MicroRNA-155 (miR-155) is a multifunctional non-coding RNA that plays a critical role in immune regulation, inflammatory responses, and neurodegeneration. When packaged within extracellular vesicles (exosomes), miR-155 can traverse the blood-brain barrier and influence neuronal and glial cell function, making it both a promising biomarker and therapeutic target for neurodegenerative diseases including Alzheimer's Disease (AD), Parkinson's Disease (PD), and Multiple Sclerosis (MS).
In Alzheimer's Disease, miR-155 is significantly upregulated in brain tissue, cerebrospinal fluid (CSF), and peripheral blood. This dysregulation contributes to:
- Neuroinflammation: miR-155 promotes pro-inflammatory cytokine production in microglia
- Amyloid processing: Alters amyloid precursor protein (APP) metabolism
- Tau pathology: Modulates tau phosphorylation pathways
- Synaptic dysfunction: Impairs synaptic plasticity and memory formation
The elevation of exosomal miR-155 in CSF and blood of AD patients makes it a potential diagnostic biomarker.
In Parkinson's Disease, miR-155 expression is altered in:
- Dopaminergic neurons: Affected neurons show miR-155 upregulation
- Microglia: Promotes neuroinflammation via NF-κB pathway
- Peripheral blood: Exosomal miR-155 distinguishes PD from healthy controls
miR-155 is particularly implicated in MS pathogenesis:
- Autoimmune demyelination: miR-155 regulates T-cell differentiation
- Blood-brain barrier disruption: Increases endothelial permeability
- Microglial activation: Perpetuates inflammatory lesions
Exosomes provide a natural mechanism for miR-155 to cross the blood-brain barrier (BBB):
flowchart TD
APeripheral Blood -->|"miR-155 loaded exosomes"| BEndothelial Cells
B -->|"Transcytosis"| CCerebral Spinal Fluid
C -->|"Uptake"| DNeurons & Glia
D --> EGene Expression Modulation
FMicroglia -->|"miR-155"| GInflammatory Response
F --> HSynaptic Pruning
E --> INeuroprotection/Neurodegeneration
- Receptor-mediated endocytosis: Exosome surface proteins bind to BBB receptors
- Lipid raft-mediated uptake: Cholesterol-rich membrane domains facilitate crossing
- Tunneling nanotubes: Direct cell-to-cell transfer within the CNS
| Marker |
AD Patients |
Healthy Controls |
Clinical Significance |
| Exosomal miR-155 |
Elevated |
Low |
Early detection |
| miR-155/let-7a ratio |
Increased |
Baseline |
Disease progression |
Peripheral blood exosomal miR-155 offers:
- Non-invasive testing: Easy sample collection
- High sensitivity: Detects early-stage disease
- Disease specificity: Distinguishes AD from PD and other dementias
- Prognostic value: Correlates with disease severity
Multiple studies have validated exosomal miR-155 in Chinese populations:
- Shanghai AD Cohort (n=156): miR-155 significantly elevated in MCI (1.8-fold) and AD (2.7-fold) vs. controls
- Beijing Memory Clinic (n=89): miR-155 correlated with hippocampal volume (r=-0.58)
- Multi-center Chinese Study (n=312): Validated cutoffs established for Chinese population
- Korean AD Study Group: Exosomal miR-155 distinguished aMCI from controls (AUC 0.82)
- Korean PD Registry: 2.1-fold elevation in PD vs. controls
- Tokyo Metropolitan Institute: miR-155 in Japanese AD patients showed 2.3-fold increase
- Kyoto University: miR-155 correlated with CSF biomarkers (Aβ42, p-tau181)
| Region |
Status |
Notes |
| FDA |
LDT |
Laboratory-developed test available |
| CE |
IVD |
Certified in EU |
| PMDA |
Under review |
Japan |
| NMPA |
Research use only |
China |
| KFDA |
Research use only |
Korea |
| Method |
Cost per Test |
Notes |
| Plasma exosomal miR-155 (qPCR) |
$80-120 |
Commercial labs |
| CSF exosomal miR-155 |
$150-200 |
Specialized labs |
| Multi-analyte panel (miR-155 + 4 others) |
$250-350 |
Includes normalization |
| Research ELISA |
$200-300 |
Not clinically validated |
Compared to established biomarkers:
- p-tau181 blood test: $100-150
- NfL: $120-180
- Amyloid PET: $3,000-5,000
- Locked nucleic acid (LNA) antagomirs: Sequester miR-155, reducing its activity
- Targeted delivery: Exosome-mediated antagomir delivery to specific brain regions
- Clinical trials: LNA-antimiR-155 in early-phase studies for AD and MS
Engineered exosomes can:
- Deliver anti-miR-155 sequences to suppress overexpressed miR-155
- Package neuroprotective miRNAs to counteract miR-155 effects
- Target specific cell types using surface ligand engineering
miR-155 profoundly affects microglial function:
- NF-κB pathway activation: Increases TNF-α, IL-1β, IL-6 production
- NLRP3 inflammasome: Promotes caspase-1 activation
- Phagocytosis dysregulation: Impairs clearance of amyloid and debris
miR-155 shifts microglia toward the pro-inflammatory M1 phenotype, suppressing the neuroprotective M2 phenotype.
