DNA methyltransferase 1 regulates reelin mRNA expression in mouse primary cortical cultures

Abstract

The polygenic nature of complex psychiatric disorders suggests a common pathway that may be involved in the down-regulation of multiple genes through an epigenetic mechanism. To investigate the role of methylation in down-regulating the expression of mRNAs that may be associated with the schizophrenia phenotype, we have adopted a cell-culture model amenable to this line of investigation. We have administered methionine (2 mM) to primary cultures of cortical neurons prepared from embryonic day 16 mice and show that this treatment down-regulated reelin and glutamic acid decarboxylase 67 (GAD67) mRNA expression but not that corresponding to neuron-specific enolase mRNA. Moreover, methionine increased methylation of the reelin promoter, suggesting a possible mechanism for the observed change. These cultures contain a mixed population of neurons and glia. Approximately 83% of the neurons are GABAergic based on GAD immunoreactivity, and these neurons coexpress high levels of reelin and DNA methyltransferase (Dnmt) 1 immunoreactivity. To examine whether Dnmt1 regulates reelin gene expression, we used an antisense approach to reduce (knock down) Dnmt1 expression. The reduced Dnmt1 mRNA and protein were accompanied by increased reelin mRNA expression. More importantly, the Dnmt1 knockdown blocked the methionine-induced reelin and GAD67 mRNA downregulation. These data support the hypothesis that the reduced amounts of reelin and GAD67 mRNAs documented in postmortem schizophrenia brain may be the consequence of a Dnmt1-mediated hypermethylation of the corresponding promoters.epigenetics ͉ gene expression ͉ methylation ͉ schizophrenia

Epigenetic Treatments for Cognitive Impairments

“…Consistent with this hypothesis, patients with schizophrenia exhibit hypermethylation at the synaptic plasticity gene reelin in the cortex, which is associated with decreased reelin expression (Grayson et al, 2005). Additionally, post-mortem samples from schizophrenic patients have revealed an overexpression of DNMT1 and DNMT3a in GABAergic neurons (Zhubi et al, 2009), which is consistent with the observation that DNMT1 regulates reelin methylation in vivo (Noh et al, 2005).…”

Regulation of the GABA cell phenotype in hippocampus of schizophrenics and bipolars

“…In SO of sector CA2/3 of SZs, HDAC1 and its epigenetic corepressor, DAXX, were both up-regulated, a pattern consistent with the hypothesis that epigenetic mechanisms play a selective role in the pathophysiology of SZ (43)(44)(45). Previous work in this area has pointed to DNA methyl transferase 1 as playing the central role in the regulation of the GAD 67 promoter in the dorsolateral prefrontal cortex (46). In BDs, on the other hand, HDAC1 and DAXX did not show significant changes in expression; however, several transcription factor genes, including PAX 5, Runx2, LHX2, TLE1, and LEF1, were all down-regulated.…”

Neurodevelopment, GABA System Dysfunction, and Schizophrenia

“…In addition to being a necessary component of cortical development, RELN also has a role in stabilizing neurons and synapses throughout life (Abraham and Meyer, 2003;Frotscher, 2010;Guidotti et al, 2000b). It is expressed by GABAergic interneurons and the expression of the GAD1 and RELN genes is tightly coordinated by a common epigenetic mechanism (Costa et al, 2004;Grayson et al, 2005Grayson et al, , 2006Guidotti et al, 2000a;Impagnatiello et al, 1998;Kundakovic et al, 2009;Maloku et al, 2010;Noh et al, 2005;Pesold et al, 1999;Rodriguez et al, 2002;Ruzicka et al, 2007;Tochigi et al, 2008;Veldic et al, 2004Veldic et al, , 2007. In addition, rodent models show that RELN deficiency alone can result in downstream reductions of both GAD1 (Kutiyanawalla et al, 2012;Nullmeier et al, 2011;Pascual et al, 2004;Takayama, 1994) and BDNF (Pillai and Mahadik, 2008).…”