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Coming dissertations at MedFak

  • Early life experiences and alcohol use in youth : An emerging role of the Vesicular Glutamate Transporters Author: Maria Vrettou Link: Publication date: 2021-01-15 10:34

    Initiation of alcohol consumption usually takes place during adolescence, a period characterized by a plethora of physical and emotional changes. Towards early adulthood, hazardous drinking patterns can emerge and potentially lead to the development of Alcohol Use Disorder (AUD). Both positive and negative experiences during early life can shape brain development and, through interactions with the genetic make-up, can contribute to the vulnerability of an individual to develop AUD. Epigenetic mechanisms, such as DNA methylation, potentially mediate the effect of environmental influences on gene expression, thus serving as the missing link between gene, environment and phenotype. Among various neuroadaptive changes seen in AUD, those within the glutamatergic system appear particularly prominent, mainly in withdrawal and relapse states, but also in stress-related outcomes. The glutamatergic phenotype can be determined by the expression of the Vesicular Glutamate Transporters 1-3 (VGLUT1-3). To date, the relationship between early life experiences, alcohol consumption, and Vgluts/VGLUTs genes (rodents/humans) in the initial stage of alcohol consumption and during the sensitive period of late adolescence/young adulthood has not been investigated.

    The present thesis, based on three studies on rodents and one on humans, aimed to examine Vglut/VGLUT1-3 correlates of early life experiences and alcohol drinking during youth. The effect of co-exposure to nicotine, because of its high comorbidity with alcohol use, as well as the role of key DNA methylation-regulating genes was also investigated. The main finding showed that individuals exposed to early life stress were more sensitive to the effect of alcohol on Vglut1-3 mRNA expression and DNA methylation, as well as expression of the DNA methylation-regulating genes, in limbic and striatal brain regions, as compared with controls. In an independent sample, prolonged nicotine co-exposure with alcohol during adolescence was associated with higher Vglut2 expression in the ventral tegmental area of young adult rats. Lastly, the single nucleotide polymorphism rs2290045 in VGLUT2 was found to moderate the environmental sensitivity to alcohol-related problems in humans. Carriers of the minor allele (T) displayed differential susceptibility to the environment; increasing quality of parenting was associated with higher and lower alcohol-related problems in the absence and presence of previous maltreatment, respectively.

    In conclusion, the findings highlight for the first time the role of Vgluts/VGLUTs in early stress-mediated sensitivity towards alcohol consumption and alcohol-related problems during adolescence and young adulthood, and especially a potential Vglut2/VGLUT2-mediated molecular signature behind the interactive mechanisms of these two aversive environmental factors, as well as of nicotine co-exposure.

  • Epigenetic dysregulation in relation to psychiatric traits in adolescence and adulthood Author: Adrian Desai Boström Link: Publication date: 2020-12-22 12:46

