Elucidation of the mammalian mitochondrial unfolded protein response network

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Mitochondria contain a dedicated protein quality control system to ensure proper folding of the mitochondrial proteome. The enzymatic activity of mitochondrial proteins is central to cellular function and perturbations of the mitochondrial proteome have been implicated in ageing and numerous diseases, such as neurodegenerative diseases. Upon mitochondrial protein misfolding, mitochondria activate the mitochondrial unfolded protein response (UPRmt) to restore mitochondrial proteostasis and function. Despite our extensive knowledge of the C. elegans UPRmt, little is known about the proteins and mechanisms underlying the mammalian UPRmt. Two functional branches form the mammalian UPRmt: a transcriptional response to increase mitochondrial chaperones levels and a translational response, recently discovered by me, that leads to decreased mitochondrial translation. Considering the important role of the UPRmt network for understanding the mitochondrial responses to stresses, ageing, and disease, the mammalian UPRmt has been vastly understudied, mainly due to the lack of experimental paradigms to study the UPRmt under defined, acute conditions.My previous work established highly specific chemical induction of mitochondrial protein misfolding to study the acute mammalian UPRmt and provided with proteins and mechanisms likely playing a role in regulating the UPRmt. Guided by this data, I propose four objectives as part of this proposal, combining mainly biochemical, quantitative mass spectrometry-based, cell biological, and gene editing techniques to elucidate and discover proteins playing a crucial role in the mammalian UPRmt and to decipher the mechanisms underlying sensing and signaling of the mammalian UPRmt: 1) The elucidation of sensing and signaling of UPRmt inside mitochondria, especially in the context of calcium signaling and studying the role of LETM1, which I identified to regulate the UPRmt; 2) Defining the temporal profile controlling progression through the UPRmt and the transition towards a pro-death response upon pro-longed UPRmt activation; 3) The extension of my preliminary and establishment of further genetic screens to identify the proteins essential for the UPRmt and to elucidate the mechanisms of their action; 4) To decipher the signaling pathways transmitting the UPRmt to the nucleus and eliciting the transcriptional response. Together, these objectives will largely extent our knowledge of the proteins forming and the mechanisms guiding the mammalian UPRmt and will form the essential foundation for understanding the processes underlying the mitochondrial response to perturbations in mitochondrial proteostasis upon ageing or disease.