Stress-induced epigenetic transcriptional memory PNAS PLUS of acetylcholinesterase by HDAC4 Badi Sri Sailajaa, Dorit Cohen-Carmona, Gabriel Zimmermanb,c, Hermona Soreqb,c, and Eran Meshorera,1 Departments of aGenetics and bBiological Chemistry, The Alexander Silberman Institute of Life Sciences, and cThe Edmond and Lily Safra Center of Brain Science, Hebrew University of Jerusalem, Jerusalem 91904, Israel Edited by Bruce S. McEwen, The Rockefeller University, New York, NY, and approved November 15, 2012 (received for review June 12, 2012) Stress induces long-lasting changes in neuronal gene expression the stress-induced long-lasting changes in AChE expression in the and cholinergic neurotransmission, but the underlying mechanism(s) brain (2, 14) are maintained and regulated at the chromatin level. are incompletely understood. Here, we report that chromatin We describe the long-lasting stress-induced expression changes structure and histone modifications are causally involved in this of AChE 5′ splice variants, the related histone modifications at transcriptional memory. Specifically, the AChE gene encoding the the corresponding promoters, reversal of these effects by histone acetylcholine-hydrolyzing enzyme acetylcholinesterase is known deacetylase (HDAC) inhibitors, and a potential mediator, HDAC4, to undergo long-lasting transcriptional and alternative splicing of stress-related transcriptional memory in the hippocampus. changes after stress. In mice subjected to stress, we identified two alternative 5′ exons that were down-regulated after stress in the Results hippocampus, accompanied by reduced acetylation and elevated Regulation of AChE Expression by Forced-Swim Stress. We pre- trimethylation of H3K9 at the corresponding promoter. These ef- viously showed long-lasting elevation of the 3′ “readthrough” fects were reversed completely by daily administration of the his- variant of AChE, AChE-R, after 4 d of forced-swim stress (FSS) tone deacetylase (HDAC) inhibitor sodium butyrate for 1 wk after (2). We subsequently wished to test whether the AChE 5′ alter- stress. H3K9 hypoacetylation was associated with a selective, so- native transcripts (E1a, E1b, E1c, E1d1, and E1e; Fig. 1A)also dium butyrate-reversible promoter accumulation of HDAC4. Hip- display long-lasting changes in expression following the same re- pocampal suppression of HDAC4 in vivo completely abolished the peated stress paradigm. To this end, we subjected mice to two long-lasting AChE-related and behavioral stress effects. Our find- FSS sessions a day, 4 min each, for 4 consecutive days (2). We NEUROSCIENCE ’ ings demonstrate long-lasting stress-inducible changes in AChE s killed the mice 2 wk later along with control mice that had un- promoter choices, identify the chromatin changes that support this dergone no stress and surgically dissected the hippocampus (Fig. long-term transcriptional memory, and reveal HDAC4 as a mediator 1B). To reveal the neuronal content in our hippocampal prep- of these effects in the hippocampus. arations, we dispersed the hippocampi to single cells using en- zymatic digestion and sorted the cells by FACS using MAP2 HDAC inhibitors | ChIP | chromatin immunoprecipitation | antibodies. This sorting showed that neurons constituted >45% histone methylation | histone acetylation of our hippocampi preparations (Fig. S1). Therefore, for all subsequent experiments, we used hippocampal preparations tress induces long-lasting changes in neuronal gene expression without sorting. After extraction of hippocampal RNA, we Sand cholinergic neurotransmission (1, 2), but the underlying analyzed transcript levels using real-time quantitative PCR mechanism(s) are incompletely understood. Neuronal gene ex- (qPCR). Because transcript levels of several of the 5′ alterna- pression, like other transcriptional processes, is modulated by a tive exons were too low for proper quantification with qPCR, we dynamic process of chromatin modifications (3–5). According to also used semiquantitative conventional RT-PCR. We found the histone code hypothesis, different modifications of histones at a differential expression of some of these exons after stress: a particular promoter region, alone or in combination, define a mE1b and mE1c transcripts were down-regulated, but all other specific epigenetic state that balances between gene activation 5′ transcripts remained essentially unchanged (P < 0.05; Fig. 1 C and gene silencing (6, 7). Although there are exceptions, histone and D). To correlate the expression level of the 5′ transcripts to hyperacetylation at promoters generally indicates an increase in the 3′ transcripts, we analyzed expression levels of the two brain 3′ gene activity, whereas hypoacetylation usually marks a decrease alternative