Brain-Derived Neurotrophic Factor (BDNF)

Overview

Brain-Derived Neurotrophic Factor (BDNF) is a critical neurotrophin encoded by the BDNF gene that supports the survival, growth, and plasticity of neurons throughout the central and peripheral nervous systems^{1Neurotrophins: roles in neuronal development and function2001 · Annual Review of Neuroscience · DOI 10.1146/annurev.neuro.24.1.677Open reference}. This secreted protein belongs to the neurotrophin family and exists in two forms: pro-BDNF (27.8 kDa) and mature BDNF (13.5 kDa), which have distinct biological activities and receptor specificities^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}. BDNF is widely expressed in the brain, with particularly high levels in the hippocampus, cortex, and basal forebrain, regions critical for learning, memory, and mood regulation^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}.

BDNF plays essential roles in neurodevelopment and adult brain function, and its dysregulation has been implicated in numerous neurological and psychiatric disorders including Alzheimer’s disease, Parkinson’s disease, depression, and anxiety^{4Exercise: a behavioral intervention to enhance brain health and plasticity2002 · Trends in Neurosciences · DOI 10.1016/S0074-7742(02Open reference}.

Biology of BDNF

Pro-BDNF vs Mature BDNF

BDNF is initially synthesized as a precursor molecule (pro-BDNF) that can be cleaved to generate mature BDNF:

The balance between pro-BDNF and mature BDNF is critical for proper neuronal function and is regulated by proteolytic cleavage via plasmin and matrix metalloproteinases (MMPs)^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}.

Receptor Signaling

BDNF signals through two classes of receptors:

TrkB (Tropomyosin receptor kinase B)

• High-affinity receptor for mature BDNF

• Tyrosine kinase signaling

• Promotes neuronal survival, differentiation, and plasticity

• Three isoforms: full-length TrkB, TrkB.T1, TrkB.T2^{5The Trk family of neurotrophin receptors1994 · Journal of Neurobiology · DOI 10.1111/j.1432-0436.1994.tb00068.xOpen reference}

p75^NTR (p75 neurotrophin receptor)

• Low-affinity receptor for both pro- and mature BDNF

• Can signal apoptosis when unoccupied by other neurotrophins

• Modulates TrkB signaling

• Expressed in developing neurons and reactive astrocytes^{6p75 and Trk: a two-receptor system2020 · Trends in Neurosciences · DOI 10.1016/j.tics.2020.04.007Open reference}

Normal Physiological Functions

Neurodevelopment

During development, BDNF is essential for:

• Neuronal differentiation: Promotes differentiation of neural progenitor cells

• Axon guidance: Directs axonal growth cones

• Synaptogenesis: Facilitates formation of functional synapses

• Pruning: Regulates developmental synaptic elimination^{1Neurotrophins: roles in neuronal development and function2001 · Annual Review of Neuroscience · DOI 10.1146/annurev.neuro.24.1.677Open reference}

Adult Brain Function

In the adult brain, BDNF supports:

• Synaptic plasticity: LTP and LTD at hippocampal and cortical synapses

• Learning and memory: Critical for hippocampus-dependent memory formation

• Mood regulation: Alters emotional processing

• Neurogenesis: Supports adult hippocampal neurogenesis^{7Neurotrophins as synaptic modulators2001 · Nature Reviews Neuroscience · DOI 10.1038/350445a0Open reference}

Activity-Dependent Regulation

BDNF expression is highly activity-dependent:

• Neuronal activity: Calcium influx increases BDNF transcription

• Exercise: Physical activity upregulates BDNF in hippocampus

• Learning: Novel experiences elevate BDNF expression

• Environmental enrichment: Enhanced sensory input boosts BDNF^{8Activity-dependent neurotrophic factor2018 · Trends in Neurosciences · DOI 10.1016/j.tins.2018.03.008Open reference}

Role in Neurodegenerative Diseases

Alzheimer’s Disease

BDNF is intimately involved in AD pathogenesis:

1. Amyloid-Beta effects: Aβ reduces BDNF expression and signaling

2. Tau pathology: NFT formation impairs BDNF trafficking

3. Synaptic loss: BDNF deficit contributes to synaptic dysfunction

4. Cognitive decline: Lower BDNF correlates with cognitive impairment

Therapeutic approaches include BDNF delivery and TrkB agonists^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}0.

