee Also
- [TDP-43 Proteinopathy](/mechanisms/tdp-43-proteinopathy)
- [Tau Pathology](/proteins/tau)
- [Stress Granules in Neurodegeneration](/mechanisms/stress-granules)
- [Alpha-Synuclein](/proteins/alpha-synuclein)
- [Aging Microglia](/cell-types/aging-microglia)
- [Non-coding RNAs in Neurodegeneration](/mechanisms/non-coding-rna-neurodegeneration)
References
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