transcripts, the soluble AChE-R and the synapse-as- in activity (8). Histone methylation, on the contrary, correlates sociated AChE-S variant (Fig. 1A), using qPCR. Although, as with either transcriptional activation (i.e., H3K4, H3K36) or re- expected, AChE-R mRNA was markedly elevated (P < 0.05; Fig. pression (i.e., H3K9, H3K27, and H4K20). Histone methylation 1E), AChE-S mRNA was significantly reduced (Fig. 1F)in also may facilitate DNA methylation, which causes further re- a manner that resembles the down-regulation of the 5′ transcript pression of the affected genes (9, 10). mE1c after stress (P < 0.05; Fig. 1D). Chromatin modification is increasingly recognized as a crucial mechanism in several important phenomena in the brain, in- Regulation of AChE Expression by FSS After Treatment with HDAC cluding neuronal differentiation, neurodegeneration, circadian Inhibitors. In light of the decreased expression of mE1b and rhythm, seizure, memory formation, and drug addiction (11, 12). mE1c after stress, we wished to test whether expression levels Here, we studied the involvement of acetylcholinesterase (AChE) chromatin structure in the long-term neuroadaptations to stress in the hippocampus, which is one of the major brain areas involved in mammalian stress responses (13). Author contributions: B.S.S. and E.M. designed research; B.S.S., D.C.-C., G.Z., and E.M. The AChE gene contains five short putative alternative first performed research; H.S. contributed new reagents/analytic tools; B.S.S., H.S., and exons in mice (14). Each exon contains its own unique promoter E.M. analyzed data; and B.S.S. and E.M. wrote the paper. region (14), which can modulate the expression of one splice The authors declare no conflict of interest. variant over another. Defeat stress/seizures/posttraumatic stress This article is a PNAS Direct Submission. can induce long-lasting changes in the promoters of several genes, 1To whom correspondence should be addressed. E-mail: [email protected]. BDNF GDNF GRE GLUR2 RELN including , , , ,and through This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. chromatin-related modifications (12, 15–19).Herewestudiedhow 1073/pnas.1209990110/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1209990110 PNAS Early Edition | 1of9 Downloaded by guest on October 2, 2021 Fig. 1. AChE expression after FSS. (A) The structure of the AChE gene. The mouse AChE gene contains five alternative exons, mE1a–mE1e, at the 5′ end of the gene. The AChE gene also contains unique promoter regions, mP1a, mP1c, mP1d, and mP1e, upstream of the various exons. For mRNA analysis of AChE mE1a– E1e, primers were designed to recognize each exon specifically. For ChIP analysis, primers were designed around the promoters, mP1a–mP1e. Alternative splicing of AChE at the 3′ end generates two isoforms: the main, synaptic form, AChE-S, and the stress-induced, soluble form, AChE-R (B) Schematic repre- sentation of the FSS paradigm. Mice were subjected to two FSS sessions a day, 4 min each, for 4 consecutive days, and were killed 2 wk later (n = 4). (C) Semiquantitative RT-PCR analysis of the AChE 5′ transcripts (mE1a–mE1e). mE1b and mE1c transcripts were down-regulated, whereas all other 5′ transcripts remained essentially unchanged. (D–F) Real-time PCR analysis before and after FSS of mE1c (D), AChE-R (E), and AChE-S (F). AChE-S mRNA is 80 times more abundant than AChE-R mRNA. AChE-R mRNA was elevated, whereas AChE-S and mE1c mRNAs were significantly reduced in the hippocampus of stressed mice. *P < 0.05, two-tailed u test. can be restored using histone deacetylase (HDAC) inhibitors at the 3′ end, likely reflecting stress-induced changes in the AChE- (HDACi). HDACi were shown to improve symptoms of several S-selective microRNA-132 (22). These results indicate that the brain-related pathologies; including stress-induced memory long-lasting stress-induced changes in AChE expression can be impairments (20, 21). To this end, we repeated the FSS experi- partly restored by TSA and fully rescued by NaBu. ment, but this time after the FSS protocol, the mice were placed back in their original cages for 1 wk and then injected with either Chromatin Regulation of AChE After Forced Swim Stress. The long- sodium butyrate (NaBu) or trichostatin A (TSA) daily for 1 wk lasting down-regulation of two of the 5′ transcripts mE1b and (Fig. 2A). Mice treated with saline injection after stress served as mE1c prompted us to investigate the mechanism by which the the control group; again, mice were killed 2 wk after the FSS. corresponding promoters elicit transcriptional memory and are Remarkably, we found that NaBu completely restored the down- differentially regulated by stress. We therefore analyzed the regulation of mE1b and mE1c exons at the 5′