Browsing by Author "Malan-Muller, Stefanie"

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    Appetitive and reactive aggression are differentially associated with the STin2 genetic variant in the serotonin transporter gene
    (Nature Research (part of Springer Nature), 2018-04) Hemmings, Sian M. J.; Xulu, Khethelo; Sommer, Jessica; Hinsberger, Martina; Malan-Muller, Stefanie; Tromp, Gerard; Elbert, Thomas; Weierstall, Roland; Seedat, Soraya
    Appetitive aggression is a sub-category of instrumental aggression, characterised by the primary intrinsic enjoyment of aggressive activity. Aggression is heritable, and serotonergic and monoaminergic neurotransmitter systems have been found to contribute to the underlying molecular mechanisms. The aim of this study was to investigate the role that genetic variants in the serotonin transporter (SLC6A4) and monoamine oxidase A (MAOA) genes play in the aetiology of appetitive aggression in South African Xhosa males (n = 290). SLC6A4 5-HTTLPR, rs25531, and STin2 variants, as well as MAOA-uVNTR were investigated for their association with levels of appetitive aggression using Poisson regression analysis. The STin2 VNTR12 allele was found to be associated with increased levels of appetitive aggression (p = 0.003), but with decreased levels of reactive aggression (p = 7 × 10−5). This study is the first to investigate genetic underpinnings of appetitive aggression in a South African population, with preliminary evidence suggesting that SCL6A4 STin2 variants play a role in its aetiology, and may also be important in differentiating between appetitive and reactive aggression. Although the results require replication, they shed some preliminary light on the molecular dichotomy that may underlie the two forms of aggression.
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    Molecular mechanisms of D-cycloserine in a fear extinction posttraumatic stress disorder (PTSD) animal model
    (Stellenbosch : Stellenbosch University, 2014-04) Malan-Muller, Stefanie; Hemmings, Sian M. J.; Seedat, Soraya; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Psychiatry.
    ENGLISH ABSTRACT: Posttraumatic stress disorder (PTSD) is a severe, chronic and debilitating psychiatric disorder that can present after the experience of a life-threatening traumatic event. D-cycloserine (DCS), a partial N-methyl-D-aspartate (NMDA) receptor agonist, has been found to augment cognitive behavioural therapy by facilitating fear extinction; however, the precise mechanisms whereby DCS ameliorates fear triggered by a traumatic context remains to be fully elucidated. This study aimed to (i) identify the molecular mechanisms of intrahippocampally administered DCS in facilitating fear extinction in a rat model of PTSD by investigating gene expression profiles in the left dorsal hippocampus (LDH) of male Sprague Dawley rats and (ii) determine whether microRNA (miRNA) expression and DNA methylation mediated these gene expression changes. An adapted version of the PTSD animal model described by Siegmund and Wotjak (2007) was utilised. The total number of 120 rats were grouped into four experimental groups (of 30 rats per group) based on fear conditioning and the intrahippocampal administration of either DCS or saline: (1) fear conditioned + intrahippocampal saline administration (FS), (2) fear conditioned + intrahippocampal DCS administration (FD), (3) control + intrahippocampal saline administration (CS) and (4) control + intrahippocampal DCS administration (CD). Behavioural tests (the light/dark [L/D] avoidance test, forced swim test and open field test) were conducted to assess anxiety and PTSD-like behaviours. The L/D avoidance test was the most sensitive behavioural test of anxiety and was subsequently used to differentiate maladapted (animals that displayed anxiety-like behaviour) and well-adapted (animals that did not display anxiety-like behaviour) subgroups. In order to identify genes that were differentially expressed between FS maladapted (FSM) (n = 6) vs. FD well-adapted (FDW) (n = 6) groups, RNA sequencing was performed on the Illumina HiSeq 2000 which generated more than 60 million reads per sample. This was followed by subsequent bioinformatics analyses (using the software programs TopHat, Bowtie, Cuffdiff and Bio-Ontological Relationship Graph (BORG) database (that identifies genes that may be biologically relevant) to identify biologically relevant differentially expressed genes between the treatment groups. Epigenetic mechanisms mediating observed differences in gene expression were investigated by conducting DNA methylation and miRNAseq analyses in the FDW and FSM experimental groups. DNA methylation was investigated using real-time quantitative PCR (qPCR) amplification followed by high resolution melt analysis on the Rotor-GeneTM 6000. Differences in miRNA expression levels between the FDW and FSM groups were investigated by sequencing the miRNA fraction on the MiSeq platform. The bioinformatics pipeline used to analyse the RNAseq data identified 93 genes that were significantly downregulated in the FDW group compared to the FSM group. Forty-two of these genes were predicted to be biologically relevant (based on BORG analysis). Integrative network analyses revealed subsets of differentially