Complex I- induced Protein Turnover, A Novel Mitochondrial Protein Quality Regulation Clipt Goes Beyond The Mitochondrial Calcium Uniporter

In the setting of mitochondrial disease, patients with cardiac involvement have a nearly threefold increased mortality. Yet, patients often survive months to years suggesting that in cardiomyocytes, there is a compensatory mechanism that maintains energy synthesis despite defective mitochondria. We have recently shown that enhanced activity of the mitochondrial Calcium (Ca 2+ ) uniporter channel preserves energetic homeostasis in mitochondrial cardiomyopathies. Here, we describe a novel mechanism responsible for this enhancement. During normal physiology, interaction between the uniporter and Complex I of the electron transport chain promotes its degradation. However, upon Complex I dysfunction, loss of this interaction results in increased functional channels. We termed this form of mitochondrial protein regulation, Complex I-Induced protein turnover (CLIPT). We hypothesize that CLIPT is not unique to the uniporter. To identify other candidates subject to CLIPT, we performed a pulse-chase screen using TurboID, a biotin-ligase proximity labeling tool. HEK cells expressing a mitochondrial TurboID were grown with or without Complex I inhibitors. Following a pulse-chase with biotin, proteins were purified with streptavidin and identified through mass spectrometry. Of these proteins, whose lifetimes increased after Complex I inhibition, Peroxiredoxin-3 (PRDX-3) is a mitochondrial antioxidant shown to provide protection against cell death and in myocardial infarction. Using heterologous expression in c2c12 cells, inhibition of Complex I prolongs PRDX-3 lifetime. Thus, our data suggests that CLIPT can affect mitochondrial proteins beyond the uniporter.