title: Rapid Down-Regulation of Glucocorticoid Receptor Gene Expression in the Dentate Gyrus after Acute Stress in vivo: Role of DNA Methylation and MicroRNA Activity.
abstract: BACKGROUND
  Although glucocorticoid receptors (GRs) in the hippocampus play a vital role in the regulation of physiological and behavioural responses to stress, the regulation of receptor expression remains unclear. This work investigates the molecular mechanisms underpinning stress-induced changes in hippocampal GR mRNA levels in vivo.
  
  
  METHODS
  Male Wistar rats were killed either under baseline conditions or after forced swim stress (FSS; 15 min in 25°C water). Rat hippocampi were micro-dissected (for mRNA, microRNA, and DNA methylation analysis) or frozen whole (for chromatin immunoprecipitation). In an additional experiment, rats were pre-treated with RU486 (a GR antagonist) or vehicle.
  
  
  RESULTS
  FSS evoked a dentate gyrus-specific reduction in GR mRNA levels. This was related to an increased DNMT3a protein association with a discreet region of the Nr3c1 (GR gene) promoter, shown here to undergo increased DNA methylation after FSS. FSS also caused a time-dependent increase in the expression of miR-124a, a microRNA known to reduce GR mRNA expression, which was inversely correlated with a reduction in GR mRNA levels 30 min after FSS. FSS did not affect GR binding to a putative negative glucocorticoid response element within the Nr3c1 gene.
  
  
  CONCLUSIONS
  Acute stress results in decreased GR mRNA expression specifically in the dentate gyrus. Our results indicate that a complex interplay of multiple molecular mechanisms - including increased DNA methylation of discrete CpG residues within the Nr3c1 gene, most likely facilitated by DNMT3a, and increased expression of miR-124a - could be responsible for these changes.
authors.affiliation: Neuro-Epigenetics Research Group, School of Clinical Sciences, University of Bristol, Bristol, UK.
authors.forename: Karen R
authors.initials: KR
authors.lastname: Mifsud
authors.forename: Emily A
authors.initials: EA
authors.lastname: Saunderson
authors.forename: Helen
authors.initials: H
authors.lastname: Spiers
authors.forename: Sylvia D
authors.initials: SD
authors.lastname: Carter
authors.forename: Alexandra F
authors.initials: AF
authors.lastname: Trollope
authors.forename: Jonathan
authors.initials: J
authors.lastname: Mill
authors.forename: Johannes M H M
authors.initials: JM
authors.lastname: Reul
mesh_terms: D000208:Acute Disease; D000818:Animals; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics; D019175:DNA Methylation; D000090205:DNA Methyltransferase 3A; D018891:Dentate Gyrus / Q000378:metabolism*; D015536:Down-Regulation; D015870:Gene Expression; D008297:Male; D035683:MicroRNAs / Q000235:genetics*; D015735:Mifepristone / Q000008:administration & dosage; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011965:Receptors, Glucocorticoid / Q000037:antagonists & inhibitors / Q000235:genetics*; D013315:Stress, Psychological / Q000235:genetics*
chemical_list: C548144:MIRN124 microRNA, rat; D035683:MicroRNAs; C542344:NR3C1 protein, rat; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D015735:Mifepristone; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A