Lasting Epigenetic Influence of Early-Life Adversity on the BDNF Gene

Tania L. Roth, Farah D. Lubin, Adam J. Funk, J. David Sweatt

Presented by Justin P. Smith

Background

• Early life maltreatment– Changes neural mechanisms– Psych illnesses: MAJOR DEPRESSION,

schizophrenia, bi-polar disorder

• Stress-induced changes– Neural plasticity in PFC and hippocampus• BDNF protein levels

*not a real baby

*

Background cont.

• Epigenetics!– Direct methylation of DNA– Posttranslational modification of histones• Either can + or – gene transcription

• Biochem view DNA methylation was a static process (consensus is changing)

Animals

• Male and Female Long-Evans rats• All behavior testing done during light period*• Food and water ad libitum

Design• Maltreatment vs Cross-foster care – 30 min/day for one week (PN1-7)

• Gene Assays– Tissue from PFC and Hippocampus collected PN8,

PN30 and PN90• Zebularine – DNA methylation inhibitor– Left lateral ventricle of maltreated adults (7 days)

• Zebularine or Vehicle• Maltreated females mated, pups cross-fostered– Controls – PN8, PFC and hippocampus isolated

Maltreatment

• Limited nesting resources in unfamiliar environment to stress mothers

• Pups were: stepped on, dropped, dragged, actively rejected, roughly handled

• Littermate controls exposed to + caregiving• 30 min of maltreatment, PN1-7

Infants experienced an adverse caregiving environment. (A) Qualitative assessment of the percent occurrence of pup-directed behaviors in the maltreatment condition indicates that pups experienced predominately abusive behaviors, which resulted in considerable audible pup vocalization. (B) In sharp contrast, pups experienced significant amounts of normal maternal care behaviors in the cross-fostered maternal care condition

Fig 1

Maltreatment During Infancy Decreases BDNF GeneExpression in the Adult PFC

• Assessed BDNF total mRNA levels (exon IX) PFC & hippocampus of adult males and females

• Exposed to the maltreatment paradigm as neonates• Suggests hippocampal ↑ was not exclusive to the experience

of maltreatment, reflective of other variables: – exposure to new caretakers– experience in a novel environment– and/or removal from the biological mother and home cage

Fig 2

BDNF gene contains nine 5’ non-coding exons (I-IXA), each linked to a unique promoter that differentially splices to thecommon 3’ coding exon IX. The activity of each noncoding promoter region dictates differential expression of BDNFexon-specific transcripts, providing tissue-specific and activity dependentregulation of the BDNF gene across development and in adulthood

BDNF

Infancy Maltreatment Elicits a Lasting Increase inBDNF DNA Methylation in the PFC

• BDNF gene expression correlated with changes in BDNF DNA methylation

• Evaluated exon IV encompassing the transcription start site and (cAMP) response element – epigenetic regulation of this region is gaining support for role in neural

activity-dependent BDNF gene expression• Evaluated exon IX, large CpG sites • Exon IV and Exon IX mRNA transcripts ↑ during postnatal

development in the cortex and hippocampus • Dynamic methylation of exon IV suggested mechanism

mediating BDNF gene expression during development and thus susceptible to environmental insults

Fig 3Maltreated groups only

Age:

Confirming methylation

• Direct bisulfite DNA sequencing PCR (BSP) on site-specific methylation of 12 CpG dinucleotides within the same region of exon IV screened by methylation specific real-time PCR (MSP)

• Significant increases in methylation across the region in adults with a history of maltreatment (Fig 4)

Fig 4*

*cAMP response element site

Deficits in BDNF Gene Expression inthe Adult PFC Rescued by Treatment with a DNA

Methylation Inhibitor

• Infused zebularine, a DNA methylation inhibitor, left ventricle over 7 days

• Sufficient to ↓ methylation of BDNF exon IV DNA and rescue both BDNF exon IV mRNA & total mRNA levels in adults with maltreatment history

Fig 5

Fig 5

Maltreated + Zebularine = no diff from normal control

BDNF DNA Methylation Patterns in the PFC fromMaltreatment Are Perpetuated to the Next

Generation

Fig 6 Females with a history of maltreatment display aberrant maternal behavior toward their own offspring

“There’s your problem”

Fig 7

• A) Cross-fostering mal-offspring to a female with a history of normal infancy (Mal-Normal)↑ site 1

• B) Reverse methyl @ site 2

• C) Cross-fostering ↓ methyl but still ↑ over normal

Fig 8 • Prepartum behavioral observationsindicate that females with history of

maltreatment displayedsignificantly more anxiety-related

behaviors

Conclusion1. Infant maltreatment results in methylation of

BDNF DNA through the lifespan to adulthood, reduced BDNF gene expression in the adult PFC

2. Altered epigenetic marks and gene expression in the adult can be rescued with chronic treatment of a DNA methylation inhibitor (zebularine)

3. Abused rats grow up and mistreat their own offspring and their offspring also have significant DNA methylation

4. Inability of cross-fostering to completely rescue CNS DNA methylation

Thank you