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Adverse early life experience and social stress during adulthood interact to increase serotonin transporter mRNA expression.

ABSTRACT: Anxiety disorders, depression and animal models of vulnerability to a depression-like syndrome have been associated with dysregulation of serotonergic systems in the brain. To evaluate the effects of early life experience, adverse experiences during adulthood, and potential interactions between these factors on serotonin transporter (slc6a4) mRNA expression, we investigated in rats the effects of maternal separation (180 min/day from days 2 to 14 of life; MS180), neonatal handing (15 min/day from days 2 to 14 of life; MS15), or normal animal facility rearing (AFR) control conditions with or without subsequent exposure to adult social defeat on slc6a4 mRNA expression in the dorsal raphe nucleus (DR) and caudal linear nucleus. At the level of specific subdivisions of the DR, there were no differences in slc6a4 mRNA expression between MS15 and AFR rats. Among rats exposed to a novel cage control condition, increased slc6a4 mRNA expression was observed in the dorsal part of the DR in MS180 rats, relative to AFR control rats. In contrast, MS180 rats exposed to social defeat as adults had increased slc6a4 mRNA expression throughout the DR compared to both MS15 and AFR controls. Social defeat increased slc6a4 mRNA expression, but only in MS180 rats and only in the "lateral wings" of the DR. Overall these data demonstrate that early life experience and stressful experience during adulthood interact to determine slc6a4 mRNA expression. These data support the hypothesis that early life experience and major stressful life events contribute to dysregulation of serotonergic systems in stress-related neuropsychiatric disorders.

SUBMITTER: Gardner KL

PROVIDER: S-EPMC2788613 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Adverse early life experience and social stress during adulthood interact to increase serotonin transporter mRNA expression.

Gardner Katherine L KL Hale Matthew W MW Lightman Stafford L SL Plotsky Paul M PM Lowry Christopher A CA

Brain research 20090923

Anxiety disorders, depression and animal models of vulnerability to a depression-like syndrome have been associated with dysregulation of serotonergic systems in the brain. To evaluate the effects of early life experience, adverse experiences during adulthood, and potential interactions between these factors on serotonin transporter (slc6a4) mRNA expression, we investigated in rats the effects of maternal separation (180 min/day from days 2 to 14 of life; MS180), neonatal handing (15 min/day fro ...[more]

PMID: 19781533

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Project description:The serotonin transporter (SERT, SLC6A4) is a Na+-dependent transporter that regulates the availability of serotonin (5-HT, 5-hydroxytryptamine), a key neurotransmitter and hormone in the brain and the intestine. The human SERT gene consists of two alternate promoters that drive expression of an identical SERT protein. However, there are different mRNA transcript variants derived from these two promoters that differ in their 5' untranslated region (5'UTR), which is the region of the mRNA upstream from the protein-coding region. Two of these transcripts contain exon-1a and are abundant in neuronal tissue, whereas the third transcript contains exon-1c and is abundant in the intestine. The 3'UTR is nearly identical among the transcripts. Current studies tested the hypothesis that the UTRs of SERT influence its expression in intestinal epithelial cells (IECs) by controlling mRNA or protein levels. The SERT UTRs were cloned into luciferase reporter plasmids and luciferase mRNA and activity were measured following transient transfection of the UTR constructs into the model IEC Caco-2. Luciferase activity and mRNA abundance were higher than the empty vector for two of the three 5'UTR variants. Calculation of translation index (luciferase activity divided by the relative luciferase mRNA level) revealed that the exon-1a containing 5'UTRs had enhanced translation when compared to the exon-1c containing 5'UTR which exhibited a low translation efficiency. Compared to the empty vector, the SERT 3'UTR markedly decreased luciferase activity. In silico analysis of the SERT 3'UTR revealed many conserved potential miRNA binding sites that may be responsible for this decrease. In conclusion, we have shown that the UTRs of SERT regulate mRNA abundance and protein expression. Delineating the molecular basis by which the UTRs of SERT influence its expression will lead to an increased understanding of post-transcriptional regulation of SERT in GI disorders associated with altered 5-HT availability.

