Elsevier

Journal of Psychiatric Research

Volume 45, Issue 9, September 2011, Pages 1229-1235
Journal of Psychiatric Research

Epigenetic regulation of spermidine/spermine N1-acetyltransferase (SAT1) in Suicide

https://doi.org/10.1016/j.jpsychires.2011.03.015Get rights and content

Abstract

We have recently shown that the expression of spermidine/spermine N1-acetyltransferase (SAT1) is downregulated across the brains of suicide completers, and that its expression is influenced by genetic variations in the promoter. Several promoter polymorphisms in SAT1, including rs6526342, have been associated with suicide and other psychiatric disorders, and display haplotype-specific effects on expression. However, these effects cannot explain total variability in SAT1 expression, and other regulatory mechanisms, such as epigenetic factors, may also be at play. In this study, we assessed the involvement of epigenetic factors in controlling SAT1 expression in the prefrontal cortex of suicide completers by mapping CpG methylation across a 1880-bp region of the SAT1 promoter, and measuring levels of tri-methylated histone-3-lysine 27 (H3K27me3) at the promoter in suicide completers and controls. Our results demonstrated that CpG methylation was significantly negatively correlated with SAT1 expression. Although overall or site-specific CpG methylation was not associated with suicide or SAT1 expression, we observed high levels of methylation at the polymorphic CpG site created by rs6526342, indicating a relationship between promoter haplotypes and methylation. There was no association between H3K27me3 and suicide, nor was this modification associated with SAT1 expression. Overall, our results indicate that epigenetic factors in the promoter region of SAT1 influence gene expression levels, and may provide a mechanism for both our previous findings of haplotype-specific effects of promoter variations on SAT1 expression, as well as the widespread downregulation of SAT1 expression observed in the brains of suicide completers.

Introduction

Suicide is one of the leading causes of death in Western countries (Nock et al., 2008), which results from the interaction of social, environmental, and genetic factors. While there is strong evidence for the involvement of the monoaminergic neurotransmitter systems in the neuropathology of suicide, it has become increasingly evident that additional systems are involved in this complex condition. In recent years, evidence has emerged implicating dysregulation of the polyamine system as an important factor in suicide and other psychiatric disorders (Fiori and Turecki, 2008). To date, alterations of spermidine/spermine N1-acetyltransferase (SAT1), the rate-limiting enzyme in polyamine catabolism, have been one of the most robust findings implicating this system in the neurobiology of suicide. Decreased expression of SAT1 has now been observed in a number of brain regions in suicide completers (Guipponi et al., 2009, Sequeira et al., 2007, Sequeira et al., 2006, Klempan et al., 2009a, Klempan et al., 2009b), and two promoter polymorphisms, rs6526342 and rs6151267, have been associated with suicide in French Canadians (Fiori and Turecki, 2010a, Sequeira et al., 2006). Several single nucleotide polymorphisms (SNPs) in the promoter were recently found to be involved in determining expression levels in vitro as well as in the brain, and interestingly two SNPs, rs6526342 and rs928931, produced haplotype-specific effects on expression (Fiori et al., 2009).

In addition to DNA sequence variants, epigenetic regulation is another important determinant of gene expression, and can involve methylation of DNA as well as modification of histones. DNA methylation is a covalent modification at the 5′ position of cytosine, occurring at CG dinucleotides (CpG), and is often associated with gene repression when found in promoter regions (Klose and Bird, 2006). Histones are the core proteins involved in packaging of DNA into nucleosomes, and can be covalently modified at specific residues by acetylation, methylation, phosphorylation, SUMOylation, and ubiquitinylation (Berger, 2007). The effect of these modifications on gene expression depends upon the histone protein (H2A, H2B, H3, H4), specific amino acid residue, the nature of the modification, and its positioning within the gene.

Interestingly, polyamine metabolism has been shown to influence both DNA methylation and histone modifications (for examples, see (Ara et al., 2008, Duranton et al., 1998, Frostesjo et al., 1997, Schipper et al., 2007)) and increased S-adenosylmethionine, a precursor in polyamine biosynthesis, has been implicated in the downregulation of several genes in the prefrontal cortex of psychotic patients through altering levels of promoter methylation (Guidotti et al., 2007). The expression of several polyamine-related genes has also been shown to be influenced by DNA methylation, including polyamine-modulated factor-1 (PMF-1) (Aleman et al., 2008), and methionine adenosyltransferase (MAT1A) (Ikeda et al., 2008), although a recent study performed by our group found no relationship between DNA methylation or histone modifications and expression of spermine synthase or spermine oxidase in the brains of suicide completers (Fiori and Turecki, 2010b). However, the expression of ornithine aminotransferase and μ-crystallin has been shown to be influenced by histone methylation in the prefrontal cortices of schizophrenia patients (Akbarian et al., 2005), suggesting that histone modifications are important modulators for the expression of polyamine genes. Several studies have now identified altered levels of CpG methylation and histone modifications in gene promoter regions in a number of psychiatric disorders, including suicide (Akbarian et al., 2005, De Luca et al., 2009, Ernst et al., 2009a, Huang and Akbarian, 2007, Keller et al., 2010, McGowan et al., 2008, Poulter et al., 2008). Overall, SAT1 appears to be a compelling target for assessing the involvement of epigenetic factors in the regulation of the polyamine system and in conferring risk for suicide.