Parkinson’s Disease

In PD, BDNF supports dopaminergic neuron survival:

• Nigral vulnerability: Reduced BDNF contributes to SNc neuron loss

• Neuroprotection: BDNF promotes dopaminergic neuron survival

• Therapeutic delivery: AAV-BDNF in clinical trials for PD

• Exercise benefits: Exercise-induced BDNF may be protective^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}1

Depression and Mood Disorders

BDNF is a key mediator of antidepressant efficacy:

• Depression association: Low BDNF levels in depressed patients

• Antidepressant effects: Most antidepressants increase BDNF

• Ketamine action: Rapid antidepressant effects via TrkB signaling

• Exercise benefits: Exercise improves mood through BDNF^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}2

Therapeutic Strategies

BDNF Delivery

1. Recombinant BDNF: Protein delivery approaches

2. Gene therapy: AAV-mediated BDNF expression

3. Cell therapy: Stem cell-derived neuronal progenitors secreting BDNF

TrkB Agonists

1. Small molecule agonists: 7,8-DHF and analogs

2. Peptide agonists: TrkB-specific peptides

3. Antibody-based agonists: Engineered TrkB antibodies

Lifestyle Interventions

Structure and Biochemistry

BDNF structure has been characterized:

The mature BDNF forms a homodimer that binds two TrkB receptors, triggering dimerization and autophosphorylation^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}3.

Genetic Variants

BDNF Val66Met Polymorphism

The most studied BDNF polymorphism:

• Location: Codon 66 in prodomain

• Prevalence: ~30% of Caucasians are Met carriers

• Effects: Alters activity-dependent secretion

• Associations: Memory performance, depression risk, AD risk^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}4

Other Variants

• Promoter polymorphisms: Affect BDNF expression

• Rare pathogenic mutations: Cause neurodevelopmental disorders

• Copy number variants: Associated with psychiatric disorders

Animal Models

BDNF Knockout Mice

• Embryonic lethal: Complete KO is perinatal lethal

• Conditional KO: Tissue-specific knockouts reveal regional functions

• Heterozygotes: Partial loss shows cognitive deficits

Transgenic Models

• BDNF overexpression: Enhanced learning and memory

• Pro-BDNF overexpression: Depression-like phenotype

• Humanized models: Express human BDNF variants^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}5

Key Publications

1. BDNF function in the brain. Annual Review of Medicine. 2009^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}6.

2. Pro-BDNF and mature BDNF. Trends in Neurosciences. 2010^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}7.

3. BDNF in Alzheimer’s disease. Neurobiology of Aging. 2019^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}8.

4. Exercise and BDNF. Neuroscience. 2020^{2BDNF-based synaptic plasticity as a therapy for depression2013 · Nature Reviews Neuroscience · DOI 10.1038/nrn3435Open reference}9.

5. BDNF and depression. Pharmacology & Therapeutics. 2020^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}0.

External Links

• UniProt: P23560

• AlphaFold: BDNF

• PDB: 1BND, 1B8M

• OMIM: 113505

• GeneCards: BDNF

See Also

• Proteins Index

• Genes Index

• Alzheimer’s Disease

• Parkinson’s Disease

• Depression

• Synaptic Plasticity

• Neurotrophin Signaling

Brain Atlas Resources

• Allen Human Brain Atlas - BDNF Expression

• Allen Cell Type Atlas - BDNF

• BrainSpan - BDNF Developmental Expression

• Allen Mouse Brain Atlas - BDNF

Additional Content (merged from /entities/bdnf)

Brain-Derived Neurotrophic Factor (BDNF)

Introduction

Brain Derived Neurotrophic Factor (Bdnf) is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes. ^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}1

Overview

Brain-Derived Neurotrophic Factor (BDNF) is a member of the neurotrophin family of growth factors that plays essential roles in neuronal survival, differentiation, synaptic plasticity, and cognitive function. BDNF is the most abundant neurotrophin in the adult brain, with particularly high expression in the hippocampus, cerebral [cortex, and basal-ganglia . In the context of [neurodegenerative diseases, BDNF has emerged as a central mediator linking synaptic dysfunction, neuronal loss, and cognitive decline. ^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}2

Reduced BDNF expression has been consistently documented in alzheimers, parkinsons, huntington-pathway, and als, making it both a promising biomarker and a therapeutic target for neurodegenerative conditions . The dual signaling system of mature BDNF (via TrkB receptors promoting survival) and proBDNF (via p75NTR promoting [apoptosis) provides a nuanced framework for understanding how neurotrophic signaling goes awry in neurodegeneration. ^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}3

