Numerous Cellular Pathways Modulate Non‐Imported Mitochondrial Protein Abundance

Abstract

Mitochondria are a central hub of metabolism in cells, and their functional decline leads to the onset of numerous metabolic and age‐related disorders. A key question regarding the link between mitochondria and disease is how exactly do changes in mitochondrial function lead to cellular toxicity? To date, most studies have focused on the idea that loss of particular mitochondrial functions is what drives toxicity. However, recent studies have identified a previously underappreciated culprit for toxicity associated with mitochondrial impairment: the accumulation of unimported mitochondrial precursor proteins. Mitochondria are protein‐rich organelles, with ~1000 proteins in yeast, and ~1500 in mammals. Out of ~1,000 mitochondrial proteins, 99% are encoded in the nucleus, translated in the cytoplasm, and imported into mitochondria post‐ or co‐translationally. The majority of these proteins require the mitochondrial membrane potential for import, which is generated by the electron transport chain on the mitochondrial inner membrane. Thus, under conditions of mitochondrial impairment, hundreds of mitochondrial precursor proteins fail import, and their accumulation leads to proteotoxic stress for the cell termed mitochondrial precursor overaccumulation stress (mPOS). We sought to develop a comprehensive understanding of the cellular pathways that operate to mitigate toxicity of unimported mitochondrial proteins. Using S. cerevisiae as a model system, we performed fluorescence microscopy and western blot based screens on ~500 GFP‐tagged mitochondrial proteins under conditions of mitochondrial protein import failure. Through these screens, we have identified at least three potential quality control mechanisms cells utilize to dispose of these proteins, and determined that loss of these systems leads to cellular toxicity under conditions of mitochondrial impairment. Our current work is focused on delineating the protein machinery involved in these quality control systems, and defining the sequence features that drive mitochondrial precursor proteins toward a given fate. Overall, these studies are a step toward understanding the role of mPOS in metabolic diseases, and will help to explore new facets of mitochondrial‐associated disorders.Support or Funding InformationUnited Mitochondrial Disease Foundation, NIH R35 GM119694. Searle Scholars Program, Glenn FoundationThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.