Mitochondria are crucial components of eukaryotic cells and exchange signalling molecules, metabolites, proteins and lipids with the rest of the cell. The organelle is key for energy metabolism as they provide most of the cellular ATP through oxidative phosphorylation and regulate intermediate metabolism. Mitochondria are also a major source of reactive oxygen species (ROS), which are by-products of aerobic respiration and recently recognised as important signalling molecules that control various cellular functions. To avoid the potential damaging effects of ROS, mitochondria contain protein antioxidant systems to help maintain thiol homeostasis. Mitochondria are emerging as an important redox signalling node and are involved in a myriad of signalling pathways, which have a redox component, either through a response to a particular ROS or the shift of the redox state of a responsive group. It is not surprising that mitochondria are therefore heavily regulated by retrograde signalling of the master regulator of cellular antioxidant defence, nuclear factor erythroid-derived 2-related factor 2 (Nrf2). Until now it has not been possible to disentangle the overlapping effects of mitochondrial ROS signalling compared to a redox signal stemming from disruption of mitochondrial thiol homeostasis. Furthermore, it is important to distinguish between disturbing the cytosolic and mitochondrial protein antioxidant systems. I characterised the effects of mitochondrial thiol homeostasis disruption on mitochondrial physiology with MitoCDNB, showing mitochondrial fission. I found that selective disruption of the mitochondrial glutathione pool and inhibition of its thioredoxin system led to Nrf2 activation, while using MitoPQ to enhance production of mitochondrial superoxide and hydrogen peroxide alone did not. To further our understanding of how mitochondrial redox homeostasis is sensed in the cytoplasm and signalled to the nucleus I used an RNAseq approach to investigate the intricacies of early mitochondrial retrograde signalling.