Structure, Processing, and Isoforms

Gene Structure

The human BDNF gene is located on chromosome 11p14.1 and has a complex structure with multiple promoters and at least nine 5’ non-coding exons, each spliced to a common 3’ coding exon. This architecture allows tissue-specific and activity-dependent regulation of BDNF expression. ^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}4

Protein Processing

BDNF is initially synthesized as a precursor protein (preproBDNF, ~32 kDa), which is cleaved to proBDNF (~28 kDa) in the endoplasmic reticulum. ProBDNF can be further processed to mature BDNF (~14 kDa) by intracellular furin or proprotein convertases, or extracellularly by plasmin and matrix metalloproteinases. Critically, proBDNF and mature BDNF have distinct and often opposing biological activities : ^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}5

• Mature BDNF (mBDNF): Promotes neuronal survival, long-term-potentiation, long-term potentiation (long-term-potentiation, and dendritic growth

• ProBDNF: Promotes apoptosis, long-term depression (LTD), and synaptic elimination

This yin-yang relationship between mBDNF and proBDNF is central to understanding BDNF’s role in both normal brain function and neurodegeneration. ^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}6

Receptor Signaling Pathways

TrkB Receptor Signaling (Pro-Survival)

Mature BDNF binds with high affinity to the tropomyosin receptor kinase B (TrkB, also known as NTRK2), triggering receptor homodimerization and autophosphorylation of intracellular tyrosine residues. This activates three major downstream signaling cascades : ^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}7

1. MAPK/ERK pathway: Ras-Raf-MEK-ERK cascade promoting neuronal differentiation, survival, and synaptic plasticity. Activates transcription factors CREB and Elk-1.

2. PI3K/Akt pathway: Phosphoinositide 3-kinase activation leading to Akt phosphorylation, which inhibits pro-apoptotic factors (Bad, gsk3-beta, caspase-9) and activates mtor-neurodegeneration signaling for protein synthesis and cell growth.

3. PLCγ/IP3/DAG pathway: Phospholipase Cγ activation generating inositol trisphosphate (IP3) and diacylglycerol (DAG), mobilizing intracellular calcium stores and activating protein kinase C (PKC). This pathway is particularly important for synaptic plasticity and long-term-potentiation.

p75NTR Receptor Signaling (Pro-Apoptotic)

ProBDNF preferentially binds to the p75 neurotrophin receptor (p75NTR), often in complex with the co-receptor sortilin. This activates : ^{3New insights into brain BDNF function in depression: implications for neuropharmacology2019 · Neuroscience · DOI 10.1016/j.neuroscience.2019.09.017Open reference}8

• JNK signaling cascade: c-Jun N-terminal kinase activation leading to apoptosis

• nf-kb pathway: Nuclear factor kappa B activation, which can promote either survival or death depending on context

• RhoA-GDI complex: Regulation of growth cone dynamics and neurite retraction

• Ceramide production: Sphingomyelin hydrolysis generating the pro-apoptotic lipid ceramide

The balance between TrkB and p75NTR signaling is critical: in neurodegeneration, reduced mBDNF levels and increased proBDNF may shift this balance toward pro-apoptotic signaling.

Val66Met Polymorphism

The Val66Met single nucleotide polymorphism (rs6265) in the BDNF gene is the most extensively studied genetic variant, present in approximately 20-30% of the population (higher frequency in Asian populations). The methionine substitution at codon 66 in the prodomain :

• Impairs activity-dependent secretion: Disrupts binding to sortilin and intracellular trafficking of BDNF-containing vesicles, reducing regulated (but not constitutive) secretion

• Reduces hippocampal volume: Met carriers show decreased hippocampal and prefrontal cortex volume on neuroimaging

• Affects memory: Associated with reduced performance on hippocampal-dependent episodic memory tasks

• Modifies disease risk: While not strongly deterministic, Val66Met modulates risk and progression of alzheimers, depression, anxiety disorders, and post-traumatic stress disorder

Role in Neurodegenerative Diseases

Alzheimer’s Disease

BDNF is profoundly reduced in alzheimers, particularly in the hippocampus and temporal cortex—regions most affected by AD pathology. The mechanisms linking BDNF deficiency to AD include :

• amyloid-beta toxicity: amyloid-beta oligomers reduce BDNF expression and disrupt TrkB signaling, creating a feedforward cycle of synaptic-dysfunction

• tau-protein(/proteins/tau pathology]: BDNF depletion accelerates tau] hyperphosphorylation] through reduced PI3K/Akt signaling and subsequent gsk3-beta activation

• Cholinergic degeneration: BDNF is a key survival factor for cholinergic neurons of the nucleus-basalis-of-meynert

