PDF《in the nucleus accumbens》

ARTICLE Received

25 Sep

2015 | Accepted

25 Apr

2016 | Published

26 May

2016 BDNF rescues BAF53b-dependent synaptic plasticity and cocaine-associated memory in the nucleus accumbens Andre ? O.

White1,2,3, Eniko ¨ A. Krama ?r1,2,3, Alberto J. Lo ?pez1,2,3, Janine L. Kwapis1,2,3,4, John Doan1,2,3, David Saldana1,2,3, M. Felicia Davatolhagh5, Yasaman Alaghband1,2,3, Mathew Blurton-Jones1,4,6, Dina P. Matheos1,2,3 &

Marcelo A. Wood1,2,3,4 Recent evidence implicates epigenetic mechanisms in drug-associated memory processes. However, a possible role for one major epigenetic mechanism, nucleosome remodelling, in drug-associated memories remains largely unexplored. Here we examine mice with genetic manipulations targeting a neuron-speci?c nucleosome remodelling complex subunit, BAF53b. These mice display de?cits in cocaine-associated memory that are more severe in BAF53b transgenic mice compared with BAF53b heterozygous mice. Similar to the memory de?cits, theta-induced long-term potentiation (theta-LTP) in the nucleus accumbens (NAc) is signi?cantly impaired in slices taken from BAF53b transgenic mice but not heterozygous mice. Further experiments indicate that theta-LTP in the NAc is dependent on TrkB receptor activation, and that BDNF rescues theta-LTP and cocaine-associated memory de?cits in BAF53b transgenic mice. Together, these results suggest a role for BAF53b in NAc neuronal function required for cocaine-associated memories, and also that BDNF/TrkB activation in the NAc may overcome memory and plasticity de?cits linked to BAF53b mutations. DOI: 10.1038/ncomms11725 OPEN

1 301 Qureshey Research Lab, Department of Neurobiology and Behavior, University of California, Irvine, California 92697, USA.

2 Center for the Neurobiology of Learning and Memory, Irvine, California 92697, USA.

3 Irvine Center for Addiction Neuroscience (ICAN), University of California, Irvine, California 92697, USA.

4 Institute for Memory Impairments and Neurological Disorders, University of California, Irvine, California 92697, USA.

5 Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.

6 Sue and Bill Gross Stem Cell Research Center, University of California, Irvine, California 92697, USA. Correspondence and requests for materials should be addressed to M.A.W. (email: mwood@uci.edu). NATURE COMMUNICATIONS | 7:11725 | DOI: 10.1038/ncomms11725 | www.nature.com/naturecommunications

