¶ CCL25 (C-C Motif Chemokine Ligand 25)
CCL25 (C-C Motif Chemokine Ligand 25), also known as Thymus Expressed Chemokine (TECK), is a chemokine originally identified in the thymus that plays crucial roles in T cell development and mucosal immunity. CCL25 binds exclusively to CCR9, making it a unique target for therapeutic modulation. In the nervous system, CCL25/CCR9 signaling has been implicated in neuroinflammation, gut-brain axis communication, and potentially in neurodegenerative diseases.
|
|
| Symbol |
CCL25 |
| NCBI Gene ID |
6374 |
| Chromosome |
19p13.2 |
| Protein Class |
Chemokine |
| Molecular Weight |
~9.4 kDa |
CCL25 has distinct functions in immune development and homeostasis:
- T cell development: Critical for thymocyte migration and T cell development in the thymus
- Gut homing: Guides α4β7+ T cells to intestinal lamina propria via CCR9
- Mucosal immunity: Important for immune surveillance of gastrointestinal tract
- Neuroinflammation: Modulates inflammatory responses in CNS
- Gut-brain axis: Potential pathway for gut-immune-brain communication
- Blood-brain barrier: May influence BBB function under inflammatory conditions
CCL25 has a unique receptor profile:
- CCR9 (CC Chemokine Receptor 9): The sole receptor for CCL25
- Expression: High on small intestinal T cells, thymocytes, and some inflammatory cells
- Alternative: Can also bind to CCR9 splice variants
CCL25/CCR9 activates characteristic chemokine signaling:
- Gαi signaling: Inhibition of adenylate cyclase
- PLC-IP3 pathway: Calcium mobilization
- PI3K/Akt pathway: Cell survival and migration
- MAPK/ERK pathway: Cell activation and proliferation
- Rho GTPases: Actin cytoskeleton reorganization
CCR9 is over-expressed in several disease contexts:
- Inflammatory bowel disease
- Colorectal cancer metastasis
- Certain leukemias
- Autoimmune conditions
CCL25/CCR9 activates characteristic chemokine signaling:
- Gαi signaling: Inhibition of adenylate cyclase
- PLC-IP3 pathway: Calcium mobilization
- PI3K/Akt pathway: Cell survival and migration
- MAPK/ERK pathway: Cell activation and proliferation
- Rho GTPases: Actin cytoskeleton reorganization
The CCL25/CCR9 axis plays a significant role in the gut-brain communication pathway, which has emerged as a critical factor in neurodegenerative disease pathogenesis.
- CCL25 is highly expressed in the small intestine, particularly in the crypt epithelium
- CCR9+ T cells home to the intestinal lamina propria under homeostatic conditions
- The intestinal immune system communicates with the CNS through multiple pathways:
- Vagal afferent nerves
- Circulating immune mediators
- Microbial metabolites (short-chain fatty acids, bile acids)
- Endocrine signaling
- Gut microbiota can influence CCL25 expression in intestinal epithelial cells
- Dysbiosis alters CCR9+ T cell trafficking and may affect systemic inflammation
- Probiotic interventions may modulate CCL25/CCR9 axis in therapeutic contexts
- CCL25/CCR9 signaling affects tight junction integrity in intestinal epithelium
- Increased intestinal permeability ("leaky gut") associated with neuroinflammation
- Potential for CCL25-targeted interventions to restore barrier function
In Alzheimer's disease, the CCL25/CCR9 axis contributes to neuroinflammation through several mechanisms:
- Amyloid-beta effects: Aβ peptides can induce CCL25 expression in astrocytes and microglia
- Microglial activation: CCR9 signaling modulates microglial phenotypic polarization
- T cell trafficking: Peripheral T cells expressing CCR9 may enter the CNS in AD
- Blood-brain barrier: CCL25 may affect BBB permeability through endothelial cell activation
Research has shown elevated CCL25 levels in cerebrospinal fluid of AD patients compared to controls, suggesting potential as a biomarker.
