BDNF Seminar Spring 2010 Maneeshi Prasad Jan 29

BDNF Seminar Spring 2010 Maneeshi Prasad Jan 29 th 2010

dl. PFC (dorsolateral prefrontal cortex) • dl. PFC is the last area (45 th) to develop (myelinate) in the human cerebrum. • dl. PFC 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)

dl. PFC • dl. PFC 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 dl. PFC. • dl. PFC 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 Trk. B receptor and p 75 NTR receptor

BDNF in CNS • Alternative promoter usage provides differential m. RNA stability and subcellular localization • Promoter IV of BDNF has been implicated in forming inhibitory synapses in the cortex • BDNF m. RNA with long 3’UTR are localized in dendrites of cortical neurons, while short 3’UTR m. RNA is restricted to soma • Loss of long 3’UTR m. RNA results in denser and thinner dendritic spines of CA 1 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 pro. BDNF to m. BDNF promotes late-phase long-term potentiation expression in hippocampus • Pro. BDNF is higher during postnatal stages while m. BDNF 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 formation of ocular dominance columns in visual cortex • High levels of BDNF m. RNA its Trk. B receptor has been seen in dl. PFC of young adults which subsequently decreases in adults

DNA-RNA-Protein Gene locus on chromosome 1 2 3 DNA Transcription 1 2 3 3 m. RNA Pre-pro 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 p. H 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 m. RNA expression of housekeeping genes with changes in p. H and RIN

BDNF m. RNA expression in dl. PFC during development

BDNF m. RNA expression in dl. PFC 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 m. RNA expression in dl. PFC during development • Transcript II-IX was low at birth, increased during 1 st 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 m. RNA expression in dl. PFC 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 m. RNA expression in dl. PFC 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 dl. PFC during development • Both pro. BDNF (28 k. Da) and mature BDNF (14 k. Da) 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 m. RNA levels

BDNF distribution in dl. PFC 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 dl. PFC • 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 m. RNA 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 h. DLPFC 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

Thank You !