    Epigenetics has evolved into a key research focus in the field of psychiatry. DNA methylation is the most researched epigenetic mechanism. In paper I-III, 130 and 93 adolescents were randomly recruited at two separate intervals. Subjects were evaluated by web-based diagnostic interviews using the Development and Well-Being Assessment (DAWBA), providing computer generated diagnostic predictions of probability of diagnosis, covering several psychiatric disorders. For Paper I-II, the genome-wide DNA methylation pattern was measured from whole blood using the Illumina 450K array, and for paper IV by the Illumina EPIC BeadChip. In paper I, a methylome-wide association study (MWAS) was conducted (n=93) followed by a validation analysis (n=78), contrasting methylation levels in groups stratified by DAWBA depression risk scores. A microRNA4646 (MIR4646) associated methylation locus was differentially methylated in the MWAS (pbonf<0.05) and results were replicated in the validation cohort (p<0.05). Methylation levels at the identified locus correlated inversely with gene expression levels of MIR4456 (p<0.05). In silico analysis suggests MIR4646 may influence synthesis of omega-3 fatty acids, previously implicated in major depressive disorder. In paper II, 37 single nucleotide polymorphisms (SNP:s) previously associated with psychiatric disease were evaluated in relation to genome-wide DNA methylation levels in 130 adolescents in a methylome-wide (mQTL) analysis. Five SNP-CpG pairs were identified (pbonf<0.05) and replicated (p<0.05). Methylation of three of these were shown to be significantly correlated with gene expression levels of the associated genes (p<0.05). One identified GAD1-coupled methylation site was differentially methylated to a general psychiatric risk score in adolescents (p<0.05). In Paper III, hypothalamic-pituitary-adrenal (HPA)-axis coupled DNA methylation loci were investigated in 88 suicide attempters to identify associations to severity of suicide attempt. One corticotropin releasing hormone (CRH)-associated CpG-site was significantly hypomethylated in the high-risk group of suicide-attempters (n=31)(cg19035496, p<0.001) and exhibited hypermethylation in an external study group of adolescents in dependency of a general psychiatric risk score (p<0.05). In paper IV, 8,852 microRNA (miRNA) associated CpG-sites were investigated for an association with hypersexual disorder (HD). A microRNA-4456 (MIR4456) associated CpG-site (cg01299774) was borderline significant in HD (pFDR=5.81E-02) and differentially methylated in alcohol dependence (p<0.05) in an independent study group. Methylation levels at cg01299774 correlated inversely with expression levels of MIR4456 (p<0.01) and MIR4456 was lower expressed in HD (p<0.05). In-silico analyses suggests MIR4456 putatively targets genes preferentially expressed in brain and that are involved in major neuronal molecular mechanisms thought to be relevant for HD, e.g., the oxytocin signaling pathway.

  • The role of glial cells in alpha-synuclein pathology : Focus on degradation, cell-to-cell propagation and inflammation Author: Jinar Rostami Link: Publication date: 2020-12-21 12:24

    Growing evidence emphasizes the role of astrocytes and microglia in Parkinson’s disease (PD) and Alzheimer’s disease (AD). Yet, little is known about their impact on specific disease processes and if their involvement is beneficial or detrimental. The aim of this thesis was to further investigate the role of astrocytes and microglia in PD and AD. To this purpose, cultured human astrocytes and microglia were exposed to aggregates of alpha-synuclein (αSYN) or amyloid-beta (Aβ), proteins that are central to PD and AD brain pathology, respectively.

    In Paper I, the toxicity and cell-to-cell spreading of aggregated αSYN in human astrocytes were evaluated. We found that astrocytes can engulf large amounts of αSYN aggregates, which are stored inside the cells instead of being degraded. This intracellular storage was found to result in severe cellular stress. As a response, stressed astrocytes were shown to transfer αSYN via tunneling nanotubes (TNT) to healthy astrocytes.

    T cells have been observed to enter the PD brain, but little is known about which stationary cell types they interact with. In Paper II, the ability of astrocytes and microglia to act as antigen presenting cells in the presence of aggregated αSYN was investigated. Both astrocytes and microglia were capable of expressing major histocompatibility class I (MHCI) and MHCII. However, only astrocytes had the capacity to express other molecules crucial for T-cell activation, such as CD80 and CD86. MHCII expressing astrocytes were also found in close vicinity to T cells in the PD brain.

    In paper III, the cross-talk between microglia and astrocytes in the presence of αSYN and Aβ aggregates was examined. When cultured separately, microglia appeared to degrade αSYN and Aβ better than astrocytes. However, co-culture experiments showed that microglia and astrocytes have a synergistic effect on the clearance of protein aggregates. Cell-to-cell contact was revealed as one of the possible mechanisms by which astrocytes and microglia communicate with each other.

    In Paper IV, the molecular mechanisms by which the compound KYP-2407 enhances αSYN clearance was investigated. We found that KYP-2407 stimulates the auto-lysosomal pathway in the presence of αSYN aggregates. Calpain proteins, which increase αSYN aggregation and diminish autophagy in PD, were also shown to be reduced in the presence of KYP-2407.

    Taken together, this thesis contributes with novel and important knowledge to the potential role of astrocytes and microglia in PD and AD.