expressed genes common across biological functions, pathways and disorders. The co-administration of DCS and behavioural fear extinction downregulated immune system genes and genes that transcribe proinflammatory and oxidative stress molecules. These molecules mediate neuroinflammation and subsequently cause neuronal damage. DCS also regulated genes involved in learning and memory processes. Additionally, a subset of the genes, which have been found to be associated with disorders that commonly co-occur with PTSD (such as cardiovascular disease, metabolic disease, Alzheimer‘s and Parkinson‘s disease), was downregulated by the co-administration of DCS and behavioural fear extinction. In order to determine whether real-time qPCR analysis would be sensitive enough to detect differential expression in those genes found to be differentially expressed in RNAseq analysis, the expression of nine genes was analysed using SYBR Green qPCR technology. In the LDH, six of the nine genes were found to be differentially expressed between FDW and FSM groups and one gene, matrix metallopeptidase 9 (MMP9), was observed to be differentially expressed between these two groups in the blood. Three of the nine genes for which differential expression levels were investigated using SYBR Green real-time qPCR, contained CpG islands and were used for CpG island DNA methylation analysis. Results indicated that CpG island DNA methylation did not mediate differential gene expression of TRH, NPY or MT2A. Bioinformatics analysis of miRNAseq data identified 23 miRNAs that were differentially expressed between the FDW and FSM groups. Several of these miRNAs have previously been found to be involved in brain development and behavioural measures of anxiety. Furthermore, functional luciferase analysis indicated that the upregulation of rno-mi31a-5p could have facilitated the downregulation of interleukin 1 receptor antagonist gene (IL1RN) as detected in RNAseq. RNAseq and miRNAseq analyses in this PTSD animal model identified differentially expressed genes and miRNAs that serve to broaden our understanding of the mechanism whereby DCS facilitates fear extinction. To this end, immune system genes and genes transcribing proinflammatory and oxidative stress molecules were among the genes that were found to be differentially expressed between the FDW and FSM groups. Based on the results obtained, it can be hypothesised that DCS attenuates neuroinflammation and subsequent neuronal damage, and also regulates genes involved in learning and memory processes. Concomitantly, these gene expression alterations mediate optimal neuronal functioning, plasticity, learning and memory (such as fear extinction memory) which contribute to the fear extinction process. Furthermore, biologically relevant differentially expressed genes that were associated with DCS facilitation of fear extinction and with other chronic medical conditions, such as cardiovascular disease and metabolic diseases, might help to explain the co-occurrence of these disorders with PTSD. In conclusion, Identifying the molecular underpinnings of DCS-mediated fear extinction brings us closer to understanding the process of fear extinction and could, in future work be used to explore novel therapeutic targets to effectively treat PTSD and related disorders.
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    Shorter telomere length : a potential susceptibility factor for HIV-associated neurocognitive impairments in South African woman
    (PLoS, 2013-03) Malan-Muller, Stefanie; Hemmings, Sian M. J.; Spies, Georgina; Kidd, Martin; Fennema-Notestine, Christine; Seedat, Soraya
    The neuropathogenesis of the human immunodeficiency virus (HIV) may manifest as various neurocognitive impairments (NCI). HIV-positive individuals also have significantly shorter telomere length (TL) in peripheral blood mononuclear cells (PBMCs) and CD8+ T cells compared to HIV-negative individuals. Additionally, reduced TL has been found to be associated with chronic psychological stress. This study focused on the effects of HIV-infection and chronic stress associated with childhood trauma on telomere length, and investigated whether leukocyte TL (LTL), in particular, represents a risk factor for NCI. Eighty-three HIV-positive and 45 HIV-negative women were assessed for childhood trauma and were subjected to detailed neurocognitive testing. Blood from each participant was used to extract Deoxyribonucleic acid (DNA). Relative LTL were determined by performing real time quantitative PCR reactions as described by Cawthon et al. (2002). As expected, relative LTL in the HIV-positive individuals was significantly shorter than that of HIV-negative individuals (F = 51.56, p=,0.01). Notably, a significant positive correlation was evident between relative LTL and learning performance in the HIVpositive group. In addition, a significant negative correlation was observed between relative LTL and verbal fluency, but this association was only evident in HIV-positive individuals who had experienced trauma. Our results suggest that reduced LTL is associated with worse learning performance in HIV-positive individuals, indicating that TL could act as a susceptibility factor in increasing neurocognitive decline in HIV-infected individuals.