Environmental Stress Affects DNA Methylation of a CpG Rich Promoter Region of Serotonin Transporter Gene in a Nurse Cohort

Auli Toivola,Mikko Härmä,Mika Kivimäki,Jussi Vahtera,Hanna M Ollila,Sampsa Puttonen,Jukka S Alasaari,Tiina Paunio,Markus Lagus,Erkki Kronholm

doi:10.1371/journal.pone.0045813

Abstract

BackgroundShift-working nurses are exposed to a stressful work environment, which puts them at an increased risk for burnout and depression. We explored the effect of environmental stress on serotonin transporter gene (SLC6A4) promoter methylation among nurses from high and low work stress environments.MethodologyUsing bisulfite sequencing, we investigated the methylation status of five CpG residues of a CpG-rich region in the promoter of SLC6A4 by comparing female shift working nurses from a high work stress environment (n = 24) to low work stress environment (n = 25). We also analyzed the association of 5-HTTLPR polymorphism at 5′ end of SLC6A4. Work stress was assessed by the Karasek’s Model and possible signs of burnout or depression were measured by the Maslach Burnout Index General Survey and Beck Depression Index. Methylation levels were assessed by bisulfite sequencing of DNA extracted from peripheral blood leucocytes. Restriction enzyme treatment followed by standard PCR was used to identify 5-HTTLPR genotypes.Principal FindingsWe found that nurses in the high stress environment had significantly lower promoter methylation levels at all five CpG residues compared to nurses in the low stress environment (p<0.01). There was no significant interaction of 5-HTTLPR genotype and work stress with methylation (p = 0.58). In unadjusted (bivariate) analysis, burnout was not significantly associated to methylation levels. However, when mutually adjusted for both, burnout and work stress were significant contributors (p = 0.038 and p<0.0001 respectively) to methylation levels.ConclusionsOur findings show that environmental stress is concurrent with decreased methylation of the SLC6A4 promoter. This may lead to increased transcriptional activity of the gene, increased reuptake of serotonin from synaptic clefts, and termination of the activity of serotonin. This could present a possible coping mechanism for environmental stress in humans that could eventually increase risk for disturbed functional capability and experience of depressed mood in long-term stress.

Highlights

Chronic work stress induces adverse emotional and physical responses, which are triggered by perception of work demands that exceed the person’s capacity and ability to cope [1]
Our findings show that environmental stress is concurrent with decreased methylation of the SLC6A4 promoter
Half (n = 12) of the 24 subjects in the high work stress group reported at least moderate burnout symptoms (MBI-GS scores .1.5)

Summary

Introduction

Chronic work stress induces adverse emotional and physical responses, which are triggered by perception of work demands that exceed the person’s capacity and ability to cope [1]. Such stress has a negative impact on job performance and is becoming a leading cause of work absence in western society, increasing economic pressure in the public sector. DNA methylation has been suggested to be one of the possible mechanisms to mediate the response of individuals to stress [5]. Shift-working nurses are exposed to a stressful work environment, which puts them at an increased risk for burnout and depression. We explored the effect of environmental stress on serotonin transporter gene (SLC6A4) promoter methylation among nurses from high and low work stress environments

Methods

Results

Discussion

Conclusion