Case Control Study
Copyright ©The Author(s) 2021. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Psychiatr. Dec 19, 2021; 11(12): 1301-1313
Published online Dec 19, 2021. doi: 10.5498/wjp.v11.i12.1301
BDNF methylation and mRNA expression in brain and blood of completed suicides in Slovenia
Sandra Ropret, Katarina Kouter, Tomaž Zupanc, Alja Videtic Paska
Sandra Ropret, Katarina Kouter, Alja Videtic Paska, Institute of Biochemistry and Molecular Genetics, Faculty of Medicine, University of Ljubljana, Ljubljana SI-1000, Slovenia
Tomaž Zupanc, Institute of Forensic Medicine, Faculty of Medicine, University of Ljubljana, Ljubljana SI-1000, Slovenia
Author contributions: Videtic Paska A and Ropret S designed the study and the experiments; Zupanc T collected patient data, brain tissue, and blood samples; Ropret S performed the majority of experiments, analyzed the data, and wrote the manuscript; Kouter K performed DNA extraction, bisulfite conversion of DNA, and helped with RNA extraction; Videtic Paska A corrected the manuscript; all the authors approved the final version of the manuscript.
Supported by Slovenian Research Agency, No. P1-0390, and No. J3-7132.
Institutional review board statement: The study was reviewed and approved by the Medicinal Ethics Committee of the Republic of Slovenia, No. 47/12/12.
Informed consent statement: The samples included in the study are post mortem samples collected during the course of autopsy at the Institute of Forensic Medicine, University of Ljubljana. The collected samples were used for routine analyses associated with the autopsy as well as for the molecular-genetic analyses. In Slovenia use of post mortem samples does not include use of informed consent, but the collection and use of the samples has to be approved by the Medicinal Ethics Committee of the Republic of Slovenia. For the collected samples the approval of the Medicinal Ethics Committee is attached.
Conflict-of-interest statement: None to declare.
Data sharing statement: No additional data are available.
STROBE statement: The authors have read the STROBE Statement—checklist of items, and the manuscript was prepared and revised according to the STROBE Statement—checklist of items.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Alja Videtic Paska, PhD, Associate Professor, Institute of Biochemistry and Molecular Genetics, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, Ljubljana SI-1000, Slovenia. alja.videtic@mf.uni-lj.si
Received: March 16, 2021
Peer-review started: March 16, 2021
First decision: May 5, 2021
Revised: May 25, 2021
Accepted: September 16, 2021
Article in press: September 16, 2021
Published online: December 19, 2021
Abstract
BACKGROUND

Suicide is a major public health problem. Worldwide, around 800000 people die by suicide every year. Suicide is a multifactorial disorder, with numerous environmental and genetic risk factors involved. Among the candidate genes, changes in the BDNF locus at the gene, epigenetic, mRNA, and protein expression levels have been implicated in psychiatric disorders, including suicidal behavior and completed suicides.

AIM

To investigate changes in BDNF methylation and expression of four alternative BDNF transcripts for association with completed suicide.

METHODS

This case-control study included 42 unrelated male Caucasian subjects, where 20 were control subjects who died following acute cardiac arrest, and 22 were suicide victims who died by hanging. DNA and RNA were extracted from brain tissue (Brodmann area 9 and hippocampus) and from blood. DNA methylation and mRNA expression levels were determined by targeted bisulfite next-generation sequencing and reverse-transcription quantitative PCR. Statistical analysis was done by use of two-tailed Student’s t tests for two independent samples, and the Benjamini-Hochberg procedure was implemented for correction for multiple comparisons.

RESULTS

In DNA from brain tissue, there were no significant differences in BDNF methylation between the study groups. However, data showed significantly reduced DNA methylation of the BDNF region upstream of exon I in blood samples of suicide victims compared to the controls (5.67 ± 0.57 vs 6.83 ± 0.64, Pcorr = 0.01). In Brodmann area 9 of the brain of the suicide victims but not in their hippocampus, there was higher expression of BDNF transcript I-IX (NM_170731.4) compared to the controls (0.077 ± 0.024 vs 0.05 ± 0.013, P = 0.042). In blood, expression analysis for the BDNF transcripts was not feasible due to extensive RNA degradation.

CONCLUSION

Despite the limitations of the study, the obtained data further support a role for BDNF in suicidality. However, it should be noted that suicidal behavior is a multifactorial disorder with numerous environmental and genetic risk factors involved.

Keywords: Suicidal behavior, Epigenetics, Next-generation sequencing, Brain, Blood, Caucasian

Core Tip: BDNF methylation analysis of brain tissues did not show differences between control subjects and suicide victims, although there was higher expression of BDNF transcript I-IX in Brodmann area 9 of the suicide victims. Furthermore, the data obtained from blood were interesting, especially in terms of the direction of the effects. Although due to the extensively degraded RNA in the blood, we were not able to confirm these effects on mRNA expression. Although suicide is a multifactorial disorder, our data overall further support the previously implicated role of BDNF in suicidality.