Mitochondrial inorganic polyphosphate in the mammalian stress response. - ABSTRACT Mitochondrial dysfunction, including bioenergetics dysregulation, has been broadly described under cellular stress conditions, such as those found in many human diseases. However, the exact mechanisms that drive mitochondria to dysfunction and failure under these conditions are still too poorly understood to enable effective therapeutic targeting. Inorganic polyphosphate (polyP) is a ubiquitous molecule, even if it shows a preferred location within mitochondria. It is extremely well-conserved throughout evolution, and it is present in every studied organism. The bonds of polyP are isoenergetic to those found in ATP, and we and others have already demonstrated that polyP is a key energy metabolite (scientific premise for this proposal). Moroever, the key role played by polyP in maintaining cellular homeostasis under stress conditions in some organisms, such as bacteria and yeast, is already known. This is also the case for polyP’s involvement in the regulation of some crucial mitochondrial processes which are i) closely related to the bioenergetic status of mammalian cells, and ii) involved in the stress response. These processes include, the regulation of mitochondrial calcium homeostasis and the formation and opening of the mitochondrial permeability transition pore. Nonetheless, the exact extent of the effects of polyP in mammalian cellular, and more specifically, mitochondrial physiology; as well as the molecular mechanism underlying these effects still remain mostly unknown. This molecular mechanism could involve the regulation of the inositol multikinase (IPMK)/AMPK-Activated protein kinase (AMPK) axis, which will place polyP as a signaling molecule in mammalian bioenergetics. The objective of this project is to elucidate the mechanistic role of mitochondrial polyP in mitochondrial physiology and cellular bioenergetics, under basal and disease-relevant stress conditions. To accomplish this objective, based on the bibliography and our preliminary data, our global hypothesis is that: mammalian mitochondrial polyP is a key regulator of cellular bioenergetics and mitochondrial physiology under disease-relevant acute stress conditions. The effects of polyP on mitochondrial physiology are also exerted via the regulation of the IPMK/AMPK axis. To test this hypothesis, we will use mammalian cellular models in which the levels of mitochondrial polyP will be modified, and a combination of biochemical, cell biology, molecular biology, and -omics techniques. We will first optimize the methods to assay mammalian polyP (this is a crucial component of the innovation of this proposal). Subsequently, we will study the plausible regulatory effects of polyP on cellular bioenergetics and mitochondrial physiology, as well as polyP’s role in bioenergetics signaling, via the regulation of the IPMK/AMPK axis. This application aligns with the PI’s and laboratory’s expertise in mitochondrial polyP and bioenergetics, accelerating the progress of their research. Moreover, it is in line with the long-term goal of the PI on this application, which is to unravel the mechanisms that drive mitochondrial to dysfunction and failure in human disease. The obtained data will not only increase our knowledge of mitochondrial physiology, it will also help us to propose polyP as a new and promising potential pharmacological tool for various pathological conditions where the dysregulation of bioenergetics has been described (significance).