• neuroinflammation: BDNF deficiency exacerbates microglial/cell-types/microglia:

• Reduced BDNF mRNA and protein levels are found in the substantia nigra of PD patients

• Downregulation of TrkB signaling contributes to dopaminergic neuron vulnerability

• alpha-synuclein aggregates impair BDNF-TrkB signaling

• BDNF supports nigrostriatal dopaminergic neuron survival, and its loss accelerates neurodegeneration

Huntington’s Disease

The mutant huntingtin protein] in huntington-pathway directly impairs BDNF transcription and axonal transport :

• Wild-type huntingtin normally promotes BDNF transcription by sequestering the repressor REST/NRSF in the cytoplasm

• Mutant huntingtin fails to sequester REST, leading to transcriptional repression of BDNF

• Cortical BDNF delivery to the striatum via corticostriatal projections is impaired

• Striatal medium spiny neurons are particularly dependent on cortically-derived BDNF for survival

Amyotrophic Lateral Sclerosis

In als, BDNF levels are altered in motor neurons and surrounding astrocytes. While BDNF supports motor neuron survival in vitro, clinical trials of BDNF delivery in ALS patients have produced disappointing results, possibly due to difficulties achieving adequate concentrations at motor neuron cell bodies .

Therapeutic Strategies Targeting BDNF

Direct BDNF Delivery

• Intracerebroventricular (ICV) infusion: Limited by poor brain penetration and short half-life

• Gene therapy: AAV-BDNF vectors delivered to the hippocampus or entorhinal cortex in AD models show neuroprotection

• Cell-based delivery: Transplantation of BDNF-secreting cells

Indirect BDNF Enhancement

Several approaches to boosting endogenous BDNF production are under investigation :

• Physical exercise: The most robust non-pharmacological intervention for increasing brain BDNF levels; aerobic exercise increases peripheral and central BDNF

• BDNF mimetics: Small molecules that activate TrkB signaling (e.g., 7,8-dihydroxyflavone, LM22A-4)

• Antidepressants: SSRIs and other antidepressants upregulate BDNF expression through CREB activation

• Ketamine: Rapidly increases BDNF translation through mtor-neurodegeneration-dependent signaling

• Dietary interventions: Caloric restriction and intermittent fasting increase BDNF expression

• hdac-enzymes inhibitors]: Epigenetic modulation to enhance BDNF transcription

• TrkB agonist antibodies: Engineered antibodies that selectively activate TrkB signaling

BDNF as a Biomarker

Serum and plasma BDNF levels have been investigated as potential biomarkers for neurodegenerative diseases. Key findings include :

• Reduced serum BDNF in early AD correlates with cognitive decline

• Decreased BDNF levels in PD correlate with motor severity and non-motor symptoms

• BDNF levels change with disease progression, potentially useful for monitoring

• Limitations include peripheral sources of BDNF (platelets store ~99% of blood BDNF), high variability, and lack of disease specificity

Brain Atlas Resources

• Allen Human Brain Atlas: Brain-Derived Neurotrophic Factor expression search

• Allen Mouse Brain Atlas: Brain-Derived Neurotrophic Factor search

• Allen Cell Type Atlas: Transcriptomic cell type reference

• BrainSpan Developmental Transcriptome: Brain-Derived Neurotrophic Factor developmental expression

See Also

• BDNF

Background

The study of Brain Derived Neurotrophic Factor (Bdnf) has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

External Links

• PubMed - Biomedical literature

• Alzheimer’s Disease Neuroimaging Initiative - Research data

• Allen Brain Atlas - Brain gene expression data

Signaling Pathways

flowchart TD
    A["BDNF Release"]  -->  B["TrkB Receptor Dimerization"]
    B  -->  C["Autophosphorylation"]
    
    C  -->  D["PI3K/Akt Pathway"]
    C  -->  E["Ras/MAPK Pathway"]
    C  -->  F["PLCgamma Pathway"]
    
    D  -->  G["Cell Survival"]
    D  -->  H["Protein Synthesis"]
    E  -->  I["Gene Expression"]
    E  -->  J["Synaptic Plasticity"]
    F  -->  K["Calcium Signaling"]
    K  -->  L["Neurotransmitter Release"]
    
    M["AD Pathology"]  -->  N["Reduced BDNF"]
    M  -->  O["Impaired TrkB Signaling"]
    N  -->  P["Synaptic Loss"]
    O  -->  P
    
    style M fill:#3b1114
    style P fill:#3b1114