Project description:BackgroundScientific enthusiasm about gene × environment interactions, spurred by the 5-HTTLPR (serotonin transporter-linked polymorphic region) × SLEs (stressful life events) interaction predicting depression, have recently been tempered by sober realizations of small effects and meta-analyses reaching opposing conclusions. These mixed findings highlight the need for further research. Converging evidence suggests that the effects of 5-HTTLPR genotype may be neurodevelopmental in origin, but we are not aware of empirical studies that have investigated whether the 5-HTTLPR genotype × SLE interaction predicts preschool-onset depression (PO-MDD), the earliest validated form of depression.MethodsChildren (n = 234) aged 3-5 were recruited for a longitudinal study designed to examine PO-MDD. In a comprehensive baseline assessment, the child's primary caregivers completed questionnaires and were interviewed about their child's behaviors, psychiatric symptoms, and exposure to SLEs.ResultsA 5-HTTLPR × SLEs interaction emerged, such that children homozygous for the short allele were more susceptible to depression in the context of elevated SLE than long allele carriers. In contrast, at low SLE exposure, short allele homozygotes had fewer depressive symptoms. The data were best fit by a plasticity model with a substantial reduction in fit by diathesis-stress models.ConclusionsExtending studies in adult and adolescent populations, these data suggest that 5-HTTLPR genotype may provide plasticity to environmental influence, for better or worse. Specifically, children homozygous for the short allele were more susceptible to the depressogenic effects of SLEs but benefitted, in the form of reduced depressive symptoms, in the context of relatively benign environmental conditions (i.e. relatively low SLE exposure). These data highlight the importance of examining gene × environment interactions across development, environment, and outcome but should be interpreted cautiously given the small sample size.

Project description:Depression is common in the elderly. The role of genetic and environmental factors in modulating depressive symptoms is not clear.We evaluated the influence of serotonin transporter gene polymorphisms and recent adverse life events on depressive symptoms in an elderly Italian population. We used data from "InveCe.Ab", a population-based study of 1321 subjects aged 70-74 years. We used the 15-item Geriatric Depression Scale (GDS) to assess depressive symptoms-a GDS score ≥5 points (GDS≥5) indicated the presence of clinically relevant symptoms-and performed 5-HTTLPR and rs25531 genotyping to obtain the triallelic polymorphism of the serotonin transporter. We used the Geriatric Adverse Life Events Scale to measure adverse life events, and logistic regression models to evaluate the role of genotype and recent adverse life events in depressive symptoms, controlling for potential confounders and independent predictors.Two hundred subjects (15.76%) had a GDS≥5. The 5-HTTLPR triallelic polymorphism was significantly associated with GDS≥5. Only S'S' carriers showed an increased risk of depressive symptoms (ORadj = 1.81, p = .022); one extra adverse life event increased this risk by 14% (p = .061) independently of genotype. Other factors significantly related to GDS≥5 were: female gender (ORadj = 2.49, p < .001), age (ORadj = 1.19, p = .007), a history of depression (ORadj = 4.73, p < .001), and comorbidity (ORadj = 1.23, p = .001). One extra adverse life event increased the risk of depressive symptoms by 57% (p = .005) only in the L'L' carriers, while antidepressant intake was directly related to GDS≥5 in the L'S' carriers (ORadj = 2.46, p = .036) and borderline significant in the S'S' carriers (ORadj = 2.41, p = .081).The S'S' genotype and recent exposure to adverse life events were independently associated with depressive symptoms. The S'S' genotype, compared with the environment, exerted a predominant effect on depressive symptoms, suggesting that it reduces the efficacy of antidepressant therapy. We conclude that genetics may be an important risk factor for depressive symptoms in late adulthood.

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Adverse early life experience and social stress during adulthood interact to increase serotonin transporter mRNA expression.

Publications

Adverse early life experience and social stress during adulthood interact to increase serotonin transporter mRNA expression.

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