In this study, we were interested in determining the role of epigenetic modifications in determining the expression of SAT1, and to assess their involvement in down regulating the expression of SAT1 in suicide completers. In addition, we were interested in investigating if epigenetic mechanisms were responsible for the haplotype-specific effects of the functional promoter variants, particularly as rs6526342 and rs928931 create polymorphic CpG sites. Using prefrontal brain tissue from a sample of suicide completers and controls, we focused on promoter CpG methylation and levels of tri-methylated histone-3-lysine 27 (H3K27), epigenetic modifications which are both associated with gene repression (Barski et al., 2007, Klose and Bird, 2006). Both of these modifications have been shown to be relatively unaffected by complications arising in post-mortem tissues such as altered pH and post-mortem interval (Ernst et al., 2008, Huang et al., 2006), and are thus well-suited for this type of analysis. Additionally, tri-methylated H3K27 was recently implicated in the downregulation of the TrkB receptor in the prefrontal cortex of suicide completers (Ernst et al., 2009a).

Section snippets

Subjects

We examined 20 male subjects, described in Table 1, comprised of 10 non-suicide controls and 10 suicide completers. Subjects were matched for age, post-mortem interval (PMI), and brain pH. Cause of death was assessed by the Quebec Coroner’s office. Samples were obtained from the Quebec Suicide Brain Bank, where they were processed and dissected at 4 °C, then snap-frozen in liquid nitrogen before storage at −80 °C, following standard procedures (Bird and Vonsattel, 1993). All subjects died

CpG methylation

In order to determine if CpG methylation is involved in the differential expression of SAT1 in suicide completers and the relationship between promoter haplotype and expression, we analyzed methylation in BA 8/9 of 20 subjects (10 suicide completers and 10 controls). This brain region was selected due to previous findings in suicide completers demonstrating both decreased expression of SAT1 (Sequeira et al., 2006), as well as elevated levels of putrescine and spermidine (Chen et al., 2010), in

Discussion

In this study, we examined the role of two epigenetic modifications, CpG methylation and histone methylation, in determining the expression of SAT1 in the brain, and assessed their involvement in the decreased expression of SAT1 previously observed in the brains of suicide completers (Sequeira et al., 2006, Sequeira et al., 2007, Klempan et al., 2009a, Klempan et al., 2009b).

We found a strong relationship between CpG methylation and SAT1 expression, such that increased overall levels of CpG

Conflict of interest

All authors declare that they have no conflicts of interest.

Funding

This work was supported by the Canadian Institute of Health Research (CIHR) MOP 79253. GT is a Fonds de la recherche en santé du Québec (FRSQ) research fellow. LMF received a scholarship from the Natural Sciences and Engineering Research Council of Canada (NSERC). These agencies had no further role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

Contributors

Both authors designed the experiments and wrote the manuscript. All experimental and data analysis steps were performed by LMF.

Acknowledgements

None.

References (45)

  • M.O. Poulter et al.

    GABAA receptor promoter hypermethylation in suicide brain: implications for the involvement of epigenetic processes

    Biological Psychiatry

    (2008)
  • H. Tomitori et al.

    Functional characterization of the human spermidine/spermine N(1)-acetyltransferase gene promoter

    Biochimica et Biophysica Acta

    (2002)
  • Y. Wang et al.

    Cloning and characterization of human polyamine-modulated factor-1, a transcriptional cofactor that regulates the transcription of the spermidine/spermine N(1)-acetyltransferase gene

    Journal of Biological Chemistry

    (1999)
  • Y. Wang et al.

    The identification of a cis-element and a trans-acting factor involved in the response to polyamines and polyamine analogues in the regulation of the human spermidine/spermine N1-acetyltransferase gene transcription

    Journal of Biological Chemistry

    (1998)
  • L. Xiao et al.

    Structure of the human spermidine/spermine N1-acetyltransferase gene (exon/intron gene organization and localization to Xp22.1)

    Biochemical and Biophysical Research Communications

    (1992)
  • S. Akbarian et al.

    Chromatin alterations associated with down-regulated metabolic gene expression in the prefrontal cortex of subjects with schizophrenia

    Archives of General Psychiatry

    (2005)
  • A. Aleman et al.

    Identification of PMF1 methylation in association with bladder cancer progression

    Clinical Cancer Research

    (2008)
  • A.I. Ara et al.

    S-adenosylmethionine inhibits lipopolysaccharide-induced gene expression via modulation of histone methylation

    Hepatology

    (2008)
  • N. Babbar et al.

    Induction of spermidine/spermine N1-acetyltransferase (SSAT) by aspirin in Caco-2 colon cancer cells

    Biochemical Journal

    (2006)
  • S.L. Berger

    The complex language of chromatin regulation during transcription

    Nature

    (2007)
  • E.D. Bird et al.

    The development of a brain bank

    Journal of Neural Transmission Supplements

    (1993)
  • G.G. Chen et al.

    Evidence of altered polyamine concentrations in cerebral cortex of suicide completers

    Neuropsychopharmacology

    (2010)
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