The CCL25/CCR9 axis is implicated in Parkinson's disease through gut-brain axis mechanisms:
- Enteric nervous system: CCR9+ T cells accumulate in the gut in PD
- Alpha-synuclein propagation: Gut inflammation may accelerate synucleinopathy spread
- Dopaminergic neurons: CCL25 may directly affect survival of dopaminergic neurons
- Microbiota-gut-brain axis: CCL25 expression modulated by gut microbiome alterations
CCL25 plays complex roles in multiple sclerosis:
- T cell recruitment: CCR9+ T cells may traffic to CNS lesions
- Intestinal immune dysfunction: MS patients often exhibit gut immune abnormalities
- Therapeutic potential: CCR9 antagonists explored for MS treatment
- Remyelination: CCL25 may influence oligodendrocyte precursor cell function
CCL25 participates in neuroinflammatory processes:
- Modulates T cell trafficking into CNS
- Influences blood-brain barrier permeability
- May interact with other chemokines in inflammatory cascades
- Potential role in autoimmune encephalitis
- Cytokine storm modulation in neuroinflammatory conditions
- Inflammatory bowel disease (Crohn's disease particularly)
- Celiac disease
- Type 1 diabetes
- Certain cancers (colorectal, pancreatic)
- HIV infection
- Graft-versus-host disease
CCL25 expression is tissue-specific:
| Cell Type |
Expression Level |
Notes |
| Thymic epithelial cells |
High |
Constitutive expression |
| Small intestine |
High |
Lamina propria |
| Dendritic cells |
Moderate |
Intestinal mucosa |
| Brain |
Low |
Inducible under inflammation |
| Astrocytes |
Low-Medium |
Inducible by cytokines |
| Microglia |
Low |
Baseline, increases in disease |
| Endothelial cells |
Variable |
BBB in inflammation |
CCL25 expression is dynamically regulated:
- Inflammatory cytokines: TNF-α, IL-1β, and IFN-γ upregulate CCL25
- Microbial signals: TLR agonists can induce CCL25 expression
- Hormonal regulation: Estrogen may modulate CCL25 levels
- Epigenetic control: DNA methylation patterns affect CCL25 transcription
The CCL25/CCR9 axis is a therapeutic target with multiple intervention strategies:
- CCR9 Antagonists: Small molecule inhibitors that block CCL25-CCR9 binding
- CCL25 Neutralizing Antibodies: Monoclonal antibodies that sequester CCL25
- Decoy Receptors: Soluble CCR9 extracellular domains that compete for ligand
- RNAi-based Therapies: siRNA or antisense oligonucleotides targeting CCL25 or CCR9
The CCL25/CCR9 axis has been targeted in several clinical contexts[yokota2006]:
- Inflammatory Bowel Disease: CCR9 antagonists in Phase I/II trials showed efficacy in Crohn's disease
- Celiac Disease: CCL25-blocking strategies investigated for refractory disease
- Asthma: Investigated for eosinophilic airway inflammation
- Cancer Metastasis: CCR9 inhibition to prevent tumor spread, particularly in colorectal cancer
- Transplant: CCR9 blockade to prevent graft-versus-host disease
Several CCR9-targeted agents have been developed:
| Drug |
Type |
Status |
Developer |
| CCX8037 |
Oral CCR9 antagonist |
Pre-clinical |
ChemoCentryx |
| CCX5216 |
Potent CCR9 antagonist |
Phase I |
ChemoCentryx |
| Anti-CCL25 mAb |
Neutralizing antibody |
Pre-clinical |
Various |
| GS-5740 |
Anti-CCL25 antibody |
Phase II |
Gilead |
- Alzheimer's disease: CCR9 antagonists may reduce neuroinflammation and Aβ-induced damage
- Parkinson's disease: Modulation of gut-brain axis inflammation through CCL25 inhibition
- Multiple sclerosis: CCR9 blockade may reduce CNS-infiltrating T cells
- Amyotrophic lateral sclerosis: Potential for modulating inflammatory responses
¶ Challenges and Considerations
- BBB penetration: Ensuring therapeutic agents reach CNS targets
- Homeostatic vs. inflammatory roles: Targeting CCL25 without disrupting normal immune function
- Biomarker development: Identifying patient subgroups most likely to benefit
- Combination therapies: Potential synergies with other immunomodulatory agents