1 D rug addiction is characterized by compulsive drug-seeking behaviour despite negative consequences1. In the ?eld of substance abuse, there remains unanswered questions about how drugs of abuse drive the establishment of long-lasting changes in the brain that support robust drug-associated behaviours and memories. A central feature of drugs of abuse that distinguishes them from non-addictive drugs is their ability to promote persistent changes in neuronal function in the reward pathways of the brain2C4. For example, cocaine is known to generate changes in histone modi?cation patterns that result in aberrant gene expression pro?les and synaptic plasticity in the nucleus accumbens (NAc) that drive several cocaine-seeking behaviours5C11. Increasing evidence supports a role for epigenetic mechanisms in memory formation (for a review, see ref. 12). In particular, epigenetic mechanisms such as histone modi?cation are integral for the formation of drug-associated memories and behaviours13,14. The basic repeating subunit of chromatin is the nucleosome, which comprises a DNAChistone complex that packages genomic DNA. Several epigenetic mechanisms including posttranslational histone modi?cation, DNA methylation and non-coding RNA serve as key regulators of chromatin structure and gene expression that are required for aspects of drug-associated behaviours (see reviews14C16). For example, histone acetylation and methylation mechanisms are pivotal for cocaine-induced changes in gene expression that underlie cocaine-induced behaviours and cocaine-context- associated memories6C11,17,18. However, there is a fourth major epigenetic mechanism (ATP-dependent nucleosome remodelling) that regulates transcription by altering chromatin structure19. Currently, it remains unclear to what extent ATP-dependent nucleosome remodelling complexes are involved in drug-induced behaviours and drug-associated memories. Nucleosome remodelling complexes are evolutionarily conserved multi-subunit complexes that replace, eject and alter nucleosomes to promote changes in gene expression20. Through their ATPase subunit, nucleosome remodelling complexes manipulate nucleosomeCDNA contacts through ATP hydrolysis, thereby allowing the binding of the transcription machinery and associated transcriptional regulators19,20. A recent study identi?ed the neuron-speci?c nucleosome remodeller, nBAF, as a regulator of gene expression necessary for neuronal differentiation21, dendritic branching22, hippocampal synaptic plasticity and hippocampus-dependent long-term memory23. nBAF contains one of two ATPase subunits (Brm or Brg1), which is necessary for ATP hydrolysis during nucleosome remodelling24. The nBAF complex also contains a unique subunit called Baf53b (also referred to as Actl6b), which appears critical for nBAF to target speci?c promoter regions22. BAF53b is only expressed in postmitotic neurons and only found in the nBAF complex22,25. The unusual dedication of BAF53b to the nBAF complex, as well its neuronal speci?city, makes BAF53b the ideal target with which to examine the role of nucleosome remodelling complexes in cocaine- associated behaviours and memories. We examined whether BAF53b has a role in the formation of cocaine-associated behaviours and memories using mice that had either a deletion mutation or traditional heterozygous knockout of BAF53b. The role of neuron-speci?c nucleosome remodelling factors in drug-associated memory formation and their in?uence on synaptic plasticity in the NAc has not been previously explored. Therefore, we extended our studies to examine the role of BAF53b in long-term potentiation (LTP) in NAc, as LTP is thought to be a candidate mechanism underlying long-term memory formation. First, we established a stimulation protocol that induced LTP using theta stimulation (theta-LTP) in slices from wild-type (WT) mice and compared the level of stable potentiation with that achieved in slices from BAF53b mutant mice. Next, we tested the possibility that (1) theta-LTP in the NAc requires TrkB receptor activation and (2) whether the ligand for TrkB, brain-derived neurotrophic factor (BDNF), could reverse de?cits in theta-LTP and cocaine-associated memory observed in BAF53b mutant mice. Together, these experiments provide the ?rst evidence for a role of neuron-speci?c nucleosome remodelling complexes in cocaine-associated memory formation and a potential mechanism for correcting related plasticity de?cits in the NAc. Results Characterization of BAF53b mutant mice. nBAF is a multi-subunit complex that is neuron speci?c (Fig. 1a). It is de?ned, in part, by the BAF53b subunit (highlighted in yellow), which is only found in the nBAF complex22,25. BAF53b is expressed in the NAc, a brain area required for cocaine-associated memory formation. BAF53b homozygous knockout mice (Baf53b? / ? ) do not survive into adulthood22. Therefore, to study the role of BAF53b in cocaine-associated memories and behaviours, we examined a deletion mutation of Baf53b (Baf53bDHD). We previously demonstrated that a similar deletion of the hydrophobic domain of BAF53a (the non- neuronal homologue of BAF53b) generates a dominant negative form of BAF53a26. The transgene in the Baf53bDHD line is expressed via the CaMKIIa promoter (Fig. 1b)23,27,28. Both WT BAF53b and the BAF53bDHD mutant protein interact with Brg1, as demonstrated by co-immunoprecipitation of either WT or BAF53bDHD with Brg1 (Fig. 1c). Using quantitative reverse-transcription PCR, we veri?ed transgene expression in the NAc (Fig. 1d). In addition to transgenic Baf53bDHD mice, we also examined a Baf53b? ........