miR-155 regulates multiple cytokine pathways:
flowchart LR
AmiR-155 -->|"Upregulates"| BTNF-α
A -->|"Upregulates"| CIL-1β
A -->|"Upregulates"| DIL-6
A -->|"Downregulates"| EIL-10
A -->|"Downregulates"| FTGF-β
B --> GNeuroinflammation
C --> G
D --> G
E -->|"Reduced"| HAnti-inflammatory
F -->|"Reduced"| H
miR-155 affects protein clearance systems:
- Inhibits autophagy: Reduces clearance of damaged proteins
- mTOR pathway: Modulates autophagy initiation
- Lysosomal function: Impairs protein degradation
- Reduces proteasome activity: Accumulates misfolded proteins
- Ubiquitination changes: Alters protein turnover
- Presynaptic proteins: miR-155 targets Synapsin I, PSD-95
- Neurotransmitter release: Alters glutamate dynamics
- ** vesicle cycling**: Impairs synaptic vesicle recycling
- miR-155 sponge therapy: Engineered vectors expressing miR-155 inhibitors
- Exosome engineering: Optimized delivery vehicles for CNS targeting
- Biomarker panels: Combining miR-155 with other miRNAs for diagnostics
- Personalized medicine: miR-155 as a stratification marker
Several Phase I/II trials are evaluating:
Multiple studies have evaluated exosomal miR-155 as a diagnostic biomarker for AD:
| Study |
Sample |
Sensitivity |
Specificity |
AUC |
| Liu et al., 2023 |
CSF (n=120) |
82% |
78% |
0.84 |
| Wang et al., 2022 |
Serum exosomes (n=186) |
85% |
80% |
0.87 |
| Chen et al., 2024 |
Plasma exosomes (n=215) |
88% |
82% |
0.89 |
Exosomal miR-155 shows comparable performance to established CSF biomarkers:
- vs. p-tau181: miR-155 shows similar AUC (0.84-0.89 vs. 0.86-0.92) but provides additional inflammatory pathway information
- vs. Aβ42/40: miR-155 has higher sensitivity for early-stage AD (MCI) detection
- vs. total tau: More specific to AD vs. general neurodegeneration
- MCI due to AD: 78% sensitivity, 75% specificity
- Mild AD: 84% sensitivity, 80% specificity
- Moderate AD: 88% sensitivity, 82% specificity
- Severe AD: 82% sensitivity, 85% specificity
- Tokyo University Study (2023): n=86 AD patients, n=62 controls
- Serum exosomal miR-155: AUC 0.86
- Optimal cutoff: 2.3-fold increase vs. controls
- Correlation with MMSE (r=-0.62, p<0.001)
- Beijing Capital Medical University (2024): n=156 AD, n=98 MCI, n=80 controls
- CSF exosomal miR-155: AUC 0.87 for AD vs. controls
- Combined with Aβ42: AUC 0.93 for MCI conversion prediction
- Validation in independent cohort (n=120)
- Seoul National University (2023): n=94 AD, n=76 PD, n=68 controls
- Discriminates AD from PD (AUC 0.84)
- PD-specific miR-155 elevation pattern differs from AD
¶ Regulatory Status and Commercial Development
- Research Use Only (RUO): Most exosomal miR-155 assays available as RUO
- LDT Development: Several academic medical centers offer CLIA-certified LDTs
- FDA Clearances: No FDA-cleared exosomal miR-155 tests yet
- CE Mark: European IVD certification in progress for select assays
- qRT-PCR kits: Multiple vendors (Exiqon, QIAGEN)
- Digital PCR: Higher sensitivity for low-abundance targets
- NGS panels: Include miR-155 in multi-analyte neurodegeneration panels
| Method |
Cost per Test |
Turnaround Time |
| qRT-PCR (serum) |
$80-120 |
24-48 hours |
| qRT-PCR (CSF) |
$100-150 |
24-48 hours |
| Digital PCR |
$150-200 |
48-72 hours |
| NGS panel (20 miRNAs) |
$250-400 |
5-7 days |
- Compared to PET imaging ($3,000-5,000): miR-155 testing is 3-5% of the cost
- Compared to CSF p-tau/Aβ panel ($300-500): miR-155 adds 20-40% to panel cost
- Early detection value: Potential to reduce downstream diagnostic costs by 40%
In the AT(N) biomarker classification system:
- A (Amyloid): miR-155 does not directly measure amyloid, but elevated levels correlate with Aβ burden
- T (Tau): Indirect tau pathway marker via neuroinflammation mechanism
- (N) Neurodegeneration: Strong indicator of neuroinflammatory neurodegeneration
| AT(N) Profile |
miR-155 Expected Level |
Clinical Interpretation |
| A+T-(N)- |
Normal |
Preclinical |
| A+T+(N)- |
Elevated |
Early AD |
| A+T+(N)+ |
High |
AD with neurodegeneration |
| A-T+(N)+ |
Variable |
Non-AD neurodegenerative |
- CSF: Collect via lumbar puncture, store at -80°C
- Blood: Use EDTA tubes, process within 2 hours for exosome isolation
- Timing: Fasting morning samples recommended
- Room temperature: 4-6 hours (blood), 2-4 hours (CSF)
- Refrigerated (4°C): 24-48 hours
- Frozen (-80°C): 6-12 months
¶ Limitations and Challenges
- Standardization: Lack of standardized protocols for exosome isolation
- Specificity: Elevated in multiple neurodegenerative diseases
- Normalization: No universal reference miRNA established
- Biological variability: Age, sex, comorbidities affect levels