Brain-derived neurotrophic factor (BDNF) trophic support loss is a critical pathogenic mechanism in Huntington's disease (HD). BDNF, produced primarily in cortical neurons, is essential for the survival and function of striatal medium spiny neurons (MSNs). Mutant huntingtin (mHTT) disrupts BDNF synthesis, transport, and signaling, leading to progressive loss of trophic support and eventual neuronal death. This pathway describes the molecular mechanisms underlying BDNF deficit in HD.
flowchart TD
A["Cortex<br/>BDNF Production"] --> B["Corticostriatal<br/>Axonal Transport"]
B --> C["Striatum<br/>BDNF Release"]
A1["Mutant Huntingtin<br/>mHTT"] --> D["Impaired Transcription<br/>Reduced BDNF mRNA"]
A1 --> E["Defective Transport<br/>Dynein/Kinesin Dysfunction"]
A1 --> F["REST Nuclear Import<br/>Repressed BDNF Gene"]
D --> A
E --> B
F --> A
C --> G["TrkB Receptor<br/>Activation"]
G --> H["Survival Signaling<br/>PI3K/Akt, MAPK, PLCγ"]
G --> I["Synaptic Plasticity<br/>Dendritic Spines"]
H --> J["Neuronal Survival"]
I --> K["Synaptic Function"]
J --> L["MSN Survival"]
K --> L
L --> M{"Trophic Support"}
M --> N["Normal Striatal Function"]
M --> O["Trophic Deprivation<br/>MSN Death"]
click A "/genes/htt" "HTT Gene"
click L "/cell-types/striatal-medium-spiny-neurons-huntingtons" "Striatal MSNs"
click O "/mechanisms/mitochondrial-dysfunction" "Mitochondrial Dysfunction"
click F "/mechanisms/htt-transcriptional-dysregulation-pathway" "Transcriptional Dysregulation"
Mutant huntingtin disrupts BDNF gene expression in cortical neurons:[@zuccato2001]
- Mechanism: mHTT loses ability to sequester REST in cytoplasm
- REST nuclear translocation: REST enters cortical neuron nuclei
- Gene repression: REST binds to RE1 elements in BDNF promoter regions
- Result: Reduced activity-dependent BDNF transcription
- Sp1 sequestration: mHTT disrupts Sp1-mediated BDNF transcription
- CREB dysfunction: Altered cAMP response element binding protein activity
- Epigenetic silencing: Histone deacetylation at BDNF promoters
One of the most critical deficits is impaired BDNF transport along corticostriatal axons:[@gauthier2004]
- Scaffold function: Wild-type huntingtin acts as scaffold for molecular motors
- Dynein complex: Facilitates retrograde transport from terminals to cell bodies
- Kinesin-dependent transport: Enables anterograde BDNF vesicle movement
- Motor protein dysfunction: mHTT impairs dynein/dynactin complex function
- Vesicle trafficking: BDNF-containing vesicles fail to traffic efficiently
- Axonal transport defects: General disruption of microtubule-based transport
- HAP40 interaction: mHTT-HAP40 complex disrupts organelle trafficking
- Dynein light chain binding: Altered interaction with dynein components
- Microtubule disruption: mHTT affects microtubule integrity
Even when BDNF reaches striatal neurons, signaling may be compromised:[@lomberos2016]
- Reduced surface expression: TrkB receptor density decreased in HD
- Impaired internalization: Defective receptor recycling
- Signaling cascade disruption: PI3K/Akt and MAPK pathway alterations
- Akt pathway: Reduced pro-survival signaling
- ERK/MAPK pathway: Impaired synaptic plasticity signaling
- PLCγ pathway: Altered calcium signaling and synaptic function
BDNF is crucial for maintaining synaptic structures and function:[@brito2014]
- Reduced spine density: Fewer dendritic spines on MSNs
- Morphological changes: Abnormal spine shapes
- Synaptic dysfunction: Impaired excitatory neurotransmission
- Anti-apoptotic signaling: Loss of BDNF-mediated survival signals
- Metabolic support: Reduced neurotrophic regulation of glucose metabolism
- Calcium homeostasis: Impaired calcium buffering and signaling
- Cortical neurons: Produce and release BDNF
- Corticostriatal afferents: Transport BDNF to striatum
- Striatal MSNs: Receive BDNF via TrkB receptors
- Trophic support: Maintains MSN survival and function
- Cortical dysfunction: Reduced BDNF production
- Transport disruption: Impaired BDNF delivery to striatum
- Receptor changes: Altered TrkB signaling
- MSN degeneration: Progressive loss of trophic support
| Feature |
HD |
Alzheimer's |
Parkinson's |
| Neurotrophin affected |
BDNF |
NGF, BDNF |
GDNF |
| Primary deficit |
Transport/synthesis |
Receptor signaling |
Retrograde transport |
| Target neurons |
Striatal MSNs |
Cholinergic, cortical |
Dopaminergic neurons |
| Therapeutic approach |
BDNF delivery, gene therapy |
NGF infusion |
GDNF delivery |
- Protein delivery: Direct BDNF infusion (limited by blood-brain barrier)
- Gene therapy: AAV-mediated BDNF expression in striatum
- Cell therapy: BDNF-secreting cell transplantation
- 7,8-DHF: TrkB agonist in preclinical development
- R13: Small molecule BDNF mimetic
- Microtubule stabilizers: Improve axonal transport
- Motor protein modulators: Enhance dynein/kinesin function
- REST antagonists: Reduce REST-mediated repression
- Activity-dependent promoters: Drive BDNF expression
- Gauthier et al., Huntingtin controls neurotrophic support and electrical activity of adult forebrain neurons (2004)
- Zuccato et al., Loss of huntingtin-mediated BDNF gene transcription in Huntington's disease (2001)
- Strathdee et al., Cortical BDNF expression in Huntington's disease (2005)
- Baydyuk et al., BDNF signaling in the pathogenesis of Huntington's disease (2020)
- Plotkin et al., Huntingtin and the microtubule motor dynein in BDNF retrograde transport (2014)
- Britto et al., BDNF deficiency and impaired corticostriatal plasticity in HD (2014)
- Lobos et al., TrkB-mediated signaling in HD pathogenesis (2016)