Expression of genes involved in DNA methylation and mitochondrial biogenesis during ageing in the brain of Nothobranchius furzeri

Details

Supervisors

Melissa Page ; Jean-François Rees

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

Ageing can be defined as a time-dependent functional decline that affects most living organisms, leading to increased vulnerability to death. For the past centuries, humans have significantly increased their lifespan with advances in medicine and hygiene. However, advanced age is the primary risk factor for several conditions such as cardiovascular diseases and neurodegenerative diseases. As global population ages, the understanding of the underlying mechanisms of ageing will be crucial to promote healthy ageing. To date, nine interconnected hallmarks of ageing have been identified, including epigenetic alterations and mitochondrial dysfunction. Mitochondria produce the majority of cellular ATP by oxidative phosphorylation and the electron transport chain, which is partly encoded in the mitochondrial genome. Mitochondrial dysfunction is reached when ATP production cannot fulfil the cellular energy requirements. Mitochondrial dysfunction is critical in high energy consuming tissues such as the brain and participates in neurodegeneration by instigating apoptotic pathways. With age, the genome undergoes an epigenetic drift that ultimately alters gene expression. A lot of research focuses on nuclear DNA methylation and the age-specific epigenetic drift. However, there is growing evidence of age-related changes in mitochondrial DNA methylation. Importantly, there is growing evidence indicating that mtDNA methylation regulates the expression of mitochondrial genes. In this thesis, we studied the role of DNA methylation machinery in mtDNA methylation in the aging brain of N. furzeri. Our first objective was to verify the results reported by Zupkovitz (2021). Therefore, we measured the expression levels of three DNA methyltransferases: dnmt1, dnmt3a, and dnmt3b. We observed that the expression levels of dnmt3a and -b significantly change with age but not dnmt1. In addition, we measured the expression levels of SLC25A26 to investigate the impact of ageing on the mitochondrial import of the methyl-group donor (i.e., SAM), which is required for mtDNA methylation. We observed no age-dependent change in SLC25A26 gene expression. We also wish to determine whether there is a correlation between the expression of genes involved in DNA methylation and the expression of genes involved in mitochondrial biogenesis, such as PGC-1, mtSsbp, and Tfam. Here, we detected a significant change in the expression of Tfam and mtSsbp but not PGC-1 Finally, to determine a potential role of DNMTs the mtDNA copy number and took first steps to detect DNMT1 in the mitochondrial fractions of the brain. As an indicator of mitochondrial function, we measured the mtDNA copy number. Unfortunately, we could not achieve these last two objectives.