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BDNF Seminar Spring 2010
Maneeshi Prasad
Jan 29th 2010
dlPFC (dorsolateral
prefrontal cortex)
• dlPFC is the last area (45th) to develop
(myelinate) in the human cerebrum.
• dlPFC is connected to the orbitofrontal cortex,
thalamus, parts of the basal ganglia (the dorsal
caudate nucleus), the hippocampus, and primary
and secondary association areas of neocortex,
including posterior temporal, parietal, and
occipital areas.
Jon S. Simons & Hugo J. Spiers
Nature Reviews Neuroscience 4, 637-648 (August 2003)
dlPFC
• dlPFC serves as the highest cortical area responsible for motor
planning, organization, and regulation.
• It plays an important role in the integration of sensory and
mnemonic information and the regulation of intellectual function
and action.
• It is also involved in working memory.
• Complex mental activities require additional cortical and subcortical
circuits that are connected with dlPFC.
• dlPFC development and maturation may last up to two decades in
humans and may thus show differential expression of genes.
BDNF
• Brain-derived neurotrophic factor belongs to
"neurotrophin" family of growth factors
• BDNF support growth and differentiation of new
neurons and synapses in CNS and PNS
• BDNF is active in the hippocampus, cortex, cerebellum
and basal forebrain—areas vital to learning, memory,
and higher thinking
• BDNF is also involved in neurogenesis
• BDNF binds to TrkB receptor and p75NTR receptor
BDNF in CNS
• Alternative promoter usage provides differential mRNA stability
and subcellular localization
• Promoter IV of BDNF has been implicated in forming inhibitory
synapses in the cortex
• BDNF mRNA with long 3’UTR are localized in dendrites of cortical
neurons, while short 3’UTR mRNA is restricted to soma
• Loss of long 3’UTR mRNA results in denser and thinner dendritic
spines of CA1 pyramidal neurons and reduced hippocampal longterm potentiation
• Rat visual cortex shows expression of transcripts III-V and IV-V in
cell soma, while IV-V is expressed in dendritic processes
BDNF in CNS
• Early postnatal development shows greater
increase in spine density which is reduced by
~40% in later life
• Conversion of proBDNF to mBDNF promotes
late-phase long-term potentiation expression in
hippocampus
• ProBDNF is higher during postnatal stages while
mBDNF is prominent in adults
Yang, J. et al. (2009) Nat. Neurosci. 12:113.
BDNF during development
• Plays a important role during cortical
development and is required for formation of
ocular dominance columns in visual cortex
• High levels of BDNF mRNA its TrkB receptor
has been seen in dlPFC of young adults which
subsequently decreases in adults
DNA-RNA-Protein
Gene locus on chromosome
1
2
3
DNA
Transcription
1
2
3
3
mRNA
Pre-pro Protein
Protein
2
Translation
Processing by cleavage
Mature protein
Alternative transcripts of BDNF
West et al, 2001
Brain-derived neurotrophic factor (BDNF) gene structure
Human BDNF gene structure
• 10 noncoding exons in the 5’UTR
• Presence of multiple translational (ATG) start
sites
The Brian
Table. 1. Brain cohort demographics
Demographic variables
• Postmortem pH values: 6.12-6.98
• Postmortem Interval (PMI): 4 hr-32 hr
• RNA integrity (RIN) varied
Expression of housekeeping genes across
development
No variation in mRNA expression of housekeeping genes with changes in
pH and RIN
BDNF mRNA expression in dlPFC during development
BDNF mRNA expression in dlPFC during development
• Transcript I-IX changed significantly across development
▫
▫
▫
▫
Higher during earlier stages
Peaked at infancy
Decreased after infancy
Constant level was maintained from school age till adulthood
BDNF mRNA expression in dlPFC during development
• Transcript II-IX was low at birth, increased during
1st few years and peaked in toddlers
▫ Lowest in neonates
▫ Increased in infants and toddlers
▫ Decreased during school age, similar to infants, and
was maintained till adulthood
BDNF mRNA expression in dlPFC during development
• Transcript IV-IX highest in infants and toddlers
▫ Lowest in neonates
▫ Increased in infants and toddlers age group
▫ Decreased gradually from school age and stayed
consistent from adolescent till adulthood
BDNF mRNA expression in dlPFC during development
• Transcript VI-IX peaks within first years of life
▫ Highest at infancy
▫ Decreased subsequently from toddler age till
adulthood
Real-Time PCR
v
BDNF Protein levels
BDNF protein expression in dlPFC during development
• Both proBDNF (28 kDa) and mature BDNF (14 kDa) bands
were seen at all ages
• Protein expression increased from neonates to infants
• Infants had highest level of BDNF expression followed by
toddlers
• Mature BDNF form varied across development and peaked at
infancy
• Increase of protein level in toddler age group might be related
to increase in level of IV-IX or II-IX transcripts
• Decrease in protein levels in adults matches with decrease in
mRNA levels
BDNF distribution in dlPFC by ISH
BDNF
transcript
Expression of BDNF transcripts in layer IV
BDNF
transcript
Expression of BDNF transcripts in layer V & VI
BDNF
transcript
BDNF distribution in dlPFC
• All 4 BDNF transcripts were highest in deeper
cortical layers V and VI
▫
▫
▫
▫
Layer I: no expression at any age group
Layer II: moderate expression
Layer III: robust expression was seen in neonates
Layer IV/mid cortical layer: lower expression
neonates and low to moderate expression in older
age group
▫ Layer V and VI: intense staining for BDNF seen in
neurons
Discussion
• Transcripts I-IX, IV-IX and VI-IX had highest
expression patters in infancy
• II-IX transcript was highest at toddler age group
and was delayed by 2-3 years as compared to the
other 3 transcripts
• Lower expression of all transcripts during school
age years
Discussion
• DLPFC layer IV showed increased BDNF signal
• DLPFC layer IV is enriched in inhibitory
neurons: cannot express BDNF by itself
• This BDNF signal may be due to the BDNF
mRNA that is targeted to the apical dendrites of
layer V pyramidal neurons
Discussion
• High level of BDNF transcripts & protein during
early years and overlaps with 1.5 fold increase in
synaptic density
• Synaptic density may decrease during
adolescence and stabilize by young adulthood
with cortex reaching maturity, which overlaps
with the decrease in BDNF levels
Discussion
• Current study differs from a previous study
(Webster, 2002), where BDNF expression was
lowest in infancy and higher in young adult
group
• This may be due to combining of neonatal and
infant groups, and differences in cohorts
Conclusions
• The dynamic regulation of BDNF gene in
hDLPFC may be activated in a promoter-specific
manner
• During postnatal cortical development, neuronal
morphology and synaptic density may be
regulated by transcript specific BDNF
expression